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Reconfigurable dual notch band antenna on Si-substrate integrated with RF MEMS SP4T switch for GPS, 3G, 4G, bluetooth, UWB and close range radar applications
Int. J. Electron. Commun. (AEÜ) 110 (2019) 152873
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Reconfigurable dual notch band antenna on Si-substrate integrated with RF MEMS SP4T switch for GPS, 3G, 4G, bluetooth, UWB and close range radar applications Kuldeep Sharma a, Ayan Karmakar b, Manish Sharma c, Ashish Chauhan b, Shonak Bansal a, Manish Hooda b, Sanjeev Kumar d, Neena Gupta a, Arun K. Singh a,⇑ a
Department of Electronics and Communication Engineering, Punjab Engineering College (Deemed to be University), Sector-12, Chandigarh, India Department of AMNSD, Semiconductor Laboratory, Mohali 110017, India c Department of Electronics & Communication Engineering, SGT University Gurgaon, Haryana 121003, India d Department of Applied Sciences, Punjab Engineering College (Deemed to be University), Sector-12, Chandigarh, India b
a r t i c l e
i n f o
Article history: Received 15 January 2019 Accepted 11 August 2019
Keywords: Reconfigurable antenna Dual notch band UWB antenna RF MEMS switch Close range radar Equivalent circuit model
a b s t r a c t In this paper, a reconfigurable co-planner waveguide (CPW) fed circular shaped monopole ultra wide band (UWB) antenna with dual band notch characteristics based on silicon substrate is presented. The dual notch band characteristics are realized by inserting two slots, namely, U- and I-shaped, in the circular radiating patch to switch-off the WiMAX IEEE 802.16 (3.30–3.80 GHz) and WLAN IEEE 802.11a/h/j/n (5.15–5.35 GHz, 5.25–5.35 GHz, 5.47–5.725 GHz, 5.725–5.825 GHz) respectively. The reconfigurability from antenna is achieved by integrating the radio frequency micro-electro mechanical system based single pole four through (RF MEMS SP4T) switch in the U- and I-shaped slots of radiating patch. The measured results demonstrate the bandwidth of 0.68–16.23 GHz resulting in fractional bandwidth of 183.91%, and are well in accordance with the simulation results. The gain of proposed antenna varies from 2.58 to 5.05 dBi with radiation efficiency of 83–95% and exhibits the omnidirectional like pattern in H-plane and nearly dipole like pattern in the E-plane. Further, the performance of proposed antenna is analyzed by implementing an equivalent RLC resonant circuit model in both the frequency and time domain. Ó 2019 Elsevier GmbH. All rights reserved.
1. Introduction Nowadays, an ultra-wideband (UWB) technology is extensively used for low cost, high data rate, and low power wireless communication applications [1–4]. The UWB communication is achieved by employing either the orthogonal frequency division multiplexing based UWB (UWB-OFDM) or the impulse radio based UWB technology (IR-UWB) [1,5]. IR-UWB communication is achieved by transmitting the extremely short pulses, whereas OFDM-UWB, communication requires orthogonal subcarriers to modulate the transmitted data [5]. The Federal Communication Commission (FCC) allocated the unlicensed frequency band (3.1–10.6 GHz) for commercialized use of UWB communication in numerous wireless applications including radar [6–8], ground penetrating system [1], and image system [1]. In addition, they include low power consumption, reduced multipath interference offering high immunity, ⇑ Corresponding author. E-mail address: [email protected] (A.K. Singh). https://doi.org/10.1016/j.aeue.2019.152873 1434-8411/Ó 2019 Elsevier GmbH. All rights reserved.
large channel capacity and strict power transmission [1,5,8–9]. The UWB antenna is one of the crucial component of UWB communication [1,4]. The design of co-planer waveguide (CPW) [3–4] and microstrip UWB antennas [2,5] is quite challenging, as it requires ultra-wide bandwidth, large impedance bandwidth, omnidirectional radiation pattern, low cost, light weight and ease of integration and fabrication [1,2,6,10–12] for operating band. However, a number of CPW and microstrip based antennas with different configurations have been designed and validated experimentally [10–17]. Moreover, narrow band communication systems such as worldwide interoperability microwave access (WiMAX) operating at 3.4–3.69 GHz [5,6] and wireless local area network (WLAN) operating at 5.15–5.825 GHz [4,7–9] also exist in the UWB spectrum [18–23]. The overall performance of UWB antenna is reduced due to interference between narrow band and UWB systems [18–22]. To overcome the interference, several UWB antennas with single or dual band notch characteristics have been reported [23–27]. These notch band characteristics are typically achieved by inserting
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slot [2,8], stub [3,4], resonators [6,22], and parasitic elements [5,7] in radiating patch, ground plane and feed line etc. which allows the leakage of electromagnetic wave through etched slot and hence depreciate the radiation pattern [6,15–17]. Most of the antennas reported so far on FR4 [5–7], RT-Duroid [4–6] and silicon [27] substrates can either work as band reject UWB antenna or just as an UWB antenna with different geometries [3,6]. The FR4 and RTDuroid substrates materials have heating issue due to their lower thermal conductivity, hence are not viable in developing the state-of-art MEMS technology. Moreover, silicon substrate is preferred due to its high thermal conductivity (1.57 W/cm °C), resistivity (>8 kO-cm), dielectric constant (11.9) and tunable RF performance by utilizing the micromachining technique [28]. Additionally, development of system on chip (SoC) is feasible by monolithic integration of other RF components on the silicon chip [29]. In addition, the reconfigurable notch band UWB antenna were developed to typically block and isolate the interference between narrow band and UWB systems with improved performances by inserting a PIN diode and ideal switch inside the slot [5–11, 30–32,33]. The potential applications of the UWB antenna with reconfigurable characteristics include the WiMAX and WLAN band frequencies [23–26]. Later, RF MEMS switch has also been utilized to eliminate the WiMAX and WLAN frequency on radiating patch [13,34]. The use of MEMS based switches are becoming increasingly popular in RF applications due to low insertion loss, high isolation, wide band operation, negligible power consumption, high power handling capability, simple biasing network requirement as compared to conventional semiconductor switches such as FET’s and PIN diode [34]. In addition, the switching operation realized by utilizing FET’s and PIN diode can operate at only lower frequencies. In this paper, a reconfigurable dual band-notched UWB antenna covering bandwidth of 0.68–16.23 GHz is presented for various applications including GPS, 3G, 4G, Bluetooth, UWB and close range radar applications etc. The proposed antenna has a planner structure having a size of 47 47 0.675 mm3, and is fabricated on a high restive silicon substrate (q > 8 kO-cm, er = 11.9, tan d = 0.001) having a thickness of 0.625 ± 0.025 mm, where q is resistivity, er is relative dielectric constant and tan d represents the loss tangent. Here, we utilize the U- and I-shaped etched slots on a circular radiating patch to exhibit dual notch band characteristics for WiMAX and WLAN band, respectively. The single pole four through
(SP4T) MEMS switch has four ports that can switch ON/OFF four bands (from 0 to 14 GHz) simultaneously. The RF MEMS SP4T switch is integrated with the proposed antenna to switch ON/OFF the two interfering bands i.e. WiMAX and WLAN by using two ports, while the other remaining ports are terminated. The developed antenna is proposed for UWB applications including GPS, 3G, 4G, Bluetooth, and close range radar applications etc. To the best of our knowledge, most of the earlier reported works [2–7] have utilized an individual switch for rejecting one interfering band, hence, requires multiple switches for multiple notch band requirements. In addition, each switch requires a separate supply for operation, making the system complex with high power consumption. 2. Antenna design and fabrication The radiating patch of UWB antenna structure is composed of a circular shape fed by CPW transmission line connected to a standard 50 O SMA connector. The configuration of proposed antenna on silicon substrate having length (Lsi) and width (Wsi) of 47 mm each is shown in Fig. 1(a). The radius of circular patch is calculated using following empirical equations considering the center frequency of 6.85 GHz for UWB [27]:
F R ¼ rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi h n o i 2hsi pF þ 1:7726 1 þ per F ln 2h si
ð1Þ
pffiffiffiffi where F ¼ 8:791 109 =f r er , hsi is the height of silicon-substrate in mm, er represents the relative permittivity of the substrate, and fr is the resonating frequency in GHz. However, the effective radius, Re of the patch antenna is estimated by [27]:
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi 2hsi pR þ 1:7726 ln 2hsi per R
Re ¼ R 1 þ
ð2Þ
The 50 O CPW based feed line has a width (Wm) and length (Lm) of 0.92 and 4.25 mm, respectively. A finite ground plane having width (Wg) of 22.64 mm and length (Lg) of 4 mm is shown in Fig. 1(b). The U- and I-shaped slots are etched on the radiating circular patch as depicted in Fig. 1(c) resulting in dual notched band
Fig. 1. (a) Schematic of antenna indicating radiating patch, substrate, ground plane. (b) Top view of antenna without notched bands. (c) Front view with dual notch. (d) Image of packaged SP4T switch (ADGM1304). (e) Cross sectional view of internal structure of SP4T.
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characteristics to eliminate WiMAX and WLAN interfering bands. The optimization of notched band frequencies is carried out by varying the respective slot lengths. The slot length of U- and Ishaped are optimized to eliminate the WiMAX (3.3–3.8 GHz) and WLAN (5.15–5.875 GHz) band frequencies, respectively, as below [27,35]:
LWiMAX ¼ c=ð4 f WiMAX LWLAN ¼ c=ð4 f WLAN
ereff ¼
2
2
ereff Þ
pffiffiffiffiffiffiffiffi
er þ 1 er 1 þ
pffiffiffiffiffiffiffiffi
ereff Þ
1=2 hsi 1 þ 12 Wm
ð3Þ ð4Þ ð5Þ
where c = 3 108 m/sec is the speed of EM wave in free space, ereff is the effective relative permittivity of substrate. The proposed reconfigurable antenna is designed utilizing ANSYS HFSS, and the optimized dimensions are Wm = 0.92 mm, Lm = 4.25 mm, R = 12.5 mm, Wg = 22.64 mm, Lg = 4.0 mm, t = 0.5 mm, G = 0.80 mm, S = 0.40 mm, L1 = 12.0 mm, L2 = 11.0 mm and L = 4.50 mm. The fabrication of proposed structure as shown in Fig. 2(a) is carried out using standard CMOS process on float zone (FZ) processed 600 high resistive silicon (q > 8 kO-cm, er = 11.8, tan d = 0.01) wafer [36]. After cleaning the wafer, deposition of buffer layers (oxide/nitride/oxide stack), and metallization of 2.5 lm to deposit the radiating patch is carried out using DC sputtering. The standard wet chemistry based etching process is employed to pattern the I- and U- shaped slots on circular radiating patch as shown in Fig. 2(b) and (c) respectively. 3. Results and discussion In this work, we have utilized packaged RF MEMS SP4T (ADGM1304) switch shown in Fig. 1(d) inside the slots of radiating patch to control the switching action of designed antenna. The switch has four ports, two ports are used for rejection of WiMAX and WLAN band while remaining ports are terminated. The RF MEMS SP4T has an isolation, insertion loss, return loss of 24 dB, 0.26 dB, and 18 dB, respectively. The maximum RF power that pass through the switch without degradation to the switch life time is 36 dBm. Fig. 1(e) demonstrate the cross sectional view of the internal structure of SP4T switch demonstrating cantilever beam which is fixed at one end and suspended at other end. The upstate and downstate of cantilever beam of RF MEMS tunes the switch in ON and OFF condition, respectively. The return loss (S11) of reconfigurable antenna suggesting four modes of operation due to RF MEMS switch control is shown in Fig. 3. The RF MEMS switch is placed studying maximum surface current density distribution for individual notch bands to eliminate the interference independently. The proposed antenna for GPS, Bluetooth and UWB covers
Fig. 3. Return loss as a function of frequency of proposed antenna indicating reconfigurability utilizing SP4T switch for WiMAX and WLAN.
entire bandwidth of 0.55–16.03 GHz when both the switches are in ON state i.e. S1 = ON & S2 = ON as observed in Fig. 3. Whereas, the antenna demonstrates characteristics covering 1.33– 14.83 GHz with dual notched bands, i.e., WiMAX (3.33–3.76 GHz) and WLAN (4.92–6.14 GHz), when S1 = S2 = OFF condition. The WiMAX and WLAN band frequency can individually be rejected utilizing a combination of switches as S1 = ON & S2 = OFF and S1 = OFF & S2 = ON, respectively, as shown in Fig. 3. The different combination of switches S1 and S2 as shown in Fig. 3 are given in Table 1. Further, to understand the effect of various parameters on antenna performance, a systematic parametric study is carried out employing EM Simulator HFSS as given in following sections. 3.1. Effect of gap width (S) & gap between ground and patch (G) In order to improve the impedance matching between feed line and radiating patch, the gap width (S) and the gap between grounds and patch (G) is optimized. Fig. 4(a) demonstrate that return loss tends to increase with the increase in G from 0.4 to 1.20 mm suggesting deterioration in impedance matching due to increase in fringing field effects. Similarly, impedance matching worsen when S is increased from 0.2 to 0.6 mm as shown in Fig. 4(b). The S & G are optimized to 0.4 and 0.8 mm, respectively covering the bandwidth of 0.55–16.03 GHz. 3.2. Effect of slot length L for WiMAX & L1 for WLAN notched bands The reconfigurability from fabricated antenna is achieved utilizing U- and I-shaped slots for WiMAX and WLAN notch bands,
Fig. 2. Image of fabricated UWB antenna. (a) Without notch band. (b) WLAN notch. (c) WiMAX and WLAN notch.
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Table 1 ON and OFF conditions of RF MEMS SP4T Switches for reconfigurable antenna. Switch (S1)
Switch (S2)
WiMAX Notch (GHz)
WLAN Notch (GHz)
Bandwidth (GHz)
ON OFF ON OFF
ON OFF OFF ON
– 3.33–3.76 3.33–3.76 –
– 4.92–6.14 – 4.92–6.14
0.55–16.03 1.33–14.83 0.68–15.21 1.15–15.01
Fig. 4. Return loss variation as a function of frequency for different (a) gap between ground and patch (G), (b) gap width (S) indicating impedance matching.
respectively as shown in Fig. 1(c). To obtain the WiMAX notch, the side length (L) as shown in Fig. 1(c) is varied from 3.5 to 5.5 mm in Fig. 5(a). Similarly, slot length (L1) shown in Fig. 1(c) is varied from 10 to 13 mm in Fig. 5(b) for demonstrating WLAN notch operation. The optimized values of L = 4.5 mm and L1 = 12 mm are considered for the fabrication of antenna as they are best suited to demonstrate the desired WiMAX and WLAN notch band operation in Fig. 5. The parametric variation of L and L1 to obtain notch band operations for WiMAX and WLAN demonstrating corresponding notch bandwidth are listed in Table 2.
Table 2 Parametric variation of L and L1 for WiMAX and WLAN notch bands.
3.3. Analysis of surface current density distribution and time domain study
uneven distribution of current density results in change in impedance matching, and hence induces the notch characteristics at WiMAX and WLAN bands reflecting back all the energy to the input port. Both the notch band characteristics can individually be controlled because of low mutual coupling between them as shown in Fig. 6(b) and (c). When both the switches are in OFF condition the current density mainly concentrated around the center of slots for WiMAX and WLAN notch frequencies, and hence concludes that the antenna does not radiate, which further suggests to fix the switches at these locations only [34]. Moreover, the surface current
Further to study the mechanism of slot on the radiating patch, surface current density distribution is simulated at the frequency of 7.00, 5.28 and 3.47 GHz for without notch, WLAN notch and WiMAX notch frequency, respectively as shown in Fig. 6(a)–(c). Fig. 6(b) and (c) demonstrate that surface current density increases at the inner and outer edges of U- and I-shaped slots in the presence of both the notch band characteristics, respectively. This
WiMAX
WLAN
Parameters (mm) L
Notch Bandwidth (GHz)
Parameters (mm) L1
Notch Bandwidth (GHz)
3.5 4.0 4.5 5.0
3.78–4.04 3.57–3.91 3.33–3.76 3.08–3.72
10 11 12 13
5.95–6.74 5.45–6.47 4.92–6.14 4.31–6.02
Fig. 5. The effect of variation in slot length (a) L, and L1 on return loss as a function of frequency for WiMAX and WLAN band, respectively.
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Fig. 6. Surface current density distribution at (a) 7.00 GHz. (b) 5.28 GHz. (c) 3.47 GHz.
is evenly distributed over the radiating patch having the slots for entire pass band except WiMAX and WLAN notch frequency. The results in Fig. 6(a) suggest that surface current density is evenly distributed over the radiating surface of the antenna without interfering bands resulting in radiation of EM waves. The pulse handling capability in the far field region of the designed antenna is studied utilizing the two identical antennas as transmitter and receiver as shown in Fig. 7(a). Both the antennas are placed in two configurations i.e., face to face and side to side. A gaussian pulse signal is excited in CST software corresponding to frequency varying from 3.1 to 10.6 GHz for antennas kept at a distance of 250 mm to ensure the far field region. The applied input pulse and the received signal normalized amplitudes for both orientations are shown in Fig. 7(a). The results suggest that more signals are received in face to face orientation rather than side to side orientation. The pulse distortion at the receiving side is due to impedance mismatch in the operating band resulting in transmission of few frequency components. The observed distortion in the received signal as shown in Fig. 7(a) is due to the frequency dispersive behaviour of the antenna. In addition, group delay that can deteriorate the phase linearity with and without notch bands is shown in Fig. 7(b). The reconfigurable antenna has demonstrated almost stable group delay (1.0 ns) for entire range of operating frequency starting from 3.1 to 10.6 GHz except notched frequency bands.
The values of RLC components which correspond to resonance impedance (ZLa) is calculated by Eq. (6) [10,27]:
Z La ¼
n X j¼1
jxRj L j
Rj 1 x2 Lj C j þ jxLj
ð6Þ
Input impedance of proposed reconfigurable antenna without notched bands is shown in Fig. 8(a) corresponding to the antenna shown in Fig. 1(b). As depicted, real and imaginary impedances vary around 50 and 0 X which indicate the matched condition of proposed antenna in entire operating band. In case of notched band characteristics high impedance mismatch is required at WiMAX and WLAN as shown in Fig. 8(b). Corresponding to WiMAX notched band center frequency of 3.65 GHz, the real impedance is 34.44 X which results in impedance mismatch and imaginary impedance varies from negative to positive. Simultaneously for WLAN frequency at 5.12 GHz (fPR from Fig. 10(a)) the estimated real impedance (Rpn from Fig. 8(b)) is 10 X and imaginary impedance varies from negative to positive. Combining real and imaginary impedance for both the notch bands two series RLC circuits connected in parallel as shown in Fig. 9(b). For unmatched condition, either short or open impedance is expected which results in mismatch when compared to match condition. The resonant frequencies and corresponding bandwidths of the series and parallel resonance circuits as shown in Fig. 9(b) can be calculated as [10,27]:
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
3.4. Equivalent circuit model
xSR ¼ 1= Lsn C sn
ð7Þ
In recent UWB technology, UWB antenna structures are more complicated and compact. Hence, an equivalent circuit model based on input impedance characteristic is necessary to discuss the mechanism of notch band characteristics. Hence, we have utilized CST software for evaluating input characteristics and RLC parameter for equivalent circuit model in Fig. 9(a) and (b) for antenna without and with notch band slots, respectively.
BW SR ¼ Rsn =Lsn
ð8Þ
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
xPR ¼ 1= Lpn C pn
ð9Þ
BW PR ¼ 1=Rpn C pn
ð10Þ
Fig. 7. Two identical reconfigurable antennas are used as transmitter and receiver kept at a distance of 250 mm, i.e. in far field to study the time domain characteristics in the CST software. (a) Input signal and received signal as a function of frequency for both the orientations. (b) Stable group delay of (1.0 ns) for antenna with and without notched band at WiMAX and WLAN. The inset shows antennas used in the two orientations, i.e., face to face, and side to side as shown in (b).
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Fig. 8. Real and Imaginary impedances of (a) proposed antenna without notched bands. (b) with notched bands at WiMAX and WLAN.
Fig. 9. Equivalent circuit model of proposed antenna (a) without notch bands. (b) with notch bands.
xSR (=2pfSR), xPR (=2pfPR) are the series & parallel resonant frequencies and BWSR, BWPR are the corresponding bandwidths which are estimated from Fig. 8(b) along with the values of series Rsn & parallel Rpn resistances. The value of Lsn, Csn, Lpn and Cpn for an equivalent circuit of proposed antenna given in Fig. 9(b) are calculated by Eqs. (7)–(10) where n = 1, 2 for dual notched band antenna. 3.5. Experimental results Fig. 10(a)–(b) demonstrates the return loss and VSWR of proposed antenna, respectively, and are well in accordance with the results obtained from the simulations implementing Ansys HFSS software. The slight variation is due to impedance mismatch between SMA connector and CPW feed conducting epoxy (silver) used to integrate the RF MEMS switch with radiating patch as shown in the inset of Fig. 10(a). The peak value of measured S11 (i.e. 5.18 and 3.15 dB) and VSWR (i.e. 3.63 and 5.28) corresponds to the rejected frequency of 3.35 and 4.95 GHz with measured bandwidth of 0.68–16.23 GHz. The results obtained from the equiv-
alent circuit model given in Fig. 9(b) are well in accordance with the measured and simulated results as shown in Fig. 10(a). The measured gain of notched frequency shown in Fig. 10(c) is found to be 6.836 and 7.96 dBi at 3.44 and 5.58 GHz, respectively, which confirms that antenna does not radiate in WiMAX and WLAN frequencies. Whereas, antenna exhibits a gain varying from 2.58 to 5.05 dBi for entire range of frequency (i.e. 0.68 to 16.23 GHz except WiMAX and WLAN notches). The proposed antenna also exhibits a good radiation efficiency (83–94%) across the entire bandwidth except in two notched bands i.e. 37 and 26.58% at 3.65 and 5.40 GHz, respectively. Fig. 11 depicts the measured normalized radiating patterns of proposed antenna including co- & cross- polarization in H (x-z plane) and E plane (y-z plane). It is observed that antenna demonstrates nearly omnidirectional and dipole like radiation characteristics with less cross polarization in H- and E-plane, respectively. At higher frequencies cross polarization increases due to increase in area of radiation. In addition, the dimension of antenna’s ground plane is less than a quarter wavelength when compared with the lowest frequency
Fig. 10. Measured and simulated (a) return loss and (b) VSWR as a function of frequency of the fabricated reconfigurable antenna shown in Fig. 2(c). The results obtained from equivalent circuit model are well in accordance with the measured and simulated results. The inset shows the packaged RF MEMS SP4T switch integrated with antenna using conductive silver epoxy. (c) Measured gain and simulated radiation efficiency as a function of frequency.
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Fig. 11. Measured and simulated radiation pattern of E and H-plane in dB at (a) 1.575 GHz (b) 2.45 GHz (c) 4.5 GHz (d) 7 GHz (e) 9 GHz (f) 11 GHz.
of UWB i.e. 3.10 GHz. As a result, few leakage current may be distributed along the external conductor of the SMA connector which corresponding affect the radiation patterns.
Table 3 shows comparison of proposed work with previously reported similar experimental studies. The proposed antenna can be used for variety of wireless applications including GPS,
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Table 3 Comparison of proposed work with previously reported similar experimental studies. Impedance Bandwidth
Notched Bands
Maximum peak VSWR at center notched frequency
Maximum Gain (dBi)
Reconfigurable Characteristics
Applications
Size (mm2)
2.7–12 GHz
WLAN X-Band WiMAX X-Band WiMAX WLAN X-Band WLAN ITS ITU WLAN WLAN WiMAX WLAN WiMAX WLAN WLAN X-Band WiMAX WLAN
[email protected] GHz [email protected] GHz 19.2 @ 3.6 GHz 9.0 @ 7.9 GHz [email protected] GHz [email protected] GHz [email protected] GHz 5.8 @5.7 GHz 5.0 @6.3 GHz 4.0 @8.2 GHz 6.0 @5.8 GHz 6.1 @5.85 GHz 5.6 @3.55 GHz 5.3 @5.68 GHz [email protected] GHz [email protected] GHz [email protected] GHz [email protected] GHz [email protected] GHz [email protected] GHz
5.32
Ideal Switches
UWB, X-Band Radar
24 32 [4]
5.43
Ideal Switches
UWB, X-Band Radar
24 32 [5]
5.53
Ideal Switches
UWB, X-Band Radar
24 32 [6]
5.12
PIN Diodes
UWB, X-Band Radar
12 18 [7]
– 5.38 4.12
PIN Diode PIN Diode PIN Diodes
UWB, X-Band Radar, Satellite Comm. UWB, X-Band Radar UWB
20 20 [8] 20 20 [9] 20 20 [20]
4.11
PIN Diodes
UWB
5.31
Ideal Switches
UWB
5.05
MEMS Switches
GPS, Bluetooth, 3G, 4G, UWB, X-Band Radar
40 45 [22] 20 21 [23] 47 47 [*]
2.7–12 GHz 2.6–12 GHz
3.1–14.12 GHz
2.4–24.53 GHz 3.05–13.1 GHz 2.5–10.6 GHz 2.63–10.71 GHz 2.81–11.3 GHz 0.68–16.23 GHz *
Proposed work.
Bluetooth, 3G, 4G, dual notch band UWB, single notch band UWB, and X-Band close range Radar applications. 4. Conclusion In this paper, CPW fed circular shape dual band notched reconfigurable UWB antenna having dimensions of 47 47 0.675 mm3 is fabricated on silicon substrate. The two notch bands at WiMAX and WLAN are achieved by inserting the U- and I-shaped slots, respectively in circular radiating patch. To achieve the reconfigurable band stop performance, the RF MEMS SP4T switches are utilized within the two etched slots. The fabricated antenna exhibits the bandwidth of 0.68–16.83 GHz with reconfigurable band reject function at WiMAX & WLAN band for variety of wireless applications including GPS, Bluetooth, 3G, 4G, UWB & close range radar in X-band. The measured radiation pattern of proposed antenna exhibits quasi-omnidirectional pattern in x-z plane and dipole like pattern in y-z plane enabling the utilization in wireless technologies. The antenna demonstrates the maximum measured gain and radiation efficiency of 5.05 dBi and >90%, respectively, in operating bandwidth except WiMAX and WLAN notch bands. Furthermore, the fabrication of proposed antenna utilizing CMOS compatible processes enables the realization of miniaturized system designs integrating antennas with other RF components for system on chip (SoC) applications. Declaration of Competing Interest The authors declared that there is no conflict of interest. Acknowledgement The authors are thankful to Jadavpur University, Kolkata for providing measurement facility. References [1] First report and order, Revision of part 15 of the commission’s rule regarding ultra-wideband transmission system FCC 02-48, Federal Communication Commission, 2002. [2] Bekali YK, Essaaidi M. Compact reconfigurable dual frequency microstrip patch antenna for 3G and 4G mobile communication technologies. Microw Opt Tech Lett 2013;55(7):1622–6.
[3] Li Y, Li W, Mittra R. A compact CPW-FED circular slot antenna with reconfigurable dual band notch characteristics for UWB communication applications. Microw Opt Tech Lett 2014;56(2):465–8. [4] Li Y, Li W, Ye Q. A reconfigurable wide slot antenna integrated with SIRS for UWB/MULTIBAND communication applications. Microw Opt Tech Lett 2013;55(1):52–5. [5] Ojaroudi N, Ghadimi N, Ojaroudi Y, Ojaroudi S. A novel design of microstrip antenna with reconfigurable band rejection for cognitive radio applications. Microw Opt Tech Lett 2014;56(12):2998–3003. [6] Li Y, Li W, Ye Q. A compact circular slot UWB antenna with multimode reconfigurable band notched characteristics using resonator and switch techniques. Microw Optical Tech Lett 2014;56(3):570–4. [7] Kakhki MB, Rezaei P. Reconfigurable microstrip slot antenna with DGS for UWB applications. Int J Microw Wirel Tech 2017. https://doi.org/10.1017/ s1759078717000034. [8] Ojaroudi M, Ghadimi N. Reconfigurable band-notched small square slot antenna with enhanced bandwidth for octave-band, multi resonance applications. Microw Optical Tech Lett 2014;56(8):1960–5. [9] Atallah HA, Rahman ABA, Yoshitomi K, Pokharel RK. CPW-Fed UWB antenna with sharp and high rejection multiple notched bands using stub loaded meander line resonator. AEU-Int J Electron Commun 2018;83:22–31. [10] Pandey GK, Singh HS, Bharti PK, Meshram MK. Design and analysis of multiband notched pitcher-shaped UWB antenna. Int J RF Microw ComputAided Eng 2016:795–805. [11] Ullah S, Ahmad S, Khan BA, Ali U, Tahir FA, Bashir S. Design and analysis of a hexa-band frequency reconfigurable monopole antenna. IETE J Res 2017. https://doi.org/10.1080/03772063.2017.1347072. [12] Jahromi MN, Falahati A, Edwards RM. Application of fractal binary tree slot to design and construct a dual band-notch CPW-ground-fed ultra-wide band antenna. IET Microw Antennas Propag 2011;12(5):1424–30. [13] Anagnostou DE, Chryssomallis MT, Braaten BD, Ebel J, Sepulveda N. Reconfigurable UWB antenna with RF-MEMS for on-demand WLAN rejection. IEEE Trans Antennas Propag 2014;62(2):602–8. [14] Srivastava G, Mohan A, Chakrabarty A. Compact reconfigurable UWB slot antenna for cognitive radio applications. IEEE Antennas Wirel Propag Lett 2017;16:1139–42. [15] Ghatak R, Karmakar A, Poddar DR. Hexagonal boundary sierpinski carpet fractal shaped compact ultrawideband antenna with band rejection functionality. AEU-Int J Electron Commun 2013;67:250–5. [16] Upadhyay G, Tripathi VS. PIN-diode based switchable multiband dual feed microstrip patch antenna. Microw Optical Tech Lett 2017;59(6):1454–60. [17] Koohestani M, Pires N, Skrivervik AK, Moreira AA. Time-domain performance of a patch-loaded band-reject UWB antenna. Electronic Lett 2013;49 (6):385–6. [18] Quintero G, Zürcher JF, Skrivervik AK. System fidelity factor: a new method for comparing UWB Antenna. IEEE Trans Antennas Propag 2011;59(7):2502–12. [19] Shahmirzadi NV, Oraizi H. Frequency and time-domain analysis of a novel reconfigurable microstrip antenna for UWB applications. J Electrom Waves Appl 2016. https://doi.org/10.1080/09205071.2016.1246210. [20] Badamchi B, Nourinia J, Ghobadi C, Shahmirzadi AV. Design of compact reconfigurable ultra-wideband slot antenna with switchable single/dual band notch functions. IET Microw Antennas Propag 2014;8(8):541–8. [21] Jetti CR, Nandanavanam VR. Trident shape strip loaded dual band notched UWB MIMO antenna for portable devices applications. AEU-Int J Electron Commun 2018;83:11–21.
K. Sharma et al. / Int. J. Electron. Commun. (AEÜ) 110 (2019) 152873 [22] Kalteh AA, DadashZadeh GR, Moghadasi NM, Virdee BS. Ultra-wideband circular slot antenna with reconfigurable notch band function. IET Microw Antennas Propag 2012;6(1):108–12. [23] Li Y, Li W, Mittra R. A CPW-fed wide-slot antenna with reconfigurable notch bands for UWB and multi-band communication applications. Microw Opt Tech Lett 2013;55(11):2777–82. [24] Emadian SR, Shokouh JA. Time-domain analysis of compact dual band-notched slot antenna in indoor environments. Int J Microw Wirel Tech 2018;10 (10):1186–95. [25] Moghadasi MN, Haraty MR, Momeni SMS, Virdee BS. Novel compact UWB antenna with reconfigurable dual-band notches using pin diode switches actuated without kg/4 dc bias lines. Microw Opt Tech Lett 2012;54 (10):2392–7. [26] Nouri M, Aghdam SA. Reconfigurable UWB antenna with electrically control for triple on-demand rejection bandwidth. Microw Opt Tech Lett 2015;57 (8):1894–7. [27] Sharma M, Awasthi YK, Singh H. Design of CPW-Fed high rejection triple band notch UWB antenna on silicon with diverse wireless applications. Prog Electrom Res C 2017;74:19–30. [28] Petersen KE. Silicon as a mechanical material. Proc IEEE 1982;70(5): 420–57.
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[29] Shim Y, Raskin PJ, Neve RC, Zadeh RM. RF MEMS passives on high-resistivity silicon substrates. IEEE Microw Wirel Compone Lett 2013;23(12):632–4. [30] Kishore N, Prakash A, Tripathi VS. A reconfigurable ultra wide band antenna with defected ground structure for ITS application. AEU-Int J Electron Commun 2017;72:210–5. [31] Shah IA, Hayat S, Basir A, Zada M, Shah SAA, Ullah S. Design and analysis of a hexa band frequency reconfigurable antenna for wireless communication. AEU-Int J Electron Commun 2019;98:80–8. [32] Majidzadeh M, Ghobadi C, Nourinia J. Novel single layer reconfigurable frequency selective surface with UWB and multi-band modes of operation. AEU-Int J Electron Commun 2016;70(2):151–61. [33] Ibrahim AA, Shubair MR. Reconfigurable band-notched UWB antenna for cognitive radio applications. Mediterr Microw Sympo Abu Dhabi 2016:1–4. [34] Ibrahim AA, Batmanov A, Burte PE. Design of reconfigurable antenna using RF MEMS switch for cognitive radio applications. Prog Electro Res Sympos 2017:369–76. St.Petersburg. [35] Emadian SR, Shokouh JA, Ghobadi C, Nourinia J. Study on frequency and impulse response of novel triple band notched UWB antenna in indoor environments. AEU-Int J Electron Commun 2018;96:93–106. [36] Karmakar A, Kaur A, Singh K. Ku-band reconfigurable MEMS antenna on silicon substrate. In: 9th Int Radar Symposium India, 2013, (IRSI-13).
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International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue
Regular paper
Reconfigurable dual notch band antenna on Si-substrate integrated with RF MEMS SP4T switch for GPS, 3G, 4G, bluetooth, UWB and close range radar applications Kuldeep Sharma a, Ayan Karmakar b, Manish Sharma c, Ashish Chauhan b, Shonak Bansal a, Manish Hooda b, Sanjeev Kumar d, Neena Gupta a, Arun K. Singh a,⇑ a
Department of Electronics and Communication Engineering, Punjab Engineering College (Deemed to be University), Sector-12, Chandigarh, India Department of AMNSD, Semiconductor Laboratory, Mohali 110017, India c Department of Electronics & Communication Engineering, SGT University Gurgaon, Haryana 121003, India d Department of Applied Sciences, Punjab Engineering College (Deemed to be University), Sector-12, Chandigarh, India b
a r t i c l e
i n f o
Article history: Received 15 January 2019 Accepted 11 August 2019
Keywords: Reconfigurable antenna Dual notch band UWB antenna RF MEMS switch Close range radar Equivalent circuit model
a b s t r a c t In this paper, a reconfigurable co-planner waveguide (CPW) fed circular shaped monopole ultra wide band (UWB) antenna with dual band notch characteristics based on silicon substrate is presented. The dual notch band characteristics are realized by inserting two slots, namely, U- and I-shaped, in the circular radiating patch to switch-off the WiMAX IEEE 802.16 (3.30–3.80 GHz) and WLAN IEEE 802.11a/h/j/n (5.15–5.35 GHz, 5.25–5.35 GHz, 5.47–5.725 GHz, 5.725–5.825 GHz) respectively. The reconfigurability from antenna is achieved by integrating the radio frequency micro-electro mechanical system based single pole four through (RF MEMS SP4T) switch in the U- and I-shaped slots of radiating patch. The measured results demonstrate the bandwidth of 0.68–16.23 GHz resulting in fractional bandwidth of 183.91%, and are well in accordance with the simulation results. The gain of proposed antenna varies from 2.58 to 5.05 dBi with radiation efficiency of 83–95% and exhibits the omnidirectional like pattern in H-plane and nearly dipole like pattern in the E-plane. Further, the performance of proposed antenna is analyzed by implementing an equivalent RLC resonant circuit model in both the frequency and time domain. Ó 2019 Elsevier GmbH. All rights reserved.
1. Introduction Nowadays, an ultra-wideband (UWB) technology is extensively used for low cost, high data rate, and low power wireless communication applications [1–4]. The UWB communication is achieved by employing either the orthogonal frequency division multiplexing based UWB (UWB-OFDM) or the impulse radio based UWB technology (IR-UWB) [1,5]. IR-UWB communication is achieved by transmitting the extremely short pulses, whereas OFDM-UWB, communication requires orthogonal subcarriers to modulate the transmitted data [5]. The Federal Communication Commission (FCC) allocated the unlicensed frequency band (3.1–10.6 GHz) for commercialized use of UWB communication in numerous wireless applications including radar [6–8], ground penetrating system [1], and image system [1]. In addition, they include low power consumption, reduced multipath interference offering high immunity, ⇑ Corresponding author. E-mail address: [email protected] (A.K. Singh). https://doi.org/10.1016/j.aeue.2019.152873 1434-8411/Ó 2019 Elsevier GmbH. All rights reserved.
large channel capacity and strict power transmission [1,5,8–9]. The UWB antenna is one of the crucial component of UWB communication [1,4]. The design of co-planer waveguide (CPW) [3–4] and microstrip UWB antennas [2,5] is quite challenging, as it requires ultra-wide bandwidth, large impedance bandwidth, omnidirectional radiation pattern, low cost, light weight and ease of integration and fabrication [1,2,6,10–12] for operating band. However, a number of CPW and microstrip based antennas with different configurations have been designed and validated experimentally [10–17]. Moreover, narrow band communication systems such as worldwide interoperability microwave access (WiMAX) operating at 3.4–3.69 GHz [5,6] and wireless local area network (WLAN) operating at 5.15–5.825 GHz [4,7–9] also exist in the UWB spectrum [18–23]. The overall performance of UWB antenna is reduced due to interference between narrow band and UWB systems [18–22]. To overcome the interference, several UWB antennas with single or dual band notch characteristics have been reported [23–27]. These notch band characteristics are typically achieved by inserting
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slot [2,8], stub [3,4], resonators [6,22], and parasitic elements [5,7] in radiating patch, ground plane and feed line etc. which allows the leakage of electromagnetic wave through etched slot and hence depreciate the radiation pattern [6,15–17]. Most of the antennas reported so far on FR4 [5–7], RT-Duroid [4–6] and silicon [27] substrates can either work as band reject UWB antenna or just as an UWB antenna with different geometries [3,6]. The FR4 and RTDuroid substrates materials have heating issue due to their lower thermal conductivity, hence are not viable in developing the state-of-art MEMS technology. Moreover, silicon substrate is preferred due to its high thermal conductivity (1.57 W/cm °C), resistivity (>8 kO-cm), dielectric constant (11.9) and tunable RF performance by utilizing the micromachining technique [28]. Additionally, development of system on chip (SoC) is feasible by monolithic integration of other RF components on the silicon chip [29]. In addition, the reconfigurable notch band UWB antenna were developed to typically block and isolate the interference between narrow band and UWB systems with improved performances by inserting a PIN diode and ideal switch inside the slot [5–11, 30–32,33]. The potential applications of the UWB antenna with reconfigurable characteristics include the WiMAX and WLAN band frequencies [23–26]. Later, RF MEMS switch has also been utilized to eliminate the WiMAX and WLAN frequency on radiating patch [13,34]. The use of MEMS based switches are becoming increasingly popular in RF applications due to low insertion loss, high isolation, wide band operation, negligible power consumption, high power handling capability, simple biasing network requirement as compared to conventional semiconductor switches such as FET’s and PIN diode [34]. In addition, the switching operation realized by utilizing FET’s and PIN diode can operate at only lower frequencies. In this paper, a reconfigurable dual band-notched UWB antenna covering bandwidth of 0.68–16.23 GHz is presented for various applications including GPS, 3G, 4G, Bluetooth, UWB and close range radar applications etc. The proposed antenna has a planner structure having a size of 47 47 0.675 mm3, and is fabricated on a high restive silicon substrate (q > 8 kO-cm, er = 11.9, tan d = 0.001) having a thickness of 0.625 ± 0.025 mm, where q is resistivity, er is relative dielectric constant and tan d represents the loss tangent. Here, we utilize the U- and I-shaped etched slots on a circular radiating patch to exhibit dual notch band characteristics for WiMAX and WLAN band, respectively. The single pole four through
(SP4T) MEMS switch has four ports that can switch ON/OFF four bands (from 0 to 14 GHz) simultaneously. The RF MEMS SP4T switch is integrated with the proposed antenna to switch ON/OFF the two interfering bands i.e. WiMAX and WLAN by using two ports, while the other remaining ports are terminated. The developed antenna is proposed for UWB applications including GPS, 3G, 4G, Bluetooth, and close range radar applications etc. To the best of our knowledge, most of the earlier reported works [2–7] have utilized an individual switch for rejecting one interfering band, hence, requires multiple switches for multiple notch band requirements. In addition, each switch requires a separate supply for operation, making the system complex with high power consumption. 2. Antenna design and fabrication The radiating patch of UWB antenna structure is composed of a circular shape fed by CPW transmission line connected to a standard 50 O SMA connector. The configuration of proposed antenna on silicon substrate having length (Lsi) and width (Wsi) of 47 mm each is shown in Fig. 1(a). The radius of circular patch is calculated using following empirical equations considering the center frequency of 6.85 GHz for UWB [27]:
F R ¼ rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi h n o i 2hsi pF þ 1:7726 1 þ per F ln 2h si
ð1Þ
pffiffiffiffi where F ¼ 8:791 109 =f r er , hsi is the height of silicon-substrate in mm, er represents the relative permittivity of the substrate, and fr is the resonating frequency in GHz. However, the effective radius, Re of the patch antenna is estimated by [27]:
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi 2hsi pR þ 1:7726 ln 2hsi per R
Re ¼ R 1 þ
ð2Þ
The 50 O CPW based feed line has a width (Wm) and length (Lm) of 0.92 and 4.25 mm, respectively. A finite ground plane having width (Wg) of 22.64 mm and length (Lg) of 4 mm is shown in Fig. 1(b). The U- and I-shaped slots are etched on the radiating circular patch as depicted in Fig. 1(c) resulting in dual notched band
Fig. 1. (a) Schematic of antenna indicating radiating patch, substrate, ground plane. (b) Top view of antenna without notched bands. (c) Front view with dual notch. (d) Image of packaged SP4T switch (ADGM1304). (e) Cross sectional view of internal structure of SP4T.
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characteristics to eliminate WiMAX and WLAN interfering bands. The optimization of notched band frequencies is carried out by varying the respective slot lengths. The slot length of U- and Ishaped are optimized to eliminate the WiMAX (3.3–3.8 GHz) and WLAN (5.15–5.875 GHz) band frequencies, respectively, as below [27,35]:
LWiMAX ¼ c=ð4 f WiMAX LWLAN ¼ c=ð4 f WLAN
ereff ¼
2
2
ereff Þ
pffiffiffiffiffiffiffiffi
er þ 1 er 1 þ
pffiffiffiffiffiffiffiffi
ereff Þ
1=2 hsi 1 þ 12 Wm
ð3Þ ð4Þ ð5Þ
where c = 3 108 m/sec is the speed of EM wave in free space, ereff is the effective relative permittivity of substrate. The proposed reconfigurable antenna is designed utilizing ANSYS HFSS, and the optimized dimensions are Wm = 0.92 mm, Lm = 4.25 mm, R = 12.5 mm, Wg = 22.64 mm, Lg = 4.0 mm, t = 0.5 mm, G = 0.80 mm, S = 0.40 mm, L1 = 12.0 mm, L2 = 11.0 mm and L = 4.50 mm. The fabrication of proposed structure as shown in Fig. 2(a) is carried out using standard CMOS process on float zone (FZ) processed 600 high resistive silicon (q > 8 kO-cm, er = 11.8, tan d = 0.01) wafer [36]. After cleaning the wafer, deposition of buffer layers (oxide/nitride/oxide stack), and metallization of 2.5 lm to deposit the radiating patch is carried out using DC sputtering. The standard wet chemistry based etching process is employed to pattern the I- and U- shaped slots on circular radiating patch as shown in Fig. 2(b) and (c) respectively. 3. Results and discussion In this work, we have utilized packaged RF MEMS SP4T (ADGM1304) switch shown in Fig. 1(d) inside the slots of radiating patch to control the switching action of designed antenna. The switch has four ports, two ports are used for rejection of WiMAX and WLAN band while remaining ports are terminated. The RF MEMS SP4T has an isolation, insertion loss, return loss of 24 dB, 0.26 dB, and 18 dB, respectively. The maximum RF power that pass through the switch without degradation to the switch life time is 36 dBm. Fig. 1(e) demonstrate the cross sectional view of the internal structure of SP4T switch demonstrating cantilever beam which is fixed at one end and suspended at other end. The upstate and downstate of cantilever beam of RF MEMS tunes the switch in ON and OFF condition, respectively. The return loss (S11) of reconfigurable antenna suggesting four modes of operation due to RF MEMS switch control is shown in Fig. 3. The RF MEMS switch is placed studying maximum surface current density distribution for individual notch bands to eliminate the interference independently. The proposed antenna for GPS, Bluetooth and UWB covers
Fig. 3. Return loss as a function of frequency of proposed antenna indicating reconfigurability utilizing SP4T switch for WiMAX and WLAN.
entire bandwidth of 0.55–16.03 GHz when both the switches are in ON state i.e. S1 = ON & S2 = ON as observed in Fig. 3. Whereas, the antenna demonstrates characteristics covering 1.33– 14.83 GHz with dual notched bands, i.e., WiMAX (3.33–3.76 GHz) and WLAN (4.92–6.14 GHz), when S1 = S2 = OFF condition. The WiMAX and WLAN band frequency can individually be rejected utilizing a combination of switches as S1 = ON & S2 = OFF and S1 = OFF & S2 = ON, respectively, as shown in Fig. 3. The different combination of switches S1 and S2 as shown in Fig. 3 are given in Table 1. Further, to understand the effect of various parameters on antenna performance, a systematic parametric study is carried out employing EM Simulator HFSS as given in following sections. 3.1. Effect of gap width (S) & gap between ground and patch (G) In order to improve the impedance matching between feed line and radiating patch, the gap width (S) and the gap between grounds and patch (G) is optimized. Fig. 4(a) demonstrate that return loss tends to increase with the increase in G from 0.4 to 1.20 mm suggesting deterioration in impedance matching due to increase in fringing field effects. Similarly, impedance matching worsen when S is increased from 0.2 to 0.6 mm as shown in Fig. 4(b). The S & G are optimized to 0.4 and 0.8 mm, respectively covering the bandwidth of 0.55–16.03 GHz. 3.2. Effect of slot length L for WiMAX & L1 for WLAN notched bands The reconfigurability from fabricated antenna is achieved utilizing U- and I-shaped slots for WiMAX and WLAN notch bands,
Fig. 2. Image of fabricated UWB antenna. (a) Without notch band. (b) WLAN notch. (c) WiMAX and WLAN notch.
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Table 1 ON and OFF conditions of RF MEMS SP4T Switches for reconfigurable antenna. Switch (S1)
Switch (S2)
WiMAX Notch (GHz)
WLAN Notch (GHz)
Bandwidth (GHz)
ON OFF ON OFF
ON OFF OFF ON
– 3.33–3.76 3.33–3.76 –
– 4.92–6.14 – 4.92–6.14
0.55–16.03 1.33–14.83 0.68–15.21 1.15–15.01
Fig. 4. Return loss variation as a function of frequency for different (a) gap between ground and patch (G), (b) gap width (S) indicating impedance matching.
respectively as shown in Fig. 1(c). To obtain the WiMAX notch, the side length (L) as shown in Fig. 1(c) is varied from 3.5 to 5.5 mm in Fig. 5(a). Similarly, slot length (L1) shown in Fig. 1(c) is varied from 10 to 13 mm in Fig. 5(b) for demonstrating WLAN notch operation. The optimized values of L = 4.5 mm and L1 = 12 mm are considered for the fabrication of antenna as they are best suited to demonstrate the desired WiMAX and WLAN notch band operation in Fig. 5. The parametric variation of L and L1 to obtain notch band operations for WiMAX and WLAN demonstrating corresponding notch bandwidth are listed in Table 2.
Table 2 Parametric variation of L and L1 for WiMAX and WLAN notch bands.
3.3. Analysis of surface current density distribution and time domain study
uneven distribution of current density results in change in impedance matching, and hence induces the notch characteristics at WiMAX and WLAN bands reflecting back all the energy to the input port. Both the notch band characteristics can individually be controlled because of low mutual coupling between them as shown in Fig. 6(b) and (c). When both the switches are in OFF condition the current density mainly concentrated around the center of slots for WiMAX and WLAN notch frequencies, and hence concludes that the antenna does not radiate, which further suggests to fix the switches at these locations only [34]. Moreover, the surface current
Further to study the mechanism of slot on the radiating patch, surface current density distribution is simulated at the frequency of 7.00, 5.28 and 3.47 GHz for without notch, WLAN notch and WiMAX notch frequency, respectively as shown in Fig. 6(a)–(c). Fig. 6(b) and (c) demonstrate that surface current density increases at the inner and outer edges of U- and I-shaped slots in the presence of both the notch band characteristics, respectively. This
WiMAX
WLAN
Parameters (mm) L
Notch Bandwidth (GHz)
Parameters (mm) L1
Notch Bandwidth (GHz)
3.5 4.0 4.5 5.0
3.78–4.04 3.57–3.91 3.33–3.76 3.08–3.72
10 11 12 13
5.95–6.74 5.45–6.47 4.92–6.14 4.31–6.02
Fig. 5. The effect of variation in slot length (a) L, and L1 on return loss as a function of frequency for WiMAX and WLAN band, respectively.
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Fig. 6. Surface current density distribution at (a) 7.00 GHz. (b) 5.28 GHz. (c) 3.47 GHz.
is evenly distributed over the radiating patch having the slots for entire pass band except WiMAX and WLAN notch frequency. The results in Fig. 6(a) suggest that surface current density is evenly distributed over the radiating surface of the antenna without interfering bands resulting in radiation of EM waves. The pulse handling capability in the far field region of the designed antenna is studied utilizing the two identical antennas as transmitter and receiver as shown in Fig. 7(a). Both the antennas are placed in two configurations i.e., face to face and side to side. A gaussian pulse signal is excited in CST software corresponding to frequency varying from 3.1 to 10.6 GHz for antennas kept at a distance of 250 mm to ensure the far field region. The applied input pulse and the received signal normalized amplitudes for both orientations are shown in Fig. 7(a). The results suggest that more signals are received in face to face orientation rather than side to side orientation. The pulse distortion at the receiving side is due to impedance mismatch in the operating band resulting in transmission of few frequency components. The observed distortion in the received signal as shown in Fig. 7(a) is due to the frequency dispersive behaviour of the antenna. In addition, group delay that can deteriorate the phase linearity with and without notch bands is shown in Fig. 7(b). The reconfigurable antenna has demonstrated almost stable group delay (1.0 ns) for entire range of operating frequency starting from 3.1 to 10.6 GHz except notched frequency bands.
The values of RLC components which correspond to resonance impedance (ZLa) is calculated by Eq. (6) [10,27]:
Z La ¼
n X j¼1
jxRj L j
Rj 1 x2 Lj C j þ jxLj
ð6Þ
Input impedance of proposed reconfigurable antenna without notched bands is shown in Fig. 8(a) corresponding to the antenna shown in Fig. 1(b). As depicted, real and imaginary impedances vary around 50 and 0 X which indicate the matched condition of proposed antenna in entire operating band. In case of notched band characteristics high impedance mismatch is required at WiMAX and WLAN as shown in Fig. 8(b). Corresponding to WiMAX notched band center frequency of 3.65 GHz, the real impedance is 34.44 X which results in impedance mismatch and imaginary impedance varies from negative to positive. Simultaneously for WLAN frequency at 5.12 GHz (fPR from Fig. 10(a)) the estimated real impedance (Rpn from Fig. 8(b)) is 10 X and imaginary impedance varies from negative to positive. Combining real and imaginary impedance for both the notch bands two series RLC circuits connected in parallel as shown in Fig. 9(b). For unmatched condition, either short or open impedance is expected which results in mismatch when compared to match condition. The resonant frequencies and corresponding bandwidths of the series and parallel resonance circuits as shown in Fig. 9(b) can be calculated as [10,27]:
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
3.4. Equivalent circuit model
xSR ¼ 1= Lsn C sn
ð7Þ
In recent UWB technology, UWB antenna structures are more complicated and compact. Hence, an equivalent circuit model based on input impedance characteristic is necessary to discuss the mechanism of notch band characteristics. Hence, we have utilized CST software for evaluating input characteristics and RLC parameter for equivalent circuit model in Fig. 9(a) and (b) for antenna without and with notch band slots, respectively.
BW SR ¼ Rsn =Lsn
ð8Þ
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
xPR ¼ 1= Lpn C pn
ð9Þ
BW PR ¼ 1=Rpn C pn
ð10Þ
Fig. 7. Two identical reconfigurable antennas are used as transmitter and receiver kept at a distance of 250 mm, i.e. in far field to study the time domain characteristics in the CST software. (a) Input signal and received signal as a function of frequency for both the orientations. (b) Stable group delay of (1.0 ns) for antenna with and without notched band at WiMAX and WLAN. The inset shows antennas used in the two orientations, i.e., face to face, and side to side as shown in (b).
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Fig. 8. Real and Imaginary impedances of (a) proposed antenna without notched bands. (b) with notched bands at WiMAX and WLAN.
Fig. 9. Equivalent circuit model of proposed antenna (a) without notch bands. (b) with notch bands.
xSR (=2pfSR), xPR (=2pfPR) are the series & parallel resonant frequencies and BWSR, BWPR are the corresponding bandwidths which are estimated from Fig. 8(b) along with the values of series Rsn & parallel Rpn resistances. The value of Lsn, Csn, Lpn and Cpn for an equivalent circuit of proposed antenna given in Fig. 9(b) are calculated by Eqs. (7)–(10) where n = 1, 2 for dual notched band antenna. 3.5. Experimental results Fig. 10(a)–(b) demonstrates the return loss and VSWR of proposed antenna, respectively, and are well in accordance with the results obtained from the simulations implementing Ansys HFSS software. The slight variation is due to impedance mismatch between SMA connector and CPW feed conducting epoxy (silver) used to integrate the RF MEMS switch with radiating patch as shown in the inset of Fig. 10(a). The peak value of measured S11 (i.e. 5.18 and 3.15 dB) and VSWR (i.e. 3.63 and 5.28) corresponds to the rejected frequency of 3.35 and 4.95 GHz with measured bandwidth of 0.68–16.23 GHz. The results obtained from the equiv-
alent circuit model given in Fig. 9(b) are well in accordance with the measured and simulated results as shown in Fig. 10(a). The measured gain of notched frequency shown in Fig. 10(c) is found to be 6.836 and 7.96 dBi at 3.44 and 5.58 GHz, respectively, which confirms that antenna does not radiate in WiMAX and WLAN frequencies. Whereas, antenna exhibits a gain varying from 2.58 to 5.05 dBi for entire range of frequency (i.e. 0.68 to 16.23 GHz except WiMAX and WLAN notches). The proposed antenna also exhibits a good radiation efficiency (83–94%) across the entire bandwidth except in two notched bands i.e. 37 and 26.58% at 3.65 and 5.40 GHz, respectively. Fig. 11 depicts the measured normalized radiating patterns of proposed antenna including co- & cross- polarization in H (x-z plane) and E plane (y-z plane). It is observed that antenna demonstrates nearly omnidirectional and dipole like radiation characteristics with less cross polarization in H- and E-plane, respectively. At higher frequencies cross polarization increases due to increase in area of radiation. In addition, the dimension of antenna’s ground plane is less than a quarter wavelength when compared with the lowest frequency
Fig. 10. Measured and simulated (a) return loss and (b) VSWR as a function of frequency of the fabricated reconfigurable antenna shown in Fig. 2(c). The results obtained from equivalent circuit model are well in accordance with the measured and simulated results. The inset shows the packaged RF MEMS SP4T switch integrated with antenna using conductive silver epoxy. (c) Measured gain and simulated radiation efficiency as a function of frequency.
K. Sharma et al. / Int. J. Electron. Commun. (AEÜ) 110 (2019) 152873
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Fig. 11. Measured and simulated radiation pattern of E and H-plane in dB at (a) 1.575 GHz (b) 2.45 GHz (c) 4.5 GHz (d) 7 GHz (e) 9 GHz (f) 11 GHz.
of UWB i.e. 3.10 GHz. As a result, few leakage current may be distributed along the external conductor of the SMA connector which corresponding affect the radiation patterns.
Table 3 shows comparison of proposed work with previously reported similar experimental studies. The proposed antenna can be used for variety of wireless applications including GPS,
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K. Sharma et al. / Int. J. Electron. Commun. (AEÜ) 110 (2019) 152873
Table 3 Comparison of proposed work with previously reported similar experimental studies. Impedance Bandwidth
Notched Bands
Maximum peak VSWR at center notched frequency
Maximum Gain (dBi)
Reconfigurable Characteristics
Applications
Size (mm2)
2.7–12 GHz
WLAN X-Band WiMAX X-Band WiMAX WLAN X-Band WLAN ITS ITU WLAN WLAN WiMAX WLAN WiMAX WLAN WLAN X-Band WiMAX WLAN
[email protected] GHz [email protected] GHz 19.2 @ 3.6 GHz 9.0 @ 7.9 GHz [email protected] GHz [email protected] GHz [email protected] GHz 5.8 @5.7 GHz 5.0 @6.3 GHz 4.0 @8.2 GHz 6.0 @5.8 GHz 6.1 @5.85 GHz 5.6 @3.55 GHz 5.3 @5.68 GHz [email protected] GHz [email protected] GHz [email protected] GHz [email protected] GHz [email protected] GHz [email protected] GHz
5.32
Ideal Switches
UWB, X-Band Radar
24 32 [4]
5.43
Ideal Switches
UWB, X-Band Radar
24 32 [5]
5.53
Ideal Switches
UWB, X-Band Radar
24 32 [6]
5.12
PIN Diodes
UWB, X-Band Radar
12 18 [7]
– 5.38 4.12
PIN Diode PIN Diode PIN Diodes
UWB, X-Band Radar, Satellite Comm. UWB, X-Band Radar UWB
20 20 [8] 20 20 [9] 20 20 [20]
4.11
PIN Diodes
UWB
5.31
Ideal Switches
UWB
5.05
MEMS Switches
GPS, Bluetooth, 3G, 4G, UWB, X-Band Radar
40 45 [22] 20 21 [23] 47 47 [*]
2.7–12 GHz 2.6–12 GHz
3.1–14.12 GHz
2.4–24.53 GHz 3.05–13.1 GHz 2.5–10.6 GHz 2.63–10.71 GHz 2.81–11.3 GHz 0.68–16.23 GHz *
Proposed work.
Bluetooth, 3G, 4G, dual notch band UWB, single notch band UWB, and X-Band close range Radar applications. 4. Conclusion In this paper, CPW fed circular shape dual band notched reconfigurable UWB antenna having dimensions of 47 47 0.675 mm3 is fabricated on silicon substrate. The two notch bands at WiMAX and WLAN are achieved by inserting the U- and I-shaped slots, respectively in circular radiating patch. To achieve the reconfigurable band stop performance, the RF MEMS SP4T switches are utilized within the two etched slots. The fabricated antenna exhibits the bandwidth of 0.68–16.83 GHz with reconfigurable band reject function at WiMAX & WLAN band for variety of wireless applications including GPS, Bluetooth, 3G, 4G, UWB & close range radar in X-band. The measured radiation pattern of proposed antenna exhibits quasi-omnidirectional pattern in x-z plane and dipole like pattern in y-z plane enabling the utilization in wireless technologies. The antenna demonstrates the maximum measured gain and radiation efficiency of 5.05 dBi and >90%, respectively, in operating bandwidth except WiMAX and WLAN notch bands. Furthermore, the fabrication of proposed antenna utilizing CMOS compatible processes enables the realization of miniaturized system designs integrating antennas with other RF components for system on chip (SoC) applications. Declaration of Competing Interest The authors declared that there is no conflict of interest. Acknowledgement The authors are thankful to Jadavpur University, Kolkata for providing measurement facility. References [1] First report and order, Revision of part 15 of the commission’s rule regarding ultra-wideband transmission system FCC 02-48, Federal Communication Commission, 2002. [2] Bekali YK, Essaaidi M. Compact reconfigurable dual frequency microstrip patch antenna for 3G and 4G mobile communication technologies. Microw Opt Tech Lett 2013;55(7):1622–6.
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