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Compact ultra-wideband circularly polarized CPW-fed monopole antenna
Int. J. Electron. Commun. (AEÜ) 107 (2019) 137–145
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International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue
Regular paper
Compact ultra-wideband circularly polarized CPW-fed monopole antenna Prashant Chaudhary a, Ashwani Kumar b,⇑ a b
Department of Electronic Science, University of Delhi South Campus, New Delhi 110021, India Department of Electronics, Sri Aurobindo College, University of Delhi, New Delhi 110017, India
a r t i c l e
i n f o
Article history: Received 21 January 2019 Accepted 17 May 2019
Keywords: Circular polarization (CP) Compact antenna Coplanar waveguide (CPW) Fed antenna Monopole antenna Ultra-wideband (UWB) Array antenna
a b s t r a c t This paper presents a coplanar waveguide (CPW) -fed quadrilateral-shaped compact planar monopole antenna for ultra-wideband (UWB) application. The fractional axial ratio bandwidth (ARBW) of the antenna for circular polarization (CP) is 56.64% (5.91–10.58 GHz) and its fractional impedance matching bandwidth (IMBW) is 137.1% (3.1–17.5 GHz), which are realized by designing a quadrilateral-shaped monopole with an asymmetric ground plane. The proposed antenna structure is simple and compact; hence its design is efficient, and it has an impedance matching (S11) in UWB band with embedded wideband circular polarization. The gain of the antenna varies between 3.33 and 8.9 dBi. Furthermore, its application for designing the linear array and planar array of 1 2 and 2 2 antenna elements are presented. The gain improves to 5.1–9 dBi for 1 2 array elements and to 9–11.2 dBi for 2 2 array with UWB IMBW. Simulated and experimental results are presented to validate the antenna design and are shown to be in good agreement. Ó 2019 Elsevier GmbH. All rights reserved.
1. Introduction In modern wireless communication system, the demand of circularly polarized (CP) planar antenna is witnessing a rapid increase because CP antennas are polarization independent of the incident wave and, hence, they find many applications in hand-held devices as well as in RFID and rotating systems. It is desirable to use antennas with circular polarization (CP) to avoid the effects of path-loss and displacement of the antennas, when the position of the transmitting and the receiving antennas are changing, or their operation is insecure to the weather conditions. The basic principle of generating the circular polarization (CP) is to excite two orthogonal modes in a phase-quadrature that have equal amplitudes [1]. A variety of approaches to realizing CP antennas have been reported in the literature. These include, for instance, the use of two orthogonal feeds, though this makes the antenna structure complex and bulky [1,2]. Circularly polarized (CP) antenna is also designed by using either a single feed at 45° along the axis of the patch or by corner truncation of the square patch. However, the single-feed techniques discussed in above references generate CP with a relatively narrow bandwidth [1,2], which may not be suitable for many applications. ⇑ Corresponding author. E-mail address: [email protected] (A. Kumar). https://doi.org/10.1016/j.aeue.2019.05.025 1434-8411/Ó 2019 Elsevier GmbH. All rights reserved.
The UWB antenna provides a high data transfer rate (110–200 Mb/s), larger bandwidth, simple hardware configuration, low power consumption, excellent immunity to the multipath interference and an omni-directional radiation pattern [15–17]. Several wireless systems, including the 3.6 GHz IEEE 802.11y, WLAN (3.6575–3.69 GHz), 4.9 GHz public safety WLAN (4.94– 4.99 GHz), 5 GHz IEEE 802.11a/h/j/n, WLAN (5.15–5.35 GHz, 5.25–5.35 GHz, 5.47–5.725 GHz, 5.725–5.825 GHz), satellite communication C-band (3.7–4.2 GHz) for downlink, and (5.925– 6.425 GHz) for uplink, X-band (8–12 GHz) for radar, and Ku-band (10.7–12.75 GHz) for direct broadcast satellite services, also operate within the same UWB band. A review of the literature reveals, that considerable effort has been invested by researchers in implementing various techniques [3–17], toward realizing circularly polarized (CP) antennas, that are both wideband and compact. Some of the suggested techniques are: using L-slot antenna with single fed by L-shaped feed line [3]; combination of slot and printed monopole [4]; chifre-shape CP monopole antenna [5]; protruded in L-shape strip and inverted L-shape strip [6]; inverted L-strip and asymmetric ground plane [7]; modified L-shaped patch with conjugation of rectangular slot in the ground plane [8]; rectangular monopole with an asymmetric ground plane and a square-ring with an open gap at the bottom [9]; artificially created ground [10]; S-shaped slots [11]; microstrip-CPW fed planar slot antenna [12]; cross-shaped CP
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antenna with a ground plane extension [13]; and slot antenna with an inverted-F shaped microstrip feed line with two linked rectangular slots in the ground plane [14]. The above suggested antennas are limited to wideband application. In recent years, some UWB antennas are also designed with embedded CP band. In [15], coplanar-waveguide (CPW)-fed circularly polarized square slot antenna presented with impedance matching bandwidth of 12.06 GHz (2.76–14.82 GHz), and CP axial ratio bandwidth of 1.86 GHz (4.27–6.13 GHz), in [16], CP square slot antenna fed by a coplanar waveguide is presented with IMBW of 8.3 GHz (2.9–11.2 GHz), and ARBW of 2.3 GHz (5.1–7.4 GHz), in [17], CP spiral antenna using integrated balun is presented with IMBW of 14.85 GHz (3.75–18.6 GHz), and ARBW of 11.5 GHz (3–14.5 GHz), while [18], presents UWB slot antenna with broadband CP with IMBW of 12.4 GHz (1.9–14.3 GHz) and ARBW of 4.0 GHz (1.9–5.9 GHz).The array antenna are preferred for high gain and phased array [20–22]. There are challenge to design array antenna for UWB with embedded wideband CP. Array antenna designed for UWB application [21], is linearly polarized while array antenna presented in [22], has narrow CP band. This paper presents the design of a compact planar monopole quadrilateral-shaped CPW feeding antenna with asymmetric ground plane for ultra-wideband (UWB) application. Proposed antenna has IMBW of 137.1% (3.1–17.5 GHz) while embedded circular polarization (CP) ARBW of 55.86% (5.96–10.58 GHz). Furthermore, linear antenna array of 1 2 elements and planar antenna array of 2 2 elements have been designed and their performances are compared with the single antenna element. 2. Antenna design Fig. 1 shows the layout and fabricated CPW-fed proposed planar antenna. The radiating surface has a quadrilateral shape and an asymmetric ground plane, both of which are built on the same side of the FR-4 substrate, with an er ¼ 4:4 and thickness of 0.8 mm. A step-impedance resonator is inserted in the central feedline to get better return loss (S11) of the proposed antenna. The length and width of the lower line are 6 mm and 1.5 mm, respectively, while they are c = 2.07 mm and d = 3 mm for the upper line. The gap between the feeding line and the ground plane is 0.75 mm. The shape of the radiator is a quadrilateral which is connected to the CPW line. An asymmetrical ground has been added to generate the circular polarization. The detailed dimensions of the proposed antenna structure (see Fig. 1) are: Wx = 30 mm, Ly = 25 mm, L = 13.43 mm, W = 13 mm, a = 7.43 mm, b = 5 mm, Gl = 3 mm, Gr = 11.3 mm, W1 = 2.8 mm, l1 = 5 mm, lx = 23 mm. The primary objective of this paper is to design an UWB antenna with a circular polarization (CP) which has a compact size and yet a wide AR
Fig. 1. Proposed antenna structure.
bandwidth. Hence, the geometry of the antenna is adjusted in such a fashion that it generates two orthogonal components of electric field (EX and EY), with equal amplitudes and a 90° phase difference, to generate the desired circular polarization (CP). Towards this end, a quadrilateral-shaped patch with an asymmetric ground plane has been used to achieve wideband circular polarization. 3. Antenna design procedure Any circularly polarized (CP) antenna should have its 3-dB axial ratio (AR) bandwidth entirely within the 10-dB impedance matching (S11) band. Hence, the primary issue for the designing of circularly polarized antenna is focused on how the quadrilateral-shape radiator and asymmetric ground plane simultaneously improves the 10-dB IMBW (S11) and 3 dB ARBW of the antenna. Therefore, the proposed antenna is designed in six steps, as shown in Fig. 2 below, with the progressive transformations designated from Step-1 to Step-6. The proposed antenna structure is simulated by using HFSS version-16. Step-1 which is linearly polarized antenna with square-shaped radiator and a symmetric ground plane, which provides impedance matching (S11) band from 3.1 GHz to15 GHz, the dimensions of this antenna are obtained for the lower frequency of the UWB band by using equation-1 [19].
fL ¼
7:2 W where r ¼ ½ðL þ r þ PÞ K 2p
ð1Þ
where L, r, P are in mm, the value of L = 13.43 mm W = 13 mm, P = 3.07 mm and K = 1.15. The length and width of the antenna-1 are 13.43 mm and 13 mm, respectively. Step-2 and step-3 are obtained by truncating upper and lower triangular portions, both the antennas are linearly polarized with IMBW from 3.1 GHz to 15 GHz and from 5.8 GHz to 18.5 GHz respectively. Step-4 is obtained by extended ground plane which is circularly polarized antenna at two center frequencies 10.2 GHz and 15.1 GHz with IMBW 4.5 GHz to 5.4 GHz and 13.2 GHz to 18.6 GHz respectively. Step-5 provides dual band CP antenna at center frequencies 8.3 GHz and 14.86 GHz while IMBW from 5.8 GHz to 15 GHz. Step-6 presents the proposed antenna with quadrilateral-shaped patch and asymmetric ground plane, which has IMBW from 3.1 GHz to 17.5 GHz while ARBW from 5.96 to 10.58 GHz. Fig. 3 shows the return loss (S11) and axial ratio for different design steps. The 3-dB axial ratio band improves when the antenna design is progressively modified from Step-4 to Step-6. The ratio of the amplitude of the electric far field components (EX/EY) and their phase difference (PD) are shown in Fig. 4. To realize the circular polarization (CP), we need to work with two electric far field com-
Fig. 2. Design steps of the proposed antenna.
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Fig. 3. Response of Step-1 to Step-6.
Fig. 4. Electric field components (EX and EY) Magnitude and Phase difference.
ponents (EX and EY) that have the same amplitudes but 90° phase difference. The electric far field components (EX and EY) of step-1 to step-3 have neither identical amplitude nor have 90°-phase difference at the same time, as may be seen from Fig. 4 (a) and (b). The electric far field components (EX and EY) of step-4 and step-5 have same amplitude and 90°-phase difference at 10.2 GHz and 15.1 GHz and 8.3 GHz and 14.86 GHz respectively. The final antenna which is step-6 has identical amplitude and 90°-phase difference at the same time from 5.91 to 10.58 GHz, which in turn generates the desired circular polarization (CP) over a wideband.
The rotating current which are distributed on the surface of final antenna (step-6) at 8.25 GHz is shown in Fig. 5, which also helps to explain the generation of the circular polarization (CP) of the designed antenna. The surface current vectors on the quadrilateral shape antenna for 8.25 GHz at different phase instants (0°, 90°, 180° and 270°) are illustrated in Fig. 5. It can be seen that the surface current vectors rotate mainly clockwise with phase, so the left-handed circular polarization (LHCP) operation is realized. This LHCP operation could be noticed at the upper half z > 0 while the RHCP operation could be observed at the lower half of the space with Z < 0.
Fig. 5. Surface current distribution of final antenna at 8.25 GHz.
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Fig. 6. Effect of lX on the return loss (S11) and 3 dB axial ratio of the final antenna.
Fig. 7. Effect of a on the return loss (S11) and 3 dB axial ratio of the Antenna.
Table 1 Effect of lX on IMBW and ARBW. lx, mm
0 4 8 12 16 20 23 24
IMBW
ARBW
(f1–f2) GHz
BW GHz
(f1–f2) GHz
BW GHz
(3.06–4.52), (5.4–15.67) (3.14–4.59), (5.37–15.51) (3.21–4.79), (4.93–15.70) (3.29–15.48) (3.34–15.38) (3.3–17.8) (3.1–17.5) (3.39–18.0)
1.46, 10.27 1.45, 10.14 1.58, 10.77 12.19 12.04 14.5 14.4 14.61
(8.11–8.45), (14.62–15.71) (8.42–10.65), (14.8–15.48) (8.66–10.03), (14.98–15.47) (7.22–8.01), (8.82–9.44) (6.81–7.38), (8.50–10.16) (6.34–10.94), (14.50–15.73) (5.91–10.58) (5.94–10.42)
0.34, 1.09 2.23, 0.68 1.37, 0.49 0.79, 0.62 0.57, 1.66 4.6, 1.23 4.67 4.48
Table 2 Effect of a on IMBW and ARBW. a, mm
0 2 4 6 7.43 8 10 12
IMBW
ARBW
(f1–f2) GHz
BW GHz
(f1–f2) GHz
BW GHz
(3.14–15.51) (3.32–15.68) (3.29–16.58) (3.28–16.52) (3.1–17.5) (3.28–18) (3.27–4.44), (5.30–17.24) (3.27–4.69), (5.34–17.10)
12.37 12.36 13.29 13.24 14.4 14.72 1.17, 11.94 1.42, 11.76
(8.13–9.01) (8–9.32), (10.16–10.50) (5.98–10.53) (5.99–10.55)) (5.91–10.58) (5.98–10.63) (5.98–10.51) (5.98–8.64), (9.98–10.52)
0.88 1.32, 0.34 4.55 4.56 4.67 4.65 4.53 2.66, 0.54
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4. Parametric study This section presents the parametric study of the antenna geometry. The best impedance matching bandwidth (S11) and 3-dB axial ratio responses of the proposed antenna (step-6) are shown in Fig. 3. Therefore, for brevity, they are not presented here, in this parametric study. Truncation of the upper
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and lower sections of the square patch are typically important elements that generates the circular polarization, which has already been discussed in detail in section-III. The effect of asymmetric ground plane length (lX) and length of lower triangular portion of the patch (a) on the axial ratio and IMBW (S11) have been discussed here in detail and presented in Figs. 6 and 7.
Fig. 8. Simulated and measured performances of the final Antenna.
Fig. 9. Simulated and measured radiation pattern of the proposed antenna at 7.0 GHz, 8.4 GHz and 10.2 GHz.
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Table 3 Comparison with the recently published work. Ref.
% IMBW, GHZ
% ARBW, GHz
Size (L W)
Er, h (mm)
Gain range (dBi)
[3] Slot [4] Slot [5] MT [6] MT [7] CPW [8] CPW [9] CPW [10] MSA with AMC [11] CPW [12] CPW slot [13] MSA extended GND [15] CPW slot [16] CPW slot Our
57% (2.18–3.92) 51% (1.9–3.2) 72% (1.5–3.4) 133.41% (1.38–6.4) 58.8% (4.8–8.8) 87.2% (2.2–5.6) 96.5% (1.48–4.24) 48.6% (4.52–7.42) 104% (1.78–5.64) 57% (1.73–3.11) 55.5% (4.36–7.71) 137.2% (2.76–14.82) 117.7% (2.9–11.2) 137.12% (3.1–17.5)
46.5% (2.18–3.5) 30% (2.0–2.6) 41.6% (2.1–3.12) 129.04% (1.38–6.4) 47.8% (5.375–8.75) 61.85% (2.2–4.17) 63.3% (2.05–3.95) 20.4% (5.40–6.63) 58.6% (2.85–5.21) 39.4% (1.98–2.95) 42.6% (4.8–7.4) 35.76% (4.27–6.13) 38.2% (5.01–7.4) 56.64% (5.91–10.58)
82 82 186 103 63 58.4 40 40 25 24 50 45 13.5 55 39 40 54 54 100 120 16 22 25 25 25 25 13.0 13.43
2.6, 1.524 2.2, 1.6 4.4, 1.5 4.4, 1.0 4.4, 1.0 4.4, 1.6 4.4, 1 2.2, 4.8 2.55, 1.0 2.55, 0.762 4.4, 1.0 4.4, 0.8 4.4, 0.8 4.4, 0.8
4.75–7.28 1.3–2.9 2.5–3.7 2.85–3.54 1.5–3.3 3.0–4.0 0.5–3.5 5.5–6.2 3.0–4.0 2.5–3.4 0.5–2.6 2.0–3.2 2.3–2.9 3.33–5.67
(a) 1×2 antenna elements
(b) 2×2 antenna elements
Fig. 10. UWB antenna array design using (a) 1 2 antenna elements and (b) 2 2 antenna elements.
Fig. 11. Simulated impedance matching (S11), 3 dB axial ratio and gain of array antenna of 1 2 elements with spacing Dx.
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This section illustrates the effect of asymmetric ground plane length (Lx) on IMBW and on ARBW with fixed a = 7.43 mm. From lX = 0 mm to 8 mm the antenna is behaving like a dual band circularly polarized antenna and from lX = 8 mm to 20 mm, the dual band starts merging with single wideband of IMBW from 3.29 GHz to 15.48 GHz while it still has dual band CP within the IMBW, which have different frequency bands, they are summarized in Table 1 and presented in Fig. 6. At lX = 23 mm, antenna becomes single band antenna with UWB IMBW and wide ARBW, which are 137.12% (3.1–17.5) and 56.64% (5.91–10.58) respectively. After lX = 23 mm the IMBW improves slightly while ARBW starts deteriorating.
fixed lX = 23 mm. For a = 0 mm the antenna has UWB impedance matching bandwidth while it has narrow CP band 0.88 GHz. For a = 2 mm the antenna is UWB with two CP bands from 8 to 9.32 GHz and 10.16–10.50 GHz. From a = 4 mm to 8 mm the antenna is behaving like a UWB antenna with wide CP band. At a = 10 mm the antenna is dual band antenna with single wideband from 5.98 to 10.51 GHz while for a = 12 mm the antenna becomes dual band antenna with IMBW from 3.27 to 4.69 GHz, and 5.34–17.10 GHz with ARBW from 5.98 to 8.64 GHz and 9.98 to 10.52 GHz respectively. We have considered a = 7.43 mm and lX = 23 mm as the final choice as they provide UWB IMBW with wideband CP. The effect of a on IMBW and ARBW has been summarized in detail in Table 2. The effect of a on impedance matching (S11) and axial ratio are presented in Fig. 7.
4.2. a- variation with fixed lX = 23 mm
5. Measurement
This section illustrates the effect of length of lower triangular portion of the patch (a) on the axial ratio and IMBW (S11) with
The proposed antenna, which is the final optimized antenna design, has been designed and fabricated (see Fig. 1) on FR-4 sub-
4.1. Lx variation with fixed a = 7.43 mm
Table 4 Comparison of performances of single element with 1 2 and 2 2 array elements. Parameters
Single Element
1 2 Elements
2 2 Elements
Dx
Dx = Dy
0.4k
0.6k
0.8k
1k
0.4k
0.6k
0.8k
1k
3.25–18.5 15.25 (6.14–10.70), (16.68–17.1) 4.56, 0.42 5.85–9.23
3.25–17.25 14.0 9.14–10.27
3.25–17.25 14.0 6.73–9.97
3.25–18.5 15.25 6.43–9.41
1.13 3.0–12.65
3.24 6.8–11.96
2.98 7.88–11.80
3.25–17.25 14.0 (6.5–8.98), (10–10.83) 2.48, 0.83 8.75–12.70
S11 IMBW (GHz) 3 dB AR
3.1–17.5 14.4 5.91–10.58
3.25–17.25 14.0 6.56–10.53
3.25–17.25 14.0 6.40–8.84
3.25–17.25 14.0 6.27–10.68
ARBW (GHz) Peak Gain (dBi)
4.67 3.33–8.9
3.97 4.3–10.11
2.44 4.8–8.77
4.41 5.3–10.41
Fig. 12. Simulated IMBW (S11), 3 dB axial ratio and gain of array antenna of 2 2 elements with spacing Dx and Dy.
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strate and its performances are measured. The measured IMBW (S11) and 3-dB ARBW for the final designed antenna are shown in Fig. 8. The proposed antenna has IMBW (S11) from 3.1 GHz to 17.5 GHz. Measured 3 dB ARBW of the antenna is from 5.91 to 10.58 GHz, representing a 56.64% fractional bandwidth. Simulated and measured results are slightly different, perhaps because of the effect of the SMA connector and due to fabrication error. The gain of the antenna (simulated and measured) is shown in Fig. 8b. Note, that the measured gain of the antenna is in between 3.33 and 8.9 dBi with 3 dB axial-ratio (AR) band ranges from 5.91 to 10.58 GHz. The simulated and measured far-field radiation patterns of the proposed antenna at 7.0 GHz,8.4 GHz and 10.2 GHz are presented in Fig. 9 for both LHCP and RHCP in XY- and YZ-planes. Radiation pattern and shapes are not uniform among these three frequencies. At low frequency radiation pattern is directional, meanwhile showing slightly distorted pattern at higher frequencies. The main reason behind this, the strong surface current on the edges of the radiator at high frequency. Finally, the performances of the proposed quadrilateral shape antenna are compared in Table 3 with the recently published works [3–16]. Our proposed antenna structure has compact size and is found to have improved IMBW (S11) in UWB band and embedded wideband 3 dB ARBW.
6. Array design UWB antenna arrays are preferred in point-to-point communications because they provide a high gain and better directionality. Here, array antenna for 1 2 and 2 2 antenna elements are pre-
sented. Fig. 10 shows the UWB array antenna by using 1 2 and 2 2 antenna elements. To reduce the complexity of the feeding network design, here the array antenna elements are placed side by side as shown in the Fig. 10, to see the effect on the performances of the proposed antenna. The UWB antenna array study has been presented in three different subsection-A, B and C. Section-A deals with linear array of 1 2 antenna elements, Section-B deals with planar array of 2 2 antenna elements while section-C compares the performances of single element with antenna arrays of 1 2 and 2 2 elements. 6.1. Linear array of 1 2 antenna elements This section illustrates the effect on the IMBW, ARBW and gain of the proposed single antenna, when it has been placed in linear array with 1 2 antenna elements as shown in Fig. 10a. The IMBW and ARBW and gain are shown in Fig. 11 with different spacing. Spacing has been chosen between edge to edge of the antenna in terms of wavelength as shown in Fig. 10a. The spacing between the 1 2 and 2 2 elements are taken as Dx and Dy = 0.8k (kat fc = 10.25 GHz), this spacing between the elements provides the improved IMBW, ARBW and gain. For spacing Dx = 0.8k = 22.528 mm, the IMBW for 1 2 is 14 GHz (3.25–17.25 GHz), 3 dB ARBW is 4.41 GHz (6.27–10.68 GHz) and gain is varying from 5.3 to 10.41 dBi within the entire IMBW. Table 4 compares the performance of single antenna with 1 2 array elements for different spacing. However, for 2 2 Elements, the IMBW is 15.25 GHz (3.25–18.5 GHz), 3 dB ARBW is 2.98 GHz (6.43–9.41 GHz) and gain is varying 7.88 to 11.80 dBi with in the IMBW.
Fig. 13. Simulated performances comparison of single element, with 1 2 and 2 2 array elements.
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6.2. Planar array of 2 2 antenna elements This section illustrates the effect on the IMBW, ARBW and gain of the proposed antenna, when it is placed in planar array of 2 2 antenna elements as shown in Fig. 10b. The IMBW, ARBW and gain are shown in Fig. 12 with different spacing (Dx = Dy). The spacing is chosen between edge to edge of the antenna elements both in X and Y direction. The spacing for 2 2 antenna elements are varied uniformly. There is no effect on the IMBW which is 15.25 GHz (3.25–18.5 GHz) and ARBW deteriorates with the spacing. The ARBW becomes narrow 2.98 GHz (6.43–9.41 GHz) for Dx = Dy = 0.8k = 22.528 mm while gain varies from 7.88 to 11.80 dBi within the IMBW. Table 4 compares the performance of single antenna with 2 2 array elements for different spacing. 6.3. Compares the performances of single element with antenna arrays of 1 2 and 2 2 elements. This section compares the performances of single element with antenna array of 1 2 and 2 2 elements. The IMBW of single element is 14.4 GHz (3.1–17.5 GHz), embedded circular polarization (CP) ARBW is 4.67 GHz (5.96–10.58 GHz) and its gain varies from 3.33 to 8.9 dBi. The spacing between the 1 2 and 2 2 elements are taken as Dx and Dy = 0.8k, this spacing between the elements provides the improved IMBW, ARBW and gain. For spacing Dx = Dy = 0.8k = 22.528 mm, the IMBW for 1 2 is 14 GHz (3.25– 17.25 GHz), 3 dB ARBW is 4.41 GHz (6.27–10.68 GHz) and gain is varying from 5.3 to 10.41 dBi within the entire IMBW. However, for 2 2 elements, the IMBW is 15.25 GHz (3.25–18.5 GHz), 3 dB ARBW is 2.98 GHz (6.43–9.41 GHz) and gain is varying 7.88 to 11.80 dBi with in the entire IMBW. The IMBW, ARBW and gain are compared in Fig. 13 for single element, with 1 2 and 2 2 array elements. The IMBW is remain same for single element, 1 2 and 2 2 elements while the ARBW changes from 4.67 GHz (single element) to 4.41 GHz (1 2 array elements) and to 2.98 GHz (2 2 array elements). The circular polarization bandwidth reduces for the 1 2 and 2 2 array elements because antennas placed in array configuration produce slightly different magnitude of the field components with different phase. 7. Conclusion A quadrilateral-shaped UWB CPW-fed monopole circularly polarized (CP) antenna has been proposed. A prototype of the antenna is fabricated, and its measured results are presented, which is useful for the modern communication system. The measured results show that the antenna has a wideband circular polarization (CP) with a 56.64% fractional ARBW and an ultra-wideband (UWB) IMBW (S11) of 137.1%. Furthermore, the single antenna elements are placed in linear array and planar array of 1 2 and 2 2 elements and their performances are compared. The performance of the proposed antenna (single element) has been compared with those of the recently published works and is shown to be favorable. Compared to legacy circularly polarized antennas, the proposed antenna has a compact size, and better impedance matching and 3 dB axial ratio bandwidths. The presented antenna is useful for satellite communication C-band, Ku band as well as for X-band.
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Declaration of Competing Interest The authors do not have any conflict of interest Appendix A. Supplementary material Supplementary data to this article can be found online at https://doi.org/10.1016/j.aeue.2019.05.025. References [1] Balanis CA. Antenna theory: analysis and design. New Delhi: Wiley; 2005. [2] Nasimuddin Qing X, Chen ZN. Compact asymmetric-slit microstrip antennas for circular polarization. IEEE Trans Antennas Propag 2011;59:285–8. [3] Yang SLS, Kishk AA, Lee KF. Wideband circularly polarized antenna with Lshaped slot. IEEE Trans Antennas Propag 2008;56:1780–6. [4] Kumar T, Harish AR. Broadband circularly polarized printed slot-monopole antenna. IEEE Antennas Wireless Propag Lett 2013;12:1531–4. [5] Han RC, Zhong SS. Broadband circularly-polarized chifre-shaped monopole antenna with asymmetric feed. Electron Lett 2016;52:256–8. [6] Chandu DS, Karthikeyan SS. Broadband circularly polarized printed monopole antenna with protruded L-shaped and inverted L-shaped strips. Wiley 2017;2017:242–7. https://doi.org/10.1002/mop.30953. [7] Chen Qiang, Zhang Hou, Yang Luchum, Xue Bin, Min Xueliang. Broadband CPW-fed circularly polarized planar monopole antenna with inverted-L strip and asymmetric ground plane for WLAN application. PIER C 2017;74:91–100. [8] Kushwaha Nagendra, Kumar Raj, Ram Krishna RVS. Design and analysis of CPW-fed wideband circularly polarized antenna for modern communication systems. J Electromag Waves Appl 2015;29:1397–409. [9] Ding Kang, Guo Yong-Xin, Gao Cheng. CPW-fed wideband circularly polarized printed monopole antenna with open loop and asymmetric ground plane. IEEE Antennas Wireless Propag Lett 2017;16:833–6. [10] Nakamura T, Fukusako T. Broadband design of circularly polarized microstrip patch antenna using artificial ground structure with rectangular unit cells. IEEE Trans Antennas Propag 2011;59:2103–10. [11] Li G, Zhai H, Li T, Li L, Liang C. CPW-fed S-shaped slot antenna for broadband circular polarization. IEEE Antennas Wireless Propag Lett 2013;12:619–22. [12] Xue Hai-Gao, Yang Xue-Xia, Ma Zhewang. A novel microstrip-CPW fed planar slot antenna with broadband and circular polarization. IEEE Antennas Wireless Propag Lett 2015. https://doi.org/10.1109/LAWP.2015.2407904. [13] Gyasi KO, Wen G, Inserra D, Huang Y, Li J, Ampoma AE, et al. A compact broadband cross-shaped circularly polarized planar monopole antenna with a ground plane extension. IEEE Antennas Wirel Propag Lett 2018;17:335–8. [14] Gyasi KO, Wen G, Inserra D, Affum EA, Huang Y, Li J, et al. A compact broadband circularly polarized slot antenna with two linked rectangular slots and an inverted-F feed line. IEEE Trans Antenna Propag 2018. https://doi.org/ 10.1109/TAP.2018.2867020. [15] Shokri M, Rafii V, Karamzadeh S, Amiri Z, Virdee B. Miniaturised ultrawideband circularly polarised antenna with modified ground plane. Electron Lett 2014;50:1786–8. [16] Pourahmadazar J, Mohammadi S. Compact circularly-polarised slot antenna for UWB applications. Electron Lett 2011;47:15. [17] Mao SG, Yeh JC, Li Chen S. Ultrawideband circularly polarized spiral antenna using integrated balun with application to time-domain Target Detection. IEEE Trans Antenna Propag 2009. [18] Li Zhenya, Zhu Xiaosong, Yin Chengyou. CPW-fed ultra-wideband slot antenna with broadband dual circular polarization. Int J Electron Commun (AEÜ) 2019;98:191–8. [19] Ray KP. Design aspects of printed monopole antennas for ultra-wide band applications. Int J Antennas Propag 2008:. https://doi.org/10.1155/2008/ 713858. 8 pages713858. [20] Morabito AF, Nicolaci PG. Optimal synthesis of shaped beams through concentric ring isophoric sparse arrays. IEEE Antennas Wirel Propag Lett 2017;16:979–82. [21] Chen Chao, Shao Jinjin, Meng Shengwei, Fang Guangyou, Yin Hejun. 4-Element planar array antenna for UWB application. J Electron 2014;41:175–9. [22] Liu Yilin, Huang Kama. CPW-fed circularly-polarized antenna array with high front-to-back ratio and low-profile. De Gruyter, Open Phys 2018;16:651–5.
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International Journal of Electronics and Communications (AEÜ) journal homepage: www.elsevier.com/locate/aeue
Regular paper
Compact ultra-wideband circularly polarized CPW-fed monopole antenna Prashant Chaudhary a, Ashwani Kumar b,⇑ a b
Department of Electronic Science, University of Delhi South Campus, New Delhi 110021, India Department of Electronics, Sri Aurobindo College, University of Delhi, New Delhi 110017, India
a r t i c l e
i n f o
Article history: Received 21 January 2019 Accepted 17 May 2019
Keywords: Circular polarization (CP) Compact antenna Coplanar waveguide (CPW) Fed antenna Monopole antenna Ultra-wideband (UWB) Array antenna
a b s t r a c t This paper presents a coplanar waveguide (CPW) -fed quadrilateral-shaped compact planar monopole antenna for ultra-wideband (UWB) application. The fractional axial ratio bandwidth (ARBW) of the antenna for circular polarization (CP) is 56.64% (5.91–10.58 GHz) and its fractional impedance matching bandwidth (IMBW) is 137.1% (3.1–17.5 GHz), which are realized by designing a quadrilateral-shaped monopole with an asymmetric ground plane. The proposed antenna structure is simple and compact; hence its design is efficient, and it has an impedance matching (S11) in UWB band with embedded wideband circular polarization. The gain of the antenna varies between 3.33 and 8.9 dBi. Furthermore, its application for designing the linear array and planar array of 1 2 and 2 2 antenna elements are presented. The gain improves to 5.1–9 dBi for 1 2 array elements and to 9–11.2 dBi for 2 2 array with UWB IMBW. Simulated and experimental results are presented to validate the antenna design and are shown to be in good agreement. Ó 2019 Elsevier GmbH. All rights reserved.
1. Introduction In modern wireless communication system, the demand of circularly polarized (CP) planar antenna is witnessing a rapid increase because CP antennas are polarization independent of the incident wave and, hence, they find many applications in hand-held devices as well as in RFID and rotating systems. It is desirable to use antennas with circular polarization (CP) to avoid the effects of path-loss and displacement of the antennas, when the position of the transmitting and the receiving antennas are changing, or their operation is insecure to the weather conditions. The basic principle of generating the circular polarization (CP) is to excite two orthogonal modes in a phase-quadrature that have equal amplitudes [1]. A variety of approaches to realizing CP antennas have been reported in the literature. These include, for instance, the use of two orthogonal feeds, though this makes the antenna structure complex and bulky [1,2]. Circularly polarized (CP) antenna is also designed by using either a single feed at 45° along the axis of the patch or by corner truncation of the square patch. However, the single-feed techniques discussed in above references generate CP with a relatively narrow bandwidth [1,2], which may not be suitable for many applications. ⇑ Corresponding author. E-mail address: [email protected] (A. Kumar). https://doi.org/10.1016/j.aeue.2019.05.025 1434-8411/Ó 2019 Elsevier GmbH. All rights reserved.
The UWB antenna provides a high data transfer rate (110–200 Mb/s), larger bandwidth, simple hardware configuration, low power consumption, excellent immunity to the multipath interference and an omni-directional radiation pattern [15–17]. Several wireless systems, including the 3.6 GHz IEEE 802.11y, WLAN (3.6575–3.69 GHz), 4.9 GHz public safety WLAN (4.94– 4.99 GHz), 5 GHz IEEE 802.11a/h/j/n, WLAN (5.15–5.35 GHz, 5.25–5.35 GHz, 5.47–5.725 GHz, 5.725–5.825 GHz), satellite communication C-band (3.7–4.2 GHz) for downlink, and (5.925– 6.425 GHz) for uplink, X-band (8–12 GHz) for radar, and Ku-band (10.7–12.75 GHz) for direct broadcast satellite services, also operate within the same UWB band. A review of the literature reveals, that considerable effort has been invested by researchers in implementing various techniques [3–17], toward realizing circularly polarized (CP) antennas, that are both wideband and compact. Some of the suggested techniques are: using L-slot antenna with single fed by L-shaped feed line [3]; combination of slot and printed monopole [4]; chifre-shape CP monopole antenna [5]; protruded in L-shape strip and inverted L-shape strip [6]; inverted L-strip and asymmetric ground plane [7]; modified L-shaped patch with conjugation of rectangular slot in the ground plane [8]; rectangular monopole with an asymmetric ground plane and a square-ring with an open gap at the bottom [9]; artificially created ground [10]; S-shaped slots [11]; microstrip-CPW fed planar slot antenna [12]; cross-shaped CP
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antenna with a ground plane extension [13]; and slot antenna with an inverted-F shaped microstrip feed line with two linked rectangular slots in the ground plane [14]. The above suggested antennas are limited to wideband application. In recent years, some UWB antennas are also designed with embedded CP band. In [15], coplanar-waveguide (CPW)-fed circularly polarized square slot antenna presented with impedance matching bandwidth of 12.06 GHz (2.76–14.82 GHz), and CP axial ratio bandwidth of 1.86 GHz (4.27–6.13 GHz), in [16], CP square slot antenna fed by a coplanar waveguide is presented with IMBW of 8.3 GHz (2.9–11.2 GHz), and ARBW of 2.3 GHz (5.1–7.4 GHz), in [17], CP spiral antenna using integrated balun is presented with IMBW of 14.85 GHz (3.75–18.6 GHz), and ARBW of 11.5 GHz (3–14.5 GHz), while [18], presents UWB slot antenna with broadband CP with IMBW of 12.4 GHz (1.9–14.3 GHz) and ARBW of 4.0 GHz (1.9–5.9 GHz).The array antenna are preferred for high gain and phased array [20–22]. There are challenge to design array antenna for UWB with embedded wideband CP. Array antenna designed for UWB application [21], is linearly polarized while array antenna presented in [22], has narrow CP band. This paper presents the design of a compact planar monopole quadrilateral-shaped CPW feeding antenna with asymmetric ground plane for ultra-wideband (UWB) application. Proposed antenna has IMBW of 137.1% (3.1–17.5 GHz) while embedded circular polarization (CP) ARBW of 55.86% (5.96–10.58 GHz). Furthermore, linear antenna array of 1 2 elements and planar antenna array of 2 2 elements have been designed and their performances are compared with the single antenna element. 2. Antenna design Fig. 1 shows the layout and fabricated CPW-fed proposed planar antenna. The radiating surface has a quadrilateral shape and an asymmetric ground plane, both of which are built on the same side of the FR-4 substrate, with an er ¼ 4:4 and thickness of 0.8 mm. A step-impedance resonator is inserted in the central feedline to get better return loss (S11) of the proposed antenna. The length and width of the lower line are 6 mm and 1.5 mm, respectively, while they are c = 2.07 mm and d = 3 mm for the upper line. The gap between the feeding line and the ground plane is 0.75 mm. The shape of the radiator is a quadrilateral which is connected to the CPW line. An asymmetrical ground has been added to generate the circular polarization. The detailed dimensions of the proposed antenna structure (see Fig. 1) are: Wx = 30 mm, Ly = 25 mm, L = 13.43 mm, W = 13 mm, a = 7.43 mm, b = 5 mm, Gl = 3 mm, Gr = 11.3 mm, W1 = 2.8 mm, l1 = 5 mm, lx = 23 mm. The primary objective of this paper is to design an UWB antenna with a circular polarization (CP) which has a compact size and yet a wide AR
Fig. 1. Proposed antenna structure.
bandwidth. Hence, the geometry of the antenna is adjusted in such a fashion that it generates two orthogonal components of electric field (EX and EY), with equal amplitudes and a 90° phase difference, to generate the desired circular polarization (CP). Towards this end, a quadrilateral-shaped patch with an asymmetric ground plane has been used to achieve wideband circular polarization. 3. Antenna design procedure Any circularly polarized (CP) antenna should have its 3-dB axial ratio (AR) bandwidth entirely within the 10-dB impedance matching (S11) band. Hence, the primary issue for the designing of circularly polarized antenna is focused on how the quadrilateral-shape radiator and asymmetric ground plane simultaneously improves the 10-dB IMBW (S11) and 3 dB ARBW of the antenna. Therefore, the proposed antenna is designed in six steps, as shown in Fig. 2 below, with the progressive transformations designated from Step-1 to Step-6. The proposed antenna structure is simulated by using HFSS version-16. Step-1 which is linearly polarized antenna with square-shaped radiator and a symmetric ground plane, which provides impedance matching (S11) band from 3.1 GHz to15 GHz, the dimensions of this antenna are obtained for the lower frequency of the UWB band by using equation-1 [19].
fL ¼
7:2 W where r ¼ ½ðL þ r þ PÞ K 2p
ð1Þ
where L, r, P are in mm, the value of L = 13.43 mm W = 13 mm, P = 3.07 mm and K = 1.15. The length and width of the antenna-1 are 13.43 mm and 13 mm, respectively. Step-2 and step-3 are obtained by truncating upper and lower triangular portions, both the antennas are linearly polarized with IMBW from 3.1 GHz to 15 GHz and from 5.8 GHz to 18.5 GHz respectively. Step-4 is obtained by extended ground plane which is circularly polarized antenna at two center frequencies 10.2 GHz and 15.1 GHz with IMBW 4.5 GHz to 5.4 GHz and 13.2 GHz to 18.6 GHz respectively. Step-5 provides dual band CP antenna at center frequencies 8.3 GHz and 14.86 GHz while IMBW from 5.8 GHz to 15 GHz. Step-6 presents the proposed antenna with quadrilateral-shaped patch and asymmetric ground plane, which has IMBW from 3.1 GHz to 17.5 GHz while ARBW from 5.96 to 10.58 GHz. Fig. 3 shows the return loss (S11) and axial ratio for different design steps. The 3-dB axial ratio band improves when the antenna design is progressively modified from Step-4 to Step-6. The ratio of the amplitude of the electric far field components (EX/EY) and their phase difference (PD) are shown in Fig. 4. To realize the circular polarization (CP), we need to work with two electric far field com-
Fig. 2. Design steps of the proposed antenna.
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Fig. 3. Response of Step-1 to Step-6.
Fig. 4. Electric field components (EX and EY) Magnitude and Phase difference.
ponents (EX and EY) that have the same amplitudes but 90° phase difference. The electric far field components (EX and EY) of step-1 to step-3 have neither identical amplitude nor have 90°-phase difference at the same time, as may be seen from Fig. 4 (a) and (b). The electric far field components (EX and EY) of step-4 and step-5 have same amplitude and 90°-phase difference at 10.2 GHz and 15.1 GHz and 8.3 GHz and 14.86 GHz respectively. The final antenna which is step-6 has identical amplitude and 90°-phase difference at the same time from 5.91 to 10.58 GHz, which in turn generates the desired circular polarization (CP) over a wideband.
The rotating current which are distributed on the surface of final antenna (step-6) at 8.25 GHz is shown in Fig. 5, which also helps to explain the generation of the circular polarization (CP) of the designed antenna. The surface current vectors on the quadrilateral shape antenna for 8.25 GHz at different phase instants (0°, 90°, 180° and 270°) are illustrated in Fig. 5. It can be seen that the surface current vectors rotate mainly clockwise with phase, so the left-handed circular polarization (LHCP) operation is realized. This LHCP operation could be noticed at the upper half z > 0 while the RHCP operation could be observed at the lower half of the space with Z < 0.
Fig. 5. Surface current distribution of final antenna at 8.25 GHz.
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Fig. 6. Effect of lX on the return loss (S11) and 3 dB axial ratio of the final antenna.
Fig. 7. Effect of a on the return loss (S11) and 3 dB axial ratio of the Antenna.
Table 1 Effect of lX on IMBW and ARBW. lx, mm
0 4 8 12 16 20 23 24
IMBW
ARBW
(f1–f2) GHz
BW GHz
(f1–f2) GHz
BW GHz
(3.06–4.52), (5.4–15.67) (3.14–4.59), (5.37–15.51) (3.21–4.79), (4.93–15.70) (3.29–15.48) (3.34–15.38) (3.3–17.8) (3.1–17.5) (3.39–18.0)
1.46, 10.27 1.45, 10.14 1.58, 10.77 12.19 12.04 14.5 14.4 14.61
(8.11–8.45), (14.62–15.71) (8.42–10.65), (14.8–15.48) (8.66–10.03), (14.98–15.47) (7.22–8.01), (8.82–9.44) (6.81–7.38), (8.50–10.16) (6.34–10.94), (14.50–15.73) (5.91–10.58) (5.94–10.42)
0.34, 1.09 2.23, 0.68 1.37, 0.49 0.79, 0.62 0.57, 1.66 4.6, 1.23 4.67 4.48
Table 2 Effect of a on IMBW and ARBW. a, mm
0 2 4 6 7.43 8 10 12
IMBW
ARBW
(f1–f2) GHz
BW GHz
(f1–f2) GHz
BW GHz
(3.14–15.51) (3.32–15.68) (3.29–16.58) (3.28–16.52) (3.1–17.5) (3.28–18) (3.27–4.44), (5.30–17.24) (3.27–4.69), (5.34–17.10)
12.37 12.36 13.29 13.24 14.4 14.72 1.17, 11.94 1.42, 11.76
(8.13–9.01) (8–9.32), (10.16–10.50) (5.98–10.53) (5.99–10.55)) (5.91–10.58) (5.98–10.63) (5.98–10.51) (5.98–8.64), (9.98–10.52)
0.88 1.32, 0.34 4.55 4.56 4.67 4.65 4.53 2.66, 0.54
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4. Parametric study This section presents the parametric study of the antenna geometry. The best impedance matching bandwidth (S11) and 3-dB axial ratio responses of the proposed antenna (step-6) are shown in Fig. 3. Therefore, for brevity, they are not presented here, in this parametric study. Truncation of the upper
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and lower sections of the square patch are typically important elements that generates the circular polarization, which has already been discussed in detail in section-III. The effect of asymmetric ground plane length (lX) and length of lower triangular portion of the patch (a) on the axial ratio and IMBW (S11) have been discussed here in detail and presented in Figs. 6 and 7.
Fig. 8. Simulated and measured performances of the final Antenna.
Fig. 9. Simulated and measured radiation pattern of the proposed antenna at 7.0 GHz, 8.4 GHz and 10.2 GHz.
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Table 3 Comparison with the recently published work. Ref.
% IMBW, GHZ
% ARBW, GHz
Size (L W)
Er, h (mm)
Gain range (dBi)
[3] Slot [4] Slot [5] MT [6] MT [7] CPW [8] CPW [9] CPW [10] MSA with AMC [11] CPW [12] CPW slot [13] MSA extended GND [15] CPW slot [16] CPW slot Our
57% (2.18–3.92) 51% (1.9–3.2) 72% (1.5–3.4) 133.41% (1.38–6.4) 58.8% (4.8–8.8) 87.2% (2.2–5.6) 96.5% (1.48–4.24) 48.6% (4.52–7.42) 104% (1.78–5.64) 57% (1.73–3.11) 55.5% (4.36–7.71) 137.2% (2.76–14.82) 117.7% (2.9–11.2) 137.12% (3.1–17.5)
46.5% (2.18–3.5) 30% (2.0–2.6) 41.6% (2.1–3.12) 129.04% (1.38–6.4) 47.8% (5.375–8.75) 61.85% (2.2–4.17) 63.3% (2.05–3.95) 20.4% (5.40–6.63) 58.6% (2.85–5.21) 39.4% (1.98–2.95) 42.6% (4.8–7.4) 35.76% (4.27–6.13) 38.2% (5.01–7.4) 56.64% (5.91–10.58)
82 82 186 103 63 58.4 40 40 25 24 50 45 13.5 55 39 40 54 54 100 120 16 22 25 25 25 25 13.0 13.43
2.6, 1.524 2.2, 1.6 4.4, 1.5 4.4, 1.0 4.4, 1.0 4.4, 1.6 4.4, 1 2.2, 4.8 2.55, 1.0 2.55, 0.762 4.4, 1.0 4.4, 0.8 4.4, 0.8 4.4, 0.8
4.75–7.28 1.3–2.9 2.5–3.7 2.85–3.54 1.5–3.3 3.0–4.0 0.5–3.5 5.5–6.2 3.0–4.0 2.5–3.4 0.5–2.6 2.0–3.2 2.3–2.9 3.33–5.67
(a) 1×2 antenna elements
(b) 2×2 antenna elements
Fig. 10. UWB antenna array design using (a) 1 2 antenna elements and (b) 2 2 antenna elements.
Fig. 11. Simulated impedance matching (S11), 3 dB axial ratio and gain of array antenna of 1 2 elements with spacing Dx.
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This section illustrates the effect of asymmetric ground plane length (Lx) on IMBW and on ARBW with fixed a = 7.43 mm. From lX = 0 mm to 8 mm the antenna is behaving like a dual band circularly polarized antenna and from lX = 8 mm to 20 mm, the dual band starts merging with single wideband of IMBW from 3.29 GHz to 15.48 GHz while it still has dual band CP within the IMBW, which have different frequency bands, they are summarized in Table 1 and presented in Fig. 6. At lX = 23 mm, antenna becomes single band antenna with UWB IMBW and wide ARBW, which are 137.12% (3.1–17.5) and 56.64% (5.91–10.58) respectively. After lX = 23 mm the IMBW improves slightly while ARBW starts deteriorating.
fixed lX = 23 mm. For a = 0 mm the antenna has UWB impedance matching bandwidth while it has narrow CP band 0.88 GHz. For a = 2 mm the antenna is UWB with two CP bands from 8 to 9.32 GHz and 10.16–10.50 GHz. From a = 4 mm to 8 mm the antenna is behaving like a UWB antenna with wide CP band. At a = 10 mm the antenna is dual band antenna with single wideband from 5.98 to 10.51 GHz while for a = 12 mm the antenna becomes dual band antenna with IMBW from 3.27 to 4.69 GHz, and 5.34–17.10 GHz with ARBW from 5.98 to 8.64 GHz and 9.98 to 10.52 GHz respectively. We have considered a = 7.43 mm and lX = 23 mm as the final choice as they provide UWB IMBW with wideband CP. The effect of a on IMBW and ARBW has been summarized in detail in Table 2. The effect of a on impedance matching (S11) and axial ratio are presented in Fig. 7.
4.2. a- variation with fixed lX = 23 mm
5. Measurement
This section illustrates the effect of length of lower triangular portion of the patch (a) on the axial ratio and IMBW (S11) with
The proposed antenna, which is the final optimized antenna design, has been designed and fabricated (see Fig. 1) on FR-4 sub-
4.1. Lx variation with fixed a = 7.43 mm
Table 4 Comparison of performances of single element with 1 2 and 2 2 array elements. Parameters
Single Element
1 2 Elements
2 2 Elements
Dx
Dx = Dy
0.4k
0.6k
0.8k
1k
0.4k
0.6k
0.8k
1k
3.25–18.5 15.25 (6.14–10.70), (16.68–17.1) 4.56, 0.42 5.85–9.23
3.25–17.25 14.0 9.14–10.27
3.25–17.25 14.0 6.73–9.97
3.25–18.5 15.25 6.43–9.41
1.13 3.0–12.65
3.24 6.8–11.96
2.98 7.88–11.80
3.25–17.25 14.0 (6.5–8.98), (10–10.83) 2.48, 0.83 8.75–12.70
S11 IMBW (GHz) 3 dB AR
3.1–17.5 14.4 5.91–10.58
3.25–17.25 14.0 6.56–10.53
3.25–17.25 14.0 6.40–8.84
3.25–17.25 14.0 6.27–10.68
ARBW (GHz) Peak Gain (dBi)
4.67 3.33–8.9
3.97 4.3–10.11
2.44 4.8–8.77
4.41 5.3–10.41
Fig. 12. Simulated IMBW (S11), 3 dB axial ratio and gain of array antenna of 2 2 elements with spacing Dx and Dy.
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strate and its performances are measured. The measured IMBW (S11) and 3-dB ARBW for the final designed antenna are shown in Fig. 8. The proposed antenna has IMBW (S11) from 3.1 GHz to 17.5 GHz. Measured 3 dB ARBW of the antenna is from 5.91 to 10.58 GHz, representing a 56.64% fractional bandwidth. Simulated and measured results are slightly different, perhaps because of the effect of the SMA connector and due to fabrication error. The gain of the antenna (simulated and measured) is shown in Fig. 8b. Note, that the measured gain of the antenna is in between 3.33 and 8.9 dBi with 3 dB axial-ratio (AR) band ranges from 5.91 to 10.58 GHz. The simulated and measured far-field radiation patterns of the proposed antenna at 7.0 GHz,8.4 GHz and 10.2 GHz are presented in Fig. 9 for both LHCP and RHCP in XY- and YZ-planes. Radiation pattern and shapes are not uniform among these three frequencies. At low frequency radiation pattern is directional, meanwhile showing slightly distorted pattern at higher frequencies. The main reason behind this, the strong surface current on the edges of the radiator at high frequency. Finally, the performances of the proposed quadrilateral shape antenna are compared in Table 3 with the recently published works [3–16]. Our proposed antenna structure has compact size and is found to have improved IMBW (S11) in UWB band and embedded wideband 3 dB ARBW.
6. Array design UWB antenna arrays are preferred in point-to-point communications because they provide a high gain and better directionality. Here, array antenna for 1 2 and 2 2 antenna elements are pre-
sented. Fig. 10 shows the UWB array antenna by using 1 2 and 2 2 antenna elements. To reduce the complexity of the feeding network design, here the array antenna elements are placed side by side as shown in the Fig. 10, to see the effect on the performances of the proposed antenna. The UWB antenna array study has been presented in three different subsection-A, B and C. Section-A deals with linear array of 1 2 antenna elements, Section-B deals with planar array of 2 2 antenna elements while section-C compares the performances of single element with antenna arrays of 1 2 and 2 2 elements. 6.1. Linear array of 1 2 antenna elements This section illustrates the effect on the IMBW, ARBW and gain of the proposed single antenna, when it has been placed in linear array with 1 2 antenna elements as shown in Fig. 10a. The IMBW and ARBW and gain are shown in Fig. 11 with different spacing. Spacing has been chosen between edge to edge of the antenna in terms of wavelength as shown in Fig. 10a. The spacing between the 1 2 and 2 2 elements are taken as Dx and Dy = 0.8k (kat fc = 10.25 GHz), this spacing between the elements provides the improved IMBW, ARBW and gain. For spacing Dx = 0.8k = 22.528 mm, the IMBW for 1 2 is 14 GHz (3.25–17.25 GHz), 3 dB ARBW is 4.41 GHz (6.27–10.68 GHz) and gain is varying from 5.3 to 10.41 dBi within the entire IMBW. Table 4 compares the performance of single antenna with 1 2 array elements for different spacing. However, for 2 2 Elements, the IMBW is 15.25 GHz (3.25–18.5 GHz), 3 dB ARBW is 2.98 GHz (6.43–9.41 GHz) and gain is varying 7.88 to 11.80 dBi with in the IMBW.
Fig. 13. Simulated performances comparison of single element, with 1 2 and 2 2 array elements.
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6.2. Planar array of 2 2 antenna elements This section illustrates the effect on the IMBW, ARBW and gain of the proposed antenna, when it is placed in planar array of 2 2 antenna elements as shown in Fig. 10b. The IMBW, ARBW and gain are shown in Fig. 12 with different spacing (Dx = Dy). The spacing is chosen between edge to edge of the antenna elements both in X and Y direction. The spacing for 2 2 antenna elements are varied uniformly. There is no effect on the IMBW which is 15.25 GHz (3.25–18.5 GHz) and ARBW deteriorates with the spacing. The ARBW becomes narrow 2.98 GHz (6.43–9.41 GHz) for Dx = Dy = 0.8k = 22.528 mm while gain varies from 7.88 to 11.80 dBi within the IMBW. Table 4 compares the performance of single antenna with 2 2 array elements for different spacing. 6.3. Compares the performances of single element with antenna arrays of 1 2 and 2 2 elements. This section compares the performances of single element with antenna array of 1 2 and 2 2 elements. The IMBW of single element is 14.4 GHz (3.1–17.5 GHz), embedded circular polarization (CP) ARBW is 4.67 GHz (5.96–10.58 GHz) and its gain varies from 3.33 to 8.9 dBi. The spacing between the 1 2 and 2 2 elements are taken as Dx and Dy = 0.8k, this spacing between the elements provides the improved IMBW, ARBW and gain. For spacing Dx = Dy = 0.8k = 22.528 mm, the IMBW for 1 2 is 14 GHz (3.25– 17.25 GHz), 3 dB ARBW is 4.41 GHz (6.27–10.68 GHz) and gain is varying from 5.3 to 10.41 dBi within the entire IMBW. However, for 2 2 elements, the IMBW is 15.25 GHz (3.25–18.5 GHz), 3 dB ARBW is 2.98 GHz (6.43–9.41 GHz) and gain is varying 7.88 to 11.80 dBi with in the entire IMBW. The IMBW, ARBW and gain are compared in Fig. 13 for single element, with 1 2 and 2 2 array elements. The IMBW is remain same for single element, 1 2 and 2 2 elements while the ARBW changes from 4.67 GHz (single element) to 4.41 GHz (1 2 array elements) and to 2.98 GHz (2 2 array elements). The circular polarization bandwidth reduces for the 1 2 and 2 2 array elements because antennas placed in array configuration produce slightly different magnitude of the field components with different phase. 7. Conclusion A quadrilateral-shaped UWB CPW-fed monopole circularly polarized (CP) antenna has been proposed. A prototype of the antenna is fabricated, and its measured results are presented, which is useful for the modern communication system. The measured results show that the antenna has a wideband circular polarization (CP) with a 56.64% fractional ARBW and an ultra-wideband (UWB) IMBW (S11) of 137.1%. Furthermore, the single antenna elements are placed in linear array and planar array of 1 2 and 2 2 elements and their performances are compared. The performance of the proposed antenna (single element) has been compared with those of the recently published works and is shown to be favorable. Compared to legacy circularly polarized antennas, the proposed antenna has a compact size, and better impedance matching and 3 dB axial ratio bandwidths. The presented antenna is useful for satellite communication C-band, Ku band as well as for X-band.
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