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Multifrequency rectangular microstrip antenna with array of L-slots
Journal Pre-proofs Regular paper Multifrequency Rectangular Microstrip Antenna with array of L-slots Antara Ghosal, Sisir Kumar Das, Annapurna Das PII: DOI: Reference:
S1434-8411(19)31168-9 https://doi.org/10.1016/j.aeue.2019.152890 AEUE 152890
To appear in:
International Journal of Electronics and Communications
Received Date: Accepted Date:
5 May 2019 28 August 2019
Please cite this article as: A. Ghosal, S. Kumar Das, A. Das, Multifrequency Rectangular Microstrip Antenna with array of L-slots, International Journal of Electronics and Communications (2019), doi: https://doi.org/10.1016/ j.aeue.2019.152890
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier GmbH.
Multifrequency Rectangular Microstrip Antenna with array of L-slots Antara Ghosal1 , Sisir Kumar Das2, Annapurna Das3 1,2,3 Department
of Electronics and Communication Engineering
Guru Nanak Institute of Technology, Kolkata, West Bengal 700114, India Maulana Abul Kalam Azad University of Technology, West Bengal 1M.tech(ECE), 2Ph.D, 3Ph.D [email protected] [email protected] [email protected]
Multifrequency Rectangular Microstrip Antenna with Array of Lslots Antara Ghosal, Sisir Kumar Das, Annapurna Das Department of Electronics and Communication Engineering Guru Nanak Institute of Technology, Kolkata, West Bengal 700114, India
Abstract A rectangular microstrip antenna containing an array of narrow L-slots and inverted L-slots is described for multifrequency operation. The patch was designed for TM010 mode of excitation at 2.1 GHz and is fed with a coaxial probe from the ground plane. The slots are cut on the patch at two opposite corners. The widths and lengths of these slots are varied to obtain the optimum performance at multiple frequencies. The performance parameters of this antenna are reflection coefficient (S11), radiation pattern, gain, and efficiency. A simple slotted structure without any additional electronic circuit was designed for multifrequency operation. The Ansoft HFSS software tool was used for the simulation and optimum design of the antenna on a FR-4 dielectric substrate above a ground plane. It is observed that the final configuration produces very good performance at penta frequencies: 1.25, 1.48, 1.8, 2.25, and 2.9 GHz with reasonable gain. The simulation results are verified with the experimental results and are found to be in good agreement.
Keywords Coaxial feed, multi frequency antenna, slotted microstrip patch antenna. 1. Introduction
In recent years, the development of telecommunication technology has increased. The technology has reached to 5G through 3/4G. Subsequently challenges in the design of mobile phone antenna have increased for multiband operation. The GSM frequency bands are 850,900,1500,1900, 2300, 2600 MHz, UMTS frequency bands are 1,885–2,025 MHz and 2,110–2,200 MHz. LTE and WiMax frequency bands are 700 MHz, 1700–2100 MHz, 1900MHz and 2500–2700 MHz. Ultra-high frequency bands are 1240–1300MHz and 2900–4100 MHz. Microstrip patch antennas are widely used in large quantities for their compact size, light weight, low profile, planar configuration, portability, robustness and low fabrication cost. But, there are some disadvantages as well. Such as narrow band, low efficiency and low gain. Slotted microstrip antennas are designed for operation at multiple frequencies for different mobile networks at different countries.
For multifrequency operations, slotted microstrip patches are used with aperture couple feed [1]. A dual frequency antenna using single co-axial feed and a pair of bent slots placed close to non radiating patch is presented and these resonant frequencies are controlled by changing the bent angle [2]. Different compact spiral microstrip antennas are described in the literature [3–4] for multiband operation in which the size of the antenna is reduced as compared with that of traditional patch antenna. A patch antenna is designed for operation at hexa-band frequency by reconfiguring the shape using electronic switching [5]. Various types of modeling techniques are proposed for broad banding, multiband operation, size reduction, and circular polarization [6–7].Formulation of the slot’s resonant length in some slotted microstrip antenna are given by using surface current and voltage distributions for dual-band operation [8–9]. A gap-coupled and multilayer-stacked microstrip antenna is presented for multiband and broadband operation[10]. A dual-fed dual-frequency dielectric resonator antenna
(DRA) is investigated for high gain [11]. A triple-band microstrip antenna with three-nested loop and a rectangular stub connected to the feed line with good impedance matching is proposed [12]. A complicated two-layered (including a partial reflecting surface) dual-band microstrip antenna is presented [13]. A slotted elliptical patch is designed for multifrequency operation and an inset-fed dualband patch antenna array with DGS is proposed [14–15]. A slotted array antenna using cavity-backed substrate integrated waveguide (SIW) for dual-band operation is investigated [16]. The operation mechanism of high-order modes is analyzed and then verified through simulations by inserting metallic vias in different positions of the resonant SIW cavity. A complicated antenna structure with T-shaped SLRR (Stub Loaded Ring Resonator) slot on the ground plane is designed. Also a U-shaped slot on microstrip feed line is there. The antenna is investigated for dual-band and triple frequency operation with wide bandwidth [17]. Some slotted triangular microstrip patch antennas with multiple parasitic patches and shorting vias are presented for bandwidth enhancement [18]. A tri-band printed quasi-Yagi antenna using double dipoles on a single layer substrate is proposed. For this antenna, the stub loading technique is used for generating additional resonant mode[19]. A compact meandered monopole antenna fed by asymmetric coplanar strip (ACS) is described [20] for dual-band operation. The resonant frequencies of the antenna are controlled by adjusting the dimensions of the radiating elements. An ACS-fed dual-band antenna using loaded capacitance terminations and a shunt inductor is also proposed [21]. Different types of MIMO antenna array is described [22–23]. These antennas are used for high isolation, gain enhancement, reduction of mutual coupling between the elements using a meta-material and neutralization line at a single frequency. A
good impedance bandwidth is obtained for a triple band monopole antenna with integrated configurations such as using a toothbrush-shaped patch, a meandered line and an inverting U-shaped patch [24] for WLAN and WiMAX applications. A reconfigurable triple-notch-band antenna integrated with defected microstrip structure band-stop filter is designed for ultra-wideband cognitive radio applications [25]. Three frequency bands are obtained for this structure. Eight modes are observed for this antenna. The switches are integrated on the filter and the slot to control the modes of this antenna. A CPW-fed Ultra Wide Band antenna is developed to obtain two stop bands. A Stepped Impedance Stub (SIS) loaded Stepped Impedance Resonators (SIR) and SIS loaded Hexagon Stepped Impedance Resonators (HSIR) are used for this antenna [26]. Here also, two ideal switches are used for multiple modes. Different structures for multifrequency operations are described in books [27–30]. But, there are some drawbacks of multiband patch antennas, which are reported in the literature. They cannot be integrated into and installed in mobile devices due to their large sizes or complex structures. Use of additional electronic circuit for switching at different frequencies makes it cost effective. The use of active components increases complexity in the design. Use of these active components is difficult to handle because it needs extra biasing network. Moreover, it is difficult to develop analytical formulations of the complex structure. As described above, the configuration and operation of multiband antennas are complicated. In this paper, a novel design of slotted patch with probe feed is presented. It can produce very low peaks of S11 at penta frequencies with reasonable gain at low cost. Without the use of additional electronic circuits for switching or use of special substrate material these performances can be acheived. The antenna consists of an array of L-shaped and inverted L-shaped narrow slots on a
rectangular patch as shown in Figures 1 and 2 for multifrequency operation. In the configuration of Figure1, four slots are used where slot lengths and widths are varied as given in Table 1. In Figure2, six slots are introduced for improvement of the performance. The widths and lengths of the slots are listed in Table 2. The patch is fabricated on a FR4-epoxy dielectric substrate having ɛr=4.4and thickness h=1.6 mm above a ground plane. Ansoft HFSS software tool is used for modeling and simulation to determine the S11(dB)vs frequency response. The slots introduce reactive elements in the antenna for resonating at five frequencies:1.25, 1.48, 1.8, 2.25 and 2.9 GHz. Resonant peaks (<–10 dB) are noted at the said frequencies for which radiation pattern, gain and efficiency are determined. The results of simulation and modeling are experimentally verified using network analyzer and found good agreement. The penta frequency response of a single antenna will have applications in wireless communication. It is observed that if the lengths and widths of the slots are varied along with the gaps between the slots, the number of resonant peaks of S11 is increased. Bandwidths are also changed with the change in the dimensions of the slots. In addition, it is seen that, slots are affecting the current distribution on the patch. There is specific observation that the depth of resonant frequencies is increased as the number of slots are increased and widths of the slots are decreased. The design is optimized using Ansoft HFSS tool for best performance.
2. Design of Slotted Rectangular Microstrip Antenna In this paper initially a square patch (L=W) is designed on a FR4 dielectric substrate of ɛr=4.4, and thickness h=1.6 mm above a ground plane. The resonant frequency of the patch antenna for excitation of TMmnp radiating mode is calculated using cavity model from the expression [11, 13]
f r ( mn )
1 2
[(
m 2 n 2 1/2 ) ( ) ] ; L W
(1)
Here 0 reff
reff
r 1 r 1 2
2
[1 12
h 12 ] ; For W / h 1 W
(2)
4 107 h / m, 0
109 F /m 36
L=the length of the patch along x-axis, W= width of the patch along y-axis, and m=0,1,2,.......; n=0,1,2,...........; p=0 For the patch without slot, initial design is made with W=L= 33.7 mm for which the fundamental resonant frequency is 2.1 GHz for TM010 or TM100 mode. Since a simple rectangular patch operates at its tuned frequency. It is modified by cutting an array of L and inverted L narrow slots on the patch to introduce additional reactive elements for multifrequency performance of the antenna as shown in Figure 1 and Figure 2. Different combinations of dimensions of the slots are cut on the patch as described in Table 1. The modification is further carried out in the configuration of Figure 2. Here the width of each slot is kept 1 mm and number of L-slots is increased to six having different lengths as given in Table 2 for improvement in the performance. All the configurations of the modified antenna are fed with a small coaxial probe from the ground plane at the center (0, 0, 0) of the patch. The gaps between the successive slots are 3 mm for each design. The S11(dB), radiation pattern, gain, and efficiency of these antennas are determined using Ansoft HFSS software tool. The dimensions of the slots are optimized for best multifrequency
operation. The results of above parameters are shown graphically and described in the following section. These parameters are also measured using a network analyzer. Both the results agree well.
Figure1.Patch Antenna with Four L-Slots
Figure2. Patch Antenna with Six L-Slots
Table 1. Dimensions of the Slots (Width x
Table 2.Dimensions of the Slots (Width x
Length) for Antenna in Figure1
Length) for Antenna in Figure 2 Slot width (mm)
Slot width (mm) Slot (mm)
length
3
2
1
l1
27.7
27.7
27.7
l2
21.7
22.7
23.7
l3
15.7
17.7
19.7
l4
9.7
12.7
12.7
3. Results and Discussions
Slot (mm)
length
1 l1
27.7
l2
23.7
l3
19.7
l4
15.7
L5
11.7
l6
7.7
The patch antennas described in Figures 1 and 2 with an array of L-shaped and inverted L-shaped narrow slots are fabricated on a FR4-eproxy dielectric substrate having r 4.4 and thickness h=1.6 mm above a ground plane. The results of reflection coefficient in terms of S11(dB), radiation pattern, gain, efficiency and bandwidth are described in the following sections. (a) Reflection coefficient (S11) characteristics of the configuration of Figure1 The dimensions of the slots are altered as given in table 1 and the corresponding results of S11vs frequency response obtained using Ansoft HFSS software tool are shown in Figure 3.It is seen that the resonant frequencies are within the range of TM010 or TM100 mode. Multiple resonant peaks for S11<– 10 dB are obtained in the frequency range from 1.2 to 2.6 GHz. It is observed that by reducing the width of the slot, the S11is improved and the number of resonant frequencies is also increased.
Figure3. Reflection Coefficient Characteristics of Design of Figure1 for Different Slot Widths (b) Reflection coefficient (S11) characteristics of the configuration of Figure2 By increasing the number of narrow L-slots in the configuration of Figure 2, the S11(dB) is further improved in depth and also additional operating peaks are generated as shown in Figure 4.Penta
frequency response with very good S11 of –28.3 dB at 1.25 GHz, –22.1 dB at 1.48 GHz, –24.8 dB at 1.8 GHz, –23.3 dB at 2.25 GHz, and –19.1 dB at 2.9 GHz is produced by this final configuration. These frequencies are used in different wireless communication.
w=1 mm; l1 =27.7 mm, l2 =23.7 mm, l3 =19.7 mm, l4 =15.7 mm, l3 =11.7 mm, l4 =7.7 mm Figure 4. S11vs Frequency Characteristics of Design of Figure 2 It has been observed that when the lengths of the slots are kept as given in Table 2 and the widths of the slots are varied, there is best S11(dB) performance obtained for width w=1 mm as shown in Figure 5. In another attempt the widths of the slots are kept 1mm and lengths of the slots are altered in steps of λ/20 from the values listed in Table 2.The corresponding results are shown in Figure 6. No improvement in the result is observed. In this process, the antenna dimensions with slots are optimized with slot width w=1 mm and the lengths as listed in Table 2 leading to the configuration of Figure 2 for best S11vs frequency response.
Figure 5.S11 (dB) vs Frequency for Different Widths of the Slots with Lengths as per Table 2 for Figure2
Figure 6. S11 (dB) vs Frequency for Different Lengths of the Slots with Width w=1mm as per Table 2 for Figure 2
(c) Reflection coefficient (S11) vs frequency for the configuration of Figure2 for different substrate materials For the antenna configuration of Figure 2, the S11vs frequency response is investigated by changing different substrate materials—FR4 epoxy, RT/Duroid, and Arlon—keeping the slot dimensions as given in Table 2.The results are shown in Figure 7(a). Next, the physical lengths, widths, and spacing are altered to retain the electrical dimensions of the slots same as those of FR4 substrate. The S11vs frequency responses of the patch is shown in Figure7(b). From the comparison of the results, it is seen that FR4 epoxy material gives a better result of S11(dB) vs frequency compared to those of other substrate materials (RT/Duroid, Arlon). The number of resonant peaks (<–10dB) and their depths are increased for FR4 epoxy substrate as compared to other substrates. Therefore, further investigations are carried out for the configuration of Figure 2 using FR4 substrate as described below.
(a)
(b) Figure 7. (a) S11 (dB) vs Frequency (GHz) for Different Substrate Materials for Given Physical Dimensions of the Slots as per Table 2. (b) S11 (dB) vs Frequency (GHz) for Different Substrate Materials with Altering Physical Dimensions of the Slots so That the Electrical Dimensions of the Slots are Same. (d) Radiation characteristics of the configuration of Figure2 The radiation patterns for the final modified configuration (Figure2) are determined at the resonance frequencies. Broadside radiation patterns are obtained as shown in Figure8. It is seen that the radiation patterns are similar because all the frequencies fall below those of next higher order mode.
(a)
(b)
(c)
(d)
(e) Figure8.TheRadiation Patternsof the Design of Figure 2at (a) 1.25 (b) 1.48 (c) 1.8 (d) 2.25,and (e)2.9 GHz From the above results, it is seen that the modified configuration of Figure 2 exhibits better performance. (e) Gain and Efficiency Characteristics The gain and efficiency characteristics of the antenna of final configuration (Figure2)are determined at resonant frequencies using Ansoft HFSS software tool. The gain is also measured using a standard gain ridge horn. Consolidated results of S11 (dB), gain and efficiency for the design of Figure 2 are shown in Table 3.
Table 3.The Performance Characteristics of Final Antenna (Figure 2) Parameters f (GHz) S11 (dB) Bandwidth (%) Gain (Simulated) (dBi) Gain (Measured) Efficiency (Simulated)% Efficiency (Measured)%
w = 1mm with lengths of slots as per Table 2 1.25 –28.3 3.2 1.1 1 62.5 63.6
1.48 –22.1 3.4 1.12 1.07 61 62
1.8 –24.8 3.33 1.15 1.1 52.7 50
2.25 –23.3 4.5 1.39 1.3 54 53
2.9 –19.1 3.1 1.4 1.35 59.4 62.5
This antenna is well suited for multifrequency operation in mobile communication. (f) Surface current distribution
(a)
(b)
(c)
(d)
(e)
Figure9.Surface Current Distributions on Patch of Configuration of Figure2 (a)1.25GHz (b)1.48GHz (c)1.8GHz (d)2.25GHz (e)2.9 GHz The distributions of current density on the patch surface at resonant frequencies 1.25 GHz, 1.48 GHz, 1.8 GHz, 2.25 GHz, and 2.9 GHz are shown in Figure9. It is observed in Figure9(a) that the electric current distribution at 1.25 GHz is concentrated near the ends of uppermost slot, which improves the lowest resonant frequency. From Figure9(b), it is seen that the current distribution is concentrated at the end of lower most slot indicating that this slot controls the second resonant frequency 1.48 GHz. From Figure9(c), it is observed that the current distribution is concentrated near the end of two uppermost slots which control the third resonant frequency 1.8 GHz. Similar
distributions are observed near the two lowermost slots and more specifically at the end of second lower slot controlling the fourth resonant frequency. In Figure9(e), the current distribution is concentrated at the edges of the lowermost slot in the upper corner that controls the fifth resonant frequency 2.9 GHz. From the current distribution, it is confirmed that the sequence of resonances occurs from the larger slot to smaller slot for lowest to highest frequencies, respectively. Conclusions The L-shaped narrow slots are introduced at two corners of a rectangular patch antenna for multifrequency operation. The performance of the modified patch is obtained from the simulation and modeling using Ansoft HFSS tool. The slots are cut at suitable locations and orientations, and the S11 (dB), radiation pattern, gain, and efficiency are obtained. The design is optimized for penta frequency operation. The HFSS results for S11and gain are verified with the experimental results and found in good agreement. The radiation patterns are also found satisfactory. This penta frequency antenna can be used in GSM, UMTS, LTE, WiMax and UHF communications. Acknowledgement Authors acknowledge Department of Electronics and Telecommunication, Jadavpur University, Kolkata, for experimental support. References [1] L. Shafai and X. H.Yang, "Antenna Performance Enhancement by Slotted Microstrip Patches" ELECTRONICS LETTERS 2nd September 1993 Vol.29 No. 18, pp. 1647-1649. [2] K.-L. Wong and J.Y. Sze, Dual frequency slotted rectangular microstrip antenna, Electron Lett 34 (1998), pp. 1368-1370.
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S1434-8411(19)31168-9 https://doi.org/10.1016/j.aeue.2019.152890 AEUE 152890
To appear in:
International Journal of Electronics and Communications
Received Date: Accepted Date:
5 May 2019 28 August 2019
Please cite this article as: A. Ghosal, S. Kumar Das, A. Das, Multifrequency Rectangular Microstrip Antenna with array of L-slots, International Journal of Electronics and Communications (2019), doi: https://doi.org/10.1016/ j.aeue.2019.152890
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier GmbH.
Multifrequency Rectangular Microstrip Antenna with array of L-slots Antara Ghosal1 , Sisir Kumar Das2, Annapurna Das3 1,2,3 Department
of Electronics and Communication Engineering
Guru Nanak Institute of Technology, Kolkata, West Bengal 700114, India Maulana Abul Kalam Azad University of Technology, West Bengal 1M.tech(ECE), 2Ph.D, 3Ph.D [email protected] [email protected] [email protected]
Multifrequency Rectangular Microstrip Antenna with Array of Lslots Antara Ghosal, Sisir Kumar Das, Annapurna Das Department of Electronics and Communication Engineering Guru Nanak Institute of Technology, Kolkata, West Bengal 700114, India
Abstract A rectangular microstrip antenna containing an array of narrow L-slots and inverted L-slots is described for multifrequency operation. The patch was designed for TM010 mode of excitation at 2.1 GHz and is fed with a coaxial probe from the ground plane. The slots are cut on the patch at two opposite corners. The widths and lengths of these slots are varied to obtain the optimum performance at multiple frequencies. The performance parameters of this antenna are reflection coefficient (S11), radiation pattern, gain, and efficiency. A simple slotted structure without any additional electronic circuit was designed for multifrequency operation. The Ansoft HFSS software tool was used for the simulation and optimum design of the antenna on a FR-4 dielectric substrate above a ground plane. It is observed that the final configuration produces very good performance at penta frequencies: 1.25, 1.48, 1.8, 2.25, and 2.9 GHz with reasonable gain. The simulation results are verified with the experimental results and are found to be in good agreement.
Keywords Coaxial feed, multi frequency antenna, slotted microstrip patch antenna. 1. Introduction
In recent years, the development of telecommunication technology has increased. The technology has reached to 5G through 3/4G. Subsequently challenges in the design of mobile phone antenna have increased for multiband operation. The GSM frequency bands are 850,900,1500,1900, 2300, 2600 MHz, UMTS frequency bands are 1,885–2,025 MHz and 2,110–2,200 MHz. LTE and WiMax frequency bands are 700 MHz, 1700–2100 MHz, 1900MHz and 2500–2700 MHz. Ultra-high frequency bands are 1240–1300MHz and 2900–4100 MHz. Microstrip patch antennas are widely used in large quantities for their compact size, light weight, low profile, planar configuration, portability, robustness and low fabrication cost. But, there are some disadvantages as well. Such as narrow band, low efficiency and low gain. Slotted microstrip antennas are designed for operation at multiple frequencies for different mobile networks at different countries.
For multifrequency operations, slotted microstrip patches are used with aperture couple feed [1]. A dual frequency antenna using single co-axial feed and a pair of bent slots placed close to non radiating patch is presented and these resonant frequencies are controlled by changing the bent angle [2]. Different compact spiral microstrip antennas are described in the literature [3–4] for multiband operation in which the size of the antenna is reduced as compared with that of traditional patch antenna. A patch antenna is designed for operation at hexa-band frequency by reconfiguring the shape using electronic switching [5]. Various types of modeling techniques are proposed for broad banding, multiband operation, size reduction, and circular polarization [6–7].Formulation of the slot’s resonant length in some slotted microstrip antenna are given by using surface current and voltage distributions for dual-band operation [8–9]. A gap-coupled and multilayer-stacked microstrip antenna is presented for multiband and broadband operation[10]. A dual-fed dual-frequency dielectric resonator antenna
(DRA) is investigated for high gain [11]. A triple-band microstrip antenna with three-nested loop and a rectangular stub connected to the feed line with good impedance matching is proposed [12]. A complicated two-layered (including a partial reflecting surface) dual-band microstrip antenna is presented [13]. A slotted elliptical patch is designed for multifrequency operation and an inset-fed dualband patch antenna array with DGS is proposed [14–15]. A slotted array antenna using cavity-backed substrate integrated waveguide (SIW) for dual-band operation is investigated [16]. The operation mechanism of high-order modes is analyzed and then verified through simulations by inserting metallic vias in different positions of the resonant SIW cavity. A complicated antenna structure with T-shaped SLRR (Stub Loaded Ring Resonator) slot on the ground plane is designed. Also a U-shaped slot on microstrip feed line is there. The antenna is investigated for dual-band and triple frequency operation with wide bandwidth [17]. Some slotted triangular microstrip patch antennas with multiple parasitic patches and shorting vias are presented for bandwidth enhancement [18]. A tri-band printed quasi-Yagi antenna using double dipoles on a single layer substrate is proposed. For this antenna, the stub loading technique is used for generating additional resonant mode[19]. A compact meandered monopole antenna fed by asymmetric coplanar strip (ACS) is described [20] for dual-band operation. The resonant frequencies of the antenna are controlled by adjusting the dimensions of the radiating elements. An ACS-fed dual-band antenna using loaded capacitance terminations and a shunt inductor is also proposed [21]. Different types of MIMO antenna array is described [22–23]. These antennas are used for high isolation, gain enhancement, reduction of mutual coupling between the elements using a meta-material and neutralization line at a single frequency. A
good impedance bandwidth is obtained for a triple band monopole antenna with integrated configurations such as using a toothbrush-shaped patch, a meandered line and an inverting U-shaped patch [24] for WLAN and WiMAX applications. A reconfigurable triple-notch-band antenna integrated with defected microstrip structure band-stop filter is designed for ultra-wideband cognitive radio applications [25]. Three frequency bands are obtained for this structure. Eight modes are observed for this antenna. The switches are integrated on the filter and the slot to control the modes of this antenna. A CPW-fed Ultra Wide Band antenna is developed to obtain two stop bands. A Stepped Impedance Stub (SIS) loaded Stepped Impedance Resonators (SIR) and SIS loaded Hexagon Stepped Impedance Resonators (HSIR) are used for this antenna [26]. Here also, two ideal switches are used for multiple modes. Different structures for multifrequency operations are described in books [27–30]. But, there are some drawbacks of multiband patch antennas, which are reported in the literature. They cannot be integrated into and installed in mobile devices due to their large sizes or complex structures. Use of additional electronic circuit for switching at different frequencies makes it cost effective. The use of active components increases complexity in the design. Use of these active components is difficult to handle because it needs extra biasing network. Moreover, it is difficult to develop analytical formulations of the complex structure. As described above, the configuration and operation of multiband antennas are complicated. In this paper, a novel design of slotted patch with probe feed is presented. It can produce very low peaks of S11 at penta frequencies with reasonable gain at low cost. Without the use of additional electronic circuits for switching or use of special substrate material these performances can be acheived. The antenna consists of an array of L-shaped and inverted L-shaped narrow slots on a
rectangular patch as shown in Figures 1 and 2 for multifrequency operation. In the configuration of Figure1, four slots are used where slot lengths and widths are varied as given in Table 1. In Figure2, six slots are introduced for improvement of the performance. The widths and lengths of the slots are listed in Table 2. The patch is fabricated on a FR4-epoxy dielectric substrate having ɛr=4.4and thickness h=1.6 mm above a ground plane. Ansoft HFSS software tool is used for modeling and simulation to determine the S11(dB)vs frequency response. The slots introduce reactive elements in the antenna for resonating at five frequencies:1.25, 1.48, 1.8, 2.25 and 2.9 GHz. Resonant peaks (<–10 dB) are noted at the said frequencies for which radiation pattern, gain and efficiency are determined. The results of simulation and modeling are experimentally verified using network analyzer and found good agreement. The penta frequency response of a single antenna will have applications in wireless communication. It is observed that if the lengths and widths of the slots are varied along with the gaps between the slots, the number of resonant peaks of S11 is increased. Bandwidths are also changed with the change in the dimensions of the slots. In addition, it is seen that, slots are affecting the current distribution on the patch. There is specific observation that the depth of resonant frequencies is increased as the number of slots are increased and widths of the slots are decreased. The design is optimized using Ansoft HFSS tool for best performance.
2. Design of Slotted Rectangular Microstrip Antenna In this paper initially a square patch (L=W) is designed on a FR4 dielectric substrate of ɛr=4.4, and thickness h=1.6 mm above a ground plane. The resonant frequency of the patch antenna for excitation of TMmnp radiating mode is calculated using cavity model from the expression [11, 13]
f r ( mn )
1 2
[(
m 2 n 2 1/2 ) ( ) ] ; L W
(1)
Here 0 reff
reff
r 1 r 1 2
2
[1 12
h 12 ] ; For W / h 1 W
(2)
4 107 h / m, 0
109 F /m 36
L=the length of the patch along x-axis, W= width of the patch along y-axis, and m=0,1,2,.......; n=0,1,2,...........; p=0 For the patch without slot, initial design is made with W=L= 33.7 mm for which the fundamental resonant frequency is 2.1 GHz for TM010 or TM100 mode. Since a simple rectangular patch operates at its tuned frequency. It is modified by cutting an array of L and inverted L narrow slots on the patch to introduce additional reactive elements for multifrequency performance of the antenna as shown in Figure 1 and Figure 2. Different combinations of dimensions of the slots are cut on the patch as described in Table 1. The modification is further carried out in the configuration of Figure 2. Here the width of each slot is kept 1 mm and number of L-slots is increased to six having different lengths as given in Table 2 for improvement in the performance. All the configurations of the modified antenna are fed with a small coaxial probe from the ground plane at the center (0, 0, 0) of the patch. The gaps between the successive slots are 3 mm for each design. The S11(dB), radiation pattern, gain, and efficiency of these antennas are determined using Ansoft HFSS software tool. The dimensions of the slots are optimized for best multifrequency
operation. The results of above parameters are shown graphically and described in the following section. These parameters are also measured using a network analyzer. Both the results agree well.
Figure1.Patch Antenna with Four L-Slots
Figure2. Patch Antenna with Six L-Slots
Table 1. Dimensions of the Slots (Width x
Table 2.Dimensions of the Slots (Width x
Length) for Antenna in Figure1
Length) for Antenna in Figure 2 Slot width (mm)
Slot width (mm) Slot (mm)
length
3
2
1
l1
27.7
27.7
27.7
l2
21.7
22.7
23.7
l3
15.7
17.7
19.7
l4
9.7
12.7
12.7
3. Results and Discussions
Slot (mm)
length
1 l1
27.7
l2
23.7
l3
19.7
l4
15.7
L5
11.7
l6
7.7
The patch antennas described in Figures 1 and 2 with an array of L-shaped and inverted L-shaped narrow slots are fabricated on a FR4-eproxy dielectric substrate having r 4.4 and thickness h=1.6 mm above a ground plane. The results of reflection coefficient in terms of S11(dB), radiation pattern, gain, efficiency and bandwidth are described in the following sections. (a) Reflection coefficient (S11) characteristics of the configuration of Figure1 The dimensions of the slots are altered as given in table 1 and the corresponding results of S11vs frequency response obtained using Ansoft HFSS software tool are shown in Figure 3.It is seen that the resonant frequencies are within the range of TM010 or TM100 mode. Multiple resonant peaks for S11<– 10 dB are obtained in the frequency range from 1.2 to 2.6 GHz. It is observed that by reducing the width of the slot, the S11is improved and the number of resonant frequencies is also increased.
Figure3. Reflection Coefficient Characteristics of Design of Figure1 for Different Slot Widths (b) Reflection coefficient (S11) characteristics of the configuration of Figure2 By increasing the number of narrow L-slots in the configuration of Figure 2, the S11(dB) is further improved in depth and also additional operating peaks are generated as shown in Figure 4.Penta
frequency response with very good S11 of –28.3 dB at 1.25 GHz, –22.1 dB at 1.48 GHz, –24.8 dB at 1.8 GHz, –23.3 dB at 2.25 GHz, and –19.1 dB at 2.9 GHz is produced by this final configuration. These frequencies are used in different wireless communication.
w=1 mm; l1 =27.7 mm, l2 =23.7 mm, l3 =19.7 mm, l4 =15.7 mm, l3 =11.7 mm, l4 =7.7 mm Figure 4. S11vs Frequency Characteristics of Design of Figure 2 It has been observed that when the lengths of the slots are kept as given in Table 2 and the widths of the slots are varied, there is best S11(dB) performance obtained for width w=1 mm as shown in Figure 5. In another attempt the widths of the slots are kept 1mm and lengths of the slots are altered in steps of λ/20 from the values listed in Table 2.The corresponding results are shown in Figure 6. No improvement in the result is observed. In this process, the antenna dimensions with slots are optimized with slot width w=1 mm and the lengths as listed in Table 2 leading to the configuration of Figure 2 for best S11vs frequency response.
Figure 5.S11 (dB) vs Frequency for Different Widths of the Slots with Lengths as per Table 2 for Figure2
Figure 6. S11 (dB) vs Frequency for Different Lengths of the Slots with Width w=1mm as per Table 2 for Figure 2
(c) Reflection coefficient (S11) vs frequency for the configuration of Figure2 for different substrate materials For the antenna configuration of Figure 2, the S11vs frequency response is investigated by changing different substrate materials—FR4 epoxy, RT/Duroid, and Arlon—keeping the slot dimensions as given in Table 2.The results are shown in Figure 7(a). Next, the physical lengths, widths, and spacing are altered to retain the electrical dimensions of the slots same as those of FR4 substrate. The S11vs frequency responses of the patch is shown in Figure7(b). From the comparison of the results, it is seen that FR4 epoxy material gives a better result of S11(dB) vs frequency compared to those of other substrate materials (RT/Duroid, Arlon). The number of resonant peaks (<–10dB) and their depths are increased for FR4 epoxy substrate as compared to other substrates. Therefore, further investigations are carried out for the configuration of Figure 2 using FR4 substrate as described below.
(a)
(b) Figure 7. (a) S11 (dB) vs Frequency (GHz) for Different Substrate Materials for Given Physical Dimensions of the Slots as per Table 2. (b) S11 (dB) vs Frequency (GHz) for Different Substrate Materials with Altering Physical Dimensions of the Slots so That the Electrical Dimensions of the Slots are Same. (d) Radiation characteristics of the configuration of Figure2 The radiation patterns for the final modified configuration (Figure2) are determined at the resonance frequencies. Broadside radiation patterns are obtained as shown in Figure8. It is seen that the radiation patterns are similar because all the frequencies fall below those of next higher order mode.
(a)
(b)
(c)
(d)
(e) Figure8.TheRadiation Patternsof the Design of Figure 2at (a) 1.25 (b) 1.48 (c) 1.8 (d) 2.25,and (e)2.9 GHz From the above results, it is seen that the modified configuration of Figure 2 exhibits better performance. (e) Gain and Efficiency Characteristics The gain and efficiency characteristics of the antenna of final configuration (Figure2)are determined at resonant frequencies using Ansoft HFSS software tool. The gain is also measured using a standard gain ridge horn. Consolidated results of S11 (dB), gain and efficiency for the design of Figure 2 are shown in Table 3.
Table 3.The Performance Characteristics of Final Antenna (Figure 2) Parameters f (GHz) S11 (dB) Bandwidth (%) Gain (Simulated) (dBi) Gain (Measured) Efficiency (Simulated)% Efficiency (Measured)%
w = 1mm with lengths of slots as per Table 2 1.25 –28.3 3.2 1.1 1 62.5 63.6
1.48 –22.1 3.4 1.12 1.07 61 62
1.8 –24.8 3.33 1.15 1.1 52.7 50
2.25 –23.3 4.5 1.39 1.3 54 53
2.9 –19.1 3.1 1.4 1.35 59.4 62.5
This antenna is well suited for multifrequency operation in mobile communication. (f) Surface current distribution
(a)
(b)
(c)
(d)
(e)
Figure9.Surface Current Distributions on Patch of Configuration of Figure2 (a)1.25GHz (b)1.48GHz (c)1.8GHz (d)2.25GHz (e)2.9 GHz The distributions of current density on the patch surface at resonant frequencies 1.25 GHz, 1.48 GHz, 1.8 GHz, 2.25 GHz, and 2.9 GHz are shown in Figure9. It is observed in Figure9(a) that the electric current distribution at 1.25 GHz is concentrated near the ends of uppermost slot, which improves the lowest resonant frequency. From Figure9(b), it is seen that the current distribution is concentrated at the end of lower most slot indicating that this slot controls the second resonant frequency 1.48 GHz. From Figure9(c), it is observed that the current distribution is concentrated near the end of two uppermost slots which control the third resonant frequency 1.8 GHz. Similar
distributions are observed near the two lowermost slots and more specifically at the end of second lower slot controlling the fourth resonant frequency. In Figure9(e), the current distribution is concentrated at the edges of the lowermost slot in the upper corner that controls the fifth resonant frequency 2.9 GHz. From the current distribution, it is confirmed that the sequence of resonances occurs from the larger slot to smaller slot for lowest to highest frequencies, respectively. Conclusions The L-shaped narrow slots are introduced at two corners of a rectangular patch antenna for multifrequency operation. The performance of the modified patch is obtained from the simulation and modeling using Ansoft HFSS tool. The slots are cut at suitable locations and orientations, and the S11 (dB), radiation pattern, gain, and efficiency are obtained. The design is optimized for penta frequency operation. The HFSS results for S11and gain are verified with the experimental results and found in good agreement. The radiation patterns are also found satisfactory. This penta frequency antenna can be used in GSM, UMTS, LTE, WiMax and UHF communications. Acknowledgement Authors acknowledge Department of Electronics and Telecommunication, Jadavpur University, Kolkata, for experimental support. References [1] L. Shafai and X. H.Yang, "Antenna Performance Enhancement by Slotted Microstrip Patches" ELECTRONICS LETTERS 2nd September 1993 Vol.29 No. 18, pp. 1647-1649. [2] K.-L. Wong and J.Y. Sze, Dual frequency slotted rectangular microstrip antenna, Electron Lett 34 (1998), pp. 1368-1370.
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