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Wideband circularly polarized parasitic patches loaded coplanar waveguide-fed square slot antenna with grounded strips and slots for wireless communication systems
Journal Pre-proofs Regular paper Wideband Circularly Polarized Parasitic Patches Loaded Coplanar Waveguide-Fed Square Slot Antenna with Grounded Strips and Slots for Wireless Communication Systems Rashmi, Ashok Kumar, Kapil Saraswat, Arjun Kumar PII: DOI: Reference:
S1434-8411(19)32004-7 https://doi.org/10.1016/j.aeue.2019.153011 AEUE 153011
To appear in:
International Journal of Electronics and Communications
Received Date: Revised Date: Accepted Date:
10 August 2019 16 November 2019 21 November 2019
Please cite this article as: Rashmi, A. Kumar, K. Saraswat, A. Kumar, Wideband Circularly Polarized Parasitic Patches Loaded Coplanar Waveguide-Fed Square Slot Antenna with Grounded Strips and Slots for Wireless Communication Systems, International Journal of Electronics and Communications (2019), doi: https://doi.org/ 10.1016/j.aeue.2019.153011
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Wideband Circularly Polarized Parasitic Patches Loaded Coplanar Waveguide-Fed Square Slot Antenna with Grounded Strips and Slots for Wireless Communication Systems Rashmi1, Ashok Kumar1, *, Kapil Saraswat2, and Arjun Kumar3 1Department
of Electronics and Communication Engineering, Government Mahila
Engineering College, Ajmer, Rajasthan, India M. Tech Scholar, [email protected] *PhD,
[email protected]
2Department
of Electrical Engineering, Indian Institute of Technology, Kanpur, Uttar Pradesh,
India PhD, [email protected] 3School
of Engineering and Applied Sciences, Bennett University, Greater Noida, Uttar
Pradesh, India PhD, [email protected] *Corresponding
author: Ashok Kumar, [email protected]
Wideband Circularly Polarized Parasitic Patches Loaded Coplanar Waveguide-Fed Square Slot Antenna with Grounded Strips and Slots for Wireless Communication Systems Rashmi1, Ashok Kumar1, *, Kapil Saraswat2, and Arjun Kumar3 1Department
of Electronics and Communication Engineering, Government Mahila
Engineering College, Ajmer, Rajasthan, India M. Tech Scholar, [email protected] *PhD,
[email protected]
2Department
of Electrical Engineering, Indian Institute of Technology, Kanpur, Uttar Pradesh,
India PhD, [email protected] 3School
of Engineering and Applied Sciences, Bennett University, Greater Noida, Uttar
Pradesh, India PhD, [email protected] *Corresponding
author: Ashok Kumar, [email protected]
Abstract— In this paper, the design, implementation, and experimental validation of a wideband circularly polarized square slot antenna (CPSSA) is presented. The proposed antenna comprises of an irregular square patch, asymmetrical grounded-L strips, an inverted-L grounded slot, a parasitic asymmetrical rectangular split ring resonator (RSRR) and invertedL strip patches with the overall size of 0.305λL×0.305λL×0.007λL. By appropriately embedding strips, slots and parasitic patches on the antenna structure, the measured wideband 3-dB axial ratio bandwidth (ARBW) of 83.2% (2.33 – 5.65 GHz) is obtained, while the measured impedance bandwidth (IBW) of 86.72% (2.165 – 5.48 GHz) is achieved. Overall, CP bandwidth is 80.66%. A parametric study of different design parameters is investigated, and the overall performance of the antenna is presented. Keywords—Circular polarization, grounded-L strip, square slot antenna, split-ring resonator.
1. Introduction A single-fed coplanar waveguide (CPW)-fed slot and monopole antennas have received substantial attention for the generation of circular polarization (CP) because of its certain benefits such as simple structured, low volume, easy fabrication, low cost and wideband characteristics [1]. One of the most popular techniques for the generation of CP for single-feed slot and monopole antennas are perturbations structure either radiating element or CPW ground plane or embedding parasitic elements [2-29]. Conventionally, the perturbed structures can generate circular polarization by exciting two orthogonal modes having identical amplitudes with a quadrature-phase difference (PD) by altering the current on the antenna. The CPW fed slot and monopole antenna have narrow CP bandwidth (CP bandwidth is a common bandwidth where |S11|<-10dB and axial ratio < 3dB) and therefore, the design of antenna with wideband CP operation using single-feed is a vital research topic in the current scenario. In recent past, several slot and monopole circularly polarized antennas have been investigated which are dual-band [2-7], triple-band [8], quad-band [9], and broadband [10-29] in nature. A CPW-fed split ring resonator loaded G-shaped rectangular slot antenna [2], a horizontal branches CPW-fed, line slot antenna, loaded with rectangular shaped parasitic patches [3], an inverted L-shaped strip loaded slot antenna with an offset feed structure [4], a strip and slots loaded compact square slot antenna [5], a circular-ring shaped antenna with spokes and asymmetric ground plane [6], and a reactively loaded annular slot antenna [7] are reported for dual-band CP radiation while tilted asymmetrical E-shaped antenna for triple-band CP radiation [8] and metamaterial inspired antenna with defected ground structure for quadband CP radiation [9] are reported. Similarly, a T-shaped and L-shaped grounded stub and strips loaded antenna with an asymmetric CPW feed line [10], a stubs and slots loaded Lshaped microstrip-line with tapered section and a square slot ground plane antenna [11], an isosceles trapezoidal antenna with an offset feed [12], an asymmetrical ground plane and Lshaped grounded strips loaded slot antenna [13], a U-shaped patch slot antenna with multiple slots and stair-shaped ground plane [14], inverted L-shaped grounded strips loaded square slot antennas [15], an L-shaped and C-shaped monopole slot antenna with G-shaped feed line [16] are studied for the generation of circular polarization. A pair of spiral parasitic strips loaded monopole antenna [17], a slot antenna with an integrated open slot [18], a square ring slot antenna with inverted-L and vertical stubs [19], a dual symmetrical L-shaped radiator and parasitic inverted-L strip [20] has been discussed which utilizes CPW feeding arrangements. An inverted L-shaped strip and modified patch slot antenna [21], an antipodal Y-strip to square
slot antenna with an U-shaped microstrip-feed line [22], lightning-shaped feed line with a pair of inverted-L grounded strips slot antenna [23] and an open-loop and asymmetric ground plane loaded monopole antenna [24] are used for the CP radiation. An asymmetric meandered-shaped monopole antenna with defected ground structure (DGS) [25], square-ring slot antenna with Lshaped microstrip and circular slot [26], a check-shaped strip loaded slot antenna [27], Gshaped parasitic strip loaded C-shaped monopole antenna [28], and a hook-shaped branch rectangular ground plane with L-shaped microstrip line monopole antenna [29] are also investigated for broadband CP radiation. However, the reported antennas [10-29] have the main constraint of small broadband CP bandwidth and large size. To overcome these shortcomings, designing a compact CP antenna with widest ARBW using single-feed becomes a great challenge for antenna researchers of wireless communication systems. In this paper, a CPW-fed parasitic patch loaded square slot antenna with grounded strips and slots is presented for wideband about 83 % CP bandwidth and small size of 0.305λL×0.305λL×0.007λL. Initially, its CP mode is produced by etching symmetrical square slots diagonally on radiating patch and further enhanced by embedding rectangular SRR, an asymmetrical pair of inverted-L grounded strips, parasitic asymmetrical inverted-L strip patches and inverted-L shaped slot in the CPW ground plane. The CP bandwidth of the proposed antenna can be tuned by altering the dimensions of the RSRR, grounded strips, parasitic patches, and grounded slot. The detailed geometry of the proposed antenna, CP mechanism, parametric study, and measured results are presented and discussed in sections 2 and 3. In section 4, the comprehensive findings of the current study are presented. 2. Antenna Design and Analysis The geometry of the proposed CPW-fed wideband CPSSA is shown in Fig. 1. The proposed antenna consists of two edges connected linked square patch, a split ring resonator, a pair of Lshaped grounded strips, grounded slot and parasitic elements. The proposed antenna is designed on a low cost FR-4 dielectric substrate (ɛr = 4.3 and tanδ = 0.025) of dimension L×L with a thickness of 1 mm. A slot of dimension Ws × Ws is etched, and a CPW fed rectangular patch is placed on the center of the slot which excites the slot (Ant. 1). To generate circular polarization, asymmetry is introduced in the slot by removing a portion from the diagonal edge of the radiator (Ant. 2). To improve the bandwidth, asymmetrical L-shaped grounded strips are placed on the inner side of the grounded slot (Ant. 3). By introducing the asymmetry within the slot, orthogonal modes are generated having equal magnitude and phase of 90o. Within the
slot, the field is perturbed by placing a pair of L-shaped parasitic elements (Ant. 4). To further enhance the CP bandwidth, a rectangular split ring resonator (RSRR) is placed on the back of the antenna at an offset of Lx and Ly as pointed out in Fig 1 (b) from the center (Ant. 5). Finally, to improve the impedance bandwidth, and axial ratio bandwidth, an inverted-L grounded slot is introduced in the ground plane near the feed line (Ant.6).
Fig. 1. Layout of the proposed CPW-fed wideband circularly polarized square slot antenna. The evolution of the proposed antenna is shown in Fig. 2. The simulated |S11| and the axial ratio of the evolution of the antenna is illustrated in Fig. 3(a) and 3(b), respectively. When the slot is excited by the CPW fed slot (Ant. 1), the antenna is narrow band and linearly polarized in nature (axial ratio > 8 dB at about 5.27 GHz). By introducing asymmetry within the slot (Ant. 2), the antenna radiating circularly polarized, and the CP bandwidth is 19.55% is achieved. Further, by introducing L-shaped grounded strips in the inner edge of the slot (Ant. 3) and by introducing the L-shaped asymmetric parasitic elements (Ant. 4) results in the CP bandwidth enhancement by 19.55% to 32.32 %, respectively. The incorporation of rectangular SRR on the back side of the antenna (Ant. 5) results in the axial ratio bandwidth enhancement by 32.32 % to 67.03% which has impact on lower band edge and upper band edge AR frequency. Finally, by introducing an inverted-L slot in the ground plane (Ant. 6), the CP bandwidth is enhanced at both upper band edge and lower band edge AR frequency band and maximum of 82.51% CP bandwidth is achieved. The |S11| and the axial ratio for the different configurations, shown in Fig. 2, are summarized in Table 1.
Fig. 2. Evolution stages of the proposed square slot antenna.
(a)
(b) Fig. 3. Simulated (a) reflection coefficient of Ant. 1–Ant 6, and (b) AR of Ant. 1–Ant. 6.
Table 1: Comparisons of IBWs and 3-dB ARBW variations of the Ant. 1–Ant. 6 Antenna
Bandwidth
3-dB ARBW
Configuration
(GHz, fc, %)
(GHz, fcp, %)
Ant. 1
1.86- 3.15, 2.50, 51.6
-
Ant. 2
1.89- 5.55, 3.72, 98.38
4.06- 4.94, 4.5, 19.55
Ant. 3
1.88- 5.41, 3.64, 96.97
3.26- 4.46, 3.86, 31.08
Ant. 4
1.89- 5.49, 3.69, 97.56
3.28- 4.65, 3.96, 32.32
Ant. 5
2.27- 5.52, 3.89, 83.54
2.40- 4.82, 3.61, 67.03
Ant. 6
2.28- 5.52, 3.9, 83.07
2.29- 5.50, 3.89, 82.51
To get the more physical insight about the generation of the circular polarization and use of the different parasitic elements, the magnitude ratio of the two field components (Ex and Ey) and phase difference between Ex and Ey components are observed for Antenna-1 to Antenna-6 at λU/4 distance from the antenna surface at +Z direction, where λU is the wavelength corresponding to the upper band edge frequency. As we know that for the generation of the circular polarization, the orthogonal field components have equal magnitude and 90o out of phase by each other. As shown in Fig. 4, for the square slot arrangement (Antenna-1), the phase difference is around 0o and magnitude ratio |Ex|/|Ey| is about 0.13. Therefore, Ey component is radiating. By introducing the asymmetry in the slot by removing a portion from the diagonal edge of the radiator (Antenna-2), the Ex field component and the phase difference is improved. It can be observed from the Fig. 4, and similar response can be observed from Fig. 3. Further, by introducing L-shaped grounded strips at the inner edge of the square slot (Antenna-3), the magnitude ratio is improved at lower band edge frequency. Further, by observing the Ex and Ey component, the parasitic elements (Antenna-4 and Antenna-5) and an inverted-L slot (Antenna-6) are introduced in such a way that the coupled field components on the parasitic elements are used to tune the magnitude ratio and the phase difference required for the wide circular polarization. CST microwave studio suite is used for the full wave EM simulation and for the parameter optimization to achieve wide CP bandwidth. The optimized antenna parameter is summarized in Table 2.
Fig. 4: Amplitude ratio (|Ex|/Ey|) and phase difference for Antenna-1 to Antenna-6 Table 2: Parameters of the proposed wideband CP square slot antenna Paramete r Value (mm) Paramete r Value (mm) Paramete r Value (mm)
L
L1
Lx1
40
24.5 6.4
g
g1
k1
0.3 0.5
1
W2 W3
W4
9
5.3
1
Lx2 W 5
5
k2
s
2.6
7
W5
Wx
1.6
7.5
Wf
Wg1 Wp1 Wp2
2.4
18.5 9
7.2
R1
R2
R3
R4
4.4
2.7
1.6
14
Wx1 Wx2 Wy
Wy1
1.9
10.8
4.5
7.9
A
Ax1 Ax2
Ay
2.7
7.3
9
1
Rx
Ry
Lx
Ly
2.6
12
11.1 15.7
Wy2 d
Ws
0.5
30
1
2. CP Mechanism Fig. 5 (a) and (b) shows the simulated surface current distributions of the proposed antenna at different time instants 00, 900, 1800, and 2700 at 2.5 and 3.5 GHz, respectively. It can be observed from Fig. 5 (a) that the stronger surface current at 2.5 GHz predominantly occurs on asymmetrical pair of inverted-L grounded strips and irregular square patch. Correspondingly,
the stronger surface current at 3.5 GHz primarily occurs on parasitic strip patches, deformed square patch and inverted-L grounded strips as shown in Fig. 5 (b). It can also be observed from Fig. 5 that the dominated surface current is rotating in the counter-clockwise direction which results in the right-handed circular polarization (RHCP) wave produced by the radiation superposition on parasitic strip patches, inverted-L grounded strip, and irregular square patch.
Fig. 5. Simulated surface current distributions at (a) 2.5, and (b) 3.5 GHz CP frequencies. 2.1. Parametric Study A parametric study is presented in this section to study the effect of geometrical parameters of the proposed antenna on the magnitude of reflection coefficient (|S11|) and axial ratio. Dominated parameters are addressed to understand the effect in axial ratio and |S11| with different values of right corner inverted-L grounded strip horizontal length Lx2 and length of square slot s. 2.1.1. Effect of inverted-L grounded strip horizontal length Lx2 The effect of variation in the length of inverted-L shaped stub placed on the inner side of the slot, Lx2 in |S11| and AR are shown in Fig. 6 (a) and (b), respectively. When the horizontal length Lx2 increased from 3.5 mm to 5.5 mm with the step size of 0.5 mm, the higher edge frequency of |S11| curve is slightly shifted towards lower side and lower edge frequency is mainly unaffected while 3-dB ARBW is significantly enhanced as depicted in Fig. 6 (b). The horizontal length Lx2 can be used to obtain the maximum of 99.32% 3-dB ARBW overlapped
impedance bandwidth for the dimensions shown in Table 1. Based on the study, the optimal value of Lx2 = 5 mm is considered. The effect of variations in Lx2 on IBW and 3-dB ARBW are summarized in Table 3.
(a)
(b) Fig. 6. Effect of inverted-L grounded strip horizontal length Lx2 on (a) |S11| and (b) AR. Table 3: Comparisons of IBW and 3-dB ARBW variations of inverted-L grounded strip horizontal length Lx2 Varying
Bandwidth
3-dB ARBW
Parameter
(GHz, fc, %)
(GHz, fcp, %)
Lx2 = 3.5 mm
2.27-5.63, 3.95, 85.06
2.28-5.04, 3.66, 75.41
Lx2 = 4.0 mm
2.27-5.60, 3.93, 84.73
2.28-5.12, 3.7, 76.75
Lx2 = 4.5 mm
2.27-5.57, 3.92, 84.18
2.28-5.24, 3.76, 78.72
Lx2 = 5.0 mm
2.28-5.52, 3.9, 83.07
2.29-5.50, 3.89, 82.51
Lx2 = 5.5 mm
2.29-5.46, 3.87, 81.91
2.27-5.59, 3.93, 84.47
2.1.2. Effect of variation in length of square slot s The effect of variation in length of square slot s on |S11| and AR are shown in Fig. 7 (a) and (b), respectively. As the length of square slot s is increased from 6 mm to 8 mm with the step size of 0.5 mm, it mainly affects the upper edge frequency of |S11| curve and shifted towards lower side while 3-dB ARBW is enhanced up to s = 6.5 mm and then reduced till s = 8 mm. The length of square slot s can be tune to attain maximum about 99.32% 3-dB ARBW overlapped impedance bandwidth with the proposed arrangement. Based on the study, the optimum value of s = 7 mm is chosen for maximum CP bandwidth. The effect of variations in s on IBW and 3-dB ARBW are summarized in Table 4.
(a)
(b) Fig. 7. Effect of variation in length of square slot s on (a) |S11| and (b) AR.
Table 4: Comparisons of IBW and 3-dB ARBW variations in length of slot s Varying
Bandwidth
3-dB ARBW
Parameter
(GHz, fc, %)
(GHz, fcp, %)
s = 6 mm
2.26-5.72, 3.99, 86.71
s = 6.5 mm
2.27-5.62, 3.94, 85.02
2.22-4.26, 3.24, 62.96 5.46-5.60, 5.53, 2.53 2.26-5.54, 3.9, 84.10
s = 7 mm
2.28-5.52, 3.9, 83.07
2.29-5.50, 3.89, 82.51
s = 7.5 mm
2.28-5.44, 3.86, 81.86
2.32-5.42, 3.87, 80.10
s = 8 mm
2.28-5.35, 3.81, 80.57
2.41-5.24, 3.82, 74.08
3. Experimental Results and Discussion A prototype has been fabricated using available FR-4 substrate (shown in Fig. 8) and tested. The simulated S-parameter of the proposed antenna is evaluated using full-wave CST studio suite and measured using Agilent's E5071c vector network analyser (VNA). The simulated and measured antenna performance (|S11| and axial ratio) is shown in Fig. 9. It can be observed from Fig. 9 (a) that the simulated and measured impedance bandwidth (IBW) of the antenna is 83.21 % (2.28-5.529 GHz) and 86.72% (2.165-5.48 GHz), respectively.
(a)
(b)
Fig. 8. Fabricated prototype (a) top view and (b) bottom view For the measurement of polarization (axial ratio), gain and radiation pattern, a wideband dual CP horn antenna (A-INFOMW LB-OSJ-20180-P03) is considered as reference antenna
and developed prototype antenna as antenna under test (AUT) in an anechoic chamber in the far-field region using two antenna setup associated with vector network analyser. Fig. 9 (b) illustrates the simulated and measured axial ratio with gain plot is observed at θ = 00. As can be seen from Fig. 9 (b), the simulated and measured 3-dB ARBW of the antenna is 82.41 % (2.29-5.5 GHz) and 83.2% (2.33-5.65 GHz), respectively. The simulated and measured gain of the proposed antenna is analyzed in the broadside direction. The gain is measured over CP frequency range as shown in Fig. 9 (b). The radiation efficiency of the proposed antenna is measured using G/D method instead of Wheeler cap method because the antenna has wide circular polarization. It can be seen from Fig. 10 that the measured radiation efficiency is more than 85 % in the entire CP band. The simulated and measured results match well, and the slight difference is due to fabricational limitation.
(a)
(b) Fig. 9. Comparison of simulated and measured antenna results (a) |S11| and (b) axial ratio
The radiation pattern of the proposed antenna in xz-plane (ϕ = 00) and yz-plane (ϕ = 900) are measured inside an anechoic chamber and compared with the simulated result. For the radiation pattern is measured at 2.4 GHz, 3.5 GHz, and 5 GHz and shown in Fig. 11, 12, and 13 respectively. As shown in Fig. 11, 12 and 13, the antenna is radiating right-handed wave in the +Z direction and left-handed wave in the –Z direction. At the boresight (θ = 00), the difference between RHCP and LHCP, i.e., cross-polarization discrimination (XPD) is below 20 dB in the XZ- and YZ-planes which shows excellent CP radiation. The radiation pattern at 5 GHz in the XZ-plane and YZ-plane is slight distorted due to incorporation of RSRR on the back side of the substrate which mainly affects the higher-edge 3-dB ARBW.
Fig. 10. Comparison of simulated and measured radiation efficiency of the proposed antenna
Fig. 11 Simulated and measured radiation pattern at 2.4 GHz (a) XZ-plane and (b) YZ-plane
Fig. 12 Simulated and measured radiation pattern at 3.5 GHz (a) XZ-plane and (b) YZ-plane
Fig. 13 Simulated and measured radiation pattern at 5 GHz (a) XZ-plane and (b) YZ-plane The proposed parasitic patches loaded square slot antenna with other reported broadband circularly polarized slot and monopole antennas are compared and summarized in Table 5. The antenna reported in [10]-[29] provides the broadband CP band with small 3-dB ARBW and has relatively large size at the lowest CP frequency as compared to the proposed antenna in this paper. Conversely, the antenna proposed in [13] has a small size in terms of wavelength at the lowest CP frequency, but the CP bandwidth is lesser about 72.4%. The CP bandwidth of 83.2% is the highest among all the broadband CP antennas [10]-[29] as compared in Table 5. Therefore, the proposed antenna has the highest 3-dB axial ratio bandwidth and relatively small size as compared with previously reported antennas [10]-[29]. 4. Conclusion In this paper, the design, analysis, and experimental demonstration of a CPW-fed parasitic patches loaded square slot antenna with wide ARBW has been presented. By embedding
unequal L-shaped grounded strips, a rectangular split ring resonator, asymmetrical L-shaped parasitic patches, and inverted-L grounded slot on the CPW-fed deformed patch square slot antenna, a wideband circular polarization has been achieved. The measured 3-dB AR bandwidth and |S11| ≤ -10 dB bandwidth of the proposed antenna are 83.2% (2.33-5.65 GHz) and 86.72% (2.165-5.48 GHz), respectively. Owing to the simply structured, small size, and wideband CP property, the proposed antenna is suitable in various wireless communication systems including 802.11a/b/g/n band, WiMAX band, and proposed 3.5 GHz 5G band.
Table 5: Comparison of proposed antenna and previously reported broadband circularly polarized slot and monopole antennas Ref.
Antenna size λ3L, AR
Antenna size (mm3)
Frequency range (GHz, fc, %)
3-dB ARBW (GHz, fcp, %) 5.07-9.22, 7.14,
[10]
0.676×0.676×0.027
40×40×1.6
5.02-10.84, 7.93, 73.39
[11]
0.753×0.753×0.015
40×40×0.8
5.15-14.05, 9.6, 92.7
[12]
0.648×0.913×0.01
103×145×1.6
1.04-4.33, 2.68, 122.53
[13]
0.308×0.308×0.005
50×50×0.8
1.89-3.9, 2.9, 69.4
1.85-3.95, 2.9, 72.4
[14]
0.349×0.349×0.006
45×45×0.8
1.9-4.5, 3.2, 81.25
2.33-3.81, 3.07, 48.2
[15]
0.98×0.98×0.013
60×60×0.8
2.67-13, 7.83, 132
4.9-6.9, 5.9, 32.2
[16]
0.45×0.45×0.024
30×30×1.6
3.32-6.95, 5.13, 70.1
4.5-6.55, 5.52, 37.1
[17]
0.421×0.383×0.007
55×50×1
1.75-4.5, 3.12, 88
2.3-4.5, 3.4, 64.7
[18]
0.533×0.533×0.008
50×50×0.8
2.13-7.46, 4.795, 111
3.2-4.2, 3.7, 27
[19]
0.375×0.375×0.005
50×50×0.78
2.25-4.40, 3.32, 64.6
2.25-4.40, 3.32, 64.6
[20]
0.426×0.426×0.017
25×25×1
3.15-7.75, 5.45, 84.40
[21]
0.366×0.33×0.011
50×45×1.6
2.2-5.6, 3.9, 87.2
2.2-4.17, 3.2, 61.85
[22]
0.41×0.41×0.023
28×28×1.6
3.25-8.0, 5.62, 84
4.4-6.67, 5.53, 41.3
[23]
0.415×0.415×0.005
60×60×0.8
2.023-3.421, 2.722, 51.4
[24]
0.341×0.375×0.007
50×55×1
1.48-4.24, 2.86, 96.5
2.05-3.95, 3, 63.3
[25]
0.522×0.637×0.026
32×39×1.6
2.4-7.4, 4.9, 102.4
4.9-6.9, 5.9, 37.5
[26]
0.633×0.633×0.012
40×40×0.8
4.56-8.5, 6.53, 60
4.75-8.45, 6.6, 56
[27]
0.506×0.538×0.01
80×85×1.6
1.45-3.15, 2.3, 73.9
1.9-3.1, 2.5, 48
58.08 5.65-9.85, 7.75, 54.2 1.89-2.86, 4.75, 34.57
5.12-7.15, 6.13, 33.08
2.07-3.415, 2.74, 48.8
[28]
0.456×0.428×0.022
32×30×1.6
3.92-7.52, 5.72, 62.94
[29]
0.349×0.349×0.012
44×44×1.6
2.25-4.0, 3.48, 56
Prop. work
0.305×0.305×0.007
40×40×1
2.165-5.48, 3.8225, 86.72
4.28-7.44, 5.86, 53.92 2.38-4.6, 3.12, 63.61 2.33-5.65, 3.99, 83.2
λL, AR is the wavelength at the lower band-edge frequency, where the AR is 3 dB. References 1. S.S. Gao, Q. Luo, F. Zhu, Circularly Polarized Antennas. UK: Wiley-IEEE Press; 2013. 2. K. Saraswat, A.R. Harish, “Dual-band CP coplanar waveguide-fed splitring resonatorloaded G-shaped slot antenna with wide-frequency ratio,” IET Microw. Antennas Propag., vol. 12, no. 12, pp. 1920-1925, 2018. 3. R.K. Saini, P.S. Bakariya, P. Kumar, “Coplanar waveguide fed dual-band dual sense circular polarized square slot antenna,” Int J RF Microw Comput Aided Eng., vol. 28, no. 9, pp. e21503, 2018. 4. R. Xu, J.-Y. Li, J. Liu, S.-G. Zhou, K. Wei, Z.-J. Xing, “A simple design of compact dualwideband square slot antenna with dual-sense circularly polarized radiation for WLAN/WiFi communications,” IEEE Trans. Antennas Propag., vol. 66, no. 9, pp. 4884-4889, 2018. 5. Jaiverdhan, A. Kumar, M.M. Sharma, R.P. Yadav, “Dual wideband circular polarized CPW-fed strip and slots loaded compact square slot antenna for wireless and satellite applications,” Int. J. Electron. Commun., vol. 108, pp. 181-188, 2019. 6. B.P. Nadh, B.T.P. Madhav, M.S. Kumar, M.V. Rao, T. Anilkumar, “Asymmetric ground structured circularly polarized antenna for ISM and WLAN band applications,” Prog. Electromag. Res. M, vol. 76, pp.167-175, 2018. 7. J. Li, J. Shi, L. Li, T.A. Khan, J. Chen, Y. Li, A. Zhang, “Dual-band annular slot antenna loaded by reactive components for dual-sense circular polarization with flexible frequency ratio,” IEEE Access, vol. 6, pp. 64063-64070, 2018. 8. A. Kumar, V. Sankhla, J.K. Deegwal, A. Kumar, “An offset CPW-fed triple-band circularly polarized printed antenna for multiband wireless applications,” Int. J. Electron. Commun., vol. 86, pp. 133-141, 2018. 9. M.V. Rao, B.T.P. Madhav, T. Anilkumar, B.P. Nadh, “Metamaterial inspired quad band circularly
polarized
antenna
for
WLAN/ISM/Bluetooth/WiMAX
and
satellite
communication applications,” Int. J. Electron. Commun., vol. 97, pp. 229-241, 2018.
10. M. Midya, S. Bhattacharjee, M. Mitra, “Pair of grounded L strips loaded broadband circularly polarised square slot antenna with enhanced axial ratio bandwidth,” Electron. Lett., vol. 54, no. 15, pp. 917-918, 2018. 11. L. Wang, W. Fang, Y. En, Y. Huang, W. Shao, B. Yao, “A new broadband circularly polarized square-slot antenna with low axial ratios,” Int J RF Microw Comput Aided Eng., vol. 29, no. 1, pp. e21502, 2019. 12. T. Kumar, K. Saraswat, A.R. Harish, “Offset-fed trapezoidal monopole antenna for broadband circular poalrization,” Int. J. RF Microw. Comput. Aided Eng., vol. 27, no. 2, pp. e21063, 2017. 13. H. Zhang, Y.-C. Jiao, T. Ni, W.-L. Liang, “Broadband circularly polarised antenna with asymmetric ground and L-shaped strips,” Electron. Lett., vol. 50, no. 23, pp. 1660-1662, 2014. 14. E. Shirazi, M.A. Honarvar, “Broadband circularly polarized stair-shaped slot antenna,” Electromagnetics, vol.35, no. 7, pp.443-452, 2015. 15. J. Pourahmadazar, Ch. Ghobadi, J. Nourinia, N. Felegari, H. Shirzad, “Broadband CPWfed circularly polarized square slot antenna with inverted-L strips for UWB applications,” IEEE Antennas Wireless Propag. Lett., vol. 10, pp. 369-372, 2011. 16. K. Oteng Gyasi, J. Li, Y. Huang, W. Guangjun, “Broadband circularly polarized square slot antenna with a G-shaped feedline,” Microw Opt Technol Lett., vol. 59, pp. 3055–3063, 2017. 17. K. Ding, C. Gao, Y. Wu, D. Qu, B. Zhang, “A broadband circularly polarized printed monopole antenna with parasitic strips,” IEEE Antennas Wireless Propag. Lett., vol. 16, pp. 2509-2512, 2017. 18. J.-Y. Jan, C.-Y. Pan, K.-Y. Chiu, H.-M. Chen, “Broadband CPW-fed circularly-polarized slot antenna with an open slot,” IEEE Trans. Antennas Propag., vol. 61, no. 3, pp. 14181422, 2013. 19. K. Saraswat, A.R. Harish, “Analysis of wideband circularly polarized ring slot antenna using characteristics mode for bandwidth enhancement,” Int J RF Microw Comput Aided Eng., vol. 28, no. 2, pp. e21186, 2017. 20. A. Kumar, J. K. Deegwal, M. M. Sharma, “Miniaturized wideband dual linearly and circularly polarized printed square slot antenna for multiradio wireless systems,” Int. J. Electron. Commun., vol. 88, pp. 44-51, 2018.
21. N. Kushwaha, R. Kumar, R.V.S. Ram Krishna, “Design and analysis of CPW-fed wideband circularly polarized antenna for modern communication systems,” J. Electromag. Waves Appl., vol.29, no.11, pp.1397-1409, 2015. 22. M. Nosrati, N. Tavassolian, “Miniaturized circularly polarized square slot antenna with enhanced axial-ratio bandwidth using an antipodal Y-strip,” IEEE Antennas Wireless Propag. Lett., vol. 16, pp. 817–820, 2016. 23. J.-Y. Sze, C.-I. G. Hsu, Z.-W. Chen, C.-C. Chang, “Broadband CPW-fed circularly polarized square slot antenna with lightening-shaped feedline and inverted-L grounded strips,” IEEE Trans. Antennas Propag., vol. 58, no. 3, pp. 973–977, 2010. 24. K. Ding, Y.-X. Guo, C. Gao, “CPW-fed wideband circularly polarized printed monopole antenna with open loop and asymmetric ground plane,” IEEE Antennas Wireless Propag. Lett., vol. 16, pp. 833–836, 2017. 25. T. Jhajharia, V. Tiwari, D. Yadav, S. Rawat, D. Bhatnagar, “Wideband circularly polarised antenna with an asymmetric meandered-shaped monopole and defected ground structure for wireless communication,” IET Microw. Antennas Propag., vol. 12, no. 9, pp. 15541558, 2018. 26. H. Zhang, Y.-C. Jiao, L. Lu, C. Zhang, “Broadband circularly polarized square-ring-loaded slot antenna with flat gains,” IEEE Antennas Wireless Propag. Lett., vol. 16, pp. 29–32, 2017. 27. Y.W. Liu, P. Hsu, “Broadband circularly polarised square slot antenna fed by coplanar waveguide,” Electron. Lett., vol. 49, no. 16, pp. 976-977, 2013. 28. M. Midya, S. Bhattacharjee, M. Mitra, “Broadband circularly polarized planar monopole antenna with G-shaped parasitic strip,” IEEE Antennas Wireless Propag. Lett., vol. 18, no. 4, pp. 581–585, 2019. 29. M. Samsuzzaman, M. T. Islam, M. J. Singh, “A compact printed monopole antenna with wideband circular polarization,” IEEE Access, vol. 6, pp. 54713-54725, 2018.
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
None
S1434-8411(19)32004-7 https://doi.org/10.1016/j.aeue.2019.153011 AEUE 153011
To appear in:
International Journal of Electronics and Communications
Received Date: Revised Date: Accepted Date:
10 August 2019 16 November 2019 21 November 2019
Please cite this article as: Rashmi, A. Kumar, K. Saraswat, A. Kumar, Wideband Circularly Polarized Parasitic Patches Loaded Coplanar Waveguide-Fed Square Slot Antenna with Grounded Strips and Slots for Wireless Communication Systems, International Journal of Electronics and Communications (2019), doi: https://doi.org/ 10.1016/j.aeue.2019.153011
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Wideband Circularly Polarized Parasitic Patches Loaded Coplanar Waveguide-Fed Square Slot Antenna with Grounded Strips and Slots for Wireless Communication Systems Rashmi1, Ashok Kumar1, *, Kapil Saraswat2, and Arjun Kumar3 1Department
of Electronics and Communication Engineering, Government Mahila
Engineering College, Ajmer, Rajasthan, India M. Tech Scholar, [email protected] *PhD,
[email protected]
2Department
of Electrical Engineering, Indian Institute of Technology, Kanpur, Uttar Pradesh,
India PhD, [email protected] 3School
of Engineering and Applied Sciences, Bennett University, Greater Noida, Uttar
Pradesh, India PhD, [email protected] *Corresponding
author: Ashok Kumar, [email protected]
Wideband Circularly Polarized Parasitic Patches Loaded Coplanar Waveguide-Fed Square Slot Antenna with Grounded Strips and Slots for Wireless Communication Systems Rashmi1, Ashok Kumar1, *, Kapil Saraswat2, and Arjun Kumar3 1Department
of Electronics and Communication Engineering, Government Mahila
Engineering College, Ajmer, Rajasthan, India M. Tech Scholar, [email protected] *PhD,
[email protected]
2Department
of Electrical Engineering, Indian Institute of Technology, Kanpur, Uttar Pradesh,
India PhD, [email protected] 3School
of Engineering and Applied Sciences, Bennett University, Greater Noida, Uttar
Pradesh, India PhD, [email protected] *Corresponding
author: Ashok Kumar, [email protected]
Abstract— In this paper, the design, implementation, and experimental validation of a wideband circularly polarized square slot antenna (CPSSA) is presented. The proposed antenna comprises of an irregular square patch, asymmetrical grounded-L strips, an inverted-L grounded slot, a parasitic asymmetrical rectangular split ring resonator (RSRR) and invertedL strip patches with the overall size of 0.305λL×0.305λL×0.007λL. By appropriately embedding strips, slots and parasitic patches on the antenna structure, the measured wideband 3-dB axial ratio bandwidth (ARBW) of 83.2% (2.33 – 5.65 GHz) is obtained, while the measured impedance bandwidth (IBW) of 86.72% (2.165 – 5.48 GHz) is achieved. Overall, CP bandwidth is 80.66%. A parametric study of different design parameters is investigated, and the overall performance of the antenna is presented. Keywords—Circular polarization, grounded-L strip, square slot antenna, split-ring resonator.
1. Introduction A single-fed coplanar waveguide (CPW)-fed slot and monopole antennas have received substantial attention for the generation of circular polarization (CP) because of its certain benefits such as simple structured, low volume, easy fabrication, low cost and wideband characteristics [1]. One of the most popular techniques for the generation of CP for single-feed slot and monopole antennas are perturbations structure either radiating element or CPW ground plane or embedding parasitic elements [2-29]. Conventionally, the perturbed structures can generate circular polarization by exciting two orthogonal modes having identical amplitudes with a quadrature-phase difference (PD) by altering the current on the antenna. The CPW fed slot and monopole antenna have narrow CP bandwidth (CP bandwidth is a common bandwidth where |S11|<-10dB and axial ratio < 3dB) and therefore, the design of antenna with wideband CP operation using single-feed is a vital research topic in the current scenario. In recent past, several slot and monopole circularly polarized antennas have been investigated which are dual-band [2-7], triple-band [8], quad-band [9], and broadband [10-29] in nature. A CPW-fed split ring resonator loaded G-shaped rectangular slot antenna [2], a horizontal branches CPW-fed, line slot antenna, loaded with rectangular shaped parasitic patches [3], an inverted L-shaped strip loaded slot antenna with an offset feed structure [4], a strip and slots loaded compact square slot antenna [5], a circular-ring shaped antenna with spokes and asymmetric ground plane [6], and a reactively loaded annular slot antenna [7] are reported for dual-band CP radiation while tilted asymmetrical E-shaped antenna for triple-band CP radiation [8] and metamaterial inspired antenna with defected ground structure for quadband CP radiation [9] are reported. Similarly, a T-shaped and L-shaped grounded stub and strips loaded antenna with an asymmetric CPW feed line [10], a stubs and slots loaded Lshaped microstrip-line with tapered section and a square slot ground plane antenna [11], an isosceles trapezoidal antenna with an offset feed [12], an asymmetrical ground plane and Lshaped grounded strips loaded slot antenna [13], a U-shaped patch slot antenna with multiple slots and stair-shaped ground plane [14], inverted L-shaped grounded strips loaded square slot antennas [15], an L-shaped and C-shaped monopole slot antenna with G-shaped feed line [16] are studied for the generation of circular polarization. A pair of spiral parasitic strips loaded monopole antenna [17], a slot antenna with an integrated open slot [18], a square ring slot antenna with inverted-L and vertical stubs [19], a dual symmetrical L-shaped radiator and parasitic inverted-L strip [20] has been discussed which utilizes CPW feeding arrangements. An inverted L-shaped strip and modified patch slot antenna [21], an antipodal Y-strip to square
slot antenna with an U-shaped microstrip-feed line [22], lightning-shaped feed line with a pair of inverted-L grounded strips slot antenna [23] and an open-loop and asymmetric ground plane loaded monopole antenna [24] are used for the CP radiation. An asymmetric meandered-shaped monopole antenna with defected ground structure (DGS) [25], square-ring slot antenna with Lshaped microstrip and circular slot [26], a check-shaped strip loaded slot antenna [27], Gshaped parasitic strip loaded C-shaped monopole antenna [28], and a hook-shaped branch rectangular ground plane with L-shaped microstrip line monopole antenna [29] are also investigated for broadband CP radiation. However, the reported antennas [10-29] have the main constraint of small broadband CP bandwidth and large size. To overcome these shortcomings, designing a compact CP antenna with widest ARBW using single-feed becomes a great challenge for antenna researchers of wireless communication systems. In this paper, a CPW-fed parasitic patch loaded square slot antenna with grounded strips and slots is presented for wideband about 83 % CP bandwidth and small size of 0.305λL×0.305λL×0.007λL. Initially, its CP mode is produced by etching symmetrical square slots diagonally on radiating patch and further enhanced by embedding rectangular SRR, an asymmetrical pair of inverted-L grounded strips, parasitic asymmetrical inverted-L strip patches and inverted-L shaped slot in the CPW ground plane. The CP bandwidth of the proposed antenna can be tuned by altering the dimensions of the RSRR, grounded strips, parasitic patches, and grounded slot. The detailed geometry of the proposed antenna, CP mechanism, parametric study, and measured results are presented and discussed in sections 2 and 3. In section 4, the comprehensive findings of the current study are presented. 2. Antenna Design and Analysis The geometry of the proposed CPW-fed wideband CPSSA is shown in Fig. 1. The proposed antenna consists of two edges connected linked square patch, a split ring resonator, a pair of Lshaped grounded strips, grounded slot and parasitic elements. The proposed antenna is designed on a low cost FR-4 dielectric substrate (ɛr = 4.3 and tanδ = 0.025) of dimension L×L with a thickness of 1 mm. A slot of dimension Ws × Ws is etched, and a CPW fed rectangular patch is placed on the center of the slot which excites the slot (Ant. 1). To generate circular polarization, asymmetry is introduced in the slot by removing a portion from the diagonal edge of the radiator (Ant. 2). To improve the bandwidth, asymmetrical L-shaped grounded strips are placed on the inner side of the grounded slot (Ant. 3). By introducing the asymmetry within the slot, orthogonal modes are generated having equal magnitude and phase of 90o. Within the
slot, the field is perturbed by placing a pair of L-shaped parasitic elements (Ant. 4). To further enhance the CP bandwidth, a rectangular split ring resonator (RSRR) is placed on the back of the antenna at an offset of Lx and Ly as pointed out in Fig 1 (b) from the center (Ant. 5). Finally, to improve the impedance bandwidth, and axial ratio bandwidth, an inverted-L grounded slot is introduced in the ground plane near the feed line (Ant.6).
Fig. 1. Layout of the proposed CPW-fed wideband circularly polarized square slot antenna. The evolution of the proposed antenna is shown in Fig. 2. The simulated |S11| and the axial ratio of the evolution of the antenna is illustrated in Fig. 3(a) and 3(b), respectively. When the slot is excited by the CPW fed slot (Ant. 1), the antenna is narrow band and linearly polarized in nature (axial ratio > 8 dB at about 5.27 GHz). By introducing asymmetry within the slot (Ant. 2), the antenna radiating circularly polarized, and the CP bandwidth is 19.55% is achieved. Further, by introducing L-shaped grounded strips in the inner edge of the slot (Ant. 3) and by introducing the L-shaped asymmetric parasitic elements (Ant. 4) results in the CP bandwidth enhancement by 19.55% to 32.32 %, respectively. The incorporation of rectangular SRR on the back side of the antenna (Ant. 5) results in the axial ratio bandwidth enhancement by 32.32 % to 67.03% which has impact on lower band edge and upper band edge AR frequency. Finally, by introducing an inverted-L slot in the ground plane (Ant. 6), the CP bandwidth is enhanced at both upper band edge and lower band edge AR frequency band and maximum of 82.51% CP bandwidth is achieved. The |S11| and the axial ratio for the different configurations, shown in Fig. 2, are summarized in Table 1.
Fig. 2. Evolution stages of the proposed square slot antenna.
(a)
(b) Fig. 3. Simulated (a) reflection coefficient of Ant. 1–Ant 6, and (b) AR of Ant. 1–Ant. 6.
Table 1: Comparisons of IBWs and 3-dB ARBW variations of the Ant. 1–Ant. 6 Antenna
Bandwidth
3-dB ARBW
Configuration
(GHz, fc, %)
(GHz, fcp, %)
Ant. 1
1.86- 3.15, 2.50, 51.6
-
Ant. 2
1.89- 5.55, 3.72, 98.38
4.06- 4.94, 4.5, 19.55
Ant. 3
1.88- 5.41, 3.64, 96.97
3.26- 4.46, 3.86, 31.08
Ant. 4
1.89- 5.49, 3.69, 97.56
3.28- 4.65, 3.96, 32.32
Ant. 5
2.27- 5.52, 3.89, 83.54
2.40- 4.82, 3.61, 67.03
Ant. 6
2.28- 5.52, 3.9, 83.07
2.29- 5.50, 3.89, 82.51
To get the more physical insight about the generation of the circular polarization and use of the different parasitic elements, the magnitude ratio of the two field components (Ex and Ey) and phase difference between Ex and Ey components are observed for Antenna-1 to Antenna-6 at λU/4 distance from the antenna surface at +Z direction, where λU is the wavelength corresponding to the upper band edge frequency. As we know that for the generation of the circular polarization, the orthogonal field components have equal magnitude and 90o out of phase by each other. As shown in Fig. 4, for the square slot arrangement (Antenna-1), the phase difference is around 0o and magnitude ratio |Ex|/|Ey| is about 0.13. Therefore, Ey component is radiating. By introducing the asymmetry in the slot by removing a portion from the diagonal edge of the radiator (Antenna-2), the Ex field component and the phase difference is improved. It can be observed from the Fig. 4, and similar response can be observed from Fig. 3. Further, by introducing L-shaped grounded strips at the inner edge of the square slot (Antenna-3), the magnitude ratio is improved at lower band edge frequency. Further, by observing the Ex and Ey component, the parasitic elements (Antenna-4 and Antenna-5) and an inverted-L slot (Antenna-6) are introduced in such a way that the coupled field components on the parasitic elements are used to tune the magnitude ratio and the phase difference required for the wide circular polarization. CST microwave studio suite is used for the full wave EM simulation and for the parameter optimization to achieve wide CP bandwidth. The optimized antenna parameter is summarized in Table 2.
Fig. 4: Amplitude ratio (|Ex|/Ey|) and phase difference for Antenna-1 to Antenna-6 Table 2: Parameters of the proposed wideband CP square slot antenna Paramete r Value (mm) Paramete r Value (mm) Paramete r Value (mm)
L
L1
Lx1
40
24.5 6.4
g
g1
k1
0.3 0.5
1
W2 W3
W4
9
5.3
1
Lx2 W 5
5
k2
s
2.6
7
W5
Wx
1.6
7.5
Wf
Wg1 Wp1 Wp2
2.4
18.5 9
7.2
R1
R2
R3
R4
4.4
2.7
1.6
14
Wx1 Wx2 Wy
Wy1
1.9
10.8
4.5
7.9
A
Ax1 Ax2
Ay
2.7
7.3
9
1
Rx
Ry
Lx
Ly
2.6
12
11.1 15.7
Wy2 d
Ws
0.5
30
1
2. CP Mechanism Fig. 5 (a) and (b) shows the simulated surface current distributions of the proposed antenna at different time instants 00, 900, 1800, and 2700 at 2.5 and 3.5 GHz, respectively. It can be observed from Fig. 5 (a) that the stronger surface current at 2.5 GHz predominantly occurs on asymmetrical pair of inverted-L grounded strips and irregular square patch. Correspondingly,
the stronger surface current at 3.5 GHz primarily occurs on parasitic strip patches, deformed square patch and inverted-L grounded strips as shown in Fig. 5 (b). It can also be observed from Fig. 5 that the dominated surface current is rotating in the counter-clockwise direction which results in the right-handed circular polarization (RHCP) wave produced by the radiation superposition on parasitic strip patches, inverted-L grounded strip, and irregular square patch.
Fig. 5. Simulated surface current distributions at (a) 2.5, and (b) 3.5 GHz CP frequencies. 2.1. Parametric Study A parametric study is presented in this section to study the effect of geometrical parameters of the proposed antenna on the magnitude of reflection coefficient (|S11|) and axial ratio. Dominated parameters are addressed to understand the effect in axial ratio and |S11| with different values of right corner inverted-L grounded strip horizontal length Lx2 and length of square slot s. 2.1.1. Effect of inverted-L grounded strip horizontal length Lx2 The effect of variation in the length of inverted-L shaped stub placed on the inner side of the slot, Lx2 in |S11| and AR are shown in Fig. 6 (a) and (b), respectively. When the horizontal length Lx2 increased from 3.5 mm to 5.5 mm with the step size of 0.5 mm, the higher edge frequency of |S11| curve is slightly shifted towards lower side and lower edge frequency is mainly unaffected while 3-dB ARBW is significantly enhanced as depicted in Fig. 6 (b). The horizontal length Lx2 can be used to obtain the maximum of 99.32% 3-dB ARBW overlapped
impedance bandwidth for the dimensions shown in Table 1. Based on the study, the optimal value of Lx2 = 5 mm is considered. The effect of variations in Lx2 on IBW and 3-dB ARBW are summarized in Table 3.
(a)
(b) Fig. 6. Effect of inverted-L grounded strip horizontal length Lx2 on (a) |S11| and (b) AR. Table 3: Comparisons of IBW and 3-dB ARBW variations of inverted-L grounded strip horizontal length Lx2 Varying
Bandwidth
3-dB ARBW
Parameter
(GHz, fc, %)
(GHz, fcp, %)
Lx2 = 3.5 mm
2.27-5.63, 3.95, 85.06
2.28-5.04, 3.66, 75.41
Lx2 = 4.0 mm
2.27-5.60, 3.93, 84.73
2.28-5.12, 3.7, 76.75
Lx2 = 4.5 mm
2.27-5.57, 3.92, 84.18
2.28-5.24, 3.76, 78.72
Lx2 = 5.0 mm
2.28-5.52, 3.9, 83.07
2.29-5.50, 3.89, 82.51
Lx2 = 5.5 mm
2.29-5.46, 3.87, 81.91
2.27-5.59, 3.93, 84.47
2.1.2. Effect of variation in length of square slot s The effect of variation in length of square slot s on |S11| and AR are shown in Fig. 7 (a) and (b), respectively. As the length of square slot s is increased from 6 mm to 8 mm with the step size of 0.5 mm, it mainly affects the upper edge frequency of |S11| curve and shifted towards lower side while 3-dB ARBW is enhanced up to s = 6.5 mm and then reduced till s = 8 mm. The length of square slot s can be tune to attain maximum about 99.32% 3-dB ARBW overlapped impedance bandwidth with the proposed arrangement. Based on the study, the optimum value of s = 7 mm is chosen for maximum CP bandwidth. The effect of variations in s on IBW and 3-dB ARBW are summarized in Table 4.
(a)
(b) Fig. 7. Effect of variation in length of square slot s on (a) |S11| and (b) AR.
Table 4: Comparisons of IBW and 3-dB ARBW variations in length of slot s Varying
Bandwidth
3-dB ARBW
Parameter
(GHz, fc, %)
(GHz, fcp, %)
s = 6 mm
2.26-5.72, 3.99, 86.71
s = 6.5 mm
2.27-5.62, 3.94, 85.02
2.22-4.26, 3.24, 62.96 5.46-5.60, 5.53, 2.53 2.26-5.54, 3.9, 84.10
s = 7 mm
2.28-5.52, 3.9, 83.07
2.29-5.50, 3.89, 82.51
s = 7.5 mm
2.28-5.44, 3.86, 81.86
2.32-5.42, 3.87, 80.10
s = 8 mm
2.28-5.35, 3.81, 80.57
2.41-5.24, 3.82, 74.08
3. Experimental Results and Discussion A prototype has been fabricated using available FR-4 substrate (shown in Fig. 8) and tested. The simulated S-parameter of the proposed antenna is evaluated using full-wave CST studio suite and measured using Agilent's E5071c vector network analyser (VNA). The simulated and measured antenna performance (|S11| and axial ratio) is shown in Fig. 9. It can be observed from Fig. 9 (a) that the simulated and measured impedance bandwidth (IBW) of the antenna is 83.21 % (2.28-5.529 GHz) and 86.72% (2.165-5.48 GHz), respectively.
(a)
(b)
Fig. 8. Fabricated prototype (a) top view and (b) bottom view For the measurement of polarization (axial ratio), gain and radiation pattern, a wideband dual CP horn antenna (A-INFOMW LB-OSJ-20180-P03) is considered as reference antenna
and developed prototype antenna as antenna under test (AUT) in an anechoic chamber in the far-field region using two antenna setup associated with vector network analyser. Fig. 9 (b) illustrates the simulated and measured axial ratio with gain plot is observed at θ = 00. As can be seen from Fig. 9 (b), the simulated and measured 3-dB ARBW of the antenna is 82.41 % (2.29-5.5 GHz) and 83.2% (2.33-5.65 GHz), respectively. The simulated and measured gain of the proposed antenna is analyzed in the broadside direction. The gain is measured over CP frequency range as shown in Fig. 9 (b). The radiation efficiency of the proposed antenna is measured using G/D method instead of Wheeler cap method because the antenna has wide circular polarization. It can be seen from Fig. 10 that the measured radiation efficiency is more than 85 % in the entire CP band. The simulated and measured results match well, and the slight difference is due to fabricational limitation.
(a)
(b) Fig. 9. Comparison of simulated and measured antenna results (a) |S11| and (b) axial ratio
The radiation pattern of the proposed antenna in xz-plane (ϕ = 00) and yz-plane (ϕ = 900) are measured inside an anechoic chamber and compared with the simulated result. For the radiation pattern is measured at 2.4 GHz, 3.5 GHz, and 5 GHz and shown in Fig. 11, 12, and 13 respectively. As shown in Fig. 11, 12 and 13, the antenna is radiating right-handed wave in the +Z direction and left-handed wave in the –Z direction. At the boresight (θ = 00), the difference between RHCP and LHCP, i.e., cross-polarization discrimination (XPD) is below 20 dB in the XZ- and YZ-planes which shows excellent CP radiation. The radiation pattern at 5 GHz in the XZ-plane and YZ-plane is slight distorted due to incorporation of RSRR on the back side of the substrate which mainly affects the higher-edge 3-dB ARBW.
Fig. 10. Comparison of simulated and measured radiation efficiency of the proposed antenna
Fig. 11 Simulated and measured radiation pattern at 2.4 GHz (a) XZ-plane and (b) YZ-plane
Fig. 12 Simulated and measured radiation pattern at 3.5 GHz (a) XZ-plane and (b) YZ-plane
Fig. 13 Simulated and measured radiation pattern at 5 GHz (a) XZ-plane and (b) YZ-plane The proposed parasitic patches loaded square slot antenna with other reported broadband circularly polarized slot and monopole antennas are compared and summarized in Table 5. The antenna reported in [10]-[29] provides the broadband CP band with small 3-dB ARBW and has relatively large size at the lowest CP frequency as compared to the proposed antenna in this paper. Conversely, the antenna proposed in [13] has a small size in terms of wavelength at the lowest CP frequency, but the CP bandwidth is lesser about 72.4%. The CP bandwidth of 83.2% is the highest among all the broadband CP antennas [10]-[29] as compared in Table 5. Therefore, the proposed antenna has the highest 3-dB axial ratio bandwidth and relatively small size as compared with previously reported antennas [10]-[29]. 4. Conclusion In this paper, the design, analysis, and experimental demonstration of a CPW-fed parasitic patches loaded square slot antenna with wide ARBW has been presented. By embedding
unequal L-shaped grounded strips, a rectangular split ring resonator, asymmetrical L-shaped parasitic patches, and inverted-L grounded slot on the CPW-fed deformed patch square slot antenna, a wideband circular polarization has been achieved. The measured 3-dB AR bandwidth and |S11| ≤ -10 dB bandwidth of the proposed antenna are 83.2% (2.33-5.65 GHz) and 86.72% (2.165-5.48 GHz), respectively. Owing to the simply structured, small size, and wideband CP property, the proposed antenna is suitable in various wireless communication systems including 802.11a/b/g/n band, WiMAX band, and proposed 3.5 GHz 5G band.
Table 5: Comparison of proposed antenna and previously reported broadband circularly polarized slot and monopole antennas Ref.
Antenna size λ3L, AR
Antenna size (mm3)
Frequency range (GHz, fc, %)
3-dB ARBW (GHz, fcp, %) 5.07-9.22, 7.14,
[10]
0.676×0.676×0.027
40×40×1.6
5.02-10.84, 7.93, 73.39
[11]
0.753×0.753×0.015
40×40×0.8
5.15-14.05, 9.6, 92.7
[12]
0.648×0.913×0.01
103×145×1.6
1.04-4.33, 2.68, 122.53
[13]
0.308×0.308×0.005
50×50×0.8
1.89-3.9, 2.9, 69.4
1.85-3.95, 2.9, 72.4
[14]
0.349×0.349×0.006
45×45×0.8
1.9-4.5, 3.2, 81.25
2.33-3.81, 3.07, 48.2
[15]
0.98×0.98×0.013
60×60×0.8
2.67-13, 7.83, 132
4.9-6.9, 5.9, 32.2
[16]
0.45×0.45×0.024
30×30×1.6
3.32-6.95, 5.13, 70.1
4.5-6.55, 5.52, 37.1
[17]
0.421×0.383×0.007
55×50×1
1.75-4.5, 3.12, 88
2.3-4.5, 3.4, 64.7
[18]
0.533×0.533×0.008
50×50×0.8
2.13-7.46, 4.795, 111
3.2-4.2, 3.7, 27
[19]
0.375×0.375×0.005
50×50×0.78
2.25-4.40, 3.32, 64.6
2.25-4.40, 3.32, 64.6
[20]
0.426×0.426×0.017
25×25×1
3.15-7.75, 5.45, 84.40
[21]
0.366×0.33×0.011
50×45×1.6
2.2-5.6, 3.9, 87.2
2.2-4.17, 3.2, 61.85
[22]
0.41×0.41×0.023
28×28×1.6
3.25-8.0, 5.62, 84
4.4-6.67, 5.53, 41.3
[23]
0.415×0.415×0.005
60×60×0.8
2.023-3.421, 2.722, 51.4
[24]
0.341×0.375×0.007
50×55×1
1.48-4.24, 2.86, 96.5
2.05-3.95, 3, 63.3
[25]
0.522×0.637×0.026
32×39×1.6
2.4-7.4, 4.9, 102.4
4.9-6.9, 5.9, 37.5
[26]
0.633×0.633×0.012
40×40×0.8
4.56-8.5, 6.53, 60
4.75-8.45, 6.6, 56
[27]
0.506×0.538×0.01
80×85×1.6
1.45-3.15, 2.3, 73.9
1.9-3.1, 2.5, 48
58.08 5.65-9.85, 7.75, 54.2 1.89-2.86, 4.75, 34.57
5.12-7.15, 6.13, 33.08
2.07-3.415, 2.74, 48.8
[28]
0.456×0.428×0.022
32×30×1.6
3.92-7.52, 5.72, 62.94
[29]
0.349×0.349×0.012
44×44×1.6
2.25-4.0, 3.48, 56
Prop. work
0.305×0.305×0.007
40×40×1
2.165-5.48, 3.8225, 86.72
4.28-7.44, 5.86, 53.92 2.38-4.6, 3.12, 63.61 2.33-5.65, 3.99, 83.2
λL, AR is the wavelength at the lower band-edge frequency, where the AR is 3 dB. References 1. S.S. Gao, Q. Luo, F. Zhu, Circularly Polarized Antennas. UK: Wiley-IEEE Press; 2013. 2. K. Saraswat, A.R. Harish, “Dual-band CP coplanar waveguide-fed splitring resonatorloaded G-shaped slot antenna with wide-frequency ratio,” IET Microw. Antennas Propag., vol. 12, no. 12, pp. 1920-1925, 2018. 3. R.K. Saini, P.S. Bakariya, P. Kumar, “Coplanar waveguide fed dual-band dual sense circular polarized square slot antenna,” Int J RF Microw Comput Aided Eng., vol. 28, no. 9, pp. e21503, 2018. 4. R. Xu, J.-Y. Li, J. Liu, S.-G. Zhou, K. Wei, Z.-J. Xing, “A simple design of compact dualwideband square slot antenna with dual-sense circularly polarized radiation for WLAN/WiFi communications,” IEEE Trans. Antennas Propag., vol. 66, no. 9, pp. 4884-4889, 2018. 5. Jaiverdhan, A. Kumar, M.M. Sharma, R.P. Yadav, “Dual wideband circular polarized CPW-fed strip and slots loaded compact square slot antenna for wireless and satellite applications,” Int. J. Electron. Commun., vol. 108, pp. 181-188, 2019. 6. B.P. Nadh, B.T.P. Madhav, M.S. Kumar, M.V. Rao, T. Anilkumar, “Asymmetric ground structured circularly polarized antenna for ISM and WLAN band applications,” Prog. Electromag. Res. M, vol. 76, pp.167-175, 2018. 7. J. Li, J. Shi, L. Li, T.A. Khan, J. Chen, Y. Li, A. Zhang, “Dual-band annular slot antenna loaded by reactive components for dual-sense circular polarization with flexible frequency ratio,” IEEE Access, vol. 6, pp. 64063-64070, 2018. 8. A. Kumar, V. Sankhla, J.K. Deegwal, A. Kumar, “An offset CPW-fed triple-band circularly polarized printed antenna for multiband wireless applications,” Int. J. Electron. Commun., vol. 86, pp. 133-141, 2018. 9. M.V. Rao, B.T.P. Madhav, T. Anilkumar, B.P. Nadh, “Metamaterial inspired quad band circularly
polarized
antenna
for
WLAN/ISM/Bluetooth/WiMAX
and
satellite
communication applications,” Int. J. Electron. Commun., vol. 97, pp. 229-241, 2018.
10. M. Midya, S. Bhattacharjee, M. Mitra, “Pair of grounded L strips loaded broadband circularly polarised square slot antenna with enhanced axial ratio bandwidth,” Electron. Lett., vol. 54, no. 15, pp. 917-918, 2018. 11. L. Wang, W. Fang, Y. En, Y. Huang, W. Shao, B. Yao, “A new broadband circularly polarized square-slot antenna with low axial ratios,” Int J RF Microw Comput Aided Eng., vol. 29, no. 1, pp. e21502, 2019. 12. T. Kumar, K. Saraswat, A.R. Harish, “Offset-fed trapezoidal monopole antenna for broadband circular poalrization,” Int. J. RF Microw. Comput. Aided Eng., vol. 27, no. 2, pp. e21063, 2017. 13. H. Zhang, Y.-C. Jiao, T. Ni, W.-L. Liang, “Broadband circularly polarised antenna with asymmetric ground and L-shaped strips,” Electron. Lett., vol. 50, no. 23, pp. 1660-1662, 2014. 14. E. Shirazi, M.A. Honarvar, “Broadband circularly polarized stair-shaped slot antenna,” Electromagnetics, vol.35, no. 7, pp.443-452, 2015. 15. J. Pourahmadazar, Ch. Ghobadi, J. Nourinia, N. Felegari, H. Shirzad, “Broadband CPWfed circularly polarized square slot antenna with inverted-L strips for UWB applications,” IEEE Antennas Wireless Propag. Lett., vol. 10, pp. 369-372, 2011. 16. K. Oteng Gyasi, J. Li, Y. Huang, W. Guangjun, “Broadband circularly polarized square slot antenna with a G-shaped feedline,” Microw Opt Technol Lett., vol. 59, pp. 3055–3063, 2017. 17. K. Ding, C. Gao, Y. Wu, D. Qu, B. Zhang, “A broadband circularly polarized printed monopole antenna with parasitic strips,” IEEE Antennas Wireless Propag. Lett., vol. 16, pp. 2509-2512, 2017. 18. J.-Y. Jan, C.-Y. Pan, K.-Y. Chiu, H.-M. Chen, “Broadband CPW-fed circularly-polarized slot antenna with an open slot,” IEEE Trans. Antennas Propag., vol. 61, no. 3, pp. 14181422, 2013. 19. K. Saraswat, A.R. Harish, “Analysis of wideband circularly polarized ring slot antenna using characteristics mode for bandwidth enhancement,” Int J RF Microw Comput Aided Eng., vol. 28, no. 2, pp. e21186, 2017. 20. A. Kumar, J. K. Deegwal, M. M. Sharma, “Miniaturized wideband dual linearly and circularly polarized printed square slot antenna for multiradio wireless systems,” Int. J. Electron. Commun., vol. 88, pp. 44-51, 2018.
21. N. Kushwaha, R. Kumar, R.V.S. Ram Krishna, “Design and analysis of CPW-fed wideband circularly polarized antenna for modern communication systems,” J. Electromag. Waves Appl., vol.29, no.11, pp.1397-1409, 2015. 22. M. Nosrati, N. Tavassolian, “Miniaturized circularly polarized square slot antenna with enhanced axial-ratio bandwidth using an antipodal Y-strip,” IEEE Antennas Wireless Propag. Lett., vol. 16, pp. 817–820, 2016. 23. J.-Y. Sze, C.-I. G. Hsu, Z.-W. Chen, C.-C. Chang, “Broadband CPW-fed circularly polarized square slot antenna with lightening-shaped feedline and inverted-L grounded strips,” IEEE Trans. Antennas Propag., vol. 58, no. 3, pp. 973–977, 2010. 24. K. Ding, Y.-X. Guo, C. Gao, “CPW-fed wideband circularly polarized printed monopole antenna with open loop and asymmetric ground plane,” IEEE Antennas Wireless Propag. Lett., vol. 16, pp. 833–836, 2017. 25. T. Jhajharia, V. Tiwari, D. Yadav, S. Rawat, D. Bhatnagar, “Wideband circularly polarised antenna with an asymmetric meandered-shaped monopole and defected ground structure for wireless communication,” IET Microw. Antennas Propag., vol. 12, no. 9, pp. 15541558, 2018. 26. H. Zhang, Y.-C. Jiao, L. Lu, C. Zhang, “Broadband circularly polarized square-ring-loaded slot antenna with flat gains,” IEEE Antennas Wireless Propag. Lett., vol. 16, pp. 29–32, 2017. 27. Y.W. Liu, P. Hsu, “Broadband circularly polarised square slot antenna fed by coplanar waveguide,” Electron. Lett., vol. 49, no. 16, pp. 976-977, 2013. 28. M. Midya, S. Bhattacharjee, M. Mitra, “Broadband circularly polarized planar monopole antenna with G-shaped parasitic strip,” IEEE Antennas Wireless Propag. Lett., vol. 18, no. 4, pp. 581–585, 2019. 29. M. Samsuzzaman, M. T. Islam, M. J. Singh, “A compact printed monopole antenna with wideband circular polarization,” IEEE Access, vol. 6, pp. 54713-54725, 2018.
Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
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