Single-layer wideband high-gain circularly polarized patch antenna with parasitic elements

Single-layer wideband high-gain circularly polarized patch antenna with parasitic elements

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Journal Pre-proofs Regular paper Single-Layer Wideband High-Gain Circularly Polarized Patch Antenna with Parasitic Elements Niamat Hussain, Huy Hung Tran, Tuan Tu Le PII: DOI: Reference:

S1434-8411(19)31685-1 https://doi.org/10.1016/j.aeue.2019.152992 AEUE 152992

To appear in:

International Journal of Electronics and Communications

Received Date: Revised Date: Accepted Date:

5 July 2019 13 October 2019 4 November 2019

Please cite this article as: N. Hussain, H. Hung Tran, T. Tu Le, Single-Layer Wideband High-Gain Circularly Polarized Patch Antenna with Parasitic Elements, International Journal of Electronics and Communications (2019), doi: https://doi.org/10.1016/j.aeue.2019.152992

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Single-Layer Wideband High-Gain Circularly Polarized Patch Antenna with Parasitic Elements Niamat Hussain1, Huy Hung Tran2,3, and Tuan Tu Le2,3,* 1Department

2Division

3Faculty

of Computer and Communication Engineering, Chungbuk National University, Cheongju, Republic of Korea.

of Computational Physics, Institute for Computational Science, Ton Duc Thang University, Ho Chi Minh City, Vietnam

of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam *Corresponding author: [email protected]

Abstract This paper presents a single-layer circularly polarized (CP) antenna with wideband operation and high gain characteristics. The antenna consists of a squared patch with a diagonal slot as a primary radiating source and a set of symmetrical multiple squared patches on the same plane as the patch, acting as parasitic elements. The parasitic elements are employed to significantly increase not only the 3-dB axial ratio (AR) bandwidth but also the broadside gain radiation. For a demonstration of the design concept, an antenna prototype with an overall volume of 1.18λo × 1.18λo × 0.05λo (λo is the center operating frequency) is fabricated and tested. The detailed design process and the measurements are described and discussed. The measured data indicates that the proposed antenna achieves operating bandwidth of 14.7% (5.05–5.85 GHz) for |S11| ≤ –10 dB and AR ≤ 3 dB. In addition, the fabricated antenna also exhibits high gain radiation from 9.1 to 10.8 dBi within the operating bandwidth. Keywords: Circular polarization, high gain, parasitic element, patch antenna, wideband

1. Introduction Circularly polarization (CP) antennas with wideband and high gain are always desirable in modern wireless communication systems due to their high immunity to interferences, multipath distortion along with high mobility and orientation freedom of antennas. Various types of wideband and high-gain CP antennas, such as spiral antennas [1–3], quadrifilar helix antenna [4], crossed dipole [5, 6] and so on, have been proposed. In addition, the method of using frequency selective surface has also been widely applied to significantly increase the antenna’s gain [7–9]. However, these structures are detrimental to the profile. The microstrip patch and slot antennas are preferred to achieve CP radiations due to their low profile, low cost, as well as ease of integration with other electronic devices [10–12]. There are significant investigations that have been implemented to overcome an inherently narrow axial ratio (AR) bandwidth (BW) of the patch antenna. In [13–20], by introducing the air gap between the radiator and the reflector, very wide AR BW of about 24% and broadside gain around 8.5 dBi can be achieved. In [21, 22], the antennas are fabricated over multiple stacked substrates with meandering probe feeding. Alternatively, studies [23–26] presented another effective solution to improve the AR BW of the single patch antenna using metasurface. In summary, although the aforementioned antennas [13–26] have the advantage of wide operation, using multiple layers is their essential drawback, leading to complicated antenna architecture and increased fabrication cost. Additionally, high profile and poor mechanical properties due to the presence of air gap is also other problems of the designs in [13–20]. In order to meet wideband performance with simple configuration, single-layer antennas have been reported in the literature [27, 28]. In such designs, all the radiating elements are printed on a singlelayer of a substrate. However, they suffer from low gain radiation limited by 8.4 dBi.

In this paper, we proposed a high-gain wideband CP antenna with a simple configuration. The antenna is fabricated on a single-layer of the substrate and single-fed by 50-Ω coaxial cable. A squared patch with a diagonal slot is chosen as a primary radiating source. Next, a set of 2 × 3 symmetrical square patches as parasitic elements are patterned around the radiator for not only operating BW enhancement but also high gain radiation.

2. Antenna configuration and performance Figure 1 depicts the geometrical configuration of the proposed antenna. The antenna is designed on a single-layer of a Taconic TLY-5 substrate with dielectric constant εr = 2.2 and loss tangent tan δ = 0.0009. Here, the primary radiator is formed by a squared shape patch with a diagonal slot. There are six (2 × 3) parasitic elements that are placed in close proximity to the driven patch. The antenna is directly excited by the 50-Ω coaxial cable, whose inner and outer conductors are respectively connected to the driven patch and the ground plane. The antenna has been simulated with the aid of high-frequency structure simulator (HFSS) and the optimized parameters of the antenna are as follows: Wg = 65 mm, Hs = 3 mm, Wd = 15 mm, ls = 12 mm, ws = 2.8 mm, lp = 6mm, wf = 4 mm, lf = 3.5 mm, g = 1.8 mm, Wp = 13.6 mm, and s = 2.4 mm. The optimized performances in terms of reflection coefficient, AR, and gain in broadside direction of the proposed CP antenna are shown in Figure 2. It is obvious that the antenna has –10 dB impedance BW of 21.2% (4.72–5.84 GHz) and 3-dB AR BW of 16.6% (4.98–5.88 GHz). Moreover, the broadside gain is in the range from 9.6 to 11.4 dBi within the AR BW.

3. Antenna design characteristics a. Wideband CP achievement

It has been known that a squared patch with single excitation is able to support a linear polarization, thus the perturbation technique of cutting a diagonal rectangular slot at the center of the patch is adopted to produce CP waves [11]. This design also uses the squared patch with a diagonal slot for CP radiations. The geometry and design parameters of the CP patch antenna are depicted in Figure 3(a). The patch is operated in two orthogonal TM01 and TM10 modes and its dimension is chosen about half-effective-wavelength at the desired frequency, fr1. The simulated AR of the single CP patch antenna is shown in Figure 4. This antenna has only one minimum AR point and narrow 3-dB AR BW. In order to improve the AR BW, two parasitic elements are added nearby the driven patch, as illustrated in Figure 3(b). Since the driven patch can excite two orthogonal modes for CP realization at fr1, the capacitive coupling between the parasitic elements and the driven patch can also realize two orthogonal modes in the parasitic elements, resulting in a CP radiation at fr2. Here, the parasitic patch is designed to produce an additional CP band in high frequency region (fr2 > fr1). The size of the parasitic element, which is smaller than the driven patch’s size, is also about half-effective-wavelength at fr2. It is noted that two parasitic elements are employed to have symmetric geometry, which can avoid the asymmetric radiation pattern in the high frequency band. Figure 4 also presents the simulated AR characteristic of this structure. As expected, the additional minimum AR point is generated at 5.8 GHz. Thus the overall 3-dB AR BW of the antenna is significantly increased. For a better understanding of the AR optimization process, the parameter studies are carried out. In fact, the lower and higher CP bands can be adjusted by tuning the dimensions of the driven patch and parasitic patch, Wd and Wp. It can be verified by observing the simulated ARs against the variations of Wd and Wp in Figure 5. In addition, the gap g is also another

critical parameter to determine the AR BW of the designed antenna. The data in Figure 6 demonstrates that tuning g has significant effects on both lower and upper CP bands. Finally, the CP radiation mechanism of the CP patch antenna with two parasitic elements can be explained by observing the simulated surface current shown in Figure 7. It can be seen that the current is strongly distributed on the patch at a low frequency of 5.3 GHz. Meanwhile, the parasitic patches also occupy a large amount of current at the high frequency of 5.8 GHz, verifying the claim that the high frequency band is attributed to the parasitic elements. Additionally, as the phase alters from 0° to 90°, the rotation of vector Js is counter-clockwise. This demonstrates that the antenna produces left-hand CP (LHCP) radiation in broadside direction. b. High broadside gain achievement Firstly, the effects of ground plane size (Wg) on the broadside gain of single CP patch antenna with two parasitic elements as shown in Figure 3(b) are considered. It is found that larger Wg leads to a gain enhancement and when Wg = 65 mm, the antenna gain will be stable. Thus, in the next step, we keep the ground plane size at the optimal value and change the number of parasitic elements (N). Figure 8 shows the boresight gains for different values of N. It can be observed that the antenna gain, particularly in the high frequency band, is significantly improved when the number of parasitic patches is increased from 2 to 6. Here, the maximum gain value is enhanced from 9.0 to 11.4 dBi. The behind reason is that since the antenna’s physical size (Ap = Wg*Wg) is unchanged, using more parasitic patches might results in higher antenna’s effective aperture (Aeff) and higher antenna’s aperture efficiency as well, which is defined by the ratio Aeff/Ap [29]. For better illustration, the simulated E-field distributions at 5.7 GHz for the different number of parasitic patches N, is shown in Figure 9. It is obvious that the effective aperture, represented by the

illuminated area, for N = 6 is much larger than that for N = 2. Thus, the antenna broadside gain, which is proportional to the aperture efficiency, will be higher for N = 6 compared to the case when N = 2. Based on the gain values at 5.6 GHz, the calculated aperture efficiencies are approximately 41% and 73% for N = 2 and N = 6, respectively. c. Impedance matching achievement In order to obtain good impedance matching performance, an additional stub with dimensions of wf × lf is used. By tuning these parameters, the antenna’s input impedance can be simply controlled and at proper values, the antenna can match with the 50-Ω coaxial cable. For illustration, Figure 10 shows the antenna’s reflection coefficients with different values of wf and lf. It is noted that the impacts of these parameters on the AR and gain are minor, thus the results are not given for brevity.

4. Design procedure Based on the key-parameter studies in Section 3, the optimization procedure for the proposed design can be suggested as follows:  Step 1: Design the single CP patch antenna 

The patch size, Wd, is chosen about half-effective-wavelength at the desired frequency, fr1. And the feeding position, lp, is near the edge of the patch.



Tune the slot’s dimensions, ls and ws, to have the minimum AR point at fr1.

 Step 2: Design the antenna with two parasitic elements 

The size of the parasitic patch, Wp, is also chosen about half-effective-wavelength at the desired frequency, fr2 > fr1.



Tune the gap, g, Wd, and Wp to have the best AR BW. At this stage, the |S11| performance is neglected.



Keep increasing the ground plane size, Wg, until the antenna’s gain is stable.

 Step 3: Optimize the number of parasitic elements 

The ground planes size is fixed at optimal value as in Step 2.



Properly choose the number of parasitic patches, N, to have the best gain value.

 Step 4: Optimize the antenna’s impedance matching 

Tune the stub’s dimensions, lf and wf, to control the matching performance.

 Step 5: Final tune all parameters to obtain the best |S11|, AR, and gain performances.

5. Measurement results To verify the simulated data experimentally, an antenna prototype is fabricated and measured. Figure 11 shows the photographs of the fabricated structure. The PNA Network Analyzer N5224A is used to measure the antenna’s S-parameter. The measurements of AR, gain, as well as radiation patterns, were carried out in an anechoic chamber [30]. In general, measurements and simulations are in good agreement. There are some discrepancies due to the errors in the fabrication and measurement setup. Figures 12 and 13 present the simulated and measured |S11| and AR of the proposed antenna. As observed, the fabricated prototype shows good performance with |S11| ≤ –10 dB and AR ≤ 3 dB from 5.05 to 5.85 GHz, equivalent to about 14.7%. Along with this, the measured boresight gain within the operating BW varies from 9.1 to 10.8 dBi, as depicted in Figure 13. The radiation patterns in x-z and y-z planes at 5.1 and 5.7 GHz are plotted in Figure 14. As observed, LHCP is the dominant radiations of the

proposed design. Additionally, the polarization isolation in the broadside direction is better than 15 dB and the front-to-back ratios are always higher than 12 dB. It can be seen that there are two major changes in the radiation pattern from lower to higher frequencies. The first one is the beam shapes in x-z and y-z planes. Since the operation at 5.7 GHz is generated by the parasitic elements, which are positioned symmetrically only along y-direction. Thus, there is a big difference between the radiation patterns in x-z and y-z planes. On the other hand, the geometry at the lower frequency of 5.1 GHz generated by the driven patch is more symmetric along both x- and y-directions. Hence, the patterns at 5.1 GHz in x-z and y-z planes are quite similar. The second change is the half power beamwidth (HPBW) and the mathematical expression for the HPBW of an antenna is as follows [31]: λ HPBW = 70 D where λ is the wavelength and D is the diameter of the antenna. This equation indicates that the HPBW is proportion to λ, or is inversely proportion to operating frequency f. In this work, since the antenna size is constant, its HPBW is gradually decreased at higher frequencies. At 5.1 GHz, the HPBW is about 30°, while it is reduced to 22° at 5.7 GHz. Finally, to show the worth of this work, the performance comparison of the proposed antenna and the other reported designs in the same domain are summarized and provided in Table 1. The antennas are compared in terms of overall size, structural simplicity (presence of vias, air gap, and the number of printed layers), BW and gain. The antennas presented in [13, 15] and [22–25] provide wider BW but have the disadvantages of multiple printed layers which result in the higher thickness, while the maximum gain is restricted to 8.6 dBi. In addition, another drawback is the design complexity due to the presence of vias [15, 22] or poor mechanical properties due to the air

gap [13, 15]. The antennas with a single printed layer [27, 28] as the proposed antenna are offering planar structure. The metasurface antenna reported in [27] has the advantages of compact size and simple geometry with no vias is having problems of low gain and narrow BW. Although the antenna [28] offers a wide BW of 15.8%, it has the metallic vias connecting the patch and the ground which could cause fabrication complexity while the gain characteristics have not been reported. In conclusion, none of the antennas collect the advantages of planar structure, design simplicity, wider BW, and high gain at one package as the proposed antenna.

6. Conclusions The single-layer wideband high-gain CP antenna has been investigated and presented in this paper. The antenna is based on a squared patch with diagonal slot and a set of parasitic squared patches. The measured data demonstrates that wide operating BW of 14.7% with peak gain of 10.8 dBi can be obtained by the proposed antenna. The proposed antenna with large size can be mounted on large objects such as vehicles, laptops, data access points, and so on. In addition, the narrowbeam antenna can provide more precise targeting of the radio signals, which is useful in tracking systems. Owing to its narrow beam, the antenna also has the advantage of less interference among multiple neighboring antennas.

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[9] Liu ZG, Cao ZX, Wu LN. Compact low-profile circularly polarized Fabry–Perot resonator antenna fed by linearly polarized microstrip patch. IEEE Antennas Wireless Propag Lett. 2016;15:524–527. [10] Li J, Shi J, Li L, Khan TA, Chen J, Li Y, Zhang A. Dual-band annular slot antenna loaded by reactive components for dual-sense circular polarization with flexible frequency ratio. IEEE Access. 2018;6:64063–64070. [11] Sharma PC, Gupta KC. Analysis and optimized design of single feed circularly polarized microstrip antennas. IEEE Trans Antennas Propag. 1983;31(6):949–955. [12] Yohandri, Sumantyo JTS, Kuze H. A new triple proximity-fed circularly polarized microstrip antenna. AEU-Int J Electron Commun. 2012;66:395–400. [13] Yang W, Zhou J, Yu Z, Li L. Single-fed low profile broadband circularly polarized stacked patch antenna. IEEE Trans Antennas Propag. 2014;62(10):5406–5410. [14] Wu J, Ren X, Wang Z, Yin Y. Broadband circularly polarized antenna with L-shaped strip feeding and shorting-pin loading. IEEE Antennas Wireless Propag Lett. 2014;13:1733–1736. [15] Wu J, Yin Y, Wang Z, Lian R. Broadband circularly polarized patch antenna with parasitic strips. IEEE Antennas Wireless Propag Lett. 2015;14:559–562. [16] Wu J, Hu W, Yin Y, Lian R. Broadband circularly polarized antennas with center-slotfeeding. Microwave Opt Technol Lett. 2015;57(12):2793–2797. [17] Zhang YQ, Qin ST, Qang XW, Shang F. Novel single-fed broadband circularly polarized antenna for GNSS applications. Int J RF Microw Comput-Aided Eng. 2018;28:e21193. [18] Mondal T, Maity S, Ghatak R, Chaudhuri SRB. Design and analysis of a wideband circularly polarized perturbed psi-shaped antenna. IET Microw Antennas Propag. 2018;12(9):1582– 1586.

[19] Li J, Liu H, Zhang S, Luo M, Zhang Y, He S. A wideband single-fed, circularly-polarized patch antenna with enhanced axial ratio bandwidth for UHF RFID reader applications. IEEE Access. 2018;6:55883–55892. [20] Wang C, Liu H, Zhang X, Zhu S, Wen P, Chen G. Single-feed wideband circularly polarized patch antenna using dual mode defected ground waveguide coupling structure. Int J RF Microw Comput Aided Eng. 2019;29:e21494. [21] Wong H, Lin QW, Lai HW, Zhang XY. Substrate integrated meandering probe-fed patch antennas for wideband wireless devices. IEEE Trans Compon Packag Manuf Technol. 2015;5(3):381–388. [22] Lin QW, Wong H, Zhang XY, Lai HW. Printed meandering probe-fed circularly polarized patch antenna with wide bandwidth. IEEE Antennas Wireless Propag Lett. 2014;13:654–657. [23] Ta SX, Park I. Low-profile broadband circularly polarized patch antenna using metasurface. IEEE Trans Antennas Propag. 2015;63(12):5929–5934. [24] Nakamura T, Fukusako T. Broadband design of circularly polarized microstrip patch antenna using artificial ground structure with rectangular unit cells. IEEE Trans Antennas Propag. 2011;59(6):2103–2110. [25] Jash SS, Goswami C, Ghatak R. A low profile broadband circularly polarized planar antenna with an embedded slot realized on a reactive impedance surface. AEU-Int J Electron Commun. 2019;108:62–72. [26] Tran HH, Hussain N, Le TT. Low-profile wideband circularly polarized MIMO antenna with polarization diversity for WLAN applications. AEU-Int J Electron Commun. 2019;108:172– 180.

[27] Liang Z, Ouyang J, Yang F. Low-profile wideband circularly polarized single-layer metasurface antenna. Electron Lett. 2018;54(24):1362–1364. [28] Yang ZJ, Zhu L, Xiao S. An implantable wideband circularly polarized microstrip patch antenna via two pairs of degenerate modes. IEEE Access. 2019;7:4239–4247. [29] Balanis CA. Antenna theory–analysis and design. Hoboken, New Jersey, US: John Wiley & Sons, Inc., 2005. [30] http://www.mtginc.co.kr. Accessed Jun 20, 2019. [31] https://www.tutorialspoint.com/antenna_theory/antenna_theory_beam_width.html

Table 1 Comparison among the single-fed, low-profile, wideband CP antennas Ref [13] [15] [22] [23] [24] [25] [27] [28] Prop.

Overall size (λo) 0.81 × 0.81 × 0.09 1.14 × 1.14 × 0.13 0.63 × 0.63 × 0.14 0.58 × 0.58 × 0.06 0.78 × 0.80 × 0.10 1.05 × 0.97 × 0.07 0.86 × 0.86 × 0.04 0.32 × 0.32 × 0.01 1.18 × 1.18 × 0.05

Air gap Yes Yes No No No No No No No

Vias No Yes Yes No No No No Yes No

Printed layers 3 2 5 2 2 2 1 1 1

Operating BW (%) 20.3 23.9 16.9 23.4 20.4 28.9 12.8 15.8 14.7

Max. Gain (dBi) 8.6 8.5 7.4 7.6 6.5 6.8 8.4 N/G 10.8

y

y

x

x

ws

SMA

ls

Wd

wf

lp g

Wg

lf s

Wp

Hs Side-view

Top-view Figure 1 Geometry of the proposed antenna.

15

9

Axial ratio (dB)

|S11| (dB)

Gain AR

-10

-20

-30 4.6

5.0

5.4

Frequency (GHz)

(a)

5.8

6.2

6

10

3

5

0 4.6

5.0

5.4

5.8

Broadside gain (dB)

0

0 6.2

Frequency (GHz)

(b)

Figure 2 Simulated (a) |S11|, and (b) AR and gain in broadside direction of the proposed antenna.

y

y

x

x

Wg

(a)

(b)

Figure 3 Geometry of the single CP patch antenna (a) without parasitic patches and (b) with 2 parasitic patches.

Axial ratio (dB)

9

W/o parasitic element With parasitic element

6

3

0 4.6

5.0

5.4

5.8

6.2

Frequency (GHz)

Figure 4 Simulated AR characteristic of the CP patch antenna with and without parasitic patches.

9 14.1 mm 14.6 mm 15.1 mm

6

Axial ratio (dB)

Axial ratio (dB)

9

3

0 4.6

5.0

5.4

6

3

0 4.6

6.2

5.8

13.5 mm 14.0 mm 14.5 mm

5.0

5.4

Frequency (GHz)

Frequency (GHz)

(a)

(b)

5.8

6.2

Figure 5 Simulated AR characteristic of the CP patch antenna with two parasitic patches for different values of (a) Wd and (b) Wp.

Axial ratio (dB)

9 1.8 mm 2.8 mm 3.8 mm

6

3

0 4.6

5.0

5.4

5.8

Frequency (GHz)

Figure 6 Simulated AR characteristic for different values of g.

6.2

Js [A/m] 20 Js

Js

16 12 8 4 0



90°

(a) Js [A/m] 20 Js

16

Js

12 8 4 0



90°

(b) Figure 7 Simulated surface current distributions at (a) 5.3 GHz and (b) 5.8 GHz.

Broadside gain (dBi)

12

9

2 4 6 8

6

3 4.6

5.0

5.4

5.8

6.2

Frequency (GHz)

Figure 8 Simulated broadside gain for different number of parasitic patches, N.

E [V/m] 10E2 8E2 6E2 4E2 2E2 0

N=2

N=6

Figure 9 Simulated E-field distributions at 5.7 GHz for different number of parasitic patches.

0 3.0 mm 4.0 mm 5.0 mm

-10

|S11| (dB)

|S11| (dB)

0

-20

-30 4.6

5.0

5.4

5.8

6.2

2.5 mm 3.5 mm 4.5 mm

-10

-20

-30 4.6

5.0

5.4

Frequency (GHz)

Frequency (GHz)

(a)

(b)

5.8

6.2

Figure 10 Simulated |S11| characteristic of the proposed CP antenna with six parasitic patches for different values of (a) wf and (b) lf.

Figure 11 Photographs of fabricated antenna prototype. 0

|S11| (dB)

Measurement Simulation -10

-20

-30 4.6

5.0

5.4

5.8

6.2

Frequency (GHz)

Figure 12 Simulated and measured |S11| of the proposed antenna.

AR (Sim.) AR (Mea.)

Gain (Sim.) Gain (Mea.)

15

6

10

3

5

0 4.6

5.0

5.4

5.8

Broadside gain (dB)

Axial ratio (dB)

9

0 6.2

Frequency (GHz)

Figure 13 Simulated and measured AR and gain in broadside direction of the proposed antenna.

(dBic)

0

15

330

LHCP (mea.) LHCP (sim.) RHCP (mea.) RHCP (sim.)

0 330

30

30

0 60

300

-15

60

300

-30 -45

90

270

90

270

-30 -15

120

240

120

240

0 150

210

15

150

210

x-z plane

y-z plane

(a) (dBic)

0

15

330

LHCP (mea.) LHCP (sim.) RHCP (mea.) RHCP (sim.)

0 330

30

30

0 -15

60

300

60

300

-30 -45

90

270

90

270

-30 -15

120

240

120

240

0 15

150

210

150

210

x-z plane

y-z plane

(b) Figure 14 Simulated and measured gain radiation patterns at (a) 5.1 GHz and (b) 5.7 GHz.

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: