Compact Patch Antenna Array With Fan-Beam Characteristics for Radar Application

In this paper, a compact <inline-formula> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> patch array antenna with a fan-beam radiation pattern is introduced for use in 3.5 GHz band applications. The proposed antenna consists of a planar two-layer printed structure so that the radiation elements and feeding network are located in the upper and lower layers respectively. In this way, the antenna has very compact dimensions while achieving a high radiation gain. Using a reflector plane under the antenna has improved the radiation pattern and decreased the antenna back radiation. The fabricated array antenna has an impedance bandwidth of 3.35-3.75 GHz (11.27%), a maximum realized gain of 10.91 dBi, and half power beamwidths (HPBWs) of 23.86° and 85.44° on the H- and E-panels, respectively. The overall dimensions of the antenna are <inline-formula> <tex-math notation="LaTeX">$209\times 32.3\times 3.708$ </tex-math></inline-formula> mm<sup>3</sup> with a <inline-formula> <tex-math notation="LaTeX">$250\times 50$ </tex-math></inline-formula> mm<sup>2</sup> conductive reflector at a distance of <inline-formula> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula>/4 from the antenna, and the theoretical and practical results show a good agreement with each other. The presented antenna is suitable for 5G systems and radar applications in the 3.5 GHz frequency band.


51
Recently, a compact 8-element array antenna with a 52 fan-beam pattern for 5G applications is introduced [20]. 53 this work, is placed behind the array antenna elements, and 55 creates a complex structure for the antenna. This antenna has 56 a multi-layer structure, which uses two layers of substrates 57 for its construction. The foremost advantages of multi-layer 58 antennas are lower dielectric loss, compact dimension, facil-59 itating the connection of the mounting surfaces with devices, 60 and integrated circuits [21], [22].

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Using the proposed power divider structure, a feeding net-132 work is designed with four outputs, according to Fig. 7 (a). of the feeding network with an insertion loss of about 137 0.6 dB (S1j ≈ −6.6 dB), and we can ignore the phase 138 difference between the output signals.

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As discussed in Section II, the presented planar patch antenna 142 in this work, similar to other patch antennas, has an average 143 gain of approximately 4 dB and an HPBW of almost 95.1 • 144 and 70.4 • on the E-and H-planes, respectively. These results 145 are not sufficient for radar applications and 5G networks. 146 According to [6] and [23], the directivity of the planar patch 147 antenna can be approximated as follows:  The measured and simulated results of the radiation pattern 175 on two panels, E and H, are demonstrated in Fig. 10. It can 176 be seen that the array antenna has a beamwidth of 94.2 • on 177 the E-plane and 21.2 • beamwidth on the H-plane. Radiation 178 patterns are relatively stable, and the difference between 179 the Co-and Cross-polarization levels at 3.5 GHz is more 180 than 25 dB.

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The gain of the array antenna is shown in Fig. 11. Accord-182 ing to the simulation result, the array antenna has a maximum 183 gain of 9.83 dB, and the maximum measured gain is 9.73 dB 184 both of them at 3.5 GHz. All the simulations are carried out 185 using a full-wave EM simulator HFSS in this study. The slight 186 difference between the experiments and the simulations in 187 this design can be associated with the measurement error and 188 the low accuracy of placing the upper and lower substrates on 189 top of each other. 192 In the design of the array antenna in the previous section, due 193 to the presence of the feeding network in the lower layer of the 194 VOLUME 10, 2022      Due to the radiation pattern of the array antenna, a decrease 231 is seen in the antenna beamwidth compared to the patch 232 antenna in Section II, which leads to an increase in the 233 antenna gain in the array configuration. Furthermore the 234 simulated radiation efficiency of the patch antenna array 235 with the reflector plane is plotted in Fig. 17. The proposed 236 antenna has a peak radiation efficiency of 89.8% at 3.5 GHz 237 frequency.

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Photos of the fabricated proposed antennas and the antenna 239 test steps in the anechoic chamber are shown in Fig. 18. In this 240 study, an Agilent E8363C Network Analyzer was used to test 241 the proposed antennas. Table 1 compares the performance of the proposed array 243 antenna with other fan-beam antennas. It can be seen that the 244 proposed array antenna has the merit of compactness due to 245 the operating frequency and realized gain.