A High Gain Circularly Polarized Microstrip Array Antenna At Millimeter-Wave Band

This paper presents the design of a $\mathrm{4} \times \mathrm{4}$ elements circularly polarized microstrip patch array at millimeter-wave band. The sequential rotation method and series-parallel feed network are employed in the power distribution circuit for antenna performance improvement. The feed network is integrated on the same substrate layer of the antenna array in order to facilitate processing and manufacturing, and the total size of the design is $\mathrm{10} \text{mm}\times \mathrm{12} \text{mm}\times \mathrm{0.127} \text{mm}$. The simulated return loss exhibits an impedance bandwidth of 7%, and the 3-dB axial ratio bandwidth of 10% with respect to 78.5 GHz is obtained. Besides, the maximal gain is 17.6dBi at 78.5GHz.

I. Introduction

With the rapid development of millimeter wave technology, millimeter wave antenna has been widely used in satellite communication, on-board radar, high-precision guidance, next generation 5G mobile communication, automotive radar, etc [1]–[4]. Compared with linear polarized antenna, circular polarization antenna can accept electromagnetic wave of arbitrary polarization or can be received by any antenna, thus, it can effectively suppress the interference of rain, fog and anti-multipath reflection. Conventional single fed circularly polarized microstrip array antenna has narrow axial ratio bandwidth. The feed network design of circularly polarized microstrip array antenna with multi-port feed is usually very complicated, which is not conducive to the compact design of the feed network. Some of the existing methods to broaden the axial ratio bandwidth, such as aperture coupling, are through designing the antenna and feed network in different layers, but the profile thickness of the antenna is increased [5]–[7]. Microstrip patch antennas usually have narrow axial ratio bandwidth which limits their application in communication system.