Compact Wideband Circularly Polarized Microstrip Antenna Array for 45 GHz Application

A wideband circularly polarized (CP) 4 × 4 millimeterwave antenna array composed of novel microstrip antenna elements is presented for IEEE 802.11 aj (45 GHz) application. Through introducing the L-shaped branches and truncated corners to the microstrip antenna element, an impedance bandwidth of 24.9% and a 3 dB axial ratio (AR) bandwidth of 17.3% are achieved. To clarify the effects of the L-shaped branches and truncated corners, the phase difference and amplitude ratios of the 180° and 90° electric field components at the point of (0,0,r) are extracted and analyzed. A simple and compact microstrip feeding network is designed to excite the CP antenna array, and two-layer PCB boards are used to implement the proposed array. The electromagnetic energy is coupled to the radiators from the feeding network through the aperture etched on the middle ground. The measured 3 dB AR bandwidth of the antenna array is 16% from 41.9 to 49.1 GHz, and the measured gain is all greater than 17 dBic within the band from 41 to 49 GHz.