Millimeter-Wave Wideband High-Efficiency Circularly Polarized Planar Array Antenna

A Ka-band circularly polarized (CP) planar array antenna with wide axial ratio (AR) bandwidth and high efficiency is presented in this paper. A crossed slot with four parasitic patches is proposed as the CP element, which is fed by a unique 90 degrees delay line. There are three minimal AR points within the operational frequency band to widen the bandwidth. The 90 degrees delay line has three branches to realize the phase delay, the amplitude compensation, and the impedance matching, respectively. Thus, the design process is clear and simple. Several short-circuited posts are added in the feeding layer to suppress the TEM wave propagating outside the feeding network. Simulated results of the element show an AR bandwidth (AR < 3 dB) of 21.2% from 25.3 to 31.3 GHz and a gain of 5.7-6.7 dBic over the same frequency band. Measured results of a fabricated 4 x 4 array demonstrate about 14% AR bandwidth and more than 17.4 dBic gain within the frequency band of 26.4-30.3 GHz. The maximum realized gain reaches to 18.2 dBic. The array antenna with a waveguide transition is fabricated through multilayer PCB process and has a size of 72 mm x 48 mm x 2.2 mm.