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° delay line. There are three minimal AR points within the operational frequency band to widen the bandwidth. The 90° 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 (
$\text{AR} < 3\;\text{dB}$
) 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
$4 \times 4$
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
$72\;\text{mm} \times 48\;\text{mm} \times 2.2\;\text{mm}$
.