A Q-Band Low-Profile Dual Circularly Polarized Array Antenna Incorporating Linearly Polarized Substrate Integrated Waveguide-Fed Patch Subarrays

An integrated low-profile dual circularly polarized (dual CP) array antenna operating in the Q-band is proposed in this paper, which is realized by sequentially rotating subarrays comprised linearly polarized (LP) substrate integrated waveguide (SIW)-fed patches. The design methodology and working mechanism of the LP SIW-fed patches is presented first, which is implemented with a two-layer printed circuit board structure where the SIW feeding network is located in the bottom substrate and the patches are on the top substrate. Four subarrays are then arranged according to the requirements of a sequential rotation array for producing CP directive beams. A two-layer SIW feeding network for providing the required amplitude and phase distributions for the four subarrays is designed, which includes two input ports for exciting CP radiation with opposite handedness, respectively. Prototypes of the LP subarray and the integrated dual CP array antenna were fabricated and measured. Good agreement between the simulation and measured results validates the designs. The proposed low-cost and lightweight dual CP antenna owns the advantages of wide useful bandwidth (8.9%), high isolation of more than 19 dB, low profile of less than $0.1\lambda _{0}$ , and good orthogonal polarization discrimination higher than 25 dB.