A Groove Gap Waveguide Feeding Network for Dual-Circularly Polarized Antenna Arrays

This paper presents a groove gap waveguide structure designed to serve as a feeding network for dual circularly polarized antenna arrays in the millimeter wave spectrum (28-32 GHz). The proposed structure comprises four groove gap waveguide elements arranged in a cross-shaped configuration. A turnstile integrated into the middle position of the structure divides the incoming RF signal into these four waveguide elements. Four matching posts are incorporated at the end of the various groove gap waveguide elements to route each corresponding RF signal to four WR-28 waveguide sections. These four sections form the output ports of the feeding network. The appropriate design of the pin distributions along the four groove gap elements allows the entire feeding network to achieve a specific phase shift between the output ports. As a proof of concept, the proposed feeding network is connected to a dual circularly polarized antenna array composed of four sub-arrays. Two of these sub-arrays emit right-handed circularly polarized waves, while the other two are designed to provide left-handed circularly polarized waves. A prototype of the feeding network demonstrates its ability to produce the needed circularly polarized radiation for a given distribution of the pins along the various groove gap elements. The results show that the feeding network can achieve an insertion loss as low as 0.55 dB with a good impedance matching across the entire operational bandwidth. In addition, when the fabricated feeding network is connected to the dual-circularly polarized antenna prototype, a maximum realized gain of 15.14 dBic is obtained.