W-band single-layer circularly-polarised antenna based on compact gap waveguide

A single-layered W band circularly polarised (CP) antenna array fed by a sequential feeding network using compact gap waveguides (GWs) with reduced pins is presented. The radiating element consists of a pair of cross slots and an open-ended rectangular cavity integrated into the top metal plate of the GW. A sequential rotation network (SRN) consisting of hybrid groove gap waveguide (GGW) and ridge gap waveguide (RGW) structure is presented. Due to the fact that conventional GWs with multiple rows of pins occupy large lateral size, thus making them difficult to realise a single-layered CP array fed by SRN. Compared with conventional GW with multiple rows of pins, compact GGW with a single row of pins is deployed here to make the presented SRN more compact, thus combining SRN and multiple CP radiators in the same layer. Particularly, a comprehensive investigation on the choice of the GGW groove depth is carried out. The groove depth is designed carefully such that the electric-field energy is more confined along the GGW line, and less rows of pins are required. For proof-of-concept demonstration, the proposed array has been fabricated and measured, exhibiting an overlapped bandwidth of 10.64% (89–99 GHz) and a peak gain of 19.48 dBi at 94 GHz. It presents a promising candidate for W band wireless applications.