LAUSR

In this communication, a low profile $4 \times 8$ air cavity-fed circularly polarized (CP) planar antenna array with high performance for W-band is proposed. This antenna array is composed of two parts: low-loss gap waveguide (GWG) feeding network and high performance magneto-electric (ME) dipole antennas. The antenna elements are fed by the transverse coupling slots right above an air-filled high-mode cavity with checkerboard structure. Moreover, a four-way ridge GWG (RGWG) power divider with transition from RGWG to groove GWG (GGWG) is designed to excite the high-mode cavity. By properly arranging the position and size of coupling slots, each ME dipoles are excited with in-phase property. Periodic pins are arranged around both the GWG transmission line and the air cavity to create a stop band and resonant frequency. The high-mode air cavity is realized using shorted pins to split the electromagnetic field into shorted-end GGWG. Thus, the normal GWG feeding technology with a GWG power divider and a $2 \times 2$ air cavity in different layers are combined in a single layer. The transmission loss and substrate loss of this metallic single-layer feeding network are reduced, as well as the array profile. Each CP ME dipole antenna is etched on the printed circuit board (PCB) with stable radiation pattern and wide axial ratio (AR) bandwidth performance. The proposed $4 \times 8$ planar antenna array is simulated and fabricated to validate the design. A measured 3 dB AR bandwidth of 17% and a gain of up to 23 dBi have been achieved. The impedance matching is lower than −10 dB over the frequency band with an overall boresight gain of above 19 dBi.