A Low-Profile, High-Gain, and Full-Band SubArray of Cavity-Backed Slot Antenna

A four-element array of cavity-backed slot antennas with high-gain and low cross-polarization is presented. The subarray is fed by a single microstrip line coupled to the low-profile cavity and provides the entire X-band bandwidth. This subarray is envisioned as the building block (tile) for the construction of scalable low-profile ultrawideband antenna arrays. The slot array is composed of a thin rectangular cavity of dimensions 1.2λ
_L
× 1.2λ
_L
× 0.15λ
_L
(λ
_L
is the free space wavelength at the lowest frequency of operation) on which four slots are cut out for electromagnetic radiation. It is demonstrated that by inserting metallic septa with appropriate locations and sizes inside the cavity, multiple resonances with desired field distribution can be excited resulting in a wideband slot antenna with consistent radiation characteristics over 60% fractional bandwidth. Also, a compact end-launch microstrip to reduced-height waveguide transition is presented to feed the antenna. Silver 3-D printing is used to fabricate the cavity and the standard printed circuit board technology is used to fabricate the feed. The overall antenna bandwidth, when integrated with the microstrip feed section, is shown to be 40% over which a minimum gain of 11 dBi is demonstrated.