Low-Profile Leaky-Wave Antenna for Continuous Fixed-Frequency Beam Steering at K-band using Mechanically Adjustable Airgap

A low-profile, high-gain parallel-plate waveguide leaky-wave antenna with continuous fixed-frequency beam scanning is presented. The antenna consists of a pillbox feeding substrate and a top radiating substrate, separated by an air layer with variable thickness, with rectangular slots etched into the metal surface of the top dielectric substrate. Continuous beam steering in the elevation plane is achieved at a given frequency by vertically adjusting the position of the top radiating layer, creating a mechanically adjustable air layer beneath it where the feeding wave propagates. This configuration results in a controlled variation in the effective permittivity, combining the relative permittivity of the top substrate material and the adjustable air layer, enabling continuous beam steering. An H-plane substrate-integrated waveguide horn with a single coaxial feeding port is utilized to excite the radiating layer in a pillbox configuration. To verify the design, an antenna prototype with 130 × 200 × 5.8 mm³ dimensions was tested at the operating bandwidth of 19.5 – 20.5 GHz. Measured results demonstrate a peak realized gain of 23.8 dBi, elevation beam steering from 0 – 38° when moving the top layer vertically from 0.3 to 3.0 mm with only 2.7 dBi gain variation. Moreover, the antenna achieves a -42 dB cross-polarization level and a -10 dB side lobe level over the operating bandwidth.