A Frequency-Scanned Slow-Wave Waveguide Antenna at Millimeter-Wave Frequencies

In this paper we describe the design, theory, implementation, and measurement results of a novel frequency-scanned slow-wave slotted waveguide antenna. The slow-wave antenna is fabricated by periodically loading a standard WR22 waveguide using cylindrical posts. The antenna has a backward radiation and can steer the beam from -72° to -12° by changing the frequency from 32.5 GHz to 37.4 GHz. The gain of the antenna remains within a 3 dB range from the maximum gain of 17 dBi throughout the steering range. The antenna is 29λ in length and 0.69λ in width. The antenna radiation efficiency is between 74% and 92% throughout its frequency range which allows for further extension of its length in order to achieve a higher gain and a smaller beamwidth. Moreover, the small lateral width of the antenna allows placing several of them side-by-side to either narrow or facilitate scanning the beam in the transverse plane. The antenna has a fast and constant scanning rate of 4.3° over a 1% bandwidth and a return loss of less than -10 dB throughout its operating frequency range.