Compact Directive Ultra-Wideband Rectangular Waveguide Based Antenna for Radar and Communication Applications

A new directive ultra-wideband antenna based on rectangular waveguide aperture antennas is presented. Conventional rectangular aperture antennas are limited by the single mode operation of the waveguide as well as relatively long and narrowband resonant feeds. To overcome these limitations, we developed a new rectangular waveguide antenna feeding structure that can establish an aperture field distribution very similar to that of the fundamental waveguide mode with a relatively short waveguide section and over two octaves of bandwidth. The overall antenna size is
$0.55 \lambda_{\rm m} \times 0.27\lambda _{\rm m} \times 0.18 \lambda_{\rm m}$
where
$\lambda_{\rm m}$
is wavelength at the minimum operating frequency. Due to the planar aperture of the antenna, a polarizer could be added to the antenna to ensure good cross-polarization performance with fabrication tolerances. The proposed feed requires a balun structure, and thus an integrated balun design is presented. It is found that a standard balun would interact with the antenna structure and thus a modified design was implemented. The antenna was fabricated and measured. The antenna had VSWR
$ < $
2.5 from 1.08 to 4.9 GHz and the measured gain showed almost constant aperture gain which increases from 5.3 dBi at the low frequency end to 11 dBi at the high frequency edge.