An Octave Bandwidth Coaxial Waveguide Feed Antenna With an Iris Matching Network

The design of a 2.2 to 4.4 GHz coaxial waveguide feed antenna for radio telescopes is described. An iris matching network is designed to improve the unmatched aperture reflection coefficient from $-$6.7 to $-$12 dB over a 2:1 bandwidth ratio. An efficient method of optimizing the irises over a wideband is presented. The properties of wideband iris matching networks including their behavior as bandpass structures are discussed. The far-field beamwidth of the feed is held constant across the octave band by a corrugated choke. Measured radiation properties agree closely with simulation.