A small-sized waveguide horn with multi-ridge impedance transformer

This paper proposes a new configuration of small-sized horn having broad beamwidth with multi-ridge impedance transformer to realize small aperture size, which is to be near cut-off frequency. The small-sized aperture near cut-off frequency causes mismatch loss because of indication of high impedance like the open-ended waveguide. In order to overcome this problem, the multi-ridge part, which reduces the characteristic impedance, is introduced at the end of the horn aperture to transform the waveguide to free space smoothly. This novel configuration can achieve impedance matching at around the cut-off frequency and keeps the broad beamwidth.