Reduction of Azimuthal Amplitude Ripple in the Rotating-Mode Feed to a Radial Waveguide by Using a Crossed Dog-Bone Slot

The use of a crossed dog-bone slot in a rectangular-to-radial waveguide transformer is proposed as a feeder for a radial line slot antenna to reduce the amplitude ripple in the azimuthal direction because the beamwidth of the dog-bone slots is wider than that of straight slots in radiating into a radial waveguide. The transformer is analyzed and designed by using the method of moments with numerical eigenmode basis functions. By the use of the crossed dog-bone slot, the measured amplitude ripple in the azimuthal direction becomes 0.80 dB, which is 1.4 dB lower than that of the conventional crossed straight slot in the 5.8 GHz band.