Compact Ka‐band conical beam filtenna

Abstract

A compact conical beam antenna composed by a filtering power divider (FPD) and circular open waveguide is presented. In order to reduce insertion loss in Ka‐band, the five‐way radial power divider and the cascaded filters are constructed using metallic waveguides. The filter is based on the principle of the magnetic field inversion characteristics of higher‐order mode resonances, using TE101 and TE102 over‐mode bypass coupling to create a pair of transmission zeros around the passband. A more compact folded structure is obtained by placing adjacent cavities back‐to‐back. Finally, TM01 mode on the circular aperture is excited by the output of the FPD, realising a conical beam radiation pattern. This proposed antenna works at the central frequency of 35 GHz, the maximum elevation angle of θ = 20° and the measured gain of 7.83 dBi have been achieved. The results shows that the impedance bandwidth is 6.29%, from 33.85 to 36.05 GHz. In terms of miniaturisation, the size of the entire antenna is 3.85λ0× $\times $2.51λ0.