Compact Ka-band conical beam filtenna

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.