Planar miniaturized Substrate Integrated Waveguide triplexer with radial symmetry

In this paper a novel design technique for a planar highly miniaturized Substrate Integrate Waveguide (SIW) based triplexer has been proposed at C band. The proposed design employs evanescent mode propagation by placing a defected two pole resonating structure on the top layer of a waveguide section, which provides a pass-band at much lower frequency than the cut-off frequency of the unloaded waveguide. Three differently scaled defected structures on each radially symmetric waveguide section provide three distinct pass-bands. The triplexer is only 36mm (1.06λg) in diameter. The achieved fractional bandwidth is about 6%, the insertion loss is below 1dB and the isolation between the three ports is more than 18 dB. The structure provides miniaturization, low loss, high isolation and good out of band performance. Also it is planar, less bulky and easy to fabricate.