Millimetre wave SIW diplexer with relaxed fabrication tolerances

Abstract

This chapter has concerned itself with the design of millimetre wave SIW diplexer circuits with an aim of improving their tolerance handling ability. A method of designing SIW components entirely in DWG and then translating a final optimised design to SIW is presented. Due to the equivalence between SIW and DWG, the translated SIW components do not require a further optimisation which is a significant advantage as it speeds up the design process. This method was demonstrated by showing simulated results of a Ka-band bandpass filter, highpass filter and hybrid coupler where good agreement is observed between the original DWG response and the translated SIW response. Using these components, the design of a Ka-band SIW diplexer based on the topology proposed in [5,6] and subsequently [7] is presented. To gain an understanding of how fabrication errors will affect the diplexer's frequency response, a tolerance analysis where errors in the via x and y position, dielectric constant, and via diameter were studied in detail. These observations suggest that the highpass filter in the diplexer is less sensitive to fabrication errors than the bandpass filter and its use in the diplexer helps to improve the tolerance handling ability of the circuit. To validate the simulations, a Ka-band diplexer was fabricated using RT 5880 in addition to an aluminium alloy waveguide-to-SIW transition where good agreement is observed between the measured and simulated frequency responses in both cases. However, the results suggest that further work is required in relaxing the fabrication tolerance of SIW bandpass filters if SIW diplexers are to be used for commercial millimetre wave applications, such as backhaul.