A novel millimetre wave waveguide diplexer topology that can be fabricated using relaxed fabrication tolerances is presented. This is achieved by using a highpass filter/hybrid coupler topology in addition to a low order capacitive iris bandpass filter. By targeting the most sensitive centre resonators in the bandpass filter and increasing their length to full wavelength, the sensitivity to fabrication errors associated with changes to the resonator length can be reduced without the introduction of spurious responses close to the passband. The main benefit of this topology is that only one bandpass filter is required to realise the final diplexing response. This is advantageous when tolerance is considered as it is found that resonating structures associated with bandpass filters contribute to tolerance effects. In addition to this, the authors find that the choice of iris discontinuity used to realise the impedance inverters in the bandpass filter can help to relax fabrication tolerances. By subjecting the proposed circuit to a tolerance analysis, simulated results suggest that the circuit can be fabricated with relaxed fabrication tolerances. These discussions are verified with the fabrication of a Kaband waveguide diplexer, where the measured and simulated scattering parameters are in very good agreement.

A novel topology is presented which can relax fabrication tolerances associated with an E-band waveguide diplexer circuit. This is achieved by using a narrow wall short slot coupler/highpass filter configuration, in addition to a low order bandpass filter which reduces the required number of resonating structures by halve when compared to other E-band diplexers in the literature. This is advantageous when tolerance is considered as it is found that resonating structures associated with bandpass filters contribute to fabrication sensitivity. In addition to this, it is found that capacitive iris coupling has benefits over inductive iris coupling due to the positive length of the impedance inverter.

This study is concerned with the development of millimetre wave substrate integrated waveguide (SIW) diplexers, with an aim of relaxing fabrication tolerances. A method of designing SIW components initially in a dielectric filled waveguide (DWG) medium, and then translating a final optimised design to SIW is presented. Owing 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. The authors demonstrate this process by presenting the design of a Ka-band diplexer that consists of a highpass filter, hybrid coupler and low-order bandpass filter, where good agreement between the DWG and translated SIW cases can be observed. To investigate how the diplexer handles fabrication errors, they subjected the circuit to a tolerance analysis where simulated results suggest that the highpass filter in the diplexer is less sensitive to fabrication errors than the bandpass filter and its use in millimetre wave SIW diplexer circuits can help to relax sensitivity to fabrication errors. These observations are verified with the measurement of a fabricated Ka-band SIW diplexer, where the measured and simulated Sparameters are in very good agreement.

A wideband Ka‐band waveguide‐to‐substrate integrated waveguide transition is presented based on a multi‐section transformer approach. We designed our transition by successfully adapting multi‐section inhomogeneous waveguide transformer theory to match a substrate integrated waveguide feedline to a standard waveguide flange, which offers more degrees of freedom than current design methods in the state of the art. We subjected our transition to a simulated tolerance analysis and have found the transition to be robust when fabrication errors are considered. We validated these simulations by measuring a back‐to‐back waveguide‐to‐substrate integrated waveguide transition, where there is very good agreement between measured and simulated results. Moreover, an insertion loss of −0.48 dB was measured at the center frequency of the required operating range. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:10–12, 2017

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