EM Design and Computer-aided Tuning of Advanced Dual-mode Filters and Multiplexers for Space and Wireless Communication Systems

The microwave payload on a communication satellite and the radio unit of a cellular base station system all need to process multi-frequency band and high-power microwave signals. Among various functional sub-systems, the high-performance non-planar microwave diplexer/multiplexer network is one of the indispensible sub-systems. In a multiplexer network, channel filters are used to select the desired microwave signals with the minimum loss and reject the interferences to a required level. To save space and mass of such sub-systems, non-planar dual-mode filters have been widely used. To facilitate the design and manufacture of a payload waveguide dual-mode filter, and also to innovate the base station filter architecture, this dissertation is devoted to the efficient computer-aided design, tuning and novel uses of dual-mode filters for space and ground applications.;In space microwave industry, circular waveguide dual-mode (CWDM) filters have been widely used on payload output multiplexers (OMUX). However, their design methods are still far from efficient. In this dissertation, a deterministic full-wave EM design technique based on EM modal analysis at center frequency is proposed. This design technique optimally designs a dual-mode waveguide filter as fast and accurate as designing a single-mode waveguide filter. With this technique, a contiguous manifold OMUX with multiple channel filters can be automatically EM prototyped. Several design examples including a contiguous OMUX are presented to show the effectiveness of the design theory. Facilitated by the rigorous EM designs, the spurious high-order mode problem that bothers OMUX designers can be readily diagnosed and fixed. In this dissertation, the spurious effects that may corrupt an OMUX response are theoretically studied and effectively remedied with different measures. As an effective means to extend the spurious-free frequency range of an OMUX, the stepped circular dual-mode waveguide (SCWDM) filter is also investigated in this dissertation. By using SCWDM channel filters, a Ku-band 17-channel contiguous OMUX with 1.5 GHz spurious-free window is successfully realized and verified by a triplexer hardware that covers the same bandwidth. Moreover, thanks to the deterministic design technique, CWDM filters in extended box coupling topology is also realized and reported for the first time in this dissertation. This topology helps a dual-mode filter to achieve versatile asymmetric filtering functions which are useful in a crowded spectrum environment.;Besides the filter for space applications, a compact TM11 dual-mode dielectric resonator filter design for ground base station system is also proposed. Comparing with a conventional single mode coaxial cavity filter, this type of filter not only saves the volume and footprint with a similar Q, but it is also friendly for tuning. Since all the tuning and coupling elements can be accessed from the filter top lid, such a novel filter is ideal for being integrated into diplexers and a filter bank. The features of the proposed dual-mode dielectric filter are successfully demonstrated by hardware prototypes.;In the end of this dissertation, a generalized analytical computer-aided tuning (CAT) technique is proposed. This technique allows much more robust computer aided tuning of advanced high-order microwave filters either for EM models or hardware prototypes. The uneven-Q effect which exists in most of practical filter hardware is accurately incorporated in this CAT technique. Both the formulas derived for the CAT technique and two challenging filter tuning examples are presented. Moreover, all filter hardwares in this dissertation are on-bench tuned by using this analytical CAT technique.