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Abstract A class of multi-band planar diplexer with sub-sets of frequency-contiguous transmission bands is reported. Such a radio frequency (RF) device is suitable for lightweight high-frequency receivers aimed at multi-band/multi-purpose mobile satellite communications systems. It consists of two channelizing filters, each of them being made up of the in-series cascade connection of replicas of a constituent multi-passband/multi-embedded-stopband filtering stage. This building filtering stage defines a multi-passband transfer function for each channel, in which each main transmission band is split into various sub-passbands by the multi-stopband part. In this manner, each split passband gives rise to several sub-passbands that are imbricated with their counterpart ones of the other channel. The theoretical RF operational principles of the proposed multi-band diplexer approach with sub-sets of imbricated passbands are detailed by means of a coupling–routing–diagram formalism. Besides, the generation of additional transmission zeros in each channelizing filter for higher-selectivity realizations by exploiting cross-coupling techniques into it is also detailed. Furthermore, for experimental demonstration purposes, a microstrip proof-of-concept prototype of second-order octo-band diplexer in the frequency range of 1.5–2.5 GHz that consists of two quad-band channelizing filters with pairs of imbricated passbands is developed and characterized. 

This paper reports on an RF design methodology for acoustic-wave-resonator-(AWR)-based bandpass filters (BPFs) with input-reflectionless behavior in both their passband and stopband regions. The proposed concept is based on acoustic-wave-lumped-element resonators (AWLRs) that are incorporated in series-cascaded reflectionless stages (RLSs). Each RLS comprises a first-order bandpass section-shaped by three impedance inverters and one AWLR-and a first-order resistively-terminated bandstop section-shaped by two impedance inverters and one AWLR-that are designed to exhibit complementary transfer functions. In this manner, an input-reflectionless behavior can be obtained both at the passband and stopband regions of the filter. In addition, the use of AWLRs in the RLSs facilitates the realization of high-quality-factor quasi-elliptic-type transfer functions with fractional bandwidths (FBWs) that are wider than the electromechanical coupling coefficient (kt 2 ) of its constituent AWRs. For proof-of-concept validation purposes, one- and two-state prototypes were manufactured, and measured at 418 MHz using commercially-available surface-acoustic-wave resonators. 

A type of wide‐band signal‐interference planar duplexer with single‐ and dual‐band channels is presented. It exploits transversal‐signal‐interference‐section‐based channels with contiguous single‐ and dual‐passband filtering transfer functions. Furthermore, by ending the dual‐band channel in a reference‐impedance resistor, a wide‐band bandpass filter (BPF) with quasi‐absorptive stopbands is realised. As experimental validation, microstrip prototypes of a duplexer and a two‐stage quasi‐absorptive BPF that operate in the 1.6–4.4 GHz range are built and tested.