In the chapter, several types of planar millimeter-wave and terahertz filters and their design methods are described. The millimeter-wave SIW filter using high-order resonating mode is introduced at first, and then a fast and accurate design method, which uses the space mapping (SM) method with different types of coarse-models, for the complex SIW components and the W-band filter is described. As followed, terahertz filters using the silicon deep reactive ion-etching process are introduced in detail.

Several designs of lossy filters for receivers in satellite transponders have been investigated in order to improve the performance in terms of flatness compared to a classical hairpin filter design. Flatness and insertion loss performances for all solutions are summarized. The reference design is a microstrip filter made of coupled hairpin resonators. Two approaches have investigated for improving the flatness of the reference design. Lossy filter designs have been compared to the reference, considering the same specifications and the same technology. An in-line network with resistive cross-couplings and a transversal network with heterogeneous Q resonators have been designed and fabricated first. Theoretically, the transversal network leads to better performances in terms of flatness, but its implementation is generally difficult, especially considering the input/output junctions between multiple paths, which are naturally dispersive, causing spurious transmissions in the stopband. Moreover, a Monte Carlo analysis has been performed, showing higher sensitivity of this later solution with respect to manufacturing tolerances. Consequently, considering measured performances, in-line networks with resistive cross-couplings appear to be the best solution for implementing our receiver filter. In particular, the version with two RCCs appears as a good compromise between flatness and insertion loss. Finally, the in-line network has been transformed introducing non-resonant nodes and additional resistive cross-couplings in order to design absorptive lossy filters. The resulting filters allow attenuating the reflected wave substantially with a reduced impact on the absolute level of losses.

The harmful effects that standing waves may have on an electronic system are well known. The symptoms of standing waves are less direct when they occur out-of-band, but the negative impact they have on system performance is no less real or important. Problems that arise from stop-band mismatches are in some ways even more troublesome than those in-band because they are too often not fully appreciated until after the first prototype is built, by which time some critical design and packaging decisions have already been made. Reflectionless filters provide a safeguard against these concerns. This chapter looks at reflectionless network topology, scaled prototype parameter tables, planar lumped-element implementations, delta-wye transformation for reduced impedance, non-canonical filter responses, transmission-line reflectionless filters, Chebyshev and Zolotarev type I filters.

This chapter has been devoted to the RF design of a new class of planar microwave RF filters in which AW resonators are effectively combined with LEs to create quasielliptic bandpass-type transfer functions with the following unique RF performance characteristics: (i) FBWs that do not depend on the kt2 of the AW resonators, (ii) high Qeffs of the order of a thousand, (iii) passbands whose in-band group delay (Tg) can be designed to be flat, and (iv) transfer functions with multiple levels of continuous analog RF tuning. In particular, we focused on a new RF design approach that uses as a basis CM-based synthesis. The extraction of CM-based models for singleand multimode AW resonators as well as their equivalents when used in series or parallel configurations have been discussed in detail. Using as a basis these CM AWLR-based models, the synthesis and RF circuit/EM design of high-order BPFs has been presented. In particular, we demonstrated quasi-elliptic transfer functions with maximally flat-, equiripple-, and Gaussian-type in-band response. Furthermore, we additionally addressed the realization of multiband bandpass-type transfer functions with symmetric or asymmetric-passbands. RF tuning methods using variable reactive elements have also been discussed and demonstrated the potential for multiple levels of transfer-function tunability including passband bandwidth, out-of-band isolation, and selectivity. Lastly, this chapter presented practical integration schemes using commercially available SAW resonators and LEs.

Several compact and high-performance HTS dual-band BPF based on multi-mode resonators have been reviewed in this chapter. Firstly a series of novel and compact dual-mode or quadruple-mode resonators are presented for constituting the loworder dual-band filters with the electrically small size and ultra-low insertion loss. Then, a novel dual-mode HRR is demonstrated and developed to an eighth-order HTS dual-band filter with sharp passband slope and deep out of band attenuation. In light of the development of more flexible resonant structures and efficient design theory, more compact and high-performance HTS dual-band, even the triple-band or quad-band filter can be designed in the future so as to meet the requirement for the high-quality service of various multi-functional wireless system.

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.