Waveguide filters are key elements present in many microwave and millimeter-wave communication systems. In recent times, ever-increasing efforts are being devoted to the development of automated computer-aided design (CAD) tools of such devices. In this paper, a novel CAD tool based on modal analysis methods, which improves the efficiency and robustness of the classical aggressive space-mapping technique, is presented for those purposes. The use of a new segmentation strategy and the hybridization of a specific combination of several well-known optimization algorithms is proposed. The CAD tool has been successfully validated with the practical design of several -plane coupled cavity filters in a rectangular waveguide for space and communication applications. A filter prototype for local multipoint distribution systems operating at-band, and two tunable -plane filters with tuning posts operating at 11 and 13 GHz, have been successfully designed, manufactured, and measured.

Abstract-The dispersion diagram of infinite periodic structures is useful for the practical design of waveguide filters. Starting from the dispersion diagram of a unit cell, it is possible to generate a finite structure with very similar pass-and stop-bands (gaps). However, truncation of the infinite periodic structure degrades the pass-band performance. In this paper, these impairments are overcome by means of suitable waveguide tapers matching the impedance of the periodic structure to the access ports. As a result, the design of practical low-pass filters, derived from passive structures based on Electromagnetic Band-Gap (EBG) waveguides periodically loaded with metal ridges, is successfully addressed. According to this procedure, a five-order and an eight-order EBG low-pass filters are obtained after an optimization step. Measurements of a manufactured prototype fully validate the proposed approach.

This paper aims at the industry interest on automated design tools able to take into account manufacturing effects. Firstly, an efficient design strategy for bandpass waveguide filters including the rounded corners arising from low-cost manufacturing procedures is presented. This technique is based on a recent enhanced prototype and synthesis methodology able to consider the real structure parts. Using the resulting EM-based synthesis technique, an excellent structure is extracted which requires, at most, only a slight final EM optimization. Secondly, this paper presents analytical expressions providing error estimates for the different filter performances in terms of manufacturing tolerances. From such expressions, designers can determine the tolerance to be requested for a tuning-less implementation. Moreover, they can also be used to set the convergence criterion for the synthesis procedure. A fully automated design tool of bandpass waveguide filters able to consider manufacturing impairments has been developed and integrated in the commercial EM software tool FEST3D.

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Multipactor is a high-power effect severely limiting the performance of satellite communication links. A reference sample is normally used in the experimental setups for multipactor testing in order to verify its correct operation. However, the low gaps required for high frequencies jeopardize the manufacturability of the devices traditionally used for this purpose. A new reference sample, based on a stepped-impedance resonator, is proposed in this paper. The key design considerations are also outlined. A prototype operating between 17 and 18 GHz has been manufactured and tested, thus proving the novel structure is suitable and advantageous for high frequency bands.