Search

In this article, we introduce a synthesis-based design approach for waveguide filters, including singlets. As is known, a singlet block comprises one resonator coupled to source and load plus an additional coupling between source and load. In this way, a pole–zero pair is produced, thus allowing the introduction of a transmission zero in the frequency response. Structure making that uses cascaded singlets (especially implemented in waveguide technology) has been successfully used to realize compact and quasi-in-line pseudoelliptic filters. The design of this configuration suffers, however, from a severe drawback; while an isolated singlet can be exactly synthesized, when these blocks are put in cascade, nonresonating nodes (NRNs) are required to allow the cascade connection. Consequently, the resulting topology includes both cross couplings and NRNs, for which no exact synthesis solution is till now available (all the design solutions proposed in the literature are based on optimization). The new design procedure here proposed overcomes this drawback, allowing the synthesis of the equivalent circuit of the cascaded-singlet topology. Once this circuit is obtained, the dimensioning of the singlets can be carried out by exploiting a full-wave simulator according to the procedure described in the article. The proposed design approach allows a very accurate initial dimensioning of the filter, which represents an excellent starting point for final adjustments/optimizations. A detailed design example is presented in the article showing how to practically implement the novel procedure. This new approach is also experimentally validated by a waveguide filter prototype, previously designed by optimization and fabricated. It is shown how this filter can be redesigned with the novel procedure, obtaining very similar physical dimensions in a noticeably shorter time. [ABSTRACT FROM AUTHOR]

This paper presents a complete design procedure for in-line evanescent mode filters using an innovative pseudoelliptic structure, namely, the strongly coupled resonator triplet (SCRT). The SCRT can be seen as the combination of a strongly coupled resonator pair (SCRP) and a third resonator next to the pair. Compared to the SCRP, which at the passband frequencies generates a pole and a transmission zero, the new SCRT is capable of generating an additional passband pole, thus leading to the design of more compact in-line filters. Similar to the SCRP, the basic structure for filter design purposes is obtained by embedding the SCRT between two outer resonators. The coupling mechanisms and functional properties of this basic structure are explained. A suitable circuit model for the SCRT is introduced, thus allowing the synthesis of a low-pass prototype as well as the evaluation of the coupling coefficients and resonating frequencies to assign to the physical filtering structure. The proposed design procedure is validated by means of several examples, one of which including the detailed dimensions and experimental results of a manufactured prototype. [ABSTRACT FROM AUTHOR]

A new class of compact in-line filters with pseudoelliptic responses is presented in this paper. The proposed filters employ a new type of mixed-mode resonator. Such a resonator consists of a cavity loaded with a suspended high permittivity dielectric puck, so that both cavity TE101 mode and dielectric TE \mathrm {01\delta } mode are exploited within the same volume. This structure realizes the transverse doublet topology and it is therefore capable of generating a transmission zero (TZ) that can be either located above or below the passband. Multiple mixed-mode resonators can be used as basic building blocks to obtain higher order filters by cascading them through nonresonating nodes. These filters are capable of implementing TZs that are very close to the passband edges, thus realizing an extreme close-in rejection. As a result of the dielectric loading, the proposed solution leads to a very compact structure with improved temperature stability. To validate the proposed class of filters, a second-order filter with 2.0% fractional bandwidth (FBW) and a fourth-order filter with 2.5% FBW have been designed and manufactured. [ABSTRACT FROM AUTHOR]

In this paper a new class of propagating waveguide in-line pseudoelliptic filters exploiting dielectric resonators is presented. The basic structure is a singlet, which is implemented by a TE01 \delta mode dielectric resonator placed into a rectangular waveguide above cutoff. Couplings are controlled by a proper positioning of the puck. The fundamental propagating mode of the waveguide is exploited to both excite and bypass the resonator so as to obtain bypass coupling capability, allowing the generation of transmission zeros. Higher order filters are obtained by cascading singlets through quarter-wave or half-wave waveguide sections. The quarter-wave section behaves as an admittance inverter, while the half-wave section behaves as a resonator, the latter resulting in filters which combine dielectric and cavity resonators. Thanks to this combination, unique performances such as wide bandwidth and sharp transition bands can be obtained. To validate the proposed method a third-order filter with 2.3% fractional bandwidth (FBW) and a fifth-order filter with 8.15% FBW have been designed and manufactured, thus demonstrating the approach feasibility. [ABSTRACT FROM AUTHOR]

A new class of dielectric resonator filters with in-line structure and pseudoelliptic response is presented in this paper. The basic idea consists of using TE01\delta single-mode resonators cascaded along an evanescent mode waveguide and oriented along orthogonal directions. By exploiting multiple evanescent modes, which can alternatively excite or bypass a resonator depending on its orientation, cross-coupling between nonadjacent dielectric pucks can be established and controlled. Various configurations, such as triplets, quadruplets, and quintuplets, can be obtained by properly orienting the various pucks and by exploiting a prescribed set of evanescent modes. In contrast with conventional techniques, pseudoelliptic filters can be implemented without using cumbersome cross-coupled architectures or reduced spurious performance multimode resonators. The experimental results of two sixth-order filters with two arbitrarily located transmission zeros, and a fifth-order filter with three transmission zeros validate the proposed filter class. [ABSTRACT FROM AUTHOR]

Previous microwave distributed bandstop filters have had their second harmonic response centered at no more than three times the fundamental bandstop mid-band frequency, due to the use of quarter-wave resonators. This limitation has now been removed by the use of compound resonators having shorter electrical length. Some configurations incorporate lumped capacitors, resulting in additional design degrees of freedom and wider passbands. The new theory has been developed to apply to both wide and narrow stopbands. Example filters having upper passband widths of up to six times the fundamental bandstop center frequency are presented [ABSTRACT FROM PUBLISHER]

Studies quasi-elliptic compact high-power notch filters using a mixed lumped and distributed circuit. Design of quasi-elliptic notch filters using a simplified version of the natural elliptic prototype; Band reject; Bandstop.