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We present an exact synthesis procedure for the low-pass prototype of extracted-zero filters. This type of filter has been recently introduced and it allows the realization of a true inline topology with up to two transmission zeros. Compared to other inline (or quasi-inline) solutions, the one here considered is the simplest to dimension and fabricate (the same techniques used for all-pole filters can be adopted). The procedure here presented has been applied to the synthesis of various prototypes and the results confirm the effectiveness of the proposed concept. A filter previously realized in a quasi-inline configuration has been re-designed in the new topology and the results obtained with the two topologies are compared and discussed. [ABSTRACT FROM AUTHOR]

This letter presents new configurations of stubbed waveguide cavities for the realization of pseudo-elliptic and self-equalized filters. The basic structure consists of a main TE102/TE201 dual-mode cavity that is loaded with a pair of waveguide stubs. The two stubs are located at the top and bottom walls of the cavity while always being parallel and in-line to each other. Such a two-stub arrangement can be seen as a TM110 mode cavity, which is embedded into the main dual-mode cavity. By properly setting the polarization of the stubs with respect to the main cavity as well as finely adjusting the difference between the lengths of the stubs, triple-resonance structures with selected topologies and controllable coupling mechanisms can be implemented. The resulting third-order filtering functions comprise three poles and two zeros, the latter being either group delay equalization zeros or finite frequency transmission zeros depending on the polarization of the stubs. The experimental results of a fifth-order filter with two finite frequency transmission zeros using one stubbed waveguide cavity between two standard cavities validate the new configuration. [ABSTRACT FROM AUTHOR]

This letter presents a practical solution to realize finite frequency transmission zeros with independent location for wideband evanescent-mode filters. The method consists of using offline resonators located at the input and/or output of the filter. In contrast with the extracted-pole technique commonly employed for narrowband filters to generate a pole-zero pair, each offline resonator is used here in such a way so that the sole transmission zero is actively used in the filtering function. The latter characteristic is what makes this technique practical for wideband filters as it prevents the presence of unfeasibly strong coupling coefficients, as well as avoiding impractical nonresonating node elements. The offline resonator, which we named extracted-zero, can be coupled to the first or last resonator of a wideband bandpass filter, and it is conveniently realized using the same technology as any other resonator of the filter. The extracted-zero can be seen as a first-order notch filter which is directly embedded into the bandpass filter (instead of being cascaded afterward). The feasibility of this solution is validated by the experimental results of a challenging 225–450-MHz bandpass filter (66.6% fractional bandwidth) which employs 17 inline resonators plus 2 extracted-zeros so as to obtain 50 dB rejection below 195 MHz. [ABSTRACT FROM AUTHOR]

Resonances and reactive effects due to higher-order modes represent a rather popular concern among microwave engineers dealing with the design and modeling of passive components. The terms spurious and parasitic are indeed the words of choice when referring to those effects, and, although such a historic bad reputation is well deserved for most applications, in the last decade or so, there has been a particular discipline where these parasitic effects have suddenly earned new respect and dignity: the discipline of microwave filters. [ABSTRACT FROM AUTHOR]

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]

A new class of reduced-size waveguide filters implementing pseudoelliptic filtering functions is presented in this article. The basic structure of these filters is the stubbed waveguide cavity (SWC), which is proposed in both single- and double-stub configurations. The SWC consists of a main TE201 mode cavity, which is loaded with one or two $E$ -plane stubs. The stubs behave as embedded half-mode cavities supporting additional resonant modes, and they are properly located so as to realize specific coupling schemes for the generation and control of transmission zeros. Depending on its configuration, a sole SWC can generate up to three poles and three transmission zeros. The design of higher order filters employing a cascade of SWCs, as well as combinations between SWCs and conventional waveguide cavities, are presented. The experimental results of a third-order filter employing one SWC (double-stub configuration) and a fifth-order filter employing two SWCs validate the feasibility of this new class of waveguide filters. [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]

This paper presents an original synthesis-based approach for the complete design procedure of pseudoelliptic in-line filters using strongly-coupled resonators pairs (SCRPs). The proposed synthesis method is based on the derivation of the coupling matrix of a new basic building block that we called SymBox. This new topology is composed of four resonators and five couplings, and allows for the generation of one finite-frequency transmission zero. Among its various properties, the most interesting feature of the SymBox including an SCRP is that all the couplings are positive regardless of the transmission zero position (above or below the passband), thus significantly reducing the complexity of the physical structure of the filter. The proposed design procedure is completed with the application of an efficient full-wave methodology, allowing one to accurately obtain the physical dimensions of the filter starting from the electrical parameters calculated in the previous synthesis phase. The complete design of a filter composed by a cascade of resonators and SymBoxes is presented and illustrated with a practical example. It is shown how the filter realized by Bastioli and Snyder in 2013 (whose design was carried out by means of a lengthy full-wave optimization procedure) can be easily designed with the proposed synthesis technique. [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]

A new cavity arrangement, namely, the generalized TM dual-mode cavity, is presented in this paper. In contrast with the previous contributions on TM dual-mode filters, the generalized TM dual-mode cavity allows the realization of both symmetric and asymmetric filtering functions, simultaneously exploiting the maximum number of finite frequency transmission zeros. The high design flexibility in terms of number and position of transmission zeros is obtained by exciting and exploiting a set of nonresonating modes. Five structure parameters are used to fully control its equivalent transversal topology. The relationship between structure parameters and filtering function realized is extensively discussed. The design of multiple cavity filters is presented along with the experimental results of a sixth-order filter having six asymmetrically located transmission zeros. [ABSTRACT FROM PUBLISHER]

An innovative class of very compact and selective waveguide dual-mode filters is presented in this paper. The basic structure is the TM dual-mode cavity. Such a cavity employs both resonant and nonresonating modes so as to provide two reflection and two transmission zeros. The high design flexibility in terms of transmission zero positioning and response bandwidth has been demonstrated by means of several single cavity designs. The design of Nth-order multiple cavity filters with N transmission zeros is presented and discussed. Different filter topologies are obtained depending on the waveguide structure used to connect adjacent cavities. An efficient mode-matching analysis method is proposed and verified for fast filter optimization. An eighth-order filter with eight transmission zeros has been designed, manufactured, and tested to demonstrate the potentialities of the filter class proposed. [ABSTRACT FROM AUTHOR]