Lukasz Szydlowski

Coupled-Resonator Filters With Frequency-Dependent Couplings: Coupling Matrix Synthesis

This letter presents a novel technique for synthesis of coupled-resonator filters with inter-resonator couplings varying linearly with frequency. The values of non-zero elements of the coupling matrix are found by solving a nonlinear least squares problem involving eigenvalues of matrix pencils derived from the coupling matrix and reference zeros and poles of scattering parameters. The proposed method was verified by numerical tests carried out for various coupling schemes including triplets and quadruplets for which the frequency-dependent coupling was found to produce an extra zero.

A Substrate Integrated Waveguide (SIW) Bandpass Filter in A Box Configuration With Frequency-Dependent Coupling

This letter presents the design of a microwave bandpass filter with frequency-dependent coupling implemented in substrate integrated waveguide (SIW) technology. The proposed filter implements a four-pole generalized Chebyshev filtering function with two transmission zeros. Resonators are arranged in an extended box configuration with dispersive coupling on a main signal path, which produces an extra zero in comparison to classical approaches. The frequency-dependent coupling is implemented as a shorted stub with an additional septum made from via-holes. Such modification allows better control of the positions of the resonant frequencies of coupled SIW cavities, as well as of the position of the transmission zero. The filter was fabricated in SIW technology and good agreement was achieved between the simulated results and those measured.

Coupled-Resonator Waveguide Filter in Quadruplet Topology With Frequency-Dependent Coupling – A Design Based on Coupling Matrix

This letter presents an application of a recently developed coupling matrix synthesis technique to design of coupled-resonator filters with dispersive inter-resonator couplings. This technique is used to design a novel coupled-cavity bandpass filter. Measurements validate the design and confirm effectiveness of the synthesis method. The filter is a four-pole generalized Chebyshev filter with three transmission zeros. Resonators are arranged in a quadruplet configuration and employ a single dispersive cross coupling to produce an extra zero in comparison to classical approaches. Frequency-dependent coupling was realized via a rectangular waveguide iris with an incomplete height conducting post.

Design of Microwave Lossy Filter Based on Substrate Integrated Waveguide (SIW)

In this letter, we propose a lossy three-pole Chebyshev filter centered at 5.15 GHz, based on the substrate integrated waveguide (SIW) with scattering characteristics shifted down by 5.68 dB. The filter is composed of three directly coupled SIW cavities with three lossy couplings between nonadjacent resonators. These additional couplings are realized using mixed coupled slot and microstrip lines connected with metal electrode leadless face (MELF) resistors. The filter was fabricated using a standard printed circuit board (PCB) process, and good agreement between the simulated and measured results has been achieved.

Synthesis of Coupled-Lossy Resonator Filters

A technique for fast synthesis of coupling matrix low-pass prototypes of generalized Chebyshev bandpass filters with lossy resonators is presented in this letter. The coupling matrix is found by solving a nonlinear least squares problem based on zeros and poles of filters transfer functions.

A Trisection Filter Design With Negative Slope of Frequency-Dependent Crosscoupling Implemented in Substrate Integrated Waveguide (SIW)

This letter reports on a novel realization of a microwave bandpass filter in a triplet configuration with a frequency-dependent crosscoupling implemented in substrate integrated waveguide (SIW). The design involves implementing dispersive coupling with a negative slope, a feature that allows the capabilities of the classic triplet topology to be extended. In this particular case, the implementation of two transmission zeros on the upper stopband is considered. The dispersive coupling with negative slope in SIW is achieved with a coupling with a positive slope whose sign is inverted using balanced line theory. The filter was fabricated in SIW technology, and good agreement was achieved between the simulated results and those measured.

A NOVEL SYNTHESIS TECHNIQUE FOR MICROWAVE BANDPASS FILTERS WITH FREQUENCY-DEPENDENT COUPLINGS

This paper presents a novel synthesis technique for microwave bandpass fllters with frequency-dependent couplings. The proposed method is based on the systematic extraction of a dispersive coupling coe-cient using an optimization technique based on the zeros and poles of scattering parameters representing two coupled resonators. The application of this method of synthesis is illustrated using two examples involving four and flve-pole generalized Chebyshev fllters implemented in substrate-integrated waveguide (SIW) technology. As a dispersive inverter, a parallel shorted stub with an additional septum was used. The septum lends greater ∞exibility to the dimensional synthesis, in that it increases the allowable range of the coupling coe-cients. The measured and simulated results are in excellent agreement, which conflrms the validity of the proposed approach.

Generalized Chebyshev Bandpass Filters With Frequency-Dependent Couplings Based on Stubs

This paper presents an accurate synthesis method for inline and cross-coupled generalized Chebyshev bandpass filters with frequency-dependent couplings implemented via open and short stubs. The technique involves the synthesis of a lumped-element prototype in the form of a coupling matrix with a frequency-dependent term and the conversion of this prototype to a distributed-element model composed of sections of TEM lines. This takes into account the impedance (or admittance) of the stubs, thus allowing compensation for the loading effect. The design equations are derived for the stub impedance in terms of a coupling coefficient and for the allowable frequency range in which the model is valid. Additionally, the proposed methodology allows the simultaneous application of frequency-dependent couplings with positive and negative dispersive parts within the same network. The validity of this method is confirmed by numerical tests and through experiments, including filters with dispersive couplings of the opposite signs.

Zero-Pole Space Mapping for CAD of Filters

In this letter, we propose a new space-mapping technique tailored to the CAD of microwave filters. The goal of space mapping is to achieve a satisfactory design with the minimal number of fine model evaluations. In our approach, the filter is represented by a rational function. To quickly align the coarse and fine models, and to speed up the direct optimization of the coarse model, we propose matching the zeros and poles of a rational function extracted from scattering parameters, rather than the frequency responses.

A Novel Coupling Matrix Synthesis Technique for Generalized Chebyshev Filters With Resonant Source–Load Connection

This paper reports a novel synthesis method for microwave bandpass filters with resonant source-load connection. In effect, a network realizing N+1 transmission zeros (where N is the number of reflection zeros) is obtained. The method is based on a prototype transversal coupling matrix (N+2, N+2) with source and load connected by a resonant circuit formed by a capacitor in parallel with a frequency-invariant susceptance. To complement the proposed synthesis technique, a method of reconfiguring the transversal coupling matrix as a more practical cross-coupled circuit is outlined. The technique is based on quickly converging gradient optimization with a cost function involving generalized eigenvalues of the transversal coupling matrix and its principal upper and lower submatrices. To illustrate and validate the proposed synthesis procedure, numerical tests have been carried out. Moreover, some aspects of implementation of the resonant connection between source and load were investigated, and experimental verification was performed. A third-order generalized Chebyshev filter with four transmission zeros was designed, fabricated, and tested. The measured results validate the proposed synthesis method.