Design Of Microwave Bandpass Filters Research Articles

Frequency-Variant Double-Zero Single-Pole Reactive Coupling Networks for Coupled-Resonator Microwave Bandpass Filters

In this work, a family of frequency-variant reactive coupling (FVRCAFVC) networks is introduced and discussed as new building blocks for the synthesis of coupled-resonator bandpass filters with real or complex transmission zeros (TZs). The FVRCAFVC is a type of nonideal frequency-dependent inverter that has nonzero elements on the diagonal of the impedance matrix, along with a nonlinear frequency-variation profile of its transimpedance parameter. The distinctive feature of these new FVRCsAFVC is that they can be modeled with a simple bridged-T network consisting of four reactive elements. Such FVRCsAFVCs can introduce one pole and up to two TZs—so that they are referred to as double-zero single-pole (DZSP) networks. DZSP networks allow the pole to be located above, below, or in-between the TZs. Depending on the choice of the elements in the bridged-T circuit, the position of the TZs and the pole can be controlled independently. The coupling matrix for filters with DZSP networks can be found by solving an inverse-structured nonlinear eigenvalue problem (ISNEVP). Examples of possible implementations of DZSP couplingAFVC networks are provided for both lumped and quasi-lumped-element circuits, as well as for transmission-line-based and waveguide technologies. The application of DZSP coupling networks to the design of microwave bandpass filters with generalized Chebyshev-type characteristics is illustrated by means of the synthesis of three microstrips and two waveguide coupled-resonator bandpass filters. The waveguide filters are verified through electromagnetic (EM) simulations and the microstrip filters are manufactured and characterized for proof-of-concept demonstration purposes, showing a fairly close agreement between EM simulations and measurements.

The Design of Microwave Bandpass Filters Using Resonators With Nonuniform$ Q$

With the exception of predistortion, most design methods for microwave filters are based on lossless prototype networks, with the effects of loss generally being considered afterwards, by analysis rather than synthesis. This paper presents new techniques, which either utilize existing losses, or add losses, to improve the performance of microwave bandpass filters. Unlike predistortion, these new techniques result in networks with nonuniform dissipation. Experimental prototype filters have been designed and the measured results demonstrate improved performance compared with that previously reported

Using the branch-line directional coupler in the design of microwave bandpass filters

This paper addresses the application of the branch-line directional coupler to the design of microwave bandpass filters. The basic idea consists of using the branch-line coupler as a transversal filtering section by loading the coupled ports of the coupler with suitable transmission-line segments ending in an open circuit and taking the isolated port as the output node. Thus, under the signal interference philosophy involved in classic transversal filter schemes, bandpass transfer functions with perceptible stopbands and sharp cutoff slopes are derived. Furthermore, the main characteristics of the synthesized filtering response, such as the bandwidth or the position of the out-of-band power transmission zeros, can be easily controlled by means of the design parameters of the transversal section. Hence, a large variety of bandpass filtering profiles different from those offered by classical filter schemes can be realized. Finally, the experimental usefulness of the transversal filtering section based on the branch-line coupler is proven with the design and construction in microstrip technology of two microwave bandpass filter prototypes at 5 GHz.

Finite-Element Modeling for the Design Optimization of Microwave Filters

This paper outlines an electromagnetic optimization technique dedicated to the design of microwave bandpass filters. The purpose is to determine the optimal dimensions of the electromagnetic model. Applying this technique, the geometrical dimensions of the distributed structure are accurately determined, and no experimental readjustment is necessary. The optimization procedure combines an electromagnetic analysis and a parameter extraction. The analysis method is a finite-element modeling coupled with a frequency parameterization technique for improving the computation time. The parameter extraction method is based on the approximation of the simulated scattering matrix and on the synthesis of the equivalent electrical network. The comparison between extracted and ideal networks enables to converge the optimal dimensions. The procedure is applied to design a dual-mode waveguide filter. In this case, within the electromagnetic model, the screws are taken into account using lumped elements which may be adjusted independently.

Modified method for the analysis and design of microwave bandpass filters containing dielectric resonators

High-Q dielectric resonators having remarkable advantages such as compactness, light weight, temperature stability, and low cost have become very valuable elements for various microwave circuits. A modified Itoh and Rudokas model is proposed to analyse the field distribution and the coupling relations between dielectric resonators and microstrip lines based on the analysis results, a convenient procedure for designing microwave filters containing parallel coupled dielectric resonators is presented. Two experimental dielectric resonator filters are also fabricated to verify the calculation and the design procedure. The outcome demonstrates that the procedure provides good accuracy and saves design time.