Tunable lumped-distributed capacitively-coupled transmission-line filter

A wide tuning range filter is proposed based on lumped-distributed capacitively-coupled transmission lines. The proposed structure maintains a constant inter-resonator coupling factor over a wide centre-frequency tuning range leading to a constant fractional bandwidth design. A bandpass filter with a two-octave tuning range has been designed, fabricated and measured.     

Miniaturized hairpin resonator filters and their application toreceiver front-end MICs

The authors describe the fundamental characteristics of miniaturized hairpin resonators having parallel coupled lines and show their applications to bandpass filters and receiver front-end microwave integrated circuits (MICs). A method for calculating filter coupling parameters using a general-purpose microwave circuit simulator is presented. The bandpass filters have a suitable structure for MICs, and their size is one-half that of conventional hairpin resonators without increasing insertion losses. Trial receiver front-end MICs using these filters have been developed and have shown good characteristics such as low noise and a high image suppression ratio. They are applicable to a frequency range above the L-band     

A unified approach to the design, measurement, and tuning ofcoupled-resonator filters

The concept of coupling coefficients has been a very useful one in the design of small-to-moderate bandwidth microwave filters. It is shown in this paper that the group delay of the input reflection coefficients of sequentially tuned resonators contains all the information necessary to design and tune filters, and that the group-delay value at the center frequency of the filter can be written quite simply in terms of the low-pass prototype values, the LC elements of a bandpass structure, and the coupling coefficients of the inverter coupled filter. This provides an easy method to measure the key elements of a filter, which is confirmed by results presented in this paper. It is also suggested that since the group delay of the reflection coefficient (i.e., the time taken for energy to get in and out of the coupled resonators) is easily measured, it is a useful conceptual alternative to coupling concepts     

Low-loss and compact V-band MEMS-based analog tunable bandpass filters

This paper presents compact V-band MEMS-based analog tunable bandpass filters with improved tuning ranges and low losses. For compact size and wide tuning range, the two-pole filters are designed using the lumped-elements topology with metal-air-metal (MAM) bridge-type capacitors as tuning elements. Capacitive inter-resonator coupling has been employed to minimize the radiation loss, which is the main loss contributor at high frequencies. Two filters have been demonstrated at 50 and 65 GHz. The 65-GHz analog tunable filter showed a frequency tuning bandwidth of 10% (6.5 GHz) with low and flat insertion losses of 3.3 /spl plusmn/ 0.2 dB over the entire tuning range.     

Full-Wave Analysis and Design of Dielectric-Loaded Waveguide Filters Using a State-Space Integral-Equation Method

A full-wave analysis method for waveguide filters based on dielectric loaded resonators is proposed in this work. For such purpose, a state-space integral-equation formulation has been developed, and the efficient numerical evaluation of all matrices and singular integrals related to the method has been detailed. The novel technique has been first validated through the accurate analysis of a dielectric loaded rectangular cavity, and a simple stopband structure based on such basic building block. Then, making use of a computer-aided design tool, a four-pole bandpass filter based on dielectric loaded resonators has been efficiently designed. The accuracy of the proposed method has been validated through successful comparisons with data from technical literature and available commercial software.     

Design of Stepped-Impedance Combline Bandpass Filters With Symmetric Insertion-Loss Response and Wide Stopband Range

An enhanced stepped-impedance combline bandpass filter employs an array of stepped-impedance resonators with tapped-transformer coupling at input and output is presented in this study. This filter has enhanced performance, including symmetric insertion-loss response around the passband and wider stopband range. The structure is compact and suitable for multilayer realization because it is free of lumped capacitors and has fewer via-hole grounds. The circuit is investigated with the characteristic mode theory of coupled lines to prove the existence of multiple transmission zeros around the passband. Numerous diagrams are given for circuit design purposes. The second- and fourth-order bandpass filters at 2.45 GHz were designed, measured, and compared with the conventional combline structure to demonstrate their performance enhancement.     

Novel Dual-Mode Dual-Band Filters Using Coplanar-Waveguide-Fed Ring Resonators

This paper presents a novel approach for designing dual-mode dual-band bandpass filters with independently controlled center frequencies and bandwidths. Two microstrip perturbed ring resonators are employed to obtain dual-mode dual-band responses. Novel feeding structures are introduced to simultaneously feed the ring resonators and conveniently control the coupling strength between resonators and feeding lines, resulting in a wide tunable range of external quality factors. Two kinds of filter configurations with compact size are proposed. Both of them provide sufficient degrees of freedom to satisfy various requirements of external qualify factors and coupling coefficients at both passbands. Therefore, the center frequencies and fractional bandwidths of both passbands can be independently tuned to desired specifications within a wide range. To verify the proposed method, four filters are implemented. The measured results exhibit dual-mode dual-band bandpass responses with high selectivity.     

Hairpin-Line and Hybrid Hairpin-Line/Half-Wave Parallel-Coupled-Line Filters

A new class of microwave filters, hairpin-line and hybrid hairpin-line/half-wave parallel-coupled-line filters, is reported. This class of filters is particularly well suited for microstrip and TEM printed-circuit realizations because grounding of the filter resonators is generally not required. Hairpin-line filters have been divided into two types. The first (Type A) is characterized by having its input and output lines open-circuited at their ends. The Type A filter has been found to yield practical impedance levels for narrow to approximately 25-percent bandwidths. The second (Type B) is characterized by having its input and output lines short-circuited at their ends. However, because of space limitations, details of the Type B filter are not presented in this paper. Theoretical background and design equations for Type A bandpass filters are presented. Experimental data for several stripline filters of 5- and 20-percent bandwidths are given. Experimental results for two microwave-integrated-circuit (MIC) filters are discussed.     

Dual-mode quasi-elliptic-function bandpass filters using ringresonators with enhanced-coupling tuning stubs

A novel microwave dual-mode quasi-elliptic-function bandpass filter structure has been designed and fabricated. The filter uses L-shaped coupling arms for enhanced coupling and dual-mode excitation. The effects of varying the length of tuning stubs and gap size between tuning stubs and ring resonator have been studied. Filters using multiple cascaded ring resonators with high rejection band are presented. The new filters have been verified by simulation and measurement with good agreement     

Compact, low insertion loss, sharp rejection wideband bandpassfilters using dual-mode ring resonators with tuning stubs

Novel wideband bandpass filters using dual-mode ring resonators with orthogonal direct-connected feed lines and tuning stubs are developed. The tuning stubs act as series resonators and provide sharp rejections for the filters. Also, a perturbation stub in each ring influences the fields of the ring resonators and generates a dual mode to extend the stop bands of the filters. The simulated and measured results agree well. This novel bandpass filter has advantages of compact size, low insertion loss, and sharp rejection     

Design of dielectric-filled cavity filters with ultrawide stopband Characteristics

A methodology is presented for the design of small cavity filters, relying entirely on the use of commercial general-purpose design software. Pertinent filter structures comprise resonated segments of ridge waveguide with evanescent-mode inter-resonator coupling sections, supplemented by impedance-transforming port networks. The ridge and evanescent-mode waveguide segments combine to form a metal-clad dielectric core made of either a single dielectric or a composite material. A parameterized equivalent-circuit model is used to describe each segment based on numerical three-dimensional electromagnetic field analyses. For a bandpass filter, the technique yields low passband insertion loss, an ultrawide upper stopband region, and excellent power handling. The approach provides the option to fabricate structures at low per-unit cost with the help of newly available moldable dielectric materials. The efficacy of the technique is demonstrated with an experimental 1-1.45-GHz bandpass filter.     

Features of the coupling coefficients of planar stepped-impedance resonators at higher resonance frequencies and application of such resonators for suppression of spurious passbands

Features of the electromagnetic coupling coefficients between stepped-impedance resonators made of the sections of symmetric strip and microstrip transmission lines at higher resonance frequencies are investigated. It is found that, in stripline resonators, these coefficients are equal to zero at some coordinates of the jump of the characteristic impedance. A new method of expansion of the stopband of bandpass filters, which is based on suppression of the first spurious bandpass and frequency diversity of the main band and the second spurious bandpass is proposed. A Chebyshev bandpass filter with a center frequency of 2.45 Hz and a spurious band at 6.06 f ₀ is manufactured and tested to demonstrate the proposed method.     

Bandpass filters using dual-mode and quad-mode Mobius resonators

Compact bandpass filters are being developed using Mobius wire-loaded cavity resonators. Initial results on tuned filters indicate that excellent filter characteristics can be attained in devices that are significantly smaller than traditional wire-loaded cavity technologies. A novel quad-mode Mobius resonator is presented which occupies the same volume as a dual-mode Mobius resonator. A four-pole bandpass filter is demonstrated using a single quad-mode Mobius resonator. Precisely controlled dielectric loading of dual-mode Mobius wire resonators has been implemented to realize bandpass filters. Two-pole and four-pole bandpass filters are demonstrated using one and two dual-mode dielectric-loaded Mobius resonators, respectively     

Design of microstrip bandpass filters with multiorder spurious-mode suppression

This paper proposes a bandpass filter design method for suppressing spurious responses in the stopband by choosing the constitutive resonators with the same fundamental frequency, but staggered higher order resonant frequencies. The design concept is demonstrated by a four-pole parallel-coupled Chebyshev bandpass filter and a compact four-pole cross-coupled elliptic-type bandpass filter. Each filter is composed of four different stepped-impedance resonators (SIRs) for which a general design guideline has been provided in order to have the same fundamental frequency and different spurious frequencies by proper adjusting the impedance and length ratios of the SIR. Being based on knowledge of the coupling coefficients and following the traditional design procedure, the resultant filter structures are simple and easy to synthesize. The measured results are in good agreement with the simulated predictions, showing that better than -30-dB rejection levels in the stopband up to 5.4f/sub 0/ and 8.2f/sub 0/ are achieved by the Chebyshev and quasi-elliptic filters, respectively.     

Compact superconducting coplanar meander line filters

Novel slow-wave coplanar waveguide (CPW) filters using high temperature superconductor (HTS) films are presented. Both half-wavelength and quarter-wavelength resonators are used in the filter topology. The miniaturisation is achieved using meander structure and interdigital grounding lines. A 3-pole Chebyshev bandpass filter has been designed, fabricated and studied. The untuned experimental results are in very good agreement with the simulated responses.     

Compact size and low insertion loss Chebyshev-function bandpassfilters using dual-mode patch resonators

A compact Chebyshev-function bandpass filter using dual-mode patch resonators is proposed. The filter presents 75% size reduction compared with the conventional Chebyshev bandpass filter using two square patch resonators. Because of inset feeding and only one coupling gap being required, the new filters can achieve a low insertion loss of 1.1 dB and reduce the fabrication uncertainties     

Angular bandpass filters: an alternative viewpoint gives improveddesign flexibility

An alternative approach for the design of angular bandpass filters composed of metal strip gratings is proposed. In the classic approach, frequency selective surfaces (gratings) are used as resonant elements and the spacing between them is adjusted to obtain the required electrical performance. Following this implementation, however, the electrical coupling to the individual resonators can not be fully controlled so that very limited design freedom is obtained. Following the approach that we propose, the resonant element is the spacing between surfaces while the individual grating geometries are adjusted to obtain the required inter-resonator couplings. With this arrangement the structure becomes effectively equivalent to a closed waveguide filter, all electrical parameters of interest can be individually controlled and considerably extended design freedom is achieved. The basic resonator performance is analyzed and complete filter design examples are discussed. Furthermore, it is shown that, following the approach proposed, the frequency behavior of the structure is completely decoupled from its angular behavior in the design process thereby further extending the design freedom     

微波线性相位环状微带滤波器

介绍了一种结构新颖、插入损耗小,且具有优异线性相位的环状微带线滤波器。该滤波器采用数个环形谐振器平行耦合,而输入输出馈线与环形谐振器之间采用直接耦合。文中列举了中心频率为8.6GHz的三环、四环和五环三种不同的滤波器,并对其进行了仿真模拟和结果比较。     

Simplified Equivalent Representations for Multicoupled Lines and Their Application to Filter Design

This paper preaents simplified lumped-type equivalent representations, which are equivalent to multiwire lines in the vicinity of a quarter-wavelength frequency. It is believed that the derived representation can easily be applied to the analysis and the design of coupled-line filters and directional couplers of narrow bandwidths composed of quarter-wavelength strips. In this paper, the general design methad for coupled-line bandpass filters is presented as one of the applications. A new bandpass filter is proposed and the design formulas of the filter are derived by using the design method. Furthermore the range of validity of the derived representations has been checked by showing numerical design examples. They have been found to give excellent results for coupled-line filters of bandwidths up to about 30 percent.     

Novel Folded Waveguide Resonator Filter Using Slot Technique

This letter presents a primary investigation into developing a compact and low-loss bandpass filter using novel folded-waveguide resonators with a footprint reduction. A slot coupling between adjacent resonators is introduced, which is characterized using full-wave electromagnetic simulations and verified experimentally. Two two-pole folded-waveguide resonator filters of this type have been designed, fabricated and tested. Simulation and measurement results are presented to validate the design and to show the advantages of this type of filter.