Narrow-Band Stripline or Microstrip Filters with Transmission Zeros at Real and Imaginary Frequencies

Simple approximate design equations are derived in this paper for an even degree (n /spl ges/ 6) low-pass inverter capacitance prototype filter having single transmission zeros at both real and imaginary frecuencies. This is achieved by utilizing one or two additional couplings. The transmission zeros improve considerably the passband group delay and increase the skirt selectivity compared to those of the ordinary Chebyshev prototype. An exact and more complicated method based on the known generalized Chebyshev rational function approximation is also presented for the comparison. The prototype with one additional coupling is utilized to realize narrow-bandpass printed circuit filters consisting of half-wave resonators.     

An original approach to the design of bandpass cavity filters withmultiple couplings

A novel approach to the design of general cavity filters with each cavity coupled to an arbitrary number of other cavities is presented. This approach is based on a suitable characterization of the filter structure which does not require one to model separately the cavities (resonators) and the coupling elements. Suitably defined equivalent admittances are associated with each cavity allowing one to design the filter structure once the parameters of a suitable low-pass prototype are given; an efficient procedure for the synthesis of such a prototype with equiripple passband response is also presented which allows one to arbitrarily prescribe transmission zeros placed in the complex plane (even asymmetrically). The described design approach is particularly convenient when the filter structure does not allow a simple modeling of the resonators and coupling elements separately. This is the case of slot-coupled cavity filters and of filter structures based on arrays of coupled transmission lines. It is also shown that the simplified design approach often adopted in the past, where only two coupled cavities at a time are considered, can produce large errors even in the case of filters with all attenuation poles at infinity (i.e., two couplings per cavity)     

A new compact microstrip two-layer bandpass filter using aperture-coupled SIR-hairpin resonators with transmission zeros

A new design of a compact two-layer bandpass filter using aperture-coupled microstrip stepped-impedance hairpin resonators is proposed and investigated in this paper. The proposed filter is composed of four stepped-impedance hairpin resonators located on two stacked microstrip layers, and the couplings between the resonators on the upper layer and those on the lower one are obtained by using three coupling apertures etched on a common ground plane placed between the two layers. In addition, the use of tapped input/output couplings allow this bandpass filter to generate two independent transmission zeros. A full-wave simulator is used to design the proposed structure and calculate the aperture coupling coefficients. With this two-layer configuration, the proposed filter becomes very compact and occupies a small space. To demonstrate the proposed design, a four-order bandpass-filter prototype was designed, fabricated, and tested at 2.14 GHz. Furthermore, a single-layer filter prototype was also designed and fabricated at the same frequency band and then compared to the first one. As a result, a significant reduction of approximately 50% was achieved. These features make the proposed structure suitable for compact and high-performance circuit component designs in microwave circuits.     

Synthesis of prototype filters with triplet sections starting fromsource and load

Describes a method for synthesizing an inline prototype filter with a triplet section starting from source and/or from load. This topology allows placing one or two transmission zeros without using cross-couplings inside the filter (it is only required to couple the source (or the load) to the first (or the last) two resonators). The proposed method employs the coupling matrix of a generic prototype, obtained through well-established procedures; then, the coupling matrix of the desired inline topology is determined with a procedure based on multiple matrix rotations (similarity transforms) and numerical optimization     

General Extracted Pole Synthesis Technique with Applications to Low-Loss TE/sub011/ Mode Filters

A novel synthesis technique is developed for two-port networks which possess finite real frequency transmission zeros. The low-pass prototype is synthesized in the form of a network with complex conjugate symmetry where the real frequency transmission zeros are extracted from both ends and realized by simple resonators separated by phase shifters. The remaining transmission zeros are realized by the central part of the filter in the form of a cross-coupled double array. This prototype is particularly suitable for designing waveguides bandpass filters and each real frequency transmission zero is independently tunable. Furthermore, in the case of the most complex transfer function with all possible types of transmission zeros, the realization requires only one type of coupling which is necessary in the important case of TE/sub011/ cylindrical mode cavity resonators. The general synthesis technique is given and the process illustrated by a nontrival example. Additionally, from the results of a computer program based upon the synthesis techniques, the important differences between the possible prototype forms for the same transfer function resulting from extracting the transmission zeros in different orders are cited.     

High-Selectivity Tunable Planar Combline Filter With Source/Load-Multiresonator Coupling

A tunable planar combline filter exhibiting multiple transmission zeros is reported in this letter. By introducing two new coupled lines, the source/load-multiresonator coupling phenomenon is obtained without using additional combline resonators. The transmission zero locations can be adjusted by means of the length of these coupled lines to improve the upper stopband rejection. Moreover, all of these transmission zeros can be tuned at the same time as the passband without distorting the filtering-response shape. Parasitic coupling effects of the proposed filter topology and guidelines for their compensation are also discussed. The described combline filter is experimentally validated with the design and manufacture of a three-stage electronically-tunable prototype with five transmission zeros.     

Cross-coupled dual-spiral high-temperature superconducting filter

A microstrip bandpass filter implemented with dual-spiral resonators is described in this letter. The dual-spiral resonators make the filter compact and allow implementation of positive and negative inter-resonator couplings. Implementation of the positive and negative couplings is used to introduce a pair of finite frequency transmission-zeros in the filter response. The two zeros are designed to be close to the passband, thus improving the selectivity of the filter. As an example, a four-stage cross-coupled dual-spiral filter is designed and fabricated using superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films deposited on LaAlO/sub 3/ substrate.     

Compact Planar Quasi-Elliptic Function Filter With Inline Stepped-Impedance Resonators

Compact microstrip bandpass filters of orders N = 4,6, and 8 with quasi-elliptic function responses are synthesized with inline stepped-impedance resonators. The filters have enhanced transition responses since two transmission zeros are generated on both sides of the passband. Existence of these two zeros is investigated by formulating the Y-matrix of the equivalent circuit for the filter and taking adjacent and nonadjacent coupling into account. Some matrix elements Y_j,j+2 representing coupling between two nonadjacent resonators are shown to have the opposite signs in both the lower and upper sides of the center frequency. This property leads to creation of the two transmission zeros on both sides of the passband. It is demonstrated that one more zero can be created in the rejection band by the tapped-line input/output scheme. Experimental circuits on substrates with epsiv_r = 2.2 and 10.2 are measured to validate the theory and design.     

A Miniaturized Conductor-Backed Slot-Line Resonator Filter With Two Transmission Zeros

In this letter, a miniaturized planar two-pole microwave filter with two transmission zeros is presented. The building block of this filter is a high-Q double spiral slot resonator backed by a conductor plane. The provision of a float back conductor plane allows vertical integration of this filter with other passive and active RF electronic components usually found in miniaturized wireless transceivers. The conductor plane also provides a coupling mechanism between the input and output of the filter giving rise to transmission zeros. It is shown that the location of transmission zeros can easily be adjusted and significant out-of-band rejection be achieved using only two miniaturized double-spiral resonators. The design procedure and fabrication of a two-pole filter operating at 2.11GHz is demonstrated and a very good agreement between measured and simulated results is shown     

Modified parallel-coupled filter with two independently controllable upper stopband transmission zeros

A microstrip cross-coupled filter with two independently controllable transmission zeros on upper stopband is presented. The initial filter structure is a conventional Chebyshev-response parallel-coupled filter that can be easily realized by the analytical method. The newly proposed coupling/shielding lines can effectively control the cross and main couplings without changing the original filter layout. This approach allows a designer to eliminate the tedious segmentation method, which is usually used to establish the relation between the coupling coefficient and physical distance between resonators. A three-order filter is designed and fabricated for demonstration.     

Novel design possibilities for dual-mode filters without intracavity couplings

This letter presents coupling schemes and design guidelines for dual-mode filters without intracavity couplings. Examples of filters of orders two and four are presented to document the flexibility of these solutions. These coupling schemes allow the change of transmission zeros from either side of the passband to the other by only detuning the resonators and without changing the coupling coefficients.     

Analysis of electric coupling between slotted cylindrical ringresonators

Electric coupling necessary for realising filters with transmission zeros is investigated for slotted cylindrical ring (SCR) resonators. The transmission line matrix (TLM) method is applied to the analysis of couplings between these resonators. Typical coupling curves of practical importance are presented, which help in the design of SCR resonator filters     

A universal building block for advanced modular design of microwave filters

A universal building block for modular design of microwave filters is introduced. The second order block contains two resonators which are not coupled to each other. By adjusting the strengths and signs of its coupling coefficients, the block can be used to design bandpass, bandstop and linear-phase filters. For bandpass filters, Chebychev as well as symmetric and asymmetric pseudo-elliptic responses with one or two finite transmission zeros can be designed. For linear-phase filters, two finite transmission zeros can placed practically anywhere in the complex plane as long as the realizability condition is met. Bandstop filters with no finite reflection zeros as well as symmetric and asymmetric pseudo-elliptic responses with one or two finite reflection zeros can be achieved by the same building block. The block is so flexible it can even generate bandstop responses with complex finite reflection zeros for group delay control. Higher order filters are designed modularly by cascading the appropriate number of building blocks. Coupling matrices of a number of cases are presented to demonstrate the flexibility and the universality of the building block.     

Dual-Band Bandpass Filter Design Using a Novel Feed Scheme

A planar dual-band bandpass filter based on a novel feed scheme is presented in this letter. The proposed filter employs two sets of resonators operating at diverse frequencies to generate two passbands. A novel scheme is introduced to feed the resonators. One set of resonators is utilized to not only generate the lower passband but also feed other resonators. Source-load coupling for upper passband is inherently realized. This scheme provides sufficient degrees of freedom to control the center frequencies and bandwidth of the two passbands. Four transmission zeros can be created close to passband edges, resulting in high skirt selectivity. To validate the proposed idea, a demonstration filter is implemented. The design methodology, filter sensitivity and experimental results are presented.      

Implementing transmission zeros in inductive-window bandpassfilters

Transmission zeros are usually implemented in microwave filters as extracted poles, or with cross couplings between nonadjacent cavities. Recent work, however, indicates that, for inductive band-pass filters, higher order-mode excitation can be usefully exploited for the purpose of creating transmission zeros. In this paper we describe a new cavity configuration that can be used to introduce transmission zeros in the electrical performance of microwave filters based on thick inductive windows in rectangular waveguides using the higher order-mode interactions. One transmission zero per filter cavity can be introduced and its frequency location can be easily controlled adjusting suitable geometrical parameters. The basic principle is discussed in detail and a computer aided design procedure is also presented. Finally, several application examples are included indicating how the new cavity design can indeed be used to improve the performance of this class of filters     

A Compact Open-Loop Filter With Mixed Electric and Magnetic Coupling

A novel cascaded microstrip open-loop resonator filter with controllable electric and magnetic mixed coupling is presented to have one or more transmission zeros. For two coupled resonators, the coupled sides with the maximum magnetic field are combined with their open gaps with the maximum electric field, creating the electric and magnetic mixed coupling. By adjusting the distances between resonators and the positions of open gaps in a mixed coupled filter, the coupling coefficients can be changed, and controllable transmission zeros can be produced in the lower stopband, upper stopband, or both. Design and fabrication of the proposed second-and fourth-order filters show the advantages: such as a smaller number of resonators, higher rejection level, as well as asymmetrical response; moreover, the location of the transmission zeros can be precisely controlled.     

Novel Patch-Via-Spiral Resonators for the Development of Miniaturized Bandpass Filters With Transmission Zeros

A novel patch-via-spiral resonator based on the dual-metal-plane configuration is proposed and examined. With the microstrip patch on the top plane serving as a capacitor and linking to the quasi-lumped spiral inductor on the bottom plane through a connecting via, the proposed dual-plane resonator structure located on the opposite sides of the single substrate may form a miniaturized one in the printed-circuit board fabrication. By suitably combining the proposed patch-via-spiral resonators, useful coupled-resonator pairs may be constructed to simultaneously provide electric and magnetic couplings. Based on these coupled-resonator pairs, a second-order bandpass filter with multiple transmission zeros is realized without requiring either the cross-coupled path or the source-load coupling. For design purpose, the equivalent-circuit model is also derived and verified. In this study, a fourth-order patch-via-spiral bandpass filter with both good passband selectivity and miniaturized size of only 22.14 mm times5.08 mm (i.e., 0.188lambda_g0times0.043lambda_g0) is implemented, where lambda_g0 denotes the guided wavelength of the 50-Omega microstrip line at center frequency     

Design of generalized Chebyshev filters with asymmetrically located transmission zeros

A simple design technique is introduced for generalized Chebyshev filters with asymmetrically located transmission zeros. The efficient and exact procedure is given for the calculation of transmission zeros for a class of generalized Chebyshev low-pass prototype filters with a maximum of four asymmetrically located transmission zeros of any multiplicity. This technique is based on obtaining the frequencies of magnitude characteristic extreme values in closed form, and after this, transmission zeros can be calculated by solving a system of nonlinear equations. Novel formulas for orders of zeros of maximally selective filters with equiripple characteristics in the passband and stopband are deduced. The obtained results are verified and illustrated by given examples.     

Complementary split ring resonators for microstrip diplexer design

A new topology for the design of microstrip microwave diplexers, based on the use of quasi-lumped resonators, is presented. Specifically, the receiver (Rx) and transmitter (Tx) filters of the diplexer are implemented by etching complementary split ring resonators (CSRRs) in the ground plane as well as series capacitive gaps and shunt inductive strips in the upper metal level. By this means, narrowband microwave diplexers with transmission zeros can be synthesised, which allow for the improvement of Rx/Tx isolation. A prototype device operative in the 2.4-3.0 GHz frequency band is presented. Measured insertion losses are lower than 2 dB while the isolation between Rx/Tx channels is in the vicinity of 40 dB. Diplexer dimensions (29.8/spl times/16.3 mm), which are small on account of the semi-lumped resonators employed, and performance point to the practical application of these structures in communication transceiver front-ends.     

A novel mixed E–M coupled filter with adjustable transmission zeros

In this article, a novel idea to introduce two coupling paths including one electric coupling and one mixed electric and magnetic coupling between adjacent resonators is proposed. Theoretical exploration based on equivalent circuit model reveals that two adjustable finite transmission zeros can be generated to improve filter performances as the result of the interaction of the two paths for either electric domain or magnetic domain coupling. As an example, a microstrip filter is designed, fabricated and measured using the proposed configuration. The measure results validate and confirm the feasibility of the proposed design methodology.