Finite Frequency Transmission Zeros Research Articles

Synthesis and design of asymmetric cul-de-sac structure HTS filter with transmission zero introduced in Pairs

An asymmetric prototype of a cul-de-sac topology filter to introduce finite frequency transmission zeros (FTZs) in pairs with the least cross-coupling is synthesized and designed in this paper, which is suitable for the design of the high temperature superconducting (HTS) narrowband filter with high selectivity sideband suppression and symmetrical frequency response about the central frequency, especially. The resonator in the cul-de-sac structure filter can adopt the same frequency resonator without self-coupling so that the cul-de-sac structure filter can have fewer coupling coefficients and fewer resonator types. These characteristics of cul-de-sac structure filters are convenient for the design of high-order HTS filters with temperature shifts. A typical 7-order HTS filter with a central frequency of 4000 MHz, 5% relative bandwidth, five coupling coefficients, one cross-coupling, and one pair of FTZs is designed and fabricated on a 0.5 mm-thick MgO wafer with double-sided YBa2Cu3O7 (YBCO) thin films employing this cul-de-sac filter theory. The analyzed frequency response characteristic obtained with full-wave tools of this filter agrees well with the synthesis results and measured results at 77 K (Kelvin temperature).

Wideband Chebyshev Bandpass Filter With Extended Upper Stopband Using Shunt Short-Ended Slotline Stubs

A wideband bandpass filter (BPF) with in-band Chebyshev equal-ripple responses and extended upper stopband is proposed, which is composed of composite microstrip, slotline, and coplanar waveguide (CPW) structure. According to the odd-mode and even-mode equivalent circuits, there are four in-band transmission poles constructing the ultrabroad bandwidth can be directly deduced. In addition, there are two sets of lowpass filter (LPF) embedding in the CPW connecting line to greatly widen the upper stopband without increasing circuit size. In order not to affect original passband Chebyshev equal-ripple responses, the LPFs are synthesized using the low-pass prototype network. Furthermore, there are two finite frequency transmission zeros (TZs) which generated by cross-coupling effects located at lower and upper side of passband to effectively improve the shirt selectivity. Finally, for experimental verification, the proposed BPF prototype is manufactured and tested. Experimental results are consistent with predicted theoretical responses, which verify the validity and feasibility of proposed approach.

New Triple-Resonance Configuration Using Stubbed Waveguide Dual-Mode Cavities

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 TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">102</sub> /TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</sub> 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 TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> 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.

The Extracted-Zero: A Practical Solution for Transmission Zeros in Wideband Filters

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.

Classes of non‐resonating‐node lowpass prototype networks suitable for realisation as evanescent‐mode waveguide bandpass filters

This work presents four classes of lowpass prototype networks comprising non-resonating-nodes (NRNs) realising generalised elliptic function transfer characteristics. Each class of networks can realise a maximum of ( N - 2) finite-frequency transmission zeros where N is the total number of the resonators in the network. The distinct feature pertinent to the proposed classes of networks is that they can be sub-classed into two types: type I networks have positive frequency-invariant elements (FIEs) located at the NRNs, and type II networks have negative FIEs located at the NRNs. type I networks are particularly suitable for the realisation as evanescent-mode waveguide (EMW) bandpass filters which is the main subject of this work, whereas type II networks could be realised as waveguide bandpass filters operating above the cut-off of the guide. Numerical examples of the four classes of the proposed networks are presented. The proposed circuit concepts are validated through the realisation of two classes of filters in EMW technology created utilising computer simulation technology (CST) microwave studio. The electrical performance of the CST filter structures and their circuit counterparts are in close agreement.

Microwave Bandpass Filters Using Re-Entrant Resonators

Design techniques for microwave bandpass filters using re-entrant resonators are presented. The key feature is that each re-entrant resonator in the filter generates a passband resonance and a finite frequency transmission zero above the passband. Thus, an ${ N} {\hbox{th}}$ degree filter can have ${ N}$ finite frequency transmission zeros with a simple physical realization. A physically symmetrical five-pole re-entrant bandpass filter prototype with five transmission zeros above the passband was designed and fabricated. Measured results showed good correspondence with theories.

Transversal directional filters for channel combining

A new concept for the design of power combiners based on matched directional filters is presented. The directional filters consist of individual balanced sections composed of hybrids and single resonators. Each of the sections corresponds to a pole of an all-pass function composed of the sum of S 11 and S 12 of the desired filter transfer function. A simple synthesis method is presented. The filter combiner has the advantage of ease of tunability because each pole is associated with a single resonator. Furthermore, no cross-couplings are required to realise finite frequency transmission zeros. Experimental results for a prototype device are presented.

Low‐pass filter of suspended stripline design with finite transmission zeros for stop‐band rejection improvement

ABSTRACTIn this article, we present the design of the suspended stripline low‐pass filter (LPF) with finite frequency transmission zeros for enhancing band‐edge roll‐off and increasing stop‐band signal rejection levels. The proposed LPF is a seventh‐order circuit which exhibits two transmission zeros in the stop‐band region. The LPF has achieved the benefits of size compactness, low dispersion, high immunity to the noise inference, and low insertion losses. An equivalent circuit model composed of lumped elements is developed to predict filter's characteristics, and ultimately it is used to calculate the LPF's frequency responses during the design. The equivalent circuit model is used to accelerate the proposed LPF design in the early stage with its calculated data validated by a commercial electromagnetic software simulation. Experiment is conducted to verify the LPF's design and its performance. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:297–301, 2014

Miniaturized Bandpass Filter with Mixed Electric and Magnetic Coupling Using Hexagonal Stepped Impedance Resonators

A miniaturized fourth-order direct-coupled bandpass filter with good stopband responses using hexagonal stepped-impedance resonators is presented. Based on the odd- and even-mode equivalent circuits, the resonance characteristics of the hexagonal stepped-impedance resonators with mixed electric/magnetic coupling are investigated. Multiple finite-frequency transmission zeros are realized in the stopband but without introducing either cross-coupling between nonadjacent resonators or source-load coupling between input/output ports. The frequency-dependent coupling matrix of the proposed filter is presented. A new bandpass filter centered at 2.45 GHz with 6.5% fractional bandwidth has been designed and fabricated to verify the validity of the proposed method. The measurement result shows four finite transmission zeros in the stopband, located at 0.98 GHz with 73.14-dB rejection, 2.10 GHz with 48.18-dB rejection, 2.75 GHz with 53.80-dB rejection, 3.12 GHz with 57.08-dB rejection, respectively. The circuit only occupies 15.9 × 9.0 mm2.

Generalized TM Dual-Mode Cavity Filters

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.

Narrowband filters with tightly coupled resonators

The design of narrowband combline filters implemented in double-layered microstrip is presented. The filters realise finite-frequency transmission zeros located within close proximity with respect to their passband edges. This is achieved by tightly coupling the resonators of the filters. Experimental evaluation of several fabricated filters demonstrates the principle.

A novel multilayered cross‐coupled substrate‐integrated waveguide (SIW) circular cavity filter in LTCC

AbstractA novel multilayered cross‐coupled substrate‐integrated waveguide (SIW) circular cavity filter is proposed in this letter. The filter is designed using standard low‐temperature co‐fired ceramic (LTCC) technology, with the fractional bandwidth of 0.25% obtained, can operate at 20 GHz and have two finite frequency transmission zeros at 19.51 and 20.51 GHz, respectively. Measured results show good agreement with simulated results and validate the structure of the proposed filter. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1686–1689, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24435

Design of Quasi-Elliptic Bandpass Filter Based on Slow-Wave Open-Loop Resonators

A microstrip bandpass filter implemented with slow-wave open-loop resonators is described in this letter. The slow-wave open-loop 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 quasi-elliptic filter is fabricated. The quasi-elliptic filter has a compact dimension of 22.1 mm × 21.16 mm, which is approximately 0.1705λg × 0.1634λ g . The experimental results are demonstrated and discussed.

Synthesis and design of in-line N-order filters with N real transmission zeros by means of extracted poles implemented in low-cost rectangular H-plane waveguide

In this paper, an extension to the extracted pole technique for synthesizing N-order filters with N-transmission zeros at real frequencies is presented. In addition, a new bandpass rectangular waveguide H-plane low-cost configuration filter for high-power low-loss application (patent pending) that implements a filtering function with finite real frequency transmission zeros is proposed. This structure operates as a resonant cavity in transmission at central frequency of the bandpass and simultaneously introduces a controlled transmission zero out of the bandpass. Since every double-controlled electrical behavior cavity introduces a transmission zero, it is possible to introduce as many transmission zeros as the order of the filtering function. In order to validate the synthesis procedure and the new structure, different filters have been designed: a second-order filter with two transmission zeros, a third-order filter with one transmission zero, a fourth-order filter with two transmission zeros, and finally, an eighth-order filter with two transmission zeros. The last two have been manufactured, showing an excellent agreement between the measurement and theoretical simulation.

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.

Synthesis of general asymmetric singly- and doubly-terminated cross-coupled filters

A new synthesis is given for the realization of cross-coupled filters in the general asymmetric case, which includes singly terminated filters useful in the design of contiguous multiplexers. The result is obtained by formation of the 2-port transfer matrix of the network, enabling circuit element extractions to be performed from both input and output ports, including the direct extraction of cross-couplings. An example is presented of an 8th degree singly-terminated filter having finite frequency and real axis transmission zeros.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.

Modified Butterworth filters†

A novel class of low-pass filters with zero pass-band loss at the origin and at the fixed frequency near the band-edge and satisfying (n − 2) magnitude flatness conditions at the latter are described. The magnitude characteristics of these filters are superior to those for the Butterworth filters and some other recently introduced classes of low-pass filters. They also compare favourably with Legendre monotonic pass-band filters. The all-pole filter functions of this type are discussed as well as the filter function with finite real frequency transmission zeros exhibiting Chebyshev stop-band attenuation characteristics.

Transitional Butterworth-Legendre filters

A new class of monotonic passband low-pass filters, referred to as transitional Butterworth-Legendre (TBL) filters, is introduced. The closed form expressions of the characteristic functions of these filters depending on one variable parameter q are derived by generalization of the results previously obtained for Legendre sharp cut-off monotonic filters. The parameter q, the values of which are restricted to non-negative integer values (q≤n) controls the number of flatness conditions in the magnitude response at the origin and enables a trade-off between the passband loss and the stopband attenuation of the resulting filters. The Legendre, Halpern and Butterworth filters are shown to be special cases of TBL filters. Only all-pole filter functions are discussed although the results can easily be extended so as to include low-pass filters with finite real frequency transmission zeros.

A Single-Sideband, Disk-Wire Type Mechanical Filter

A mechanical filter with real frequency transmission zeros on the high-frequency side of the passband has been developed. These points of infinite attenuation are produced through the coupling of alternate disk resonators by short lengths of wire. A procedure for designing this type of filter through use of electrical analogies is discussed in some detail. The amplitude and envelope delay characteristics of a presently manufactured 100 kc/s, single-sideband (SSB) filter being used in broadband carrier systems are described. This filter is one of a set of twelve SSB filters having carrier frequencies ranging from 64 kc/s to 108 kc/s. The use of finite frequency transmission zeros has made possible a 30 per cent reduction in differential delay over conventional constant-K models.