Produce Transmission Zeros Research Articles

Substrate Integrated Waveguide Filter With Flexible Mixed Coupling

This article investigates flexibly using mixed coupling in substrate integrated waveguide (SIW) filters to efficiently improve selectivity. To this end, a mixed coupling structure is proposed, which can be used as a universal coupling module to efficiently produce transmission zeros (TZs) in an inline/conventional SIW filter without degrading the superiority of SIW. On this basis, a trisection with mixed cross-coupling is further proposed, which encloses all the structures inside two general SIW cavities and can be used as a universal cavity module to efficiently produce a quasi-elliptic response in an inline/conventional SIW filter without degrading the superiority of SIW. Three prototypes are designed, fabricated, and measured, and the results agree with the expectations well. The proposed techniques should facilitate the development of high-performance SIW filters in microwave/wireless circuits and systems.

Design of a high-order narrowband superconducting balanced filter based on asymmetrically coupled stepped-impedance resonators

This study investigates a sixth-order narrowband superconducting balanced filter with high frequency selectivity and wide stopband based on asymmetrically coupled stepped-impedance resonators (SIRs). Three types of coupled SIR pairs with different characteristics are investigated. The differential-mode (DM) phase shifts, coupling coefficients, and common-mode (CM) levels of the three SIR pairs are then analyzed. The spurious frequencies of DM responses can be pushed far away from the fundamental frequency to widen the stopband by properly choosing the impedance ratio of the SIR and using dissimilar SIRs with dispersed harmonics. Moreover, an inherent CM suppression can also be obtained because of the different resonant frequencies in DM and CM equivalent circuits. Results also show that the electromagnetic coupling pair can contribute a weak coupling coefficient for narrowband design without increasing the circuit size. The structure of the electric coupling pair is beneficial for high-order circuit interconnection. The magnetic coupling pair possesses the highest CM rejection. Moreover, the weak coupling properties are well-utilized for narrowband design. For validation, a sixth-order balanced bandpass filter is designed using the three coupled SIR pairs, and a cross-coupling structure is further introduced to produce transmission zeros (TZs) and enhance the passband selectivity. The magnitude and phase delay of the DM transmission paths are analytically illustrated to explain the TZ production. Eventually, the proposed balanced filter is implemented by a high-temperature superconducting technique to reduce the insertion losses and is measured at the temperature of 77 K. The measured results show that the fractional bandwidth of the passband is 1.6$%$ with less than 0.37 dB in-band insertion loss. The $-60$ dB bandwidth/$-3$ dB bandwidth rectangle ratio is less than 1.45 while the in-band CM suppression is better than 40 dB. The $-$20 dBłinebreak stopband is up to about 5$f_{0}^{d}$ ($f_{0}^{d}$ is the DM fundamental frequency).

Substrate‐integrated waveguide filtering crossovers with improved selectivity

Two substrate-integrated waveguide (SIW) filtering crossovers with high selectivity are presented. The orthogonal degenerate TE201 and TE102 modes in center square cavity are employed to realize the cross transmission and channel isolation. The offset coupling positions are then exploited for surrounding TE101-mode rectangular cavities to produce transmission zeros (TZs) above the passband in the first crossover design or for TE201-mode oversized rectangular cavities to generate one TZ on each side of the passband in the second crossover design. The footprint of first crossover has greatly been reduced, while the selectivity of both crossovers has been greatly improved. Two prototypes centered at 20 GHz are designed, fabricated, and tested for demonstration, showing good agreement between the simulated and measured results.

Multilayer SIW Dual-Band Filters with Independent Band Characteristics and High Selectivity

Abstract This work presents an approach to developing dual-mode dual-band substrate integrated waveguide (SIW) bandpass filter based on multilayer process. TE102/TE201 and TE101/TE102 modes are used to feature the two passbands, respectively. To begin with, large range of band location ratios are decided by the effective dimension of the SIW resonator. With reference to the field distribution, independent coupling schemes of the dual-modes are then realized by slots or circular apertures etched on the middle metal layer. It allows to not only introduce a large design freedom of bandwidth but also keep compactness. Finally, source-load and mixed couplings are deployed to produce transmission zeros around the passband in providing a sharp selectivity in the two filters, respectively. The details to independently control the center frequencies and bandwidth of two passbands are also presented. A two-order double-layered and a triple-layered SIW dual-band bandpass filter are prototyped to evaluate the proposed design approach, respectively. Results show a good agreement between simulations and measurements. The proposed filter exhibits flexible design freedom, high selectivity as well as good out-of-band rejection.

A Lowpass Filter Design Using Curved and Fountain Shaped Resonators

AbstractIn this paper a new lowpass filter (LPF) with curved line resonators and fountain shaped resonators is proposed. The proposed filter has achieved wide stopband, compact size, sharp roll-off rate and low return loss. Two tapered resonators are used to produce transmission zeros and widen the stopband. Also, a fountain shaped resonator is proposed using curved transmission lines to obtain good sharpness in the filter response. The cut-off frequency of the designed LPF is 1.74 GHz and the overall size of the designed LPF is 0.135 λg × 0.132 λgwhere λgis the guided wavelength at the cut-off frequency. The results show that the overall size of the lowpass filter could be reduced using curved line resonators and curved transmission lines.

Wide‐stopband and high selectivity step impedance resonator bandpass filter using T‐network and antiparallel coupled line

A wide-stopband attenuation with high-selectivity step impedance resonator (SIR) bandpass filter (BPF) is presented in this study. The T-network stubs are used to produce transmission zeros (TZs) close to the centre frequency ( f 0 ) with a high-selectivity. Moreover, the antiparallel coupled lines can produce a TZ at spurious frequency of conventional SIR BPF for all step impedance ratio ( K ). For the validation, a half-wavelength ( λ /2) SIR BPF with T-network stubs at the input/output ports was designed at f 0 of 2.6 GHz. From the experiment, the insertion and return losses at f 0 were determined to be 0.91 and 21.25 dB, respectively. The insertion and return losses were better than 1.1 and 16.5 dB, respectively, of the 180 MHz bandwidth. The TZ frequencies ( fZ 1 , fZ 2 , and fZ 3 ) were located at 1.69 GHz (0.63 f 0 ), 2.98 GHz (1.12 f 0 ), and 3.17 GHz (1.19 f 0 ), respectively, with a high selectivity. The stopband attenuation was better than 25 dB from DC to 2.23 GHz and from 2.89 to 9.82 GHz.

Design of Quasi-Elliptic Bandpass Filter for Substrate Integrated Waveguide (SIW) Using Cross Coupling Technique

<p>This paper proposes a quasi-elliptic band pass filter in substrate integrated waveguide (SIW) by using cross coupling technique to produce transmission zeros (TZs) at both side. Finally, a fourth pole SIW quasi-elliptic filter at 5.75 GHz is designed in single layer substrate. Simulation results show that the filter has a center frequency of 5.75 GHz with the bandwidth of 100 MHz. The minimum insertion loss in the passband is 0.3 dB, and the return loss is better than 20 dB. Due to the TZs, the SIW filter has rapid transition performance at both lower and upper sidebands, good selectivity is achieved, while the SIW filter presents a very compact implementation and good<br />spurious rejection.</p>

A novel triple‐band bandpass filter based on equilateral triangle substrate integrated waveguide

AbstractA novel compact triple‐mode triple‐band bandpass filter (TB‐BPF) based on equilateral triangle substrate integrated waveguide is first proposed. The first passband response is achieved by the fundamental modes of the first and third cavities. To obtain the second and third passbands, a new postperturbation method is proposed. And based on it, the perturbed TM101 and TM201 modes of the second cavity can couple with TM102 modes of first and third cavities via inductive window, respectively. By adjusting the width of the inductive window, the second and third passbands can be achieved. Source‐load coupling and complementary split‐ring resonators (CSRRs) are introduced to produce transmission zeros (TZs). Total eight TZs are obtained, which highly improve the performance of the out‐of‐band. Finally, a TB‐BPF is designed, fabricated, and measured. The simulated and measured results show good agreement.

$K$ -Band Substrate-Integrated Waveguide Filter Using TM21 Mode With Enhanced Stopband Attenuation

In this letter, we present a method for enhancing the stopband attenuation performance of a $K$ -band TM21 mode filter using substrate-integrated waveguide resonators. To improve the stopband response, we suppress and move spurious resonant peaks and produce transmission zeros. The step-by-step procedure of the proposed three-step method is shown in detail. The measurements show that when using the presented method, the filters exhibit better stopband performances than those in which the presented steps are not followed.

Compact quad‐band bandpass filter based on sextuple‐mode stepped impedance stub‐loaded resonator

A novel compact quad-band bandpass filter (BPF) with multi-transmission zeros is proposed. This filter utilises a sextuple-mode impedance resonator to achieve three passbands, and the fourth passband composes of single-end short-circuited resonators. Adopting an embedded and folded structure is employed to realise miniaturisation. Stub–stub coupling is introduced to produce transmission zeros, which can improve the passband selectivity. Finally, a quad-band BPF centring at 0.9/1.45/2.45/3.5 GHz is designed, fabricated and measured. The measured results have good agreement with the simulated ones.

Analysis of transmission zeros for coaxial filter with capacitive cross coupling

ABSTRACTCross coupling filters have been paid attention in reducing volume and improving stopband attenuation. The structures are designed by coupling matrix, which are based on known transmission zeros. This article describes a new design method to produce transmission zeros in the stopband. The production of transmission zeros is accomplished by inserting a wire into the inner holes of nonadjacent coaxial resonators. A cross coupling capacitor is formed between the metal wire wrapped with plastic and inner conductor of coaxial resonators. The transmission zeros of the filters are obtained by analysing the scattering parameter of the equivalent circuits, which only include resonator(s) with cross coupling capacitor, it is a new method being different from the others published. The transmission zeros can be calculated directly and are not set in advance. The results indicated that positions of transmission zeros are determined by coupling between adjacent resonators and position of cross coupling. The third-order filter with transmission zero in the lower stopband and the fourth-order filter with transmission zero in both stopbands are designed and fabricated using ceramics. The validity of this design approach is demonstrated by computer simulations. The measured results of transmission zeros closely agree with the simulated ones and the calculated values.

Advanced lumped-element filters for digital microwave power amplifiers

In this paper, two compact lumped-element band pass reconstruction filters for digital microwave power amplifiers applications in the800 MHzband are presented. The filters, based on the trisection and quartet topologies, include cross-couplings which produce transmission zeros for maximum selectivity, and can be designed with practical element values. In contrast to common filter designs the input impedance characteristic is optimized broadband to values different from50 Ω, as required for proper amplifier operation. Both filters achieve an insertion loss of around0.8 dBand an equiripple bandwidth of240 MHz (trisection)and290 MHz (quartet), respectively, with improved out-of-band suppression. Results show that a considerable improvement in amplifier linearity and efficiency can be obtained with the new proposed filters, as compared with simpler filters traditionally used in power amplifier applications.

A FOLDED SIR CROSS COUPLED WLAN DUAL-BAND FILTER

A compact cross-coupled dual-band bandpass fllter based on folded Stepped Impedance Resonators (SIRs) with four controllable transmission zeros is proposed in this paper. A pair of stepped impedance tapped lines is utilized to improve the dual band impedance matching, which reduces the insertion loss of the fllter; meanwhile the tapped lines are also coupled with non-adjacent resonators to produce transmission zeros to improve skirt characteristics. At the end of this paper, the simulated and measured results are compared with each other, and good agreement is achieved.

High Selective Bandpass Filter Using Inductive‐Coupled Quarter‐Wavelength Stepped‐Impedance Resonators

ABSTRACTA compact microstrip bandpass filter with reduced size and high selectivity is proposed. The inductive‐coupled quarter‐wavelength resonators are studied and used to produce transmission zeros. In addition, quarter‐wavelength stepped‐impedance resonators are adopted to reduce the size of the filter and also to raise the spurious frequency. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:3010–3014, 2013

Switched Delay Line Reconfigurable L‐Band Filter with High Out‐of‐Band Suppression

ABSTRACTA switched delay line reconfigurable filter with high out‐of‐band suppression using double‐behavior resonator (DBR) is presented. The novel filter has features of higher stopband rejection and easy processing compared to the conventional one. The DBR resonator can produce transmission zeros, which obviously improves the out‐of‐band suppression. The prototype of the filter operating at 1G/1.3G/1.6G with 50‐dB suppression is designed and fabricated. The simulated and measured results show good agreement. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2438–2440, 2013

DUAL-BAND BANDPASS FILTER USING A SINGLE SHORT-ENDED DUAL-MODE RESONATOR WITH ADJUSTABLE FIRST PASSBAND

In this paper, a novel dual-band bandpass fllter (BPF) based on a single short-ended dual-mode resonator (SEDMR) is presented. According to the voltage distribution of the resonator, two pairs of loaded open stubs, inside and outside of the resonator, are utilized to tune the center frequency and the external quality factor of the flrst passband respectively, while there is no in∞uence on the second passband. Meanwhile, source-load coupling is introduced to produce transmission zeros to improve the passband selectivity and band-to-band isolation. For demonstration, a dual-band fllter working at 1.52GHz for GPS and 3.5GHz for WiMax is designed, fabricated and measured with insertion losses of 1.47 and 0.95dB. In addition, two transmission zeros, introduced by source-load coupling, located at 2.19 and 2.67GHz between the flrst and second passband improve passband selectivity and band-to-band isolation better than 50dB.

Compact Quadruplet Bandpass Filter Based on Alternative J/K Inverters and $\lambda/4$ Resonators

This letter presents the proposal and synthesis design of a novel compact microstrip quadruplet bandpass filter (BPF) based on alternative J/K inverters and λ/4 resonators. The proposed quadruplet bandpass prototype is firstly derived from the conventional one with lumped LC resonators and the J-inverters. The mainline coupling is implemented by cascading four λ/4 resonators via the alternative J and K inverters, resulting in the achievement of the generalized Chebyshev in-band response. Meanwhile, the first and fourth resonators are cross-coupled via magnetic coupling so as to simultaneously produce transmission zeros below and above the desired passband. Finally, a microstrip quadruplet BPF at 2.5 GHz with a fractional bandwidth of 12.0% is designed, and the measured results of the fabricated filter show consistent match with its theoretical ones.

Dimensional synthesis for wide-band pseudo-elliptic waveguide filters using cavity-backed inverters

This study presents a dimensional synthesis method for the design of wide-band pseudo-elliptic waveguide filters without resorting to global full-wave optimisation. In this approach, the authors introduce and employ two novel cavity-backed inverters, which produce transmission zeros (TZs) in the out-of-band response, however, the frequency response in the passband is similar to that of normal iris inverters. So, the design procedures for the passband and out-of-band filter responses are carried out independently. As design examples, pseudo-elliptic waveguide filters with TZs in the lower and upper frequency bands are designed, respectively. The results show good equal-ripple performance in the passband and improved rejection performance with preset TZs beyond the passband.

Design of Wide-Band Pseudo-Elliptic Waveguide Filters With Cavity-Backed Inverters

This letter presents a method for the design of wide-band pseudo-elliptic waveguide filters without resorting to global full-wave optimization. In this approach, we introduce and employ two novel cavity-backed inverters, which produce transmission zeros in the out-of-band response, however, whose frequency response in the passband is similar to that of normal iris inverters. As a design example, a pseudo-elliptic waveguide filter with transmission zeros in the lower and upper frequency bands are designed and fabricated. The results show good equal-ripple performance in the passband and improved rejection performance with preset transmission zeros beyond the passband.

A compact U‐shaped defected ground structure microstrip low‐pass filter with wideband rejection

AbstractA compact triple U‐shaped slots etched on the microstrip ground are used to implement a novel low‐pass filter.A rectangular open stub and a radius stub are used to produce transmission zeros and thus result in wide stopband. Good low‐pass performance and wide stopband characteristics can be achieved by this new structure. One prototype is fabricated to demonstrate the validity of the design strategies. The simulated and measured results indicate that the insertion loss is less than 0.25 dB and the return loss is less than −16.7 dB in the whole passband. In addition, significant improvement on rejection band can be observed; the stopband bandwidth better than −25 dB is about 105% (from 2.6 to 8.4 GHz). © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 497–499, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24960