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This paper presents a compact multifunctional reconfigurable filter based on double coupled‐line structures with three different filtering modes. Three different working modes of the wideband bandpass filter (BPF), bandstop filter (BSF) and wideband filter with single notch can be switched. One prototype of the reconfigurable filter is constructed and measured. For the wideband BPF mode, the 3‐dB bandwidth is 84.5%with in‐band return loss (RL) higher than 21.5 dB and minimum insertion losses (IL) of 0.9 dB, and rejections for the upper stopband is higher than 22.5 dB. For the wideband filter with single notch mode, the 3‐dB bandwidth is 39.7% and 24.9%, with the minimum in‐band IL of 1.13 dB and 1.5 dB, respectively. The maximum rejections between the two bands are 32 dB, and the upper stop band rejections are higher than 19 dB. For the BSF mode, the 3‐dB bandwidth is 29.6%. [ABSTRACT FROM AUTHOR]

In this paper, a new kind of absorptive bandstop filter composing three series‐coupled lines is designed, investigated, and fabricated. The proposed circuit is indeed a combination of a dual‐band conventional notch filter and a single‐band absorptive filter generating two conventional and an absorptive notch. More precisely, the circuit introduces a fixed absorptive notch at 4.22 GHz and two electronically tunable (approximately 20%) conventional notches at 1.62–2 and 4.71–5.75 GHz, respectively. Besides, the FBWs of the first conventional notch, the second one, and the absorptive notch are 5.5 ± 1, 3.5 ± 1, and 3 ± 1%, respectively. The instantaneous surface current density of the circuit is depicted to investigate the generation of notches. The circuit has a compact size of 44.7 × 11.85 mm2 equaling to 0.489 × 0.129 λg2; moreover, it can successfully absorb more than 98% of the input power at its absorptive notch. [ABSTRACT FROM AUTHOR]

The design and analysis of two defected ground structures (DGS)‐based filters have been proposed in this article. The first is a multifrequency bandstop filter (BSF) which utilizes a semi‐H defect in the ground plane. This structure is then prototyped on a Rogers 4350B substrate of overall size 45 mm × 15 mm with an external SMD capacitors employed to control the resonance of the circuit for the stopband frequencies of 433, 700, and 915 MHz. An equivalent π‐circuit is modified to validate this multiband filter. The second filter is a combination of a BSF and bandpass filter in one structure. The filter operating with a controllable passband and stopband frequency is fabricated on Rogers 4350B lossy substrate. Two SMD capacitors are loaded in the filter structure to control the passband and stopband frequencies of the filter with a structure size of 20 mm x 20 mm. Finally, the equivalent circuit from the BSF is modified further to encompass the bandpass and bandstop frequency response of the proposed work. [ABSTRACT FROM AUTHOR]

Conventional synthesis techniques for general Chebyshev lowpass, highpass, and bandstop filters are usually based on general Chebyshev filtering function, from which lowpass prototype is set up. By applying the lowpass to lowpass, highpass, or bandstop frequency transformation on realization networks of lowpass prototypes, final realization networks of general Chebyshev lowpass, highpass, and bandstop filters are obtained. In this paper, direct synthesis techniques for general Chebyshev lowpass, highpass, and bandstop filters are discussed. Transmission zeros can be placed wherever they are desired to control the performance of the filters. Unlike conventional synthesis techniques, they derive filtering polynomials constituting network parameters directly in the lowpass, highpass, or bandstop domain, which might find applications in analogue and digital filter design. Several examples are presented for demonstration. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Wideband microwave filters cover a wide band of continuous frequencies. In this paper, the design and implementation of an ultra-wideband filter is firstly introduced. In real applications, there might be interference inside the passband of the filter, and it is usually necessary to suppress the interference to make most use of the available bandwidth. Traditionally this can be done either by cascading a bandstop filter to the wideband filter, or by designing multiband filters. To achieve compactness, it will be shown in this paper that it is possible to add an extra resonator weakly coupled to the filter. Without any other changes to the original filter, a transmission zero can be produced in the passband of the filter, while the performance of the filter at other frequencies is not significantly affected. This zero can be used to suppress any potential in-band interferences. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2165-2168, 2013 [ABSTRACT FROM AUTHOR]

One-dimensional slot resonator-based photonic bandgap for coplanar waveguide (SR-PBG-CPW) is proposed in this paper. The SR-PBG-CPW unit is realized by replacing the conventional rectangular holes on ground plane with a slot resonator. The proposed SR-PBG-CPW unit exhibits more excellent bandgap and slow-wave characteristics and better selectivity at cutoff frequency than the conventional PBG-CPW unit. Furthermore, the SR-PBG-CPW is applied effectively to design a bandstop filter. Comparison between simulations and measurement confirms the validity of the proposed filter configuration and design procedure. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1602–1606, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21696 [ABSTRACT FROM AUTHOR]

This paper presents a novel, compact, low-insertion-loss, sharp-rejection, wideband microstrip bandpass filter. The filter is based on a ring resonator with direct-connected orthogonal feed lines, and uses two stepped-impedance open stubs to construct a wideband passband with two sharp stopbands. The unit cell of the ring resonators is easily cascaded and also has the feature of a compact structure. The filter is designed to reduce interference in full-duplex systems for satellite communications. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 312–315, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20807 [ABSTRACT FROM AUTHOR]

In this paper, several microwave devices using a ferromagnetic composite demonstrate great tunability under weak magnetizing field conditions. Indeed, a tunable bandstop of 50% tunability and phase shifters of 35°/dB figure of merit around 3 GHz and 7.8°/dB in the X-band are obtained when a 250 Oe dc magnetic field is applied. Moreover, a magnetic switch near 25 dB isolation and less than 1 dB insertion losses is realized. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 272–276, 2001. [ABSTRACT FROM AUTHOR]

This paper presents a novel microwave oscillator incorporating a simple microstrip ring-type resonant cell as its terminating resonance component. Reduced chip size, higher DC-AC power efficiency, and superior harmonic characteristics can be achieved from the introduction of this type of compact microstrip ring resonator cell. The oscillator provides a second harmonic suppression of 26.51 dB and an output power of 2.046 dBm, with 28% efficiency at an oscillation frequency of 2.11 GHz. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 413–415, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21366 [ABSTRACT FROM AUTHOR]

An improved tunable coplanar waveguide (CPW) bandstop filter, which exhibits good performance, is proposed in this paper. A novel tunable open stub and a useful formula for frequency shift and impedances are also presented. Further, air bridges and a special method of step compensation in the angle bends are employed to overcome differences in the radiation effects as much as possible. From the measured results, a 33% narrower rejection bandwidth with sharper roll-off was achieved, particularly in comparison to that of the bent filter. An enormous size reduction of 53% was obtained, compared to the conventional open-stub structure. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 198–200, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20091 [ABSTRACT FROM AUTHOR]

A new type of compact one dimensional (1D) microstrip photonic bandgap (PBG) used for filters is presented. A semiconductor-based structure of a miniature band-stop filter with three cells is simulated, realized, and measured. Basic agreement between the experimental and simulated results have been achieved. The filter with the proposed PBG structure exhibits wide, deep, and steep stop-band characteristics, and also has less loss and ripples in the pass-band. Thus, the new PBG structure can be used for low-pass as well as high-pass filters. The period of the PBG lattice is about (1/5 ∼ 1/4) λe (λe is the guiding wavelength at the center frequency of the stop-band), or 0.08 λ0 (λ0 is the wavelength in air). The filter with the new PBG structure is much easier to fabricate and integrate with other circuits and is more compact than conventional filters. The results in our paper are based on semiconductor substrate and can be applied directly in MIC and MMIC. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 150–152, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11153 [ABSTRACT FROM AUTHOR]

In this paper, ring-resonator bandstop filters (BSFs) with three attenuation poles are designed and analyzed using a two-port ABCD matrix of the transmission-line model. The symmetrical geometry of the ring-type BSFs allows us to explain the resonance operation via even and odd modes. Moreover, perturbation elements are employed to control the attenuation poles and obtain good performances. In order to validate the analytic method, three different BSFs are built using the microstrip-ring resonator. The simulated and measured results are presented and compared with the theory over a wide frequency range. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 114–118, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20562 [ABSTRACT FROM AUTHOR]

Design procedure of a novel transmission line low‐pass filter is presented. The filter has a flexible rejection response for a prescribed cut‐off frequency and an in‐band ripple factor. It is compact by using a Z‐shaped coupled‐line section, which is loaded with open‐circuited stubs. All of the transmission line elements are identical in electrical length, and the impedances can be calculated by solving certain specific equations according to prescribed in‐band specifications. The simulated results show that the circuit can generate low‐pass responses with third‐, fifth‐, and seventh‐order filtering functions. The filter order depends on the number and position of the loading stubs. For verification, two sample filters with cut‐off frequency of 0.5/0.3 GHz are fabricated using a three‐/five‐layer PCB process, which generate seventh‐order low‐pass filtering responses with good selectivity. The experimental results agree well with the predictions. [ABSTRACT FROM AUTHOR]

A new doubly tapered photonic bandgap (DT-PBG) technique in both planar and cylindrical coplanar waveguide (CCPW) structures is proposed and analyzed. The DT-PBG structure of a coplanar waveguide (CPW) bandstop filter not only can reduce the passband ripple but can also increase the stopband rejection bandwidth without degrading the upper passband loss. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 274–277, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11036 [ABSTRACT FROM AUTHOR]

In this article, a novel dual-mode dual-band bandstop filter design with independently tunable center frequencies is presented by using dual-mode square loop resonators. Tuning operation can be achieved with a constant fractional bandwidth. Varactor diodes are used instead of perturbation and reference elements. Two dual-mode square loop resonators in different electrical lengths are coupled to a transmission line connecting input and output ports. Center frequencies of both stopbands can be independently tuned by changing the capacitances of varactor diodes of both perturbation and reference elements. While the perturbation and reference varactors tune even mode resonance frequency together, odd mode resonance frequency can only be tuned by reference varactors. The designed filter was also fabricated for the experimental studies and it exhibits acceptable tunability operations in measurements. Center frequencies of the first and second stopbands can be tuned between 2.2 and 2.54 GHz and between 3 and 3.38 GHz, respectively. Rejection levels for both stopbands were obtained as better than −13 dB in the whole tuning range. [ABSTRACT FROM AUTHOR]

ABSTRACT This article proposes a compact microstrip tri-band bandstop filter (TBBSF) operating at 2.57, 4.62, and 7.92 GHz. The proposed design composed of open-stubs loaded in a meandered stepped-impedance-resonator (SIR). Three different open-stubs are loaded in a SIR, among which first open-stub is responsible for realizing the second resonance frequency, whereas additional two identical open-stubs are capable of tuning the third resonance frequency. This allows the possibility of individual tuning of the resonance frequencies by adjusting the electrical length of the respective resonators. Based on the design concept, an experimental circuit is designed and fabricated, offering a simple design methodology and a very compact circuit size of 0.08 λg × 0.08 λg, which is more than 15 % smaller than the previously reported literatures. The simulation results are verified from the measurement and are found in good agreement. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:815-818, 2017 [ABSTRACT FROM AUTHOR]

ABSTRACT A novel reconfigurable dual-band bandstop filter (DBBSF) with tunable lower stopband is presented. This DBBSF is a double-layer structure composed of a pair of quarter wavelength ( λ/4) open-end resonators on the top layer and a pair of novel slot-shaped structures occupying the bottom layer. Two varactors embedded in the λ/4 resonators are utilized to adjust the center frequency of the first stopband. Without increasing size, a fixed stopband located at 2.76 GHz is produced by the slot-shaped defected ground structure (DGS). Both stopbands are independent of each other thus great design flexibility can be obtained. For demonstration, a prototypical filter is implemented with tunable lower stopband of 1.47-1.84 GHz (22.4%) and a fixed upper stopband at 2.76 GHz. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2273-2276, 2016 [ABSTRACT FROM AUTHOR]

ABSTRACT A new coplanar waveguide bandstop filter using double hairpin-shaped defected ground structures is proposed. The proposed bandstop filter is composed of double hairpin-shaped defected ground structures etched on the ground plane of a coplanar waveguide, and can provide a narrow bandwidth rejection with a high Q factor. Numerical simulations revealed that the bandwidth and resonance frequency of this device can be controlled by adjusting the parameters of the defected ground structure. Moreover, numerical simulations and measurements revealed that a cascade of coplanar waveguides with double hairpin-shaped defected ground structures can increase the bandwidth, and attenuation level in the rejection band. Optimized cascaded coplanar waveguides loaded with double hairpin-shaped defected ground structures provide a Q factor of 21.1 with more than −40 dB suppression at 4.67 GHz. In many RF applications, this filter will be effective in rejecting unwanted signals with a high Q factor. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1265-1268, 2016 [ABSTRACT FROM AUTHOR]

In this article, we propose a new compact defected ground structure (DGS) bandstop filter with broad pass-band, low insertion loss in the stop-band, and sharp transition from pass- to stop-band. The bandstop filter structure is simple as it is composed of a pair of octagonal DGS slots and open stubs as a compensated microstrip capacitance. The filter is realized as a multiplayer structure with wide lossless stop-band. The behavior of the filter has been investigated using EM as well as lumped-element equivalent circuit model simulations. The design equations are derived using an equivalent circuit model of a parallel L–C resonator. The proposed filter has been optimized, fabricated, and measured. The agreement between the simulated and measured results confirms the effectiveness of the proposed concept. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2810–2813, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24770 [ABSTRACT FROM AUTHOR]

In this article two switchable bandstop filters able to switch precisely between two different center frequency and bandwidth states are presented. The filter topologies allow precise control over the design parameters frequency and bandwidth, achieved by choosing adequate resonator sections switched by PIN diodes. Center frequency control was obtained by modifying resonator length. Bandwidth control was achieved by choosing a resonator width and controlling the normalized reactance slope parameter of the decoupling resonators by means of switchable resonator extensions. Both filters were designed to have a 32.5% center frequency tuning range at L band between a low and high filter center frequency. One topology focuses on producing an 8% fractional stopband bandwidth for both filter states. The second filter topology focuses on producing 7 and 9% fractional stopband bandwidths for the low and high filter center frequency states, respectively. Measured results show a very good agreement with the simulations, for the first topology a 32.2% measured center frequency tuning range was obtained with 8.1 and 8.75% fractional stopband bandwidths for the low and high filter center frequency states, respectively. The second filter topology showed a 31.2% measured center frequency tuning range with 6.94 and 9.66% fractional stopband bandwidths for the low and high filter center frequency states, respectively. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2573–2578, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24679 [ABSTRACT FROM AUTHOR]

A generic lumped-element circuit of dual-band bandstop filter (DBBSF) is proposed based on novel composite shunt resonators, and its design method is developed with closed-form formulas. As an example, a DBBSF with center frequencies of 1.7 and 2.3 GHz is designed and fabricated using microstrip lines. The measured frequency response agrees excellently with the theoretical predictions, validating well the proposed design theory and filter structure. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2888–2892, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23822 [ABSTRACT FROM AUTHOR]

A compact coplanar waveguide (CPW) defected ground structure is investigated. Its frequency characteristics are modeled by full-wave EM simulations. Some applications are investigated, including two electronic bandgap (EBG) devices which are constructed based on a periodical structure of the proposed defected ground without and with loading of lumped-element capacitors. Also, a varactor-tuned defected ground structure of this type has been demonstrated. The theoretical, simulated, and experimental results are presented. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 47: 26–31, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21071 [ABSTRACT FROM AUTHOR]