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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]

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]

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]