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This paper presents, a novel second order E-plane planar insert based dual band bandstop waveguide filter. The circular shape with two T-shape resonators are printed on Roger RO4350 dielectric substrate to form planar insert. The insert are placed in such a way that positioned in E-plane of the standard WR-90 rectangular waveguide. The independent resonant frequency and bandwidth of the stopband can be adjusted by tuning the resonators. To achieve second order dual band bandstop filter response four asymmetrical circular shape with two T-shape resonators are designed on dielectric substrate to form different stopbands and separated by some specific distance to eliminate the unwanted coupling between them. The numerical analysis of the proposed filter is carried out using CST microwave studio. To validate the numerical analysis of the proposed filter, resonator, WR-90 rectangular waveguide is fabricated and measured. The measured results shows stopband characteristics having centre frequencies f01g = 8.56 GHz and f02 = 11.21 GHz and exhibits the bandwidth of 0.4146 GHz and 0.3824 GHz. The simulated and measured result are in good agreement. [ABSTRACT FROM AUTHOR]

This paper presents a frequency- and bandwidth-tunable bandstop filter using substrate-integrated wave- guide (SIW) resonators. For designing such a filter, this paper also presents a tunable coupling structure between a microstrip line and an SIW resonator for obtaining the bandwidth tuning capability. The coupling structure has two coupling slots between the microstrip line and the resonator, and the phase shift between the two slots determines the overall external coupling value of the resonator. This external coupling value can be controlled by making use of a phase shifter, which in turn makes it possible to adjust the bandwidth of a bandstop filter. A thorough mathematical analysis is shown using the equivalent circuit model of the presented coupling structure, and it has been verified by measuring an SIW resonator containing the presented structure. The presented tunable coupling structure has also been applied to a design of bandstop filter that can be tuned from 2.8 to 3.4 GHz. The measured results at 3.1 GHz show that the bandwidth can be tuned from 0 (all-pass) to 96 MHz reaching the attenuation level of 44 dB. [ABSTRACT FROM PUBLISHER]

This paper reports a method for micrometer-scale linear and angular displacement measurement based on a gradient grating period guided-mode resonance (GGP-GMR) filter. When the filter is mounted on a moving or rotating object, the displacement on the object can be observed through the changes in the resonant wavelength, which are detected by the GGP-GMR filter. In this paper, the GGP-GMR filter comprised grating periods from 250 to 550 nm with 2-nm increments. Each period comprised 100 repeated cycles, resulting in a total length of 6 mm. For linear displacement, we achieved an average sensitivity of 67 nm/mm for a detection range of 6 mm and a theoretical limit of detection of $3~\mu \text{m}$. To demonstrate the measurement of angular displacement, the GGP-GMR filter was attached to a cylinder with a diameter of 8 cm. The experimental results revealed an average sensitivity of 51.7 nm/° for a range of 7° and an experimental limit of detection of 0.002°. [ABSTRACT FROM AUTHOR]

Impedance translation using passive N-path mixers has been used to achieve local oscillator (LO)-defined series bandstop and shunt bandpass filtering. In this paper, we generalize N-path filtering using a correlator-based approach and propose N-path passive mixers driven by orthogonal sequences. Such sequence-driven N-path filters can potentially reject or select signals based on their properties in the spectral, spatial, and code domains. Specifically, a Walsh-function (WF) sequence (WF-seq)-based N-path shunt filter is implemented, demonstrating the feasibility of shunt bandstop filtering using LO sequences other than nonoverlapping pulses. The WF-seq approach enables reconfigurable concurrent filtering at two different frequencies with shunt operation avoiding penalties due to the switch drive overlap. A 65-nm CMOS implementation achieves 20-dB rejection at one frequency and 14-dB rejection concurrently at two frequencies between 0.3 and 1.4 GHz. The reconfigurable bandstop filter is implemented using analog gyrators and consumes 35–62.5 mW and achieves 2.9-dB noise figure and −2.5–5-dBm IIP3. [ABSTRACT FROM AUTHOR]

In this paper, a dual-bandstop frequency-selective surface (FSS) implemented using a four-legged Minkowski square and s hexagonal ring is presented. The proposed FSS shows dual stopbands at 4.9 GHz and 7.1 GHz in the C band. The size of the unit cell is 0.36λ0 × 0.36λ0, which is designed on an FR4 substrate with a thickness of 1.6 mm and a loss tangent of 0.02. The frequency response of the bandstop FSS is verified using circuit simulation, and its optimised dimensions are determined at the desired frequencies of operation. The results reveal that the ratio of the two stopband frequencies can be adjusted over a wide range by properly selecting the geometrical parameters. The impedance bandwidths for S11< –10 dB of 0.9 GHz and 1 GHz have been realised at the lower and upper frequency bands, respectively. A prototype is fabricated and measurements show a reasonable agreement with the simulated results, thus validating the design concept. It has been shown that the proposed bandstop FSS exhibits excellent stability upto 60° at oblique incident angles in both TE and TM polarisations. This FSS is suitable for C-band maritime applications due to wide stopbands and highly stable angular operation. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid model chipless radio frequency identification (RFID) tag is introduced. It is constructed by using multi-resonator circuit with a bandstop filter simultaneously. Bandstop filter section is conventionally designed by quarter-wave open-circuited stubs, while the multi-resonator circuit is developed by coupling dual-band codirectional split ring resonators (CDSRRs) to a feeding line. Each stub and CDSRR can provide two and four frequency codes, respectively. The open-circuited stubs can form the resonant frequencies within wide frequency range, while the CDSRRs have notch band characteristics. The proposed hybrid model approach has the ability of combining notch and wide band resonant frequencies on a single circuit. A 12-bit chipless RFID tag is designed by locating two wideband monopole antennas vertically and horizontally at the end of the multi-resonator circuit. The monopole antennas are formed by using two orthogonal ellipses. 000000000000 and 100100100100 frequency coded two tags have been experimentally investigated. [ABSTRACT FROM AUTHOR]

A novel structure of microstrip-based instantaneous frequency measurement (IFM) receiver is presented in this paper. The proposed structure employs open-ended resonators as the core part of the receiver. Compact frequency-shifted filters are designed to achieve high-frequency resolution, instead of conventional binary division. To overcome the reliability issues that conventional binary division has in high-bit IFMs, we introduce a novel complementary filter design, which leads to a highly reliable and robust system design for IFMs. The proposed structure is simulated by Advanced Design System (ADS) and fabricated on Rogers Ro4003 substrate with 8-mil thickness. There is a good agreement between simulation and measurement results. According to the measurement results, the measured root mean square of frequency error is less than 15 MHz in the S-band. Sensitivity and dynamic range of the proposed receiver are better than −65 dBm and 70 dB, respectively. [ABSTRACT FROM AUTHOR]

This paper presents two novel on-chip bandstop to bandpass reconfigurable filters in C and X bands. Designed on a silicon substrate, filter reconfigurability is achieved using semiconductor-distributed doped areas (ScDDAs), such as an N+PP+ junction integrated into the substrate. The active element is therefore co-designed with the passive parts, allowing flexibility in ScDDA size and position. This flexibility offers advantages in terms of integration, ease of manufacture, and performance. The synthesis was developed in the OFF-state in order to match with the well-known one in the ON-state. As proof of concept, 5 GHz and 10 GHz filters were built. The simulated and measured results showed good agreement in both bandpass and bandstop configurations. [ABSTRACT FROM AUTHOR]

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]

This paper presents a novel tunable dual-band bandstop filter based on doubly tuned RF transformers. This design results in two distinct notch frequencies in a single resonator using silicon varactor diodes. The 2-pole tunable dual-band bandstop filters are implemented using printed circuit board (PCB) transformers and air-coil transformers. With PCB transformers, the lower frequency can be tuned at 513–845 MHz while the higher frequency can be tuned at 715–1151 MHz with a \notch level > 16~\dB. With air-coil transformers, a single-band 2-pole notch filter with wide rejection bandwidth is achieved. The design results in 604–982 MHz tuning with a 20-dB rejection bandwidth of 27–45 MHz. Also, by implementing a series varactor in a transformer, the separation between two coupled frequencies can be changed. The topology can be easily extended to higher order filters and design equations are presented. [ABSTRACT FROM PUBLISHER]

In this paper, we present the design of a new wide dual-band bandstop filter (DBBSF) using nonuniform transmission lines. The method used to design this filter is to replace conventional uniform transmission lines with nonuniform lines governed by a truncated Fourier series. Based on how impedances are profiled in the proposed DBBSF structure, the fractional bandwidths of the two 10 dB-down rejection bands are widened to 39.72% and 52.63%, respectively, and the physical size has been reduced compared to that of the filter with the uniform transmission lines. The results of the electromagnetic (EM) simulation support the obtained analytical response and show an improved frequency behavior. [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]

A new approach for protecting sensitive receivers through large attenuation and its realization on-chip is presented for the first time. This paper demonstrates the use of absorptive bandstop filters that gives anomalously deep notches for a given quality factor. This approach is used in a fabricated design example to isolate a sensitive wideband LNA from interference in 45-nm SOI complementary metaloxide-semiconductor (CMOS). For reconfigurable RF front-ends, a frequency-agile design is newly developed with Q tunable resonators because an absorptive bandstop filter must balance both intrinsic Q of the resonators and the resonant frequency of the filter. Therefore, the design requires variable resistors, variable capacitors, and intimate coupling of inductors of disparate values. The layout of overlapping inductors on closely spaced metal layers is required for proper absorptive properties. The size of one filter presented in this paper is 310 by 340 μm, making it the smallest absorptive bandstop filter demonstrated so far. Despite using small-size, on-chip low-Q resonators in the bandstop filter design, an attenuation level from 31 to 63 dB and a frequency tuning range from 2.9 to 4.3 GHz are achieved with potential to suppress potential interference or an image frequency signal. [ABSTRACT FROM AUTHOR]

In this paper, we present a reconfigurable filter capable of having three different responses, such as bandstop, bandpass, and all-pass responses. For designing the tri-function filter, we have developed a new topology containing coupled resonators and a switch-embedded transmission line running from the input to output ports. A bandpass response can be obtained by opening the switches embedded in the transmission line. On the other hand, closing the switches produces bandstop and all-pass responses. The details of the coupling structure design satisfying three sets of the coupling coefficients for the three responses are presented. In addition, we also discuss in detail an approach for incorporating the measured parameters of the nonideal switch in our filter design. For demonstration, a frequency-tunable tri-function filter has been designed using substrate-integrated waveguide resonators. It is shown that the designed filter is able to exhibit three responses over a 1.2:1 frequency tuning range. [ABSTRACT FROM AUTHOR]

In this paper, we present a reconfigurable filter capable of having three different responses, such as bandstop, bandpass, and all-pass responses. For designing the tri-function filter, we have developed a new topology containing coupled resonators and a switch-embedded transmission line running from the input to output ports. A bandpass response can be obtained by opening the switches embedded in the transmission line. On the other hand, closing the switches produces bandstop and all-pass responses. The details of the coupling structure design satisfying three sets of the coupling coefficients for the three responses are presented. In addition, we also discuss in detail an approach for incorporating the measured parameters of the nonideal switch in our filter design. For demonstration, a frequency-tunable tri-function filter has been designed using substrate-integrated waveguide resonators. It is shown that the designed filter is able to exhibit three responses over a 1.2:1 frequency tuning range. [ABSTRACT FROM PUBLISHER]

A novel wideband bandstop filter is proposed in this paper. Using one uniform impedance resonator and two stepped impedance resonators, five transmission zeros are introduced in the stopband. Appropriate positioning of these zeros ensures the high selectivity and flat rejection level of the stopband. The bandwidth of the filter can be conveniently controlled by the characteristic impedances of the connecting lines and resonators. A complete analytic analysis is proposed to fully control the positions of transmission zeros, and the design equations and design rules for the bandstop filter are given in detail by using the lossless transmission line model. To illustrate the concept, a wideband bandstop filter with center frequency at 2 GHz and rejection level below 20 dB is fabricated. Theoretical, simulated, and measured results are found in good agreement with each other, and the measured 20-dB rejection bandwidth is as wide as 150%. [ABSTRACT FROM PUBLISHER]

This paper presents a novel design method of bandstop filters (BSFs) and dual-band bandstop filter (DBBSF) with completely controlled bandwidth and centre frequency, high rejection levels at mid-stopband and compact sizes. First, bandstop units with simple structures are proposed. Through theoretical analysis, the centre frequency and bandwidth of the bandstop units can be independently controlled by tuning the parameters of the loaded stubs. Then, single-band, dual-band bandstop units and compact J-inverters are adopted to design the filters. Finally, to demonstrate the proposed design method, 2-order, 3-order and dual-band BSFs are fabricated and measured. From the experimental results, the maximum rejection levels at mid-stopband of 2- and 3-order are around 50 dB and 70 dB, respectively. The two stopbands of the DBBSF can be fully controlled. The measured maximum rejection levels at the two mid-stopbands are both around 60 dB. Furthermore, all the simulation and measurement show good agreement. [ABSTRACT FROM PUBLISHER]

This paper presents a new lumped-element absorptive bandstop filter topology. It exhibits infinite attenuation at the center frequency and no reflection regardless of the quality factor ( $Q$ -factor) of the resonators. The new topology exhibits the absorptive characteristic with extremely low- $Q$ resonators, whereas an absorptive bandstop filter topology in the literature cannot be used for such resonators. This superiority of the new filter topology is verified by comparing it with the topology in the literature. The filter designed using the new topology can change its center frequency by tuning only the capacitor values of the resonators. A 1.6:1 frequency tuning range maintaining the absorptive characteristic has been obtained by measurement. [ABSTRACT FROM PUBLISHER]

In this paper, we show a new bandstop filter circuit topology. Unlike conventional bandstop filter circuit topologies, the new circuit topology has inter-resonator coupling structures. The presence of these inter-resonator coupling structures enables convenient switching from a bandstop to a bandpass filter. Using the new bandstop filter topology, this paper demonstrates a design of a frequency-agile bandstop-to-bandpass switchable filter. The filter is composed of tunable substrate-integrated cavity resonators and can be switched to have either a bandstop or bandpass response. Switching is achieved by turning on and off switches placed within the filter structure. A prototype of the proposed design is fabricated and the concept is verified experimentally. [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]

This paper presents the design and development of a new microstrip multistopband filter based on tree fractal slotted resonator. A single square patch with tree fractal slots of different iterations are employed for realizing dual stopband and tri-stopband filters. The tree fractal slotted resonators are generated from conventional square patch using an iterative tree fractal generator method. First, second and third level iterations of the tree fractal slot resonator are used to design dual and tri-stopband filters respectively. The first level iteration introduced for the tree fractal slot realizes dual bands at 2.64 GHz and 3.61 GHz while the second level iteration provides better stopband rejection and insertion loss at 2.57 GHz and 3.56 GHz. The tristopband filter generates three resonance frequencies at 1.53 GHz, 2.53 GHz and 3.54 GHz at third level iteration. By varying the slot length and width of the tree fractal slot, the resonant frequencies can be adjusted, and stopbands of the proposed filter can be tuned for the desired unwanted frequency to be rejected. The proposed narrowband filters find application in removing the interference of GPS and Wi-Max narrowband signals from the allotted bands of other wireless communication systems. [ABSTRACT FROM AUTHOR]

This paper develops a novel ultra-wideband bandpass filter by cascading a broadband bandpass filter with another broadband bandstop filter. Properly selected impedances of transmission lines achieve broadband bandpass and bandstop filters and make independent designs possible. Detailed design and synthesis procedures are provided; moreover, agreement between measured and theoretically predicted results demonstrates feasibility of the proposed filter. Due to its simple structure, the ultra-wideband bandpass filter newly introduced in this paper is suitable for integration in the single-chipped circuit or implementation on printed circuit boards. [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]

In this paper, the design procedure of a compact dual-band bandstop filter (DBBSF) based on coupled open-ended Hilbert lines is proposed. The proposed filter topology consists of two pairs of coupled open-ended lines bended in the shape of the Hilbert fractal curves and a stepped-impedance line section (SIS). In that manner, tree transmission paths are crated allowing the independent control of filter characteristic in both bands. To obtain appropriate coupling between resonators, and the independent control of the center frequencies and in-band characteristics of the filter, the SIS is introduced as matching section. Design rules are derived using lossless transmission line model and even/odd analysis. To validate the design concept, two compact DBBSFs have been designed, fabricated, and measured. The proposed filters exhibit excellent in-band characteristics, high selectivity, and small dimensions. [ABSTRACT FROM AUTHOR]

A novel dual-band microstrip bandstop filter with multiple poles using open/shorted coupled lines is proposed in this paper. Nine transmission poles near the two stopbands can be easily realized by conventional coupled lines and transmission lines. The two center frequencies of the dual-band bandstop filter can be adjusted flexibly by only changing the even/odd-mode of the coupled lines. The planar microstrip dual-band bandstop filter ( $\varepsilon r = 2.65$ and $h = 0.5$ mm) with nine transmission poles is designed and fabricated. High selectivity and good in-band performances can be achieved in the proposed filter. [ABSTRACT FROM PUBLISHER]

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]

This paper presents the synthesis and design of the multi-mode dual-band bandstop filter (MM-DBBSF). A highly selective multi-mode dual-band bandstop response is obtained using a quarter wavelength coupled line structure. It has been shown that by increasing the coupled line’s order, the selectivity and the transmission zeros are increased in the desired stopband. Moreover, a step impedance resonator (SIR) is used between two coupled lines to achieve more transmission poles for better out of band selectivity. The paper show a detailed theoretical synthesis of the coupled line and SIR structure. In order to validate the theoretical model, ideal and microstrip topologies are designed and simulated. Furthermore, a high-frequency substrate is used to fabricate four prototypes. The simulated and measured results show good concurrence.

We present a new design method for bandpass filters capable of adjusting center frequencies, bandwidths, and notches. For designing such filters, filter topologies employing frequency-tunable resonators in cul-de-sacs are developed. The cul-de-sac resonators are mainly responsible for constructing notches, while the resonators in main paths form passbands. For verifying the presented design method, we have designed two bandpass filters. Each filter consists of two different resonator types: microstrip-line resonators for forming passbands and substrate-integrated waveguide resonators for producing notches. The measured results of the two designed filters show that frequency-tunable notches can be placed next to the passbands without producing unwanted resonant peaks that are usually observed in bandpass-bandstop filter cascades. This indicates that the filters designed using the presented topologies can replace bandpass-bandstop filter cascades. [ABSTRACT FROM PUBLISHER]

In this paper, a comparative performance of microstrip filters loaded with various dumbbell-shaped defected ground structures (DB-DGS) has been studied in terms of their bandstop characteristics. During this course, a new dumbbell shaped DGS having transmetal slit in the connecting slot of the square head in the ground plane has been proposed. This proposed design provides an improved bandstop response. For comparative analysis, all the filter characteristics have been simulated and studied at a fixed cutoff frequency using HFSS and co-simulation has been carried out with ADS-EM. In addition, a microstrip bandstop filter with the proposed DGS has been fabricated and tested. Measurements are in close agreement with the simulated results. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to design RF tunable bandstop filters with constant absolute bandwidth. The filters are based on a doublet configuration which is attractive for high-order filter designs. In the doublet, two varactor-tuned resonators, arranged in a mirror-symmetrical manner, are coupled to a main transmission line. A novel coupling scheme is utilized between the resonators and the main line. Theoretical analysis indicates that, as the resonant frequency varies, the coupling coefficient within the fixed coupling region can be inherently changed to desirable values to meet the requirement of constant absolute bandwidth. Using the coupling scheme, constant absolute bandwidth can be obtained without extra circuits to control the coupling strengths. For demonstration, first-order and high-order filters are designed. Comparisons of experimental and simulated results are presented to verify the theoretical predications. [ABSTRACT FROM PUBLISHER]

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 addresses the tunability issue of the all-fiber acoustooptic tunable filter (AF-AOTF) when it is used to design optical filters that are capable of producing tunable complex spectrums. A strain control scheme implemented on a loop-structure AF-AOTF is proposed for the filter design. In this paper, the mathematical model of the proposed scheme is first derived. Based on this model, the tunability of the composite spectrum obtained via the proposed scheme is analyzed and compared with existing AF-AOTF schemes. It is shown in theory that, when compared to existing schemes, the strain control scheme implemented on a loop-structure AF-ATOF has a better capability of maintaining a composite spectrum while the spectrum is being tuned. The theoretical analysis is verified by simulations and experiments. [ABSTRACT FROM PUBLISHER]

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]

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Coplanar stripline (CPS) bandpass and bandstop filters may be built using spurline stub resonators. Previous papers have demonstrated these filters, but they had a parasitic resonance that may limit spurline resonators from being used in CPS. This letter explains the parasitic resonance and introduces an alternative circuit model of the stub and a method to suppress it. [ABSTRACT FROM AUTHOR]

This paper reports on the design and experimental validation of a new class of frequency-tunable filters with switchable bandpass-to-bandstop transfer function characteristics. Single- and dual-band filter topologies are developed by coupling dual-mode loop resonators (DMLRs) to the feedline between the RF input and output ports of the filter. The bandpass-to-bandstop reconfigurability is realized by adding/removing an in-parallel cascaded thru line using single pole double throw (SPDT) switches. Center frequency tunability is achieved by incorporating three varactor diodes in the DMLRs. For experimental validations purposes, two filters with single- and dual-band responses were implemented and tested and appear to be in a good agreement with the EM simulated performance. For the single-band bandpass-to-bandstop filter, the RF-measured tuning range for the bandpass mode of operation is 1.65-1.96 GHz, and for the bandstop mode or operation it is 1.68-1.93 GHz. The dual-band bandpass-to-bandstop filter exhibits the RF-measured tuning ranges of 1.38-1.53 GHz for the first passband and 1.82-2.08 GHz for the second passband in the bandpass mode operation. The minimum insertion loss varies between 3.3 and 6.8 dB for the first passband, whereas it is between 2.2 and 4.7 dB in the second passband. The RF-measured tuning ranges in its bandstop mode of operation were measured between 1.35-1.47 GHz and 1.75-2.01 GHz.

A bandstop filter with flat negative group delay (NGD) is proposed. The flatter NGD and reduced insertion loss have been achieved in the passband of the bandstop filter. This paper provides the group delay and insertion loss equations for each component of bandstop filter, then analyzes the effects of different unit values on bandwidth, flatness, and minimum NGD. The experimental results show that the flatness is 5.06% and the NGD is −0.498 ns. The insertion loss is 6.72 dB, and the relative NGD bandwidth is 85.2%. The simulation and measurement results are basically consistent with the theoretical results. The feasibility of the design is proved.

This work proposes a spiral filter-based diplexer antenna for dual-band full-duplex 5G application in C-band. The shared radiator is formed by a cross-shape Yagi-Uda antenna. The dual-band fullduplex characteristic is obtained by applying a diplexer with two different band-stop filters (BSFs) based on a high-order rectangular spiral-shaped open-stub filter. The proposed diplexer antenna is suitable for modern 5G full-duplex communication system applications with a small frequency ratio and high isolation between two ports by applying a Wilkinson power divider. The diplexer antenna is designed, fabricated, and measured, showing good performance of channel isolations of 27 dB/23 dB and the antenna gain of 4.7 dBi/4.2 dBi at two operation bands from 3.56 GHz to 3.68 GHz and from 3.72 GHz to 3.83 GHz covering the required 100 MHz maximum bandwidth in C-band while its frequency ratio is only 1.04. [ABSTRACT FROM AUTHOR]

In this paper first a dual band bandstop filter is proposed using a unique spiral defect at the signal plane for Wi-Fi communication and remote sensing applications. The spiral defects is studied, simulated and measured. Next proposed spiral defect is combined with the hexagonal head defected resonators at ground plane to improve the rejection band. In addition a study is also done to observe the effects of the proposed defects at both signal plane and ground plane. A comparison is done among the response of individual defects filters and combined defect filter. It is observed that later shows improved overall bandwidth with compactness. The proposed combined defect filter with improved stopband displays 92.6% FBW and 112.5 dB/GHz sharpness factor with very compact in size as 0.26 λ0 × 0.25 λ0. All measurement results are in good agreement with the simulated results.

In this paper, complementary split ring resonators (CSRRs) defected ground structure (DGS) is introduced to suppress surface waves and to reduce the mutual coupling between E-plane coupled two elements of a microstrip patch MIMO antenna array. The CSRRs-DGS is easily etched on the ground plane between the array elements. The CSRRs-based DGS acts as a bandstop filter between the array elements and operates in the same desired frequency band of the array at 9.2 GHz. Significant reduction of the electromagnetic (EM) mutual coupling is achieved between array elements with a reduced edge-to-edge spacing of 7.5 mm (0.22 ?o). Experimental results show that more than 30 dB isolation between the array elements is obtained using an array of CSRR-based DGS. Moreover, the antenna array parameters are successfully optimized with a numerical experimentation technique using a 3D full-wave EM simulator. The design of the proposed array is fabricated and measured for verification purposes. The proposed design has been simulated and validated experimentally. Good agreement is found between the simulated and the measured data. [ABSTRACT FROM AUTHOR]

This paper presents the design of a negative group delay circuit (NGDC) using the filter synthesis approach. The proposed design method is based on a frequency transformation from a low-pass filter (LPF) to a bandstop filter (BSF). The predefined negative group delay (NGD) can be obtained by inserting resistors into resonators. To implement a circuit with a distributed transmission line, a circuit conversion technique is employed. Both theoretical and experimental results are provided for validating of the proposed approach. For NGD bandwidth and magnitude flatness enhancements, two second-order NGDCs with slightly different center frequencies are cascaded. In the experiment, group delay of 5.9±0.5 ns and insertion loss of 39.95±0.5 dB are obtained in the frequency range of 1.935-2.001 GHz. [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]

This paper proposes a novel design of a triple band frequency selective surface (FSS) that acts as a bandstop filter at 1.92 GHz, 3.5 GHz and 5.64 GHz. The bandstop frequencies resemble to GSM, WLAN and WiM4X application bands respectively. The structure is polarization insensitive since its frequency response remains unaltered for both TE and TM modes of electromagnetic wave propagation. The main attractive feature of the structure is its highly stable response under oblique incident angle up to ±80° at both TE and TM polarizations. Surface current distribution and equivalent circuit modeling are presented to demonstrate the resonance characteristic of the FSS. The structure is compact with an overall unit cell area of 0.092. x 0.092, where 2 is the wavelength corresponding to the lowest resonant frequency. The proposed structure is compared with other multi-bandstop FSS structures in literature to highlight its superior functionality in terms of stability under oblique incidence and compactness. A prototype comprising of 6 x 6 array of the proposed unit cell is fabricated and the measured results are in good agreement with the simulated results. [ABSTRACT FROM AUTHOR]

This paper presents a novel designing approach for tunable bandstop filters (BSPs) with constant absolute bandwidth (CABW). A simple bandstop unit is introduced to design tunable BSPs. Through the analysis, the bandwidth and center frequency of the unit can be fully controlled. Furthermore, when the center frequency is tuned, the bandwidth can be kept constant by choosing proper loaded stub impedances. Then, profiting from this unique property, tunable filter designs with CABW are introduced. A compact cascade structure is adopted to satisfy the tuning requirement onJ-inverter while designing tunable filters with CABW. For demonstration, second-order tunable BSP is designed, fabricated, and measured. The filter can be tuned from 1.55 to 2.21 GHz with CABW, a wide fractional tuning range up to 43%. High rejection levels are realized at the mid-stopband. The measurement shows good agreement with the simulation. [ABSTRACT FROM AUTHOR]

In this paper, the performance of bandstop Frequency Selective Surface (FSS) is presented which can be used to provide wireless security on airports and other sensitive places, where a mobile phone can be used to set-off an explosive device. It can also be used to block the mobile signals at the places of worship, hospitals and cinemas where the annoying voice of a mobile phone may irritate the masses. The FSS unit cell consists of two metallic square-loop elements printed on FR-4 substrate with different periodicities. The outer and inner square-loop elements are tuned to 900 MHz and 1800 MHz, respectively. It has a stable frequency response at oblique incidences for both perpendicular (TE) and parallel (TM) polarizations. Simulation results are presented to give an overview for the performance of proposed FSS design. [ABSTRACT FROM AUTHOR]

In this paper, a novel band-notched ultrawideband (UWB) monopole antenna with high notch-band-edge selectivity is proposed and demonstrated. The proposed antenna consists of a radiation patch and an embedded second-order bandstop filter. Using the same substrate area as a fundamental UWB antenna, a bandstop filter composed of a nonuniform short-circuited stub and coupled open-/short-circuited stub resonators, is designed into the fundamental antenna. A detail design procedure for the proposed antenna with a second-order maximally flat bandstop filter at 5.5 GHz is presented. As compared to the fundamental antenna, the proposed UWB antenna provides good notch-band suppression from 5.15 to 5.95 GHz, in which the normalized total radiated powers in the notch band are lower than -12 dB. Also, the proposed structure provides high band-edge selectivity and flat return loss in the notch band. The measured results, including the return loss and total radiated power, agree with the designed ones. [ABSTRACT FROM PUBLISHER]