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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]

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]

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]

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]

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]

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 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]

Abstract Laser striking is a growing safety concern for pilots and aircraft passengers and there is a great need to develop a wide-angle and shift-free laser filter and protection device. This paper presents one of such design that can effectively block out a Class 3B 532 nm green laser with an Optical Density (OD) of 1.88+ for all polarisation states over a wide range of incident angles up to 85 degree. The design consists of anti-reflection layer, active blocking and substrate layers. The central active blocking layer is designed to be a metamaterial composite media made of silver nanoparticles (AgNP) organised in a three-dimensional (3D) primitive hexagonal Bravais lattice configuration and embedded in a high-index dielectric of Zinc Sulphide (ZnS). The designed filter can be placed onto a number of devices ranging from personnel goggles to aircraft windows. The work may lead to the realisation of next generation laser protection devices that are currently sought by major aerospace companies and government defence agencies. [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]

A metamaterial (MTM) based filter with multiple band rejection characteristics is presented in this paper. By etching out two U shaped slots of different length from signal line, band notch characteristics at 5.8 GHz and 8.4 GHz are obtained. However by incorporating a pair of capacitive loaded loop (CLL) on either side of signal line, two more notches are obtained at 3.4 GHz and 6.9 GHz to avoid possible interference with few existing licence band. The prototype of the proposed micro strip band rejected filter is fabricated on RT-Duroid substrate of relative permittivity 2.2 and height of 0.787 mm. The electromagnetic full wave simulation results agree well with the measured result to validate the proposed idea. Simple design, compact size, good linearity and easy integration with other circuit like filtering antenna could be an attractive option in wireless environment. [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]

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]

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 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]

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 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]

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 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]

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]

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]

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]

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]

Abstract: In this paper, inner T-shaped defected microstrip structure (DMS) is studied, and new bandstop filters with a single band, dual-band and tri-band are developed. The new designs have adjustable multi-band operation and simple circuit topologies, and the symmetrical periodic T-shaped DMS introduces transmission zeros which improve the filter frequency selectivity greatly. The circuit sizes are also reduced because of the inner T-shaped DMS introduces more resonances in a frequency range of 10GHz but without the requirement of certain coupled lines or resonators. The dual-band and tri-band designs are demonstrated by measurement. [Copyright &y& Elsevier]

In this paper, a planar graphene-based bandstop filter is designed and simulated for the resonant frequency of 1 THz. The transmission line model of the bandstop filter is considered, which consists of open-circuited shunt stubs that are interconnected through unit elements. The bandstop filter design is carried out from the normalized low pass Chebyshev prototype. By using frequency transformation, Richard's transformation, and Kuroda's identity, the desired bandstop filter can be designed from the low pass prototype. The graphene layer is introduced between the conductor layer and the dielectric for supporting the propagation of plasmonic waves. The simulation results show that the desired frequency response can be obtained for the designed graphene-based bandstop filter. By varying the chemical potential of the graphene layer, the resonant frequency of the bandstop filter can be tuned over the range of 0.1 THz with the constant absolute bandwidth. [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]

In this paper, we show a new absorptive banstop filter topology that is capable of creating large attenuation using low-Q small-size resonators. In addition, the implementation of a lumped-element absorptive bandstop filter is shown for the first time. Compared with the conventional absorptive filter structure, the new absorptive filter structure is smaller in size because there is no quarter-wavelength transmission line between two resonators and the resonators are lumped elements. For verification of the new topology, a lumped-element low-temperature co-fired ceramic (LTCC) bandstop filter with low-Q resonators has been designed and measured. Theory, simulation, and measurement showed good agreement between them, and the measurement showed 60-dB attenuation level at the center frequency. This attenuation level of the absorptive bandstop filter is 50 dB larger than the one obtained from the reflective bandstop filter with the same Q-factor and bandwidth. The small size and absorptive nature of the filter allow us to cascade the filters to create many different filter responses. It is shown that the lumped-element implementation makes the filter very amenable to realization of higher order responses in small form factors. [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]

This paper presents tunable lumped-element bandstop filters for the UHF-band cognitive radio systems. The two-pole filters are implemented using lumped elements with both single- and back-to-back silicon varactor diodes. The single diode filter tunes from 470 to 730 MHz with a 16-dB rejection bandwidth of 5 MHz and a filter quality factor of 52–65. The back-to-back diode filter tunes from 511 to 745 MHz, also with a 16-dB rejection bandwidth of 5 MHz and a quality factor of 68–75. Both filters show a low insertion loss of 0.3–0.4 dB. Nonlinear measurements at the filter null with \Delta f = 2 MHz show that the back-to-back diode filter results in 12-dBm higher third-order intermodulation intercept point than the single diode filter. A scaling series capacitor is used in the resonator arm of the back-to-back diode filter and allows a power handling of 25 dBm at the 16-dB rejection null. The cascaded response of two tunable filters is also presented for multiband rejection applications, or for a deeper rejection null (>36 dB with 0.6-dB loss at 600 MHz). The topology can be easily extended to higher order filters and design equations are presented. [ABSTRACT FROM AUTHOR]

Abstract: By inscribing long period grating (LPG) in a photonic crystal fiber (PCF), optical filters for communication wavelengths can be fabricated. In this paper, by utilizing coupled-mode theory and enhanced improved vectorial effective index method, a design of bandstop filter based on optimal LPG parameters is presented where the optimized full-width half-maximum (FWHM), the number (N) and total length of gratings of LPGs (L) are determined. As a result, by the determination of optimized LPG parameters with an optimum length of L opt=6.5mm and optimum number of grating N opt=27 inscribed in the PCF, a bandstop optical filter with FWHM=1nm is designed. [ABSTRACT FROM AUTHOR]

In this paper, a reconfigurable filter using micromachined switches is designed, fabricated, and experimented. An equivalent-circuit model is derived for the reconfigurable cell structure. Extracted parameters show the characteristics of both bandpass and bandstop filters, which can be accurately analyzed using circuit analysis. Coplanar waveguide transmission lines for the reconfigurable filter are also analyzed. The bandpass filter is formed by cascading the unit cell structure. This bandpass filter can be switched to bandstop filter using the micromachined switches and p-i-n diode. Dispersion characteristics are obtained to investigate the electromagnetic wave behavior within the unit cell using Floquet's theorem. Measurement results with micromachined switches show that insertion loss is 1.55 dB for the bandpass filter whereas band rejection level is >20 dB and the insertion loss in the passband is 1.2 dB for the bandstop filter. With the p-i-n diode, the insertion loss is 2.1 dB and the 3-dB bandwidth is 5.2 GHz for the bandpass filter, the 20-dB rejection bandwidth is 5.3 GHz, and the insertion loss in the passband is 1.6 dB for the bandstop filter. [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]

Integration of bandstop filters with the bandstop or bandpass filter are presented in this paper. By replacing the series quarter-wavelength connecting lines of conventional open-stub bandpass/bandstop filters with the equivalent T-shaped lines, one could have compact open-stub bandstop/bandpass filters with second harmonic suppression. Transmission-line model calculation is used to derive the design equations of the equivalent T-shaped lines. Experiments have also been done to validate the design concept. Compared with the conventional open-stub bandpass/bandstop filters, over 30-dB improvement of the second harmonic suppression and 28.6% size reduction are achieved [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, 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]

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]