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In this letter, a method of designing quasi‐elliptic bandpass filter with ultrabroad reflectionless bandwidth and high selectivity is proposed. It is implemented on the basis of a quasi‐elliptic absorptive lowpass filter (ALPF) prototype that features both a low‐reflection response over all normalized frequencies and two controllable transmission zeros near the passband. A distributed‐element absorptive bandpass filter (ABPF) scheme using coupled‐line units is derived from this quasi‐elliptic ALPF prototype. With this distributed‐element ABPF scheme, both ultrabroad reflectionless bandwidth and compact size can be realized. Equations for closed‐form design are derived. A microstrip ABPF operating at 2.0 GHz (i.e., f0) is designed for validation. The measured roll‐off rates of the upper and lower transition bands are 116.44 and 157.41 dBc/GHz, respectively. The return loss is better than 10 dB from direct current to 6.25f0. The size of the overall circuit is 0.12λg2. [ABSTRACT FROM AUTHOR]

This paper introduces a compact ultra-wideband (UWB) microstrip filter featuring both a fixed and an electronically tunable notch band. Operating within the frequency range of 3.27 GHz to 5.61 GHz, the filter incorporates a permanent notch at 4.08 GHz and a tunable notch at 4.88 GHz. Utilizing a traditional ground plane and a short-circuited transmission line, we develop a bandpass filter with a stable notch-band positioned and another tunable notch band. Systematic defects are made to the ground plane to increase the coupling between input and output ports leading to UWB response. The stable notch band is created using a rectangular slot resonator, while the tunable notch employs a varactor diode (NXP BB135 Varactor Diode) integrated into a rectangular stub. Operating in the even-mode with symmetrical current distribution, the filter exhibits a -3dB passband bandwidth of 740 MHz, 610 MHz, and 240 MHz across its respective passbands. Notch band attenuation measures at -10 dB and -9 dB, respectively. Experimental results from the prototype demonstrate excellent agreement with simulated results, confirming the efficacy of the design.

In this study, designs of dual-band microstrip absorptive (reflectionless) bandstop filters are represented by simulation and experimental studies. Absorptive bandstop filter responses are obtained by adding resistors to the third order bandstop filter designed by loading open circuit meandered stubs to the transmission line connected to the input and output ports. The designed absorptive bandstop filters have low reflection loss at the input port. Reflectionless bandstop filter design can be realized by adding a resistor to the open circuit stub near the input port. In this type of filter, depending on the position of the resistor, bandstop filter with only first or only second absorptive stopband can be designed. The dual-band bandstop filter response having two absorptive stopbands can be obtained by adding two resistors to the stub located near the input port and to the open circuit stub located in the middle. Three dual-band bandstop filters having first absorptive stopband, second absorptive stopband and two absorptive stopbands were fabricated and measured. The center frequencies of the stopbands were measured at 1.18 GHz and 3.5 GHz. The measured results have been obtained in a very good agreement with the simulations. [ABSTRACT FROM AUTHOR]

Electronically tuned bandpass filters are crucial frequency-selective devices in tunable RF front-ends and are extensively utilized in the fields of communications and sensing. For low-cost and easy integration, varactor based tunable microstrip filters have been widely used in circuit design. The miniaturization, tuning flexibility, and performance optimization of tunable microstrip filters are all areas of concern. This paper reviews the research conducted on the varactor-diode-based tunable bandpass filters over the past decade. Numerous filters with various structures are introduced in the following sequence: frequency tuning, frequency and bandwidth tuning, transmission zero tuning, and tunable bandpass filter with special functions. The existing problems and limitations of various types of tuned filters have been discussed. The performance of several outstanding works has been analyzed and compared. Finally, the development direction of varactor-based microstrip tunable filters is objectively summarized, which will advance the research of microstrip filters.

A simple technique for frequency-static multi-notch/transmission-zero (TZ) creation in RF filters with single- and dual-band bandpass transfer functions is presented. It is based on the direct connection of two identical inline filtering units without stopband TZs in an in-parallel configuration by means of unequal input/output transmission-line segments for each branch. Unlike in typical transversal-signal-interference and channelized filter architectures, the overall length of these connecting transmission-line segments for both branches is the same. Thus, the multi-notch/TZ generation in the whole filtering action is accomplished by differently distributing this total electrical length between the input/output transmission-line segments for the two branches. As such, enhanced selectivity in the filtering response with several embedded notches when compared to the filtering transfer function of an isolated branch can be obtained. To experimentally demonstrate the generality of this approach, two proof-of-concept filter prototypes corresponding to a 2$/$3-GHz microstrip dual-band bandpass filter (BPF) and a 62-GHz waveguide BPF are built and tested.

In the paper, a tunable split-ring based microstrip band-pass filter is proposed and the corresponding measurement and simulation results are presented. The proposed filter has a band-pass performance around 2.2 GHz. The prototype of the proposed filter is fabricated by using Arlon DiClad 880 substrate with an electrical permittivity of ϵ r = 2.2. There is a quite good agreement between the measurement and simulation results with a slight ( ∼ 0.3 GHz) discrepancies. Also, the frequency tuning performance is achieved by using a simplistic varactor diode model of SMV1247-079LF placed on one gap of the ring. By changing the capacitance on the model, the center resonance frequency of the filter can be adjusted in the range of 2.4–3.4 GHz band. The simulation results demonstrate tunable band-pass characteristics of the proposed design. Modelling and the numerical analysis of the filter design are carried out by using CST Microwave Studio simulator. An equivalent circuit modeling of the proposed filter is presented along with the corresponding simulations. The results of the analysis on the effects of the physical dimensions of the filter on the filter performance are presented. Also, the variation of the resonance frequency with respect to the voltage value on the varactor diode was summarized with cubic spline method and displayed. [ABSTRACT FROM AUTHOR]

Microstrip filters are widely used in signal processing because of their light weight, compact structure and high reliability. Designing these filters is very time consuming, and a designer generally needs much knowledge of electromagnetic theory. In recent years, artificial intelligence (AI) technology has been used to accelerate the design process. However, current AI models retain the human design mindset (adopt a regular structure) and thus cannot be applied to the automatic design of irregular structures. We proposed a clustering-reinforcement learning model named parallel advantage actor-critic with K-means (PAAC-K). The PAAC-K model is based on a reinforcement learning model, in which the size of the overlapping area is used as the reward function, and a clustering algorithm was added to extract characteristics for learning. We used the stepwise training method to avoid repeated exploration in a design with different frequencies. The PAAC-K model realized superhuman intelligence that automated the design of irregular structures, which was proven with four application examples. This work presents an AI model and a design mindset for irregular structures, which is of great significance in promoting the development of filter devices. [ABSTRACT FROM AUTHOR]

This work presents a non-invasive method to determine the glucose levels in blood samples using a planar Yagi-Uda antenna and a novel microstrip filter. The proposed antenna operates at 5.5 GHz and exhibiting uni-directional pattern giving a maximum gain of 6.74 dBi at the operating band. A commercially available and low-cost FR-4 substrate of dimensions 30 mm×40 mm×1.6 mm is used as a dielectric substrate. A finger phantom resembling a human finger is designed in the simulation environment, which consists of bone, skin, blood, fat as different layers. The glucose concentration is varied from 0 mg/dL to 500 mg/dL and the shifts in the frequencies are observed by keeping the phantom at various locations surrounding the antenna. A good frequency shift of 26 MHz is observed when the phantom is placed below the antenna. A good similarity is observed between the simulation and measurement results. Also, a novel microstrip filter, operating at 5.5 GHz, is developed, and the frequency shifts are studied by keeping a finger phantom at the top of the filter. The designed filter is shown to give a maximum frequency shift of 4 MHz when the glucose concentration changes from 250 mg/dL to 500 mg/dL. This study is supported by analysing transmission coefficient parameters and group delay characteristics.

The proposed novel design reports dual wideband filter switching from bandpass to bandstop and vice versa using PIN diodes. The hexagonal open loop resonator is used as a unit cell to develop a bandstop filter. Two vias (Pin Through Hole) are used near the opening of the hexagonal open loop resonator. The connection of the hexagonal open loop resonator to the vias through PIN diodes makes it a bandpass filter, and the open connection between them makes it a bandstop filter. The equivalent circuit of the proposed design is simulated for the bandstop and bandpass filters. The proposed design shows a bandstop filter in the frequency range for the first band (1.3 GHz-3.2 GHz) and the second band (5.6 GHz-7.5 GHz), which fall into the S band and C band, respectively. The proposed novel design provides small size, better bandstop rejection, and less insertion loss in the passband, which are better compared to the mentioned literature in the comparison. The area of the proposed design is 0.45λg × 0.45λg mm². [ABSTRACT FROM AUTHOR]

A compact parallel-coupled-line microstrip bandpass filter with a very wideband passband and a narrow notched band is demonstrated in this paper. The presented bandpass filter was constructed from one section of three parallel-coupled-lines which has a length of a quarter wavelength at a midband frequency of 6.9 GHz. For the purpose of increasing the filter selectivity, the middle line is extended by a length of a quarter-wavelength and connected at one end to the ground plane. Therefore, a transmission zero was generated at each side of the passband which effectively improved the filter performance. In addition, a narrow notched band at a precise frequency inside the proposed passband was exhibited by placing a stepped-impedance resonator near the parallel-coupled-line for blocking the unwanted radio signal. The proposed filter was designed, simulated, fabricated, and measured. The fabricated filter has a very compact circuit size and its measured response shows an excellent agreement with the simulated results. [ABSTRACT FROM AUTHOR]

In this article, we present the first demonstration of distributed and symmetrical all-band quasi-absorptive filters that can be designed to arbitrarily high orders. The proposed quasi-absorptive filter consists of a bandpass section (reflective-type coupled-line filter) and absorptive sections (a matched resistor in series with a shorted quarter-wavelength transmission line). Through a detailed analysis, we show that the absorptive sections not only eliminate out-of-band reflections but also determine the passband bandwidth (BW). As such, the bandpass section mainly determines the out-of-band roll-off and the order of the filter can be arbitrarily increased without affecting the filter BW by cascading more bandpass sections. A set of 2.45-GHz one-, two-, and three-pole quasi-absorptive microstrip bandpass filters are designed and measured. The filters show simultaneous input and output absorption across both the passband and the stopband. Measurement results agree very well with the simulation and validate the proposed design concept.

A class of balanced dual-band bandpass filters (BPFs) with planar transversal-signal-interference coupled-line sections is reported. In their building balanced dual-band BPF stage under differential-mode excitation, a second-order quasi-elliptic-type dual-band bandpass filtering transfer function is obtained. Specifically, from the transversal interaction among their two open-ended and virtually-short-ended half-wavelength coupled-line paths, sharp-rejection differential-mode dual passbands with several out-of-band transmission zeros at both sides are realized. To attain high common-mode suppression levels within the differential-mode passbands, two open-ended line segments are connected at the symmetry plane of the devised balanced dual-band BPF stage. Moreover, higher-order schemes based on in-series-cascaded multi-stage designs to further increase differential-mode selectivity and in-band common-mode rejection are illustrated. The operational principles and parametric-analysis design rules of the engineered transversal-coupled-line-based balanced dual-band BPF approach are detailed. Additionally, for a rigorous interpretation of their zero/pole characteristics, a digital-modeling framework is applied to them to connect RF balanced filters with their discrete-time versions. For practical-validation purposes, a microstrip prototype of two-stage/fourth-order balanced dual-band BPF is built and tested. It exhibits measured differential-mode dual passbands with center frequencies of 1.464 GHz and 2.294 GHz, 3-dB fractional bandwidths of 8.74% and 9.68%, and in-band common-mode rejection levels above 23.16 dB and 31.36 dB, respectively. [ABSTRACT FROM AUTHOR]

Microstrip filter is a type of Radio Frequency (RF) filter that uses a thin electrical conductor separated from the ground plane by using a dielectric called the substrate. Microstrip filters are generally printed on Printed Circuit Boards or PCBs where high-frequency signals are directed from one part of the system to another with high efficiency. There are several types that can be applied to the operation of microstrip filters, one of which is a band pass filter. Band pass filter is a filter that can pass a signal with a certain frequency that is limited by a low cut-off frequency and a high cut-off frequency, and is able to dampen signals that are below the cut-off frequency and above the high cut-off frequency. There are several types of resonator designs that can be used for reference in the manufacture of microstrip filters, such as tapped line input hairpin filters, stub loaded filters, stepped impedance filters, and combline filters. By using the reference form of the tapped line input hairpin, this journal is intended for planning the manufacture of microstrip filters in the application of Telkomsel's 5G technology.

This work presents a non-invasive method to determine the glucose levels in blood samples using a planar Yagi-Uda antenna and a novel microstrip filter. The proposed antenna operates at 5.5 GHz and exhibiting uni-directional pattern giving a maximum gain of 6.74 dBi at the operating band. A commercially available and low-cost FR-4 substrate of dimensions 30 mm×40 mm×1.6 mm is used as a dielectric substrate. A finger phantom resembling a human finger is designed in the simulation environment, which consists of bone, skin, blood, fat as different layers. The glucose concentration is varied from 0 mg/dL to 500 mg/dL and the shifts in the frequencies are observed by keeping the phantom at various locations surrounding the antenna. A good frequency shift of 26 MHz is observed when the phantom is placed below the antenna. A good similarity is observed between the simulation and measurement results. Also, a novel microstrip filter, operating at 5.5 GHz, is developed, and the frequency shifts are studied by keeping a finger phantom at the top of the filter. The designed filter is shown to give a maximum frequency shift of 4 MHz when the glucose concentration changes from 250 mg/dL to 500 mg/dL. This study is supported by analysing transmission coefficient parameters and group delay characteristics. [ABSTRACT FROM AUTHOR]

This brief reports on the RF design and practical development of a non-reciprocal balanced bandpass filter (BPF) that exhibits a highly-selective quasi-elliptic response in the forward direction of propagation that is shaped by four transmission poles and two transmission zeros (TZs). By modulating some of the filter’s resonators with phase-progressed AC signals, a non-reciprocal response is obtained in the differential mode. Its common-mode is also highly suppressed due to the incorporation of a balanced network that results in two additional TZs and resistive loss that are unique to the common-mode. The filter order can be increased by cascading additional resonators. For validation purposes, a microstrip prototype centered at 725 MHz was designed, manufactured, and measured. It showed a high isolation in the differential-mode reverse transmission of up to 62.1 dB. Moreover, the common-mode was suppressed by over 45 dB in a bandwidth greater than one octave. [ABSTRACT FROM AUTHOR]

In this paper a fifth order wide-band Chebyshev micro-strip filter is designed at 5.2 GHz frequency, where the spectrum contains white spaces. The fifth order is extended to 7th, 9th, 11th, and 13th order and simulated using HFSS EM simulator. Simulation results show that compared to 5th order, the higher order filters provide more and more reduction in out-of-band emissions in increasing order from 5th to 13th order filter. A 13th order filter is fabricated and tested for more reduction in the OOBE by using dumbbell shaped slots as defected ground plane structure. Five such slots are made in the ground plane for better results to reduce more OOBE. This 13th order filer with slots is fabricated and tested. The substrate chosen is FR4 with height 1.6 mm. Here we have given a mathematical treatment for emission mask for OOBE according to ITU recommendations. The designed filter’s transmission characteristics from port 1 to port 2 give good agreement with the recommendations.

This paper includes two new microstrip filter configurations for high frequency and ultra-wideband applications. The first proposed filter is a composition of four parallel open-circuited stubs connected by optimized fractal-structured microstrip line. The filter response is a combination of three passing regions, namely, low pass from 0.1 GHz to 3 GHz, band-pass from 4.5 GHz to 9 GHz, and high pass from 10.5 GHz to 13 GHz, separated by two rejection regions from 3 GHz to 4.5 GHz and 9 GHz to 10.5 GHz. Deep and sharp rejection regions reaching up to -44.6 dB with 40 % fractional bandwidth (FBW) are observed with a good electrical performance. Furthermore, with a comparative table, the advantages of this proposed BSF in terms of FBW, compactness, and insertion loss are compared with recently reported related studies. Secondly, a dual-band band-pass filter implementing a stepped-impedance resonator (SIR) and a modified H-shaped structure is presented. This filter is designed to operate in a low pass region up to 3.58 GHz and a band-pass region from 15.38 to 21.65 GHz, with a wide stopband region between 4.46 and 14.07 GHz. The simulated and measured results are in good agreement. Compared to its peers, the compact size and low price allow for a wide application of these filter configurations, while passing frequencies allow operation in the unlicensed frequency spectrum, which is popular for high-speed communication. [ABSTRACT FROM AUTHOR]

A type of multilayer microstrip diplexer with highly- selective wideband filtering channels is reported. Its closely-spaced fourth-order passbands are attributed to two circuit parts: (i) two third-order quasi-elliptic-type microstrip-to-microstrip wideband vertical transitions and (ii) a shunt two-stub dual-band bandpass filter (BPF) junction printed on the top layer. The two microstrip vertical transitions are developed by means of open-/short-circuit-ended microstrip lines and slotline stepped-impedance resonators (SIRs), respectively, and they correspond to the constituent lower and upper channels. The shunt dual-band BPF junction produces one additional transmission pole and one more pair of close-to-passband transmission zeros (TZs) for each channel to further increase their filtering selectivity. The RF theoretical foundations and design procedure of the engineered broadband diplexer are detailed. For practical-validation purposes, a proof-of-concept prototype of two-layer fourth-order microstrip wideband diplexer is simulated, manufactured, and tested. Its measured lower and upper channels has two closely-spaced sharp-rejection passbands with center frequencies of 1.496 GHz and 2.759 GHz and 3-dB fractional bandwidths of 62.83% and 24.83%, respectively, while featuring power-isolation levels above 27.39 dB from 0.5 to 4 GHz. [ABSTRACT FROM AUTHOR]

A compact parallel-coupled-line microstrip bandpass filter with a very wideband passband and a narrow notched band is demonstrated in this paper. The presented bandpass filter was constructed from one section of three parallel-coupled-lines which has a length of a quarter wavelength at a midband frequency of 6.9 GHz. For the purpose of increasing the filter selectivity, the middle line is extended by a length of a quarter-wavelength and connected at one end to the ground plane. Therefore, a transmission zero was generated at each side of the passband which effectively improved the filter performance. In addition, a narrow notched band at a precise frequency inside the proposed passband was exhibited by placing a stepped-impedance resonator near the parallel-coupled-line for blocking the unwanted radio signal. The proposed filter was designed, simulated, fabricated, and measured. The fabricated filter has a very compact circuit size and its measured response shows an excellent agreement with the simulated results.

A compact dual-mode bandpass filter with independently tunable second passband is proposed based on modified V shaped resonators. By switching the pin diodes at each end of the studied resonators, the second passband is independently tuned without affecting the first passband. A prototype of the dual-mode bandpass filter with a dual-passband of 2.54 GHz and 3.36 GHz or a single passband of 2.54 GHz is designed and verified experimentally. [ABSTRACT FROM AUTHOR]

This paper presents a design method of four-port microstrip filter circuits that have increased filter passbands for multiplexer operation using a simple feed structure. The proposed circuits can be used as different diplexers or even triplexers according to different application requirements. The stub-loaded resonator is used as the basic element to design each filter channel. A simple feed structure with asymmetrical U-shaped feedlines is deployed using the discriminating coupling method. As a result, for each filter channel, specific transmission zero is introduced in other channel frequency bands, thus achieving high channel isolation. Firstly, a compact four-port filter circuit is proposed with four diplexer functions. By exciting one port as the input while two adjacent ports as the output, two filter passbands can be utilized for duplexing channels. Then, without adding extra ports, a four-port five-passband filter circuit is designed. It features a high integration level since it can be used as either diplexers or triplexers, once the corresponding ports are excited. For proof of concept, two design examples are fabricated. The prototypes show good agreement between the simulated and measured results, verifying the feasibility of the proposed design methodology. In addition, the operating frequency and bandwidth of each filter passband can be tuned to desired values. These characteristics are promising in multi-band base-station antenna array feed systems.

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.

This article reports the design of coupled-resonator-based microwave dispersive delay structures (DDSs) with arbitrary asymmetric-type group delay response. The design process exploits a coupling matrix representation of the DDS circuit as a network of resonators with frequency-variant couplings (FVCs). The group delay response is shaped using complex transmission zeros (TZs) created by dispersive cross-couplings. We also present an optimization-based synthesis procedure for characteristic polynomials with a prescribed group delay profile. Thus, when compared with prior-art DDS approaches, the proposed DDS solutions allow a general group delay profile to be patterned while incorporating optimization-based coupling matrix design techniques for their synthesis. The design method is validated by full-wave simulations and measurements of three built proof-of-concept prototypes of DDS devices with different shapes of group delay response in waveguide and microstrip technologies. [ABSTRACT FROM AUTHOR]

This paper introduces a compact microstrip low-pass filter (LPF) with a very sharp rejection. The proposed LPF is designed to be used for electronic warfare in defense industry. It has 62 dB/GHz attenuation rate, 10 GHz of stopband width and 48.6 dB of stopband attenuation. Moreover, it also has a wide passband and has a high cut-off frequency (fc) of 6 GHz. The designed filter has been fabricated using alumina (Al2O3) substrate and titanium-gold (Ti-Au) coating on top of that with thin film technique in a clean room. The experimental measurements of the proposed LPF show great agreement with the simulation results, which validates that the presented filter is convenient to be used for applications up to C-band in electronic warfare systems. [ABSTRACT FROM AUTHOR]

This article presents the realization of a bandpass filter on a flexible biopolymer substrate with a suitable fabrication process. We used copper adhesive tape and laser structuring to fabricate the filter based on a quasi‐lumped microstrip structure. The filter characteristics are a central frequency of 2.45 GHz, a bandwidth of 20%, and insertion loss of 1.2 dB. It is demonstrated that the filter's performance remains almost constant under different bending, folding, and rolling conditions. The results show that the proposed bio‐sourced polymer is a good candidate for flexible green electronics and wearable applications. [ABSTRACT FROM AUTHOR]

A rapid growth in 4G and 5G in wireless communication applications demand compact and reconfigurable microstrip filters structures. However, meeting these requirements comes with many challenges, namely the increased design complexity, system size, fabrication process, and cost‐effectiveness. Accordingly, the paper aims to design a reconfigurable microstrip filter in terms of its geometrical structures of compactness and its operational performances. A reconfigured compact parallel‐coupled microstrip bandpass filter is a modified Minkowski fractal geometrical shape of inverted alphabet C structure and the first iteration of Minkowski is proposed. The proposed work shows the design technique, parametric analysis, and simulated results of a compact parallel‐coupled microstrip Minkowski fractal bandpass filter for dielectric constant 4.4 and thickness 0.8 mm, operating at 5.1 GHz and bandwidth of 1.5 GHz. A good agreement between simulated results and designed values is achieved, the filter is compact with good bandwidth, less loss, and is dedicated to wireless communication applications. [ABSTRACT FROM AUTHOR]

A general coupling-matrix-based synthesis methodology for inline ${N}$ th-order microwave bandpass filters (BPFs) with frequency-variant reactive-type couplings that generate ${N+1}$ transmission zeros (TZs) is presented in this brief. The proposed approach exploits the formulation of the synthesis problem as three inverse nonlinear eigenvalue problems (INEVPs) so that the coupling matrix is built from their sets of eigenvalues. For this purpose, an optimization nonlinear least-squares procedure is employed. The theoretical foundations of the engineered INEVP coupling-matrix-based synthesis framework are described. In addition, its effectiveness is verified through various synthesis examples of a third-order BPF with four TZs based on different circuit models. Moreover, as experimental validation, a 2.4-GHz microstrip prototype of the distributed-element BPF synthesis example is built and measured. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a compact elliptic-response microstrip low pass filter (LPF) is presented with a wide stop-band using stepped impedance resonators. With high attenuation in the stop-band, the overall size reduction of the proposed filter is achieved using a novel defected ground structure technique using an interdigital capacitor and complementary split ring resonator (CSRR). A 4.2 GHz LPF is designed and simulated on FR4 substrate and a stop band of 8.8 GHz is obtained by utilizing interdigital and complementary split ring resonator. Results further show that the use of U-shaped high impedance line on the top layer of filter enhances the stop-band bandwidth by 2.2 GHz. In the final design, the passband insertion loss is found below 0.5 dB, and –10 dB is obtained over a band from 5.06 GHz to 17.06 GHz between input and output ports. The normalized circuit size of the filter is 0.417× 0.202 and the figure of merit is calculated about 55 at the cut-off frequency. These proposed LPFs have promised significant advantages in the stop-band characteristics with an acceptable roll-off rate for spurious-free communications.

In this article, a novel triple wideband bandstop filter design is proposed with two adjacent microstrip square loop resonators (MSLR) having different edge lengths. Degenerate modes of the square loop resonators are induced by using direct coupling mechanism. Perturbation and loading elements are located on resonators and used to control reflection zeros between the second and third bands. Even odd mode analysis of a single direct coupled dualmode resonator is also extracted to elucidate the filter topology. The proposed resonator structure is designed by using a full-wave EM simulator and three different filter responses are obtained from the designed resonator structure. One of the filters is fabricated and, it is observed that measured results are compatible with simulated results. [ABSTRACT FROM AUTHOR]

This article demonstrates a 10.23–15.7-GHz varactor-tuned microstrip bandpass filter (BPF) with fully controllable center frequency, bandwidth, and transmission zeros. The concept of cascading a tunable low-pass unit together with a tunable high-pass unit is adopted to achieve the reconfigurable BPF. A comprehensive loss analysis is carried out to determine the preferable circuit topologies for low-pass filter (LPF) and high-pass filter (HPF), respectively. This not only overcomes the limitation of low quality factor of varactor at high frequency, but also contributes to a highly flexible reconfigurability of the BPF. A reconfigurable LPF using defected ground structure (DGS) and a quasi-elliptic HPF using microstrip technology are then proposed to demonstrate the improved BPF performance at high frequency. The measured results show that the designed BPF is capable of operating in five working modes, with a center frequency tuning range from 10.23 to 15.7 GHz and a fractional bandwidth (FBW) tuning range from 32.48% to 95.76%. The minimum in-band insertion loss reaches 2.55 dB. A steep cutoff characteristic and ultrawide stopband with high rejection level are successfully achieved and are well preserved during the whole tuning process, demonstrating the superiority of the designed BPF. [ABSTRACT FROM AUTHOR]

This letter presents V-band components which are manufactured in PCB technology and designed for 60-GHz center frequency. A proposed multifinger dc-block provides 30% bandwidth (BW) with an input reflection coefficient < −10 dB. On the same criteria, a modified-triangular design shows 55% BW covering 85% of the $V$ -band which is, to the best of the authors’ knowledge, the highest achieved BW of a PCB compatible dc-block in millimeter wave range. The bias-tee structures are realized by integrating an RF choke with the dc-blocks. The bias-tee with a multifinger dc-block shows 31% BW while with the modified-triangle dc-block allows for 48% BW with RF/dc isolation >20 dB. The proposed wideband designs provide a cost-effective solution, e.g., of RF components testing while shielding the respective lab equipment from dc or RF. [ABSTRACT FROM AUTHOR]

The substrate integrated waveguide (SIW) structure is the candidate for many application in microwave, terahertz and millimeter wave application. It because of SIW structure can integrate with any component in one substrate than others structure. A kind components using SIW structure is a filter component, especially bandpass filter. This research recommended SIW bandpass filter using rectangular open loop resonator for giving more selectivity of filter. It can be implemented for short range device (SRD) application in frequency region 2.4-2.483 GHz. Two types of SIW bandpass filter are proposed. First, SIW bandpass filter is proposed using six rectangular open loop resonators while the second SIW bandpass filter used eight rectangular open loop resonators. The simulation results for two kinds of the recommended rectangular open loop resonators have insertion loss (S21 parameter) below 2 dB and return loss (S11 parameter) more than 10 dB. Fabrication of the recommended two kind filters was validated by Vector Network Analyzer. The measurement results for six rectangular open loop resonators have 1.32 dB for S21 parameter at 2.29 GHz while the S11 parameter more than 18 dB at 2.26 GHz - 2.32 GHz. While the measurement results has good agreement for eight rectangular open loop resonators. It has S21 below 2.2 dB at 2.41-2.47 GHz and S11 16.27 dB at 2.38 GHz and 11.5 dB at 2.47 GHz. [ABSTRACT FROM AUTHOR]

A new printed microstrip band-stop filter is proposed and implemented. A systematic design approach is presented to realize the filter for a specific band of operation employing the concept of SIR and embedded stub. The proposed filter design is suitable for multiple stop band applications. Moreover, the filter configuration can be easily incorporated in the microstrip feed line connected with a radiating element to reject the signal at the desired band for mitigating the electromagnetic interference. A prototype model of the proposed design is developed, and characteristics are measured and compared with the simulation result. A good agreement between the two is evident. [ABSTRACT FROM AUTHOR]

This paper studies the corona discharge power thresholds in microstrip bandpass filters (BPFs) and, in particular, is focused on a solution based on λ/2 cover-ended resonators to enhance their peak power handling capability (PPHC). First, a parametric analysis is carried out to evaluate the variation of the maximum electric field and the unloaded quality factor (Qu) as a function of the cover's geometrical dimensions (i.e. height, length, and width). Next, several microstrip BPFs centered at 1.6 GHz are designed, and their behaviors under moderate-to-high applied RF power signals are simulated to corroborate the previous study. A suitable number and size of covers are selected to enhance PPHC without barely degrading the filters' electrical performance and, consequently, without hardly increasing the insertion losses. Finally, two third-order filters with covers and without covers (benchmark prototype) are manufactured, by way of illustration, and they are tested in the European High-Power RF Space Laboratory to validate the good performance of the proposed solution, where a PPHC enhancement of 3.1 dB at high pressures is achieved as compared to the benchmark prototype. [ABSTRACT FROM AUTHOR]

In this paper, a new Defected Ground Structure (DGS) is introduced and analyzed. The effect of the structure's dimensions on the location of the attenuation pole and the cutoff frequency to study the frequency characteristics is investigated. In the following, a lowpass filter with 3 dB cutoff frequency at 3 GHz is designed and optimized using the proposed defected ground structure, and its frequency characteristic is reported. The designed lowpass filter is fabricated to verify the simulation process. Also, simulation results, the equivalent circuit, and the measured results with the Network Analyzer are compared. [ABSTRACT FROM AUTHOR]

This paper presents an efficient microstrip trisection bandpass filter consisting of cross-coupled open-loop resonators for IF band filtering in Ku band Direct to Home (DTH) applications. The proposed filter has been designed and investigated using Advanced Design System (ADS) software. The filter provides fractional Bandwidth (FBW) of 13.84% at the centre frequency, which is much higher than most of the cascaded trisection filter designs previously reported in literature. The fabricated filter has been experimentally tested on aKu band DTH downlink and the effect of the filter on the received signal has been analysed. [ABSTRACT FROM AUTHOR]

In this study, a new method and structure are proposed to design of a switchable and fully tunable microstrip bandpass filter (BPF). The central frequency and bandwidth (or the resonance frequency of the resonators, coupling coefficient between resonators, and external quality factor of the I/O resonator) of the proposed BPF can be efficiently controlled using varactor diodes as tuners. In addition, the proposed BPF is designed to have three operating states, each with a different frequency tuning range. The three operating states can be switched between independently by introducing three pairs of switching diodes in the input and output feeding structures. Because of the ability to switch among the three operating states, an extra-wide frequency tuning range can be achieved. For demonstration, a two-pole switchable and tunable BPF was designed and implemented using microstrip technology. The experimental and simulation results were consistent and indicate that a wide frequency tuning range from 0.54 to 2.4 GHz, corresponding to a fractional tuning range of 127%, and a nearly constant absolute bandwidth of 82 MHz are achieved. In addition, the proposed switchable and tunable BPF is small (0.24λg × 0.15λg).

High-order quasi-reflectionless bandpass filters with improved passband flatness and good impedance matching both in-band and out-of-band are proposed in this work. The proposed design consists of conventional coupled-lines bandpass sections loaded with absorptive stubs at the input and output. Analysis shows that the absorptive stub is equivalent to a 2-pole bandstop filter. Compared to the prior art, the higher-order nature of the presented absorptive stub enables a flatter passband and better out-of-band rejection. The overall filter stopband attenuation can be readily improved by increasing the number of coupled-lines sections without altering the passband responses. Furthermore, cross-coupling between the two absorptive stubs can be used to improve the out-of-band rejection by introducing two transmission zeros without affecting the absorption characteristics. The proposed design concepts are experimentally validated by the design and fabrication of a set of 2.4-GHz 1-, 2-, and 3-pole microstrip quasi-reflectionless bandpass filters. Measured frequency responses of these filters closely match those of the simulation.

The importance of filter structures in RF/microwave applications is very high. Band-stopping filters are also frequently used in biomedical devices. When measuring biomedical devices, filters that stop signals at this frequency are placed on the devices so that unwanted signals circulating in the air do not cause deviations. IEEE 802.11 b has a maximum speed of 11mbits/s, and is used to connect the same devices to the original standard. IEEE 802.11 b standard devices are experiencing interference due to other devices running at 2.45 GHz (microwave oven, Bluetooth devices, wireless phones). The main objective of this work is; In order to prevent these interferences, band stop filter design at 2.45 GHz frequency was realized. Thanks to the filter designs that stop this band, unwanted signals have been filtered and the desired signals have been successfully transmitted.

Dual-mode patch resonator-based microstrip filters with finite real or imaginary transmission zeros are discussed by combining the analytical studies with numerical investigations. The analytical study presents the coupling scheme of a dual-mode patch resonator, while the numerical simulation discusses the coupling nature between the source (input) and load (output), which constitutes the presented half-analytical model. Furthermore, the difference of in-band losses between the two different responses can also be qualified based on this model. The contribution and novelty of this work is the coupling nature between the source and load which is explained for the first time, and based on this, the half-analytical model can further estimate the transmission zeros of the microstrip patch resonator filter. For demonstration purposes, two prototype filters that exhibit transmission zeros at the real and imaginary frequencies, respectively, are developed and confirmed experimentally. The measurements agree closely with the predications. [ABSTRACT FROM AUTHOR]

In this paper, a microstrip filter using a modified stepped impedance resonator with high return loss, low insertion loss, and ultra-wide stopband is presented. The frequency response of the filter based on the layout and LC model is presented. The presented LPF consists of stepped impedance resonators to achieve a − 20 dB suppression level from 3.26 GHz up to 30 GHz. Using stepped impedance resonators results in multiple transmission zeros in the stopband. The proposed filter has an insertion loss of 0.1 dB, return loss of 26 dB, and cut-off frequency of 3 GHz. The transition band of the filter (with attenuation levels of − 3 dB and − 20 dB) is 0.26 GHz. The simulated results are close to the measured results, which shows the accuracy of our design. [ABSTRACT FROM AUTHOR]