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An ultra-wideband (UWB) microstrip bandpass filter is designed and developed on a low-cost FR4 substrate with a dimension of 1.15λ g × 0.38λ g × 0.06λ g. The filter has been designed using ANSYS High Frequency Structure Simulator (HFSS) electromagnetic (EM) software. It is based on a modified stepped impedance square ring resonator excited by quarter wavelength interdigital parallel coupled microstrip lines (PCML) on both ends to obtain UWB performance. Two dumbbell-shaped resonators and rectangular defected ground structures (DGS) are introduced to get a sharper transition from passband to stopband and to minimize the insertion loss respectively. Due to the symmetric structure of the filter, it is analyzed using odd–even mode analysis to find the resonant mode. To validate the EM simulated results, a lumped element equivalent circuit has been proposed. Further, the fabricated filter has been tested using Vector Network Analyzer (VNA) and the passband of the filter is found to be from 2.98 GHz to 9.59 GHz with a fractional bandwidth of 105.2 % and a minimum insertion loss of 0.38 dB. High return loss of −20.4 dB is observed with a group delay variation of 0.36 ns throughout the passband. The proposed filter is suitable for UWB applications like high-speed wireless communication and radar applications. [ABSTRACT FROM AUTHOR]

This study introduces a compact microstrip lowpass filter that offers a wide stopband and a low transition band. The couple radial stubs are designed for having sharp roll-off. The filter has a −3 dB cut off frequency of 1.6 GHz, with a transition band ranging from 1.6 to 1.7 GHz with attenuation levels of −3 dB and −20 dB, respectively. To ensure a wide stopband, the filter utilizes bended transmission lines with stepped impedance suppressing cells, resulting in a stopband attenuation of 20 dB from 1.7 to 28 GHz. The insertion loss in the passband is less than 0.1 dB, and the overall size of the filter is 0.127 × 0.087 λg2. [ABSTRACT FROM AUTHOR]

A method of designing beam-steerable patch antennas with wide stopband suppression is proposed in this article. The wide stopband suppression characteristic is realized by designing suitable parallel coupled lines and open-circuited stubs. The beam steering characteristic is achieved by using a driven patch and two pairs of metal walls vertically placed on both sides of the driven antenna. By controlling the different states of the switching PIN diodes loaded between metal walls, the stable beam steering characteristic can be obtained over the entire operating bandwidth. An experimental antenna is designed and manufactured to validate the approach. The beam steering angles of the simulation and measurement results are ±30°. Moreover, in the three proposed operating states, the out-of-band suppression from 2.6 GHz to 10 GHz is more than 16 dB. The proposed antenna can achieve the characteristic of both wide stopband suppression and beam steering. In addition, the proposed antenna is able to maintain good impedance characteristics during beam steering and maintain stable beam over the entire operating bandwidth. [ABSTRACT FROM AUTHOR]

In this paper, highly selective dual-mode microstrip bandpass filters (BPFs) are presented utilizing novel square patch resonator loaded with short via and periodic metallic vias array. Characteristics of the patch resonator are studied, and a new nondegenerate dual-mode patch resonator operating with the second and third higher-order modes is proposed. A two-pole BPF based on one dual-mode patch cavity is analyzed, and two transmission zeros (TZs) are produced. To realize higher-order filtering responses, four-pole BPFs with two cascaded dual-mode patch resonators are proposed, and different cascaded methods of two dual-mode patch resonators by a λ g /4 microstrip connecting line (MCL) are analyzed and compared to maintain high selectivity and small size. For the demonstration, two four-pole filters with the center frequency at 3.3 GHz and five transmission zeros is designed, fabricated and measured. [ABSTRACT FROM AUTHOR]

This article presents a compact microstrip low-pass filter (LPF) with a sharp roll-off rate (ROR) and an ultra-wide stopband for modern telecommunication applications. To achieve a relatively sharp transition band (−3 dB and −40 dB at the cut-off frequencies of 1.3 GHz and 1.57 GHz, respectively), a modified fifth-order circuit has been presented as the primary resonator. The frequency response of the primary filter is then enhanced by incorporating a few stubs in the primary resonator structure, which act as harmonic suppressors and help create a wide stopband. Simulation results show that the proposed LPF has a wide stopband width of approximately 28.43 GHz (from 1.57 to 30 GHz). The proposed LPF is fabricated on Rogers substrate with a total footprint of 35.3 mm × 15.9 mm. The measured values of ROR, suppression factor (SF), relative stopband band (RSB), and figure of merit (FOM) (137 dB/GHz, 2.2, 1.92, and 54,082, respectively) present the proposed LPF as a suitable choice for state-of-the-art communication circuits. [ABSTRACT FROM AUTHOR]

By utilizing transversal signal interference concepts, a tri-band bandpass filter with a triple transmission path is proposed in this paper. Triple transversal transmission paths are respectively constructed with the employ of parallel coupled stub loaded resonator, microstrip gap coupled line and parallel coupled shorted stub loaded resonator. Based on the triple transversal transmission path, nine transmission poles (TPs) are excited; therefore, triple independently controllable wideband passbands are realized. Due to the transversal cancellation between transmission paths with the virtual short mechanism of each transmission path, seven transmission zeros (TZs) can be excited and managed. Therefore tri-wideband characteristics with high selectivity and high band-to-band isolation can be obtained by properly adjusting the TPs and TZs. To further demonstrate the proposed design methodology, a prototype tri-wideband bandpass filter operating at 1.93/3.52/5.11 GHz with fractional bandwidth of 11.8 %, 19.8 % and 22.8 % for LTE, WiMAX, Wi-Fi and 5G applications is synthesised. The presented tri-wideband bandpass filter is designed, manufactured and measured. The measured results agree well with theoretical predictions, which exhibit superior performance such as sharp shirts, high band-to-band isolation compact size and ideal out-of-band suppression. [ABSTRACT FROM AUTHOR]

A unique low-profile microstrip lowpass filter (LPF) is introduced. It features a broad range of stopband and sharp roll-off. The suggested LPF is built utilizig a T-shaped configuration which includes a stub for resonance and utilizes open stubs as attenuator cells. To further improve the stopband, a double circular ring is engraved into the ground plane. The developed filter features a cut-off frequency of 3 dB at 3.4 GHz, a roll-off rate of 108 dB/GHz, and a stopband range from 3.7 to 22.8 GHz. The attenuation is less than −20 dB. The prospective LPF is designed using a lumped LC circuit model and validated using Keysight Advanced Design System (ADS) simulation and theory. The final design is realized using RT/Duroid 4003C, which boasts a small footprint of 12.4 m m × 8.69 m m × 0.8 m m. The modelling findings and measurements of the suggested LPF are in fairly good agreement. [ABSTRACT FROM AUTHOR]

This paper presents a design of magnetless microstrip line circulator with filtering response and extended isolation bandwidth through integration of mixed static and time-modulated resonators. By effectively coupling static resonators with time-modulated resonators, the proposed circulator can achieve a low forward transmission insertion loss with filtering response along with a wide isolation bandwidth. Wideband isolation can be achieved by creating two isolation nulls within the passband. For proof-of-concept, a microstrip line circulator is designed, simulated, and fabricated at center frequency of 1.75 GHz. The measured results are well agreed with simulations. The measurement results show maximum forward transmission insertion loss of 2.70 dB, in-band 20-dB isolation of 80 MHz, and in-band return losses better than 18 dB. [ABSTRACT FROM AUTHOR]

The C-band is extensively utilized in aviation radars and satellite communications (Satcom). Bandpass filters (BPFs) are crucial components in microwave systems operating within this frequency range. Therefore, it is important to develop a straightforward and effective method for designing BPFs with desired response characteristics. Currently, the prevailing approach for designing wideband microstrip BPFs involves employing multiple microstrip resonators and empirical techniques. However, some of these approaches lack comprehensiveness and a systematic design process. The design steps used for a specific type of microstrip filter with a particular cut-off frequency may not be directly applicable to developing a different filter with a distinct cut-off frequency. Conversely, having a systematic design process and software that can generate filter structures based on the filter order and response characteristics provides significant advantages in designing LC filters. Therefore, if we can design an LC filter with the desired response using conventional methods and subsequently convert it to a microstrip filter, we can achieve a more systematic design approach. The present paper proposes an innovative method to convert LC bandpass filters obtained using classical functions such as Elliptic, Butterworth, Chebyshev, and Bessel functions into microstrip BPFs. The designed microstrip BPFs offer a simple and repeatable design process and possess the flexibility to adjust the working frequency by employing a specific scaling factor. This adaptability makes the designed microstrip BPFs suitable for various applications, including Satcom and 5G systems. [ABSTRACT FROM AUTHOR]

A compact microstrip bandpass filter (BPF) with sharp roll-off skirt and broad stopband, consisting of the proposed modified 0 ° feed structure and the shorted stub-loaded tri-section stepped impedance resonator (SSLTSIR), is presented. The first two high-order parasitic resonant frequencies of the conventional 0 ° feed structure can be suppressed when a pair of open-circuited SIRs is loaded on its upper transmission path. Thus, the proposed modified 0 ° feed structure with broad stopband response is realized. Moreover, the theoretical analysis and numerical investigations are carried out. Furthermore, by embedding the SSLTSIR into the proposed modified 0 ° feed structure, a BPF with sharp roll-off skirt and broad upper stopband is achieved. A demonstrated BPF is fabricated and measured, and its measured results agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

A miniaturized dual-mode microstrip bandpass filter (BPF) based on fractally slotted patch resonator is presented in this paper. The proposed filter is centered at 2.4 GHz desirable for Wireless LAN applications. The dual-mode filter is realized using the fractally slotted structure on an octagonal patch resonator with perturbation. The design offers transmission zeros (TZs) at 2.19 GHz and 2.66 GHz on either side of the filter passband ensuring high selectivity. The locations of TZs from the center frequency can be adjusted by tuning the perturbation size. The filter is fabricated on a substrate with high permittivity and found to have a 3-dB fractional bandwidth (FBW) of 5% in the passband. Moreover, the measured minimum insertion loss is less than 0.91 dB and the return loss is greater than 23 dB in the passband. The prototype filter is fabricated and tested. Good agreement is accomplished between the experimental and simulation results. Furthermore, the footprint of the fabricated filter is about 0.416 λ g × 0.416 λ g where λ g is the guided wavelength at 2.4 GHz. [ABSTRACT FROM AUTHOR]

In this article, a compact bandstop filter (BSF) with desirable four attenuation narrow bands is developed for multiple wireless network systems. The developed filter composes of two microstrip circuits. In the first microstrip circuit, stepped-impedance and two open-circuit stubs in defected microstrip structure (DMS) are analyzed to generate the first and the second rejection bands. The third and the fourth stopbands are realized using a second microstrip circuit consist of two dual-mode resonators. This circuit are capacitively coupled to the DMS-circuit. The filter attitude is very well explained using a coupling mechanism diagram. To demonstrate the developed concept, dual and quad-bandstop filters are designed, fabricated, and measured to supress the frequencies of (2.4 GHz and 5 GHz WLAN) and (1.56 GHz GPS, 2.4 GHz WLAN, 3.5 GHz WiMax, and 5.25 GHz WLAN) respectively. The measured results agree with the predicted ones closely. The measured responses improved that the quad-BSF can apply 10 dB attenuation bandwidths of 81 MHz, 73 MHz, 60 MHz, and 129 MHz centred at 1.56 GHz, 2.4 GHz, 3.5 GHz, and 5.25 GHz respectively. The designed filter has overall circuit area of 125 mm2 excluding the feeding ports. [ABSTRACT FROM AUTHOR]

High- Q antennas are highly sought after for their narrow bandwidth and compact size, enabling them to occupy minimal volume in a given structure. In this paper, we present a new ultra-narrow band filter/antenna designed for LoRa applications. The filter/antenna consists of an elliptical slot loaded with a high permittivity rectangular dielectric resonator, excited by a coupled microstrip line. The proposed antenna serves not only as a radiating element but also as a filter, offering the significant benefit of eliminating loss between the filter and the antenna. To assess the influence of the SMA power cable on miniature antennas, we conducted a comparison of the antenna with and without a radio frequency (RF) module, focusing on radiation pattern. Our proposed filter/antenna provides a compact profile of 25 × 40 mm 2 (λ / 13 × λ /8), an omnidirectional radiation pattern, and remarkable rejection in the stop-band. The validity of the proposed design is accomplished by comparing the electromagnetic simulation with fabrication and measurement results, achieving a high level of agreement between simulation and measurement. Thanks to its exceptional performance, small size, low cost, and low-power characteristics, this innovative structure is suitable for IoT applications at UHF band with a stop-band outside this frequency to avoid potential interference from adjacent bands. [ABSTRACT FROM AUTHOR]

The demands for high flexibility in signal phase modulation, operating frequency, and amplitude modulation in contemporary wireless communication systems present challenges for reconfigurable devices. To address this issue, two tunable couplers have been designed, which consist of two parallel microstrips couplers with one-eighth wavelength and phase-shift networks composed of two varactors and coupling lines. Adjusting the even-odd mode impedances of one-eighth wavelength parallel coupled microstrip lines has been established as a means to control the coupling. The alteration of the capacitance of the varactors allows for manipulation of the phase differences in the couplers. Considering the disparities among simulation, manufacturing, and theoretical models, to get the capacitance combinations corresponding to the specific phase differences more quickly and accurately, the linear programming solve-predict method is introduced to this design. Finally, the errors between the predicted values and the theoretical values for the actual values are compared. The relative errors of the theoretical values are not less than 31.76 %, and the maximum errors of the predicted values are not more than 12.5 %, which shows the effectiveness of the method. For demonstration, two couplers operating at 2.4 GHz with different tuning ranges were designed and fabricated, work -1 with a tuning range of 45–135° and work -2 with a tuning range of 0–180° degrees. Based on the standard of 10 dB return loss and 1 dB unbalanced coupling, the relative bandwidths of work -1 and work -2 are not less than 42 % and 25 %. The relative bandwidths of phase differences effective modulation (±5°) are 20.1–42 % and 6–25%, respectively. [ABSTRACT FROM AUTHOR]

Abstract A novel memristor-based multilayer dual-mode resonator is presented, which is suitable for the design of reconfigurable multi-band filters. The memristor is used as an RF/microwave switch. A dual-band bandpass filter is realized with the proposed memristor-based dual-mode resonators. The corresponding memristor setup circuitry is optimized in order to minimize the circuitry influence on the desired filter frequency response. [ABSTRACT FROM AUTHOR]

This paper presents the design of a compact, ultra-sharp roll-off lowpass filter using stepped impedance modified T-type with stepped impedance stub (SMTS). The position of the transmission zero obtained due to the SMTS transmission line can be varied by changing the impedances and electrical lengths of the stepped impedance shunt stub (SIS) of SMTS and therefore, different roll-off rates can be obtained. The design equations used to obtain the parameters of the proposed SMTS structure are derived using the even and odd mode analysis and this enables the designers to calculate the parameters for a specific cut-off frequency ( f C ). Two SISs are connected, one at the input and another at the output side of SMTS to achieve good stopband characteristics. Finally, a lowpass filter with f C = 1.24 GHz and having a transition band of 0.11 GHz from 1.24 to 1.35 GHz with corresponding attenuation levels of 3–40 dB (roll-off rate is 336.36 dB/GHz) is designed, fabricated and tested. Good agreement is found between the simulated and experimental results. [ABSTRACT FROM AUTHOR]

The research paper proposes a compact dual notched band ultra-wideband (UWB) bandpass filter (BPF). The basic architecture of the filter is developed using the hybrid microstrip-to-coplanar waveguide (CPW) technology, wherein a short circuited CPW in ground is coupled vertically via the dielectric to the microstrip lines on the top plane. The broadside alignment generates a three pole BPF with dual transmission zeros (TZs) on either passband/stopband edges which leads to minimum insertion loss passband and sharp roll-offs. Later, multiple spirals and split ring resonators (SRRs) are embedded in the CPW of the UWB filter to introduce the dual notches and widen the stopband respectively. The proposed filter is fabricated to justify its measured response. The proposed filter measures only 14.6 × 7.3 mm 2 . [ABSTRACT FROM AUTHOR]

A dual-band Ultra-wideband (UWB) bandpass microstrip filter with triangular dumbbell shaped defected ground structure (DB-DGS) for wireless local area network applications in DSRC band is proposed in this article. The proposed dual-band filter has center frequencies at 2.67 GHz and 4.68 GHz, return loss obtained is −33.40 dB and −16.55 dB respectively, wide bandwidth of 1.21 GHz (26%), pass band between 2.14 GHz and 6.44 GHz and high gain of 10.30 dB which makes it suitable for modern applications in dedicated short range communication operating in 5.8 GHz band. To further validate the design concept, a microstrip UWB filter is designed, fabricated and tested. Comparison is made among circular, square and triangular dumbbell shaped DGS on the basis of scattering parameters and bandwidth, in which triangular shaped DB-DGS outperforms the other two. Further, parametric analysis of triangular DB-DGS has been performed and comparison is made with filters of similar nature. Experimental results are in good agreement with simulations. The fabricated filter is compact in size, has low insertion loss, exhibits high selectivity and demonstrates excellent out of-band performance. [ABSTRACT FROM AUTHOR]

In this paper, two compact tuneable bandpass filters (BPFs) based on the coupled feed lines are introduced. To approach a compact size, the coupled feed lines are bended. To design a high performance single-band bandpass filter (BPF), coupled feed lines are loaded by T-shaped stubs (as main resonators) and rectangular stubs (as suppressor stubs). Also, the mechanism of coupled feed lines combining with T-shaped open stubs is analyzed to show a tunable passband. The dual-band BPF includes two big radial-stubs, two small radial-stubs, two T-shaped structures and spiral coupled feed lines. The LC model of big radial-stubs is analyzed to compute the equation of transmission zero using its transfer function. The passband frequency of single-band BPF resonates at 2.12 GHz (3G) with corresponded insertion loss of 0.83 dB. Also, for dual-band BPF, the measured insertion-losses of first and second passbands are close to 0.8 and 1.1 dB, respectively. The frequency responses of BPFs are easily adjusted by altering the physical dimensions, demonstrating a adjustable performance. To verify the correct operation of circuits, the proffered filters are implemented and tested. [ABSTRACT FROM AUTHOR]

A simple chiral medium is used to enhance the response of a conventional microstrip coupled line bandpass filter (BPF). The approach is applicable to both narrowband and wideband BPFs using the presented chiral topology. The topology is based on an ultra-subwavelength planar chiral particle that is utilized in the interface between two slabs of substrate. More specifically the medium realizes the suppression of the second spurious response of the filter at a large bandwidth, which enables its practical application in wideband coupled-line based BPFs. The effect of the chiral particles on the substrate's effective permittivity and on the phase velocities of the even and odd mode of two coupled transmission lines on top of the substrate structure is explicitly used in the design of the filter. The methodology is applicable to any coupled-line BPF order. Two wideband microstrip coupled-line prototype filters are designed, fabricated, and measured, one involving a substrate without particles and one involving the chiral substrate. Measurement results are in good agreement with the simulations. The chiral medium based filter results in a wide fractional bandwidth (FBW) of 81% for a 1 GHz center frequency and a measured suppression level of −60 dB. [ABSTRACT FROM AUTHOR]

In this paper, a compact lowpass filter (LPF) with ultra-wide rejection band has been presented. In fact, a novel meandered semi-hairpin resonator has been used and the stopband characteristics have been improved by using a combinatorial suppressing unit. The suppressing unit contains a combination between T-shaped and semi-circular patches, which are loaded symmetrically to the designed resonator. For the proposed LPF, the-3 dB cut-off frequency has been adjusted to 2.2 GHz. After simulations, the proposed LPF has been fabricated and tested. The experimental results validated that the rejection bandwidth is expanded from 2.471 GHz to 28.62 GHz with corresponding attenuation level of −20 dB. The transition band is only 0.271 GHz from 2.2 GHz to 2.471 GHz with corresponding attenuation levels of −3 dB to −20 dB, respectively. In addition, the measured maximum insertion loss and return loss in the passband, from DC to 2.04 GHz (93% of the passband region) are 0.2 dB and 17 dB, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a compact microstrip lowpass filter (LPF) using triangle-shaped resonators is presented. The designed LPF includes three symmetric triangle-shaped resonators to provide a suitable passband and sharp response. A suppressing unit composed of several suppressing cells is designed to obtain a wide rejection band and low insertion loss in the passband. The fabricated LPF has been measured and indicts that it has −3 dB cut off frequency at 5.15 GHz. The rejection band has been expended from 5.51 GHz to 43.2 GHz with maximally flat return loss in this region nearby to 0 dB. Also, simulation and experimental results show that the proposed filter has a very flat group delay in the passband, which is the minimum value in comparison with the published works since 2017. [ABSTRACT FROM AUTHOR]

• A novel microstrip bandpass filter with ultra-wide rejection band. • 3rd-order BPF with central frequency of 2 GHz and bandwidth of 44% • More than 32 dB rejection in stopband up to 10f0 i.e., 20 GHz. • The measured passband insertion loss is 1.3 dB. • Simple structure design, via less, low cost, no lumped elements. The analysis and design of a microstrip bandpass filter featuring an ultrawide stopband are presented and investigated in this paper. In this filter, single radial stubs are exploited in combination with a regular hairpin structure to achieve suppression of harmonic responses of the filter passband up to 10 f 0. The passband of the filter remains almost intact compared to the conventional hairpin filter. A 3rd-order BPF with a central frequency of 2 GHz and a bandwidth of 44% is designed and the simulation results are verified with the measurement results. The proposed filter shows more than 32 dB rejection from 3 GHz to 20 GHz in S21 and the measured passband insertion loss is 1.3 dB. The filter structure is simple, without the need for defected ground structures, multilayers, lumped elements, and even vias. The proposed filter can be in demand anywhere easy fabrication, low cost, ultrawide stopband together with a good rejection level are considered crucial. [ABSTRACT FROM AUTHOR]

In this paper, a design procedure for multi-mode diplexers having closely located bands and an alternative coupling matrix arrangement suitable for all types are reported. The proposed topology includes the interdigital capacitive fingers as a loading element. In addition, the theoretical approach is based on the combination of a polynomial synthesis procedure and the coupling matrix synthesis method. The validation is shown by the design and fabrication of new microstrip diplexers having two different dual/quad modes bandpass filters to explain how the required selectivity and the isolation between the close channels are obtained. To obtain the best performance without an extra matching circuit, the capacitively loaded loop resonators used as a channel filter are fed by a T -junction. To obtain a sufficient coupling effect a serial capacity is used in the input/output. The proposed resonator is investigated by using the even–odd mode analysis to evaluate the resonance frequencies, transmission zeros, and return loss level. An interdigital loading element not only achieves dual-mode characteristics without the requirement of any extra surface area but also moves the transmission zeros to the desired side of the passband. The proposed diplexers have advantages such as compact size, good selectivity, interconnection capability, and high isolation. [ABSTRACT FROM AUTHOR]

In this paper, a novel method is developed in order to design a harmonic control circuit block using a compact microstrip low-pass filter (LPF) for a P-HEMT class-F PA. The design procedure is performed using Harmonic-Balance analysis. The key benefit is a novel compact defected Elliptic-Function resonator to design a LPF, which has a wide rejection band. The advantages of the presented method are the attenuation of nth harmonics in AM-AM distortion, high power added-efficiency (PAE) and more linearity in comparison with a conventional class-F PA. The experiment is carried out at 1.8 GHz and shows a maximum PAE about 77% with 40 dBm output power. [ABSTRACT FROM AUTHOR]

Abstract: A miniaturized microstrip bandpass filter based on a rectangular dual spiral resonator (DSR) is proposed in this paper. The rectangular DSR bandpass filter is centered at 3.65GHz to suit for Wireless LAN (IEEE802.11y) application. The proposed filter offers transmission zero at the high side of out-of-band response. Across the bandwidth, the measured minimum insertion loss is about 1.7dB, while the measured return loss is better than 19dB. Measurement results are good agreement and closed to the simulated ones. The total circuit size of the miniaturized bandpass filter is about 0.145λ g by 0.135λ g, where λ g is the guided wavelength at 3.65GHz. [Copyright &y& Elsevier]

In this paper, a microstrip lowpass filter employing a T-shaped resonator and high-impedance curved bend transmission lines loaded by rectangular patches operating at 2.4 GHz is presented. To improve the transition band slope, the above-mentioned cells have been coupled. Next, four attenuators composed of L-shaped and radial patches are placed symmetrically at both sides of the coupled resonators to broaden the stopband with an acceptable suppression level. By exploiting the even-mode and odd-mode analysis of the equivalent lumped circuit of each resonator and their combination, the relations of the transmission coefficient, reflection coefficient and the transmission zeros of them have been derived, independently. Studying these equations can clarify the roll of each lumped element and consequently its corresponding microstrip structure in the scattering parameters of the utilized cells. Employing the main resonators and the introduced suppressors results in a very steep roll-off rate (860.46 dB/GHz) and an acceptable relative stopband bandwidth (1.73) with the suppression factor of 2.53. From DC to 2.389 GHz, the insertion loss and return loss are better than 0.178 dB and 16.95 dB, respectively. Furthermore, the occupation area of this lowpass filter is 10.8 mm × 14.65 mm. Eventually, the designed filter has a high figure of merit equal to 110308.34. [ABSTRACT FROM AUTHOR]

In this paper, a reconfigurable filter is designed by adjusting the microstrip line impedance for the first time, which breaks the single situation that the resonator can only adjust the electrical length in the previous microstrip reconfigurable circuits. This fully reconfigurable filter loads varactors between three parallel coupling lines to realize the reconfiguration of equivalent impedance. Changing the equivalent impedance of the resonator can use harmonics to introduce transmission poles (TPs) and transmission zeros (TZs), which not only effectively improves the selectivity of the filter but also greatly improves the stopband suppression. Finally, this fully reconfigurable filter can not only tune the center frequency but also the bandwidth. A total of six TZs are introduced, three can be generated by the resonator itself, and the other three are introduced by loading adjustable stubs. The final size of this filter is 0.34 λ g × 0.25 λ g. The measured results are in good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of bandpass filters for millimeter-wave (mm-Wave) applications. The filter structures are based on transmission line hybrid T-resonators and consist of differential input, differential output (DIDO) and differential/single-ended input, single-ended/differential output (DISO/SIDO) configurations. A prototype from each configuration is designed and fabricated using a microstrip substrate. In addition to good agreement with the simulation results, the measurement results of the fabricated prototypes exhibit higher selectivity, common-mode (CM) suppression and upper stopband attenuation compared to the state-of-the-art balanced filters, rendering the proposed concept suitable for the fifth generation (5G) telecommunication applications. Besides, this work presents the first reported balanced microstrip bandpass filter based on printed circuit board (PCB) at mm-Wave frequencies. [ABSTRACT FROM AUTHOR]

A three-line coupled-line narrowband bandstop filter is proposed to obtain wide upper bandpass bandwidth and avoid the tightly-coupled limitation. This structure of the proposed bandstop filter has two three-line coupled-line sections, four open-circuit stubs and one through transmission line. The main advantages of this filter include very narrow band rejection, wide upper bandpass bandwidth, high selectivity with sharp roll-off skirt, small and flat group delay performances. The measured results indicate that the stop bandwidth with 10-dB suppression at the center operating frequency of 0.97 GHz is about 4.12% and the highest frequency of the upper passband with 15-dB return loss is 6.44 GHz (the frequency ratio h is almost 6.64). The circuit size is 0.027 λ g 2. In addition, this proposed bandstop filter is very suitable for low-cost single-layer microstrip implementations with small size. [ABSTRACT FROM AUTHOR]

In high-frequency devices, controlling the effects of circuits on each other is especially important in compact space. In this regard, a diplexer consists of a lowpass (LP) filter and a bandpass (BP) filter has been designed, fabricated, and measured, which has appropriate responses in compact size. The BP filter is designed based on the new equivalent circuit model, which is analyzed using even–odd mode. The LP filter consists of a single-resonator suppressor and the main resonator. The effects of the filters on each other are investigated by the transmission zeros (TZs) in the output response of each filter. The measured results of the designed BP filter have a bandwidth of 0.2 GHz with a center frequency of 2.42 GHz, the lower stopband bandwidth of 2 GHz and upper stopband bandwidth of 4.68 GHz. The proposed LP filter has a wide stopband bandwidth of 7.35 GHz, from 1.75 to 9.1 GHz with a suppression level of 20 dB. The 3 dB cut-off frequency is located at 1.46 GHz with a transition band of 0.29 GHz. Finally, the proposed diplexer was fabricated and measured, and a good adaptation between simulation results and fabrication ones was observed. [ABSTRACT FROM AUTHOR]

This paper presents a unique structure of a dual-band microstrip bandpass filter (BPF) that works at 1.25 GHz, 1.9 GHz for global positioning systems (GPS) and TV broadcast auxiliary service applications, respectively. The proposed BPF provides compactness, small fractional bandwidth (FBW), small frequency separation, and low IL. The prospective filter is constructed employing broadside-coupling techniques to achieve low insertion loss (IL). The feeding structure is accomplished utilizing a 50 Ω co-planar waveguide (CPW) scheme due to its low loss characteristics. The small 3-dB FBW is accomplished by inserting four transmission zeros (TZs). The size of the overall structure, including I/O transmission lines, is 34.9 × 23.5 mm2. The measured and simulated results fit well with each other and show an IL of 0.77 dB and 0.5 dB, and FBW of 7.6% and 8.4% at 1.25 GHz and 1.9 GHz, respectively. [ABSTRACT FROM AUTHOR]

This paper reports a narrowband bandpass filter with low insertion loss and compact size. The presented filter has a symmetrical structure and consists of a high impedance coupled line, low impedance triple coupled line, and simple low impedance lines. The employed triple coupled lines improve the selectivity of the proposed filter. The odd/even mode analysis based on the impedance and electrical length is presented. The center frequency is 2.4 GHz, which is a very practical frequency. the 3 dB bandwidth and insertion loss are 0.29 GHz and 1.2 dB, respectively. The miniaturized size of the filter in mm2 is 19.1 × 11.2. [ABSTRACT FROM AUTHOR]

In this paper, an efficient microstrip low pass filter (LPF) using arrow-shaped resonators has been proposed. For attenuating undesired harmonics in stop band, stepped-impedance attenuators have been applied. To suppress components in frequency band of 6–10 GHz, two single-base high-impedance stubs have been exploited. To analyze the proposed structure accurately and define the role of each element in the filter, L-C equivalent circuit has been presented. Using this L-C equivalent model, poles and zeros of transfer function can be calculated and discussed. The structure design is based on reducing the coupling effect of elements on each other and neglecting these effects in obtaining the transfer function. Two symmetric arrow-shaped resonators with high-length basis provide 3-dB cut-off frequency as 1.447 GHz. The proposed filter has flat pass band with insertion loss as −0.08 dB and wide stop band with relative stop-band bandwidth (RSB) equal to 1.728. The figure of merit (FOM) is 113,355 which is much interesting compared to other similar works in this field as shown in simulation results. [ABSTRACT FROM AUTHOR]

In this article, an application of regression-based machine learning (ML) approaches to compute resonant frequency at dominant mode TM 10 , slot dimensions of square patch, and patch dimensions of compact microstrip antenna (SPCMA) in the frequency band of 0.4856–7.8476 GHz is presented. In the design process, a squared patch microstrip antenna with two identical slots at the opposite side of a radiating edge of the antenna is loaded. The resonant frequencies of three thousand eight hundred and twenty-two SPCMAs have simulated with CST microwave studio 2019 by varying slot size, the thickness of the material, patch length, and dielectric materials is in accordance with specification of VHF, ULF, L, S, and C band applications. A comparison of 20 regression-based machine learning algorithms including artificial neural network is presented, and it is observed that the Gaussian Process Regression(GPR) model predicts physical or electrical parameters more accurately. The proposed GPR model is validated by fabricating and characterizing a prototype of a microstrip antenna. The fabricated antenna performance is very close to the designed antenna and predicted by GPR. [ABSTRACT FROM AUTHOR]

A compact high-temperature superconducting (HTS) low-pass filter (LPF) with an ultra-wide stopband and a sharp transition band is designed by integrating the fifth-order low-pass filter branch and closed loop cross-coupled (CLCC) microstrip structure. The fifth-order low-pass filter consists of two radial-stubs (RSs), one butterfly-shaped stub (BSs), and two T-shaped stubs (TSs), which can introduce five transmission zeros (TZs) with independently controllable frequency and position, so as to obtain good sideband suppression or upper stopband characteristics. The CCLC microstrip circuit is composed of cascaded high and low impedance microstrip lines, which can widen the width of the upper stopband and realize the ultra-wide stopband characteristic. The operating mechanism of the fifth-order LPF resonator and the CLCC microstrip structure are analyzed by the LC equivalent circuit models. The implemented LPF on a 0.5-mm thick MgO wafer with double-sided YBCO films demonstrates 1-dB cut-off frequency (f c) at 2 GHz and 0.12 GHz narrow transition bandwidth from −1dB to −40 dB. The measured results show a 30-dB harmonic suppression from 1.08 f c to 11.7 f c i.e., above 23 GHz, a steep roll-off rate of 326 dB/GHz, an in-band insertion loss (IL) <0.10 dB, and a miniaturized size of 0.24 λ gc × 0.08 λ gc (λ gc is the guided wavelength at the cut-off frequency). [ABSTRACT FROM AUTHOR]

In this paper, a very small microstrip low-pass filter (LPF) has presented for utilization in microwave systems. This device is composed of mirrored stepped impedances with two boxes at each side. A transfer function has been extracted from the relevant LC circuit, which expresses the function of this design. The operating frequency of the LPF is located at 3.5 GHz. The proposed LPF blocks a wide rejection with a rejection level of −20 dB or stronger. The return loss of 33 dB is another competence of the LPF. The overall size of the fabricated prototype is 9.5 mm × 5.8 mm (56 mm2). These dimensions maybe give the most compact lowpass filter operating in such frequency among the published work until now. The measurement results mimic the simulations. [ABSTRACT FROM AUTHOR]

We propose the concept of nonreciprocal filtering power dividers, which are compact devices able to merge the functionalities of power dividers and combiners, the selectivity of bandpass filters, and magnetless nonreciprocity from time-modulation. A prototype of this type of devices operating at microwaves has been implemented in microstrip technology. The device is composed of a Wilkinson power divider integrated with two identical microstrip filters based on quarter-wavelength coupled lines. The resonators of the filters are terminated with varactors that are time-modulated using low-frequency harmonic signals from a Coplanar Waveguide (CPW) feeding network printed on the ground plane of the microstrip structure. The resulting compact device behaves as a nonreciprocal power divider, nonreciprocal power combiner, or a common filtering power divider depending on the modulation parameters. In addition, it exhibits electrical frequency reconfigurability (over 15%), high rejection out of the passband, and enhanced isolation among the ports. A manufactured prototype shows relative fractional bandwidth of 3.1% measured at a return loss level of 11 dB, and insertion losses of 5.9 dB, together with a nonreciprocal response with over 21 dB of directivity at the center frequency. [ABSTRACT FROM AUTHOR]

This manuscript presents an ultra-wideband (UWB) bandpass filter (BPF) with dual transmission zeros (TZ) embedded in the passband for interference free operation in indoor environment. Based on the vertical electromagnetic (EM) coupling of microstrip-to-coplanar waveguide (CPW) transition, the structure has two similar microstrips placed adjacent on the top plane whereas a short-circuited CPW forms the ground. The response of this BPF is quasi-elliptical in nature with two TZs at either passband edges which enhances selectivity and improves insertion/return loss. To this basic BPF, novel sectoral folded split ring resonator (SFSRR) and spiral resonator (SR) are appended in the slots of the ground plane which produce dual TZs in the passband at 4.5 and 8 GHz respectively. A prototype of the proposed structure is fabricated and tested. The dual notched BPF is developed on a low cost substrate and is of compact size occupying an area of 21.2 × 16 mm2. [ABSTRACT FROM AUTHOR]

In this letter, a switchable microstrip quadruplexer based on asymmetrical dual-mode loop resonators (ADMLRs) is presented. Four ADMLRs at different electrical lengths for creating four channels are coupled to input/output (I/O) ports by means of thin film capacitors. Each resonator has two patch elements behaving as reference capacitors that are needed for switching process. In order to achieve the switching ability, varactor diodes are employed to provide variable capacitances at each resonator. Thus, all channels can be independently switched on/off by changing the capacitances of the varactor diodes. Moreover, all channels have fine bandwidth tuning mechanism depending on the capacitance changes. The designed quadruplexer was fabricated and the measurements were observed in a good agreement with the predicted results. Center frequencies of the proposed quadruplexer are adjusted to 1.8, 2.1, 2.4, and 2.7 GHz with the frequency ratios between the adjacent channels of 1.17, 1.14, and 1.13. Isolations between the outputs have been observed as better than 28 dB. [ABSTRACT FROM AUTHOR]

A high selectivity wideband bandpass filter (BPF) is proposed based on a stepped impedance open-stub loaded ring resonator. The resonant modes can be adjusted by the parameters of the stepped impedance stubs and eventually to tune the bandwidth conveniently. The even resonant modes can be tuned lower than the first odd resonant mode that is excited by the half wavelength resonator. Due to the analysis of the electric field distributions on the resonator, three adjacent resonant modes can be employed to form a wide bandwidth by electric coupling between input/output feeding line and the resonator. In addition, by introducing two more resonant modes in the passband using the parallel-coupled feeding open stubs, the selectivity is further improved. The related coupling topology is theoretically analyzed and experimentally verified. As the design example, a wideband BPF centered at 3.24 GHz with a 3-dB fractional bandwidth of 58.3% is fabricated and measured. The experimental results fit the simulations well. [ABSTRACT FROM AUTHOR]

In this paper, a new compact microstrip lowpass filter (LPF) with a sharp roll off and wide stopband is presented. The structure is composed of a defected rectangular-shaped resonator and a rectangular shape resonator as a suppressing cell. All resonators and their additional components are analyzed based on their LC equivalent circuits, and the role of each section and its equivalent circuit are described. The LPF with 3 dB cutoff frequency at 1.44 GHz has advantages such as low insertion loss and high return loss. Based on the measurement results, the proposed LPF has a sharp transition band that is 0.22 GHz from −3 to −20 dB. On the other hand, the measured value of the group delay in the whole passband is only 47 ns, which is one of the essential advantages of this filter. The designed LPF has been simulated, fabricated and, measured. There is a proper agreement between simulation and measured results. [ABSTRACT FROM AUTHOR]

The capability of the coupling matrix-based band stop filter in mutual coupling reduction between the MIMO arrays is presented. Initially, a microstrip band-stop filter with 3 GHz center frequency is designed using coupling matrix method. This filter structure is then placed between 2×1 radiating patches separated by 0.22 λ in a reference MIMO antenna designed for 3 GHz WiMAX applications. Both array antennas with/without band stop filters are fabricated and the scattering parameters are obtained separately and plotted comparatively. A good agreement is achieved between measurement and simulation results, and about 28 dB isolation is observed at operating frequency after the proposed filter application. Besides, the Envelope Correlation Coefficient (ECC) is computed and surface current distributions are simulated for both cases. It is observed that ECC has dropped to almost zero and the surface currents induced in the second patch due to the first patch excitation are extinguished with the implementation of the proposed isolation wall. Finally, to clarify the advantages of our approach, a few related studies are summarized in a comparative table. [ABSTRACT FROM AUTHOR]

This paper presents a very efficient design procedure for a high-performance microstrip lowpass filter (LPF). Unlike many other sophisticated design methodologies of microstrip LPFs, which contain complicated configurations or even over-engineering in some cases, this paper presents a straightforward design procedure to achieve some of the best performance of this class of microstrip filters. The proposed filter is composed of three different polygonal-shaped resonators, two of which are responsible for stopband improvement, and the third resonator is designed to enhance the selectivity of the filter. A holistic performance assessment of the proposed filter is presented using a Figure of Merit (FOM) and compared with some of the best filters from the same class, highlighting the superiority of the proposed design. A prototype of the proposed filter was fabricated and tested, showing a 3-dB cut-off frequency (f c) at 1.27 GHz, having an ultrawide stopband with a suppression level of 25 dB, extending from 1.6 to 25 GHz. The return loss and the insertion loss of the passband are better than 20 dB and 0.25 dB, respectively. The fabricated filter has a high FOM of 76331, and its lateral size is 22.07 mm × 7.57 mm. [ABSTRACT FROM AUTHOR]

This work presents the design, fabrication and measurements of third-order multilayered filters by additive manufacturing technology. The filters are fabricated using conventional half-wavelength line resonators and a low-cost 3d polylactic acid polymer additive manufacturing process, which allows rapid prototyping and fabrication of complex topologies. The designs, performed at a centre frequency of 2.0 GHz, aim to provide fast manufacturing and get enhanced performances when compared to conventional coupled line third order filters using microstrip technology on commercial substrates. The simulated and measured responses of the fabricated prototypes are in all cases in good agreement. [ABSTRACT FROM AUTHOR]

• An accurate ANN model is used to design a microstrip multiplexer. • A novel design process based on the ANN model is proposed to obtain four BPFs. • S-parameters of the fabricated multiplexer are measured to validate the ANN method. • Our multiplexer has the smallest size and the lowest losses in comparison with the previous works. In this paper, a mathematical model based on artificial neural network (ANN) is used to design, fabricate and measure a quad-channel microstrip multiplexer. Multi-layer perceptron (MLP) neural network trained with back-propagation algorithm is adopted to model a new microstrip bandpass filter (BPF) based on a novel stub-loaded open-loop resonator. Then, a design process is proposed to obtain four BPFs. Finally, using the obtained BPFs a high-performance microstrip multiplexer is designed. The designed multiplexer has the smallest size and the best insertion and return losses in comparison with the previous multiplexers. It operates at 2.2 GHz, 2.8 GHz, 3.5 GHz and 4 GHz, which are appropriate for multi-band RF wireless communications systems. To validate the ANN model and the simulation results, the proposed quad-channel microstrip multiplexer is fabricated and measured where a good agreement is achieved. [ABSTRACT FROM AUTHOR]

A novel microstrip bandpass filter with wide passband, good skirt selectivity and very good passband reflection characteristics using asymmetric funnel shaped resonators is presented in this paper. IE3D simulation software is used for the design and analysis of the proposed filter and the electric field intensities at various frequencies of interest are plotted and verified the role of even and odd mode resonances in achieving wide passband. There are six modes, including three even and three odd modes for the developed filter. Novel equations are derived for finding out the location of transmission zeros and the role of resonators in achieving sharp selectivity are verified. The out of band performance of filter is very good with a suppression level greater than 20 dB upto 24.2 GHz. The centre frequency of the filter is 5.68 GHz with a fractional bandwidth of 97.57%. The fabrication process is carried out using MITS 11 Autolab fabrication machine with the low cost FR4 substrate and verified the performance improvement of the developed filter. [ABSTRACT FROM AUTHOR]

A compact microstrip lowpass filter with sharp selectivity and wide stopband designed on the basis of dual-plane, is presented. Initially, a basic one pole defected ground structure (DGS) filter is modified so as to achieve sharp selectivity as well as compact size. The modified DGS reduces the circuit size of the filter by 68.8%. To suppress the higher order harmonics, mirrored symmetrical uniform impedance stubs are designed in the top surface of the substrate, thereby wide stopband up to 20 GHz is achieved. The stopband suppression level of the filter is improved by incorporating a spurline resonator which acts as a defected microstrip structure (DMS) in the top microstrip line. The designed filter has 3 dB cutoff frequency of 2.11 GHz with high relative stopband bandwidth of 159.2% within the rejection level of 18 dB. The wide passband frequency range of the proposed filter covers the GSM, GPS, Wi-Fi communications and various L-band applications such as aircraft surveillance etc. [ABSTRACT FROM AUTHOR]

A reactively loaded microstrip line based 1-D periodic structure is discussed. An off-centered via configuration is introduced to the conventional center-shorted square patch mushroom type electromagnetic bandgap (EBG) structures. In this work, a rectangular transversal patch is used to load a longitudinal microstrip line reactively. Reactive loading is varied by changing the via position away from the patch center while keeping all other structure parameters constant. This asymmetric loading causes the structure to exhibit EBG characteristics at much lower frequency with the same structure dimensions when compared to conventional centered via setup. Propagating modes are investigated using eigenmode dispersion analysis for different via positions. An equivalent circuit model of the proposed unit cell is developed. Transmission matrix (ABCD) based phase constant calculations for the circuit model agrees with the dispersion analysis results. Finally, experimental results confirm that the proposed asymmetric configuration allows the structure to lower the bandgap resonance by 28.6% with negligible impact on other performance attributes of the structure. Using the proposed configuration, compact filter structures can be designed where the stopband resonance can be flexibly placed in the band of interest within a wide frequency range, by optimizing the via position. [ABSTRACT FROM AUTHOR]

This paper presents an intelligent design methodology of microstrip filters in which a dynamic neural network model based on Bayesian Regularization Back-Propagation (BRBP) learning algorithm is used. In this approach, a Low-Pass Filter (LPF) composed of multiple open stubs, and stepped impedance resonators is initially designed for which an Artificial Neural Network (ANN) is trained to improve the performance of the filter. The predicted and measured results of the filter verify the effectiveness of the presented method, suggesting an excellent in and out-of-band performance. According to the measurement, the filter has a very small transition band from 2.087 to 2.399 GHz with 3 and 40 dB attenuation points, respectively, leading to a sharp roll-off rate of 118.6 dB/GHz. In addition the optimized filter has an ultra-wide stopband, extending from 2.399 to 15.01 GHz with attenuation level of 22 dB are The overall size of the fabricated filter is only 0.190 λ g × 0.094 λ g , where λ g is the guided wavelength at 3 dB cut-off frequency (2.087 GHz). A performance comparison with some of the recent published LPFs presented, showing the superiority of the proposed filter. [ABSTRACT FROM AUTHOR]