Stub‐loaded square loop bandpass filter with equiripple response in both delay and magnitude

It is shown that a stub loaded square loop filter, composed of six sections of commensurate transmission line, can achieve equiripple response in both magnitude and group delay simultaneously, when the admittances of the lines are properly chosen. Design formulas are given to calculate the admittances by given specifications such as fractional bandwidth and in‐band magnitude ripple. An interesting property of this filter is that the group delay can be adjusted while the in‐band magnitude response keeps almost unchanged. For verification, a filter sample is designed, fabricated and measured. In experiment, it exhibits a delay variation of 0.22 ns and minimal insertion loss of 0.21 dB within its passband (|S₁₁| < ?13.8 dB) from 0.48 to 1.52 GHz, which agree well with the theoretical predictions.     

Wideband and spurious‐suppressed differential bandpass filter based on strip‐loaded slot‐line structure

In this article, a wideband and spurious‐suppressed differential bandpass filter based on strip‐loaded slot‐line structure is presented. By means of the differential microstrip‐slot‐line‐microstrip transition, the proposed filter has a wideband bandpass filtering response. Simultaneously, the utilization of the strip‐loaded slot‐line extends its upper stop‐band. The proposed bandpass filter has wider upper‐stopband, wideband bandpass response, and intrinsic high common‐mode (CM) suppression. To verify the design concept, one filter example has been designed, fabricated, and measured. It has a differential‐mode (DM) 3‐dB fractional bandwidth of 157% with a low 0.82 dB minimum insertion loss. What's more, it shows a very wide 20 dB DM stop‐band bandwidth of 6.5 f_0d. The experienced results are in good agreement with the theoretical and simulated results.     

A wideband circularly polarized slot antenna with antipodal strips for WLAN and C‐band applications

A single‐fed circularly polarized square shaped wide slot antenna with modified ground plane and microstrip feed has been presented. The field in the slot is perturbed by introducing an antipodal strips section attached with a microstrip line to produce circular polarization in a wide band of frequencies. The antipodal strip section consists of a group of four strips of unequal length and separation. The presence of asymmetric perturbations in the slot is mainly responsible for exciting two orthogonal modes in the slot having equal magnitude and 90° phase difference which results in circular polarization. A wide bandwidth of 3.3 GHz (4.4 GHz‐7.7 GHz) has been achieved for an axial ratio value AR < 3 dB with the minimum axial ratio value being 0.3 dB. The impedance bandwidth for |S₁₁| < ?10 dB ranges from 4.3 GHz to 8 GHz, and therefore covers most of the C‐band communication systems. The antenna exhibits stable radiation patterns throughout the circular polarization bandwidth with a gain around 6 dBi in entire operational bandwidth. A prototype of antenna was fabricated and measured. The antenna has a planar size 0.40λ₀ × 0.40λ₀ and thickness of 0.02λ₀ where λ₀ is the wavelength in free space at the lowest frequency. With its compact size and low profile, the antenna is a favorable choice for WLAN (5.15‐5.85 GHz) and a wide variety of C‐band wireless applications.     

Spoof surface plasmon polariton band‐stop filter with single‐loop split ring resonators

A novel band‐stop filter with single‐loop split ring resonators (SRRs) is proposed for spoof surface plasmon polaritons (SPPs) at millimeter wave frequencies, achieving a miniaturized size of 0.052λ₀ × 0.278λ₀ at its resonant frequency. The SRRs provide both a low‐pass response as the rectangular corrugations used in the conventional SPPs and an additional band‐stop response induced by the resonance of SRRs. To verify this design, a back‐to‐back device with two coplanar waveguides as the input and output feeding was fabricated and characterized, the measured S‐parameters of which agree well with the simulation. The measured stop band is centered at 49 GHz with a ?10‐dB bandwidth of 4.1 GHz and a high Q‐factor of 93, in which the maximum attenuation is 31 dB. The filter has a low insertion loss of less than 2.8 dB in the pass band. Such approaches may find many applications to achieve compact millimeter wave circuits.     

A compact reconfigurable bandpass/lowpass filter with independent transmission zeros based on generalized NRI metamaterial

This article introduces a new design and analysis of a compact reconfigurable bandpass/lowpass filter based on compact negative refractive index metamaterial transmission line. The filter equivalent circuit has been designed as a cascade of three cells of bisected‐Π/Π configuration. The reconfigurable function was achieved using inserted switches in ON and OFF modes within the cells. The filter works as bandpass when all switches are in ON condition and for lowpass switch‐1 is in OFF and switch‐2 in ON condition. The low pass filter has 3‐dB cutoff frequency of 3.25 GHz with a selectivity of 170 dB/GHz. The bandpass filter is cantered at 3.65 GHz and has a well‐matched pass band with insertion loss of 0.2 dB and wide stop band with two transmission zeros (TZs). The frequency positions of TZs are independently varying with series and shunt loading elements. The filter performance has been validated through circuit model, electromagnetic simulation, and experimental measurements. The electrical size of bandpass filter excluding feed line is 0.22 λ_g × 0.20 λ_g (12 × 11 mm²) at center frequency of 3.65 GHz and for lowpass filter is 0.19 λ_g × 0.18 λ_g at cutoff frequency of 3.25 GHz. The filter can be applied in suitable for different wireless applications.     

Novel configuration of ultra‐wide band uni‐planar configuration of complementary split ring resonator composite right/left‐handed based band pass filter with sharp roll off and good stopband attenuation

In this paper, a compact novel simple design of ultra‐wide bandpass filter with high out of band attenuation is presented. The filter configuration is based on combining an ultra‐wide band composite right/left‐handed (CRLH) band pass filter (BPF) with simple uni‐planar configuration of complementary split ring resonator (UP‐CSRR). By integrating two UP‐CSRR cells, the ultra‐wideband CRLH filter roll‐off and wide stopband attenuation are enhanced. The filter has 3 dB cutoff frequencies at 3.1 GHz and 10.6 GHz with insertion loss equals 0.7 dB in average and minimum and maximum values of 0.48 dB and 1.05 dB, respectively over the filter passband. Within the passband. The transition band attenuation from 3 dB to 20 dB is achieved within the frequency band 1.9 GHz to 3.1 GHz (48%) at lower cutoff and the frequency band 10.6 GHz to 11.4 GHz (7%) at upper stopband. Moreover, the filter has a wide stopband attenuation >20 dB in frequencies 11 GHz to 13.6 GHz (21%) and ends with 3 dB cutoff frequency at 14.8 GHz. Furthermore, the designed filter size is very compact (23 × 12 mm²) whose length is only about 0.17 λ_g at 6.85 GHz. The filter performance is examined using circuit modeling, full‐wave simulations, and experimental measurements with good matching between all of them.     

Compact ultra‐wideband bandpass filter with variable notch characteristics based on transversal signal‐interaction concepts

A novel technique is presented to design highly compact microstrip ultra‐wideband (UWB) bandpass filters that exhibit high selectivity quasi‐elliptical response. The design is based on transversal signal‐interaction concepts that enable the inclusion of single or dual notch‐bands within the filter's passband to eliminate interference from other services that coexist within the UWB spectrum. The filter configuration comprises of two transmission paths which include folded T‐shaped stepped impedance resonators (SIRs) that are capacitively coupled with the input/output lines to enable signal transmission. It is shown that by combining the filters of different passband centre frequencies an UWB filter can be realised with either a single‐ or dual‐notch function. The theoretical performance of the filter is corroborated via measurements to confirm that the proposed filter exhibits UWB passband of 123% for a 3 dB fractional bandwidth, a flat group‐delay with maximum variation of less than 0.3 ns, passband insertion loss less than 0.94 dB, high selectivity, a sharp rejection notch‐band with attenuation of ?23 dB, and a good overall out‐of‐band performance. Furthermore, the filter occupies a significantly small area of 94 mm² compared with its classical counterparts. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:549–559, 2014.     

Recessed ground microstrip line at 60 GHz and its application of band‐pass filter

The effect of finite‐size recessed ground on characteristic features of a microstrip transmission line is investigated and verified experimentally on alumina substrate of height 0.127 mm with ε_r = 9.8 at 60 GHz. A measured characteristic impedance of 238 Ω, effective dielectric constant of 3.09, and attenuation constant of 3.4 Np/m is achieved by using a recessed ground of dimensions (width × depth) 4.5 mm × 0.95 mm, below a 50‐Ω (on conventional ground plane) microstrip line. The effect of recessed ground on lumped equivalent circuit elements of microstrip line discontinuities including series‐gap, open‐end, and step discontinuities is also studied. To show the usefulness of recessed ground microstrip line, a prototype of fifth‐order Chebyshev‐type recessed ground end‐coupled band‐pass filter is designed and fabricated at 60 GHz. The filter exhibits measured insertion loss lower than 2.2 dB and return loss better than 13 dB over 3‐dB passband of 6% centered at 60 GHz. The measured results show good consistency with simulated results and confirm the usefulness of recessed ground plane microstrip line.     

A high BDR microstrip‐line fed antenna with multiple asymmetric elliptical wide‐slots for wideband applications

In this study, a novel printed wide‐slot antenna for wideband applications is presented. The designed antenna consists of four merged elliptical wide‐slots (EWSs) of different dimensions in the ground plane. An open‐ended microstrip line having a characteristic impedance of 50 Ω is used to excite the EWS. Each EWS corresponds to the different frequency of operation and hence when merged together give a wideband response. The fabricated prototype of the designed antenna shows the 10 dB return loss bandwidth (RLBW) of about 157.72% ranging from 2.21 to 18.7 GHz. The peak gain varies from 0.1 to 6.5 dB within the RLBW is reported. An almost constant group delay, low variation (<?40 dB) in the transfer function S₂₁ and linear phase variation for both side by side and face to face orientations of the designed antenna shows its applicability for wideband applications. The electrical dimensions of about 0.176λ _L × 0.162λ _L (where λ _L is the lowest operating wavelength) give rise to the bandwidth dimension ratio of about 5505 which is highest among the antenna structures reported in the literature. The measured results are found in good concordance with the results obtained from numerical simulations.     

Coupled‐line band‐pass filter with T‐shaped structure for high frequency selectivity and stopband rejection

A coupled‐line band‐pass filter (BPF) with T‐shaped stub structure is presented. Five transmission poles within the passband and eight deep transmission zeros (TZs) from 0 to 2f₀ (f₀ denotes filter's center frequency) are realized through input impedance calculations. With the simple T‐shaped structure, the positions of six TZs can be appropriately adjusted to achieve high frequency selectivity and stopband rejection. For demonstration, a BPF prototype centered at 2.05 GHz is designed and fabricated, whose measured rejection levels are of over 45.5 dB at lower stopband and better than 19.5 dB at upper stopband. The simulation and measurement results are in good agreement, which validates the design idea.     

A compact printed ultra‐wideband multiple‐input multiple‐output prototype with band‐notch ability for WiMAX,LTEband43, and WLAN systems

A compact ultra‐wideband multiple‐input multiple‐output (UWB‐MIMO) antenna with good isolation and multiple band‐notch abilities is developed in this work. It consists of two quadrant shaped monopole antennas backed by ground stubs. A good isolation is achieved due to the two proposed extended curved ground stubs. The frequency rejection for the WLAN system is realized by loading a capacitive loaded loop resonator adjacent to the feed line. The band rejection for the WiMAX and LTE band43 system is achieved by embedding a quadrant shaped CSRR on each radiator's surface. The measured bandwidth of the antenna is 3.06 GHz‐11 GHz (|S₁₁| < ?10 dB and |S₂₁| < ?18 dB) with a band rejection from 3.5 GHz‐4 GHz to 5.1 GHz‐5.85 GHz, respectively. Time domain performances are investigated in terms of group and phase delay characteristics. Diversity characteristics are evaluated in terms of the envelope correlation coefficient, mean effective gain, and channel capacity loss.     

A compact dual‐band zeroth‐order resonator antenna loaded with meander line inductor

A novel zeroth‐order resonator (ZOR) meta‐material (MTM) antenna with dual‐band is suggested using compound right/left handed transmission line as MTM. In this article, suggested antenna consists of patch through series gap, two meander line inductors, and two circular stubs. The MTM antenna is compact in size which shows dual‐band properties with first band centered at 2.47 GHz (2.05‐2.89 GHz) and second band is centered at 5.9 GHz (3.70‐8.10 GHz) with impedance bandwidth of (S₁₁ < ? 10 dB) 34.69% and 72.45%, respectively. At ZOR mode (2.35 GHz), the suggested antenna has overall dimension of 0.197λ_o × 0.07λ_o × 0.011λ_o with gain of 1.65 dB for ZOR band and 3.35 dB for first positive order resonator band which covers the applications like Bluetooth (2.4 GHZ), TV/Radio/Data (3.700‐6.425 GHz), WLAN (5‐5.16 GHz), C band frequencies (5.15‐5.35, 5.47‐5.725, or 5.725‐5.875 GHz) and satellite communication (7.25‐7.9 GHz). The radiation patterns of suggested structure are steady during the operating band for which sample antenna has been fabricated and confirmed experimentally. It exhibits novel omnidirectional radiation characteristics in phi = 0° plane with lower cross‐polarization values.     

Compact ultra‐wideband bandpass filter with configurable stopband based on diamond‐shape resonator

An ultra‐wideband compact bandpass filter (BPF) with configurable stopband by tuning transmission zeroes is proposed in this paper. The ultra‐wideband bandpass response is based on a diamond‐shape resonator consisting of a pair of broadside coupled diamond‐shape microstrip lines, within which a diamond shape defected ground structure (DGS) is etched in the middle. Flexible transmission zeros realized by open and short stubs can be easily adjusted to improve band selectivity and harmonic suppression. Measurement result shows that the dedicated device has a 3 dB fractional bandwidth of 148% (0.94‐6.36 GHz) with 20 dB rejection stopband from 6.87 to 9.7 GHz (77.5%) which agrees good with the simulate performance. The overall size of the proposed BPF is 0.27 λ_g × 0.23 λ_g.     

A covering Ka‐band two‐way switch filter module using a three‐line and an E‐plane waveguide band‐pass filters

A millimeter‐wave ultrawideband two‐way switch filter module is presented in this article. The switch filter module covers whole Ka‐band (26–40 GHz), and is composed of two wideband band‐pass filters and two monolithic microwave integrated circuit (MMIC) single pole two throw (SP2T) switches. One filter is realized using E‐plane iris waveguide band‐pass filter, and another is realized by a novel 11‐pole three‐line microstrip structure band‐pass filter. Compared with the traditional three‐line filter, the proposed three‐line filter not only retains virtues of the traditional three‐line filter, but also resolves drawbacks of it, which include discontinuities between adjacent sections, many parameters of design, and no effective matching circuits at input/output ports. The developed switch filter module is fabricated using hybrid integrated technology, which has a size of 51 × 26 × 9.8 mm³, and interconnections between MMICs and microstrip are established by bond wires. The fabricated switch filter module exhibits excellent performances: for two different states, the measured insertion loss and return loss are all better than 7 and 10 dB in each pass‐band, respectively. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:305–310, 2015.     

Compact tri‐notched ultrawideband bandpass filter design using CSRR,DGS, and FMRR configurations

The folded multiple‐mode resonators with complementary split ring resonator (CSRR), and defected ground structures (DGS) are introduced for notched ultrawideband (UWB) bandpass filter (BPF) design in this article. Using the CSRR, FMRR, notched wide‐band BPF, a notch response can exist in the UWB passband for blocking the interference. Adjusting the size factor of CSRR, the wide tuning ranges of notch frequencies included the desired frequencies of 5.2/5.8 GHz are achieved. The lower insertion loss (0.31 dB), higher rejection level (?48.40 dB), wider bandwidth (FBW 75%), and wider stopband (extended to 2.01 f₀ below ?20 dB rejection level) of UWB band at the central frequency f₀ = 4.58 GHz are obtained. Second, design a CSRR, DGS, FMRR, tri‐notched UWB filter, the wider bandwidth (3.1–9.8 GHz) with FBW = 126%, lower insertion loss (0.26 dB), and higher rejection level (?44 dB) of UWB band at central frequency f₀ = 5.6 GHz are presented. Using the CSRR and interdigital couple, three notch responses can exist in the UWB passband for blocking the interference signals. Adjusting the size factor of CSRR and interdigital couple, the wide tuning ranges of notch frequencies included the desired frequencies of 5.18/6.10/8.08 GHz are achieved. The wide tuning ranges of three notched frequencies cover from 5.0 to 8.4 GHz. It is a simple way to control the notch responses. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:571–579, 2014.     

High inter‐port isolation dual circularly polarized slot antenna with interdigital capacitor

A planar dual circularly polarized slot antenna is presented. The designed antenna has two tilted “8” shaped slots fed by microstrip lines, one each for transmission (T_X) and reception (R_X) operations. The isolation between the two ports (T_X and R_X) is augmented by means of an interdigital capacitor based bandstop filter. The proposed antenna has an impedance bandwidth of 361 MHz centered at 2.293 GHz (2.113‐2.474 GHz) with the isolation between the ports being >17.6 dB which goes up to a value as high as 46 dB within the band of operation. The 3 dB axial ratio (AR) bandwidth is 11.52% centered at 2.1275 GHz (2.005‐2.25 GHz). Because of its high inter‐port isolation within the AR bandwidth, the design is suitable as a full‐duplex antenna for applications in S‐band.     

Wideband and wide stopband superconducting bandpass filter using asymmetric stepped‐impedance resonators connected to open stub

A wideband wide stopband filter is designed using asymmetric stepped‐impedance resonators (ASIRs) connected to a large open stub. The capacitive open stub and the parallel‐coupled microstrip line are used to achieve the strong couplings for large fractional bandwidth (FBW). For a wide‐stopband performance, the proposed filter uses ASIRs to improve the high‐order spurious resonant frequency. The first and last resonators of the proposed filter are further optimized to suppress the spurious resonant frequency caused by open stub. The final filter has a 70% FBW centered at 4.87 GHz with 20‐dB‐rejection stopband up to 15.78 GHz (approximately 3.24 f₀). The measured insertion loss is less than 0.15 dB and the return loss is better than 17 dB.     

A dual‐band superconducting filter with a large bandwidth ratio

In this study, we propose a stepped‐impedance‐stub loaded interdigital capacitor resonator for design of a dual‐band band‐pass filter with a large bandwidth ratio. The presented resonator has strong and weak couplings in the upper passbands (UPs) and lower passbands (LPs), respectively, so as to form a large upper/lower bandwidth ratio. Adopting a dual‐branch phase‐matched feedline structure can meet the external quality factors required for the UP/LP. Therefore, these two passbands, defined by their respective center frequencies and bandwidths, can be manipulated independently. A four‐pole dual‐band example filter with a lower bandwidth of 20 MHz at 1576 MHz and an upper bandwidth of 200 MHz at 2450 MHz is successfully designed on an YBCO/MgO superconducting wafer. The filter exhibits excellent frequency responses. The upper/LPs show insertion losses below 0.07/0.22 dB and return losses above 15.3/15.3 dB. The stopband rejection is better than 57 dB until the first spurious passband up to 6150 MHz (3.9f_L).     

Wide stopband harmonic suppressed low‐pass filter with novel DGS

In this article, a wide stopband 20 dB harmonically suppressed low‐pass filter (LPF) using novel defected ground structures (DGSs) is proposed. The DGSs has been analyzed as a low pass filter which shows a significant harmonics suppression in the stopband. The lumped parameter equivalent of the DGSs has been developed to show its effectiveness. The modified equivalent circuit model of the filter helps in placing the transmission zero near ?3 dB cutoff frequency. The LPF is designed on a 0.10 λ_g× 0.09 λ_g substrate size where λ_g is guided wavelength at ?3 dB cut‐off frequency (f_c) equal to1 GHz. The simulation shows a 20 dB harmonic suppression up to 50 f_c. The prototype of the LPF has been developed and with the available vector network analyser, the S‐parameters have been measured upto 20 GHz (20 f_c).The state of the art comparison of the LPF shows a high figure of merit equal to 26 250 which is higher than many recently published works.     

A comparative study of group delay equalizers for satellite communications

This article presents a comparative study of four different group delay (GD) equalizers with a narrow band filter used as input multiplexer for a Ku‐band satellite transponder. A dual mode cylindrical filter with 36 MHz bandwidth is designed and fabricated. The filter GD is measured and two types of group‐delay equalizers are designed to fulfill the requirements of the transponder's GD mask. Two rectangular and two cylindrical equalizers are designed and their performance parameters, such as insertion loss and equalized bandwidth, are compared. In addition, a comparison between the designed first order (C‐section) and second order (D‐section) GD equalizers is done.