Good Stopband Research Articles

Compact wide-stopband slow-wave half-mode substrate integrated waveguide filter with interdigital complementary split-ring resonator metasurface

Abstract In this work, a compact slow-wave half-mode substrate integrated waveguide (HMSIW) bandpass filter is developed by loading the proposed interdigital complementary split-ring resonator (IDCSRR) metasurface for wireless communication and sensing applications. The IDCSRR metasurface is constituted by etching interdigital slots inside the conventional CSRR, which can effectively enhance the product of the equivalent capacitance and inductance of the structure, and eventually reduces the resonant frequency. Through the evanescent-mode transmission generated in HMSIW by the negative permittivity effect of IDCSRR metasurface, miniaturized filter can be realized. Later, to further reduce the filter’s size, the capacitance-enhanced ring-mushroom units are patterned into HMSIW to generate slow-wave effect. Then, to improve the filter’s out-of-band suppression, the source-load coupling scheme is utilized to generate extra transmission zero. Meanwhile, to further widen the stopband, meander spurlines are etched on the input and output microstrip lines to suppress the higher-order harmonics with its bandgap function. To demonstrate the availability of the aforementioned concepts, a bandpass filter based on the HMSIW-IDCSRR unit cell is realized. Measurements show that the fabricated prototype exhibits an center frequency (f0) of 0.97GHz. Moreover, the out-of-band suppression can reach 30dB, with the upper stopband up to 4.31 f0. Hence, the proposed filter achieves good stopband and miniaturization performance.

Fabrication of C-Band High-Temperature Superconducting Microstrip Triplexer with High Accuracy

This article presents a miniaturized C-band triplexer fabricated with high-temperature superconducting (HTS) microstrip lines and to be applied to quantum computers. The triplexer consists of three bandpass filters and branch lines. In the design of the bandpass filters, folded step impedance resonators (SIRs) are firstly used to achieve good stopband performances by harmonic suppression. Secondly, cross-coupling structures are also utilized to further improve the passband edge steepness of the bandpass filters. Finally, the parasitic transmission zeros originating from the assembling box sizes are employed to achieve a deeper out-of-band rejection. Three bandpass filters are designed and connected to the common input port of the triplexer. After that, the triplexer is coarsely optimized by advanced design system (ADS) for time-saving and is finely optimized by Sonnet for better accuracy. The optimized layout of the triplexer is fabricated on a 2-inch diameter and 0.5 mm thickness MgO wafer; here, the MgO wafer is double-sided coated with HTS YBa2Cu3O7 (YBCO) thin films. The measured passband bandwidths (return loss greater than 12 dB) of the triplexer are 6.420-6.680 GHz, 6.780-7.030 GHz, and 7.110-7.380 GHz, respectively, which satisfy the required design specifications.

Dual‐band filtering power amplifier with extended passband bandwidths and wide stopband rejection

AbstractThis article presents a dual‐band filtering power amplifier (DB‐FPA) with extended passband bandwidths and wide stopband rejection, which is helpful in reducing the number of microwave components in the dual‐band radio frequency front end, resulting in compact circuit size and low loss. In the designed DB‐FPA, a wideband low‐pass filter is applied as the input matching network (IMN) to provide wideband impedance matching and good stopband rejection, while a dual‐band filtering impedance transformation is adopted as the output matching network (OMN) to provide dual‐band impedance matchings and filtering responses simultaneously. Specifically, the IMN is constructed by high‐impedance transmission‐line sections and low‐impedance open‐circuit stubs. The OMN is designed based on the specific external quality factors and coupling coefficients during two bands, resulting in dual‐band impedance transformations and dual‐band filtering responses. Then, based on the above IMN and OMN, the design procedure of the presented DB‐FPA is summarised. To verify the proposed idea, a novel DB‐FPA has been fabricated and measured. During the two frequency bands, the measured maximum power added efficiencies are 55.11% and 47.78% within 33.0 dBm input power, while the measured peak gains are 15.4 and 14.0 dB within 15.0 dBm input power.

Compact Half-Mode SIW Filter With High Selectivity and Improved Stopband Performance

In this letter, a novel filter with high selectivity is proposed using a hybrid multilayer half-mode substrate-integrated waveguide (HMSIW). First, a rectangular HMSIW is used to realize a third-order cross-coupling topology, which could introduce a transmission zero (TZ) on the left side of the passband. Then a ring microstrip resonator is added to form the new dangling block, which realizes the fourth-order response with an additional TZ located on the right side of the passband. Sharp skirt and high selectivity are then achieved. In addition, since each mode of the HMSIW has different external coupling strengths at the same feeding position, harmonic suppression can be achieved easily by moving the feeding position. Therefore, a good stopband can be obtained with decent out-of-band performance. Size reduction is also achieved through the multilayer HMSIW and hybrid microstrip structures as well.

Design for a Self-Packaged All-PCB Wideband Filter With Good Stopband Performance

A new design of a self-packaged all-printed circuit board (PCB) wideband filter based on the cascade connection of high-pass filter (HPF) and low-pass filter (LPF) is presented. The novel low- and high-pass quasi-lumped filter structure differs from the known ones by the existence of cross coupling between elements producing transmission zeroes (TZs) at the desired frequency. It is shown that high-order structures make it possible to design a wideband filter having the number of TZs in the low-frequency stopband equal to the order of the applied HPF and the number of TZs in the high-frequency stopband equal to half the order of the LPF. An implementation of two-layer metallization of the capacitor plates made it possible to manufacture all three types of filters using the common technology of multilayer PCBs with a good coincidence of the characteristics of the model and the fabricated filters. The filter fabricated using materials with a rather low quality factor (F4BM/RO4450B/RO4003C) has demonstrated a good performance: the central frequency is 0.99 GHz, the 1-dB fractional bandwidth is 152%, the minimum in-band loss is 0.3 dB, the selectivity ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta f_{\mathrm {30~dB}}/\Delta f_{\mathrm {3~dB}}$ </tex-math></inline-formula> ) is 1.21, and the 40-dB stopband width is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.16f_{0}$ </tex-math></inline-formula> .

Compact SIDGS Filtering Power Divider With Three-Port 10-GHz Reflectionless Range

In this brief, a compact high isolation filtering power divider (FPD) with wide stopband and wide-band three-port reflectionless operation is proposed. Such FPD consists of a trigonometric substrate-integrated defected ground structure (SIDGS) based resonator and three absorptive networks. The good stopband performance is achieved by using the trigonometric SIDGS. Meanwhile, the absorptive networks based on common-gate topology capable of absorbing the out-of-band reflected signals are connected to the SIDGS resonator, which provides the wideband reflectionless operation in all three ports of the FPD. To verify the mechanisms mentioned above, a FPD operated at 2.10 GHz (i.e., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {f_{0}}$ </tex-math></inline-formula> ) is fabricated, which exhibits a 42 dB stopband rejection level up to 20 GHz (i.e., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.5\boldsymbol {f_{0}}$ </tex-math></inline-formula> ). The measured reflectionless range with return loss lower than −10 dB is up to 10 GHz in all three ports. The core size of the FPD is about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.36\,\,\boldsymbol {\lambda _{g}} \times 0.38\,\,\boldsymbol {\lambda _{g}}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\lambda _{g}}$ </tex-math></inline-formula> is the microstrip guided wavelength at the center frequency.

Reconfigurable high-Q terahertz filtering of VO2-based metamaterials using optical tunneling

Up to date, reconfigurable terahertz (THz) band-pass filters based on the design of metamaterials with vanadium dioxide (VO2) have been investigated extensively. However, VO2-based THz metamaterials with high-quality tunable narrowband transmission and good stop-band rejection have yet to be reported, which are essential for THz wave filtering components or systems. Here, we propose a reconfigurable filter in combination with a dielectric metastructure and a VO2 thin film. Utilizing the optical tunneling effects of a cavity layer, the filter has a high band-pass transmission up to 98% at 0.246 THz with a narrow bandwidth of 0.0009 THz, an ultra-high Q-factor of 273, and two broad nearly-suppressed sidebands. The transmission intensity can be modulated by the phase transition of VO2, and the modulation depth is as high as 96.4%. By efficiently tuning the cavity layer thickness, the filter can be designed for a series of transmission wavelengths and further accomplish the switch between the narrow band-pass filtering and wideband reflection. Moreover, the manipulation of the incident angle and polarization can be adopted as an additional degree to achieve a similar switching function. Our study implies a potential for developing various THz applications, where reconfigurable high-Q THz filtering is required.

A compact S-band band-pass filter with ultra-wide stopband

Abstract A novel compact S-band band-pass filter (BPF) with ultra-wide stopband is presented. The proposed filter mainly consists of three parts, a novel crossed resonator, parallel-coupled microstrip lines, and defect ground structures (DGSs). The resonator is constructed by three capacitive open stubs, while a defect is etched in the center stub to eliminate high frequency harmonics. The parallel-coupled microstrip lines are mainly used to improve the passband and the roll-off rate (the ratio of height to width of the filter transition band). And the DGSs are utilized to improve the stopband performances. The proposed BPF has the merits of compactness, good insertion loss and good stopband characteristic. The measured 3 dB operating band is 1.80–4.03 GHz (76.5% at f 0 = 2.92 GHz), The upper out-of-band suppression was better than 20 dB for the frequency up to 20 GHz (6.33f 0), and the upper roll-off rate reaches 75.59 dB/GHz.

Realization of absorption, filtering, and sensing in a single metamaterial structure combined with functional materials.

In this paper, a hybrid vanadium dioxide (VO2)-graphene-based bifunctional metamaterial is proposed. The realization of the different functions of perfect transmission and high absorption is based on the insulator-metal phase transition of VO2 material. The Fermi energy level of graphene can be treated to dynamically tune the absorption and transmission rates of the metamaterial structure. As a result, when VO2 is in the insulating state, the designed metamaterial can be used as a filter providing three adjustable passbands with center frequencies of 1.892 THz, 1.124 THz, and 0.94 THz, and the corresponding transmittances reach 93.11%, 98.62%, and 90.01%, respectively. The filter also shows good stopband characteristics and exhibits good sensing performance at the resonant frequencies of 1.992 THz and 2.276 THz. When VO2 is in metal state, the metamaterial structure acts as a double-band absorber, with three absorption peaks (>90%) in the range of 0.684 THz to 0.924 THz, 2.86 THz to 3.04 THz, and 3.28 THz to 3.372 THz, respectively. The designed structure is insensitive to the polarization of vertically incident terahertz waves and still maintains good absorption performances over a large range of incidence angles. Finally, the effects of geometric parameters on the absorption and transmission properties of the hybrid bifunctional metamaterials have also been discussed. The switchable metamaterial structures proposed in this paper provide great potential in terahertz application fields, such as filtering, smart sensing, switching, tunable absorbers, and so on.

A Compact Wideband Circularly Polarized Planar Filtenna Using Synthesis Technique for 5 GHz WLAN Application

This paper presents a compact wideband circularly polarized planar filtenna based on filter synthesis methodology. The proposed filtenna consists of third order hairpin line resonator filter coupled with an circularly polarized hexagonal shaped radiating element. The better integration between antenna and filter helps in achieving both compactness and high frequency selectivity. The proposed filtenna exhibits a wideband filtering response with an impedance bandwidth of 35.77% (3.92–5.63 GHz), a wide axial ratio bandwidth of 34.94% (3.66–5.21 GHz), and a peak gain of 2.25dBic within its operating bandwidth. In order to validate its practicability, the filtenna is designed and fabricated. The measurement results shows that the proposed filtenna exhibits good stopband gain rejection, good selectivity at band edges, flat passband gain, and a wide axial ratio bandwidth well suited for 5 GHz WLAN application.

Substrate integrated waveguide omnidirectional filtering antenna with a controllable radiation null for 5.8 GHz WiFi application

A filtering antenna composed of a monopole and two stacked circular substrates integrated waveguide (SIW) cavity for 5.8 GHz WiFi application is proposed in this letter. Cross-coupling between the feeding probe and the second SIW cavity resonator is utilized to generate a radiation null at the frequency above the working band. By properly designing the location of the feeding probe and the size of the coupling slot between the two SIW resonators, the frequency of the radiation null can be adjusted. Experimental results of the fabricated filtering antenna show good agreement with the simulated performance. The measured filtering antenna response has a return loss greater than 10 dB with a fractional bandwidth of 16.4% centered at 5.48 GHz while there is a radiation null at 6.85 GHz. Omnidirectional patterns are achieved in horizontal plane with a maximum gain of 1.1 dBi. The proposed filtering antenna has the merits of compact size and good stopband radiation suppression.

Temperature-tunable THz metamaterial absorber based on vanadium dioxide

To solve the limitation that the absorber can not be adjusted actively according to the external environment, a terahertz wave modulator is proposed and designed based on the adjustable conductivity of temperature-controlled phase change material vanadium dioxide thin film, which can realize switching metamaterial absorber. The absorber is composed of a metal substrate, insulating substrate and metal resonant unit. The transmission characteristics of the absorber are simulated by CST 2016 simulation software. The results show that the transmission coefficient of the designed filter can reach −41.62 dB at the resonant frequency, showing good stopband characteristics.

Design of dual-band power amplifier based on tri-band impedance matching circuit

In this paper, a dual-band power amplifier based on tri-band impedance matching circuit is proposed. This amplifier uses reverse thinking to combine the tri-band impedance matching network with the power amplifier to mismatch the intermediate frequency as the isolation band. And the intermediate frequency is 3.0 GHz. Besides, the design process of dual-band power amplifier is given, and an example is given. Through the actual test results of the amplifier, it can be seen that the additional power efficiency of the amplifier at the frequencies of 2.6GHz and 3.4GHz is about 60%, the output power is more than 40dBm, and the gain is above 10dB. In the test results, it can be seen that the stopband of the power amplifier is 2.95-3.05GHz, the minimum gain and the minimum drain efficiency output power of the stopband are −1dB and 2%, which has a good stopband suppression effect.

A high‐selectivity wideband bandpass filter with multiple transmission poles and zeros

In this paper, a simple high-selectivity wideband bandpass filter based on a novel π-shaped coupled-line structure is introduced. The presented filter realizes wide bandwidth, excellent passband selectivity and good stopband suppression by using two coupled lines with diagonal open-circuited ports and three coupled lines with cascaded ports. The design theoretical analysis and the complete equation derivation are provided in detail. Furthermore, a prototype with 3-dB fractional bandwidth of 50.9% is simulated, fabricated, and measured. The simulated and measured results have a good consistency, which verifies the analytical design principle.

A Differentially Fed Dual-Polarized Filtering Patch Antenna With Good Stopband Suppression

A differentially-fed dual-polarized filtering patch antenna with no extra filtering circuits involved is proposed. The filtering response is realized by symmetrically loading four short strips and a long cross-type strip, and a square ring slot to insert radiation zeros on the dual-polarized antenna element. The short and long strips can generate two transmission zeros at lower and upper band edges, respectively, leading to a sharp skirt selectivity. In addition, the long cross-type strip and the square ring slot can respectively introduce an extra resonance close to the original one, broadening the impedance bandwidth. Also, the equivalent circuit is presented to show that the two zeros can be brought by the two equivalent series resonant circuits extracted from the short/long strips resulting in the bandpass response. We may note that the proposed filtering structure owns the merits of simple, compact and complete symmetry, thus it can be well integrated with the dual- polarized antenna. Consequently, a compact and high-gain dual- polarized filtering antenna with good stopband suppression, low cross-polarization level and symmetrical radiation patterns is obtained. It can achieve an impedance bandwidth about 15% and a maximum gain of 8.4 dBi. The simulated cross-polarization level is below -40 dB, and the measured one is lower than -22 dB. Moreover, the upper stopband can be up to 2.6 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the center frequency of the antenna), where the stopband radiations from all the directions can be suppressed and the measured suppression ratio can reach 90%.

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 λg 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 narrowband high-order dual-band superconducting bandpass filters using stub-loaded double-folded resonators

Compact narrowband high-pole dual-band high-temperature superconducting (HTS) bandpass filters (BPF) have been developed that use newly developed stub-loaded double-folded microstrip resonators. The resonators have a weak coupling property that enables the distance between resonators to be reduced and that suppresses unwanted nonadjacent coupling. Moreover, it enables independent control of the resonant frequencies of the first and second passbands. Additional microstrip lines and a dual-feeding structure are introduced to enable flexible adjustment of the internal and external couplings of the two passbands. A prototype ten-pole dual-band HTS BPF operating at 1.5 and 2.0 GHz was designed and constructed. The filter for both passbands has a 1% fractional bandwidth and was fabricated using YBa2Cu3Oy thin film on an Al2O3 substrate. The measured frequency responses of the filter were in good agreement with the simulated ones. These results demonstrate that the compact filter has high selectivity, low insertion loss, and good stop-band rejection.

Millimeter-Wave CMOS 30/80 GHz Sharp-Rejection Dual-Band Bandstop Filters Using TFMS Open-Stepped-Impedance Resonators

In this brief, for the first time, dual-band bandstop filters (DBBSF) for millimeter-wave operation at 30/80 GHz bands are presented in 0.18 μm CMOS process. The filter design is based on TFMS shunt open-ended stepped-impedance resonators, which exhibit dual stopband response with impedance controlled center frequencies and bandwidths. Lossless transmission line model is used for theoretical analysis, where the conditions for acquiring two stopbands and to achieve good stopband isolation are investigated using single and double resonators. Furthermore, an improved design for good passband at mid-band has been proposed, resulting in a DBBSF that could also replace a wideband bandpass filter with sharp-rejection on both sides. Two prototype filters with optimally compact geometries are fabricated and characterized to demonstrate dual-band bandstop characteristics at 30/80 GHz. The measured results are in good agreement with full-wave electromagnetic simulations.

Synthesis and design of SIW dual-band narrow-band bandstop filter

ABSTRACT In this letter, a general approach to synthesize arbitrary order dual-band narrow-band bandstop filter (BSF) is proposed. Simple formulas are derived to calculate the design parameters for the filter. To validate the method, a third-order dual-band BSF using substrate integrated waveguide (SIW) technology is fabricated. Taking the advantage of the high Q SIW resonators, the fabricated filter shows good stopband suppression. The measured center frequencies of the filter are 6.81 and 7.213 GHz, and the corresponding relative 3-dB bandwidths are 4.6% and 4.1%.

A novel wideband bandpass filter based on CSRR‐loaded substrate integrated folded waveguide

A novel wideband bandpass filter based on folded substrate integrated waveguide (FSIW) is presented in the article. Five square complementary split-ring resonators (CSRRs) are etched in the middle layer of the FSIW. By adjusting the physical size of the CSRR structure, the resonant frequency of the CSRRs can be tuned at the same time and the stopband performance can be changed. As transverse electromagnetic (TEM) mode can be transmitted in the stripline, FSIW excited by stripline shows wider passband than that excited by microstrip line directly. To achieve perfect impedance matching, two microstrip lines to stripline transitions are added in two ports of the filter. The proposed bandpass filter exhibits compact size, high selectivity, good stopband rejection, lower radiation loss, and wideband performances. The measured results show that the fractional bandwidth of the filter is about 35.5%. The measured return loss is better than 15 dB from 4.84 GHz to 6.90 GHz, and the insertion loss is less than 1.2 dB. The comparison between the simulated results and the measured ones validate the possibility of the technology that combines the FSIW and CSRR.