Stepped-impedance Open Stubs Research Articles

A dongle-sized bandwidth-reconfigurable filtenna for UWB/5G-n77 band applications

ABSTRACT This paper presents a frequency reconfigurable filtenna for efficiently switching between ultra-wideband (UWB) and 5G-n77 band. The filter section with the UWB state of operation is realised by a stepped impedance open stub loaded at the middle of a stepped impedance resonator. Switching to 5G-n77 band is accomplished by appending two open-circuited uniform impedance stubs to the UWB filter section through PIN diodes. The antenna section is coplanar waveguide (CPW) fed and is based on a quasi-self-complementary design with a half- hexagonal-shaped radiator. The microstrip to CPW transition is realised by connecting the ground planes through vias. The overall size of the filtering antenna is 18.5 mm × 57 mm. The filtering antenna has stable radiation patterns with good agreement between simulated and measured results. The peak gain in 5G-n77 band and UWB band is 4 dBi.

A compact diamond-shaped dual-band bandpass filter with multiple transmission zeros

In this paper, a compact diamond-shaped dual-band bandpass filter with seven transmission zeros in the stopband and two poles in each passband is designed, analyzed, and implemented. The proposed filter consists of coupled lines and stepped impedance open stubs. Theoretical analysis based on lossless transmission line theory is carried out to verify the transmission zero frequencies. A filter prototype with center frequencies of 1.17 GHz and 2.85 GHz is fabricated to exhibit the feasibility of the design. The prototype is printed on a 0.79 mm Rogers RT Duroid 5880 with a dielectric constant of (ϵr = 2.2) and occupies an area of 0.29λg×0.17λg, where λg is the guided wavelength at the first center frequency. The experimental results show a 3-dB fractional bandwidth of 13.65% and 3.5% at low and high center frequencies, respectively. The simulated and experimented frequency responses are consistent with each other.

A miniaturized dual-band bandpass filter with sharp roll-off rate using coupled lines and dual transmission lines

This paper presents a compact, high roll-off rate second-order dual-band bandpass filter with seven transmission zeros. The proposed filter design constructs of dual transmission lines, coupled lines, stepped impedance open stubs, and quarter-wavelength transmission lines. The proposed filter has a size of 0.31λg × 0.24λg and is printed on RT/duroid 5880 substrate to operate at two different frequencies (1.16 GHz and 2.71 GHz). The proposed filter is fabricated and measured, and good input matching is obtained at desired frequencies. Excellent isolation is achieved between two passbands due to the stopband effect created by the dual transmission lines. The simulated and tested frequency responses are in high agreement with each other.

A dual‐band filtering structure for highly selective reconfigurable bandpass filter and filtering balun

This article proposes a filtering structure consisting of two half-wavelength resonators and two open-stub loaded resonators, which generates two third-order passbands. Multiple transmission zeros are introduced by the newly developed coupling scheme, resulting in extremely sharp roll-off desirable for highly selective filters. The proposed structure is applied to design a PIN-diodes switch-controlled reconfigurable dual-band bandpass filter (BPF) with four-state filtering responses: both passbands ON, both passbands OFF, high-frequency passband ON, and low-frequency passband ON. Stepped-impedance open stubs and one-end-grounded coupled lines are studied and employed in the design to suppress unwanted responses. In addition, two filtering structures are placed symmetrically to design a dual-band balun BPF. Double-sided parallel-strip lines are added in the input port of the filter, and their inherent out-of-phase feature enables the balun filter to convert unbalanced signal to balanced signal at desired frequencies. The measured results of both fabricated devices agree well with the simulated results. The switchable BPF and balun BPF have two passbands (2.8 and 4.8 GHz) with high selectivity with the minimum roll-offs from −3 to −15 dB are 1.70 × 103 and 2.71 × 103 dB/decade, respectively. The insertion loss of the switchable BPF is 2.3/2.0 dB and the minimum signal suppressions level OFF state is measured as −18.2 dB. The insertion loss of the balun BPF is 1.8/1.4 dB, and the phase and magnitude imbalances are less than 0.3 dB and 5°, respectively. The excellent performances of the implemented filter and filtering balun successfully demonstrate the advantages and design efficacy of the proposed filtering structure for different applications.

Efficient design approach of triple notched UWB filter

In this article, a triple notched bands (TNB) utra-wideband (UWB) bandpass filter (BPF) is designed based on accurate analytical approach. This study has led to a simple structure composed of an uniform transmission line (UTL) loaded by four stepped-impedance open stubs (SIOS). The proposed design approach allows to accurately define two transmission zeros (TZ) at the cut-off frequencies of the UWB spectrum (3.1 and 10.6 GHz) and three narrow notched bands at 5.18 GHz, 5.86 GHz and 7.92 GHz. The notched band bandwidths could also be controlled as well as the out of band rejection. The simulated and measured results of the designed filter are in good agreement. Interesting performances are obtained satisfying the UWB applications requirements, i.e. insertion loss<1.5 dB, return loss better than 15 dB, high cancellation of the unwanted in-band interferences.

Design of sextuple-mode triple-ring HTS UWB filter using two-round interpolation* *Project supported by the National Natural Science Foundation of China (Grant No. 61471094).

A single-stage ring resonator capable of introducing six modes within the ultra-wideband (UWB) passband is presented. The sextuple-mode resonator consists of three rings and three sets of stepped-impedance open stubs. Based on this sextuple-mode resonator, a UWB filter fed by the interdigital-coupling line (ICL) is designed. And we propose a two-round interpolation method to obtain the filter’s initial dimensions. The designed filter is fabricated on a double-sided YBCO/MgO/YBCO high-temperature superconducting (HTS) thin film for demonstration. The experimental results show that this UWB filter produces eight resonances in the passband eventually, which effectively improves the in-band reflection and the band-edge steepness. Moreover, the upper stopband performance is enhanced due to the transmission zeros (TZs) generated by the stepped-impedance open stubs and the ICL structure. The measured good performance verifies the practicability of the two-round interpolation approach, which can also be extended to other odd–even-mode filter designs.

High selectivity wideband bandpass filter based on stepped impedance open stubs loaded ring resonator

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.

Design of Dual Band and Tri-band Bandpass Filter (BPF) with Improved Inter-band Isolation Using DGS Integrated Coupled Microstrip Lines Structures

A novel approach to design dual-band as well as a triple-band BPF with improved isolation is ventured in this paper. In dual-band filter, dual mode property of coupled line filters is utilized to obtain resonant frequencies at 2.4 GHz and 7.4 GHz suitable for WLAN and WiMAX application respectively. Additionally a rectangular-ring DGS element is introduced within the coupled line filter to obtain a separate mid-band resonance at 5.2 GHz. The frequency shifting property of the pass bands due to cross-coupling between the microstrip line resonators and the DGS element is mostly eliminated by implementing stepped impedance open stub (SIOS) technique. All filter configurations are fabricated, measured and compared with the simulated models to validate the practical effectiveness. Stop band isolation > 40 dB and insertion loss (IL) < 0.8 dB is attained in all the filter configurations.

Design of a wideband filtering power divider with good in‐band and out‐of‐band isolations

In this article, a wideband filtering power divider with good in-band and out-of-band isolations is designed based on a hybrid Wilkinson and Gysel structure. To achieve a good in-band response, two additional in-band transmission poles can be introduced by installing the coupled-line structures at each port. By mounting a stepped impedance open stub at the input port, two transmission zeros are generated near the passband to improve the passband skirt. Furthermore, the out-of-band rejection and isolation are achieved by the other two transmission zeros, which are produced by the open stub and the three coupled-line sections mentioned above. Additionally, a good in-band isolation is realized by the isolation resistor between output ports. For the demonstration, a wideband filtering power divider centered at 1.5 GHz with a 56% fractional bandwidth and 20-dB isolation is designed and fabricated. The simulated and measured results are in good agreement with each other.

Design and band coalition of dual band microstrip filter using DGS, coupled line structures and series inductive metallic vias

An approach to design compact dual band BPF and technique to unite the two bands into a single wide band is presented in this paper. The novelty of the filter stands on the application of series of metallic vias which are used to merge the bands obtained using coupled line circuits and DGS structure. The coupled line filter and the coupled line filter integrated with DGS shows passband resonance at 4.5 GHz and 5.1 GHz within the microwave frequency of operation. Series metallic vias are used to merge the passbands into a single wider passband of bandwidth 1.6 GHz (3.5–5.1 GHz). The filter configurations are fed using stepped-impedance open stub technique to reduce cross coupling between adjacent structures. Moreover effects of several salient filter parameters like gap between edge of the microstrip coupled line resonator and via series GV and gap between mid-point of the open ended feed line and via row GM are studied to achieve greater isolation at higher frequencies. All simulated designs are fabricated and experimentally studied to vindicate the practical performance of all filter configurations.

High-Temperature Superconducting Multimode Ring Resonator Ultrawideband Bandpass Filter

This letter presents a new multimode ring resonator ultrawideband (UWB) bandpass filter by loading a microstrip line on the vertical symmetrical plane of a ring resonator and a pair of stepped-impedance open stubs at the center of this microstrip line. Five modes are allocated within UWB band, and a pair of transmission zeros are introduced to improve the passband selectivity. By adopting the parallel-coupled lines, not only suitable external coupling is achieved, but also the performance of upper stopband is improved. This quintuple-mode high-temperature superconducting UWB filter is designed on a 0.5-mm-thick MgO substrate with double-sided YBCO films. The measured results show that 3-dB bandwidth covers 1.57–6.51 GHz, the return loss is better than 10.70 dB, the out-of-band rejection is greater than 24.75 dB in the lower stopband, and the upper stopband with 20-dB attenuation level is extended to about 9 GHz.

New approach for dielectric constant detection using a microstrip sensor

Abstract A novel dielectric constant detection method using a microstrip sensor is presented in this paper. The aim was to estimate the dielectric constant in the space above a resonator which was the basic part of the sensor. Variation in resonant frequency of the resonator was considered as the criterion for detection of the dielectric constant variation. The microstrip resonator was designed using coupled stepped impedance open stubs. The circuit model of the resonator was then extracted and the resonant frequency as a function of the dielectric constant was obtained. Applicability of the proposed method was verified in experimental studies.

A Novel Design of Dual-Band Coupler with Stepped-Impedance Open Stubs

This paper presents a novel dual band coupler design that can operate at two frequency bands. It is accomplished by modifying the length and impedance of the branch lines in the conventional structure. Open stubs are used to achieve dual band branch line coupler with compact size and improve the performances. The dimensions of a conventional BLC “Branch Line coupler” occupy large area, according to the length of the transmission line which is always (g/4 of the operating frequency, ( is so long at low frequencies. When we use open ended stubs the dimensions of the new BLC is reduced compared to the conventional design. The proposed model was shown to reduce the size of the dual-band BLC around 61% based on the proposed topology. It was designed and simulated using EM solver tools for both DCS and WIMAX systems. The final optimized microstrip coupler was fabricated and measured. The simulation and measurement results are in good agreements.

X‐band substrate integrated waveguide bandpass filter using novel defected ground structure cell

ABSTRACTIn this letter, an X‐band wide stopband bandpass filter is presented, which combines substrate integrated waveguide with defected ground structure (DGS) cells. Three DGS cells, including a pair of face to face modified dumbbells embedded with E‐shape slots, are adopted to achieve bandpass performance. The wide stopband is implemented by loading low pass filter, which is designed using stepped impedance open stubs, at the input/output ports. To validate the methodology, a filter with center frequency of 8.55 GHz is designed and measured, and the measured results are in good agreement with simulated ones. The designed filter has an insertion loss of 1.45 dB, a return loss of 18.8 dB in passband, and a wide upper stopband of more than 30‐dB suppression up to 45 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1156–1160, 2015

A Novel Design Method for Compact UWB Bandpass Filters

In this letter, a new design method of ultra wideband bandpass filter (UWB BPF) is proposed. Based on a symmetrical structure of a simple uniform line loaded by a stepped-impedance open stub (SIS) connected at its center, the proposed design method employs simultaneously the optimization of a defined objective function in the range of frequency 3.1-10.6 GHz and the transmission zeros at cut-off frequencies for a rapid convergence. Obtaining different filter sizes with good performance, the compact UWB BPF is simulated, fabricated, and measured. A good agreement between simulation and measurement is obtained while achieving good performances such as a return loss better than 10 dB, an upper stopband attenuation higher than 20 dB up to 17.6 GHz, and a sharp selectivity.

Wideband Single-Layer 90$^{\circ}$ Phase Shifter Using Stepped Impedance Open Stub and Coupled-Line With Weak Coupling

This letter proposes a novel design approach of wideband 90 ° phase shifter, which comprises a stepped impedance open stub (SIOS) and a coupled-line with weak coupling. The result of analyses demonstrates that the bandwidths of return loss (RL) and phase deviation (PD) can be expanded by increasing the impedance ratio of the SIOS and the coupling strength of the coupled-line. For RL > 10 dB, insertion loss (IL) 1.1 dB, and PD of ±5°, the fabricated microstrip single-layer phase shifter exhibits bandwidth of 105% from 0.75 to 2.4 GHz.

Design of Miniaturized Microstrip LPF and Wideband BPF With Ultra-Wide Stopband

This letter presents a novel lowpass filter (LPF) structure which consists of a section of high-impedance microstrip line (HIML) with a pair of radial stubs (RSs) loaded at its center and a pair of stepped-impedance open stubs (SIOSs) loaded on both ends of HIML. The RSs loaded HIML exhibits a lowpass property and has a wide stopband. The loaded SIOSs not only can improve the roll-off rate of LPF significantly but also is able to extend the stopband. Based on such a LPF structure, a pair of highpass shorted HIMLs are paralleled on both sides of LPF to construct a wideband bandpass filter (BPF) with wide stopband. To validate the proposed method, two filters, i.e., a LPF with cutoff frequency fc at 1.07 GHz and a BPF centered at f0 = 0.89 GHz with -3 dB fractional bandwidth of 87%, are designed and fabricated. The measured results show the fabricated LPF has a -20 dB isolation bandwidth from 1.27 fc to 13.7fc while the fabricated BPF has a -20 dB isolation bandwidth from 1.56 f0 to 15 f0. Moreover, the fabricated LPF and BPF also have the compact size of 0.107 λgc ×0.083 λgc and 0.123 λg0 ×0.073 λg0, respectively. Good agreement can be observed between the simulation and measurement.

A novel miniaturized directly coupled UWB BPF

A novel ultra-wideband (UWB) bandpass filter (BPF) structure with directly coupled I/O ports is presented in this paper. The presented structure consists of a two-end short stepped-impedance resonator with a pair of stepped-impedance open stubs (SIOSs) and one uniform-impedance open stub (UIOS) symmetrically loaded on its high-impedance section. The presented structure has multiple resonant modes. The directly coupled configuration, the SIOSs and UIOS can provide three transmission zeros on its upper stopband, which not only improve the skirt of the upper transition band but also extend the upper stopband. As an example, an UWB BPF is designed, fabricated, and measured. The measured results show that the fabricated filter has a less than 0.7 dB insertion loss, better than 14 dB return loss and wide stopband up to 18.5 GHz. The measurement agrees well with the simulation.

Compact Wideband Circularly Polarized Patch Antenna for CNSS Applications

A compact wideband circularly polarized (CP) patch antenna utilizing a quad-feed network (QFN) and quadruple semi-fan-annulus (QSFA) patches is proposed. For using a coupled-line dual-band power divider (PD) and improved phase shifter (PS) with stepped-impedance-open-stub (SIOS), the QFN has a compact size and exhibits the electromagnetic (EM) simulated bandwidth over 96% for the power distribution -6.5±0.5 dB, return loss (RL) > 14 dB, and a consistent 90° (±9°) phase deviation. Moreover, the QSFA patches can expand the CP bandwidth and reduce the size of the antenna effectively. Measurement results show that the proposed antenna achieves CP bandwidth of 72% from 1.15 to 2.45 GHz for RL > 10 dB, axial ratio dB, and 3-dB gain variation (gain > 4.4 dBi). Therefore, the proposed antenna is a good candidate for Compass Navigation Satellite System (CNSS) applications.

Design of Novel Ultra-Wideband Bandpass Filter with High Selectivity and Wide Stop Band and Optimizing it with Neuro-Genetic Method

This paper develops a novel ultra-wideband bandpass filter with high selectivity, deep stop band and compact size. By linking a broadband bandstop filter at two sides with two feed lines via interdigital coupled lines with enhanced coupling degree, an initial ultra-wideband bandpass filter is created. In this filter, all undesired pass bands are rejected by broadband bandstop filter embedded in middle of ultra-wideband filter. Then, stepped impedance open stubs are used for realizing transmission zeros in pass band edges to increase selectivity. Finally, a neuro-genetic method is applied for optimizing of proposed ultra-wideband bandpass filter. For this task, first a nonlinear relation is established between the input (layout parameters) and output (electrical responses) data by using neural network. Then, genetic algorithm is used in conjunction with neural network model for optimizing the ultra-wideband bandpass filter parameters. The designed filter was fabricated and measured that showed good characteristics including deep stop band and very high pass band selectivity.