Stopband Performance Research Articles

E-Band Plate-Laminated Waveguide Filters and Their Integration Into a Corporate-Feed Slot Array Antenna With Diffusion Bonding Technology

This paper demonstrates plate-laminated waveguide filters in diffusion bonding technology for the first time and shows their uses in the integration with a corporate-feed slot array antenna for E-band ultrahigh capacity point-to-point communications. First, a single-cavity resonator model is studied and the measured high unloaded quality of 2121 at 79.07 GHz indicates its potential in the design of low-loss filters. Consequently, a sixth-order T-shaped cavity bandpass filter that comprises of ten cavity resonators is developed. It exhibits insertion losses of 3.4 and 3.3 dB at 78.5 GHz at two output ports, a 3-dB fractional bandwidth of 20.5%, as well as a small in-band amplitude/phase difference. Then, a fourth-order bandstop filter based on a band-rejection element is presented. It provides a high rejection level of 55 dB at 78.5 GHz and insertion losses of 0.44 and 0.28 dB at 73.5 and 83.5 GHz. The architectures of the proposed filters show attractive compatibility properties for integration. Finally, the proposed filters are fully integrated into a corporate-feed circuit of a $16 \times 16$ -element slot array antenna without an interconnection circuit. With the seamless integration, the proposed building blocks demonstrate well-preserved high efficiency (only a low loss is introduced by the filters) and unchanged radiation characteristic (low sidelobe level, low cross polarization, and high directivity) in the designed passband, as well as specified bandstop performance.

Compact dual‐band BPF with wide stopband using stub‐loaded spiral stepped‐impedance resonator

A compact dual-band bandpass filter (BPF) with wide stopband performance using stub-loaded spiral short-circuit λ/4 stepped-impedance resonator is proposed. Spiral configuration has been used for compactness of filter. Both passbands can be controlled individually by changing the geometric parameters of resonator. Multiple transmission zeros provide high selectivity to both passband and extend stopband up to 3 GHz. The filter has compact size of 0.06λg × 0.09λg. A dual-band BPF has been designed and fabricated for terrestrial trunked radio (TETRA) band and global system for mobile communication applications.

Dual‐band balanced‐to‐unbalanced filtering power divider by coupled ring resonators

A dual-band balanced-to-unbalanced filtering power divider by coupled ring resonators is proposed. Two passbands can be easily realised by the two coupled ring resonators. Three transmission zeros near the two passbands are used to improve the selectivity. The common mode can be easily suppressed by the bandstop performance of the open stubs. A fabricated prototype ( e r = 2.65, h = 1 mm, tan δ = 0.003) with centre frequencies located at 2.82 and 3.22 GHz is designed and measured to prove the proposed methods.

A Compact Half-Mode Substrate Integrated Waveguide Bandpass Filter With Wide Out-of-Band Rejection

A compact bandpass filter exhibiting an ultra-wide out-of-band rejection is studied and developed. A combination of electromagnetic bandgap (EBG)-loaded half-mode substrate integrated waveguide (HMSIW) and composite right/left-handed (CRLH) HMSIW is used in this development. The proposed filter operates below the characteristic cutoff frequency of HMSIW. The CRLH HMSIW loaded with EBG structures is investigated first. The filter with a miniaturized size is then implemented with two slots etched on HMSIW to reduce coupling effects between EBG structures and interdigital capacitors. Defected microstrip structure (DMS) as feed lines are used to obtain an ultra-wide out-of-band rejection. Measured results show that this effective stopband can cover up to 10.3 times the design center frequency for a rejection level of 20 dB. The filter exhibits high selectivity, good stopband performance, and compact size.

Optimisation of SIW bandpass filter with wide and sharp stopband using space mapping

ABSTRACTThis work presents a substrate integrated waveguide (SIW) bandpass filter with wide and precipitous stopband, which is different from filters with a direct input/output coupling structure. Higher modes in the SIW cavities are used to generate the finite transmission zeros for improved stopband performance. The design of SIW filters requires full wave electromagnetic simulation and extensive optimisation. If a full wave solver is used for optimisation, the design process is very time consuming. The space mapping (SM) approach has been called upon to alleviate this problem. In this case, the coarse model is optimised using an equivalent circuit model-based representation of the structure for fast computations. On the other hand, the verification of the design is completed with an accurate fine model full wave simulation. A fourth-order filter with a passband of 12.0–12.5 GHz is fabricated on a single layer Rogers RT/Duroid 5880 substrate. The return loss is better than 17.4 dB in the passband and the rejection is more than 40 dB in the stopband. The stopband is from 2 to 11 GHz and 13.5 to 17.3 GHz, demonstrating a wide bandwidth performance.

Compact microwave planar band pass filter

The need for the compactness of microwave filter at high frequency application has lead to the design of microwave planar band pass filter which passes certain range of frequencies. The aim of this paper is to study and implement a compact microwave planar band pass filter operates in 3.1GHz-10.6GHz which is the ultra-wide band range. It uses multiple mode resonator (MMR) and inter digital coupled lines to improve upper stop band performance and coupling degree. Simulation of the proposed microwave filter structures is done with the help of HFSS (High Frequency Structure Simulator) software.

Compact continuous tunable low-pass filter with high selectivity and wide stopband

This letter presented a novel compact continuously tunable low-pass filter (LPF) using varactor-loaded coupled rhombic stubs. The proposed LPF demonstrated excellent roll-off selectivity, wide stopband range as well as good cut-off frequency tunability. This LPF consisted of three varactor-tuned coupled rhombic stubs loaded on a section of high-impedance microstrip line symmetrically and two coupled line LPFs which could further improve the stopband performance. A detailed explanation of the tuning mechanism was illustrated by adopting lumped-element equivalent circuit model. The measured results showed not only a wide cut-off frequency tuning range of 56% from 350 to 800 MHz, but also an excellent steepness factor of less than 1.14. Additionally, a rejection level of greater than 20 dB up to 8 GHz (>10 fc) was observed in the stopband. The proposed ideas were verified by the measured results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1641–1644, 2016

A smaller step impedance line Wilkinson power divider with an improved better stop-band

This article proposes the stepped impedance line Wilkinson power divider (SIL WPD) and extracts the design formulae of SIL WPD. In the process of forming the WPD and executing a simulation based on the calculated design parameters, this study found that the SIL WPD improves stop-band performance compared to the conventional one. In addition, it is useful in reducing the size due to the characteristics of SIL. Finally, the consistency of the simulated and measured results confirmed the validity of the SIL structure. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1607–1610, 2016

Design of Single- and Dual-Band Power Dividers Integrated Filtering Responses Based on SIRs

Abstract In this paper, two single- and dual-band equal power dividers (PDs) integrated filtering responses are proposed using quarter-wavelength stepped-impedance resonators (SIRs). By appropriately adjusting the impedances and electric length ratios of SIRs, the proposed structures can achieve compact sizes and wide stop-band performances. In addition, source-load coupling is applied to create a pair of transmission zeros at each side of the pass-bands, which can improve effectively the frequency selectivity and the out-of-band rejection. To validate the design theory, two single- and dual-band PDs with good filtering responses are designed, implemented and measured, respectively. The predicted results on S parameters are compared with the measured ones and good agreement is achieved.

An ultracompact CRLH‐TL bandpass filter for VHF applications

ABSTRACTThis article proposes a new design approach to an ultracompact composite right‐/left‐handed transmission line (CRLH‐TL) bandpass filter with good passband and very broad stopband performances. In order to reduce the size, a series connection of the interdigital capacitor and shorted spiral inductor for realizing CRLH‐TL is adopted and optimized to create the target Terrestrial‐Digital Multimedia Broadcasting (T‐DMB, 174–216 MHz) bandpass filtering. T‐DMB was developed in South Korea. The results of a Bloch impedance analysis suggest that the proposed approach generates good impedance matching. The proposed filter has overall dimensions of λg/19 by λg/34 in terms of a center frequency of 180 MHz, a 3 dB fractional bandwidth of over 28%, an insertion loss of much lower than 2 dB, and a good return loss performance in the predicted and measured results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:694–697, 2016

Compact Dual-Layer Bandpass Filter Using Novel Stepped-Impedance Resonators

ABSTRACTIn this article, a compact third-order bandpass filter with high-frequency selectivity using novel dual-band stepped-impedance resonators is presented. In the proposed novel dual-band stepped-impedance resonator, the conventional low-impedance stub of the stepped-impedance resonator is replaced by a closed rectangular loop. The high-impedance stub is embedded in the closed loop for more compact structure. Multiple transmission zeros are introduced near the passband to improve the frequency selectivity and stopband performance. The proposed filter was designed, simulated, and fabricated to verify the validity of the proposed method. The measured results show that the center frequency is 2.83 GHz with a fractional bandwidth of 9.32%, and five transmission zeros were introduced near the passband, which are located at 1.76 GHz with 70.2-dB rejection, 2.53 GHz with 30.7-dB rejection, 3.95 GHz with 67.2-dB rejection, 8.85 GHz with 45.5-dB rejection, and 12.3 GHz with 34.5-dB rejection, respectively. The circuit only occupies 0.11λg × 0.08λg.

Artificial Ground Plane Based on Electromagnetic Bandgap for Stripline Transmission Line

This paper presents a study of the interaction between mushroom-type electromagnetic bandgap (EBG) surfaces replaced the conventional electric conductor ground plane of a stripline. The proposed EBG surface has both artificial magnetic conductor (AMC) and stopband performances. Compared to the conventional stripline, the EBG as artificial ground plane exhibits bandstop behavior which unlike all-pass behavior of the conventional stripline with electric conductor ground plane. The rejected frequency range is resulted from 6.76 to 10.08GHz (3.32GHz), which has fractional bandwidth of 40%. Promising results give future possibilities for practical suppression noises and interferences of systems.

Compact Integrated Lumped Element LCP Filter

The filter presented in this letter is a novel, compact, 4-pole, UHF-band integrated lumped element filter with a 20% fractional bandwidth operating at center frequency f0=500 MHz with a 17 dB passband return loss and a wide upper stopband with high rejection. The circuit was designed to minimize the overall footprint, as well as ensuring a wide, high attenuated stopband. This was achieved by building on previous work using LCP as a fabrication medium which implemented a block of shared vias; however, by adding a new controlled coupling between two capacitors, the stopband performance was significantly improved. The final filter dimensions are 0.03λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ×0.06λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> , and the out-of-band rejection is significantly larger than its predecessor at 50 dB up to 3f0 and 40 dB up to 5f0 with a stopband width extended to 7 times the center frequency.

Design of multi‐band bandpass filters based on stub loaded stepped‐impedance resonator with defected microstrip structure

The design of multi-band bandpass filters (BPFs) employing stub loaded stepped-impedance resonator with defected microstrip structure (SL-SIR-DMS) is presented in this study for the first time. The proposed SL-SIR-DMS is created by embedding DMS on the low-impedance line of the SL-SIR. It is found that different defected structures can lead to different frequency responses. In addition, by using DMS, tri-band and even quad-band responses can be easily achieved without increasing the resonator size. As verification, one tri-band SL-SIR-DMS and one quad-band SL-SIR-DMS are designed and analysed using even/odd-mode method. Subsequently, one tri-band BPF and one quad-band BPF have been developed with pseudo-interdigital coupling to realise good out-of-band performance. The predicted results are compared with measured ones and good agreement is achieved. Compared with BPFs using only SL-SIR, the proposed filters with DMS are more compact due to the slow-wave characteristic. Compared with the BPFs using defected ground structure to improve the stopband performance, the proposed ones can realise comparable wide stopbands but maintaining the signal integrity on the ground plane for packaging purpose.

A NOVEL WIDEBAND BANDPASS FILTER USING COUPLED LINES AND T-SHAPED TRANSMISSION LINES WITH WIDE STOPBAND ON LOW-COST SUBSTRATE

This paper presents the design, simulation, fabrication and measurement of a wideband bandpass filter with wide stopband performance operating at 3.5 GHz. The proposed filter consists of two parallel coupled lines (T-PCL) centred by T-inverted shape. The location of transmission zeros can be adjusted by varying the physical lengths of T-inverted shape to improve the filter selectivity. The wide bandwidth is achieved through enhanced coupling between the input and the parallel coupled lines. Due to the transmission zeros in the lower and upper stopbands, the filter exhibits good performance including an extremely wide stopband and sharp attenuations near the passband together with low insertion and good return losses in the passband. The filter performance is investigated numerically by using CST-MWS. Finally, the microstrip wideband BPF with minimum insertion losses 0.3 dB, centred at 3.5 GHz with a 3-dB fraction bandwidth of 70% and four transmission zeros is implemented and verified experimentally. In addition, good agreement between the simulated and measured results is achieved.

COMPACT INLINE TRIPLET SIW FILTER WITH EMBEDDED SHORT-ENDED MICROSTRIP LINE

A compact triplet inline substrate integrated waveguide (SIW) bandpass filter is presented with sharp lower skirt and deep lower-stopband performance. The filter is composed of two SIW rectangular cavities and an embedded short-ended strip line on the top surface of two adjacent SIW cavities. A transmission zero can be generated by the cross coupling near the lower passband edge, which allows the filter implementation in inline with sharp lower skirt. Deep lower stopband performance is inherited from SIW. To validate the concept, a filter prototype with fractional bandwidth (FBW) of 4% at 5.75 GHz is designed, fabricated and measured. Good agreement can be obtained between the measured and simulated results.

Exact Design of a New Class of Generalized Chebyshev Low-Pass Filters Using Coupled Line/Stub Sections

A method for the design of a new class of distributed low-pass filters enables exact realization of the series short-circuited transmission lines, which are normally approximated via unit elements in other filter realizations. The filters are based upon basic sections using a pair of coupled lines, which are terminated at one end in open-circuited stubs. The approach enables realization of transmission zeros at the quarter-wave frequency, hence giving improved stopband performance. A complete design theory starting from a distributed generalized Chebyshev low-pass prototype filter is presented. A design example demonstrates excellent performance in good agreement with theory.

High-Temperature Superconducting Bandpass Filter Using Asymmetric Stepped-Impedance Resonators With Wide-Stopband Performance

This paper presents a wide-stopband high-temperature superconducting (HTS) bandpass filter (BPF). The filter is implemented by the asymmetric stepped-impedance resonators (SIRs) with only one step discontinuity, which leads to low loss and compact size. With varied characteristic impedance ratios and length ratios, the diversity of asymmetric SIR has been studied, and the spurious resonant-mode responses are discussed. Adopting different asymmetric SIR units operated at the same fundamental frequency $f_{0}$ (2.4 GHz), its wide upper stopband can be realized by dispersing the higher order spurious resonant modes of these resonators. Furthermore, a modified input/output (I/O) feedline structure has been utilized to enhance the stopband performance. Finally, a fourth-order HTS BPF for wireless application is designed and fabricated on a MgO wafer with double-sided YBCO films. The filter measurement shows excellent performance with 0.05-dB minimum insertion loss and better than −20-dB rejection level in the stopband up to 10.46 GHz (about 4.4 $f_{0}$ ). In addition, the size of the HTS filter is 12.45 mm $\times$ 23 mm (i.e., 0.256 $\lambda_g$ by 0.472 $\lambda_g$ , where $\lambda_g$ is the guided wavelength at the center frequency).

K-Band Substrate-Integrated Waveguide Resonator Filter With Suppressed Higher-Order Mode

In this letter, we present a design method for K-band substrate-integrated waveguide (SIW) resonator filters utilizing TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">02</sub> mode. More importantly, a methodology for suppressing an unwanted higher-order mode ( TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ) close to the passband is demonstrated. It is shown that suppressing the unwanted mode give rise to the improved stopband performance. In addition, the resonator used in this filter design has capability of adjusting the resonant frequency, and this allows for compensating the fabrication error. Verification of the presented design method has been carried out by fabricating and measuring the filter.

Dual-mode substrate integrated hexagonal cavity (SIHC) filter with uncoaxial feeding structure

Novel uncoaxial dual-mode substrate integrated hexagonal cavity (SIHC) filters are presented for high selectivity application. The SIHC filters with uncoaxial feeding structure can add two extra coupling paths to their topologies: one is a source–load coupling path, and the other is a non-physical higher order modes cross-coupling path. Under the circumstances, the proposed filter can generate up to three transmission zeros (TZs) for improving stopband performance. Meanwhile, the numbers and the locations of TZs can be controlled conveniently by tuning the uncoaxial feeding structure. Accordingly, the filter not only has good selectivity due to flexible TZs, but also has a small size by virtue of its single-cavity structure. Two experimental filters at the same central frequency of 10 GHz but with different fractional bandwidths of 2 and 5% and numbers of TZs from 2 to 3 are designed, fabricated, and measured to validate the proposed structure. The measured results agree well with the simulated ones, with their good performance just as pedicted.