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This work deals with data-driven control for non-minimum phase (NMP) systems, where the goal is to design a controller for a plant whose model is unknown by using a batch of input–output data collected from it. The approach is based on the Model Reference paradigm, where a transfer function matrix – the reference model – is used to specify the desired closed-loop performance. The NMP systems issue in Model Reference approaches is a well-known problem in control literature and it is no different in data-driven methods. This work explains how to adapt the formulation of the Optimal Controller Identification (OCI) method to cope with this class of systems. Considering a convenient parametrization of the reference model and a flexible performance criterion, it is possible to identify the NMP transmission zeros of the plant along with the optimal controller parameters, as it will be shown. Both diagonal and block-triangular reference model structures are treated in detail. Simulation examples show the effectiveness of the proposed approach. • Data-driven control approach to cope with non-minimum phase (NMP) systems. • Knowledge of the NMP transmission zero and/or its direction not required. • Desired closed-loop performance specified by a flexible reference model. • Identification of NMP transmission zeros along with controller parameters. • Monte Carlo simulations show the effectiveness of the method. [ABSTRACT FROM AUTHOR]

This paper proposes a cross-coupled filter that utilizes a coplanar waveguide (CPW) resonator and triangular substrateintegrated waveguide (TSIW) resonant cavities. The filter consists of a CPW resonator etched on the upper metal surface of a second-order triangular SIW resonant cavity. By adjusting the dimensions of the CPW resonator and optimizing the width of the inductive coupling window, precise control can be achieved over cross-coupling between resonators, enabling fine-tuning of both filter bandwidth and transmission zero placement. Simulation and test results indicate that the filter has a center frequency of 11.85 GHz, a −3 dB bandwidth of 1.82 GHz, a relative bandwidth of 15.4%, an insertion loss of −0.9 dB in the passband, a return loss over 15 dB, and a transmission zero point located at 15 GHz. The filter has a simple structure, wide bandwidth, low insertion loss, small circuit size, and a flexible and controllable transmission zero point, making it potentially valuable for various applications. [ABSTRACT FROM AUTHOR]

A highly miniaturized bandpass filter with quad-band response is demonstrated in this article. The proposed quad-band bandpass filter has a novel topology comprising series quarter wavelength transmission lines loaded with tri-stepped impedance openended resonators and a dual-stepped impedance short-ended resonator. The proposed quad-band bandpass filter configuration is validated by theoretically verifying the transmission zeros and pole frequencies using even-odd mode analysis. A prototype operating at 0.475 GHz, 1.695 GHz, 3.48 GHz, and 4.53 GHz is designed, implemented, and experimented. The tested insertion losses at these center frequencies are 0.38 dB, 0.71 dB, 1.03 dB, and 1.22 dB, and the return loss is better than 10 dB in each passband. Each passband is isolated by a transmission zero with a rejection better than 40 dB. The proposed quad-band filter occupies a compact size of 0.146 × 0.087λ²g and is distinguished by its high compactness, wide bandwidth, multiple transmission zeros and poles, and high performance compared to benchmark designs making it more suitable for multi-band wireless applications. [ABSTRACT FROM AUTHOR]

This manuscript introduces an advanced architecture for a reconfigurable band-pass filter, utilizing substrate-integrated waveguide (SIW) technology. To induce a transmission zero in the passband response of the filter, the design involves coupling two identical open-loop ring resonators in a back-to-back configuration on top of the SIW cavity. The work includes a comprehensive investigation of the variation in notch frequency with respect to the ring diameter. Further incorporating PIN diodes into the structure enabled the realization of a reconfigurable filter that can be switched between a broad passband and two narrow passbands with a notch. Also, a planar DC biasing network has been specifically designed to bias the diodes. Additionally, a prototype has been developed to validate the concept and the performance in terms of reflection and transmission coefficients. The miniaturized reconfigurable filter design presented is well suited for the use in both Ku- and K-band applications due to its specific performance characteristics. [ABSTRACT FROM AUTHOR]

This paper presents and validates a compact dual-band bandpass filter with independent controllable passbands and isolation. The proposed filter is constructed by two transmission paths from input port to output port. Based on the transversal cancellation mechanism of two transmission paths, dual passband with independent controllable characteristics can be approached. The transversal cancellation techniques yield extra transmission zeros, which are located at 2.56 GHz, 3.58 GHz and 4.43 GHz respectively. Therefore, two passbands centered at 2.25/3.9 GHz are divided by triple transmission zeros. These transmission zeros also improve the out-of-band suppression performance of proposed filter. The designed prototype filter is implemented and tested, the measured 3 dB passband fractional bandwidths are 12.4 % and 7.5 %, respectively, and the minimum insertion losses are 0.48 dB and 0.88 dB respectively. Additionally, the dual-band transversal filter only occupies 0.012 λ g 2 , which λg is the guided wavelength at 50 Ω microstrip line at 2.25 GHz. [ABSTRACT FROM AUTHOR]

This study proposes a novel simple structure based on evanescent‐mode theory for the design of miniaturized filters with good out‐of‐band rejection and controllable passband number characteristics. The filter structure is realized by embedding serpentine microstrip resonators in the upper metal surface of the substrate‐integrated waveguide (SIW). These resonators are composed of upper and lower parts, which form a single‐passband filter when the lengths are equal and a double‐passband filter when the lengths are unequal. This paper proposes a novel method for switching between single‐ and dual‐passband configurations by modifying the length of the serpentine microstrip resonators without altering the overall SIW dimensions. Furthermore, finite transmission zeros are incorporated into the filter to augment the out‐of‐band rejection capability of the filter and the isolation effect between the passbands of the dual‐passband filter. To ascertain the viability of the proposed design, a two‐stage single‐passband filter and a two‐stage dual‐passband filter were fabricated and tested in this study. The experimental results align closely with the simulation outcomes, effectively validating the efficacy of this design. [ABSTRACT FROM AUTHOR]

The design of a miniaturized dual-band bandpass filter featuring a broad bandwidth and a high center frequency ratio is demonstrated in this article. A novel symmetrically loaded shunt coupled line with dual stepped impedance stubs has been investigated for the first time and it is utilized to realize a dual-band bandpass filter with seven transmission zeros. The transmission zeros frequencies of the filter response have been theoretically verified using even-odd mode analysis. For experimental validation purposes, a dual-band filter with a center frequency ratio of 4.06 covering 5G applications is implemented using Rogers RT/duroid 5870 substrate and tested. The tested filter has wide 3 dB fractional bandwidths of 53.8% and 17.9% in the first and second passbands, respectively, and has a compact topology of 0.20 × 0.09 λg2. The full-wave simulated and tested magnitude and group delay responses of the proposed filter are in good congruence. [ABSTRACT FROM AUTHOR]

In this paper, a coupled‐line‐based wideband four‐way filtering power divider (FPD) with unequal power division is presented. It is composed of three groups of coupled lines (CLs), four types of open‐ended stubs, and three kinds of resistors. By setting the CLs in each group with different parameters, unequal power distribution is obtained. Besides, open‐ended stubs with different characteristic impedances are inserted to each output port to generate two extra transmission zeros, at the same time maintaining good impedance matchings. Resistors are inserted to each group of the CLs to improve the isolations. By applying twice parity mode analysis, the exact synthesis of the proposed FPD is first derived. For demonstration, a prototype with power division ratio of 1:1.2:1.5:1.8 is designed and manufactured. Measurement results verified that more than 60% fractional bandwidth (FBW) is obtained under the criterion of 10 dB return loss and 10 dB isolation. Besides, the 3 dB passband FBWs for the four outputs reach 70% with high frequency selectivity and low insertion loss. And more than 15 dB out‐of‐band rejections are achieved for both the lower and upper stopbands. [ABSTRACT FROM AUTHOR]

This article presents an ultrawideband (UWB) bandpass filter (BPF) using integrated passive device technology on a GaAs substrate. This bandpass filter uses a multistage coupled line to achieve an ultrawide passband. The filter with a 3 dB fractional bandwidth can achieve a UWB of 106.1% (11.8–38.5 GHz). Introducing short‐circuit capacitors and two open microstrip lines between coupling lines achieved two transmission zeros on both sides of the passband and excellent frequency selectivity. Furthermore, to improve impedance matching performance within the ultrawide passband, a step impedance resonator (SIR) structure was adopted for the coupling line. To demonstrate the working mechanism of the proposed BPF, an LC equivalent circuit model was proposed and analyzed to investigate transmission poles and zeros. The suggested filter was fabricated into a small size of 1.4 × 0.85 mm2. According to the measurement results, the filter's insertion loss in the 13–34 GHz range was less than 2 dB, and its return loss exceeded −12 dB. The improved performance of the suggested filter was validated by the consistency between simulation results and measured findings. [ABSTRACT FROM AUTHOR]

This paper designs a bandpass filter for D‐band and 0.18 μm complementary metal oxide semiconductor (CMOS) process. The bandpass filter is composed of an inverted L‐shaped coupling microstrip line and a cross‐coupled resonator, and is coupled to produce two controlled transmission zeros. A defected ground structure is used to make a good impedance match. The designed filter has a 3 dB impedance bandwidth of 52 GHz (149–201 GHz) with a center frequency of 175 GHz and an insertion loss of 3.23 dB. The design of this paper is a CMOS 0.18 μm process capable of applying the D‐band bandpass filter with the advantages of lower insertion loss, broadband, and compact size. [ABSTRACT FROM AUTHOR]

In this paper, a new approach for the design of wideband bandpass frequency selective surface (FSS) is proposed based on the microstrip patch resonator and substrate integrated waveguide (SIW) cavity. Originating from the similarity of field distributions between the patch and SIW resonators, the patch resonator is concentrically embedded within the SIW cavity. In this context, resonant modes in both patch resonator and SIW cavity can be generated without enlarging the circuit size. Then, the slotlines are introduced to the ground layer to establish cross‐couplings to produce transmission zeros (TZs) for better out‐of‐band performances. For demonstration, a fourth‐order bandpass FSS is constructed, simulated, and fabricated. The measured results agree with the simulated ones, verifying that the proposed design method possesses attractive advantages of low profile, compact size, high frequency selectively, and nice universality. [ABSTRACT FROM AUTHOR]

In this study, a novel bandpass filter (BPF) characterized by low insertion loss (IL) and the presence of two transmission zeros (TZs) based on integrated passive device (IPD) technology is introduced. The design incorporates a low‐pass filter and a high‐pass filter which both exhibit strong out‐of‐band suppression performance. The control structure for TZs is constructed by cascading the inductance and capacitance components. The TZ controlling structure primarily generates TZs at high frequencies, resulting in a further bandwidth enhancement in the stopband. The lumped circuit of the proposed BPF is first constructed, and rigorous design formulas are provided to assist in constructing the proposed design. After schematic optimization, the second step involves layout optimization and simulation based on the specific IPD process. Experimental results mounted on a printed circuit board demonstrate that the bandwidth spans from 3.3 to 4.2 GHz with an IL of only 2.0 dB at the center frequency. Additionally, this BPF achieves impressive sideband suppression, exceeding 18 dB in the 0–1.7 GHz range and 30 dB in the 9–15 GHz range. Remarkably, the BPF is exceptionally compact with only 0.5 mm × 1.0 mm (0.006λc × 0.012λc). The proposed BPF exhibits outstanding performance with minimal IL and extensive sideband suppression at such a compact size based on the IPD technology. [ABSTRACT FROM AUTHOR]

This article proposes a switchable filter with four operating states, namely dual‐band mode, lower band mode, upper band mode, and all‐stop mode. The transition between these states is achieved by using positive intrinsic negative diodes, while the center frequency tuning is done by using varactors. In order to verify the design concept, a prototype has been fabricated on an F4BME substrate with a dielectric constant of 2.25 and a thickness of 1 mm, and the measured results were in agreement with the simulations. Notably, the dual‐band mode yields four transmission zeros (TZs), while the single‐band mode produces two TZs. The final circuit size of the designed filter is 0.18 × 0.14 λg, making it ideally suited for reconfigurable multi‐band communication systems. [ABSTRACT FROM AUTHOR]

New coupling scheme substrate‐integrated waveguide (SIW) diplexers based on dual‐mode cavities are proposed for millimetre‐wave applications. Dual‐mode SIW cavities are simultaneously employed in common input and coupling cavity to produce filtering transmission poles and transmission zero (TZ). A common input SIW cavity with two orthogonal modes is employed instead of the traditional T‐junction for circuit miniaturisation, insertion‐loss reduction, and intrinsically high isolation. A critical dual‐mode SIW cavity with diagonally distributed modes has been employed in each channel to realise a controllable stopband TZ for high selectivity of passband's skirt. To further improve channel isolation and passbands' selectivity, a SIW diplexer based on dual‐ and single‐mode cavities is proposed, and four‐pole responses for each passband channel are designed. For the verification, two millimetre‐wave diplexers have been fabricated and tested. [ABSTRACT FROM AUTHOR]

In this paper, a novel inline network realization of non-resonating node (NRN) and dangling resonator (R) pair direct synthesis approach is presented. Arbitrary prescribed transmission zeros at real frequencies are realized through independently controlling the dangling resonators of the NRN-R pairs with impedance inverters between adjacent nodes. The bandpass element values for fourth order acoustic wave filter with a center frequency at 98 MHz are obtained through execution and mapping of the synthesis results based on the Generalized Chebyshev polynomials. The layout of prototype is presented. Finally, the prototype is constructed and measured using network analyzer to validate the proposed concept in realizing the BAW filter using Butterworth Lowpass Van Dyke (BVD) model. The filter has an insertion loss of 3.45 dB, a return loss of 8.5 dB, and two transmission zeros (TZs). In terms of implementation, this synthesis technique allows flexibility to synthesize and realize a conventional filter with transmission zeros as an inline network without cross couplings. This offers advantages in terms of size and cost reduction in filter production due to the inline resonator arrangement and reduced sensitivity in the design and tuning process. [ABSTRACT FROM AUTHOR]

This letter describes the design of a compact, wideband waveguide filtering antenna with a transmission zero (TZ) in the upper stopband. A novel frequency-variant coupling (FVC) network that provides a TZ in addition to the pole is used to achieve compactness and higher selectivity. The position of the TZ can be changed in the upper stopband by altering the physical parameters of the proposed FVC. The radiating waveguide aperture is matched to the real admittance of the generator over a wide bandwidth by utilizing coupledresonator theory. This leads to a wide fractional bandwidth of 23%, along with a TZ at the upper stopband. The filtering antenna has been manufactured using metal 3-D printing to achieve low manufacturing costs and light weight. The measured results are in good agreement with the simulated ones, which shows the feasibility of the proposed FVC structure for the design of the compact waveguide filtering antenna with a TZ. [ABSTRACT FROM AUTHOR]

This paper proposes a hybrid cross-coupled filter that utilizes a coplanar waveguide (CPW) resonator and a hybrid electromagnetic coupling structure. The filter features a flexible and controllable position of transmission zeros and a quasi-elliptical response. It is composed of two CPW structures etched within the upper metal surface of a second-order substrate-integrated waveguide (SIW) resonant cavity. By adjusting the dimensions of the two CPW structures between the SIW resonant cavities and the width of the inductive coupling window, the strengths of the electric and magnetic couplings can be easily controlled to achieve a controllable hybrid crosscoupling effect in order to adjust the position of the transmission zeros and ultimately to realize the third-order filter with quasi-elliptical response characteristics. Simulation and test results indicate that the filter has a center frequency of 4.55 GHz, a -3 dB bandwidth of 180 MHz, a relative bandwidth of 4%, an insertion loss of -0.9 dB in the passband, a return loss of over 15 dB, and two transmission zeros located at 4.4 GHz and 4.7 GHz, respectively. The filter has several advantages, including a simple structure, low insertion loss, small circuit size, good frequency selectivity, and flexible and controllable transmission zeros. These features make it suitable for the use in 5G (sub-6 GHz) wireless communication systems. [ABSTRACT FROM AUTHOR]

This paper presents a novel bandpass filter with reconfigurable bandwidth or transmission zeros. The proposed filter is based on a multiple-mode stub-loaded resonator. Three PIN diodes are utilized as switching elements to achieve four switchable operating states. The measurement results indicate that the 3 dB fractional bandwidth (FBW) of the filter can be varied from 32.3% to 70% at the centre frequency of 2.2 GHz, and the stopband attenuation is higher than 35 dB. The filter size is only about 0.28λg × 0.19λg. [ABSTRACT FROM AUTHOR]

In this work, we designed and fabricated an acoustic metamaterial with unidirectional zero reflection. The metamaterial was developed based on the concept of a parity-time symmetric material using one-dimensional (1D) orifice-type unit cells as a loss material and cylindrical closed-end tubes as a gain material. Twenty such composite unit cells were connected in series to construct a one-dimensional loss–gain balanced metamaterial. The characteristics of reflection and transmission were studied at frequencies between 1100 and 1800 Hz, ensuring that the metamaterial met the conditions of a homogeneous medium. From the experiments, it was found that the designed loss–gain balanced metamaterial had nearly complete unidirectional zero reflection (r ≲ 1.6 %) at f = 1202 Hz; in addition, it was shown to exhibit bidirectional zero transmission (t ≃ 0) at f = 1501 Hz. [ABSTRACT FROM AUTHOR]

In the paper, a high‐selectivity wideband four‐way filtering power divider with input absorptive feature is presented. It consists of two parallel‐coupled lines (CLs), two three‐coupled lines (TCLs), two open‐ended stepped branches, one absorptive branch, and two isolation resistors. The wideband filtering response is achieved by cascading the TCLs and CLs. While high selectivity is obtained by loading the open‐ended stepped branch, where two extra transmission zeros are generated. In addition, wide absorptive bandwidth with good isolations between adjacent output ports are realized by combining the absorptive branch with the isolation resistors. Equations are derived by using the two‐parity mode analysis, and main parameters are investigated in detail. For validation, a prototype was designed and fabricated. Test results show that the 3‐dB FBW can reach 87% with a 10‐dB input absorptive FBW of 200%. Besides, for the output ports with 10‐dB return loss and 10‐dB isolation, the FBWs are 94% and 91.5%, respectively. It also features high frequency selectivity and low insertion loss. [ABSTRACT FROM AUTHOR]

A submerged flexible breakwater can be used to control waves in shallow water as an advanced alternative to traditional rigid submerged structures. Submerged flexible breakwaters not only cost less to build than conventional submerged breakwaters but also allow ships and marine life to bypass them if they are deep enough. These marine structures decrease the intensity of the shock wave and prevent standing waves from forming. We present a solution for transmission/reflection using a series of submerged identical elastic scatterers. Scattering and transfer matrices will be used to compute the transmission and reflection coefficients for N-submerged elastic scatterers. The behavior of the transmission for different values of physical parameters such as submergence depth, length of the scatterer, the gap between two successive scatterers, stiffness of the scatterer, and the number of submerged elastic scatterers is given. In doing so, we can achieve the frequencies and the incident amplitudes at which these submerged elastic scatterers can be effectively used as breakwaters in water of finite depth. We have looked at the transmission and reflection behaviors for a range of physical parameter values, such as the submergence depth, the length of the scatterer, the spacing between successive scatterers, the stiffness of the elastic scatterer, and the number of scatterers over a wide frequency range. We have given a spectrum of frequencies for which, given certain values of physical parameters, we can achieve zero transmission. Furthermore, even at high frequencies, we have demonstrated an incidence amplitude range for which zero propagation of transmission is feasible. [ABSTRACT FROM AUTHOR]

An innovative ceramic filter is presented in this paper. The filter is composed of six tuning apertures, coupling channels, and a six-blind-hole coupling structure. The six blind holes are divided into two groups: one situated between the first and second cavities to induce inductive coupling, and the other positioned between the second and third cavities to facilitate capacitive coupling. Employing this structure facilitates the formation of a cascade quadruple (CQ) coupling unit among the 1, 2, 3, and 4 resonant cavities, thereby introducing two transmission zeros. Subsequently, an analysis of the influences of the depth and spacing of each blind hole on the coupling coefficients is presented. Finally, to further validate the theory, the filter tailored for base station applications was designed and implemented. The measurement results demonstrate a center frequency of 3.5 GHz with a bandwidth of 200 MHz. In the passband, the insertion loss was below 1.2 dB, and the return loss surpassed 19 dB. The test outcomes align closely with the simulation, confirming the reliability of the design. [ABSTRACT FROM AUTHOR]

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This article presents a novel concept for a tiny stepped impedance resonator (SIR) to ease the application of bandpass filters. In recent years, its significance has expanded due to the growing availability of ground plane windows and a floating conductor in the substrate. We propose a small BPF that utilizes a folded SIR transmission line to achieve high performance at low size. The suggested BPF replaces the λg/4 transmission line present in traditional stub BPFs with a T-shaped SIR coupled to a J-inverter structure (transmission line). In addition to the short stubs included in regular stub BPFs, a folded SIR is included here. With this method, we are able to drastically cut the BPF's footprint. The benefits of a BPF are its compact size, negligible insertion loss, and high bandwidth. Because of the ground plane window, the characteristic impedance of the microstrip line is enhanced. This new value is then applied to the calculation that determines the inductive area of the quasi-lumped stepped impedance resonator. This resulted in a slightly smaller device than it would have been otherwise. In addition, a floating conducting microstrip patch is placed directly below the capacitive zone, pushing the filter's initial spurious band even higher. After this, the out-of-band rejection of the gadget sees a significant improvement. By strengthening the coupling between nearby resonators, achieving a wider spectrum of bandwidths within the range conceivable is also feasible. This article aims to compare several filter designs that incorporate newly developed resonator and regular resonators that are already in use. The proposed filter has the centre frequency response at 3.6GHz having insertion loss of 2.5dB and bandwidth increment of 115%, reduction in size dimension of 0.527×0.25mm2. The suggested BPF is flat, making it amenable to semiconductor fabrication at scale. The potential for this design's application in fields as diverse as defense, healthcare, and industry is high. [ABSTRACT FROM AUTHOR]

This research addresses the critical challenge of broadband matching in radio engineering, focusing on enhancing phase-frequency response (PFC) linearity across wide frequency bands. A novel approach, utilizing modified Chebyshev functions, demonstrates significant potential in reducing phase distortions within 5G technology applications. Unlike traditional Chebyshev functions, this method incorporates strategically placed transmission zeros--complex conjugate pairs on the s-variable complex plane--without increasing the filter circuit's order. This innovation results in a low-order filter circuit characterized by uniform phase response and group delay characteristics (GDT), offering an effective solution for matching circuit design with less phase-frequency distortion and improved group delay uniformity across diverse load conditions. The modified Chebyshev approximation outperforms its classical counterpart in both phase linearity and selectivity within the 1 to 1.2 cutoff frequency range. This enhancement is crucial for the development of low-frequency filters, with broader implications for creating high-frequency, band-pass, and band-stop filters via known frequency transformations. Empirical results validate the proposed method's reliability and effectiveness, marking a significant advancement in the field of radio engineering by addressing broadband matching challenges with increased efficiency and simplified design implementations. [ABSTRACT FROM AUTHOR]

This article presents a miniaturized dual layer angularly stable quad-band frequency selective surface (FSS) for shielding applications. The shield consists of four metallic square rings on a thin FR4 substrate of relative permittivity 4.4 and thickness 0.5 mm with two rings on top layer and other two rings in the bottom layer. The dimension of the shielding unit cell is 0.2λ × 0.2λ, for the lowest frequency. These shields have been analyzed in both planar and conformal configurations. The equivalent circuit models as well as analytical model are determined. The shield exhibits quad band band-stop characteristics with transmission zeros at 5 GHz (4.3– 5.8 GHz), 6.6 GHz (6.3–6.8 GHz), 8.3 GHz (7–8.8 GHz), and 15 GHz (11–17 GHz). These bands find their application in shielding upper WLAN band, sub-6 GHz 5G band C/Ku band for satellite communication. The proposed FSS prototype is fabricated and tested for shield effectiveness in an anechoic chamber. The proposed FSS design offers stable angular response up to 60° for planar and geometry. Simulated and measured transmission coefficients are in good agreement and hence well suited for shielding applications. As the structure is fourfold symmetric, it exhibits polarization insensitive and angular stability in all four bands. [ABSTRACT FROM AUTHOR]

In order to achieve miniaturization and high performance in microwave filters, this paper proposes two double-layer bandpass filters with different structures, both equivalent to square-coupled topologies. These filters employ dual-cavity single-mode and single-cavity dual-mode substrate-integrated waveguide resonators. In this configuration, the upper layer comprises two single-mode resonators connected to the input and output feed lines, while the lower layer contains dual-mode resonators coupled to the upper layer’s single-mode resonators through two slots on the middle metal layer. A comprehensive analysis is conducted on the impact of primary parameters on filter characteristics and transmission zero positions. The second filter is fabricated and tested, yielding results consistent with simulation outcomes. The center frequency of the filter is 4.77 GHz, with a 3 dB bandwidth of 0.16 GHz (relative bandwidth: 3.35%). Additionally, its rectangularity coefficient at 10 dB approximately equals one, an ideal value for practical applications. [ABSTRACT FROM AUTHOR]

This paper presents a novel highly selectivity tunable filter with transmission zero. Yttrium iron garnet/gadolinium gallium garnet layer structures are added to the filter structure as bandstop units to achieve transmission zero. CST Studio Suite simulates and optimizes the filter structural parameters. Transmission zero and filter passband are tuned simultaneously. Skirt selectivity can be significantly increased by placing the transmission zero at the lower side of the filter passband. The parasitic response can be suppressed by about 20 dBc when the transmission zero is located on the upper side of the filter passband. With the magnetic field shifted from 3250 to 5005 Oe, the filter tuning range is 11–16 GHz with an insertion loss of about 3.5 dB. The addition of transmission zero enhances filter selectivity and provides more flexibility in suppressing interfering signals that vary in frequency or parasitic responses at specific frequencies. This method presents an approach for designing wide tuning range filters with transmission zeros. [ABSTRACT FROM AUTHOR]

This paper describes and validates an advanced synthesis design process of Frequency-Selective Surfaces (FSSs) with elliptic band-stop responses. A systematic procedure based on the Generalized Chebyshev Function and the extracted pole technique enables control of the position of the transmission zeros and the attenuation level to obtain an equiripple rejection response. A systematic process is followed to obtain the lumped LC values of the resonator circuits extracted as poles and the impedance inverters. Then, equivalent dipoles and transmission lines are obtained to carry out the electromagnetic design at normal incidence for a linearly polarized field. The impact of the higher-order modes of the periodic structure on the electrical response of the FSS, which can be relevant due to the stringent selected specifications, has been also analyzed. A fourth-order band-stop filter with a 3 GHz bandwidth centered at 30 GHz and its attenuation at 50 dB has been designed considering three different implementations: two filters using a vacuum as a transmission line with different connection lengths and a third one using a dielectric substrate to enable its manufacturing. In order to verify the design procedure using experimental results, the third filter with printed dipoles in the dielectric substrate has been manufactured and measured, thus validating the developed process. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to present the simulation, fabrication and testing of a novel ultra-wide band (UWB) band-pass filters (BPFs) with better transmission and rejection characteristics on a low-loss Taconic substrate and analyze using the coupled theory of resonators for UWB range covering L, S, C and X bands for radars, global positioning system (GPS) and satellite communication applications. Design/methodology/approach: The filter is designed with a bent coupled transmission line on the top copper layer. Defected ground structures (DGSs) like complementary split ring resonators (CSRRs), V-shaped resonators, rectangular slots and quad circle slots (positioned inwards and outwards) are etched in the ground layer of the filter. The circular orientation of V-shaped resonators adds compactness when linearly placed. By arranging the quad circle slots outwards and inwards at the corner and core of the ground plane, respectively, two filters (Filters I and II) are designed, fabricated and measured. These two filters feature a quasi-elliptic response with transmission zeros (TZs) on either side of the bandpass response, making it highly selective and reflection poles (RPs), resulting in a low-loss filter response. The transmission line model and coupled line theory are implemented to analyze the proposed filters. Findings: Two filters by placing the quad circle slots outwards (Filter I) and inwards (Filter II) were designed, fabricated and tested. The fabricated model (Filter I) provides transmission with a maximum insertion loss of 2.65 dB from 1.5 GHz to 9.2 GHz. Four TZs and five RPs are observed in the frequency response. The lower and upper stopband band width (BW) of the measured Filter I are 1.2 GHz and 5.5 GHz of upper stopband BW with rejection level greater than 10 dB, respectively. Filter II (inward quad circle slots) operates from 1.4 GHz to 9.05 GHz with 1.65 dB maximum insertion loss inside the passband with four TZs and four RPs, which, in turn, enhances the filter characteristics in terms of selectivity, flatness and stopband. Moreover, 1 GHz BW of lower and upper stopbands are observed. Thus, the fabricated filters (Filters I and II) are therefore evaluated, and the outcomes show good agreement with the electromagnetic simulation response. Research limitations/implications: The limitation of this work is the back radiation caused by DGS, which can be eradicated by placing the filter in the cavity and retaining its performance. Practical implications: The proposed UWB BPFs with novel resonators find their role in the UWB range covering L, S, C and X bands for radars, GPS and satellite communication applications. Originality/value: To the best of the authors' knowledge, for the first time, the authors develop a compact UWB BPFs (Filters I and II) with BW greater than 7.5 GHz by combining reformed coupled lines and DGS resonators (CSRRs, V-shaped resonators [modified hairpin resonators], rectangular slots and quad circle slots [inwards and outwards]) for radars, GPS and satellite communication applications. [ABSTRACT FROM AUTHOR]

A compact bandpass filter (BPF) with wide stopband performance is proposed and implemented on Si‐based integrated passive device (IPD) technology. A modified topology consisting of a novel Pi‐section and two capacitors are introduced in this BPF. The Pi‐section topology can achieve a band‐pass performance and generate four transmission zeros out‐of‐band. These two capacitors can improve the in‐band matching and also widen the stopband. The proposed BPF with a compact size of 1.0 mm × 0.5 mm × 0.3 mm is fabricated using Si IPD technology and measured by on‐wafer probing. It shows that the insertion loss is less than 1.75 dB, the return loss is better than 18 dB in the 5G band, and the upper stopband suppression level is better than 17.5 dB up to 18 GHz. The simulated and measured results of the proposed BPF are in reasonably good agreement. [ABSTRACT FROM AUTHOR]

A very compact three‐pole bandpass filter with wide upper stopband is proposed and implemented by gallium arsenide integrated passive device technology. By organizing inductor and capacitor in parallel with an LC series network, a dual‐frequency bandstop structure is constructed in the first step to achieve transmission zeros (TZs). Then, the lowpass capacitor network and highpass inductor network are wisely cascaded with the bandstop structure, thus to the realization of three‐pole bandpass filter with a wide upper stopband. Based on the even‐/odd‐mode analysis, theoretical equations for the in‐band resonances and out‐of‐band TZs are given. Then, one filter prototype centered at 4.4 GHz with 3‐dB fractional bandwidth of 45.5% is designed, fabricated, and measured. Both simulated and measured results indicate that the proposed filter exhibits a wide stopband rejection of 25 dB from 6.4 to 22.8 GHz as well as a very compact size about 0.026λg × 0.031λg. [ABSTRACT FROM AUTHOR]

In this brief, a dual-band filtering power divider (FPD) with high selectivity and independently controllable passbands is designed. The proposed FPD consists of asymmetric folded F-type resonators (AFFRs) and quarter-wavelength three parallel-coupled lines (TPCLs). The center frequencies of the dual bands can be determined by adjusting the physical lengths of AFFRs. Meanwhile, TPCLs can increase the transmission paths and introduce multiple transmission zeros (TZs) to achieve high selectivity. For demonstration, the proposed FPD is designed, fabricated, and measured. The center frequencies are 2.59/3.63 GHz with the 3-dB fractional bandwidths (FBWs) of 12.95% and 7.88%, and the isolation between port 2 and port 3 is better than 12.56/21.03 dB. The minimum insertion losses are better than 0.54/0.32 dB in each passband. The simulated results are compared with measured ones, and good agreement is realized. [ABSTRACT FROM AUTHOR]

A substrate-integrated waveguide (SIW) miniaturization filter is proposed, which features high attenuation characteristics, effectively reduces filter loss and size, and improves frequency selectivity. The filter is miniaturized using the evanescent-mode theory and embeds a nested U-shaped resonator in the upper metal surface of the SIW. The proposed filter's equivalent circuit structure incorporates two LC parallel resonant loops with resistance characteristics that can, in turn, create two transmission zeros in the filter's stopband to enhance its selectivity. The filter has an effective size of only 0.39λ×0.23λ with a center frequency of 2.5 GHz. The-3 dB bandwidth measures 120 MHz, while the relative bandwidth is 4.8%. The insertion loss is -0.6 dB in the passband, and the return loss is more than 25 dB. Out-of-band rejection exceeds 40 dB in the range of 2.9 ~ 4.4 GHz. The measured and simulated results agree well. The filter offers benefits in terms of high rejection, miniaturization, and low insertion loss. It can be implemented in 5G (sub-6 GHz) wireless communication systems. [ABSTRACT FROM AUTHOR]

This paper presents a compact wideband circularly polarized cross-dipole antenna with a low-pass filter response. It consists of two pairs of folded cross-dipole arms printed separately on both sides of the top substrate, and the two dipole arms on the same surface are connected by an annular phase-shifting delay line to generate circular polarization. A bent metal square ring and four small metal square rings around the cross-dipoles are employed to introduce new resonant frequencies, effectively extending the impedance and axial-ratio bandwidth. Four square patches printed on the middle substrate are connected to the ground plane by the vertical metal plates in order to reduce the antenna height. Thus, a compact wideband circularly polarized antenna is realized. In addition, a transmission zero can be introduced at the upper frequency stopband by the bent metal square rings, without using extra filter circuits. For verification, the proposed model is implemented and tested. The overall size of the model is 90 mm × 90 mm × 33 mm ( 0.37 λ 0 × 0.37 λ 0 × 0.14 λ 0 ; λ 0 denotes the center operating frequency). The measured impedance bandwidth and 3 dB axial-ratio (AR) bandwidth are 53.3% and 41%, respectively. An upper-band radiation suppression level greater than 15 dB is realized, indicating a good low-pass filter response. [ABSTRACT FROM AUTHOR]

In this article, waveguide dual-band filter and diplexer working on W-band are synthesized through cascading mixed TE301- and TE102-mode cavities as well as TE101-mode resonators. Based on the discussion of top resonance modes in single cavity, the TE301&TE102 dual-mode resonator which features oversized dimension, technological insensitivity and high Q-factor is the strong candidate for designing high-frequency filters and diplexers. For dual-band filter, such dual-mode resonator can be shared by both bands as T-junction, and each band can be independently controlled. Besides, a W-band diplexer is proposed based on the analogous method. Two extra zeros have also been generated for each channel with adopting the singlet concept. Finally, the filter and diplexer prototypes are machined by CNC-milling. The filter has obtained 3-dB FBWs of 4% (86.7–90.2 GHz) and 6.3% (96.7–103 GHz), low insertion losses (ILs) of -0.9 dB and -0.5 dB, as well as less than -16 dB return loss, respectively. The diplexer has achieved 3-dB FBWs of 4.9% (86.3–90.6 GHz) and 6.5% (96.9–103.4 GHz), low ILs of -0.7 dB and -0.4 dB, high insolation with more than 40 dB, respectively. All the experimental results including transmission zeros on out-of-band are very close to the simulations in the full band. The performance of dual-band filter and diplexer is highlighted comparing with the reported ones too. [ABSTRACT FROM AUTHOR]

This article discusses the design and implementation of a balanced linear-phase bandpass filter (BPF) equalized with a negative group delay circuit (NGDC). The proposed filter aims to achieve differential-mode linear-phase filtering and common-mode suppression characteristics. The design method involves a compact balanced BPF and negative group delay circuits loaded on the ports of the filter. The results of the simulation and measurement show that the proposed filter has reduced group delay fluctuations and excellent differential-mode linear-phase transmission and common-mode suppression performances. The document also discusses the design process of the filter, including determining the filtering performance, adjusting the coupling coefficient and loaded quality factor, and designing the NGDC. The fabricated and measured filter demonstrates good performance in terms of insertion loss, return loss, and group delay. The document concludes that the proposed filter has the smallest group delay fluctuation and a wide flat group delay bandwidth, making it suitable for improving the performance of electronic and communication systems. [Extracted from the article]

This paper discusses N-order bandpass filter (BPF) with all mixed couplings between adjacent resonators, and between end resonators and loads. It has (2N + 1) transmission zeros (TZ) at real frequencies. To the existing (N + 1) TZs generated by mixed couplings, another N TZs are added, which generated by resonators with special properties. Each such resonator is a λ/4 resonator, in which the connection point is located relatively close to the short-circuited end. In this case, the input admittance of the resonator Y(jω) has a pole ωp, which is located to the right and at a small distance from the main resonant frequency ω0. This pole ωp of the Y(jω) function leads to the appearance of a right-handed TZ in a BPF characteristic. If we use N resonators with different connection points, then N additional TZs will appear. The design of that BPF is considered. The measured and simulated frequency responses of the second-order BPF with 5 TZs are presented. [ABSTRACT FROM AUTHOR]

This paper proposes a microstrip filter with controllable transmission zeros based on the λ/4 stepped impedance resonator. This filter utilizes hybrid electric-magnetic coupling to generate transmission zeros, which can improve selectivity and stop-band performance. A fifth-order filter is designed and manufactured on a ceramic substrate with a center frequency of 26 GHz, bandwidth of 2 GHz and the signal suppression level is better than 42.51 dB from 10 to 22.8 GHz and 48.23 dB from 29.1 to 40 GHz. Furthermore, the proposed filter has a compact size of 2.074 × 1.071 mm (0.566λg × 0.292λg). [ABSTRACT FROM AUTHOR]

A novel hybrid bandpass filter (BPF) with wideband and high selectivity is proposed in this paper. The hybrid BPF is composed of two film bulk acoustic resonator (FBAR) cells and three lumped component resonators realized by the integrated passive device (IPD) technology. The ABCD matrix to S-parameters matrix method is used to calculate the frequency response of the BPF. Moreover, the expressions of transmission zeros (TZs) have been extracted. In the design process, an iterative design approach is proposed to improve the circuit and layout of the hybrid filter based on the packaged acoustic-electric hybrid simulation effect. Finally, two parts of the filter are packaged based on the flip-chip method, and two prototypes for the BPF are measured. The measured results of two chips with 3 dB fractional bandwidth of 13.7% and 15.8% are designed and fabricated, which verifies the validity of the proposed design principle. [ABSTRACT FROM AUTHOR]

The structure–performance mechanism is essential to achieve comprehensive characteristics for advanced communication system. In the present work, F− ions were adopted to fabricated Li 3 Mg 2 NbO 6- x /2 F x ceramics at a nitrogen atmosphere to modify dielectric characteristics. Correlation between bond characteristics, crystal structure and enhanced microwave dielectric characteristics was investigated through vibration analysis, P–V-L theory, Rietveld refinement, and First-principle calculations. Raman analysis and Rietveld refinement show that F− substitution led to a single phase. First-principle calculations indicates a high energy gap of 3.676 eV and p orbit contributed to Fermi energy. F− substitution led to the increase of Nb O bond ionicity and lattice energy, accounting for the variation in Q×f value and dielectric constant. The τ f value was related to the expansion coefficient of the Li–O bond. Remarkably, the samples (x = 0.08) exhibited comprehensive dielectric characteristics with ε r = 15.9, Q×f = 143,000 GHz and near-zero τ f = −2.1 ppm/°C, proving an effective strategy for collaborative regulation. Based on structure simulation, 5G filter with ultra-low loss and high-suppression was designed through introducing transmission zeros from cross coupling. More specifically, a dielectric filter exhibited an interpolation loss of 0.2 dB at 3.3–3.6 GHz and high attenuations of 15 dB for 20 MHz outside the passband, verifying the feasibility for 5G applications. [ABSTRACT FROM AUTHOR]

A broadband out-of-band rejection capability and multiple transmission zeros of wideband bandpass filter are proposed and validated in this article, which employ quadruple anti-parallel coupled-line structures to form a novel cross-shaped resonator planar topology. The centered frequency of the single wideband bandpass filter designed for verification is located at 2.4 GHz (f0) with a fractional bandwidth of 50%. The interaction of crossed multiple anti-coupled lines with a lowpass-loaded fan constitutes the wideband with nine transmission zeros in the 5 f0 frequency range for improved suppression extending to 26.5 GHz (10.7 f0) with a suppression level of 12.5 dB. Moreover, the designed prototype filter is implemented and tested with a measured minimum insertion loss of 0.9 dB. Good agreement between the measured and simulated results is attained to successfully validate the correctness of the proposed design approach. [ABSTRACT FROM AUTHOR]

Absorptive bandpass filters (ABPFs) are highly attractive in modern microwave communication systems due to their ability to internally absorb the harmful stopband RF-power reflections. This paper reports an approach to designing quasi-elliptic ABPFs with ultra-wide reflectionless range, enhanced selectivity, and compact size. The method is realized based on a fourth-order quasi-elliptic absorptive lowpass filter (ALPF) prototype with a simplified structure. This ALPF prototype exhibits both good impedance-matching over the whole normalized frequency domain and an adjustable transmission zero close to the passband. By applying an equivalent impedance transformer model, a coupled-line-based ABPF scheme is devised from the ALPF prototype, which eliminates conventional dispersive transmission line inverters, resulting in an ultra-wide reflectionless range and a compact size. Closed-form equations are derived to support the filter synthesis. A 2.45 GHz microstrip ABPF with 30% fractional bandwidth is designed for verification. The measured minimum in-band insertion loss is 0.83 dB and the reflectionless range of return loss better than 10 dB is from DC to 12.88 GHz. Both the upper and lower stopband suppression exceed 20 dB, with the upper stopband extending up to 6.80 GHz. The upper and lower out-of-band roll-off rates are 93.9 and 121.4 dB/GHz, respectively. The overall circuit size is 0.12 λg2. [ABSTRACT FROM AUTHOR]

The design procedure of a novel compact ultra-wideband (UWB) filter with high selectivity and low insertion loss is presented in this paper. The proposed filter consists of a simple planar combline filter at the top of a substrate and a non-intuitive shape of the defected ground structure (DGS) on the other side. The UWB filter is obtained by optimizing the shape of DGS and the combline parameters with a mixed integer genetic algorithm. The mixed integer genetic algorithm optimizes both continuous and binary values simultaneously. The continuous values define the combline parameters while the binary values define the shape of DGS. The detail of the design procedure is presented and validated by fabricating a prototype of the proposed filter. The measured insertion loss of the proposed filter in the mid-band frequency is less than 0.5 dB. The measurement results also show that the proposed UWB filter with a very compact structure has five transmission zeroes at the upper and lower stop bands. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to introduce a new type of sensor which uses microwave metamaterials and direct-coupled split-ring resonators (DC-SRRs) to measure the dielectric properties of solid materials in real time. The sensor uses a transmission line with a bridge-type structure to measure the differential frequency, which can be used to calculate the dielectric constant of the material being tested. The study aims to establish an empirical relationship between the dielectric properties of the material and the frequency measurements obtained from the sensor. Design/methodology/approach: In the proposed design, the opposite arm of the bridge transmission line is loaded by DC-SRRs, and the distance between DC-SRRs is optimized to minimize the mutual coupling between them. The DC-SRRs are loaded with the material under test (MUT) to perform differential permittivity sensing. When identical MUT is placed on both resonators, a single transmission zero (notch) is obtained, but non-identical MUTs exhibit two split notches. For the design of differential sensors and comparators based on symmetry disruption, frequency splitting is highly useful. Findings: The proposed structure is demonstrated using electromagnetic simulation, and a prototype of the proposed sensor is fabricated and experimentally validated to prove the differential sensing principle. Here, the sensor is analyzed for sensitivity by using different MUTs with relative permittivity ranges from 1.006 to 10 and with a fixed dimension of 9 mm × 10 mm ×1.2 mm. It shows a very good average frequency deviation per unit change in permittivity of the MUTs, which is around 743 MHz, and it also exhibits a very high average relative sensitivity and quality factor of around 11.5% and 323, respectively. Originality/value: The proposed sensor can be used for differential characterization of permittivity and also as a comparator to test the purity of solid dielectric samples. This sensor most importantly strengthens robustness to environmental conditions that cause cross-sensitivity or miscalibration. The accuracy of the measurement is enhanced as compared to conventional single- and double-notch metamaterial-based sensors. [ABSTRACT FROM AUTHOR]

An antenna‐filter‐antenna (AFA) based frequency selective surface (FSS) with excellent spatial filtering performance is proposed. This FSS design incorporates two back‐to‐back microstrip patch antennas, which not only ensures a high roll‐off rate at the passband edge and excellent flatness within the passband, but also achieves an ultra‐low profile. Significantly, the upper and lower band edges demonstrate a substantial drop from −3 to −10 dB within the 0.006 and 0.02 GHz ranges, respectively, resulting in a sharp roll‐off skirt. Furthermore, the frequency of radiation null can be controlled by manipulating the length of the quarter‐wavelength open‐ended stub, thereby possessing exceptional out‐of‐band suppression. A prototype of the proposed FSS with low profile is fabricated and measured. The simulations and measurements of the AFA‐based FSS show that a quasi‐elliptical bandpass filtering response with superior performance is achieved. [ABSTRACT FROM AUTHOR]

A miniaturized bandpass filter (BPF) with low insertion loss based on a modified T‐section and a grounded transmission‐zero resonator is proposed. The novel T‐section consists of two resonators, which can achieve the bandpass performance with two transmission zeros (TZs) in the upper band. The grounded transmission‐zero resonator can generate an extra transmission zero in the lower band. Therefore, high frequency selectivity can be achieved by the above three transmission zeros near the passband. The proposed BPF can achieve an insertion loss of 0.8 dB and a return loss of 22 dB covering 3.3–4.2 GHz, and the upper‐stopband attenuation is better than 20 dB up to 12.5 GHz (3.3f0). The proposed BPF with a miniaturized size of 1.2 mm × 0.5 mm × 0.3 mm have been fabricated using Si‐based integrated passive devices (IPDs) technology and measured by on‐wafer probing. The simulated and measured results of the proposed BPF are in reasonably good agreement. [ABSTRACT FROM AUTHOR]

This paper presents a lowpass-bandpass diplexer with ultra-wide stopband and low insertion loss using hexagon-shaped resonators. The proposed diplexer consists of a bandpass (BPF) and a lowpass filter (LPF), representing the core concept of the proposed design method that aims to concurrently design BPF and LPF. In this proposed design method, the influence of the LPF filter on the BPF's design has been identified through coupling matrix analysis for the first time. Initially, an LPF is designed based on three coupled hexagon-shaped elliptical resonators. Subsequently, a novel model for BPF design, utilizing coupled high-impedance lines, has been introduced. Following this, the BPF model is developed using coupling matrix analysis while considering the impact of LPF resonators. The LPF have a 1.32 GHz cut-off frequency and ultra-wide stopband up to 17.42 GHz. The BPF consisted of four resonators and the hexagon-shaped structure is used instead of low impedance lines. The utilization of hexagon-shaped resonators serves the purpose of enhancing the precision of the coupling effect, aligning with the proposed coupling matrix analysis. Additionally, hexagon-shaped resonators exhibit a greater capacitive effect, leading to a reduction in insertion loss within the passband when compared to rectangular-shaped resonators. The BPF has narrow passband with center frequency of is 2.25 GHz and 0.31 GHz bandwidth. The measured insertion losses of LPF and BPF are < 0.75 dB and 0.81 dB, respectively in 60% of passbands. [ABSTRACT FROM AUTHOR]

In this paper, a novel sextuple mode resonator (SMR) is proposed to design a compact ultra-wide dual-band bandpass filter (BPF) with high selectivity. An even- and odd-mode analysis method is employed to analyze the proposed SMR, and the SMR can excite six resonant modes simultaneously. In addition, a cross shape and several open-circuit stubs are used in the proposed SMR for generating multiple transmission zeros (TZs). The TZs can divide the transmission poles into two groups to form the two passbands. With properly tuned the TZs and the transmission poles, the proposed dual-band ultra-wideband BPF is of high selectivity. The center frequencies (CFs) of the BPF are centered at 1.6 GHz and 5.2 GHz, respectively. The 3-dB fractional bandwidths (FBW) of the two passbands are larger than 145% and 25%, respectively. To demonstrate the performance of the proposed method, an ultra-wide dual-band BPF is fabricated. Measurement results show that the proposed BPF has high band-to-band isolation, wide stopband, low insertion losses (ILs), controllable bandwidth, and compact size. The stopband is up to 12.5 fc1 (fc1 is the center frequency of passband 1st), and the circuit size is only 0.1λg × 0.12λg. [ABSTRACT FROM AUTHOR]