Transmission Zeros Research Articles

Design of a quad-band bandpass filter based on 13-mode resonator

ABSTRACT A quad-band microstrip bandpass filter (BPF) based on a 13-mode resonator is proposed in this article with compact size, high band‐to‐band isolation, and multiple transmission zeros (TZs). The proposed filter is constructed by two transmission paths from the input to the output port, which employs the transversal cancellation mechanism of two transition paths to introduce extra nine TZs. Therefore, a total of 12 TZs are located at 0.2, 1.8, 2, 3.88, 4.61, 5.24, 5.9, 9.26, 9.51, 12.32, 12.75, and 13.27 GHz, respectively, realizing high selectivity. Moreover, the designed filter can achieve quad passbands with centered frequency at 0.95, 2.78, 7.32, and 10.63 GHz for the requirement of multi-service in modern communication systems, with wide bandwidth of 235, 790, 2200, and 1540 MHz, respectively. The measured results agree well with the simulation results, which proves the feasibility of the design method.

A wideband reconfigurable filtering phase shifter based on Stub-loaded multimode resonators

Abstract In this paper, a type of reconfigurable filtering phase shifters (RFPSs) composed of stepped-impendence stub-loaded multimode resonators (SLMMR) is proposed. High frequency selectivity and wideband characteristics are realized in the presented work. Four transmission poles (TPs) are generated in the passband to exhibit a flat and wide passband. Meanwhile, the proposed SLMMR produces two controllable transmission zeros (TZs), which improves the frequency selectivity effectively. Meanwhile, radiofrequency switches are utilized to facilitate the transition between different phase shifts. Finally, the proposed RFPSs are designed and fabricated to verify the method. The measured results indicate that the designed RFPSs, which can be turned from 45° to 90° and from 135° to 180°, are capable of realizing more than 40 % FBW with a center frequency of 3.5 GHz.

Design of Compact HTS Bandpass Filter with High Selectivity Operating Above 100 k

In this manuscript, a miniature high-temperature superconductor (HTS) bandpass filter (BPF) with multi-transmission zeros (TZs), high selectivity, and great attenuation of stopband is presented. A couple of dual-mode resonator (DMR) is employed to achieve the proposed BPF, which can be characterized by using the classical even-odd mode analysis technique. The presented cascaded DMR can excite four resonant modes, which can be individually managed. Plus, a pair of intrinsic transmission zeros can be yielded at both the lower and upper edges of the passband, which results in sharp shirt performance. As an example, the HTS BPF is designed, fabricated, and tested, in which the center frequency is centred at 3.95 GHz and the 3-dB fractional bandwidth (FBW) is 2.5%. The proposed HTS BPF is implemented by using Tl2Ba2CaCu2O8 (Tl-2212) thin films which are fabricated by two-step processing and the superconducting critical temperatures (Tc) of the HTS films can reach 103 K. The design methodology is confirmed since the experimental results are in good agreement with theoretical results, showing desired bandpass characteristics, high selectivity, and the attenuation of lower and upper stopbands above −50 dB. Further, the circuit size is only 0.4 cm2.

Miniaturized broadband high out-of-band rejection bandpass filter based on spoof surface plasmon polaritons with defected ground structure

In this paper, a novel compact bandpass filter (BPF) with a wide out-of-band rejection is proposed. It can achieve broadband characteristics by combining hollow bowtie-type spoof surface plasmon polaritons (SSPPs) with complementary H-type defected grounded structures (DGSs) through aperture coupling. Compared with the conventional SSPP unit cells, the hollow bowtie-type structure exhibits much better slow-wave characteristics. The introduced slant antenna type port-coupling can produce a very strong high-performance rejection outside the high frequency stopband. Simulation results show that the SSPPs-DGS-based BPF has an excellent band pass characteristics in a broadband range with − 3dB fractional bandwidth of 43.5% at center frequency f0 of 2.04 GHz. The return loss in the passband is better than − 12 dB. Furthermore, because of the multiple transmission zeros generated in upper-stop-band, the designed BPF has an extremely strong out-of-band rejection of -40dB from 1.5 f0 to 4 f0 (f0 is the center frequency). The designed SSPPs-DGS-based BPF is fabricated by conventional printed circuit board (PCB) technology with a compact size of only 0.68λg*0.34λg (λg is the wavelength at the center frequency). The measured results have a good agreement with the simulation ones, which verifies the rationality and feasibility of the design. The miniaturized wideband BPF with broad out-of-band rejection may make it has good application prospect in the new generation microwave communication field.

Design of Absorptive Bandpass Filters With General Chebyshev Response Based on λ/4 Microstrip Lines

ABSTRACTIn this brief, a synthesis design method is proposed for one‐port absorptive bandpass filters (BPFs) with general Chebyshev response and transmission zeros. The method is based on coupling matrix theory, enabling the derivation of normalized coupling matrix coefficients based on user‐defined parameters, including 3 dB bandwidth, in‐band reflection coefficient, and out‐of‐band rejection. Moreover, it offers design equations for designing absorptive filters using transmission lines, coupling lines, and stubs, all with a length of one‐quarter wavelength at the center frequency of the passband. To illustrate this method, a fourth‐order absorptive BPF with a general Chebyshev response and two transmission zeros is designed, fabricated, and measured. The experimental results verify the effectiveness of the design method.

A self‐packaged multilayer all‐metal integrated suspended slotline dual‐band filter

AbstractThis paper introduces a novel implementation technology for realizing dual‐band bandpass filtering responses using high‐ slotline resonators with self‐packaged multilayer configuration. The concept of a 3D slotline is introduced, which utilizes the innovative metal‐integrated suspended line (MISL) technology. This technology utilizes an all‐metal structure, effectively eliminating dielectric loss. Furthermore, the implementation of an encapsulated structure significantly reduces radiation loss in the slotlines. Thus, the factors are greatly improved. Based on MISL, a dual‐band bandpass filter with wideband responses and multiple transmission zeros was designed, fabricated, and tested based on 3D cascaded‐mode half‐wavelength resonators. The test results demonstrated a high level of consistency with the simulation results, confirming the high‐ characteristics of the proposed 3D slotlines.

A planar three-section coupled-line high-selectivity wideband bandstop filter

A planar three-section coupled-line high-selectivity wideband bandstop filter (BSF) is proposed. The proposed filter topology contains three coupled-line sections (CLs) and two transmission-line sections (TLs). The four locations of transmission zeros (TZs) are obtained through the deduction of the theoretical equations, which validates the proposed topology. During circuit simulation, the effect of the Z e1 on the skirt roll-off is investigated. A highly selective wideband BSF with center frequency at 2.4 GHz, rejection level below 20 dB and attenuation rate at 278.69 dB/GHz is designed and manufactured. The theoretical and simulation results are in good agreement. Indeed, it illustrates the correctness of the theoretical analysis.

Quad Band Filter with Controllable Transmission Zeros using Vertical and Diagonal Coupling of Triple and Dual Step Impedance Resonators

Quad Band Filter with Controllable Transmission Zeros using Vertical and Diagonal Coupling of Triple and Dual Step Impedance Resonators

High selectivity wideband two‐channel bandpass filter for 5G microwave communication systems

AbstractA two‐channel high‐selectivity, wideband bandpass filter has been presented. This is based on a microstrip mixed‐impedance resonator and defected ground structure with the mixed coupling strategy. Two pairs of peripheral stepped‐impedance resonator (SIR) structures are used as stubs, achieving TZs at the immediate lower and upper cut‐off sides of the passband and control the bandwidth, while the other two transmission zeros on the upper cut‐off side are yielded through the defected ground structure, and the coupling between the SIR and uniform‐impedance resonators components, respectively. A prototype of the circuit is fabricated and measured for validation. The measured results exhibited insertion and return losses better than 1.1 and 20.5 dB, respectively, and high isolation levels exceeding 19 dB. In total, four transmission zeros are achieved. The designed filtering circuit realized a 3‐dB fractional bandwidth of 58.1%. There is a 0.95f0 stopband at the upper cutoff. The fabrication of the prototype shows good agreement between the simulated and measured performance.

Highly selective tri-wideband bandpass filter with adjustable passbands for high-performance space-based assets applications

A straightforward approach to designing a tri-wideband bandpass filter employing an E-shaped stepped impedance resonator loaded by an open-circuited tri-section stepped impedance stub (OSLTSIR) is explored in this paper. Upon analysis, it is ascertained that this resonator offers a distinct advantage by providing increased degrees of freedom for adjusting resonant frequencies, and the strength to generate transmission zeros at lower/upper stopbands. Capitalizing on these attributes, a tri-band bandpass filter is examined by combining this OSLTSIR with a half-wavelength resonator. The incorporation between the OSLTSIRs gives rise to creating a dual-wide band, while the introduced λ/2 resonators led to split the second passband into two, yielding in tri-band performance. The resultant filter operates at 8.25 GHz, 11.1 GHz, and 15.35 GHz with wide fractional bandwidths of 25.57 %, 18.45 %, and 24.6 %, respectively. Resonant frequencies and bandwidth can be controlled with substantial flexibility. The Experimental assessments confirm the existence of seven transmission zeros, showcasing high selectivity and good isolation. Besides, the fabricated structure maintains a compact size of (6.2 × 8.4) mm, about 0.12 λg2. The close agreement between the simulated and measured findings verifies its applicability for space-based asset applications.

On-chip Wi-Fi filter with FBW of 16.3 % and IL of 1.8 dB using novel T-type transmission zeros structure

A novel T-type topology is proposed for the first time to generate a pair of transmission zeros (TZs), enabling a wide range of resistive band rejection within a specific range. The working mechanism is elucidated through its even- and odd-mode equivalent circuits, and the design process is outlined. Moreover, an enhanced third-order high-pass filter is integrated with the T-type circuit to form a bandpass filter (BPF). This proposed BPF is fabricated using on-chip integrated passive device (IPD) technology. The measured and simulated results confirm its performance. Notably, the proposed IPD BPF has fractional bandwidth (FBW) of only 16.3 % and an insertion loss (IL) of 1.8 dB within the passband, thereby making it promising for narrowband applications. In addition, its compact size makes it suitable for Wi-Fi applications.

A compact dual‐band bandpass filter based on coupled stub‐loaded square ring resonators by using transversal signal‐interaction concepts

AbstractIn this paper, a novel dual‐band wideband bandpass filter (BPF) based on transversal signal‐interaction concepts with a wide upper stopband is proposed and investigated. The designed specification of two passbands can be managed and satisfied based on the independent controllable fractional bandwidth of the two passbands and the centered frequencies. The centered frequencies of dual‐band BPF are, respectively, 0.79 GHz (ƒ1) and 1.24 GHz (ƒ2) with 3 dB fraction bandwidths of 26.54% and 11.3%. Two transmission paths consisting of coupled stub‐loaded square ring resonators and anti‐coupled shorted lines are used to realize signal cancellation of multiple transmission path signal transmission from Port 1 to Port 2. Eleven transmission zeros (TZs) modify harmonic suppression up to 10 ƒ1 with stopband rejection higher than 15 dB. Butterworth lumped notch network and step impedance resonator (SIR) are also utilized to improve the selectivity and harmonic suppression. A compact filter with a circuit size of 0.08λg × 0.08λg is implemented and tested. Good agreement between simulation and measured results verifies the reliability of the designing scheme.

Design of HTS linear phase bandpass filter based on the inline topology

Abstract Inline topology filters have the advantages of a simple structure and fewer coupling coefficients. Based on the inline topology, this paper constructs a phase compensation topology of the filter, which can independently and controllably introduce two types of transmission zeros (TZs), and is convenient to realize the Chebyshev-like function response and compensate group delay. The finite frequency transmission zero is directly introduced through the source and load (S/L), and the real zero point is introduced and adjusted through the cross-coupling unit of the main path in this inline phase compensation topology. The two types of TZs can be introduced and regulated independently, so the side-band suppression and group delay compensation can be freely adjusted. A High-temperature superconducting (HTS) filter with inline is designed and processed with a typical structure based on application requirements. The filter introduces two pairs of symmetrical real TZs to improve sideband rejection and a pair of real TZs to control group delays to realize the linear phase. In addition, it has a small size and straightforward construction, and the results of the full-wave analysis method and the theoretical analysis approach match well with the measured results of the frequency response characteristics.

High-selectivity wideband bandpass filter based on quintuple-mode stub-loaded resonator and defected ground structures

Abstract A high-selectivity wideband bandpass filter (BPF) based on a quintuple-mode stub-loaded resonator and defected ground structures (DGSs) is presented. Thanks to the symmetrical topology, the even/odd theory is adopted for analyses. By properly adjusting the stub dimensions, the resonant frequencies of the transmission poles and zeros can be controlled to obtain wide passband and sharp out-of-band rejection performances. The bandwidth of the upper stopband is further extended by introducing a pair of DGSs under the interdigital coupled line feeding structures, and the spurious response rejection is improved by 18.9 dB. A BPF prototype that operates at 6 GHz with a fractional bandwidth (RBW) of 70 % is manufactured for validation. The measured insertion loss and return loss are 1.3 and 17 dB, respectively. The measured out-of-band rejection over DC-2 GHz and 8.8–21 GHz are better than −30 dB.

High-Performance monolithic ceramic waveguide filter with isosceles Right-Angled triangular resonator for base station applications

This paper presents a high-performance integrated monolithic ceramic dielectric waveguide (DW) filter featuring isosceles right-angled triangular (IRAT) resonators. The fabrication process of the filter involves embedding a specific number of blind holes (BHs) or through holes/slots (THs/TSs) in a hexagonal ceramic dielectric block, fully metallizing the dielectric surface, and forming a monolithic ceramic DW filter. To achieve magnetic coupling, four THs and a BH are introduced in the oblique edges of two IRAT resonators; alternatively, a TS and BH are introduced in their right-angled edges. Electrical coupling is realized through a deep BH on the right-angle side of the resonators. Two non-adjacent resonators initiate weak cross-coupling by cascading a T-shaped rectangular TS, shallow BHs, and deep BH, creating two transmission zeros (TZs) outside the band. The filter was fabricated to ensure theoretical correctness and process reliability. The measured results show an insertion loss between 0.5 – 1 dB and a return loss greater than 18 dB at a bandwidth of 3.4 – 3.6 GHz. Two steep out-of-band TZs occur at 3.26 GHz and 3.72 GHz, aligning with simulation results. Therefore, the filter not only exhibits excellent performance but is also convenient for mass production and manufacturing, offering significant potential for future applications in 5G / 6G communication base stations.

Highly miniaturized dual-band bandpass filter with wide bandwidth and large center frequency ratio

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 λg 2. The full-wave simulated and tested magnitude and group delay responses of the proposed filter are in good congruence.

E-plane waveguide bandpass filters based on high-order modes of spoof surface plasmon polaritons

In this paper, a new design method of E-plane waveguide bandpass filter (BPF) using high-order modes of spoof surface plasmon polaritons (SSPPs) is proposed. The high-order modes of the double-layer SSPP (DL-SSPP) unit cell can be effectively manipulated by adjusting the dimensions of grounded metallic patterns in SSPP array, which mainly determines the filtering characteristics of E-plane waveguide BPFs. For improving the out-of-band rejection, two extra transmission zeros (TZs) are designed at the upper and lower stopbands of E-plane waveguide BPF, and then the operating mechanism of TZs is clearly investigated. Moreover, the filtering characteristics of the E-plane waveguide BPF with different transition parts are discussed to demonstrate the generalization of proposed design method. To verify the design feasibility, two examples of E-plane waveguide BPF are fabricated and measured. Good agreement between measurements and simulations shows that the proposed design method possesses good potential for the applications of high-performance E-plane waveguide BPF design.

Miniaturized bandpass filter with ultrawide-stopband and high selectivity using glass-based IPD technology

A miniaturized bandpass filter (BPF) with ultrawide-stopband and high selectivity performance is proposed by virtue of glass-based integrated passive devices (IPD) technology. The proposed BPF consists of two modified second-order units and an impedance inverter. In the modified second-order units, two capacitors are added to the traditional second-order Chebyshev bandpass filter, which can generate two additional transmission zeros locating in the lower and upper bands, respectively. Moreover, these two modified second-order units are cascaded to improve the selectivity and achieve the ultrawide-stopband of the proposed BPF. In addition, the cascaded impedance inverter is introduced to further improve impedance matching of the proposed BPF. The proposed BPF is fabricated using glass-based IPD technology and measured by on-wafer probing. The fabricated BPF has a compact size of 1.0 mm × 1.0 mm × 0.35 mm. The measured results show that the fabricated BPF can cover the wide operating band from 3.3 GHz to 5.0 GHz with an insertion loss of 1.4 dB, a return loss better than 17.5 dB in the passband, and an upper stopband suppression better than 21.6 dB up to 43.5 GHz (10.48f0). In addition, the fabricated BPF can achieve a good frequency selectivity with a rectangular coefficient of 1.33. The simulated and measured results exhibit good agreements.

Design of a miniaturized multi resonance resonator based highly selective dual wideband bandpass filter

This paper presents the design of a highly selective dual-wideband bandpass filter. The filter is designed by using multi-resonance resonator consisting of two stub-loaded step impedance resonators separated by an inter-digital capacitor. The inter-digital capacitor generates capacitive coupling, resulting in multiple resonating modes. The proposed filter generates two passband frequencies centered at 5.75 GHz and 11.5 GHz. Experimental measurements show that the maximum insertion loss in the passbands is 0.83 dB and 0.87 dB, while the reflection losses are better than 10.8 dB and 12.6 dB, respectively. The resonant frequencies can be adjusted by changing the length of the loaded stubs. The proposed dual-wideband bandpass filter offers improved out-of-band rejection and selectivity by generating seven transmission poles and seven transmission zeros around both passbands. The experimental results confirm the effectiveness of the proposed filter. Furthermore, the filter has a compact size of (0.61×0.66)λg, making it suitable for integration into microwave sensing devices.

A Novel 5G Multi-mode Resonator and Filter with Symmetric Transmission Zeros

5G construction is becoming increasingly important. This paper introduces the theoretical basis of multi-mode filter, and on the basis of theoretical calculation and analysis, a novel 5G cavity multi-mode resonator and filter is designed by using ads/HFSS simulation software. The electric field characteristic of resonator is analyzed, and the mutual coupling between modes is realized by the way of screw perturbation. The electric field distributions of the mode is changed by adding tuning screws, two coupled degenerate modes act as two coupled resonators, so that the numbers of resonator can be reduced while keeping the resonance loop unchanged. For example, the characteristics of 3N section filter can be realized in the physical space of a traditional n-section filter by using three modes of a resonator, thus greatly reducing the volume of the filter. The results show that in the pass-band (3.5 GHz ~ 3.6 GHz): return loss > 17.9 dB, standing wave ratio < 1.29, insertion loss < 0.31 dB, a transmission zero point is introduced at 4 GHz on the right side of the pass-band, which makes the right side out of band attenuation rapidly. The filter has the advantages of small insertion loss, small size and good rejection of out of band, which can be applied to 5G band wireless communication system for better reliability.