Broadband Bandpass Research Articles

Freely tunable phase-locked dual-frequency microwave signal generation from injection-locked broadband optoelectronic oscillator

We propose and experimentally demonstrate an injection-locked broadband optoelectronic oscillator (OEO) to generate freely tunable phase-locked dual-frequency microwave signals. When two single-tone signals inside and outside the passband of the electrical broadband bandpass filter (BPF) are, respectively, injected into the OEO, a phase-locked dual-frequency microwave signal with ultra-low near-end side-mode spurs can be generated from the OEO cavity. Therefore, one frequency of the output signal is equal to the frequency of the injected signal within the BPF, and the other frequency is equal to the sum frequency or the differential frequency of two injected signals. By changing the frequencies of two injected signals, two frequencies of the generated dual-frequency microwave signal can be arbitrarily tuned over the passband of the BPF. In our experiment, freelytu nable phase-locked dual-frequency microwave signals within the frequency range of 8∼12 GHz can be generated, where the side-mode suppression ratios (SMSRs) are more than 90 dB during the frequency tuning.

Metal Mesh Metasurfaces as Dual-Band Bandpass Filters for Terahertz Frequencies

In the paper, we propose a new strategy to design of metal mesh filters (MMFs) based on spatial symmetry analysis of bound states in the continuum(BICs) and manipulating and control with resonances, when BICs transformed to the resonances due to spatial perturbations in the MMF structure. The design of a dual-band polarization-insensitive terahertz bandpass filter with wide upper stopband characteristics using a single conducting layer patterned with rectangular holes is presented. The transmission response of the MMF with two poles is obtained to realize dual-band characteristics and three zeros to suppress the stopband. The proposed design has achieved broadband bandpass transmission characteristics under both TE and TM polarizations with canter frequencies at 0.516THz and 0.734THz and 3dB bandwidths of 25% and 17%, respectively, and upper stopband from 0.887THz to 1.6THz with over 10dB suppression.

Multi-stacked polarization insensitive broadband terahertz metamaterial

In this article, we present a polarization-insensitive terahertz metamaterial designed by stacking resonators capable of providing ultra-wideband terahertz transmissions. Our design includes a square ring resonator situated between two windmill-shaped resonators, separated by a polyimide spacer. We optimized the spacer thickness to achieve a broadband response in transmission. These optimized broadband metamaterial designs were fabricated through multiple steps of the photolithography process. Terahertz time-domain spectroscopy of the fabricated samples indicates broadband terahertz transmission, in agreement with both simulation findings and results calculated from the transmission line model for the multi-layered metamaterial geometry. Our research reveals a strong near-field coupling between resonators, leading to wideband transmission of terahertz waves. The stacking of these metamaterials is crucial in designing broadband bandpass filters and broadband modulators for terahertz photonics while keeping the resonance strength almost intact.

Design of Low-Cost Full W-Band 8th Harmonic Mixers for Frequency Extension of Spectrum Analyzer

High-order harmonic mixer is popular for frequency extension of spectrum analyzer (SA) from microwave to millimeter-wave or even terahertz band. The manufactures of SA usually offer expensive harmonic mixers where frequency extension is needed. In this work, low-cost designs of 2-port and 3-port W-band 8th harmonic mixers covering 75–110 GHz are proposed, and design method of two port mixer without frequency diplexer to separate local oscillator (LO) and intermediate frequency (IF) signals are first presented. These two kinds of mixers are compatible with almost all the current SAs with frequency extension options, which provides LO for the external harmonic mixer. The mixers are designed with planar microstrip lines and antiparallel Schottky diodes. The circuit of 2-port mixer includes the input broadband bandpass filter, diodes, output lowpass filter, and matching circuits. As for 3-port mixer, only an extra diplexer is needed to separate the IF signal and LO signal. The diplexer is composed of a planar semi-lumped lowpass and a highpass filter. The planar circuits are easily fabricated with low-cost print circuit board process on polytetrafluoroethylene substrate. The measured conversion loss of 2-port 8th harmonic mixer is from 20 to 26 dB, and 23 to 28 dB for 3-port mixer at full W-band. The good measured results indicate the proposed mixers are simple and effective.

Design of compact and broadband filtering balun based on N-shaped spoof surface plasmon polaritons

This paper presents a novel compact and broadband filtering balun using N-shaped spoof surface plasmon polaritons (SSPPs). The N-shaped SSPP unit cell’s lateral size has a 48% reduction compared to the rectangle-shaped counterpart. The proposed filtering balun is constructed by periodically etching N-shaped and mode-matching SSPP unit cells into the slotline balun consisting of the microstrip-to-slotline transition (MST) structures. The combination of the N-shaped SSPP unit cells and slotline balun realize the compactness and the broadband bandpass filtering response. Moreover, we can individually adjust the passband’s lower and upper cut-off frequencies. Due to the larger phase constant of the N-shaped SSPP unit cell, the field-confined ability of the proposed filtering balun is enhanced. The proposed design is fabricated and measured. It has advantages in bandwidth, stopband performance, size, and degree of design freedom compared with existing SSPP filtering baluns.

Compact broadband bandpass filter with wide stopband based on halberd-shaped spoof surface plasmon polariton

In this paper, a compact broadband bandpass filter with wide out-of-band rejection characteristics based on halberd-shaped spoof surface plasmon polariton (SSPP) is proposed. The filtering structure is achieved by etching a periodic halberd-shaped groove at the bottom of the substrate and a microstrip-to-slot line transition with a crescent-shaped patch at the top. Compared with the traditional dumbbell-shaped SSPP, the halberd-shaped SSPP has good slow-wave property, and the designed bandpass filter based on halberd-shaped SSPP can achieve a more compact size. The upper cutoff frequency and lower cutoff frequency of the passband can be adjusted by regulating the SSPP structure and the transition structure from microstrip-to-slot line, respectively. The simulation results show that the center frequency of broadband bandpass filter is 2.85 GHz, with the relative bandwidth of 130%, and the return loss in the passband is better than –10 dB, and the extreme strong out-of-band rejection of –40 dB from 5.6 GHz to 20.0 GHz. The size of the broadband bandpass filter is compact, only 1.08<i>λ</i><sub>g </sub>× 0.39<i>λ</i><sub>g</sub>, where <i>λ</i><sub>g</sub> is the wavelength at the center frequency. In order to verify the effectiveness of the wideband bandpass filter, the traditional printed circuit board technology is used to fabricate the wideband bandpass filter. The measurement results are in good agreement with the simulation results, verifying the feasibility of the design. The proposed broadband bandpass filter shows promising prospects for developing SSPP functional devices and circuits at microwave frequencies.

A Switchable Bandpass Filter for Broadband, Dual-Band and Tri-Band Operations

In this brief, a novel microstrip switchable bandpass filter (BPF) is presented. By switching RF p-i-n diodes on/off, the proposed topology could provide three different filtering states: broadband bandpass filter (BBPF), dual-band bandpass filter (DBPF) and tri-band bandpass filter (TBPF). For each state, the relationship between bandwidths and return losses are newly analyzed by proposed algorithm, then the design charts can be easily summarized. In order to improve selectivity and stopband rejection, two cascaded proposed topologies are also considered and discussed briefly. For demonstration, two switchable circuits are designed, fabricated and measured in the experiment. Simulated and measured results are matched very well.

Flexible and Polarization Independent Miniaturized Double-Band/Broadband Tunable Metamaterial Terahertz Filter.

In this paper, the design of a double-band terahertz metamaterial filter with broadband characteristics using a single conducting layer is presented. The design uses a structured top metallic layer over a polyimide material. The proposed design has achieved broadband band-pass transmission characteristics at the resonances of 0.5 THz and 1.65 THz, respectively. The 3-dB bandwidths for these two resonances are 350 GHz and 700 GHz, respectively, which indicates that dual-band resonance with broadband transmission characteristics was obtained. The design has achieved the same transmission characteristics for two different orthogonal polarizations, which was confirmed using numerical simulation. The design was tested for a different angle of incidences and it was observed that this results in angle-independent transmission behavior. In addition, for obtaining tunable resonant behavior, the top conductor layer was replaced by graphene material and a silicon substrate was added below the polymer layer. By varying the Fermi level of graphene, modulation in amplitude and phase was observed in numerical simulation. The physical mechanism of double-band behavior was further confirmed by surface current distribution. The proposed design is simple to fabricate, compact, i.e., the size is λ0/8, and obtained dual-band/broadband operation.

Compact single‐ and dual‐band band‐pass filters employing mixed eighth‐mode substrate‐integrated waveguide and microstrip line resonators

In this study, single- and dual-band band-pass filters (BPFs) employing mixed eighth-mode substrate-integrated waveguide (EMSIW) and microstrip line (MSL) resonators are proposed and investigated. The mixed resonators feature compact circuit size, moderate quality factor and flexible design topology. By exploiting the mixed resonators to implement the BPF designs, a single-band BPF is developed, exhibiting four-order broadband band-pass filtering responses in a single-layered substrate. Several transmission zeros are introduced near the working passband to enhance the frequency selectivity. Moreover, the proposed BPF has the capability to suppress the harmonics superior to 20 dB rejection level up to 2.36 f0. Meanwhile, two dual-band BPFs are designed in double-layered substrates with magnetic and electric coupling schemes. Both dual-band BPFs exhibit compact circuit size and low insertion loss. To the best of the authors' knowledge, it is the first time to develop single- and dual-band BPFs based on mixed EMSIW and MSL resonators in this study. For demonstration, a series of single- and dual-band BPFs with mixed SIW/MSL resonators are developed and fabricated. The simulated, measured and synthesised results have reached satisfactory agreements.

Design of a broadband bandpass filtering power amplifier for 5G communication

AbstractThis paper presents a broadband power amplifier (PA) based on a bandpass filtering (BPF) matching network. Terminated coupled line structure (TCLS) is employed to realize the broadband BPF matching network and ensure high selectivity, which also can achieve impedance transformation for PA. In addition, a harmonic control network is added in front of the TCLS to improve the efficiency of PA. To verify the effectiveness of the proposed method, a broadband bandpass filtering PA is designed and fabricated. The measured results show that the output power is from 39.5 to 41.6 dBm and the drain efficiency is between 58.8% and 72% in 3.3–3.7 GHz. These superior performances illustrate that the implemented filtering power amplifier can be applied well in 5G communication.

A design of broadband bandpass frequency selective surface

AbstractIn this paper, a broadband frequency selective surface (FSS) based on a multilayer coupling cascade is presented. The overall structure consists of three metallic layers and two dielectric substrates. In addition, a crosspatch terminated with an E‐shaped structure and a gradient cross structure with a slot is introduced in the middle metallic layer to control the transmission zero and extent of the current path, respectively. The unit cell periodicity is about 0.27 , and the overall thickness of the dielectric layer is about 0.087 . Prototypes of the proposed FSS are designed and simulated, and an equivalent circuit model is developed to explain the mechanism further. Finally, the FSS prototype works at the center frequency of 12.2 GHz with a relative −0.5 dB bandwidth of 70% and a relative −3dB bandwidth of 104%. The frequency responses are relatively stable with the variation of incidence angles from 0° to 60°.

Chiral Absorber-Based Frequency Selective Rasorber With Identical Filtering Characteristics for Distinct Polarizations

In this article, we propose a new paradigm to design frequency-selective rasorber (FSR) with two-sided efficient absorptions and broadband transmission in a chiral structure. The proposed FSR is implemented via combining two chiral absorber layers with a bandpass frequency-selective surface (FSS). An absorptive split-ring resonator (ASRR) inserted with a resistive film is designed to provide efficient spin-sensitive absorption. Then, four ASRRs are arranged to form a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{4}$ </tex-math></inline-formula> symmetric split-ring absorber (SRA) with identical absorption for distinct polarized incident waves. The physical mechanisms of spin-selective absorption and polarization-insensitive absorption are discussed theoretically. The broadband bandpass FSS is introduced to provide a transparent window and ground plane for the absorbers. A prototype is fabricated and measured to verify the feasibility of the method. The simulation and experimental results manifest over 90% absorptive bands of 1.5–3.6 and 15.2–21.6 GHz and a transmission band of 8–12 GHz with insertion loss less than 2 dB. Compared with previous FSRs, the proposed FSR has a broadband transmission, efficient absorptions with high-frequency selectivity, and easy geometric structure.

Broadband bandpass filter and filtering power divider with enhanced slow-wave effect, compact size, and wide stopband based on butterfly-shaped spoof SPPs

This paper introduces butterfly-shaped spoof surface plasmon polaritons (SSPPs) to design a broadband bandpass filter and filtering power divider (FPD) with enhanced slow-wave effect, compact size, and wide stopband. The dispersion and transmission characteristics of the proposed butterfly-shaped SSPP unit-cell are analyzed. It has higher slow-wave features than the conventional rectangle-shaped SSPP unit-cell with same lateral size. Accordingly, compact devices with enlarged confinement of surface waves can be implemented. The proposed filtering structures are realized by etching periodic butterfly grooves on the bottom layer of the substrate and using microstrip-to-slotline transition based on radial stubs. The lower and upper cutoff frequencies of the passband can be adjusted independently by tuning the dimensions of the radial stubs and butterfly grooves, respectively. The designed SSPP bandpass filter and FPD are fabricated. The measured results show a fractional bandwidth of 135.8% and 109.7% with an out-of-band rejection of greater than 31 dB from 6.9 to 18 GHz and 33 dB from 6.6 to 18 GHz for the bandpass filter and FPD, respectively. Moreover, the butterfly-shaped SSPPs achieve a lateral size reduction of about 39% compared to the rectangle-shaped SSPPs. Considering the above advantages, the presented structures provide a highly efficient solution for future telecommunication systems.

Broadband Bandpass Filter for UWB Networks with Multiple In-Band Transmission Zeros

Proposed in this manuscript is a broadband bandpass filter (BPF) with dual in-band transmission zeros (TZs) and elongated stopband for application in ultra-wideband (UWB) networks. The basic structure is developed on the principle of broadside coupling of microstrip-to-coplanar waveguide (CPW). Semi-elliptical microstrips on the top are arranged in back-to-back manner and coupled to the open circuited CPW in the ground. The basic BPF is of 3rd order with good insertion/return loss. To this basic BPF structure multiple defected ground structures (DGS) in the shape of complimentary split ring resonator (CSRR) are appended to place dual Tzs within the passband and later dumbbell-shaped DGS are engraved in the CPW to widen the stopband. Also, an approximate equivalent lumped element circuit model is developed and its frequency characteristics matched against full-wave EM simulation. The proposed dual notched BPF is finally fabricated and is found to occupy a compact area of 13.6 × 6.75 mm2.

Exploiting Parasitic Capacitances in 3-D Inductors to Design RF CMOS Quasi-Elliptic-Type Broad-Band Bandpass Filters

A class of RF broad-band bandpass filter (BPF) with quasi-elliptic-type response in low-cost bulk CMOS technology is reported. It is based on the in-series cascade connection of lowpass and highpass filtering stages with 3-D inductors, whose parasitic capacitances are properly exploited. Specifically, they are used to transform the basic inductor into an LC tank, thus allowing to generate an upper transmission zero (TZ) that increases filtering selectivity and out-of-band power-rejection levels in a spurious-free/extended upper stopband. The layout of a basic third-order BPF cell shaped by four 3-D inductors and its lossless equivalent lumped-element circuit are detailed. By means of this lossless equivalent lumped-element model, its scalability to higher-order BPF designs by in-series cascading various BPF-cell replicas is also demonstrated. For experimental-validation purposes, an on-chip RF CMOS BPF prototype with 11-GHz center frequency and 68.5% 3-dB fractional bandwidth is developed using a 0.13- μm bulk CMOS technology. According to the measured results, it shows an upper stopband with minimum attenuation of 31.7 dB from 22.5 GHz to 67 GHz, alongside with TZs at 3.5 GHz and 22.5 GHz to produce sharp-rejection filtering.

Study on the influence of coil configuration on electromagnetic characteristics of inductively coupled plasma superimposed frequency selective surface

Aiming at the limitation of frequency selective surface (FSS) used in radome, a new type of active frequency selective surface (AFSS) based on inductively coupled plasma (ICP) is proposed. The structure consists of a square plasma discharge cavity with a size of 20 × 20 × 5 cm3 and a FSS with broadband bandpass response. By comparing the simulation results of COMSOL Multiphysics with the experimental results of microwave interference diagnosis, the influence of coil configuration on the characteristic parameters of ICP source is analyzed. The transmissivity of ICP-FSS with different coil configurations was measured by time domain measurement system. The experimental results show that the bandwidth of passband of the structure is 6.4 GHz–19.1 GHz when the ICP source is not excited. When the ICP source is excited, the ICP-FSS structure presents different stopband transmission characteristics under different coil configurations. The bandwidth of stopband widens as the RF power increases, and the transmission coefficient valley also increases, which can effectively reduce the detection probability of the radar in the off state. Therefore, the proposed AFSS based on inductively coupled plasma is an effective candidate for radome application.

АНАЛИЗ ИСПОЛЬЗОВАНИЯ ОТФИЛЬТРОВАННЫХ С ПОМОЩЬЮ ПОЛОСОВОГО ФИЛЬТРА ХАОТИЧЕСКИХ СИГНАЛОВ ДЛЯ ПЕРЕДАЧИ ДАННЫХ В СИСТЕМАХ РАДИОСВЯЗИ

The analysis of the use of chaotic signals filtered through a broadband bandpass filter to ensure stealth and reliability of data transmission operations in radio communication systems is carried out. Time realizations of chaotic signals generated by the well-known Chua and Rikitake generators are obtained. They were filtered using a broadband bandpass filter, and the data obtained was studied using BDS-statistic and crest factor. As a result of the studies, it was found that under certain research conditions, time realizations of Chua generator and Rikitake generator, obtained by broadband filtering, are suitable. Other considered time realizations are not suitable for radio communication systems, since either they have low stealth from the outside observer, or they have an unacceptable crest factor value for radio communication systems. From this we can conclude that filtering chaotic signals using a broadband bandpass filter as a whole is a promising approach to ensure the stealth and reliability of data transmission in radio communication systems. The authors, basing on the conducted research and conclusions from well-known works, consider it appropriate to use broadband filtering to ensure the stealth and reliability of data transmission in radio communication systems when using chaotic signals, along with widely used methods.

Millimeter-Wave Wide-Band Bandpass Filter in CMOS Technology Using a Two-Layered Highpass-Type Approach With Embedded Upper Stopband

An on-chip millimeter-wave (mm-wave) broad-band bandpass filter (BPF) developed in bulk CMOS technology is reported. It is based on a two-layered implementation in which the circuit structure patterned in the top layer exhibits a highpass-type filtering response, whereas an upper stopband is created by the bottom-layer cell when coupled to the top-layer one to obtain a composite overall quasi-elliptic-type wide-band BPF functionality. The locations of the transmission zeros (TZs), which confer sharp-rejection capabilities to the overall frequency response, can be flexibly adjusted with the values of the capacitors that are employed in both layers. A simplified equivalent lumped-element circuit model of the proposed wide-band BPF approach is provided and applied to multi-stage BPF arrangements for higher-selectivity designs. Furthermore, for practical-demonstration purposes, an on-chip passive-integrated single-stage broad-band BPF prototype on silicon with 34.5-GHz center frequency and 61.2% 3-dB relative bandwidth is designed, manufactured, and characterized.

A tunable broadband bandpass filter based on quarter wavelength resonators

In this letter, a tunable broadband bandpass filter (BPF) based on quarter wavelength resonators was proposed. The resonators and coupling structures were mainly consisted of quarter wavelength transmission lines and tunable devices loaded at the two ends of the transmission lines. The resonant frequency of the BPF can be adjusted through changing the total capacitance at the both ends of the resonators. Especially, the coupling strength between resonators can be adjusted by adjusting the value ratio of the capacitor between the two ends. The tunable BPF in this scheme had the advantages of simply design. The bandwidth and center frequency of the tunable BPF can be tuned independently at the same time. As a demonstrator, an eight-orders filter was designed and fabricated on Rogers3006 substrate. The center frequency can be tuned in the range of 0.81 to 1.28 GHz, the relative tuning range was 45%. The relative bandwidth of the tunable filter can be tuned in the range of 14% to 38%. The simulated results were agreement well with the measured ones.

Triple-Mode Microwave Filters With Arbitrary Prescribed Transmission Zeros

This article presents a new filter design for arbitrary placement of real frequency transmission zeros in triple-mode filters, allowing for either asymmetric or symmetric responses. Triple-mode filters can be viewed, in general, as a series combination of coupled resonators with non-adjacent couplings, allowing for the realisation of transmission zeros. The strength and phase of couplings dictate the transmission zeros locations. The arbitrary placement of transmission zeros requires controlling all amplitude and phase rations, i.e., the ability to realise both negative and positive couplings. In general, this necessitates the use of capacitive and inductive probe structures complicating the construction and hence increasing the filter cost. The method presented in this article enables arbitrary placement of transmission zeros using only inductive or only capacitive couplings structures. In addition, broadband filtering characteristics can be realised using triple-mode filters. Examples of several narrow and broadband bandpass filters are given indicating that this method is valid for most triple-mode structures.