Wideband Bandpass Research Articles

The Beam Squint Effects in Antenna Arrays at Millimeter Bands

Beam squint phenomenon is considered one of the most drawbacks that limit the use of (mm-waves) array antennas; which causes significant degradation in the BER of the system. In this paper, a uniform linear array (ULA) system is exemplified at millimeter (mm-waves) frequency bands to realize the effects of beam squint phenomena from different directions on an equivalent gain response to represent the channel performance in terms of bit error rate (BER). A simple QPSK passband signal model is developed and tested according to the proposed antenna array with beam squint. The computed results show that increasing the passband bandwidth and the number of antenna elements, have a significant degradation in BER at the receiver when the magnitude and phase errors caused by the beam squint at 26 GHz with various spectrum bandwidths.

Ultra-wideband bandpass microstrip filter with electronically tunable notch-band

This paper introduces a compact ultra-wideband (UWB) microstrip filter featuring both a fixed and an electronically tunable notch band. Operating within the frequency range of 3.27 GHz to 5.61 GHz, the filter incorporates a permanent notch at 4.08 GHz and a tunable notch at 4.88 GHz. Utilizing a traditional ground plane and a short-circuited transmission line, we develop a bandpass filter with a stable notch-band positioned and another tunable notch band. Systematic defects are made to the ground plane to increase the coupling between input and output ports leading to UWB response. The stable notch band is created using a rectangular slot resonator, while the tunable notch employs a varactor diode (NXP BB135 Varactor Diode) integrated into a rectangular stub. Operating in the even-mode with symmetrical current distribution, the filter exhibits a -3dB passband bandwidth of 740 MHz, 610 MHz, and 240 MHz across its respective passbands. Notch band attenuation measures at -10 dB and -9 dB, respectively. Experimental results from the prototype demonstrate excellent agreement with simulated results, confirming the efficacy of the design.

Compact on-chip dual-band bandpass filter with wide out-of-band suppression based on hybrid coupling technique

A compact dual-band bandpass filter (BPF) with wide out-of-band suppression based on a hybrid coupling technique is proposed. This BPF consists of two hybrid spiral coupled resonators, in which the electrical coupling and magnetic coupling between resonators can generate two transmission paths for dual bands. This dual-band BPF has wide out-of-band suppression. Moreover, its passband frequency and bandwidth can be readily controlled. To illustrate its working principle, an equivalent circuit with even- and odd-mode analysis is presented. This dual-band BPF is fabricated using a silicon integrated passive device (IPD) technology. The fabricated dual-band BPF has a compact size of 1.6 mm × 0.54 mm × 0.23 mm and is measured. The measured results show that this dual-band BPF can generate two bands at 2.45 GHz and 6.15 GHz. In addition, more than 20 dB of suppression is achieved from 7.8 to 20 GHz (8.16f0). The simulated and measured results exhibit good agreements.

Design and performance evaluation of a novel metamaterial broadband THz filter for 6G applications

Terahertz (THz) radiation, which has applications in the imaging of objects, non-destructive testing, satellite communication, medical diagnostics, and biosensing, has generated a great deal of attention due to its remarkable properties. This paper proposes a novel broadband filter for THz applications. The main idea is to overcome the insertion loss and bandwidth issues by modeling a frequency-domain finite difference method and guided-mode resonance (GMR). The optimal design scheme of the wideband pass filter based on the circular resonant ring is discussed by comparing the transmission parameters under various parameters. This scheme overcomes the restriction of the narrow passband bandwidth of the prior THz filters and achieves approximately 3 dB bandwidth of 0.54 THz. The proposed THz filter paper also has the advantages of a straightforward structure, low processing costs, and ease of conformal with other structures, and it can be used for stealth fighters, new communication technology, and precise instruments. In addition, when compared to existing models, the suggested filter offers higher 3 dB BW operation, increased transmittance, low insertion loss, and stable performance at various oblique angles.

Synthesis of Wideband All-Frequency Absorptive Filtering Power Divider with High Selectivity and Flat Output Port Distributions

In this paper, a wideband absorptive filtering power divider (AFPD) which features the characteristics of high selectivity and flat output distributions is proposed. It is composed of one unequal width three-coupled line (TCL), two coupled lines (CLs), two stepped open-circuited stubs, two kinds of isolation resistors, and two types of absorptive branches. The design equations of the proposed AFPD are derived using an even-odd decomposition method, and parametric investigations are also performed. It is found that the passband bandwidth can be adjusted by the stepped open-circuited stub which generates two transmission zeros (TZs). By combining the TCL with the CLs, the passband bandwidth is effectively enlarged. In addition, two isolated resistors are utilized for achieving good isolation and output-port matching performance. Without affecting the passband responses, the input port absorptive feature within the whole frequency band can be obtained by loading the absorptive branches both on the input and output ports. For validation, an example operating at the center frequency of 2 GHz was modeled and tested. Results exhibit that the passband FBW reaches 72% under 1 dB criterion, which illustrates flat output port distributions. In addition, for 10 dB return loss, the input and output impedance matching bandwidths are 250% and 78%, respectively. The features of good filtering responses are demonstrated by realizing the rectangle coefficient of 1.24 and the out-of-band suppression of more than 20 dB.

Fabrication of C-Band High-Temperature Superconducting Microstrip Triplexer with High Accuracy

This article presents a miniaturized C-band triplexer fabricated with high-temperature superconducting (HTS) microstrip lines and to be applied to quantum computers. The triplexer consists of three bandpass filters and branch lines. In the design of the bandpass filters, folded step impedance resonators (SIRs) are firstly used to achieve good stopband performances by harmonic suppression. Secondly, cross-coupling structures are also utilized to further improve the passband edge steepness of the bandpass filters. Finally, the parasitic transmission zeros originating from the assembling box sizes are employed to achieve a deeper out-of-band rejection. Three bandpass filters are designed and connected to the common input port of the triplexer. After that, the triplexer is coarsely optimized by advanced design system (ADS) for time-saving and is finely optimized by Sonnet for better accuracy. The optimized layout of the triplexer is fabricated on a 2-inch diameter and 0.5 mm thickness MgO wafer; here, the MgO wafer is double-sided coated with HTS YBa2Cu3O7 (YBCO) thin films. The measured passband bandwidths (return loss greater than 12 dB) of the triplexer are 6.420-6.680 GHz, 6.780-7.030 GHz, and 7.110-7.380 GHz, respectively, which satisfy the required design specifications.

A Balanced BPF with Wide Bandwidth and Steep Selectivity Based on Slotline Stub Loaded Resonators (SSLRs)

A balanced bandpass filter (BPF) with a wide differential mode (DM) bandwidth and steep DM passband selectivity and high common-mode (CM) block based on slotline stub-loaded resonators (SSLRs) is designed in this brief. The proposed SSLR, which is composed of a half-wavelength slotline resonator and a shorted slot stub loaded at the symmetrical plane, is applied to achieve a broad DM passband with a center frequency at 5.1 GHz and a 3 dB bandwidth of 92%. Meanwhile, two transmission zeros (TZs) are introduced to realize a steep DM passband selectivity. The center frequency and bandwidth of the DM passband can be adjusted by changing the dimensions of SSLRs and the gaps between them. Meanwhile, one narrow notched band with a 3 dB bandwidth of 4.9% is realized by employing one coupled quarter-wavelength short-circuited stub at the input ports. In addition, the DM stopband with a rejection level of 10 dB can be extended to 20 GHz. The designed balanced broadband filter is stimulated by a U-shaped microstrip line to slotline transition structure, which can realize wideband a CM block with a high suppression level without influencing the DM one, and this can reduce the design complexity. In order to prove the idea, a balanced broadband filter is designed and measured. The predicted results of S parameters are compared with the measured ones, and a good agreement is achieved.

Design of Superconducting Hex-Band Bandpass Filter Using New External Quality Factor Adjustment Method

A compact high-performance superconducting hex-band bandpass filter (HB-BPF) using a new external quality factor adjustment method has been developed. It consists of three five-pole dual-band bandpass filters (DB-BPFs) with center frequencies of 2.0 and 3.0 GHz, 2.5 and 3.5 GHz, and 2.74 and 4.0 GHz and, passband bandwidths of 2.0%. The DB-BPFs use stub-loaded dual-band resonators. Additional microstrip lines between the resonators enables flexible control of the coupling coefficient of each passband. To avoid affecting the external quality factors of the other two DB-BPFs, that of each DB-BPF is adjusted by placing the resonator on the feedline and changing the first (last) resonator configuration without changing the feedline configuration. A compact (20.9 mm × 40 mm; 0.36λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> × 0.68λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> ) HB-BPF was fabricated using YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> thin film on a 0.5-mm-thick sapphire substrate. The measured frequency responses agreed well with the simulated ones.

Compact wideband filtering Balun Based on SISL Technology

AbstractA new compact wideband filtering balun based on substrate-integrated suspended line technology is presented in this brief. The proposed device is composed of a λg/4 suspended stripline open-circuited stub, a λg/2 suspended stripline resonator, and a λg/2 suspended slotline resonator. These striplines and slotline are encapsulated in an electromagnetic (EM) shielding box consisting of air cavity, surrounding substrate layers, and metal layers to achieve EM shielding performance. By properly exciting the suspended stripline and slotline resonators, three transmission poles are generated to achieve high frequency selectively. The intrinsic 180∘ phase difference between the two output ports can be obtained by using the electric field distribution caused by the perpendicular coupling between the suspension stripline and the slotline resonator. The wideband passband is achieved with magnitude balance and out-of-phase properties. To validate our proposal, a wideband filtering balun operating at 2.56 GHz with fractional bandwidth of 65.6% is designed and fabricated.

Dual‐band filtering power amplifier with extended passband bandwidths and wide stopband rejection

AbstractThis article presents a dual‐band filtering power amplifier (DB‐FPA) with extended passband bandwidths and wide stopband rejection, which is helpful in reducing the number of microwave components in the dual‐band radio frequency front end, resulting in compact circuit size and low loss. In the designed DB‐FPA, a wideband low‐pass filter is applied as the input matching network (IMN) to provide wideband impedance matching and good stopband rejection, while a dual‐band filtering impedance transformation is adopted as the output matching network (OMN) to provide dual‐band impedance matchings and filtering responses simultaneously. Specifically, the IMN is constructed by high‐impedance transmission‐line sections and low‐impedance open‐circuit stubs. The OMN is designed based on the specific external quality factors and coupling coefficients during two bands, resulting in dual‐band impedance transformations and dual‐band filtering responses. Then, based on the above IMN and OMN, the design procedure of the presented DB‐FPA is summarised. To verify the proposed idea, a novel DB‐FPA has been fabricated and measured. During the two frequency bands, the measured maximum power added efficiencies are 55.11% and 47.78% within 33.0 dBm input power, while the measured peak gains are 15.4 and 14.0 dB within 15.0 dBm input power.

Parallel-Coupled-Line Bandpass Filter with Notch for Ultra-Wideband (UWB) Applications

A compact parallel-coupled-line microstrip bandpass filter with a very wideband passband and a narrow notched band is demonstrated in this paper. The presented bandpass filter was constructed from one section of three parallel-coupled-lines which has a length of a quarter wavelength at a midband frequency of 6.9 GHz. For the purpose of increasing the filter selectivity, the middle line is extended by a length of a quarter-wavelength and connected at one end to the ground plane. Therefore, a transmission zero was generated at each side of the passband which effectively improved the filter performance. In addition, a narrow notched band at a precise frequency inside the proposed passband was exhibited by placing a stepped-impedance resonator near the parallel-coupled-line for blocking the unwanted radio signal. The proposed filter was designed, simulated, fabricated, and measured. The fabricated filter has a very compact circuit size and its measured response shows an excellent agreement with the simulated results.

High Performance Multiple Passband Substrate Integrated Plasmonic Filters

We proposed a new variety of substrate integrated plasmonic filters (SIPFs) with multiple passband characteristics based on the concept of spoof surface plasmon polaritons (SSPPs). By etching a periodic interdigital structure array on the top metal layer of substrate integrated waveguide (SIW), we can achieve high-efficiency microwave SSPP transmission with an insertion loss of 1 dB in the passband of 7.4-12.5 GHz, and a high rejection level of 27 dB in the rejection bands. By introducing antisymmetric C-ring resonators (ASCRs) in the filter structure, the passband number and bandwidth of the filter can be flexibly manipulated. To validate the proposed design, four SSPP filters prototypes are fabricated and tested, showing good filtering performances with a high transmission coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}21\mathbf {&gt;}-$ </tex-math></inline-formula> 1 dB) and low reflection coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}11\,\,\mathbf { &lt; } - $ </tex-math></inline-formula> 12 dB) in their passbands, and a high rejection level over 15 dB between them. By changing the geometric parameters of ASCR, the number of passbands can be increased from 1 to 3, and the passband center frequency and bandwidth can be engineered accordingly. The proposed SSPP filters with good multiple passband characteristics may have great potential applications in microwave wireless integrated plasmonic circuits and communication systems.

A miniaturized highly selective MTM‐inspired filter for lowpass and triple‐band bandpass performance with configurable transmission zeros and bandwidth

SummaryThis paper presents a novel, compact, and highly selective metamaterial inspired filter with low insertion loss, lowpass, and triple‐band bandpass characteristics. The presence of five transmission zeros and seven poles facilitates highly selective filtering performance. The improved impedance matching and transmission characteristics have been achieved by embedding complementary split ring resonator as defected ground structure. The filter circuit area excluding 50 Ω feed lines is merely 0.17λg × 0.05λg at 3‐dB cut‐off frequency of lowpass passband (1.11 GHz). The 3‐dB fractional bandwidths of the three bandpass regions are 39.50% (1.3–1.94 GHz), 21.20% (3.12–3.86 GHz), and 21.06% (4.04–4.99 GHz) at the center frequencies of 1.62, 3.49, and 4.51 GHz, respectively. Intended filter also offers a wide stopband extending from 2.15 to 2.96 GHz at close to 20 dB attenuation level. Further, position of transmission zeros and 3‐dB passband bandwidths can be adjusted by carefully choosing structural design parameters. The metamaterial effect of the proposed filter has been demonstrated by plotting refractive index followed by validating the performance with the help of experimental measurements. No filter shows lowpass characteristic along with three bandpass performances as found by the authors exploring literature, which presents the novelty of the proposed work.

Compact Wideband Absorptive Filtering Power Divider With a Reused Composite T-Shape Network

This paper presents a compact structure for the filtering power divider (FPD) with wide absorptive bandwidth as well as good isolation between the output ports. A composite T-shape network that consists of a pair of resistors and a central shorted stub is used for realizing good isolation and absorption simultaneously. The isolation resistors that are essential in the FPD can be shared to absorb the signal reflected back to the input port. To enhance the absorption performance, only one synergistic absorptive stub is required and added to the input port. It allows the absorption performance to be independently controllable without affecting the passband response. The dual functions of wideband filtering response and power division are achieved by integrating the power divider and the bandpass filter using a compact three-line coupled structure. A pair of shorted stubs loaded at the ends of coupled-feed lines for outputs can provide controllable passband bandwidth and transmission zeros. To verify the proposed design concept, the multifunctional FPD with the compact structure is fabricated and measured. Good agreements between the measured and simulated results verify the calculated predictions.

Single Longitudinal Mode Parity-Time Symmetric Brillouin Fiber Laser Based on Lithium Niobate Phase Modulator Sagnac Loop

A single longitudinal mode (SLM) parity-time (PT) symmetric Brillouin fiber laser (BFL) based on z-cut lithium niobate phase modulator (LN-PM) Sagnac loop with Hz level linewidth is proposed and experimentally verified. A 10 km single-mode fiber provide SBS gain, while an LN-PM Sagnac loop consisting of an LN-PM and two polarization controllers (PCs) is used to achieve PT symmetry. Two mutually linked feedback loops supporting orthogonally polarized light are created by utilizing inherent birefringence of LN waveguide from LN-PM without electrical signal modulation. One of the feedback loops experiences gain in a clockwise direction and the other loss in a counterclockwise direction. The polarization state of the stokes injected into the LN-PM is controlled by adjusting the PC, and SLM BFL can be achieved when the gain and loss are well matched and exceed the coupling coefficient to break the PT symmetry. Compared with existing BFL studies, this design does not call for frequency matching of several composite cavity structures or precise control of ultra-narrow bandwidth bandpass filters. In addition, a frequency-locking system based on Pound-Drever-Hall technology is employed to lessen the instability and external disturbances brought on by the ring cavity. In the experiment, the linewidth of PT symmetry BFL based on LN-PM Sagnac loop is 3.85 Hz, according to the measured linewidth of 77 Hz at the −20 dB power point. A 65 dB optical signal-to-noise ratio and a 43 dB maximum side mode suppression ratio are measured. Furthermore, the PT symmetry BFL's wavelength is tuned between 1550 and 1550.41 nm.

A single‐layer differential‐fed dual‐band filtering antenna for WLAN application

AbstractIn this letter, a single‐layer differential‐fed dual‐band filtering antenna for wireless local area network application is proposed. The proposed antenna consists of a square patch, and two pairs of stepped impedance resonators (SIRs). The lower operating passband is realized by exciting the square patch with a pair of differential ports. Then, a pair of SIRs is connected with the radiating edge of the square patch to introduce another resonance, thus forming the upper passband. And a radiation null is simultaneously produced to enhance the frequency selectivity between the two passbands. Moreover, another pair of SIRs is utilized to connect with the nonradiating edge of the square patch, which generates an additional high‐frequency in‐band resonance and a radiation null to further improve the bandwidth and frequency selectivity of upper passband. The developed prototype was fabricated and measured to verify the design concept. The measured results are in good agreement with the simulated ones, demonstrating that it exhibits −10 dB fractional impedance bandwidths of 3.68% and 7.35%, maximum realized gains at boresight direction of 5.5 and 8.7 dBi, and cross‐polarization levels smaller than −30 dB, in lower and upper passbands, respectively.

Miniaturized frequency selective rasorber with absorption in S–C band and transmission in X band

A miniaturized frequency selective rasorber (FSR) that has a wide absorption band in the S–C band and a wide transmission band based on X-band is presented in this paper. The FSR consists of a lossy layer loaded with lumped resistors and a bandpass layer with a three-screen cascade structure, which has the advantages of low insertion loss, wide passband bandwidth, and stable structural performance in the operating band. The rectangular spiral resonant (RSR) is loaded in the middle of the four arms of the cross to form a lossy layer. The aggregate resistance is loaded between the units to form a closed loop, which will absorb the detection signal and thus greatly reduce the radar cross section (RCS). The bandpass layer is divided into three layers, with two identical square patches coupled with a layer of complementary cross grids to form a multi-order bandpass filter. Furthermore, the operating mechanism of low absorption and high transmission is analyzed and verified based on equivalent circuit theory and impedance matching theory. The simulation results show that the 1 dB transmission band of the FSR is 8.0–12.5 GHz and the 10 dB absorption band is 2.8–6.6 GHz. The highest transmittance reaches over 97% at 10.0–11.5 GHz and the lowest insertion loss is 0.012 dB. It has important theoretical reference value and great application in the field of the new stealthy radome.

A Novel Method for Microphone Channel Frequency Response Calibration Based on Newton Algorithm

Microphone arrays are widely applied in practical applications. In an array, each channel conventionally contains an acoustic sensor and a following signal conditioning circuit (SCC). Frequency response mismatches among channels will adversely affect array’s overall performance. Existing calibration methods provide promising results; however, their accuracy varies considerably across full frequency band and the passband bandwidth shrinkage problem also arises. To address these problems, we propose a novel calibration method based on Newton algorithm. The proposed method cascades calibration filters after channel output signals allowing the frequency response calibration to be equivalent to the optimization of calibration filter coefficients. First, all uncalibrated channels’ bandwidths are analyzed using a chirp calibration signal, resulting in appropriate construction of the desired output. Next, a spectrum mean square error criterion between each channel output and the desired signal is utilized to formulate the frequency response mismatch. Finally, we employ Newton algorithm to design the calibration filter coefficients corresponding to each channel. Explicit mathematical derivation is provided. Since the cost function is quadratic, expressions of the constant Hessian matrix and its inverse are derived. Furthermore, the inverse Hessian can be efficiently computed using spectral coefficients of channel outputs. Simulation results reveal that the proposed method significantly outperforms the state-of-the-art calibration approaches in terms of calibration accuracy, calibrated passband bandwidth performance, and convergence rate. Real-world experiments also verify its effectiveness.

Design and Characterization of the Fully Metallic Gap Waveguide-Based Frequency Selective Radome for Millimeter Wave Fixed Beam Array Antenna

This article presents a bandpass frequency selective surface (FSS) radome based on fully metallic gap waveguide (GW) technology. The element of the proposed FSS radome consists of a conventional cross-dipole slot etched on metallic plates and positioned over a groove GW cavity. A design with a single GW-cavity layer was initially produced which was later optimized for performance, to comprise a dual GW-cavity layer, while considering both functionality and manufacturability. It is shown that the proposed FSS element offers a stable and wide bandpass (from 26 to 30 GHz) performance in the broadside direction for both transverse electric (TE) and transverse magnetic (TM) polarizations. For oblique angle of incidence, the suggested FSS element works up to 30° with a reduction in usable bandpass bandwidth performance to 26–28 GHz for both TE and TM polarizations. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20 \times 20$ </tex-math></inline-formula> -element GW-FSS array prototype has been fabricated and measured, which was integrated with a fixed-beam array antenna to further validate its functionality as a filtering radome. The findings show an excellent agreement between simulations and measurements. Hence, the proposed GW-FSS represents a great opportunity to develop an all-metallic FSS with low insertion loss, sharp-roll-off filtering, wideband performance, and inexpensive fabrication cost.

Design of cost effective variable bandwidth 2D low-pass, high-pass and band-pass filters with improved circularity

This paper discusses two-dimensional (2D) finite impulse response (FIR) filter structures to achieve improved circularity and variability in bandwidth without restructuring. The P3 transformation employed in this work for the design of circular filters helps to achieve better circularity and less complexity. The variability is obtained by using two different approaches. In Method 1, the bandwidths of the 2D circular filters are changed by adjusting a parameter in the one-dimensional (1D) domain. In contrast to Method-1, Method-2 directly adjusts the bandwidths of the 2D filters using a parameter in the 2D domain. Low-pass, high-pass, and band-pass variable bandwidth filters are designed using both methods to illustrate the benefits of the two approaches. Comparing their implementation complexity, contour approximation error, and normalized root mean square error to those of other multiplier-less transformations demonstrates their efficacy. It can be seen that Method 1 and 2 respectively achieve around 5% and 20% reduction in the number of multipliers with a maximum normalized root mean square errors of 0.3129 and 0.3532 when compared to that of the 2D filters designed using the latest existing transformation.