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This letter introduces a straightforward method for designing a tri-band bandpass filter using a loaded symmetrical dual-step impedance resonator (D-SIR) structure, augmented by multiple open and short circuit stubs. The resulting filter operates at 2.2, 7.9, and 14.1 GHz, showcasing high-band selectivity. Experimental measurements confirm six transmission zeros and six transmission poles across the passbands, yielding fractional bandwidth (FBW) of 42.6%, 63.8%, and 27.9%. Particularly noteworthy is the broader upper stopband rejection, enhancing the filter’s overall performance. The design achieves impressive performance metrics, with minimal insertion loss (IL) of 0.71, 0.87, and 0.76 dB, accompanied by substantial return loss (RL) of 23, 18, and 13.8 dB across the three passbands. Furthermore, the fabricated design have a compact size of ($0.20\times 0.15$) $\lambda _{g}$ on a Rogers Duroid RT/5880 substrate. Remarkable agreement between measured and simulated results underscores its viability for Internet of Things-based communication systems. [ABSTRACT FROM AUTHOR]

A novel circuit of impedance inverter has been proposed, which allows for efficient design of bandpass microwave filters. The synthesis approach relies on direct application of Richard’s transform to a lumped element prototype. Further impedance inverters are applied, which are composed of transmission-line sections with quarterwave-long shorted sections having negative impedance. The proposed impedance inverters are well suited for filters having from narrow to broad bandwidths. The proposed design method has been applied in the design of exemplary 5th and 9th order badndpass filters with directly connected transmission-line sections. The obtained measurement results support the proposed design method showing a good agreement with the theoretical results.

In this paper, a multifunctional microwave balun filter and balun diplexer design method is introduced. Through the proposed novel coupling structure and the use of miniaturized grid resonators, not only can the overall circuit area be reduced, but also features such as frequency selection, out-of-phase power splitting, and frequency division can be realized. This study actually designed and fabricated two balun filters and one balun diplexer. The simulated predictions of their frequency responses are in good agreement with the measurement results, validating the feasibility of the proposed technique. The results show that the circuit area of the developed balun filter and balun diplexer is approximately $0.08{\lambda }_{g}^{2}$ and $0.136{\lambda }_{g}^{2}$ , respectively. They also exhibit satisfactory performance, with in-band insertion loss $ < 0.7 \mathrm {dB}$ , in-band return loss $>15 \mathrm {dB}$ , port-to-port isolation $>30 \mathrm {dB}$ , maximum in-band magnitude imbalance of 0.9 dB, and in-band phase imbalance of 180°±8°.

Recently, the spurious self-suppression method has been introduced and applied to the bandpass TM cavity filters to improve their stopband performance. However, this method has the limitation of being applicable only to TM narrow-band filters. This paper shows how to overcome this limitation. In particular, it shows how to increase the bandwidth and improve the stopband performance by removing the spurious resonance of the coupling irises due to TE10 mode. The conventional rectangular iris is replaced by a new bent c-shaped iris. In this way, the resonance of the iris TE10 mode can be shifted to lower frequencies (below the cut-off), improving the stopband performance of the filter. Moreover, this new iris shape provides large couplings that allow wide passbands, and strong excitation of the spurious resonant modes that allows for an efficient implementation of the spurious self-suppression method. Furthermore, double slot iris has been used to connect the two central cavities to increase the central coupling of the filter. Design examples of 4th order and 6th order TM cavity filters with wide spurious free range up to 18 GHz having fractional bandwidth (FBW) of 5% and 4%, respectively, are presented. Finally, the 6th order TM cavity filter has been manufactured and measured. Good agreement has been achieved between simulated and measured frequency responses.

In this paper, a very efficient procedure for designing waveguide combline bandpass filters with an advanced electrical response is presented. The proposed technique is based on a segmentation strategy, which reduces the number of variables to be optimized by dividing the design process into simpler stages. The electrical response of an appropriate equivalent circuit model of the waveguide structure considered in each stage is used to generate the target curve needed in the optimization process. Moreover, the well-known Aggressive Space Mapping technique has been also implemented to improve the computational efficiency of the whole method. In order to validate the proposed design procedure, two high-order combline bandpass filters, with symmetric and asymmetric electrical responses including transmission zeros, have been successfully designed and simulated with full-wave analysis tools. Furthermore, as an experimental validation, a prototype of the symmetric filter has been manufactured, showing a good agreement between simulated and experimental data.

To meet the demand for simultaneously supporting the microwave and millimeter-wave technologies in emerging industrial wireless systems, research on dual-band components with a large frequency ratio has been conducted recently. However, it is challenging to implement independent frequency tunability on bandpass filters with both compactness and high performance. This article presents a dual-band bandpass filter with a large frequency ratio, independently tunable frequencies, and an ultrawide stopband. This is achieved by artfully incorporating a harmonic-controllable varactor-loaded microstrip BPF and a wide-stopband dielectric-loaded cavity BPF with the bandgap-embedded aperture coupling mechanism. Extremely compact size can be achieved without additional filtering elements. Two pairs of transmission zeros can be allocated beside two passbands for good selectivity due to the separate path and cross-coupling in the resonators. For validation, a prototype is designed, fabricated and measured. It can provide two independent tunable frequency ranges (3.22–3.52 GHz and 25–27.06 GHz), exhibiting a large frequency ratio up to 8.3. Mid-band suppression better than 20 dB and ultra-wide stopband up to 32.5 GHz with 20 dB suppression level are achieved. Low insertion loss and good selectivity can also be observed. [ABSTRACT FROM AUTHOR]

The instantaneous output power of the two-stage single-phase inverter pulsates at double-line frequency, generating a large amount of second harmonic current (SHC) in the front-end dc-dc converter and input dc source. The SHC is harmful to the system performance. To address the issue, a control strategy based on port-impedance editing, where inductor current feedforward (ICFF) and bus voltage feedforward paths are employed, is proposed to reduce the low frequency ripple in the article. Due to only bandpass filter employed in each feedforward path, the proposed control scheme is relatively easy to be implemented. Under the control strategy, the dc-bus port-impedance of dc-dc converter is increased rapidly at double-line frequency, while staying low impedance for other frequencies. What is more, different ICFF paths are taken into insight to obtain optimized path. Meanwhile, the small signal model of front-end dc-dc converter is established and the design principle of key parameters is provided for the derived control strategy. Furthermore, the dynamic response with bandwidth limitation is also discussed in this article. Finally, a two-stage single-phase inverter prototype was fabricated and tested. The experimental results verify the performance of the proposed strategy with SHC reduction. [ABSTRACT FROM AUTHOR]

This article reports an ultra-low-power (ULP) Bluetooth low-energy (BLE) receiver with an improved spurious-free dynamic range (SFDR). It features two passive-intensive RF techniques: an $N$ -path passive balun-LNA and a pipeline down-mixing baseband (BB)-extraction scheme. They together offer a high- $Q$ bandpass response at RF, and a high passive gain to suppress the noise of the BB hybrid complex filter. Specifically, the balun-LNA is a step-up triple-coil transformer aided by an $N$ -path switched-capacitor (SC) network to perform in-band voltage amplification, high- $Q$ bandpass filtering, $I/Q$ down-mixing, and input-impedance matching. Instead of using active amplifiers as the first-BB gain stage, we passively extract the four-phase ($I/Q$ and differential) BB signals using a pipeline of passive-SC networks that can stack up the voltage gain. Prototyped in TSMC 28-nm CMOS, the BLE receiver consumes only 266 $\mu \text{W}$ , of which 75 $\mu \text{W}$ in the BB hybrid filter at 1 V, and 191 $\mu \text{W}$ in the LO divider + buffer at 0.6 V. Measured at the maximum RF-to-BB gain of 61 dB, the receiver exhibits a noise figure (NF) of 6.1 dB and an out-of-band (OOB)-IIP3 of 22.5 dBm. The corresponding SFDR is 77 dB for a 1-MHz BLE channel and a 10-dB minimum signal-to-noise ratio (SNR $_{\mathrm {min}}$). The OOB-B−1 dB is −3 dBm. [ABSTRACT FROM AUTHOR]

A compact on-chip dual-band bandpass filter (BPF) at millimeter-wave frequencies is proposed in 0.15- ${\mu }\text{m}$ GaAs technology. To understand the working mechanism of the BPF, an LC equivalent circuit model is presented and analyzed for position estimation of the transmission zeros and poles. For demonstration, an on-chip BPF example is fabricated and tested, whose simulation and measurement are in good agreement. There are two frequency bands at 60.2 and 79.7 GHz with bandwidths of 9% and 6.8%, respectively. The chip, excluding the feedings, is only 0.304 mm $\times0.464$ mm.

This article presents a millimeter-wave (mmWave) dual-band dual-polarized filtenna, which can achieve desirable out-of-band rejection for 5G applications. The dual-band dual-polarized antenna element consists of two fully-shielded quarter-mode substrate integrated waveguide (FSD-QMSIW) cavities and a dual-band stacked ring antenna. Two parts are coupled through the slot on the ground. The cavities are completely enclosed by the metal holes and copper cover to eliminate radiation loss. The loaded slots can tune the frequencies of the first two modes in the FSD-QMSIW cavity for dual-band operation. The inherent transmission null between the dual modes is generated to improve the stopband attenuation. To verify the proposed method, a dual-band dual-polarized filtenna with a three-order filtering function and four radiation nulls is designed and fabricated. The −10 dB impedance bandwidth can effectively cover 5G n258 (24.25–27.5 GHz) and n260 (37–40 GHz) bands in the measurement. The gains of two polarizations drop over 20 dB between the two bands. A four-element filtenna array is constructed to test its beam-scanning ability and further integrated with active beamformer integrated circuits (ICs). The measured results show that the fabricated filtenna array maintains satisfactory out-of-band rejection performance and can be one of the most promising 5G communication candidates. [ABSTRACT FROM AUTHOR]

A new method for frequency selective surface (FSS) with high selectivity, namely, filtenna–filtenna (FA-FA)-based technique, is proposed, which consists of two filtering antennas and impedance matching network. Based on the reciprocity theorem, the radiation null of filtenna can provide a stopband of the proposed FSS. In this work, it is validated by using a periodic array of back-to-back magnetoelectronic (ME)-dipole antennas with split-ring resonators (SRRs), and a slotted GND plane is used to connect the two ME-dipole antennas for impedance matching. Bandpass response of the proposed FSS is realized by the intrinsic high-pass characteristic of ME-dipole antennas and the bandstop characteristic of SRRs. Four transmission zeros (TZs) and three transmission poles (TPs) are generated, exhibiting a high-order filtering response. TZs and TPs are analyzed by equivalent circuit model and current distributions. The 3 dB fractional bandwidth (${\mathrm {FBW}}_{\mathrm {3\,dB}}$) of 38.5% in the passband and the 20 dB fractional bandwidths $({\mathrm {FBW}}_{\mathrm {20\,dB}})$ of 8.7% in the lower rejection band and 13.8% in upper rejection band are obtained in this design. Finally, a prototype is fabricated and measured to further validate the proposed FA-FA-based technique. Simulated and measured results show that the proposed FA-FA-based FSS is with the distinct advantages, including wide passband, low profile, tunable TZs, and dual-polarized application, which verifies the proposed method of FSSs. [ABSTRACT FROM AUTHOR]

In this article, a multilayer reflective polarization conversion metasurface with both high-frequency selectivity and low profile is proposed. The frequency selective polarization conversion metasurface (FSPCM) is composed of four metal layers separated by three substrates. The cross-shaped patch on the top layer is connected to the folded microstrip line on the bottom layer with two via holes through the circle slots inside two ground layers, which converts the linearly polarized electromagnetic incident wave into cross-polarized wave after reflection. The second-order response can extend to the third-order response by introducing a coupled half-wavelength microstrip resonator on the bottom metal layer, which achieves high-frequency selectivity with a transmission zero and high polarization conversion rate (PCR) without increasing the thickness. The equivalent circuit analysis, structure simulation, and experimental demonstration are conducted in detail; the frequency selectivity of the fabricated FSPCM at the lower and upper band edge is 94 and 192 dB/GHz, respectively; PCR is more than 97% from 4.85 to 5.12 GHz, and the thickness is only $0.028\lambda _{0}$ , where $\lambda _{0}$ is the free space wavelength at the center operating frequency. Our findings pave a new way for enhancing the anti-interference capability and electromagnetic compatibility in applications of communication system, microwave imaging, and stealth technology. [ABSTRACT FROM AUTHOR]

For the linear compressor system driven by a linear oscillatory machine (LOM), the piston stroke is very important to realize the high working efficiency for the whole system. In order to obtain precise and reliable piston stroke signals without using the position sensor, this article proposes a stroke estimation method for the LOM using an improved sliding mode observer (SMO). For the improved SMO, the integral sliding surface is chosen to reduce the chattering phenomenon and the steady-state error of the system, and a novel reaching law is introduced to construct the sliding control law, which can further reduce the influence of the sliding chattering. Due to the piston stroke being obtained by integrating the back electromotive force (EMF) as estimated by the improved SMO, the pure integration saturation problem will occur due to that the measured current and voltage signals always contain some dc components. In order to cope with this problem, a self-adaptive bandpass filter is designed, which can obtain a filtered signal with almost no amplitude and phase deviation by adaptively adjusting its center frequency. Simulation and experimental results confirm that the proposed improved SMO has higher stroke estimation accuracy than the back EMF integration and the conventional SMO. [ABSTRACT FROM AUTHOR]

Image demoireing is a multi-faceted image restoration task involving both moire pattern removal and color restoration. In this paper, we raise a general degradation model to describe an image contaminated by moire patterns, and propose a novel multi-scale bandpass convolutional neural network (MBCNN) for single image demoireing. For moire pattern removal, we propose a multi-block-size learnable bandpass filters (M-LBFs), based on a block-wise frequency domain transform, to learn the frequency domain priors of moire patterns. We also introduce a new loss function named Dilated Advanced Sobel loss (D-ASL) to better sense the frequency information. For color restoration, we propose a two-step tone mapping strategy, which first applies a global tone mapping to correct for a global color shift, and then performs local fine tuning of the color per pixel. To determine the most appropriate frequency domain transform, we investigate several transforms including DCT, DFT, DWT, learnable non-linear transform and learnable orthogonal transform. We finally adopt the DCT. Our basic model won the AIM2019 demoireing challenge. Experimental results on three public datasets show that our method outperforms state-of-the-art methods by a large margin. [ABSTRACT FROM AUTHOR]

The back-electromotive force (BEMF) model-based observer is an attractive sensorless control strategy for permanent magnet synchronous motor (PMSM) drives. However, the accuracy of BEMF observer is deteriorated due to the dc offsets caused by current measurement and inverter nonlinearity. To address this problem, the article proposed a two-degree-of-freedom structure-based backstepping observer (TSBO) for sensorless PMSM drives. First, a two-degree-of-freedom structure is presented to improve the frequency-domain response of the BEMF observer. Second, a second-order complex vector transfer function is inversely introduced into the studied structure to achieve bandpass characteristics. Compared with the conventional BEMF observer, the studied TSBO can achieve dc error suppression without introducing the extra bandpass filter. The studied algorithm is verified by the experimental results on a 4.4 kW PMSM platform. [ABSTRACT FROM AUTHOR]

This article presents a synthesis method to design a new type of bandpass frequency selective surfaces (FSSs) with multiple transmission zeros (TZs). To briefly show the concept of our synthesis method, a generalized topology of the bandpass FSS based on cascaded slotline sections paralleled with bandpass resonators is first presented to map with an alternative $n$ th-order bandpass filtering network with $J$ -inverters and typical LC parallel resonators. Then, two kinds of composite LC parallel resonators, named as LC – LC and ${L}$ – LC parallel resonators, are introduced and discussed to replace the typical LC parallel resonators, which can produce TZs at skirts of the passband and increase the out-of-band selectivity. The derivations of equivalent relationships between the composite and typical LC resonators are given. Furthermore, for the exploration of bandpass FSS with multiple out-of-band TZs, the realization of these two discussed composite LC parallel resonators is exhibited by inductive and capacitive strip lines loading on slotline structures. The design curves and guidelines are given and discussed correspondingly. To validate our design concept, two FSS examples, a second-order bandpass FSS with four out-of-band TZs and a third-order one with five out-of-band TZs, are synthesized and designed. In final, these two designed bandpass FSS prototypes are fabricated and then measured by the free-space measurement method. The measured results show that the desired stable bandpass filtering performance and independently multiple out-of-band TZs are successfully realized. [ABSTRACT FROM AUTHOR]

A new class of 3-D integrated multiband bandpass filters (BPFs) based on substrate integrated waveguide (SIW) technology is presented in this work, for the first time. Split-type dual-extended doublet (SDED) coupling topologies are developed to propose these BPFs with a desired multiband response by the LEGO-style assembly of planar SIW resonant-mode blocks. These design schemes offer attractive and promising advantages with regard to compact size, low cost, flexible and expandable topology, as well as integration of high-density integrated circuits. For demonstration, dual- and triple-band BPFs are designed, fabricated, and measured. The measurement results are in good agreement with the simulation ones. Results indicate that the proposals can provide not only nice selective multiband signal transmission in such flexibly extensible topologies with new spatial schemes but also increase space utilization and reduce footprint. [ABSTRACT FROM AUTHOR]

In this article, a novel design of compact frequency-selective rasorber exhibiting absorption–transmission–absorption characteristics and having high passband selectivity has been proposed. A square-loop resonator with mounted lossy elements serves as the elemental broadband absorber from 4 to 12 GHz. The transmission frequency at 8.4 GHz is realized by printing a Minkowski fractal-shaped resonator with a high-Q factor on the resistive layer, which provides a transmission pole at the frequency corresponding to the passband of a double-cross-slot-shaped bandpass layer. The functioning of the proposed frequency-selective rasorbers (FSR) is explained by a corresponding equivalent circuit model. The proposed FSR exhibits higher selectivity at the passband, thus making it a suitable candidate for shielding the narrowband radiating system. Measurements performed on the fabricated prototype of a 17 × 17 unit cell array provides experimental validation. Further, a low radar cross-section antenna is realized by integrating a patch antenna with the proposed FSR, which achieves an average out-of-band monostatic radar cross-section (RCS) reduction of 11.92 and 5.04 dB in the lower (4–7.5 GHz) and upper (9.2–10.8 GHz) absorption bands, respectively, while maintaining the other antenna parameters. Furthermore, the bistatic total RCS reduction of 77% and 60% are achieved in the lower and upper frequency bands, respectively. [ABSTRACT FROM AUTHOR]

A high selectivity frequency selective rasorber (FSR) with an ultraminiaturized unit based on 2.5 dimensional (2.5-D) parallel resonator (PR), exhibiting low insertion loss passband between two absorption bands, is investigated. The lossy unit is realized by inserting a 2.5-D strip-type PR structure into the center of each side of the metal square ring and loaded with resistors connected at the four corners. The novel 2.5-D PR consists of interdigitated capacitors and strip metal wire connecting the other side of the lossy layer obtained by using metallized vias. The 2.5-D PR can effectively alleviate the congestion of the single-sided structures and achieve a high degree of miniaturization by means of tortuous extension inductance structure; as an additional feature, the values of L and C can be independently adjusted to determine the passband frequency allowing to provide additional degree of freedom to the design. An equivalent circuit model is proposed to analyze its operating principle. The dimensions of the miniaturized unit are 0.13λf × 0.13λf × 0.16λf (being λf the free space wavelength at the passband). A transmission window with low insertion loss of 0.125 dB is obtained at 4.65 GHz under normal incidence. The fractional bandwidth for −10 dB reflection is about 96%. The miniaturized FSR satisfies the characteristic of polarization insensitivity (TE and TM) and angular insensitivity (up to 45°). A prototype of miniaturized FSR has been manufactured and measured, showing a reasonable agreement with simulations. [ABSTRACT FROM AUTHOR]

A class of millimeter-wave E-plane waveguide bandpass filters (BPFs) based on spoof surface plasmon polaritons (SSPPs) have been presented in this article. Three kinds of SSPPs, with different patterns coated on the dielectric substrate, are inserted into the E-plane of WR-10 standard rectangular waveguide for the design of BPFs. To clarify the filtering characteristics of the proposed BPFs, the dispersive properties of different SSPP unit cells are investigated and discussed. The electromagnetic simulation results demonstrate that the bandwidths and center frequencies of the proposed E-plane waveguide BPFs can be flexibly adjusted by controlling the asymptotic frequencies of SSPP unit cells. For verifying the design feasibility, these three E-plane waveguide BPFs are fabricated and measured. Good agreement between measurements and simulations indicates that the proposed idea will be a good candidate for the BPF design with low insertion loss and flexible adjustment of center frequency and bandwidth. [ABSTRACT FROM AUTHOR]

In this article, quarter-mode substrate-integrated waveguide (QMSIW) filters featuring ultrawide stopband and flexibly allocated transmission zeros (TZs) are proposed. Eight higher modes with resonant frequencies up to 4.7 times of the fundamental mode are highly suppressed. It is realized by the combination of three approaches without extra circuit areas. First, a slot is cut in the first and last QMSIW resonators to make their resonant frequencies of higher modes different from those of other resonators. Second, avoid exciting the specific higher modes by setting the feed point in the area where the electric field strength of the higher modes is weak. Third, mismatch the higher modes when matching the passband. It is realized by using a stripline impedance transformer with its main body not exceeding the area of QMSIW resonators. Furthermore, except for the TZs derived by the classical cross-coupling matrix, two more independently controlled TZs are generated. The packaged filter is fabricated by using a benzocyclobutene (BCB)-based microelectromechanical systems (MEMS) process, which is suitable for millimeter-wave 3-D system-on-package (SOP) applications. The fabricated thin-film filter is measured with an insertion loss of 2.96 dB at 29.4 GHz and a fractional bandwidth (BW) of 17%. Higher mode suppressions up to 138.3 GHz are achieved. [ABSTRACT FROM AUTHOR]

A parameter extraction method for the LC circuit of a dual-band bandpass filter (DB-BPF) based on the fully connected network is proposed in this article. The network learning process consists of two stages: 1) pretraining and 2) fine-tuning. The network after pretraining has the ability to output the inaccurate values of LC circuit parameters with the desired ${S}$ -parameters (obtained according to the filter design requirements) as input. The precise LC circuit parameters can be obtained from the network during the subsequent fine-tuning process. This parameter extraction method can be applied to LC circuits of various bandpass filters. In addition to the amplitude of S-parameter, the phase of S-parameter is also used as learning data for the pretraining network. Comparative experiments show that the most accurate LC circuit parameters can be predicted using the network trained with phase information compared with the network trained without phase information. Two 7-order narrowband and two 9-order wideband DB-BPFs with four transmission zeros at different center frequencies are designed to demonstrate the validity of the proposed method, and the experimental results show that the proposed method is valid and effective. [ABSTRACT FROM AUTHOR]

This article presents a Ka-band switchable filtering power combiner monolithic microwave integrated circuit (MMIC), which unifies the functionalities of the switch, bandpass filter, and power combiner. For effective integration, a codesign approach is proposed by sharing the switchable resonant units and coupling matrix based impedance matching technique. Moreover, this approach offers great design freedom to realize arbitrary bandwidth and power ratios. For good return loss, the input external quality factor (Qe) is ensured as half of output Qe based on even-mode analysis. By analyzing the odd-mode circuit, the complex isolation element is introduced to improve the isolation between input ports. For demonstration, one prototype is implemented using a 100-nm GaN-on-Si process. Over 18-dB return loss, 1.7-dB minimum insertion loss (excluding 3-dB power ratio), >22 dB input–input isolation, and over 47-dB off-state isolation can be observed throughout 24–32 GHz. Besides, the proposed MMIC shows good linearity with a measured IP1dB of over 30 dBm within the passband, while the die size is 0.81 mm2. [ABSTRACT FROM AUTHOR]

This letter presents a microwave gas sensor based on planar coupled open loop ring resonators (OLRRs) embedded with carbon nanotube sensing film for ammonia gas sensing. The sensing area adopts the interdigitated electrode patterns to provide a larger contact area for better sensitivity. By integrating carbon nanotube films as the local variable resistors into a microwave sensor platform, the platform can transduce the gas concentration to its electromagnetic properties. According to the step response of NH3 from 100 to 1000 ppm, the sensitivity is estimated as $- 11~\mu $ dB/ppm and −232 Hz/ppm for the insertion losses and resonant frequency variations, respectively. The sensor repeatability and reversibility are also measured by maintaining the concentration from 300 to 700 ppm and repeating ten cycles with the average value of each concentration consistent with the step response. The results show a linearly response and a high repeatability of OLRRs via the real-time detection for gas sensing at high frequency and room temperature. Microwave gas sensors can be further integrated in the IoT or RF front-end system, offering low-cost, lightweight, reliable, and power efficient system for remote monitoring. [ABSTRACT FROM AUTHOR]

In this communication, a tunable circularly polarized (CP) antenna with a reconfigurable integrated feed network is proposed for cognitive radio (CR) applications. The integrated feed network is composed of an ultrawideband (UWB) bandpass filter (BPF), a continuously tunable T-shaped resonator, and an L-shaped microstrip line. The feed network employs three p-i-n diodes to switch between different RF paths, resulting in three modes of operation: an UWB mode (3.5–8.5 GHz), a narrowband bandpass (BP) mode and a narrowband bandstop (BS) mode. The continuous tuning range of the BP/BS narrowband mode is realized by two dc-controlled varactor diodes. The stand-alone antenna attains a −10 dB impedance bandwidth of 92.3% (3.5–9.5 GHz), while it attains an axial ratio (AR) bandwidth of 88.3% (3.1–8 GHz) in its wideband mode. The overlapped bandwidth (matching and AR) of the reconfigurable antenna is 78.2% (3.5–8 GHz). The communicating state covers 80% of the sensing spectrum while maintaining CP radiation. The measured peak realized gain values for the wideband mode range from 2 to 3.2 dBic while the maximum gain for the narrowband mode ranged from 1.95 to 3.1 dBic. The measured results show that the proposed filtenna is suitable for UWB CR systems. [ABSTRACT FROM AUTHOR]

An accurate and prompt estimation of phase angles, frequency, and magnitudes of the grid voltage is extremely important in paving a good platform for a fast and reliable operation of power grid monitoring, protection, and control. The phase-locked loop (PLL) served this purpose for decades, while the concept of the frequency-locked loop (FLL) has been proposed more recently. Even though the FLL and the PLL share some similarities, some differences still exist. Further research on FLLs can boost their capabilities and open up new windows in designing devices for grid synchronization. Multiple delayed signal cancellation (MDSC) filters are a peculiar system of filters. Their applications to FLLs can enrich FLL’s performance. This article focuses on applying the stationary reference frame MDSC filters at in-loop and prefiltering stages of the FLL and compares its effectiveness with widely used cascaded delayed signal cancellation (CDSC) and complex bandpass filter (CBF) based filtering techniques. The application of the $K$ -factor-methodology-based controller design to FLLs has also been explored for dynamic performance enhancements. A new cascaded multiple delayed signal cancellation (CMDSC) filter is proposed and is compared with its CDSC counterpart proposed in the literature to address the effects of dc offsets and imbalances under adverse grid conditions. The effectiveness of the proposed method is verified through OPAL-RT real-time simulations and dSPACE ds1104 and TMS320F28335 microcontroller experimental test bench. [ABSTRACT FROM AUTHOR]

A system for simultaneous measurement of micro-wave Doppler frequency shift (DFS) and angle of arrival (AOA) is proposed based on a silicon integrated chip. In the chip, two dual-drive Mach–Zehnder modulators (DDMZMs) with a microring resonator (MRR) inserted between them are integrated. When an external laser is coupled into the chip, it is first modulated by two echo signals via the first DDMZM and then goes through the MRR to introduce an optical phase shift to one of the first-order sidebands that falls into the resonance of the MRR. After being remodulated by the transmitted signal at the other DDMZM, the lightwave is coupled out from the chip and separated into two channels by an optical coupler. In each channel, a bandpass filter (BPF) is employed to select the upper and lower sidebands. By measuring and comparing the powers, frequencies, and phases of the beat signals in the two channels, the DFS (without direction ambiguity) and AOA can be acquired. Based on the proposed method, DFS within ±100 kHz at 10, 15, and 20 GHz is successfully estimated with a maximum error of ±0.028 Hz, and AOA measurement from 0° to 75° with errors less than ±1.53° is also realized. [ABSTRACT FROM AUTHOR]

This article focuses on the synthesis equations of three-section coaxial stepped impedance resonators (SIRs) for the design of Tx bandpass filters and on the benefits of adding a third section compared with using a two-section SIR. In this topology, the three coaxial structures fit inside ones another. In terms of the electrical scheme, the model is a succession of coaxial sections in a cascade, where the ground conductor of one becomes the central core of the next and vice versa. An advantageous property of SIRs is that they allow the size and the distance from the next harmonic to be controlled. The SIR effect depends on the ratio of the characteristic impedances of two adjacent coaxial TEM sections. For a resonator based on three sections, two impedance ratios need to be considered to electrically characterize the resonator in terms of fundamental resonant frequency and transmission zeros. Thanks to the equations obtained by modeling its frequency behavior, we are able to show the added value of changing such a resonator from two to three sections. This makes it possible to enlarge the minimal gap between the cylinders, decreasing the sensitivity to technological variations in manufacture and improving immunity to multipactor phenomena under constrained conditions of height and bandwidth. It also makes the first transmission zero frequency and fundamental frequency independent, as the relative proximity of these two frequencies has an impact on the quality factor and the power handling of the structure. To demonstrate the advantages, we designed an example of a three-section fourth-order filter in the L-band. This was compared with equivalent two-section filters, considering electrical performances and power handling, particularly the multipactor effect. This filter was fabricated in aluminum and tested. The experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

This article reports on a new class of additive manufacturing (AM) and monolithically integrated multiband coaxial bandpass filters (BPFs). They are based on $N$ in-series cascaded multiresonant sections that each of them consists of $K$ resonators and $K - 1$ admittance inverters. In this manner, a transfer function containing $K N$ th-order passbands in between $K - 1$ stopbands can be realized. A monolithic stereolithography apparatus (SLA)-based integration concept is proposed for these BPFs for the first time. For proof-of-concept validation purposes, multiple multiband BPF prototypes at the $S$ - and $C$ -bands were designed, manufactured, and tested. They include: 1) a dual-band second-order BPF with passbands centered at 3.7 and 4.2 GHz, fractional bandwidths (FBWs) of 8.1% and 4.2%, and effective quality factors ($Q_{\mathrm{ eff}}$) above 1000 for both of its passbands; 2) a dual-band third-order BPF with passbands centered at 3.7 and 4.0 GHz, FBWs of 4.9% and 3.3%, and $Q_{\mathrm{ eff}}$ above 1300; and 3) a triband second-order BPF with passbands centered at 3.5, 3.7, and 4.2 GHz, FBWs of 4.6%, 2.7%, and 5.5%, and $Q_{\mathrm{ eff}}$ above 1100, successfully validating the proposed monolithic multiband coaxial BPF concept. [ABSTRACT FROM AUTHOR]

Miniaturized dual-band filtering switches are proposed in this article using multimode dielectric resonators (DRs). The planar printed circuit boards (PCBs) are utilized not only to construct the hybrid electromagnetic boundary for quad-mode DR, but also to offer the switchable multimode feeding structures with the p-i-n diodes. When the diodes are reversely biased, all the four modes are excited simultaneously by the mixed electric and magnetic couplings and controlled flexibly to construct the dual-band response. In this manner, extra losses from diodes are avoided, and low-loss transmission is realized. When the diodes are forward biased, all the four modes are shut off at the same time. Owing to the used mixed electric and magnetic couplings, the isolation is enhanced further by the cancellation of the electric and magnetic couplings between the feeding line and the resonant modes. For demonstration, both dual-mode and quad-mode filtering switches with dual-band operations are fabricated and tested. With only one quad-mode DR, high performance, including low-loss dual-band transmission and high-level isolation, is observed in the measurement, making the proposed switches promising in high-standard multiband time division duplex (TDD) systems. [ABSTRACT FROM AUTHOR]

A fully integrated 490-GHz receiver (RX) adopting a dual-locking receiver-based FLL (DL-RBFLL) is presented. The proposed RBFLL structure saves the power consumption by reusing the existing blocks in RX instead of the power-hungry blocks such as dividers and buffers operating at sub-THz. Contrary to the single-loop implementation, the dual-loop RBFLL, which consists of the coarse and fine locking loops, extends the locking range by six times with negligible additional power dissipation. In the RF front-end (FE), the proposed 2nd-order sub-harmonic mixer (SHM) enhances interport isolation and suppresses the undesired LO leakage using a simple passive network. In the IF path, a 2-stage low-noise amplifier (LNA) followed by a 10-stage programmable gain amplifier provides a controllable gain of 0–80 dB with 4-dB step. An N-path filter, which serves as a high-Q bandpass noise filter, improves SNR in the IF path and thus RX sensitivity. Implemented in a 65-nm CMOS, the 490-GHz RX achieves the measured noise figure of 51.1 dB and noise equivalent power (NEP) of 0.85 pW/Hz $^{0.5}$ for the noise bandwidth of 17 MHz. The estimated sensitivity of the proposed RX is −92.9 dBm for a 1 kHz noise bandwidth, which dissipates 31.8 mW from a 1.2-V supply. [ABSTRACT FROM AUTHOR]

A 1 $\times $ 3 filtering dielectric resonator antenna (DRA) array is investigated in this communication. The central DRA is excited by a microstrip-coupled slot, while the two side DRA elements are, respectively, excited by the central DRA via a low-profile patch-loaded dielectric bridge laid between them. In order to integrate the filtering function, the open stub of the microstrip feed line is elaborately designed to generate a radiation null at the upper band edge, while two vertical metallic strips are added onto the sidewalls of the central DRA to provide another radiation null at the lower band edge. On the other hand, in order to achieve an enhanced gain in the operating passband, the higher order TE113 mode of the DRA elements is excited. It is found that due to the loading effects of metallic patches and conformal strips, three stepping resonances of the TE113 mode are generated in the passband, leading to a wide impedance bandwidth of 13.7% and a stable gain of 11.4 dBi. As a result, both good radiation and filtering performance are achieved without requiring complex filtering circuits. To demonstrate the extensibility of the array, a larger 3 $\times $ 3 filtering DRA array with a high peak gain of 14.7 dBi is further designed by just using a three-way power dividing network. [ABSTRACT FROM AUTHOR]

This communication presents a compact dual-band dual-polarized filtering antenna for base-station applications. The proposed dual-band antenna consists of a high-band (HB) dipole element and a low-band (LB) patch element, both with filtering responses. The HB element is embedded into the LB element, minimizing the overall size. The strong mutual coupling between the HB and LB elements is reduced by employing filtering HB and LB elements. For demonstration, a prototype of the dual-band antenna operating at LTE band 41 (2.5–2.7 GHz) as well as LTE bands 42 and 43 (3.3–3.8 GHz) is fabricated and measured. The antenna features a compact size of 41 $\times\,\,41$ mm2 ($0.52\,\,\lambda _{hh} \,\,\times0.52\,\,\lambda _{hh}$ , where $\lambda _{hh}$ denotes the guided wavelength at the highest frequency of HB). The cross-band isolation is higher than 27 dB without using extra filtering or decoupling circuits. In addition, a measured average gain of 7.8 dBi in LB and 7.7 dBi in HB is achieved. These merits make the proposed antenna suitable for 5G multiband aperture-shared array application. [ABSTRACT FROM AUTHOR]

In this communication, a dual polarized (DP) stacked patch filtenna (filtering antenna) with a wide stopband is developed for tile array applications. The bandpass filtering property is realized by improving the feeding network and patch without adding extra bandpass circuit or size. An elaborate feeding structure with complementary pair of a short-circuited stub and an open-circuited stub (CSSOS) is developed, which generates two transmission nulls effectively enhancing the selectivity and suppressing the harmonic. Moreover, CSSOS has a small size and broadens the impedance bandwidth apparently by introducing an in-band resonance. By properly etching four U-shaped slots on the driven patch, a radiation null in the upper stopband is also generated. The nulls generated by the two approaches can be adjusted independently in wide ranges. For further harmonic suppression, bandstop striplines (BSSs) with ultralow insertion loss are developed. Measured results show that the filtenna performs a wide operating band (3.10–3.95 GHz) and a wide stopband up to 8 GHz with a rejection level higher than 16 dB. Besides, a 32-element tile phased array employing the filtennas is also fabricated and measured. A compact configuration, high selectivity, and good beam steering capacity are exhibited. [ABSTRACT FROM AUTHOR]

A new broadside and conical beam reconfigurable dielectric resonator antenna (DRA) with three orthogonal linear polarizations (LPs) and two orthogonal circular polarizations (CPs) agility is presented. It consists of a quad-strip-fed DRA element and a reconfigurable feeding network. First, the DRA element is designed to make unidirectional ${\mathrm{HEM}}_{11 \delta }$ mode and omnidirectional ${\mathrm{TM}}_{01 \delta }$ mode operate in the same wide band by tactfully removing a concentric annular column from its interior. Furthermore, a center-loaded metal post helps to improve the impedance matching of the ${\mathrm{TM}}_{01 \delta }$ resonance significantly. Afterward, the switchable feed network is designed to implement diverse phase distributions of four output ports, i.e., providing the quad-port in-phase excitation, dual-port differential excitations, and quad-port sequentially rotated phase excitation strategies for a vertical LP, ±45° slant horizontal LPs, and two CPs, respectively. Finally, a fully functional prototype is designed, fabricated, and measured to validate the design. The measured results show that the overlapping impedance bandwidth of 36.8% for all the states and the axial-ratio bandwidth of 33.8% for the CPs are obtained. [ABSTRACT FROM AUTHOR]

A novel integrated silicon micromachined diplexer-antenna module for compact terahertz (THz) heterodyne receiver is proposed. The module is composed of a radio frequency (RF) antenna, a local oscillator (LO) antenna, and a waveguide diplexer which are realized by using the silicon micromachining technology and stacking nine equal-thickness layers. The corrugated conical horn antenna and quasi-diagonal horn antenna are applied as the RF- and LO-antenna, respectively. The diplexer is composed of two third-order waveguide bandpass filters and an H-plane T-junction, providing the isolated RF and LO channels. An experimental study is carried out in the 340 GHz band, demonstrating its application potential in THz heterodyne receiver element and array. [ABSTRACT FROM AUTHOR]

This article presents a frequency–amplitude independently tunable bandpass filter (BPF). The filter uses an electrically tunable coaxial substrate integrated waveguide (SIW) resonator, which has a compact size and a constant fractional bandwidth (FBW). The surface-gap coaxial SIW resonator is loaded with eight varactors and a thin graphene sheet at the top and bottom, respectively, which results in possessing independent tuning characteristics of frequency and quality factors. The variable capacitance values of the varactor are used to achieve frequency reconfigurability, and the graphene located on the bottom surface of the resonator is equivalent to a tunable lumped resistor used to control the $Q$ -factor. In addition, detailed steps of BPF design are provided. For validation, a prototype third-order varactor–graphene-loaded multitunable coaxial SIW BPF is fabricated. The measurements show that within the tunable range of the varactors, the proposed filter can be tuned from 0.68 to 1.03 GHz with 5% ± 0.2% 1-dB FBW and the insertion loss of passband can be continuously tuned over 2.68–6.37 dB. The frequency tuning and amplitude tuning functions are not dependent on each other. Over the frequency tuning range, the transmission amplitude at an arbitrary center frequency can be dynamically tuned by controlling the bias voltage applied to the graphene. [ABSTRACT FROM AUTHOR]

In this article, a class of wideband bandpass filters (BPFs) using triple-mode coaxial resonators has been introduced. Each triple-mode resonator is utilized with TM010 mode, TE− mode, and TE+ mode orthogonal to each other. Two L-shaped feeding probes and a loading disk are adopted to implement the miniaturization of these wideband BPFs. To observe the degree of miniaturization, we set a design specification of the same fractional bandwidth (FBW) of 40% at the same central frequency of 2.5 GHz. After employing the L-shaped feeding probes and loading disk, the efficient circuit size without cavity thickness is reduced by 80% compared with the triple-mode wideband filter without L-shaped feeding probes and loading disk. In contrast, the unloaded quality factors are slightly changed. In addition, another advantage of this work is that the upper stopband is extended to $2.5f_{0}$. Three experimental wideband BPFs in the large, medium, and small sizes are designed, manufactured, and tested for demonstration. Good agreements are obtained between simulation and experiment. [ABSTRACT FROM AUTHOR]

In this article, a design and synthesis method to realize filtering phase shifter with tunable insertion phase and passband center frequency is proposed. The filtering phase shifter is based on a circuit consisting of three resonators in a triplet topology. Coupling matrix analysis is employed to obtain the detailed relationship between the insertion phase and the amplitude response of the filter. Then, differential evolution (DE) algorithm-based optimization method is proposed to obtain the coupling matrix with an arbitrary prespecified insertion phase. The proposed optimization method can not only obtain the coupling matrix with desired insertion phase but also can align the phase slope of different phase states, resulting in a low-phase error over the filter passband. Furthermore, a method is proposed to extend the phase shift range to full 360° by switching the signs of specific terms in the coupling matrix, significantly simplifying the required optimization procedure. Finally, a filtering phase shifter using lumped elements is designed, fabricated, and measured to validate the design concept. The phase-shifting range of the circuit can achieve 360° with continuously reconfigurable center frequency covering from 650 to 860 MHz. [ABSTRACT FROM AUTHOR]

In this article, we present a frequency tunable magnetless nonreciprocal bandpass filter (BPF) that uses time-modulated quarter-wave microstrip line resonators. The proposed nonreciprocal BPF can transform real-to-real, real-to-complex, and complex-to-complex termination impedances. To achieve nonreciprocity, a modulation signal is directly applied to the varactor through the transmission line. The modulation scheme in the proposed nonreciprocal BPF, while simple, nevertheless achieves an excellent nonreciprocal response. The center frequency (f0) and nonreciprocal response of the proposed BPF are tuned by changing the dc bias voltage of the varactor. The design is validated by experiments using four prototypes of nonreciprocal BPFs (filter A: 50-to-50 Ω, filter B: 20-to-50 Ω, filter C: 25+j10-to-50 Ω, and filter D: 25+j10-to-55+j10 Ω). The measured results confirm that the f0 of the nonreciprocal BPF is tuned from 1.64 to 1.97 GHz (330 MHz) with a forward insertion loss variation of 4.96 to 3.94 dB and backward isolation of 20 dB over a bandwidth of 50 MHz. [ABSTRACT FROM AUTHOR]

A new structure magnetically tunable bandpass filter with five stages was designed and realized in this article. Yttrium iron garnet/gadolinium gallium garnet/yttrium iron garnet (YIG/GGG/YIG) film multi-layer structure was set as the basic resonant unit, and the metal rectangular ring was added between the YIG/GGG/YIG film structures to improve the out-of-band suppression and adjust the bandwidth of the filter. Based on CST Studio Suite and experimental results, the parameters of the bandpass filter structure were determined. The filter center frequency can be tuned from 10 to 15 GHz as the bias magnetic field changing from 2850 to 5560 Oe, the out-of-band suppression was greater than 80 dBc, the insertion loss was less than 6.5 dB, and the bandwidth varied from 51 to 70 MHz in the whole working band range. [ABSTRACT FROM AUTHOR]

A new 3-D-printed wideband circularly polarized (CP) dielectric resonator antenna (DRA) with two printing materials is investigated. The DRA has a multilayer comb-shaped structure at its top for generating CP fields. Three dielectric strips are embedded inside the DRA body to support multiple transverse-electric (TE) DRA modes to widen the DRA bandwidth. To slightly improve the axial-ratio (AR) performance, the DRA is twisted in the horizontal plane. For demonstration, a prototype operating in C-band was designed and printed with two different materials. The reflection coefficient, AR, radiation pattern, antenna gain, and efficiency of the antenna are measured, and reasonable agreement between the measured and simulated results is observed. The prototype has a measured 10 dB impedance bandwidth of 69.7% (4.80–9.94 GHz) and 3 dB AR bandwidth of 68.6% (4.52–9.24 GHz), achieving a wide overlapping bandwidth of 63.2% (4.80–9.24 GHz). Both the AR and overlapping bandwidths are record-high for a single-fed CP DRA. The prototype has a measured peak antenna gain of 8.3 dBic inside the overlapped passband. [ABSTRACT FROM AUTHOR]

This communication presents a novel stacked multi-resonator two-layered suspended rectangular microstrip antenna (MSA) backed by double-cavity, which yields a wide bandwidth (BW) of 64% at the center frequency of 2.6 GHz, due to additional resonances introduced by the cavity. The proposed antenna has high radiation efficiency above 89.5% throughout the band yielding a maximum gain of 14.7 dBi and an average gain of 12.5 dBi. It has a stable radiation pattern and low cross-polarization better than −45 dB and yields uniform isolation better than 40 dB between two such antennas. Compared to without cavity-backed configuration, the proposed double cavity-backed configuration yields 82% more BW, 1.8 dB more gain, and 10 dB more isolation between the antennas. Simulated results are validated by measurements with a close agreement. Improved characteristics of the proposed antenna make it suitable for several applications including through the wall and ground penetrating radars (GPR). [ABSTRACT FROM AUTHOR]

In this work, we address the challenging problem of completely blind video quality assessment (BVQA) of user generated content (UGC). The challenge is twofold since the quality prediction model is oblivious of human opinion scores, and there are no well-defined distortion models for UGC content. Our solution is inspired by a recent computational neuroscience model which hypothesizes that the human visual system (HVS) transforms a natural video input to follow a straighter temporal trajectory in the perceptual domain. A bandpass filter based computational model of the lateral geniculate nucleus (LGN) and V1 regions of the HVS was used to validate the perceptual straightening hypothesis. We hypothesize that distortions in natural videos lead to loss in straightness (or increased curvature) in their transformed representations in the HVS. We provide extensive empirical evidence to validate our hypothesis. We quantify the loss in straightness as a measure of temporal quality, and show that this measure delivers acceptable quality prediction performance on its own. Further, the temporal quality measure is combined with a state-of-the-art blind spatial (image) quality metric to design a blind video quality predictor that we call STraightness Evaluation Metric (STEM). STEM is shown to deliver state-of-the-art performance over the class of BVQA algorithms on five UGC VQA datasets including KoNViD-1K, LIVE-Qualcomm, LIVE-VQC, CVD and YouTube-UGC. Importantly, our solution is completely blind i.e., training-free, generalizes very well, is explainable, has few tunable parameters, and is simple and easy to implement. [ABSTRACT FROM AUTHOR]

This letter presents an on-chip ultra-wideband (UWB) bandpass filter (BPF) in 0.18- $\mu \text{m}$ SiGe BiCMOS Process. The proposed UWB BPF is constituted by cascaded quasi-elliptic response high-pass filter (HPF) and low-pass filter (LPF). A series LC circuit is introduced in the classical fifth-order lumped-element HPF, so that a transmission zero (TZ) is generated to form quasi-elliptic response. The microstrip line LPF with two series of open stubs can generate another two TZs, which also result in quasi-elliptic response. Step-to-step design procedure is given to guide the UWB BPF design. The measured result shows that the fabricated UWB BPF covers the frequency range of 10 – 50 GHz with the in-band return loss better than 13.5 dB, and the minimum in-band insertion loss is 1.99 dB. The core size of fabricated UWB BPF is 382 $\mu \text{m}\,\,\times 428\,\,\mu \text{m}$ excluding testing pads. [ABSTRACT FROM AUTHOR]

This brief proposes a wideband interdigital bandpass filter (IBPF), exploiting the through-silicon via (TSV)-based 3-D integrated circuit (3-D IC) technology. IBPF is a structure composed of multiple groups of parallel-coupled line resonators, which can increase the bandwidth and out-band suppression (OBS) characteristics of a bandpass filter. Through the transformation of the Chebyshev low-pass circuit model, a seventh-order IBPF centered at 85 GHz is obtained. By combining TSV technology with the coupling coefficient method, the design process from the Chebyshev low-pass circuit model to the final optimization of IBPF is given. The fractional bandwidth (FBW) of IBPF based on TSV is 63%, the out-of-band suppression is greater than 80 dB, the insertion loss is 1.3 dB, the return loss is 20 dB, and the size of the compact IBPF is only $0.50\times0.34$ mm2 ($0.48\times 0.33\,\,\lambda \text{g}^{2}$). [ABSTRACT FROM AUTHOR]

Numerous state-of-the-art solutions for neural speech decoding and synthesis incorporate deep learning into the processing pipeline. These models are typically opaque and can require significant computational resources for training and execution. A deep learning architecture is presented that learns input bandpass filters that capture task-relevant spectral features directly from data. Incorporating such explainable feature extraction into the model furthers the goal of creating end-to-end architectures that enable automated subject-specific parameter tuning while yielding an interpretable result. The model is implemented using intracranial brain data collected during a speech task. Using raw, unprocessed timesamples, the model detects the presence of speech at every timesample in a causal manner, suitable for online application. Model performance is comparable or superior to existing approaches that require substantial signal preprocessing and the learned frequency bands were found to converge to ranges that are supported by previous studies. [ABSTRACT FROM AUTHOR]

In this communication, a flexible, bandwidth-enhanced, electrically small, electric near-field resonant parasitic (NFRP) filtering antenna is presented. The inherent radiation null of the dipole-driven NFRP antenna is first presented. In addition, by properly adjusting the relative position of the NFRP element and the driven dipole, this radiation null can be placed at either the lower or upper operational band edge. Then, by implementing multiple NFRP elements and properly allocating their relative positions, excellent bandpass-filtering response together with the enhanced bandwidth of the electrically small NFRP filtenna is accomplished. A prototype of the optimized design operating centered at 1.9 GHz was fabricated and measured. The simulation and experimental results are in good agreement, indicating that the antenna exhibits a wide ~11.3% impedance bandwidth with good out-of-band rejection, while maintaining its electrically small size: ka ~ 0.924. The flexibility of this antenna is experimentally analyzed under different bending conditions and the results confirm that its performance characteristics are substantially maintained. [ABSTRACT FROM AUTHOR]

Cameras with RGB-infrared (IR) image sensors are advantageous for applications that can benefit from simultaneous capture of color and near-IR (NIR) images. High quantum efficiency (QE) in NIR is desired for RGB-IR image sensors because it allows to reduce power of NIR illuminants, however, there is a tradeoff. As imaging with RGB-IR sensors is often done with visible/NIR dual bandpass filters, high NIR signal can lower the dynamic-range and the signal-to-noise ratio (SNR) of the color images. This work studies the effect of the NIR signal on the dynamic-range and the SNR of color and NIR images of RGB-IR image sensors. It presents a model that allows to evaluate these metrics using image sensor, camera, and scene parameters. The model is applied for the case of varied illuminant NIR content and for the case of varied pixel QE in NIR. Both cases are evaluated theoretically and experimentally, and experimental results are in good agreement with simulations. [ABSTRACT FROM AUTHOR]

An interdigital bandpass filter (BPF), diplexer, and triplexer are proposed based on the through-quartz via (TQV) technology in this article. TQVs are inserted between adjacent resonators to adjust the coupling coefficients, resulting in the reduction in the total area of the filter. Equivalent lumped circuit of the filter is researched. The proposed BPF operates at 28.56 GHz, and the 3-dB fractional bandwidth (FBW) achieves 10%. The out-of-band rejection is better than 20 dB with frequencies up to 2.59 $f_{0}$. Based on the proposed filter, interdigital diplexer operating at 28.85 and 37.18 GHz, respectively, is constructed, which exhibits an isolation better than 30 dB and a stopband up to 2.61 $f_{1}$ of the lower channel. The triplexer operating at 22.24, 29.6, and 36.46 GHz is also designed in this article, which exhibits a wide stopband up to 2.96 $f_{3}$ of the lower channel with lower insertion loss. Measurement results agree well with the simulations over the whole band. [ABSTRACT FROM AUTHOR]