Search

We propose an automated heterogeneous trench-assisted multi-core fibre (MCF) design method. This method uses neural networks to speed up coating loss estimation by $\sim$ $10^6$ times and using particle swarm optimization (PSO) algorithm to explore the optimal MCF design under various objectives and properties constraints. The latter reduces the permutation evaluations by ten orders of magnitude compared with the brute force method. The artificial intelligence (AI)-based method is used to design MCFs on two objectives: minimizing crosstalk (XT) and maximizing effective mode area ( $A_\text {eff}$ ). By optimizing XT with different $A_\text {eff}$ and cutoff wavelength constraints combinations for 6-core fibres, we achieved −92.1 dB/km ultra-low XT for C+L band fibre and −64 dB/km for E+S+C+L-band fibre. Meanwhile, we explored the upper limit of $A_\text {eff}$ given different bandwidth constraints resulting in a 6.82 relative core multiplicity factor. We performed capacity analysis of fibres for two transmission lengths. It is shown that bandwidth is the dominant factor while the increase brought by $A_\text {eff}$ and the penalty caused by XT are relevantly small. Our fibres exceed the cutoff-limited capacity of the 7-core fibre in literature by 35.1% and 84.8% for 1200 km and 6000 km transmission respectively.

This communication presents a compact end-fire leaky wave antenna (LWA) is presented on the coplanar stripline (CPS) with narrow width property under a new operation mechanism. By periodically loading stubs between two strip lines in parallel, the leaky region of its fundamental mode can be generated in the CPS with forward beam scanning property, and the end-fire radiation is realized at the frequency where its normalized phase constant is equal to one. Since the leaky region of the fundamental mode owns a relatively low cutoff frequency, the proposed antenna generally has the property of small overall size in this region. The end-fire operating frequency is firstly discussed based on the circuit model, and the corresponding radiation property is then analyzed from the antenna array point of view. The leakage constant as well as characteristic impedance of the proposed antenna are further investigated with the full-wave extraction method. Moreover, a modified structure is proposed as the last element of the antenna to leak out the rest of the energy at its end. Finally, a CPS leaky-wave prototype antenna is designed and fabricated, where the measured results show good agreement with the simulated ones and thus validate the predicted performances.

A de-embedding technique for high-Q or high-cutoff frequency ( $f_{{T}})$ one-port structures such as metal-oxide-semiconductor (MOS) varactors and Schottky diodes for millimeter- and submillimeter-wave applications is proposed to mitigate the limitation of vector network analyses of structures with a large ratio between the |reactance| and resistance (| X|/R). A subarray with a fewer number of cells of the device under test that has a lower | X|/R is used instead of an ultrahigh-Q OPEN structure for de-embedding. This technique provides more accurate measurements of cutoff frequency ( $f_{{T}})$ . The resulting average of %-variations of measured $f_{{T}}$ and series resistance over the measurement frequency range (50-55 GHz) are decreased by 30%-45%. More importantly, the %-variation range of $f_{{T}}$ for the proposed method over samples and frequencies is less than ~20% which is ~50% smaller than the de-embedding using a conventional ultrahigh-Q OPEN structure.

This article presents a millimeter-wave (mmW) frequency synthesizer based on a new charge-sharing locking (CSL) technique. A charge-preset capacitor is introduced for charge sharing with a resonant LC-tank for phase correction, while the resulting charge residue on the sharing capacitor is processed by a digital frequency-tracking loop (FTL) against the process, voltage, and temperature (PVT) variations. Furthermore, a general phase noise (PN) theory of CSL, with injection locking (IL) being a special case, is proposed based on a unified multirate z-domain model, supporting any frequency division ratio N and CSL (or IL) strength β. The new theory sheds light not only on all IL-like PN phenomena (chiefly, its ``loop'' bandwidth being up to half of the reference frequency, and the oscillator PN increasing 3 dB beyond the ``loop'' cutoff frequency) but also on how to choose the CSL bandwidth via the sharing capacitor in order to optimize the rms jitter performance. The prototype in 28-nm CMOS achieves 77-fs rms jitter in 21.75--26.25 GHz while consuming 16.5 mW for mmW quadrature frequency generation.

In this communication, a novel dual-polarized (DP) epsilon-near-zero (ENZ) antenna is proposed with its operating frequencies independent to lengths for both polarizations. To obtain a DP implementation of ENZ antenna, an anti-phase epsilon-near-zero (AP-ENZ) mode is used based on a slot-fed substrate-integrated waveguide (SIW) antenna at its cutoff frequency, in which the electric field presents a sign function-like distribution, presenting a fixed operating frequency independent on length. The proposed DP length-irrelevant antenna design is composed by a cross-shaped SIW operating on two orthogonal AP-ENZ modes, which are excited by a cavity-backed cross-shaped slot with good port isolation. The SIW lengths for both polarizations can be tuned independently without disturbing the operation frequency with controllable radiation patterns. To be specific, we study two cases of different lengths where sidelobe elimination and high gain radiation are realized, respectively. To verify this design, two antenna prototypes Ant. 1 and Ant. 2 are fabricated and tested, exhibiting agreements between simulation and experiment. The proposed Ant. 1 presents no sidelobes at 2.42 GHz while Ant. 2 shows a high gain of 10.56 dBi from 2.45-2.55 GHz. The proposed design method enables antennas with a variety of radiation patterns to be designed at a fixed frequency and both symmetric and asymmetric patterns for DP antennas. It also inspires the design of a flexible antenna with unchanged operating frequency when folded in both dimensions.

A nonparametric generalized inversion technique has been used to derive source parameters, attenuation characteristics, and site amplification effects from S-wave spectra of the Mw 7.3 Sarpol-e Zahab, November 12, 2017 aftershocks recorded at 13 stations in the hypocentral distance of 9–70 km. We used a total number of 87 Fourier amplitude spectra from 30 aftershocks with ML 3.8–5.3 in the frequency range 0.5–25 Hz. The inverted source spectra fitted with the omega-square source model and obtained some of the source parameters. The estimated stress drop varies from 0.98 to 30.18 MPa, which is compatible with values of the stress drop for crustal earthquakes in other regions. There is a linear correlation between the moment magnitude Mw and the local magnitude ML as Mw = 0.71 ML + 1.27. This equation is close to the other relationships obtained for the Zagros region in the previous studies. The seismic moment and the cube of corner frequency are inversely related to each other as M0fc3 = 3 × 1016. The obtained nonparametric attenuation functions are curves that decay almost uniformly and slowly with distance for all frequencies. The quality factor is estimated as Q = 107.75f0.87. The value of Q0 is small and the power of the frequency is close to 1, which is characteristic of an active tectonic environment. The site effects obtained from generalized inversion and the H/V method were compared, and it was observed that both results were almost the same.

We present an S-band high-power microwave (HPM) oscillator based on crossed-elliptical metamaterial (MTM) rings in a circular waveguide and powered by a high-power electron beam. Particle-in-cell (PIC) simulations demonstrate that when an output horn antenna of radius of 200 mm is used, an output power of 443 MW of a backward wave TE41 mode below its cutoff frequency at 2.80 GHz can be generated using a pulsed electron beam with a voltage of 990 kV and a current of 1.736 kA in a 1.8-T solenoidal magnetic field, corresponding to an electronic efficiency up to 26%. Meanwhile, another degenerate frequency of 2.80 GHz of a forward wave in the TM01 mode with an output power of 9 MW is also observed. When an output horn antenna of radius 150 mm is used, this crossed-elliptical MTM oscillator operates mainly in a forward TM01 mode at 2.80 GHz with an output power of 325 MW at an electronic efficiency of 19%, and at the same time, a backward wave TE41 mode below its cutoff frequency of 2.80 GHz with an output power of 8 MW can be observed. Simulations indicate that this slow-wave structure (SWS) consisting of a periodically crossed-elliptical MTM loaded circular waveguide can support degenerate mode operation. This result suggests that this configuration is favorable for mode switching and this work seeks to design a compact HPM source.

The azimuthally rippled cavity for a large-orbit, coharmonic gyro-multiplier, designed to operate at the second and fourth harmonics, at frequencies of 37.5 and 75 GHz, respectively, has been numerically and experimentally confirmed to be insensitive to the polarization of quadrupole, ${\text{TE}}_{2,n}$ -like modes, including the second-harmonic operating mode of the multiplier, a cylindrical TE2,2-like waveguide mode. To test the cavity with this mode required the design, construction, and measurement of ripple wall mode converters, converting the cylindrical TE2,1 mode into the TE2,2 mode. These were designed to operate at a central frequency of ~37.9 GHz, with predicted mode purity of better than 85%, and 3-dB bandwidth of 161 MHz. The constructed converter had a central operating frequency of 37.7 GHz, with $S$ -parameter measurements used to infer suitable mode purity and an operational 3-dB bandwidth of 50 MHz. This has allowed far-field phase measurements of the corrugated cavity to be conducted, where the orientation of the geometry to the polarization of both the TE2,1 and TE2,2 modes was shown to have no effect on the dispersion.

Extremely low-frequency (ELF: below 30 Hz) wave penetration theory in the layered oceanic lithosphere is essential for studying submarine communications. In this article, we investigate the mode theory of ELF wave propagation in a layered oceanic lithosphere waveguide. Based on the real situation of the oceanic lithosphere approximated by the stratified prototype, in which a low-conductivity layer lies between two overlying and underlying high-conductivity regions, a theoretically sound physical model of oceanic lithosphere waveguide is built. The modal equations for transverse magnetic (TM) and transverse electric (TE) polarized guided modes are delivered using surface impedance boundary conditions. By evaluating the reflection coefficients of the upper and lower waveguide boundaries, formulas for the modal equation’s roots are derived. Analytical expressions for propagable mode parameters, such as the phase velocity, attenuation rate, excitation factor, and the field strength for different components, are obtained, and the cutoff frequency for high-order modes is given. Computations show that the field component curves exhibit typical peaks and nulls associated with multiple-mode propagation in the waveguide region, with each mode traveling at different phase velocities and attenuation rates. Moreover, it is found that all the high-order modes are evanescent below the cutoff frequency.

This paper proposes a bio-signal instrumentation amplifier (Bio-IA) with fast recovery and constant bandwidth for wearable bio-sensors. To shorten the offset calibration time of the Bio-IA and reduce the loss of bio-signal in the calibration process, a digital-controlled DC servo loop (DCDSL) with fast recovery is designed, which achieves a larger offset calibration range and a faster calibration speed. The proposed programmable gain amplifier (PGA) with constant bandwidth uses dual-biased pseudo-resistor (PR) to stabilize the passband width under different gains, effectively preventing the loss of low-frequency signals. Besides, this paper analyzes the noise of the DCDSL and the noise of dual-biased PR for the first time. The presented Bio-IA was implemented in a 0.18- $\mu \text{m}$ CMOS process, occupying a core area of $849 ~\mu {\sf m}\times 451 ~\mu {\sf m}$ . The measured results show that the Bio-IA can calibrate a DC offset of ±511 mV, and the response time is less than 70 ms when the offset polarity changes suddenly. When the gain of the Bio-IA varies from 26 to 40 dB, its passband width remains constant, and the high-pass and low-pass cut-off frequencies are 0.4 Hz and 200 Hz, respectively. The input-referred noise over the range of 0.1-200 Hz is $0.72~\mu $ Vrms. The proposed Bio-IA consumes $5.5~\mu \text{W}$ from 1.2 V supply voltage.

A compact high-efficiency GW-level ${S}$ -band relativistic magnetron (RM) with TE11 mode output is proposed. In order to achieve high efficiency and high power, an eight-cavity slow wave system with rectangular vanes is adopted, which can provide a larger resonant system where the high-frequency energy is directly stored. All cavity axial extraction (ACAE) is applied with four 90° sector waveguides arranged azimuthally around the anode block. The four 90° sector waveguides play a significant role in converting sector waveguide TE11 mode to circular waveguide TE11 mode. The entire tube is designed without any increase in the radial dimension, which is propitious to a compact and lightweight magnet system design. In particle-in-cell (PIC) simulations, the proposed rectangular vane-type 8-cavity (R8) RM with ACAE can generate a microwave power of 2.1 GW with a pure TE11 mode at the frequency of 2.475 GHz when the applied voltage is 460 kV and the axial magnetic field is 0.46 T, and the power conversion efficiency is 68.4%.

In0.71Ga0.29As/InP (12/2 nm) quantum well MOSFETs using sacrificial amorphous silicon (a:Si) spacers to achieve low parasitic capacitance are fabricated. Radio frequency characterization of 73 devices is used to study the intrinsic and extrinsic capacitances. The total gate intrinsic parasitic capacitance of 0.55 fF/ $\mu \text{m}$ is achieved with an intrinsic gate capacitance of $0.39~\mu \text{F}$ /cm2. The various parasitic capacitances are modeled using finite element electrostatic simulations, and semi-analytical expressions are provided. A device with a gate length ${L}_{g}=80$ nm has SS $_{\text {min}}=168$ mV/dec, dc transconductance ${g}_{\textit {m,e}} =1.0$ mS/ $\mu \text{m}$ at ${V}_{\text {DS}}=0.5$ V, and exhibits a peak cutoff frequency $\it f_{\!{T}} $ of 243 GHz, and a maximum oscillation frequency $\it f_{\text {max}}$ of 147 GHz at ${V}_{\text {GS}}=0.25$ V, ${V}_{\text {DS}}= {1}$ V.

We propose a method to construct the broadband 90° balun with low-phase-imbalance performance based on a U-shaped periodic slow wave structure (PSWS) transmission line (TL), whose dispersion curve has a linear region in a wide frequency band. By introducing meander lines and U-shaped TLs, the linearity, cutoff frequencies and slope of dispersion curves of PSWS can be controlled flexibly. Simulated and measured results show good agreements. Both reflection coefficient and isolation of the proposed balun are below −15 dB from 1.5 to 2.0 GHz. The phase deviation is within ±3°, covering a fractional bandwidth of 28.6%. Compared with that based on the traditional corrugated periodic slow wave TL unit, the operating bandwidth of the proposed balun is increased by more than six times. Moreover, the proposed PSWS keeps excellent ability of field confinement and therefore improves the isolation between the output ports. In a word, based on the proposed method, the microwave devices and circuits which realize the function of phase shifting can be designed.

A technique for gain enhancement of transversely slotted substrate integrated waveguide (SIW) leaky-wave antennas is proposed based on higher modes. Two SIW leaky-wave antennas based on the ${\mathrm {TE}}_{m0}$ ( $m = 3$ , 5) higher modes are investigated. The antennas possess the advantage of simplicity, in which the feeding structures are compact and simple. Compared with published transversely slotted SIW leaky-wave antenna based on the fundamental mode (TE10 mode), the proposed antennas exhibit higher and more consistent gains. Besides, the antennas maintain the scanning capability from near broadside to endfire. The working principles of the antennas are explained. The propagation characteristics are investigated with a magnetic field integral method. The aperture efficiencies are analyzed. Two leaky-wave antenna designs based on the TE30 and TE50 higher modes are demonstrated and compared with a TE10-mode antenna design (with almost the same dispersion characteristics). Prototypes of the three designs are fabricated and measured for comparisons. Compared with the TE10-mode antenna, the TE30- and TE50-mode antennas have the transverse beamwidths markedly narrowed and have the gains improved by about 5.5 and 8 dB, respectively.

We investigate the reflection of low-harmonic fast magnetosonic (MS) waves at the local two-ion cutoff frequency (fcutHe+). By comparing the wave signals of the two Van Allen Probes satellites, a distinct boundary where wave energies cannot penetrate inward are found in the time–frequency domain. The boundary is identified as the time series of local fcutHe+. For a certain frequency, there exists a spatial interface formed by fcutHe+, where the incident waves should be reflected. The waves with small incident angles are more likely to penetrate the thin layer where the group velocity reduces significantly and then slow down in a period of several to tens of seconds before the reflection process complete. The cutoff reflection scenario can explain the intense outward waves observed by probe A. These results of MS reflection at fcutHe+ may help to predict the global distribution of MS waves and promote the understanding of wave–particle dynamics in the radiation belt.

In this article, we report on the effective transconductance ( ${g}_{m}$ ) and gain linearity improvement of submicrometer gate AlN-barrier-based transistors using GaN/InGaN coupling-channel structures. The fabricated AlN/GaN/InGaN coupling-channel high electron mobility transistor (CC-HEMT) showed flat ${g}_{m}$ profile, greatly reduced ${g}_{m}$ derivatives, and constant dynamic source resistance compared with an AlN/GaN HEMT using the same fabrication process. The highest extrinsic current gain cutoff frequency ( ${f}_{T}$ ) of 55 GHz and the maximum oscillation frequency ( ${f}_{\text {max}}$ ) of 80 GHz were obtained for 0.15- $\mu \text{m}$ gate-length transistors, both of which remain constant values across wide input voltage ( ${V}_{\text {GS}}$ ) of 4 V. Moreover, a significant theoretical OIP3 value boost by 7.1 dB has been observed using the CC-HEMT as compared to the AlN/GaN HEMT. The superior linearity performance of the CC-HEMT can be attributed to the strong channel-to-channel coupling effect. The drain bias-dependence of ${g}_{m}$ , ${f}_{T}$ , and ${f}_{\text {max}}$ versus ${V}_{\text {GS}}$ profiles illustrate that the linearity characteristics of the CC-HEMT greatly improve with an increase in ${V}_{\text {DS}}$ . These results demonstrate the AlN/GaN/InGaN material system as a viable platform for high frequency requiring high-linearity applications.

In this brief, a novel reconfigurable bandpass filter with adjustable center frequency and wide bandwidth reconfiguration is presented. The proposed bandpass filter is formed by cascading tunable high-pass (HP) and low-pass (LP) filter sections directly. Both the operating frequency and bandwidth of the reconfigurable bandpass filter can be reconfigured independently by tuning the frequencies of the band edges, which are controlled by the cut-off frequency of the HP and LP filter sections. Finally, the proposed filter is designed, fabricated and measured for validation purposes. The measured results demonstrate that the bandwidth can be tuned from 180 MHz to 1390 MHz at the fixed center frequency with tuning ratio up to 7.8:1. Center-frequency agility is also verified with different constant absolute bandwidth of 400 MHz, 600 MHz, and 800 MHz The measured results show that proposed filter possesses the advantages of simple implementation, wide bandwidth tuning range, wide frequency tuning range, and compact size.

It is well known that there is the commutation interference pulse in zero-crossing points (ZCPs) of back electromotive force (EMF) for brushless direct current (BLdc) motors. Generally, the interference pulse is handled by a low-pass filter (LPF) with a low cutoff frequency. However, the phase delay caused by LPF will deteriorate the performance of BLdc motors. In this letter, a novel phase-delay-free commutation method based on terminal voltage is proposed. The ZCPs and commutation freewheeling signals are obtained according to terminal voltages. Then, the main part of commutation interference pulse is removed through detected freewheeling signals. Finally, the remaining part is eliminated through a fixed delay digital filter (FDF). Comparing with the conventional commutation methods, the faster starting and the phase-delay-free commutation are achieved reliably by the proposed method. The effectiveness of the proposed method is verified through an 80 W BLdc motor.

The design results of a charge-sensitive amplifier (CSA) with a pseudo-differential output are presented. The CSA is intended for operation with signals of both polarities at the dynamic range up to 100 fC and parasitic detector capacitances up to 100 pF. In order to form a pseudo-differential signal, a first-order low-pass filter having a cutoff frequency of several hertz was used. CSA is designed in 180 nm CMOS process.

An analysis of the operational parameters of an acousto-optic delay line (AODL) with direct detection, that is, the range of continuously controlled signal delay and the cutoff frequency of the passband, has been carried out. It is shown that the range of the smoothly controlled signal delay is limited by the maximum length of the photoelastic cell and the minimum velocity of propagation of the elastic wave in it. At the same time, the cutoff frequency is directly determined by the time of crossing the optical beam by the elastic wave packet. An equation for the transient response of the AODL was obtained, which was then used to study the nature of the dependence of the cutoff frequency of the transmission band on the diameter of the light beam and the velocity of propagation of an elastic wave in a photoelastic cell. The results of the numerical analysis were tested experimentally on the AODL model with direct detection.

An active electrode (AE) for vital signal acquisition with accurately-tunable Sub-Hz high-pass-corner frequency ( $f_{HP}$ ) has been proposed. Thanks to the proposed PVT-insensitive pseudo-resistor (PR) with embedded calibration circuit, the sub-Hz $f_{HP}$ of the AE can be accurately tuned by an external clock frequency. The AE is implemented in a standard 55nm CMOS process with a core area of 0.11 mm2. The post-layout simulation results show that up to 310 $\text{G}\Omega $ of the PR value can be achieved. Compared with the conventional PR, the variation of the calibrated PR value is reduced by 3 decades within a temperature range of 0 to 85°C under all process corners. Besides, the bootstrap technique improves the linear-input-range of the AE up to 164 mVpp, demonstrating its potential capability to be applied to recording vital signals merged with large artifacts.

Optimizing the adaptive circuit of piezoelectric sensors is important in accurately measuring blast waves. This study analyzed the impact of the bandpass cut-off frequencies and quality factor of adaptive circuits on shock wave measurements. We proposed a Multi-objective particle swarm optimization based on weighted Pareto-dominance sort (W-MOPSO) for optimizing the multi-objective function of an adaptive circuit in order to improve precision during shock wave measurements. W-MOPSO obtained a Pareto-optimal solution set through Pareto-dominant sorting of global optimal solutions to the weighted sum of a multi-objective function. The relative mean error in the optimized adaptive circuit mostly ranged between −2% and +2%. Simulations were used to analyze the impact of the optimized adaptive circuit on shock wave measurements. The effectiveness of W-MOPSO was verified through a real-world experiment using a TNT explosive and blast wave gauges. W-MOPSO provided a basis for adapter circuit design and optimization in shock wave measurement.

In this letter, high-order mode dispersion of a novel spoof surface plasmon polariton (SSPP) unit cell is reported, which has excellent bandpass propagation feature. Its asymptotic frequency and intersection frequency with light line can be independently manipulated by changing the geometric parameters of the slot in proposed SSPP unit cell. In order to validate the feasibility of high-order mode of SSPPs applied in the design of bandpass filters, two SSPP waveguides based on the method with different bandwidths are fabricated and measured. No mode-conversion transition part is introduced in the procedure of waveguide design which avoids extra addition of layout area and reduces complexity of devices. The measurements show that the proposed SSPP waveguide based on high-order mode characteristics can achieve bandpass signal propagation smoothly with controllable bandwidth.

This letter presents a method to convert the split dual-beam into a single one in the quasi-E-plane with low cross-polarization level for the pin-loaded fundamental EH0-mode microstrip leaky-wave antennas (MLWAs). By exciting a pair of them under differential operation with proper configuration, the ϕ -polarized dual beams can be reshaped to achieve a single-beam radiation, so as to widen its potential application. The proposed method for transversal single beam still preserves the merits of the original pin-loaded EH0-mode MLWA with simple structure and freely designed narrow width. A prototype MLWA with single-beam radiation in the quasi-E-plane is designed, fabricated, and measured. Good agreement is attained between simulated and measured results, and thus validates the unique feature of the proposed method in design of single-beam pin-loaded EH0-mode MLWAs.

In this letter, we explore the impact of configuration parameters for Fin-like high-electron-mobility transistors (HEMTs) formed by partially etching barrier under the gate on improving transconductance (Gm) and cutoff frequency ( ${f}_{\text {T}}$ ) linearity. It is found that the Gm profile for Fin-like HEMTs can be optimized by choosing appropriate device parameters, including the etching depth ( ${H}_{\text {R}}$ ) and width ( ${W}_{\text {R}}$ ) of recess region, as well as the duty ratio ( $\alpha $ ) of the planar elements in a periodic unit along the gate width. In general, not only does ${W}_{\text {R}}$ affect the gate voltage swing (GVS) but also ${H}_{\text {R}}$ and $\alpha $ have an important role in Gm profile flatness. In addition, the fabricated Fin-like HEMTs shows a GVS of the transconductance plateau larger than 5.6 V and a constant ${f}_{\text {T}}/{f}_{\text {max}}$ of 45 GHz/65 GHz over a wide gate voltage range. Furthermore, the proposed architecture also features an exceptional linearity performance at 8 GHz with an output third-order intercept point (OIP3) of 38.5 dBm, whereas that of the planar HEMT is 31 dBm. The device demonstrated in this article has great potential to be a new paradigm for future wireless communication systems where high linearity is essential.

A radiophysical technique is proposed for calculating mesospheric temperatures using experimental measurements of the frequencies of resonant atmospheric oscillations (the acoustic cutoff frequency and the Brunt–Vaisala frequency). The partial reflection method is used to measure temperatures at sunset and an altitude of 75 km for days when the planetary index of geomagnetic storms was Kp ≤ 1. These temperatures are in good agreement with data from other researchers.

This brief describes a novel technique for the distribution of dc power based on synthetic transmission lines with a low cutoff frequency. Since after the cutoff the impedance of these lines approaches that of an open , these components are well suited to feed dc power in circuit nodes where high impedance values are required. Narrowband bias networks based on inductors or lambda-quarter ( $\lambda $ /4) stubs can be substituted by the presented wideband design solution. To experimentally validate the approach, two prototypes have been implemented in a 130nm SiGe technology. The first prototype is a synthetic line with a cutoff frequency of 12GHz, while the second design is a distributed amplifier (DA) where a synthetic line in cutoff feeds the voltage supply. Compared to traditional approaches based on inductors or $\lambda $ /4 stubs, the presented technique improves the DA bandwidth by 50% and the flatness of the frequency response. Compared to biasing achieved via the DA termination resistor, the power-added-efficiency (PAE) is doubled. To the best knowledge of the authors, this is a novel general technique for feeding dc power to any circuit from a wideband high-impedance.

For processing signals in the time area an efficient tool is the acousto-optic delay line (AODL). The smoothly controlled delay of signals in a broad time interval permits to build high-performance radiolocation simulators. In the work, the design of the AODL has been considered, and the parameters, determining the limit of using its potential have been noted. The features of photoelastic interaction in AODL have been considered for the case when the duration of the input pulse is shorter than the time of crossing the optical beam by an elastic wave packet. It has been found that under these conditions the duration of the output response is determined by the time of crossing the optical beam by an elastic wave packet and does not depend on the duration of the input action. It has been shown that the AODL response to the input action in the form of a rectangular pulse is determined as the sum of three terms. In this case, the process of the entry of the elastic wave packet into the optical beam determines the first term, the second one – by the process of propagation of the elastic wave packet in the optical beam aperture, and the third – by the process of the exit of the elastic wave packet from the optical beam aperture. The corresponding equations have been obtained for calculating the pulse parameters at the AODL output. It has been shown that for a sufficiently short input pulse duration, the output signal parameters contain the information on the energy-geometric characteristics of the laser radiation. The results of numerical simulation have been tested experimentally on AODL layout with the direct detection. A comparative analysis of the results of theoretical and experimental studies have unambiguously has confirmed that AODL can also be used at frequencies above the cutoff frequency, both in terms of its main functional purpose and for solving a number of other engineering problems.

We study the torsion of a flexoelectric semiconductor rod with a rectangular cross section. The macroscopic theory of flexoelectric semiconductors is used. A one-dimensional model is established from the three-dimensional theory using double power series expansion of the coordinates within the cross section. The angle of twist of the rod and warping of the cross section are taken into consideration by retaining the proper lower-order terms in the expansion. Solutions of wave propagation in an unbounded rod and static torsion of a finite rod are presented, showing that electromechanical couplings exist when warping varies along the axis of the rod. The torsional wave is essentially nondispersive, but the warping wave is dispersive with a cutoff frequency. The mobile charges concentrate at the corners of the cross section. The electric potential and charge carrier distributions produced by mechanical loads are sensitive to the geometric and physical parameters of the system. The results are potentially useful for making flexotronic devices based on torsional modes.

A tunable high-frequency operational transconductance amplifier (OTA) is presented along with its application in the implementation of a Gm-C filter. The OTA is tuned by varying the negative resistance produced by a positive feedback at the output. Post-layout simulation results (using TSMC 90 nm CMOS technology and a 1-V supply voltage) show that the differential DC gain, common-mode gain and OTA unity gain frequency are 34 dB, −26 dB and 10 GHz, respectively. Moreover, for precise control of filter performance, an auto-tuning circuit is presented to adjust the filter cutoff frequency at low power consumption (i.e., 0.6 mW, about 16.3% of the total circuit power consumption). The filter has a cutoff frequency of 1 GHz with a group delay variation less than 6% up to 1.3 fc. The size of filter is 0.040 × 0.023mm2 and the third order intermodulation (IM3) value at cutoff frequency is −37 dB. The Monte Carlo simulation results are presented for predicting the manufacturing process errors.

A new approach to enhance the bandwidth of Tightly Coupled Dipole Arrays (TCDA) is presented. The new design achieves the integration of a semi-resistive Frequency Selective Surface network (FSS) composed of a non-resistive low-pass FSS and two resistive band-stop FSSs. The integration of this FSS network within a dual-polarized Tightly Coupled Dipole Array (TCDA) led to an increased impedance bandwidth of 28:1 from 0.20GHz to 5.6GHz. Notably, the use of an FSS superstrate allowed for scanning down to 60° at VSWR

In this work, a new structure of Schottky tunneling MOSFET has been designed and simulated. The proposed device structure uses floating gates and dual material main gates to counter short channel effects and to improve RF/Analog figures of merit for low power design applications. The use of floating gates modulates the Schottky barrier width, hence improves the ON state and RF/Analog figures of merit performance of the proposed device in comparison to a conventional device. A significantly high ION( $1.231\times 10^{-4}\text{A}/\mu \text{m}$ ) and ION/IOFF ratio ( $2.52\times 10^{5}$ ) is achieved in the proposed ST-MOSFET in comparison to conventional ST-MOSFET having $\text{I}_{\mathrm {ON {}}}(1\times 10^{-7}\text{A}/\mu \text{m}$ ) and ION/IOFF ratio ( $1\times 10^{2}$ ). It has been observed that there is more than 100 times improvement in cutoff frequency ( $f_{\mathrm {T}}$ ), transconductance frequency product (TFP), gain frequency product (GFP), gain transconductance frequency product (GTFP), gain bandwidth product (GBP) and max oscillation frequency ( $f_{\mathrm {max}}$ ) in comparison to conventional ST-MOSFET. In addition, there are reductions of 98% and 33.33% in switching ON and OFF delays respectively in the proposed device-based inverter circuit in comparison to conventional ST-MOSFET based inverter circuit. Furthermore, the proposed ST-MOSFET device does not require any highly doped regions, hence does not have any doping related issues.

A combination of lowpass and dual band bandpass filter with improved selectivity is presented in this manuscript. Two circular split ring resonators which are connected at the upper side, provide a lowpass filter characteristics. In order to achieve combined lowpass with dual passband response two L-shape stubs are incorporated into the lowpass filter structure. The parametric analysis of the proposed filter has been carried out using CST microwave studio. The numerical result shows a 3-dB cutoff frequency for lowpass at 1.22 GHz, first and second passband resonant frequencies are 2.44 GHz and 3.7 GHz respectively. The proposed filter is compact and overall size of the proposed filter is 32.9 mm?15mm.

In this paper, we proposed an integrated hybrid antenna based on spoof surface plasmon polaritons (SSPPs) which combines with omnidirectional antenna (ODA) and the frequency beam scanning antenna (FBSA). The ODA is fed by the SSPPs and the operating principle of FBSA is based on the higher-order modes of the SSPPs. The radiation mechanisms of the proposed integrated antenna are that the low-pass transmission modes of SSPPs are used to excite the ODA and the higher-order modes of SSPPs are utilized to generate the frequency beam scanning waves. That is to say, the SSPP design not only serves as the feeding structure for the ODA, but also acts as the radiating element for the FBSA. Simulated results show that the proposed integrated antenna achieves two impedance bandwidths. Within the operating bandwidth 2.32 GHz to 4.42 GHz, the proposed integrated antenna achieves omnidirectional radiation patterns, which enables the simultaneous use for wireless local area network (WLAN) and 5 G applications. Meanwhile, from 11.45 GHz to 25.5 GHz, the proposed integrated antenna acts as a wide-angle frequency beam scanning characteristic and can be used for planar integrated communication systems. Additionally, a prototype of the proposed integrated hybrid antenna is fabricated and tested. The measured results have a good agreement with the simulated ones.

This paper introduces analytical solutions to gap waveguide slot antenna structures. The reciprocity method is used for the analysis by exploiting Green’s function of a bed of nails structure employing a homogenized plane-wave spectral-domain approach. Green’s function is found using parallel plate waveguide and surface admittance concepts. The spectral surface admittance of the pin structure is calculated using asymptotic boundary condition (ABC), and the unknown antenna slot currents are solved using moment methods. The structure is designed to have a cutoff frequency of 10–15 GHz, and the central operating frequency of the slot is 12.5 GHz. This approach is applied to the specific geometry of a propagating ridge gap waveguide single transverse broad wall slot antenna structure. The equivalent series impedance and far zone fields and patterns are calculated, and the results are compared with a full-wave commercial software, and they are proved to be accurate.

This letter proposes a compact low-pass filter (LPF) using dielectric filled capacitor based on the substrate integrated suspended line (SISL) platform. A dielectric filled capacitor with high capacitance density is presented for the first time. Using this type of capacitor, a three-order lumped element LPF with a cutoff frequency of 120 MHz is designed, fabricated, and tested. The measured results agree with the simulated ones. The circuit size of the implemented SISL LPF is only $0.005\,\,\lambda \text{g}\,\,\times0.013\,\,\lambda \text{g}$ , which is very small when compared to the state of art. The measured insertion loss of SISL LPF in the passband is 0.12 dB and the stopband is from 0.35 to 2.27 GHz with a suppression level greater than 20 dB. A seven-order LPF is also designed to further demonstrate the good property of the proposed capacitor.

To miniaturize directional couplers, the replacement of their quarter-wave sections with electrodynamic structures with equivalent characteristics at smaller physical dimensions is used. It is shown that the structures used have filtering properties and act as low-pass filters. It is set at what cutoff frequency the low-pass filters must be calculated to obtain a phase shift of 90 degrees.

This paper presents a third-order Butterworth low-pass filter (LPF) with continuously tuning capability to be used in the receiver front-end for Wireless Body Area Network (WBAN). To realize the bandwidth tuning for multi-standard operation in WBAN receivers with ultra-low power consumption and minimized area, a novel transconductor-capacitor (Gm-C) filter is proposed. The proposed transconductor core uses an additional gain stage with regulated cascode structure to control the transconductance ( $G_{m}$ ) by tuning the drain-source voltage $V_{ds}$ of the input transistors operating in linear region. Based on fundamental analysis, $V_{ds}$ should be reduced to attenuate the nonlinear effects caused by higher-order harmonic components. This proposed transconductor circuit enables the $G_{m}$ tuning and widens the tuning range while maintaining good linearity with negligible power and area consumption. This work is then implemented into a third-order Butterworth LPF. Measurements show that with external control voltage varying from 450 mV to 550 mV, the cutoff frequency of the LPF can be continuously adjusted from 20 MHz to 80 MHz. This design is implemented in 40 nm CMOS process with 1.1 V supply voltage. The total power consumption of this work is below 2 mW with an active area of 0.0105 mm2. Its low power consumption and good area efficiency makes this LPF suitable for WBAN applications. Ministry of Education (MOE) Published version This work was supported by the Singapore Ministry of Education Academic Research Fund Tier 2 under Grant MOE2019-T2-1-114.

Design and microwave measurement of a linearly polarized circular TE11 mode coupler are reported in this article. Based on our earlier designed input coupler with smooth wall, we proposed an improved structure with ridges loading resulting in a bandwidth up to 29.2%. Simulation results show the port reflection ${S}_{11}$ less than −10 dB is in 7.9–10.6 GHz. And the split transmission ${S}_{21}$ and $S_{31}$ are over −3.4 dB in this frequency range. According to the simulation results, the designed input coupler is fabricated and measured with the vector network analyzer. The measurement results show excellent performance, which is in good agreement with the simulation when the conductor loss is taken into consideration. In addition, an input coupler with a cutoff waveguide is designed to improve the efficiency of single-port transmission and the power utilization. Simulation results show the transmission efficiency of the single port achieves 91%.

This study deals with free, forced undamped vibration and the random, damped vibration of an inhomogeneous beam composed of two materials with significantly different elastic moduli and material densities. Exact solution is obtained for natural frequencies and the mode shapes using Krylov-Duncan functions, along with the comparison with the results furnished by the Galerkin's method. Random vibrations of the bi-material beams are studied for the first time in the literature for the case of proportional damping. Novel element of this study consists in the unintuitive finding that the response of the bi-material beam may considerably exceed the responses of its homogeneous counterparts, composed of a single material. This finding appears of design significance, suggesting that the natural frequencies of the bi-material beam must be made so as to lie above the cutoff frequency of broad-band cutted white noise.

In this letter, spoof surface plasmon polaritons (SSPPs) are developed in a slotted half-mode substrate integrated waveguide (HMSIW) to realize a bandpass propagation feature instead of a traditional low-pass one. We investigate the dispersion properties to analyze the performance of an SSPP unit cell. Parametric sweepings are further performed to reveal the direct relationships between geometry and cut-off frequencies. We design a compact transition by etching gradient slots on a tapered microstrip-to-HMSIW transition. Then, we finally design an SSPP bandpass filter (BPF) with both wide passband and upper rejection band. The measured 3-dB relative bandwidth is 59.25% ranging from 4.24 to 7.81 GHz. The measured upper rejection band can reach up to 16 GHz with a rejection level better than -31.6 dB. The total size of the filter is only $2.69\lambda _{g} \times 0.42\lambda _{g}$ . This work can provide a new concept to design novel wideband and ultra-wideband (UWB) microwave filters. Significant potential applications of the strategy of developing SSPPs in HMSIW can be found in microwave versatile planar circuits and devices.

In this article, a novel double-square planar electromagnetic bandgap structure for suppressing wideband simultaneously switching noises is proposed. The equivalent circuit model for its periodic structure design is carefully developed and analyzed for the function as a band-stop filter. The performance of the circuit model is experimentally verified and lower cutoff frequency $(f_{L})$ can be effectively predicted, while keeping the compact size of the structure. Two test boards are fabricated and the measurement results show that the noise suppression performance can reach –30 dB between two adjacent ports from 3.2 to 21.2 GHz. To prove the solid signal transmission quality of the proposed structure in high-speed printed circuit board, feasibility studies on eye patterns are conducted at four different coded rates. All the performance results and the comparison with other works show its salient feature of solid signal integrity in both the frequency and time domains.

The gradual transition from a reactive to a radiative regime is studied for leaky modes supported by multilayered planar open waveguides. The so-called leaky cutoff condition, i.e., the frequency for which the leaky phase constant $\beta $ equals the leaky attenuation constant $\alpha $ , originally introduced for microstrip lines and other printed structures, is investigated here with the aim of providing detailed information on the relative amount of reactive and radiative attenuation for leaky modes excited by finite sources and propagating as cylindrical waves along general planar waveguides. Analytical results are derived on the basis of a lossy parallel-plate-waveguide model and are validated through full-wave numerical simulations of 2-D leaky-wave structures based on grounded slabs covered with lossless or lossy partially reflecting surfaces (including, e.g., graphene layers) that can be treated as homogenized sheets. An analysis of the complex wave impedance of the considered leaky modes is also provided, in order to assess the frequency ranges where a good input matching can be expected for practical sources. In this regard, an ad hoc impedance matching network is designed and full-wave validated for a specific case to show that is indeed possible to achieve a good impedance matching below the cutoff in practical designs.

This article presents a compact 4-bit switched-line true-time delay (TTD) circuit over a wide frequency range extending from 3 to 30 GHz using novel delay elements. The delay elements, namely, the cascading coupled all-pass network (CAPN) and noncoupled all-pass network (NCAPN), were employed in the proposed TTD circuit to improve the delay-bandwidth product (DBW) while maintaining its compact size and low delay variation (DV). For comparison, a theoretical analysis for understanding the group delay feature of the APN with various coupling coefficients is presented along with low-pass network (LPN). To verify the proposed structure, the proposed delays are applied to construct the 4-bit switched-line TTD by utilizing two single-pole double-through (SPDT) and three double-pole double-through (DPDT) switches in a 28-nm CMOS process. The circuit has a compact size of 1.7 mm $\times0.2$ mm, with a maximum delay of 68.5 ps and a minimum delay of 4.6 ps. The measured average insertion loss is 13.5 dB, and the in/out return loss is better than 10 dB across 3–30 GHz. The measured rms delay and gain errors are less than 2 ps and 3.2 dB, respectively, over the operating frequency range. To the best of our knowledge, the proposed TTD achieves the largest figure of merit (FoM) among the integrated TTD circuits.

This article presents an analytical method that offers both spectral and spatial information to predict local electric fields capable of driving neural activities for neuromuscular activation, and the findings of an experimental investigation on a common strategy utilizing multiple high-frequency (HF) electric fields to create an interference to recruit neural firing at depth. By introducing a cut-off frequency ${f} _{\text {cut}}$ too high to recruit neural firing in a frequency-based field descriptor, the analytical method offers an effective means to position a focused temporal interference (TI) without mechanically moving the electrodes. The experiment, which was conducted on both forearms of five healthy volunteers, validates the feasibility of the method for selective neuromuscular stimulation, where three nerve/muscles that control human fingers were independently stimulated with two current channels. The numerical and experimental findings demonstrate that the frequency-based method overcomes several limitations associated with surface-based electrical stimulation.

A novel compact spoof surface plasmon polaritons (SPPs) waveguide integrated with blind vias is proposed in this brief. Depending on the groove orientation, the SPP structure leads to asymmetrical electromagnetic (EM) field confinements in the transverse plane, where the EM field is strongly confined around the groove orientation but much weaker in the opposite side. Due to this strong field confinement, the measured crosstalk between two SPP waveguides with 1 mm edge separation is −25 dB in 3–13 GHz band, a reduction of 18 dB on average when compared with microstrip line implementation. Due to the weaker field confinement, energy from the SPP waveguide can be easily coupled into other parasite structures for filter designs. By loading quarter-wavelength SPP resonators along the main SPP waveguide, we can introduce notched frequencies in the transmission. The number of notches and their frequencies can be controlled by SPP dispersion.

This article presents a dual-band bandpass filter based on the double-sided spoof surface plasmon polaritons-line. The whole structure consists of a dual-band filtering part and two SSPPs lowpass filtering parts. Simulated results show that the proposed dual-band bandpass filter has an excellent dual-band filtering performance and wide upper band suppressions. Simulated bandwidths of two passbands are 41% (2.36–3.58 GHz) and 13.9% (6.7–7.7 GHz). It can realize the suppression of $S_{21}$ below −40 dB from 9.6 to 39.7 GHz. A prototype has been fabricated and measured. Measured results are in a good agreement with simulated ones, which validates our design concepts and methods. The proposed dual-band bandpass filter will have significance in microwave device designing, especially in the plasmonic device in microwave frequencies.