Arbitrary Bandwidth Research Articles

Ultracompact isolated multilayer broadside-coupled balun with arbitrary isolation bandwidth

Abstract An isolated low-profile multilayer all-ports-matched broadside-coupled balun (BCB) with arbitrary isolation bandwidth is presented. Analytical relations are derived and provided for the isolation circuit (IC) design in terms of electrical and physical parameters. Accordingly, instructions are given on obtaining optimum bandwidth and isolation responses for the IC. Design procedure for the BCB is presented together with a case study for power amplifier application. The BCB is validated theoretically, analytically, and experimentally, and results are in good agreement. The fabricated balun has insertion loss of 0.27 dB, input and output return losses of 19 dB, isolation of 20 dB at fc, and phase and magnitude imbalance better than 2° and 0.2 dB across the Bandwidth (BW), respectively. The realized isolated balun has dimensions of 0.06λg × 0.03λg.

A Thermopile-Based Colorimetric Temperature Measurement Method for Arbitrary Bandwidth

Colorimetric temperature measurement is an essential technique in radiometric thermometry. Traditional colorimetric methods determine temperature by comparing the ratio of radiative energies within two narrow bands at specific wavelengths, effectively mitigating the effects of the emissivity of the measured object and ambient conditions. However, these methods typically approximate integration using area calculations when calculating radiative energy. This article eliminates this approximation and calculates the radiative energy with accurate integration. Based on the principle of monotonicity, this article demonstrates for the first time that when two narrow-band infrared radiations are selected, as long as their wavelength ranges do not overlap, the ratio of radiative energies within these bands maintains a monotonic relationship with the measured temperature. This allows the temperature to be inferred from the energy ratio. Furthermore, this conclusion is extended to arbitrary widths of bands as long as their wavelength ranges do not overlap. Building on this foundation, a thermopile-based colorimetric temperature measurement method for arbitrary bandwidth is proposed. Simulation experiments validate this method, showing that the energy ratio maintains a monotonic relationship with the measured temperature as long as the infrared radiation wavelength ranges absorbed by the thermopile do not overlap. The simulation results are consistent with the mathematical proof.

Efficient and Rapid Modeling of Radar Echo Responses for Complex Targets under Arbitrary Wideband Excitation

Efficient and Rapid Modeling of Radar Echo Responses for Complex Targets under Arbitrary Wideband Excitation

A Design Method and Application of Meta-Surface-Based Arbitrary Passband Filter for Terahertz Communication.

A meta-surface-based arbitrary bandwidth filter realization method for terahertz (THz) future communications is presented. The approach involves integrating a meta-surface-based bandstop filter into an ultra-wideband (UWB) bandpass filter and adjusting the operating frequency range of the meta-surface bandstop filter to realize the design of arbitrary bandwidth filters. It effectively addresses the complexity of designing traditional arbitrary bandwidth filters and the challenges in achieving impedance matching. To underscore its practicality, the paper employs silicon substrate integrated gap waveguide (SSIGW) and this method to craft a THz filter. To begin, design equations for electromagnetic band gap (EBG) structures were developed in accordance with the requirements of through-silicon via (TSV) and applied to the design of the SSIGW. Subsequently, this article employs equivalent transmission line models and equivalent circuits to conduct theoretical analyses for both the UWB passband and the meta-surface stopband portions. The proposed THz filter boasts a center frequency of 0.151 THz, a relative bandwidth of 6.9%, insertion loss below 0.68 dB, and stopbands exceeding 20 GHz in both upper and lower ranges. The in-band group delay is 0.119 ± 0.048 ns. Compared to reported THz filters, the SSIGW filter boasts advantages such as low loss and minimal delay, making it even more suitable for future wireless communication.

Arbitrary electro-optic bandwidth and frequency control in lithium niobate optical resonators.

In situ tunable photonic filters and memories are important for emerging quantum and classical optics technologies. However, most photonic devices have fixed resonances and bandwidths determined at the time of fabrication. Here we present an in situ tunable optical resonator on thin-film lithium niobate. By leveraging the linear electro-optic effect, we demonstrate widely tunable control over resonator frequency and bandwidth on two different devices. We observe up to ∼50 × tuning in the bandwidth over ∼50 V with linear frequency control of ∼230 MHz/V. We also develop a closed-form model predicting the tuning behavior of the device. This paves the way for rapid phase and amplitude control over light transmitted through our device.

Design of Intelligent Channelizer for Extracting Signals of Arbitrary Centre Frequency and Bandwidth

There are two standard approaches to the problem of wideband signal channelization, namely those based upon the use of a digital down conversion (DDC) unit and those based upon the use of a polyphase discrete Fourier transform (DFT) or PDFT. There are clear advantages and disadvantages with both approaches, however, in that: a) with the DDC approach, optimal performance and flexibility is obtained but at the expense of a heavy computational load; whereas b) with the PDFT approach, a sub optimal and less flexible performance is obtained but at a greatly reduced computational cost through the exploitation of a suitably defined fast Fourier transform (FFT). An intelligent channelizer is described herein which possesses a flexible design able to exploit the merits of both approaches for the case where the input data comprises real-valued samples. The two key design features are: a) optimal setting of the PDFT parameters to ensure that for every signal of interest there is at least one channel completely containing it; and b) simultaneous computation of two real-data FFTs: the first as required by the PDFT and the second, a high-resolution FFT with high update rate, able to accurately direct the application of the low-rate DDC units to the relevant PDFT channel outputs.

A novel power divider with arbitrary power ratio, arbitrary phase difference and controllable bandwidths

In this paper, a set of general constraint conditions of 3 port power divider is newly established for arbitrary power ratio and arbitrary phase difference, where, the relationship between power ratio and phase difference can be newly summarized as a very simple equation. To verify this theory, a novel power divider with three standard 50 Ω ports is presented, and it consists of an isolation resistor and seven transmission lines. From the design charts and several design examples, the proposed power divider could not only provide arbitrary power ratio and arbitrary phase difference, but also independently control their fractional bandwidths (FBWS11 or FBWS32) under various combinations of power ratio and phase difference. In final, two prototypes are fabricated, and the measured results matched very well with simulated results.

Reduction formula for cross-spectral purity ofnonstationary light fields.

We examine cross-spectral purity of random, nonstationary (pulsed), scalar light fields with arbitrary spectral bandwidth. In particular, we derive a reduction formula in terms of time-integrated coherence functions, which ensures cross-spectral purity of interfering fields having identical normalized spectra. We further introduce fields that are cross-spectrally pure in either a global or local sense. Our analysis is based on an ideal field superposition realizable with all-reflective wavefront-shearing interferometers. Such devices avoid certain problems related to Young's interferometer, which is the framework customarily employed in assessing cross-spectral purity. We show that any partially coherent beam can be transformed into a locally cross-spectrally pure beam whose cross-spectral density is specular. On the other hand, lack of space-frequency (and space-time) coupling ensures cross-spectral purity in the global sense, i.e.,across an entire transverse plane, regardless of the spectral bandwidth or the temporalshape of the pulses.

Spin of random stationary light

We develop a theoretical foundation for the spin angular momentum (SAM) of random, statistically stationary polychromatic light fields within the framework of classical optical coherence theory. The formulation is valid for fields of arbitrary frequency bandwidth and dimensionality. Both temporal and spectral representations are given, and we further elucidate the relationship between the SAM and the polarization characteristics of such fields as compared to monochromatic light. The special cases of quasimonochromatic light and planar fields are analyzed separately. Generally, our paper offers deeper insights into the SAM and polarization structures as well as their interlinked connections in random stationary light, which could be beneficial in exploiting SAM in stochastic optical near fields and tightly focused beams exhibiting complex polarization character.

On coupled envelope evolution equations in the Hamiltonian theory of nonlinear surface gravity waves

This paper presents a novel theoretical framework in the Hamiltonian theory of nonlinear surface gravity waves. The envelope of surface elevation and the velocity potential on the free water surface are introduced in the framework, which are shown to be a new pair of canonical variables. Using the two envelopes as the main unknowns, coupled envelope evolution equations (CEEEs) are derived based on a perturbation expansion. Similar to the high-order spectral method, the CEEEs can be derived up to arbitrary order in wave steepness. In contrast, they have a temporal scale as slow as the rate of change of a wave spectrum and allow for the wave fields prescribed on a computational (spatial) domain with a much larger size and with spacing longer than the characteristic wavelength at no expense of accuracy and numerical efficiency. The energy balance equation is derived based on the CEEEs. The nonlinear terms in the CEEEs are in a form of the separation of wave harmonics, due to which an individual term is shown to have clear physical meanings in terms of whether or not it is able to force free waves that obey the dispersion relation. Both the nonlinear terms that can only lead to the forcing of bound waves and those that are capable of forcing free waves are demonstrated, in the case of the latter through the analysis of the quartet and quintet resonant interactions of linear waves. The relations between the CEEEs and two other existing theoretical frameworks are established, including the theory for a train of Stokes waves up to second order in wave steepness (Fenton, ASCE J. Waterway Port Coastal Ocean Engng, vol. 111, issue 2, 1985, pp. 216–234) and a semi-analytical framework for three-dimensional weakly nonlinear surface waves with arbitrary bandwidth and large directional spreading by Li & Li (Phys. Fluids, vol. 33, issue 7, 2021, 076609).

High Resolution Backscattering Acoustic Tomography Method Based on Reverse Time Migration for Arbitrary Wideband Sounding Signal

Backscattered wave acoustic tomography using wideband probing signals makes it possible to obtain three-dimensional (3D) images of scattering inhomogeneities. Signal processing based on the reverse time migration (RTM) method allows one to take into account the influence of background refractive obstacles of the medium to minimize distortions of reconstructed tomographic images. We propose a noniterative method of acoustic tomography in an immersion medium based on RTM approach supplemented with linear signal preprocessing to enhance resolution of reconstructing tomography images. The visualization of scattering objects is based on wave inversion from the measurement area considering the probing wave field specially distorted to perform regularized back convolution. The applicability of the proposed method for visualizing scattering objects in water is shown analytically, numerically and experimentally. The proposed method is resistant to noise according to regularization. The results obtained show the agreement between the numerical and analytical solution. Using the example of sounding with linear frequency modulation signals, it is demonstrated that the proposed method allows increasing the resolution of tomographic images in comparison with conventional RTM. The novelty of the proposed method is the preliminary filtration of the forward propagation wave in the course of solving the inverse problem. This approach improves the resolution of tomographic images and allows considering the influence of obstacles.

Anomalous reflection with customized high-efficiency bandwidth.

Anomalous reflection from metasurfaces with 100% efficiency at optical frequencies was not achieved until an all-dielectric quasi-three-dimensional subwavelength structure was proposed. The desired nonlocal control of light waves is realized by designing phase responses of multilayer films at a single wavelength. However, a high-efficiency bandwidth is not controllable by designing only the phase response at a single wavelength. Here, we propose the use of a multilayer metasurface to achieve anomalous reflection with a customized high-efficiency bandwidth. The interference of the successive light waves scattered from the structure at multiple wavelengths is controlled by phase dispersion regulation of multilayer films. As a proof of concept, two sets of multilayer films with different phase dispersions were designed to realize broadband (∼110 nm) and narrowband (∼15 nm) anomalous reflections, both with an efficiency of over 80%. The results offer a general strategy to design high-efficiency anomalous reflection with arbitrary bandwidth and might stimulate various potential applications for metadevices.

Maximum electromagnetic local density of states via material structuring.

The electromagnetic local density of states (LDOS) is crucial to many aspects of photonics engineering, from enhancing emission of photon sources to radiative heat transfer and photovoltaics. We present a framework for evaluating upper bounds on the LDOS in structured media that can handle arbitrary bandwidths and accounts for critical wave scattering effects. The bounds are solely determined by the bandwidth, material susceptibility, and device footprint, with no assumptions on geometry. We derive an analytical expression for the maximum LDOS consistent with the conservation of energy across the entire design domain, which upon benchmarking with topology-optimized structures is shown to be nearly tight for large devices. Novel scaling laws for maximum LDOS enhancement are found: the bounds saturate to a finite value with increasing susceptibility and scale as the quartic root of the bandwidth for semi-infinite structures made of lossy materials, with direct implications on material selection and design applications.

Polarization, Angle, and Delay Estimation for Tri-Polarized Systems in Multipath Environments

A new signal processing algorithm proposed here is aimed at estimating five-dimensional (5-D) polarization-space-time (polarization, angle, delay) channel parameters for a tri-polarized system that works in a multipath environment. Unlike most channel estimation algorithms, where spatially spread antenna arrays are deployed, our algorithm is designed for a spatial col-located tripole antenna. A third-order tensor model is firstly established for the multipath polarization-space-time channel. This tensor is subsequently solved by exploiting low-rank decomposition techniques. After that, a closed-form solution of 2-D angles, 2-D polarizations, and multipath delay estimates for each multipath ray are derived. The proposed algorithm requires no computation for iterative searching and parameter pairing, thus offering an advantage in time-sensitive applications. In addition, it is applicable to either narrowband or wideband systems of arbitrary bandwidth and center-frequency.

Low-Complexity Self-Interference Cancellation for Multiple Access Full Duplex Systems.

Self-interference occurs when there is electromagnetic coupling between the transmission and reception of the same node; thus, degrading the RX sensitivity to incoming signals. In this paper we present a low-complexity technique for self-interference cancellation in multiple carrier multiple access systems employing whole band direct to digital sampling. In this scenario, multiple users are simultaneously received and transmitted by the system at overlapping arbitrary bandwidths and powers. Traditional algorithms for self-interference mitigation based on recursive least squares (RLS) or least mean squares (LMS), fail to provide sufficient rejection, since the incoming signal is far from being spectrally flat, which is critical for their performance. The proposed algorithm mitigates the interference by modeling the incoming multiple user signal as an autoregressive (AR) process and jointly estimates the AR parameters and self-interference. The resulting algorithm can be implemented using a low-complexity architecture comprised of only two RLS modules. The novel algorithm further satisfies low latency constraints and is adaptive, supporting time varying channel conditions. We compare this to many self-interference cancellation algorithms, mostly adopted from the acoustic echo cancellation literature, and show significant performance gain.

Mechanism of chirp excitation

In design of a chirp inversion pulse, we keep the sweep rate a≪ω12, where ω1 is the amplitude of the pulse. This is the adiabaticity condition for the inversion to work. We can convert a chirp inversion pulse to an excitation pulse by keeping the chirp rate high, with a>ω12. To be precise a=2.8ω12. The analysis of such a pulse breaks the evolution into three phases. The first and third phase are adiabatic phases while the second phase is non-adiabatic. Starting from north pole such a pulse brings the magnetization to equator, however there is a nonuniform phase which depends on the resonance offsets. We show how by following this pulse with a chirp inversion pulse at twice the sweep rate of excitation pulse, we can refocus this uniform phase. We find there is still some phase dispersion. This can be further eliminated by bringing in a second inversion pulse. The combination of these three chirp pulses allows us to excite arbitrary large bandwidth without increasing the peak amplitude of the pulse. Refocusing properties of pair of chirp has been studied before but our description is very different.

Theory of frequency-selective homonuclear dipolar recoupling in solid-state NMR.

In solid-state nuclear magnetic resonance, frequency-selective homonuclear dipolar recoupling is key to quantitative distance measurement or selective enhancement of correlations between atoms of interest in multiple-spin systems, which are not amenable to band-selective or broadband recoupling. Previous frequency-selective recoupling is mostly based on the so-called rotational resonance (R2) condition that restricts the application to spin pairs with resonance frequencies differing in integral multiples of the magic-angle spinning (MAS) frequency. Recently, we have proposed a series of frequency-selective homonuclear recoupling sequences called SPR (short for Selective Phase-optimized Recoupling), which have been successfully applied for selective 1H-1H or 13C-13C recoupling under from moderate (∼10kHz) to ultra-fast (150kHz) MAS frequencies. In this study, we fully analyze the average Hamiltonian theory of SPR sequences and reveal the origin of frequency selectivity in recoupling. The theoretical description, as well as numerical simulations and experiments, demonstrates that the frequency selectivity can be easily controlled by the flip angle (p) in the (p)ϕk(p)ϕk+π unit in the pSPR-Nn sequences. Small flip angles lead to frequency-selective recoupling, while large flip angles may lead to broadband recoupling in principle. The result shall shed new light on the designof homonuclear recoupling sequences with arbitrary frequency bandwidths.

Synthesis of Linear-Phase FIR Filters With a Complex Exponential Impulse Response

In this paper, a novel recursive realization method with word length reduced is proposed to synthesize linear-phase FIR filters for arbitrary bandwidth. By exploring the sparsity in the frequency domain, it constructs the desired impulse response with few complex exponential series (CES) and very sparse additional coefficients (AC) with equal length. The design problem is formulated as a combinatorial optimization problem by confining the frequencies of CES to a finite dictionary. To reduce the computational complexity at optimization, an iterative algorithm is presented, where appropriate frequencies of CES and zero locations of AC can be quickly determined. Thereafter, an efficient parallel structure is introduced to implement the proposed filter. To verify the performance of the proposed method, MATLAB simulation and Field-programmable gate array (FPGA) implementation are made. It shows that the proposed method requires 18bits23bits word length while the existing advanced recursive realization method the piecewise-polynomial-sinusoidal recursiveneeds 59bits59bits for the same filter specifications. Meanwhile, the method can achieve comparable multiplier reduction compared with the state-of-the-art low-complexity techniques but produce a low extra group delay. Moreover, it can realize variable bandedges with a fixed filter structure.

Computational Bounds to Light-Matter Interactions via Local Conservation Laws.

We develop a computational framework for identifying bounds to light-matter interactions, originating from polarization-current-based formulations of local conservation laws embedded in Maxwell's equations. We propose an iterative method for imposing only the maximally violated constraints, enabling rapid convergence to global bounds. Our framework can identify bounds to the minimum size of any scatterer that encodes a specific linear operator, given only its material properties, as we demonstrate for the optical computation of a discrete Fourier transform. It further resolves bounds on far-field scattering properties over any arbitrary bandwidth, where previous bounds diverge.

Wideband Active Load–Pull by Device Output Match Compensation Using a Vector Network Analyzer

This work investigates wideband active load-pull (WALP) on microwave electron devices with a standard vector network analyzer (VNA), solely using calibrated frequency-domain relative measurements. Differently from the methods requiring full time-domain waveform acquisition capabilities, this approach removes any instantaneous bandwidth (BW) requirement, allowing to target modulated signals with arbitrarily large BWs. A VNA-based measurement setup is presented, and a novel mathematical framework is developed in order to enable the synthesis of an arbitrary wideband load profile using suitable numerical algorithms. A linear precompensation of the LS output match of the device, here implemented by different methods, is shown to significantly improve the speed and the stability of the basic secants' iterative method used to reach the target. Performance results, investigating the convergence properties of the approach and the effects of the setup dynamic range, are reported for a gallium nitride (GaN) high-electron-mobility transistor (HEMT) for up to 120-MHz output BW in the sub-6-GHz range.