In-band Reflection Research Articles

Adaptive denoising of photoacoustic signal and image based on modified Kalman filter.

As a burgeoning medical imaging method based on hybrid fusion of light and ultrasound, photoacoustic imaging (PAI) has demonstrated high potential in various biomedical applications, especially in revealing the functional and molecular information to improve diagnostic accuracy. However, stemming from weak amplitude and unavoidable random noise, caused by limited laser power and severe attenuation in deep tissue imaging, PA signals are usually of low signal-to-noise ratio, and reconstructed PA images are of low quality. Despite that conventional Kalman filter (KF) can remove Gaussian noise in time domain, it lacks adaptability in real-time estimation due to its fixed model. Moreover, KF-based denoising algorithm has not been applied in PAI before. In this paper, we propose an adaptive modified KF (MKF) targeted at PAI denoising by tuning system noise matrix Q and measurement noise matrix R in the conventional KF model. Additionally, in order to compensate the signal skewing caused by MKF, we cascade the backward part of Rauch-Tung-Striebel smoother, which utilizes the newly determined Q. Finally, as a supplement, we add a commonly used differential filter to remove in-band reflection artifacts. Experimental results using phantom and ex vivo colorectal tissue are provided to prove validity of the algorithm.

Synthesis of Generalized Strongly Coupled Resonator Triplet Filters by Regulating Redundant Resonant Modes

This article proposed an analytical synthesis approach of generalized strongly coupled resonator triplet (GSCRT) filters, which eliminates the need for negative couplings regardless of the location of transmission zeros (TZs). The principle of removing negative couplings in GSCRTs is explained from circuit level for the first time. In contrast with conventional filter function synthesis with all in-band reflection zeros (RZs), some RZs are preassigned out of the passband, which are named redundant resonant modes (or even modes). By regulating the frequency of the redundant modes, flexible synthesis solutions can be achieved and the previously published strongly coupled resonator triplet (SCRT) becomes a special case of this new generalized version. Besides, a novel physical interpretation of GSCRT from the basis of modes is presented, which shows the modes routing clearly within the coupling matrix framework. Due to the proposed theories, additional approximation and optimization can be avoided during the synthesis procedure. Due to the redundant mode, all couplings in the GSCRT are positive, thus easing the design and manufacturing process. Also, GSCRT brings compact and in-line configuration of filters. Moreover, due to the higher flexibility provided by redundant resonant modes, reasonable synthesis solutions can be selected depending on the specifications or other physical limitations, such as bandwidth and size. A group of synthesis examples with simulations are elucidated. The simulated results show a good agreement with the synthesis theories. The simulated and measured results of an anti-interference C-band eight-pole filter with four TZs below the passband further validate the effectiveness of the proposed theories.

Wafer-level testing of inverse-designed and adjoint-inspired vertical grating coupler designs compatible with DUV lithography.

Perfectly vertical grating couplers have various applications in optical I/O such as connector design, coupling to multicore optical fibers and multilayer silicon photonics. However, it is challenging to achieve perfectly vertical coupling without simultaneously increasing reflection. In this paper, we use the adjoint method as well as an adjoint-inspired methodology to design devices that can be fabricated using only a single-etch step in a c-Si 193 nm DUV immersion lithography process, while maintaining good coupling and low reflection. Wafer-level testing of devices fabricated by a pilot line foundry confirms that both design paradigms result in state-of-the-art experimental insertion loss (<2 dB) and bandwidths (∼20 nm) while having only moderate in-band reflection (<-10 dB). Our best design has a (median) 1.82 dB insertion loss and 21.3 nm 1 dB-bandwidth.

On-chip terahertz bandpass filter based on substrate integrated plasmonic waveguide

In this paper, we propose and demonstrate a terahertz bandpass filter based on substrate integrated plasmonic waveguide (SIPW) using the standard 0.25-μm InP DHBT fabrication process. In this design, a Yagi-Uda antenna-like subwavelength array with effective asymptotic frequency reduction, is etched on the top metal layer of substrate integrated waveguide (SIW) to support a spoof surface plasmon polaritons (SSPPs) mode. The bandpass transmission with unique dispersion characteristics of the SIPW can be easily engineered by tuning the SIW and the SSPPs geometric parameters to independently adjust the low-cutoff and high-cutoff frequency, respectively. The simulated results show that, from the frequency range of 208 GHz to 265 GHz, the transmission coefficients is less than 2 dB, and the in-band reflection coefficients is better than 20 dB. To further verify the proposed design, a similar bandpass filter with geometry size scaled up operating in microwave frequency range is fabricated and measured. The measured results show that the great bandpass features and high-efficiency propagation are validated. In the passband of 13.5 GHz to 18.4 GHz, the reflection coefficients is better than 10 dB and the maximal transmission coefficients is 2 dB. Our work presents a novel 0.25-μm InP DHBT-based bandpass filter with dimensions of 900 μm × 285 μm in the terahertz range using SIPW for the first time, which may have extensive potential applications in integrated terahertz plasmonic devices.

Theoretical Investigation of the Passive Transmitter Based on Reconfigurable Metasurface

Wireless communication has become a standard solution to satisfy the ever-increasing demands of information transfer in our daily life. Furthermore, reconfigurable metasurfaces comprised of multiple tunable unitcells have drawn significant attention due to their superior electromagnetic performance, while the desired electromagnetic response can be controlled by computer. We therefore present a prototype of a wireless communication system based reconfigurable metasurface that works in the microwave frequency range. A 2-D periodical array of a reconfigurable metasurface is loaded with a varactor diode to effectively adjust the in-band transmission and reflection coefficients that maintain different far-field electromagnetic characteristics. The reconfigurable metasurface does not radiate electromagnetic waves and only carries information by adjusting its reflection and transmission coefficients. With this reconfigurable metasurface, a passive communication method can be realized.

Design of sextuple-mode triple-ring HTS UWB filter using two-round interpolation* *Project supported by the National Natural Science Foundation of China (Grant No. 61471094).

A single-stage ring resonator capable of introducing six modes within the ultra-wideband (UWB) passband is presented. The sextuple-mode resonator consists of three rings and three sets of stepped-impedance open stubs. Based on this sextuple-mode resonator, a UWB filter fed by the interdigital-coupling line (ICL) is designed. And we propose a two-round interpolation method to obtain the filter’s initial dimensions. The designed filter is fabricated on a double-sided YBCO/MgO/YBCO high-temperature superconducting (HTS) thin film for demonstration. The experimental results show that this UWB filter produces eight resonances in the passband eventually, which effectively improves the in-band reflection and the band-edge steepness. Moreover, the upper stopband performance is enhanced due to the transmission zeros (TZs) generated by the stepped-impedance open stubs and the ICL structure. The measured good performance verifies the practicability of the two-round interpolation approach, which can also be extended to other odd–even-mode filter designs.

SIW planar balun with enlarged bandwidth

An X-band substrate integrated waveguide (SIW) balun, based on a Y-type divider with enlarged bandwidth, is presented in this study. In most SIW Y-type dividers, the undesired TE30 mode either leads to the deterioration of the in-band reflection or constrains the bandwidth by a transmission zero. The cause of the transmission zero is analysed and the modes coupling, rather than the step impedance matching, is utilised to reduce its impact. In the traditional Y-type divider, the frequency band is split by this transmission zero, while in the proposed wideband configuration, the co-existences of the TE10 and TE30 modes are employed to combine the two non-contiguous bands. A broadband balun is designed and fabricated, with the improved Y-type wideband divider serving for the power-dividing part. The dividing ports are connected to the reversely placed transitions, achieving inherent out-of-phase performance and good amplitude property. The measurement of the balun suggests a 43.94% bandwidth from 8.23 to 12.89 GHz, with 15 dB return loss. The measured amplitude and phase imbalance between two output ports are below 0.7 dB and ±3°, respectively. The performance of the fabricated balun is in agreement with the simulation, and it is promising for wideband applications.

Feedline Alterations for Optimization-Based Design of Compact Super-Wideband MIMO Antennas in Parallel Configuration

This letter presents a technique for size reduction of wideband multiple-input–multiple-output (MIMO) antennas. Our approach is a two-stage procedure. At the first stage, the antenna structure is modified to improve its impedance matching. This is achieved through incorporation of an n -section tapered feedline , followed by reoptimization of geometry parameters. Reducing the maximum in-band reflection well beyond the acceptance level of −10 dB creates room for size reduction, realized in the second stage as explicit footprint area minimization with the constraints imposed on the maximum in-band reflection level (| S 11| ≤ −10 dB) and element isolation (| S 21| ≤ −20 dB). The technique is generic and can be applied to various monopole-based MIMO structures. It is validated using two antenna structures operating from 2.8 to 20 GHz. Various complexities of the tapered lines are also investigated, from n = 1 to 5. To the best of the authors’ knowledge, the obtained footprints (452 and 546 mm2, respectively) are the smallest to date while ensuring acceptable performance, specifically impedance matching, isolation, envelope correlation coefficient ( 9.99 dB).

Novel design of microstrip antenna array with low scattering performance

In this paper, the idea of electromagnetic surface (EMS) is introduced into the design of microstrip antenna array. The antenna element proposed in this paper is treated as an EMS element, whose reflection characteristics are taken into consideration in the process of antenna array design. Firstly, a rectangular patch antenna element is designed. Then, by cutting arc-shaped structure into a rectangular patch, another element is created to generate 180° ± 30° effective phase difference compared with original antenna element. As a consequence, 180° ± 30° effective phase difference is obtained from 5.5 GHz to 6.9 GHz for the &lt;i&gt;y&lt;/i&gt;-polarized incidence. Meanwhile, for the &lt;i&gt;x&lt;/i&gt;-polarized incidence, each of the two elements possesses high absorptivity over the operating frequency as a result of matching load. Besides, the two elements work in the same resonant mode and the same resonant frequency band when treated as radiators. In order to further explain the consistency in radiation and difference in reflection between the two structures, current distribution at 5.8 GHz is investigated in terms of radiation and reflection. Then, the two elements are arranged into a chessboard array to achieve the low scattering performance based on phase cancellation principle under the &lt;i&gt;y&lt;/i&gt;-polarized incidence. Based on the absorption principle, the matching load is added to improve the scattering performance of the composite antenna array with the &lt;i&gt;x&lt;/i&gt;-polarized incidence. Simultaneously, the proposed antenna array maintains good radiation characteristics due to the consistency between the radiation performances of the two elements. The corresponding antenna array is fabricated and tested. Simulated and measured results prove that the proposed antenna array also achieves good radiation performance. And a 6 dB radar cross section reduction is obtained from 5.6 to 6.2 GHz under the &lt;i&gt;x&lt;/i&gt; polarization and from 5.5 to 7.0 GHz under the &lt;i&gt;y&lt;/i&gt; polarization for the normal incident wave, implying 10.1% and 24% in relative bandwidth, respectively. In-band reflection suppression in the specular direction is demonstrated for an incident angle of 30° under both polarizations. The measured results are in good agreement with the simulated ones. Additionally, the approach proposed in this paper offers an effective way to deal with the confliction between radiation and scattering performance, and can also be applied to other kinds of antenna arrays.

Analysis of circular polarization antenna design trade‐offs using low‐cost EM‐driven multiobjective optimization

Circular polarization (CP) antennas are vital components of modern communication systems. Their design involves handling several requirements such as low reflection and axial ratio (AR) within the frequency range of interest. Small size is an important criterion for antenna mobility which is normally achieved as a by-product of performance-oriented modifications of the structure topology. In this work, multiobjective optimization is used in order to identify and analyze design trade-offs for miniaturized CP antenna including the antenna capability for maintaining small size while retaining acceptable levels of other performance figures. We use a population-based metaheuristic algorithm to obtain a set of designs which represent the best attainable compromise between the imposed requirements. To maintain a low optimization cost, the algorithm is executed on a cheap approximation model and the results are further corrected to bring them to the EM model accuracy level. Here, the analysis is carried out for a planar CP antenna. Achievable size reduction of the considered structure—while maintaining acceptable performance—is around 11%. Antenna performance in terms of in-band reflection and AR varies from −14 to −10 dB and from 1.3 to 3 dB, respectively. The numerical results are validated by measurements of fabricated antenna prototypes.

Miniaturisation of wideband antennas by means of feed line topology alterations

It is a common practice to achieve reduction of wideband antenna size by incorporating appropriate geometrical modifications into conventional antenna topologies (e.g. monopoles or uniplanar structures). The authors investigate a particular type of modification, which is changing the geometry of the feed line. The two basic geometries include a taper and a stepped-impedance line. They carry out systematic investigations concerning the effect of these feed line geometries on obtainable antenna miniaturisation rates. For the sake of generality, feed line geometries of various complexities are considered (from two to six sections). An automated adjustment of antenna geometry parameters through numerical optimisation is performed to ensure design optimality for each combination of antenna/feed structure. The optimisation process is formulated as an explicit size reduction task with a constraint on the maximum in-band reflection level. The investigations are performed using two selected ultra-wideband monopoles. The results indicate clear advantage of the stepped-impedance feed line over the tapered one. On the other hand, considerable size reduction can be obtained by increasing the geometrical complexity of the feed line, although the design problem becomes more challenging due to the increased number of antenna parameters. Numerical results are validated experimentally for selected antenna prototypes.

Multi-objective design optimization of antennas for reflection, size, and gain variability using kriging surrogates and generalized domain segmentation

Cost-efficient multi-objective design optimization of antennas is presented. The framework exploits auxiliary data-driven surrogates, a multi-objective evolutionary algorithm for initial Pareto front identification, response correction techniques for design refinement, as well as generalized domain segmentation. The purpose of this last mechanism is to reduce the volume of the design space region that needs to be sampled in order to construct the surrogate model, and, consequently, limit the number of training data points required. The recently introduced segmentation concept is generalized here to allow for handling an arbitrary number of design objectives. Its operation is illustrated using an ultra-wideband monopole optimized for best in-band reflection, minimum gain variability, and minimum size. When compared with conventional surrogate-based approach, segmentation leads to reduction of the initial Pareto identification cost by over 20%. Numerical results are supported by experimental validation of the selected Pareto-optimal antenna designs.

Detection of Military Underground Structures through the Remote Sensing Investigation of Phenological Cycle of Crops

This paper aims to explore how field spectroscopy is essential for remote sensing studies for the detection and monitoring of various features such military underground structures in Cyprus. A SVC-HR1024 field spectroradiometer was used and in-band reflectances were determined for medium resolution Landsat-7 ETM satellite sensor, in order to study possible differences of the spectral signature of vegetation throughout the phenological cycle of plant growth. In this study, two test areas were identified, analyzed and modelled: 1) Military Structure Area (MSA) where underground structure exists, and 2) Reference Area (RA) where underground military structure does not exist. The Normalized Difference Vegetation Index (NDVI) was applied to Landsat-7 ETM and Sentinel-2 satellite images in order to identify the presence or absence of underground structures in the study area.

Precise control of reflection response in bandwidth-enhanced planar antennas

In this work, the issues of bandwidth enhancement of planar antennas and the relevance of precise and automated response control through numerical optimization have been investigated. Using an example of a planar antenna with parasitic radiator we illustrate possible effects of even minor modifications of the antenna geometry (here, applied to the ground plane) on its reflection performance. In particular, a proper handling of geometry parameters may lead to considerable broadening of the antenna bandwidth. For the sake of computational efficiency, the adjustment of geometry parameters is carried out using surrogate-based optimization methods exploiting coarse-discretization EM simulations as the underlying low-fidelity antenna model. Additionally, suitably defined penalty function allows us to precisely control the maximum in-band reflection so that sufficient margin to accommodate possible manufacturing tolerances can be achieved. The optimized designs of the two antenna structures considered in this work exhibit over 1.75 GHz (>31%) and 2.15 GHz (>38%) bandwidth, respectively, for the center frequency of 5.6 GHz. Simulation results are validated using measurements of the fabricated prototypes. Comparison with state-of-the-art designs is also provided. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:653–659, 2016.

Structure and design optimisation of compact UWB slot antenna

A structure and computationally efficient design optimisation procedure of a novel miniaturised UWB slot antenna has been proposed. Upon geometry parameter adjustment, the structure exhibits a very small footprint of just 161 mm2. This has been achieved by introducing sufficient number of degrees of freedom, including the parameterised multi-section slot and a multi-section load of the feed line as well as efficient numerical optimisation of all relevant geometry dimensions of the structure. The design process has been formulated as explicit size reduction problem. The electrical performance parameters (here, a maximum in-band reflection) are controlled by suitably defined constraints. The final design has been verified through full-wave electromagnetic simulation as well as physical measurements of the fabricated antenna prototype.

Synthesis of Wideband Parallel-Coupled Line Bandpass Filters With Non-Equiripple Responses

This letter proposes a synthesis of wideband parallel-coupled line bandpass filters with controllable non-equiripple frequency responses. Different from the traditional Chebyshev transfer function filters, the reflection lobes of the proposed non-equiripple filters can be redistributed within the operating passband. As a result, the proposed filters have a reduced sensitivity to manufacturing errors and exhibit good tolerance control for maximum in-band reflection loss. By deriving the transfer functions, a synthesis approach with a set of nonlinear equations can be established according to the specifications such as the bandwidth and predetermined reflection lobes. Without performing any post optimization in the full-wave simulation, the non-equiripple synthesized results have less sensitivity in comparison with those obtained from traditional Chebyshev transfer functions with equiripple frequency responses.

High-reflectivity fiber-optic bandpass filter designed by use of the iterative solution to the Gel’fand–Levitan–Marchenko equations

A fiber Bragg grating bandpass filter has been investigated. The profile of the 3.1-cm-long grating was synthesized for high reflectivity and low dispersion by use of the iterative solution to the Gel'fand-Levitan-Marchenko equations. A grating designed according to this synthesis was written into a boron-codoped germanosilica fiber. The measured spectral response was in good agreement with simulations. The achieved in-band reflection was 97%, and the passband ripple was only 0.06 dB.

F.E.T. oscillation frequency domain solution

A new approach is used to determine when the necessary condition for oscillation, Re (Za)<0, holds in a microwave oscillator. Here Za is the Schottky GaAs f.e.t. active network impedance. This analysis has been used to develop a computer program that calculates the frequencies at which the above condition holds. The computer program also provides inband impedances and reflection coefficients and has been utilised to study Ku-band y.i.g.-tuned oscillators. Bandwidth and initial frequency of oscillation curves as functions of f.e.t.-model lumped elements are generated from the computer program.