A method for bandwidth enhancement of radar cross section (RCS) reduction by metasurfaces was studied. Scattering cancellation is one of common methods for reducing RCS of target scatterers. It occurs when the wave scattered by the target scatterer and the wave scattered by the canceling scatterer are the same amplitude and opposite phase. Since bandwidth of scattering cancellation is usually narrow, we proposed the bandwidth enhancement method using metasurfaces, which can control the frequency dependence of the scattering phase. We designed and fabricated a metasurface composed of a patch array on a grounded dielectric substrate. Numerical and experimental evaluations confirmed that the metasurface enhances the bandwidth of 10dB RCS reduction by 52% bandwidth ratio of the metasurface from 34% bandwidth ratio of metallic cancelling scatterers.

The accurate calculation of the inductance is the most basic problem of the inductor design. In this paper, the core flux density distribution and leakage flux in core window and winding of core-type inductor are analyzed by finite element analysis (FEA) firstly. Based on it, an improved magnetic equivalent circuit with high accuracy flux density distribution (iMEC) is proposed for a single-phase core-type inductor. Depend on the geometric structure, two leakage paths of the core window are modeled. Furthermore, the iMEC divides the magnetomotive force of the winding into the corresponding core branch. It makes the core flux density distribution consistent with the FEA distribution to improve the accuracy of the inductance. In the iMEC, flux density of the core leg has an error less than 5.6% compared to FEA simulation at 150A. The maximum relative error of the inductance is less than 8.5% and the average relative error is less than 6% compared to the physical prototype test data. At the same time, due to the high computational efficiency of iMEC, it is very suitable for the population-based optimization design.

In this letter, an active complex filter with finite transmission zeros is proposed. In order to obtain a complex prototype ladder filter including no inductors, a new circuit transformation is proposed. This circuit is classified into the RiCR filter. It is shown that it includes no negative capacitors when it is obtained through a frequency transformation. The validity of the proposed method is confirmed through computer simulation.

We fabricate and characterize a GaAsSb/InGaAs backward diode (BWD) toward a realization of high sensitivity zero bias microwave rectification for RF wave energy harvest. Lattice-matched p-GaAsSb/n-InGaAs BWDs were fabricated and their current-voltage (I-V) characteristics and S-parameters up to 67 GHz were measured with respect to several sorts of mesa diameters in μm order. Our theoretical model and analysis are well fitted to the measured I-Vs on the basis of WKB approximation of the transmittance. It is confirmed that the interband tunneling due to the heterojunction is a dominant transport mechanism to exhibit the nonlinear I-V around zero bias regime unlike recombination or diffusion current components on p-n junction contribute in large current regime. An equivalent circuit model of the BWD is clarified by confirming theoretical fitting for frequency dependent admittance up to 67 GHz. From the circuit model, eliminating the parasitic inductance component, the frequency dependence of voltage sensitivity of the BWD rectifier is derived with respect to several size of mesa diameter. It quantitatively suggests an effectiveness of mesa size reduction to enhance the intrinsic matched voltage sensitivity with increasing junction resistance and keeping the magnitude of I-V curvature coefficient.

To address the bandwidth bottleneck that exists between LSI chips, we have proposed a novel, high-sensitivity receiver circuit for differential optical transmission on a silicon optical interposer. Both anodes and cathodes of the differential photodiodes (PDs) were designed to be connected to a transimpedance amplifier (TIA) through coupling capacitors. Reverse bias voltage was applied to each of the differential PDs through load resistance. The proposed receiver circuit achieved double the current signal amplitude of conventional differential receiver circuits. The frequency response of the receiver circuit was analyzed using its equivalent circuit, wherein the temperature dependence of the PD was implemented. The optimal load resistances of the PDs were determined to be 5kΩ by considering the tradeoff between the frequency response and bias voltage drop. A small dark current of the PD was important to reduce the voltage drop, but the bandwidth degradation was negligible if the dark current at room temperature was below 1µA. The proposed circuit achieved 3-dB bandwidths of 18.9 GHz at 25°C and 13.7 GHz at 85°C. Clear eye openings in the TIA output waveforms for 25-Gbps 27-1 pseudorandom binary sequence signals were obtained at both temperatures.

An equivalent circuit of a circular patch array absorber has been proposed, however the method to identify a winding ratio of a transformer in its circuit have never been reported. In this paper, it is indicated that the ratio is proportionate to the area ratio between patch and unit cell of the absorber, and the design method of the winding ratio is proposed. The winding ratio derived by the proposed method is agreed well with that by using electromagnetic simulator within 3% error. Moreover, the operating frequency and 15 dB bandwidth of the fabricated absorber designed by proposed method are agreed with those derived by the circuit simulation within 0.4% and 0.1% errors. Thus the validity of the proposed method is verified.

A penta-band antenna based on the mu-negative transmission line is presented for radio frequency (RF) energy harvesting application. The antenna utilizes five radiation modes; two quarter wavelength resonances, three quarter wavelength resonance, zeroth order resonance, and first order resonance. The parasitic radiating strip antenna generates quarter wavelength resonance radiation. The dual band antenna based on two unit cell mu-negative (MNG) transmission line gives birth to the zeroth order resonance (ZOR) mode and the first order resonance (FOR) mode. The parasitic radiating strip and dual band antenna based on two unit mu-negative (MNG) transmission line are magnetically coupled by a feed monopole with gap. This feed monopole, simultaneously, radiates at quarter and three quarter wavelength resonance frequency to cover the other bands. The multi-mode coupling mechanism of this penta-band antenna is well modeled by our derived equivalent circuit. The measured radiation efficiencies are more than 87% over the entire penta-band.

This paper proposes a circuit modeling technique for electrically-very-small devices, e.g. electrodes for intrabody communications, coils for wireless power transfer systems, high-frequency transformers, etc. The proposed technique is based on the method of moments and can be regarded as an improved version of the partial element equivalent circuit method.

This paper expands Bartlett's bisection theorem. The theory of modal S-parameters and their circuit representation is constructed from a group-theoretic perspective. Criteria for the division of a circuit at a fixed node whose state is distinguished by the irreducible representation of its stabilizer subgroup are obtained, after being inductively introduced using simple circuits as examples. Because these criteria use only circuit symmetry and do not require human judgment, the distinction is reliable and implementable in a computer. With this knowledge, the entire circuit can be characterized by a finite combination of smaller circuits. Reducing the complexity of symmetric circuits contributes to improved insights into their characterization, and to savings of time and effort in calculations when applied to large-scale circuits. A three-phase filter and a branch-line coupler are analyzed as application examples of circuit and electromagnetic field analysis, respectively.

We investigate a finite-sized self-complementary bow-tie antenna (SC-BTA) integrated with a semiconductor mesa with respect to radiation characteristics such as the peak radiation frequency and bandwidth around the fundamental radiation mode. For this investigation, we utilize an equivalent circuit model of the SC-BTA derived in our previous work and a finite element method solver. Moreover, we derive design guidelines for the radiation characteristics in the form of size scaling-rules with respect to the antenna outer size for a terahertz transmitter.

An equivalent-circuit model is an effective tool for the analysis and design of metamaterials. This paper describes a systematic and theoretical method for the circuit modeling of meta-atoms. We focus on the structures of wired metallic spheres and propose a method for deriving a sophisticated equivalent circuit that has the same topology as the wires using the partial element equivalent circuit (PEEC) method. Our model contains the effect of external electromagnetic coupling: excitation by an external field modeled by voltage sources and radiation modeled by the radiation resistances for each mode. The equivalent-circuit model provides the characteristics of meta-atoms such as the resonant frequencies and the resonant modes induced by the current distribution in the wires by an external excitation. Although the model is obtained by a very coarse discretization, it provides a good agreement with an electromagnetic simulation.

We have derived the physics-based equivalent circuit model of a semiconductor-integrated bow-tie antenna (BTA) for expressing its impedance and radiation characteristics as a terahertz transmitter. The equivalent circuit branches and components, consisting of 16 RLC parameters are determined based on electromagnetic simulations. All the values of the circuit elements are identified using the particle swarm optimization (PSO) that is one of the modern multi-purpose optimization methods. Moreover, each element value can also be explained by the structure of the semiconductor-integrated BTA, the device size, and the material parameters.

This paper describes an equivalent circuit analysis of a meta-surface using a double-layered patch-type frequency-selective surface (FSS); the analysis considers the coupling between FSSs. Two types of double-layered structures are examined. One is a stacked structure and the other is an alternated structure. The results calculated using the equivalent circuit are in agreement with the results of the FDTD analysis. In addition, it is clarified that the stacked and alternated structures exhibit the common mode and the differential mode coupling, respectively. Moreover, experiments support analysis results for both stacked and alternated structures.

A frequency-reconfigurable dipole antenna, whose dual resonant frequencies are independently controlled, is introduced. The antenna's conductor consists of radiating conductors, lumped and distributed elements, and varactors. To design the antenna, current distribution, input impedance, and radiation power including higher-order modes, are analyzed for a narrow-angle sectorial antenna embedded with passive elements. To derive the formulae used, radiation power is analyzed in two ways: using Chu's equivalent circuit and the multipole expansion method. Numerical estimations of electrically small antennas show that dual-band antennas are feasible. The dual resonant frequencies are controlled with the embedded series and shunt inductors. A dual-band antenna is fabricated, and measured input impedances agree well with the calculated data. With the configuration, an electrically small 2.5-/5-GHz dual-band reconfig-urable antenna is designed and fabricated, where the reactance values for the series and shunt inductors are controlled with varactors, each connected in series to the inductors. Varying the voltages applied to the varactors varies the measured upper and lower resonant frequencies between 2.6 and 2.9GHz and between 5.1 and 5.3GHz, where the other resonant frequency is kept almost identical. Measured radiation patterns on the H-plane are almost omni-directional for both bands.

Wireless power transfer (WPT) based on electric coupled resonance can withstand a great level of variability in antenna separation. In this paper, we propose an independent electrical coupled resonance WPT system to further increase such systems' power transfer distance and ensure flexibility in the antenna location. The proposed system's power transfer function, critical coupling point, and resonance frequency splitting are investigated via the equivalent circuit, simulation, and experiment. Moreover, the input impedance characteristic of two electric coupled resonance antennas is also analyzed according to the transfer distance. In the region of under coupled, an appropriate impedance matching method is required to achieve effective power transfers. Here, we proposed a fixed configuration type matching loop with a series-connecting variable capacitance that can be added into both the source and load antennas. Experimental results demonstrate that the proposed matching loop can convert the two electric coupled resonance antennas' input impedance to the feed port impedance very well at varying transfer distances; these results are in good agreement with the simulation results.

The reliability of electromagnetic relay (EMR) which contains a permanent magnet (PM) can be improved by a robust design method. In this parameter design process, the calculation of electromagnetic system is very important. In analytical calculation, PM is often equivalent to a lumped parameter model of one magnetic resistance and one magnetic potential, but significant error is often caused; in order to increase the accuracy, a distributed parameter calculation model (DPM) of PM bar is established; solution procedure as well as verification condition of this model is given; by a case study of the single PM bar, magnetic field lines division method is adopted to build the DPM, the starting point and section magnetic flux of each segment are solved, a comparison is made with finite element method (FEM) and measured data; the accuracy of this magnetic field line based distributed parameter model (MFDPM) in PM bar is verified; this model is applied to the electromagnetic system of a certain type EMR, electromagnetic system calculation model is established based on MFDPM, and the static force is calculated under different rotation angles; compared with traditional lumped parameter model and FEM, it proves to be of acceptable calculation accuracy and high calculation speed which fit the requirement of robust design.

This study proposes a novel method for evaluating the transmission characteristics of a three-phase filter using the “Fortescue-mode S-parameters,” which are S-parameters whose variables are transformed into symmetrical coordinates (i.e., zero-/positive-/negative-phase sequences). The behavior of the filter under three-phase current, including its non-symmetry, can be represented by these S-parameters, without regard to frequency. This paper also describes a methodology for creating modal equivalent circuits that reflect Fortescue-mode S-parameters allowing the effects of circuit components on filter characteristics to be estimated. Thus, this method is useful not only for the measurement and evaluation but also for the analysis and design of a three-phase filter. In addition, the physical interpretation of asymmetrical/symmetrical insertion losses and the conversion method based on Fortescue-mode S-parameters are clarified.

The equivalent circuit of aperture-coupled cavities filled with a lossy dielectric is considered by means of an eigenmode expansion technique founded on the segmentation concept. It is different from a series LCR resonant circuit, and the resistor which symbolizes the dielectric loss is connected to the capacitor in parallel. If the cavities are formed by a short-circuited oversize waveguide, then the input admittance can be represented by the product of a coupling factor to the connected waveguide port and the equivalent admittance of the short-circuited waveguide. The transmission line model is effective even if lossy wall effect and dielectric partially-loading effect are considered. As a result, three-dimensional eigenmode parameters, such as the resonant frequency and the Q-factor, become dispensable and the computational complexity for the cavity simulation in the field of microwave heating is dramatically reduced.

This paper describes how to design matching structures to improve the frequency characteristics of one-dimensional finite periodic structures. In particular, it deals with one-dimensional finite superlattices. A downhill simplex method is used to determine some of the structural parameters of the matching structure. Numerical examples show that this method is effective in improving the frequency characteristics of finite superlattices.

A two-dimensional negative refractive index material is proposed. The material has a bulky structure composed of dielectric prism cells with metal patterns. The material is expressed by an equivalent circuit. The propagation regions of two left-handed modes calculated from the equivalent circuit exist near the propagation regions obtained by electromagnetic simulation. It is confirmed by simulation that the incident plane wave goes into the material with low reflection by using the second left-handed mode and attaching metal conversion strips around the material. A negative refractive index slab lens with 15×9 cells is made to measure the field distribution of wave out of the lens. It is shown that the resolution of the slab lens exceeds the diffraction-limit.