An impedance synthesis problem of 2D antenna arrays consisting of slotted spherical radiators, whose geometric centers are located at nodes of a flat rectangular grid with double periodicity, has been solved. The problem is formulated as follows: to determine complex impedances distributed over surfaces of the spherical radiators which allows us to steer the radiation pattern (RP) of the antenna array to given directions. Analytical solution of the impedance synthesis problem (as an alternative to numerical solution) was obtained under the assumption that spherical radiators are excited by axially symmetric magnetic currents with equal amplitudes. The approach was verified by simulation of the five-element linear antenna array. The possibility of RP scanning in a wide range was confirmed by using the synthesized distributions of complex impedances.

This paper presents the pole-zero analysis of microwave filters using contour integration method exploiting right-half plane (RHP). The poles and zeros can be determined with only S₂₁ by exploiting contour integration method on the RHP along with certain S matrix properties. The contour integration in the argument principle is evaluated numerically via the finite-difference method. To locate the poles or zeros, the contour divide and conquer approach is utilized, whereby the contour is divided into smaller sections in stages until the contour enclosing the pole or zero is sufficiently small. The procedures to determine the poles and zeros separately are described in detail with the aid of pseudocodes. To demonstrate the effectiveness of the proposed method, it is applied to determine and analyze the poles and zeros of various microwave filters.

Miniature Air Launched Decoy (MALD) is an electronic warfare technique for inducing an angular deception in a monopulse radar by recreating glint angular error. MALD flies cooperatively with the true target, forms unresolved group targets within the radar beam, and destroys the detection, tracking and parameter estimation of monopulse radar for the true target. In this paper, a typical scenario for one target and one decoy was discussed, and the measurement model of target and decoy based on the actual non-ideal sampling conditions was established. The joint multi-targets probability density was adopted to dynamically describe the number and state of the targets within the radar beam. Based on the original observation without threshold decision, a joint detection and tracking algorithm for unresolved target and decoy was proposed under the Bayesian framework, and the judgment of existence of jamming and the target state estimation were deduced. Simulation results showed that the proposed method enabled quick detection of the appearance of MALD and estimated the state of target with minimal delay and high precision. Stable tracking of the true target was achieved under severe jamming conditions.

We present an optimization procedure for wireless power transfer (WPT) applications and test it numerically for a WPT system design with four resonant circuits that are magnetically coupled by coaxial coils in air, where the magnetic field problem is represented by a fully populated inductance matrix that includes all magnetic interactions that occur between the coils. The magnetically coupled resonators are fed by a square wave voltage generator and loaded by a rectifier followed by a smoothing filter and a battery. We compute Pareto fronts associated with a multi-objective optimization problem that contrasts: 1) the system efficiency; and 2) the power delivered to the battery. The optimization problem is constrained in terms of: 1) the physical construction of the system and its components; 2) the root-mean-square values of the currents and voltages in the circuit; and 3) bounds on the overtones of the currents in the coils in order assure that the WPT system mainly generates magnetic fields at the operating frequency. We present optimized results for transfer distances from 0.8 to 1.6 times the largest coil radius with a maximum power transfer from 4 kW to 9 kW at 85 kHz, which is achieved at an efficiency larger than 90%.

In this paper, a simple and fast calibration algorithm is proposed for an active phased antenna array measurement of the amplitude and phase of all the antenna elements. Euler's numerical method is used to simultaneously measure and calibrate the array element's electric field and array factor. Each element's phase shifts are periodically varied with a reference state, and their variations are calculated and analyzed for signal calibration. The method is theoretically studied using numerical simulations providing accurate performance and a very low tolerance to errors. This method provides a multiple element far field calibration technique applicable to radar, satellite, and wireless communication.

Wireless power transmission (WPT) based on near-field inductive coupling is a promising solution to power a tether-less capsule robot (CR) for medical application, and it is normally implemented with a one-dimensional transmitting coil for exciting an alternating magnetic field and an three-dimensional (3-D) receiving coil onboard the CR for induction. The connection way of the 3-D receiving coil has an influence on its output power supplied to the CR, but a method for quickly selecting series/parallel connection is not available yet. This paper is dedicated to developing such a method. Firstly, an analytical expression of the output power of the 3-D receiving coil when selecting series/parallel connection was derived, and its correctness was experimentally validated: the calculated output power using the analytical expression matched well with the measured one, having an average deviation of 1.42%/0.57% when selecting series/parallel connection. Then, a criterion for quickly selecting the connection way was deduced from the analytical expression, which indicates that the connection way is much related to the CR load: when the CR load is smaller than a critical load, parallel connection enables a larger output power average; otherwise, series connection does. A calculation method of the critical load is also given, which can be determined by available parameters relating to the transmitting coil and 3-D receiving coil. Thus, this paper provides a guidance for quickly selecting the connection way of the 3-D receiving coil.

This paper presents a miniaturized dual-band antenna with a rectangular patch and symmetrically placed circles in the partial ground plane. The dimensions of the proposed antenna are 15 * 20 * 1.5 mm³, and the antenna is excited by a 50 Ω microstrip line from the bottom. The proposed antenna is fabricated on the commercially available low-cost FR4 substrate having relative permittivity ε_r = 4.3 and loss tangent 0.025. By introduction of a rectangular slot with a T-shape in the ground plane and a rectangular patch, the lower frequency band is achieved. The peak gain and radiation efficiency of the proposed antenna are 2 dB and 78%. The proposed antenna operates at 2.846 GHz to 3.24 GHz and 4.05 GHz to 6.22 GHz frequency range. The antenna finds its application in S-band, 5.5/5.8 GHz WiMAX bands, and 4.9/5/5.9 GHz Wi-Fi bands.

A mathematical model is constructed for calculating a three-dimensional quasistationary electromagnetic field in a piecewise-homogeneous medium containing massive conductors which is excited by a variable magnetic field. The field is varying in time according to an arbitrary law. It is proposed to use the integral relation instead of the boundary condition written at a point, which allows one to get away from the problem of collocation points and at the same time increase the computational efficiency of the numerical model. The magnetic field is calculated for the case of the excitation of eddy currents in a conducting sample containing a cut of finite size. The results obtained are confirmed by natural experiments.

In this paper, we investigate the secrecy design in a sustainable relay network, where the relay is energy harvesting enabled and utilizes time switching to harvest wireless power. Specifically, assuming half-duplex amplify-and-forward relaying, we investigate the worst-case secrecy rate maximization by jointly designing the relay beamforming matrix, artificial noise covariance, and the time switching ratio. However, the formulated problem is highly non-convex due to the secrecy rate function and the dynamic relay transmit power constraint. By decoupling the original problem, we propose a two-layer optimization algorithm, where the outer problem is solved by two-dimensional search while the inner problem is solved by semi-definite relaxation. Numerical results show the effectiveness of the proposed scheme.

A dual-passband frequency selective surface (FSS) is designed in this paper. Two passbands are 2-3.4 GHz and 5.5-6.8 GHz, respectively. It is used as a spatial filter to improve the radiation and scattering performance of an antenna. The structure is combined with two layers. One is metal, and the other is intermediate medium. The requirements of wide-band, polarization-independent, wide incidence angle and miniaturized FSS with a thickness of only 0.0085λ are achieved by parameter optimization. When the FSS is used to improve the proposed microstrip antenna, the relative bandwidth can be increased by 31.4% and 50%, and the peak gain is increased by 2.53 dB and 1.86 dB at 5.8 GHz and 6.4 GHz, respectively. Meanwhile, the maximum RCS reduction of the microstrip antenna is 16 dB. On the other hand, the FSS is able to be applied to a dipole antenna to improve the transmission coefficient and phase. Simulation and measurement results of the transmission coefficient and phase of the antenna are almost the same.

A novel C-L-L π-type feeding network is presented to tune the working frequency and impedance matching of antenna. Two varactors are used in the tunable feeding network as tunable elements for antenna resonating frequency and impedance matching tuning. The tunable capability of the network is studied, and a patch antenna is used to verify the tunable feeding network. The tunable feeding network is designed, fabricated and measured. The measurement results show that the patch antenna can be tuned from 630 MHz to 1.04 GHz with a maximum impedance bandwidth of 24 MHz of S₁₁ less than -10 dB.

Compared to low Earth orbit (LEO) synthetic aperture radar (SAR), geosynchronous (GEO) SAR has a larger coverage and shorter revisit period. However, due to its longer integration timeit will be affected byionospheric time-variant total electron content (TEC), which introduces a phase error into the SAR azimuth signal.Using U.S. total electron content (USTEC) data, TEC variation with timeon GEO SAR trackis analyzed. It is shown thatquadratic phase error caused by time-variant TEC is main effect on image focusing compared to higher order errors. Therefore, contrast optimization autofocus (COA) algorithm can beusedfor compensation. The key steps of COA are given. Simulations based on scenes derived from PALSAR2 data demonstrate the effectiveness of COA.

This paper aims to estimate the shape of microwave scattering objects using linear sampling method (LSM) with multifrequency data. LSM is a simple, reliable linear inverse algorithm and uses multiview multistatic single frequency scattered field data measured around target objects. Despite its simplicity and computational effectiveness, the output LSM results depend on the frequency of operation. To improve the LSM performance, the present work proposes a new formulation that incorporates frequency information in the LSM equation. As a result, LSM finds the target's shape by a simple solution to a linear inverse problem via multifrequency data. The output results are tested with various types of numerical examples of synthetic data as well as experimental data provided by the Institute of Fresnel.

A compact wideband filtering power divider is presented in this paper, by using coupled transmission lines at two output ports to realize filtering function. The return loss and insertion loss of the design in the passband are improved by inserting fan-shaped open stubs and etching a T-shaped slot at the input port. The central frequency of the power divider is 2.4 GHz. The measured results show a 10-dB fractional bandwidth of 60%, and a wideband filtering response can be obtained. The material object is designed by using FR4, and the size is 0.4λ_g*0.2λ_g. The design is well used in the WiFi band.

A novel miniaturized multilayer substrate integrated waveguide (SIW) filter is designed. The filter is constructed with four compact SIW resonator cavities, and each cavity supports TE₁₀₁ mode, which can be controlled by the slot located between layers. The area of the compact SIW resonator is just 1/16 of that of original substrate integrate waveguide (SIW) resonator. Meanwhile, the area of the four-order filter is 13.2 mm×26.4 mm. The insertion loss and return loss of the fabricated filter are -1.8 dB and -14.6 dB, respectively. Meanwhile, the tunable filter realizes center frequency linearity, which works at 1.6 GHz with an adjustable range of 51.8%. The insertion loss is -1.2 dB, and the return loss is less than -15 dB. The coplanar cavity coupling structure achieves a switchable bandwidth.

In this paper, design of a triple band ultrathin compact polarization insensitive metamaterial absorber for S-, C- and X-band applications is proposed. The proposed absorber consists of periodic arrangement of a modified triple circular slot ring resonator as unit cell printed on the top of a continuous metal backed FR-4 dielectric substrate. The proposed absorber is ultrathin having thickness of λ₀/135.66 at the lowest absorption center frequency. The measured wide stable absorption bands of 0.40 GHz, 0.45 GHz and 0.47 GHz with absorption peaks of 97%, 96.45% and 98.20% at absorption center frequencies of 2.90 GHz, 4.18 GHz and 9.25 GHz respectively are observed. The temperature profile of absorber is measured by using lock in infrared thermography, and a temperature increase of 1°C at absorbing frequency as compared to non-absorbing frequency is observed. The absorber is demonstrated to be polarization insensitive to TE and TM polarized angles of incidence of electromagnetic wave with wide angular stability up to 45°. The absorber is fabricated and tested in an anechoic chamber. Experimental results agree well with measured ones.

This paper studies distribution characteristics of paraxial magnetic field of solenoid with inner relaxation polarization medium and driven by ac signal. Firstly, the paraxial electromagnetic field model of hollow solenoid was constructed by Maxwell equations, and the influence of the driving signal frequency was analyzed. Then, based on the established paraxial electromagnetic field model of hollow solenoid, the magnetic field model of solenoid with inner relaxation polarization medium was established by ampere loop law. Finally, the effects of relaxation polarization medium and driving signal frequency on magnetic field amplitude and phase shift were analyzed in detail. The conclusions were drawn as follows: driving signal frequency affects magnetic field amplitude; the relaxation polarization medium will cause the phase shift of magnetic field; and the phase shift will increase as the driving signal frequency increases.

In this paper, a new compact microstrip low-pass filter (LPF) with ultra-wide stopband characteristics is presented. The combinations of DGS-DMS along with quasi octagonal resonators are employed in the design of the proposed filter to achieve compact size and ultra-wide stopband suppression level. The proposed filter has been designed, simulated, optimized and tested. The design procedure is validated using the commercial full-wave EM MoM simulator Microwave Office. Simulated as well as measured results of low-pass filter exhibit sharp roll-off (ξ) of 19 dB/GHz and creating transmission zero at around 7.8 GHz with attenuation level -54 dB. The measurement results show good agreement with the simulations. The cutoff frequency of the proposed low-pass filter is 2.4 GHz with the insertion loss less than 0.3 dB. The ultra wide stop band with over 20 dB attenuation extended from 3.42 GHz to 12 GHz. The spurious passband suppression up to six harmonics (5fc) is achieved for the proposed design. The addition of two parasitics DGS elements in the ground plane leads to suppression of the undesired harmonics and thus to improve the stopband. The size of the whole structure is less as (0.44λ_gx0.26λ_g) with λ_g = 68 mm. The proposed filter is useful for microwave L band, GPS system, and RADAR applications.

This paper presents an exact expression for the mutual impedance of two coaxial loops located on the surface of a conductive ground. The semi-infinite complete integral representation for the impedance is first converted into a finite integral. Then the spherical Hankel function contained in the integrand is expanded according to Gegenbauer addition theorem. This makes it possible to perform analytical integration and express the mutual impedance as a sum of products of spherical Bessel functions. Since no simplifying assumption is introduced in the mathematical derivation, the obtained formula is valid in quasi-static as well as non-quasi-static frequency ranges. Numerical examples show how, accuracy being equal, the proposed expression is less computationally expensive than standard Gauss-Kronrod numerical integration technique.

In this work, we propose a compact CMOS power amplifier using a differentially coupled series inductor for motion detection radar applications. The proposed switching-mode power amplifier is designed with a cascode and differential structure. To realize a compact size matching network, a differentially coupled series inductor is used in the input matching network. In the proposed power amplifier, two typical spiral series inductors for the input matching network are replaced with a single differentially coupled series inductor. As a result, the used chip area of the differentially coupled series inductor is smaller than half that of a typical inductor for the given inductances of each inductor. Additionally, to obtain a high gain characteristic, we adapt modified mode-locking techniques for the power stage of the power amplifier. To verify the feasibility of the power amplifier, we design a 9.5-GHz power amplifier with a 130-nm RFCMOS process. We obtain saturation power of 15 dBm while the power-added efficiency is approximately 28%.