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%.

This paper presents the design of a continuous polyharmonic-tuned mode (CPHTM) power amplifier (PA) with an introduced optimal knee voltage waveform control parameter in a continuous harmonic-tuned voltage waveform equation. The optimal knee voltage waveform control parameter works in unison with derived equations, providing bandwidth and efficiency potentials over the limiting factors of the conventional harmonic-tuned power amplifiers (PAs). The effectiveness of the design strategy is proven by the realisation of a CPHTM type-I (CPHTMT-I) PA as compared with a non-continuous polyharmonic-tuned mode type-II (NCPHTMT-II) PA. Test results with continuous-wave (CW) signals show drain efficiency (DE) levels within 53.6%-79% (1.31-2.39 GHz) with 58.4% fractional bandwidth for CPHTMT-I and 64%-78% (1.65-1.95 GHz) with 16.7% fractional bandwidth for NCPHTMT-II. The CW result evidently shows the validation and efficacy of the proposed theory.

Crosstalk is one of the bottlenecks in improving the speed and density of high-speed interconnection systems. In this paper, multi-way and 2-level transmission is changed to one-way and multi-level transmission. Under the condition to maintain the data transmission capacity of the system, the number of microstrip lines is reduced, and the distance between microstrip lines is increased to reduce crosstalk. The simulation results show that over 50% of crosstalk is suppressed in multilevel signal transmission systems.

In this paper a novel robust beamforming method is devised to receive multipath signals effectively. The new algorithm constructs a transformation matrix derived through high-order angle constraint to suppress the interferences with the directions of arrival (DOA) of interference signals. Using the transformed data, the composite steering vector of the multipath signals is estimated as the principal eigenvector of the signal subspace, and then it is utilized in minimum variance distortionless response (MVDR) beamforming to compute the optimal weight vector. The new method is improved in robustness to DOA error by forming wide nulls in incident directions of the interferences, and keeps effective in the presence of coherent interferences. Simulations analyses are provided to illustrate the robustness and effectiveness of the new beamformer.

Jamming and anti-jamming techniques for global position systems (GPS) play important roles in electronic countermeasure. Least mean square (LMS)-based anti-jamming algorithm is widely used in GPS receivers, since it can avoid matrix inversion and has low complexity. For convenience, we call them LMS-GPS receivers. To improve the anti-jamming performance of the LMS-GPS receivers, it is very meaningful to study the jamming technique. Considering that existing jamming signals are easily suppressed by LMS-GPS receivers, a new jamming method named as optimal power difference jamming is proposed in this paper to improve the jamming effect further. Specifically, the analytical relationship between jamming-to-signal ratio (JSR) and the power difference of two interference signals is firstly given. Then, the conclusion that there is always an optimal power difference where the JSR can take the extreme value is drawn. Finally, the optimal power difference is derived as about 22 dB for single-tone interference and 29 dB for band-limited Gaussian noise interference. Simulation results show that the proposed method with optimal power difference is able to improve the JSR remarkably.

A multifunction antenna system providing a radar function and a communication function simultaneously is proposed. The system is composed of a horn antenna whose feeding waveguide is loaded with slots. The horn radiation is used for the main radar function. The slotted waveguide radiation is controlled independently from the horn radiation to perform a direct binary phase shift keying (BPSK) communication provided that each radiating slot is equipped with a simple switching mechanism. Then, the antenna system provides two different functions using orthogonal polarizations and directions. Measured results show 9.1 dB and 32 dB isolation between the two functions at the working frequency. In addition, the proposed system can be integrated with the existing radars which use horns by replacing only the feeding waveguide.

A compact microstrip diplexer based on dual closed loop stepped impedance resonator (DCLSIR) is proposed. The proposed microstrip diplexer is composed of the combination of two DCLSIR bandpass filters (BPFs), which are designed for X-band application. For the demonstration, a dual-channel diplexer has been designed and fabricated using microstrip and printed circuit board (PCB) technologies, respectively. The fabricated diplexer operating at 8.3/10 GHz for X-band application has compact size (15.17 mm x 2.69 mm). The measured results are in good agreement with the full-wave simulation results. Good isolation between two channels is achieved.

A CPW-fed ultra-wideband (UWB) monopole antenna design which exhibits triple band stop functions is demonstrated. The proposed antenna comprises a Split Ring Resonator (SRR) and inverted U slots on a metallic patch to exhibit triple band-notch functions for WiMAX (3.3-3.6 GHz), C-band (3.8-4.2 GHz) and WLAN (5.1-5.8 GHz) bands. The slot width optimization is examined to tune the band-notch resonance frequency, and their effects are exhibited by surface current distributions. The antenna has compact size of 26*30 mm², and it functions over 3 to 11 GHz with VSWR < 2 except notched bands. The SRR loaded dual band-notched antenna and amended inverted U slot integrated antenna both are fabricated and their VSWR, radiation characteristics measured. The antenna demonstrates excellent agreement between measured and calculated results.