The dynamics of a system of two bilaterally coupled chaotically oscillating X-band Gunn oscillators (GOs) has been studied by numerical simulation and by hardware experiment. The effect of variation of the coupling strengths between two oscillators in two paths has been explored. The chaotic oscillations in two GOs have become synchronized in most of the cases when coupling factors (CFs) are around 20% or more. However, the transformation of chaotic states of the GOs to quasi-periodic ones has been observed for some values of CFs. A detailed numerical analysis on the instantaneous error parameters of the GO state variables is presented to identify different steady state dynamical conditions of the system. Experimental observations of the GO output frequency power spectra and the averaged product of the two GO outputs in the coupled mode confirm the occurrence of synchronization as well as quenching of chaotic oscillations for different values of CFs.

Features of the spatial power spectrum (SPS) of multiple scattered ordinary and extraordinary waves in randomly inhomogeneous magnetized plasma are investigated using the smooth perturbation method taking into account diffraction effects. Second order statistical moments are derived for arbitrary correlation function of electron density fluctuations at oblique illumination of magnetized plasma by mono-directed incident radiation. Numerical calculations have been carried out for anisotropic Gaussian correlation function taking into account anisotropy factor and angle of inclination of prolate irregularities with respect to the external magnetic field. It was shown that SPS has a double-peaked shape. External magnetic field narrows SPS for ordinary wave and the gap arises in the direction of prolate irregularities. For extraordinary wave the gap increases with a distance passing by the wave in anisotropic magnetized plasma, the width broadens and maximum slightly displaced.

This paper presents a low voltage wideband down-conversion mixer using current-mode approach for multi-standard receivers. The proposed mixer uses a current mirror amplifier with an embedded passive switching core to achieve mixing function, which can combine the advantages of active and passive mixers simultaneously. The mixer is implemented using a 0.18 μm CMOS technology and covers frequency band from 0.5 GHz to 4.0 GHz. A comparison with conventional CMOS down-conversion mixer shows that this current-mode mixer has advantages of large conversion gain, low noise figure and high linearity. Over the entire bandwidth, the mixer features a conversion gain of 8.0~8.7 dB, a double-sideband (DSB) noise figure of 6.7~9.1 dB and an input third-order intercept point (IIP3) of 1.5~5.2 dBm, while consuming 8 mA from a 1.2 V supply voltage. The mixer occupies the active area of 0.43×0.46 mm² including testing pads.

We have applied the phase unwrapping technique to resolve the phase ambiguity problem arising from complex expressions of scattering parameters, for reflection-only measurement configurations, since, at some instances, only one side of the sample under test is accessible for electromagnetic measurements. We considered two different measurement configurations for testing the applicability of the phase unwrapping technique as: 1) two identical samples with different lengths flushed by a short-circuit termination and 2) one sample shorted by a varying short-circuit termination. For each measurement configuration, the underlying expressions for the reflection scattering parameters are derived. For both cases, we evaluated the suitability of the phase unwrapping technique by considering a highly-dispersive medium (distilled water) as our test sample. We note that continuity of the real part of the complex wavelength is a key issue in the unwrapping technique for (one-port) reflection-only measurements.

The multimode beam wave interaction behavior in a tapered, cylindrical cavity RF interaction structure of a 42 GHz gyrotron operating in the TE₀₃ mode has been investigated through nonlinear analysis and PIC simulation. A technique for producing the annular gyrating electron beam in PIC simulation code CST Particle Studio has been described. An energy transfer phenomenon from electron beam to RF has been demonstrated. The performance of cavity has been monitored to ensure the device operation in the desired mode and frequency. In the PIC simulation, the effect of beam velocity spread on the power output has been discussed. Using multimode behaviour, the effect of presence of nearby modes on the cavity performance has been observed. The simulation results have been compared with the results obtained from self-consistent single-mode analysis and time-dependent multimode analysis. It has been found that output power is well above the desired 200 kW level for the designed 42 GHz gyrotron operating in TE₀₃ mode.

Electromagnetic (EM) scattering properties from the ship wakes on the two-dimensional (2-D) perfect electric conductor (PEC) sea surfaces are studied by utilizing the small-slope approximation (SSA) theory. Considering the limitations of using the ideal plane EM wave incident upon a rough sea surface of the limited size, the expressions of the scattered field and scattering amplitude are derived by utilizing the modified tapered incident field. Based on a simplified segmented ocean spectrum model, the bistatic and monostatic normalized radar cross sections (NRCS) from the PEC sea surfaces with and without ship wakes are calculated, respectively. Meanwhile, the variation of scattering coefficient as scattering angles is given and compared under different polarization states. The results show that the scattering from the PEC sea surfaces with ship wakes is evidently different from that without them in bistatic and monostatic scattering. This provides a basis to extract ship wake characteristics. Also it shows that the SSA is a very effective analysis method to deal with the EM scattering from the rough sea surface. Finally, the effect of different tapered factors on backscattering coefficient is discussed, and it is concluded that an artificial reflection from the boundaries and a scattering upwarping from low-grazing incidence can be avoided just when the tapered factor is relatively smaller. This gives the theoretical basis for the analysis of EM scattering characteristics of ship wakes on the PEC sea surface.

This paper gives an overview of various electric machines for application to renewable energy harvesting, and reveals the corresponding challenges and research opportunities. After introducing various renewable energies and electric machines, the concept of renewable energy machines is coined. Then, the existing machines, including the DC, induction and synchronous types, for renewable energy harvesting are challenged. Consequently, research opportunities of advanced machines, including the stator-permanent magnet (PM), direct-drive PM and magnetless types, are elaborated. Finally, both near-term and long-term renewable energy machines are identified especially the emerging stator-PM, vernier PM and stator doubly fed doubly salient types.

An alternative approach for robust electromagnetic pulse (EMP) protection circuit was proposed by using a parallel coupled band-pass filter (BPF) with high thermal conductivity AlN substrate in between with a traditional gas discharge tube (GDT) and fast response metal oxide varistor (MOV). This proposed configuration can suppress slow as well as fast voltage surges. The fabricated BPF with a center frequency of 2.5 GHz on the high thermal conductive (180~200 W/m·K) AlN substrate could efficiently suppress high power over voltage surge. Through the purposed cascade protection configuration, it is observed that 6KV ESD fast introduced pulse (5 ns/50 ns) and 4 KV lightning surge pulse(1 us/50 us) were attenuated to 511V and 396 V, respectively, and that is capable to be applied to an EMP protection circuit in the front end of a linear amplifier applications.

A broadband circularly polarized patch antenna with high gain and wide axial ratio beamwidths is proposed for ultra-high-frequency (UHF) RF identification (RFID) applications in this paper. The antenna is composed of a square patch, a feed network printed on the bottom side of the substrates and an antenna radome. The CP radiation of the proposed antenna is excited by four cylinder probes which transmit four signals that have equal amplitude with quadrature phase difference (0˚, 90˚, 180˚, and 270˚) generated from the feed network. To obtain an optimum peak gain and a broad CP bandwidth, 100 Ω isolation resistor is omitted in the feed network for obtaining high radiation efficiency, and the effects of varying the feed positions and dimensions of the various parameters on the antenna performances are respectively investigated. Simulation results are compared with the measurements, and a good agreement is obtained. The measured results show that the proposed antenna can provide broad impendence bandwidth of 19.7% (815-993 MHz) (reflection coefficient less than -15 dB), a maximum gain of 9.65 dBi, and a 3-dB axial ratio (AR) bandwidth of about 11% (860-960 MHz). The results indicate that the proposed antenna is an excellent candidate for UHF RFID reader system. At last, read performance of the proposed antenna array in RFID systems is presented, which verify the superior features of the proposed antenna in practical RFID system applications.

The comparative evaluation based on the power speed density of several types of portable Permanent Magnet Generator (PMG) considered for agricultural applications is presented. These generators are purposely designed to be used in agriculture sectors and thereby it should be of lightweight, small in size and ease to use. Six different generator topologies are developed for investigation of such purposes. A number of design parameters are considered to analyze the performance characteristics for each type of developed PMG. Based on the power speed density factor that is used to describe better generator performance, the suitable PMG for the agricultural application is identified through a comprehensive evaluation.

The scattering of electromagnetic spherical wave by a perfectly conducting circular disk is studied by using the method of Kobayashi Potential (abbreviated as KP method). The formulation of the problem yields the dual integral equations (DIE). The spherical wave is produced by an arbitrarily oriented dipole. The unknowns are the induced surface current (or magnetic field) and the tangential components of the electric field on the disk. The solution for the surface current is expanded in terms of a set of functions which satisfy one of a pair (equations for the magnetic field) of Maxwell equations and the required edge condition on the surface of the disk. At this stage we have used the vector Hankel transform. Applying the projection solves the rest of the pair of equations. Thus the problem reduces to the matrix equations for the expansion coefficients. The matrix elements are given in terms of the infinite integrals with a single variable and these may be transformed into infinite series that are convenient for numerical computation. The far field patterns of the scattered wave are computed and compared with those computed based on the physical optics approximation. The agreement between them is fairly good.

General side-looking synthetic aperture radar (SAR) cannot obtain scattering information about the observed scenes which are constrained by lay over and shading effects. Downward-looking sparse linear array three-dimensional SAR (DLSLA 3D SAR) can be placed on small and mobile platform, allows for the acquisition of full 3D microwave images and overcomes the restrictions of shading and lay over effects in side-looking SAR. DLSLA 3D SAR can be developed for various applications, such as city planning, environmental monitoring, Digital Elevation Model (DEM) generation, disaster relief, surveillance and reconnaissance, etc. In this paper, we give the imaging geometry and dechirp echo signal model of DLSLA 3D SAR. The sparse linear array is composed of multiple transmitting and receiving array elements placed sparsely along cross-track dimension. The radar works on time-divided transmitting-receiving mode. Particularly, the platform motion impact on the echo signal during the time-divided transmitting-receiving procedure is considered. Then we analyse the wave propagation, along-track and cross-track dimensional echo signal bandwidth before and after dechrip processing. In the following we extend the projection-slice theorem which is widely used in computerized axial tomography (CAT) to DLSLA 3D SAR imaging. In consideration of the flying platform motion compensation during time-divided transmitting-receiving procedure and parallel implementation on multi-core CPU or Graphics processing units (GPU) processor, the convolution back-projection (CBP) imaging algorithm is proposed for DLSLA 3D SAR image reconstruction. At last, the focusing capabilities of our proposed imaging algorithm are investigated and verified by numerical simulations and theoretical analysis.

This paper presents the novel design of a wideband circularly polarized (CP) Radio Frequency Identification (RFID) reader microstrip patch antenna for worldwide Ultra High Frequency (UHF) band which covers 840-960 MHz. The proposed antenna, which consists of a microstrip patch with truncated corners and a cross slot, is placed on a foam substrate (ε_r = 1.06) above a ground plane and is fed through vias through ground plane holes that extend from the quadrature 3 dB branch line hybrid coupler placed below the ground plane. This helps to separate feed network radiation, from the patch antenna and keeping the CP purity. The prototype antenna was fabricated with a total size of 225 x 250 x 12.8 mm³ which shows a measured impedance matching band of 840-1150 MHz (31.2%) as well as measured rotating linear based circularly polarized radiation patterns. The simulated and measured 3 dB Axial Ratio (AR) bandwidth is better than 23% from 840--1050 MHz meeting and exceeding the target worldwide RFID UHF band.

In this paper, we examine the close relationship that exists between the phenomenon of electromagnetic (EM) wave tunneling through stacks of single-negative metamaterial slabs and classical microwave filter theory. In particular, we examine the propagation of EM waves through a generalized multi-layer structure composed of N ϵ-negative layers separated from each other by N-1 μ-negative layers, where N≥2 is a positive integer. We demonstrate that, if certain conditions are met, this multi-layer structure can act as a capacitively-coupled, coupled-resonator filter with an Nth-order bandpass response. Exploiting this relationship, we develop a generalized, analytical synthesis method that can be used to determine the physical parameters of this structure from its a priori known frequency response. We present several design examples in conjunction with numerical EM simulation results to demonstrate the validity of this analogy and examine the accuracy of the proposed synthesis procedure.

The aim of this study is to determine the effects of the thermal treatment with microwaves on the germination of wheat seeds, type Apache × Renan for different processing parameters. With the experimental data we intend to find out the optimum balance between applied energy and material humidity so that the material can be dried without its structure being adversely affected. From the analyze of experiments regarding wheat seeds drying with the aim of obtaining a quality product we mention that the best results are referring to the situation of using the microwave power of 0.3 W/g combined with hot air stream and having the measured temperature in the seed bed below the value of 75°C.

In this paper, we propose a new kind of broadband microwave gain equalizer in microstrip circuit. The equalizer uses open stepped impedance resonators (SIRs) to increase the adjust parameters so that the equation curve can be more flexible. Simplified topology of the gain equalizer is used to make the match net easier. The power distribute on each resistance is analyzed and the error analysis of the resistance values is done. Finally we design and manufacture a gain equalizer, and the measured results show that the equalization curve meets requirements well and proves that this structure is practical and effective.

This paper presents a novel contribution to the analysis of skin-effect like phenomena in radially inhomogeneous tubular geometries that fit in the category of Euler-Cauchy structures (ECS). The advantage of ECSs is that solutions for the electromagnetic field can be described by very simple closed form formulae. This work addresses the evaluation of the per unit length complex magnetic reluctance of tubular ferrites, taking into account that their complex permeability strongly depends on the frequency. The motivation for this research is linked up with the nascent theory of magnetic transmission lines (MGTL), where the wave guiding structure is made of a pair of parallel ferrimagnetic pieces, and whose performance is critically dependent on the complex magnetic reluctance of its component pieces. The analysis presented is mainly focused on high frequency regimes up into the GHz range.

The reflection, transmission spectra and the polarization transformation of linearly polarized waves in the ferrite-semiconductor multilayer structure are considered. In the long-wavelength limit, the effective medium theory is applied to describe the studied structure as a uniaxial anisotropic homogeneous medium defined by the effective permittivity and effective permeability tensors. The investigations are carried out in the frequency band where the real parts of the diagonal elements of both the effective permittivity and permeability tensors are close to zero. In this frequency band the studied structure is referred to a gyrotropic-nihility medium. An enhancement of polarization rotation, impedance matching, backward propagation are revealed.

In this paper, a novel G-shaped defected microstrip structure (DMS) is presented. Compared with the conventional DMS, the proposed G-shaped DMS exhibits lower resonant frequency and wider stopband. A lowpass filter with 3 dB cutoff frequency at 3.17 GHz using four pairs of parallel cascaded G-shaped DMS units is designed and fabricated. The measured results show that the transition band is only 0.09 GHz and the stopband over 25 dB attenuation covers 3.4 GHz to 10 GHz.The measured and simulated results are in good agreement.

A fast method for circular SAR three-dimensional imaging system by near-field elevation scanning is proposed in this paper. It is based on cylindrical spectrum theory which exploits the Fourier decomposition of the targets distribution instead of point by point imaging in earlier works. The proposed method sets up the relationship between the target image and the scattering field in spatial frequency domain. This leads to overcome the problem of computational inefficiency which was observed previously in projection-slice theorem. The near-field scattering is firstly analyzed by relating the return signal to the near-field focus function. The near-field focus function is then transformed to spatial frequency domain and evaluated by the method of stationary phase. Finally, the imaging result is given by three-dimensional inverse Fourier transformation from spatial frequency domain of targets. The proposed method is validated by the simulation results of distributed targets. In addition, experimental validation was also achieved in microwave chamber at X-band with targets placed on the turntable.