This paper presents a new approach to calculate the accurate fourth-order Doppler parameters for Geosynchronous Synthetic Aperture Radar (Geo-SAR). To get exact calculation results, the Earth is modeled as an ellipsoid and the relative motion between the sensor in an elliptical orbit and the rotating Earth is analyzed. The J₂, J₃ and J₄ orbital perturbation items and attitude steering are analyzed. Ignoring the perturbation force would produce errors of the Doppler parameters for spaceborne SAR because it can influence the six orbital elements. Since the Doppler parameters are related to the antenna beam pointing directions and influenced by attitude of SAR platform, the calculation results before and after attitude steering are shown. Furthermore, the Doppler parameter properties during the whole orbital periods of Geo-SAR are compared with those of Low-Earth-Orbital SAR (Leo-SAR). Finally, the effects on Doppler parameters stemmed from the radar beam pointing accuracy are analyzed.

Based on the observation that sparsity assumption is well satisfied in the synthetic aperture radar (SAR) imaging applications, there is increasing interest in utilizing compressive sensing (CS) in SAR imaging. However, there are still several problems which should be concerned in CS-based imaging approaches. Firstly, inevitable noise and clutter challenge the performance of CS algorithms. Secondly, the super-resolving ability of CS algorithms is not sufficiently exploited in most cases. Thirdly, nonideal characteristics of mutual coherence affect the performance of CS algorithms in complex scenes. In this paper, a novel CS imaging framework is proposed for the purpose of improving the imaging performance of stepped frequency SAR. Meanwhile, a super-resolving imaging algorithm is proposed based on the nonquadratic optimization technique. Simulated and rail SAR measured data are applied to demonstrate the effectiveness of the novel framework with the proposed super-resolving algorithm. Experimental results validate the superiority of this method over previous approaches in terms of robustness in low SNR, better super-resolving ability and improved imaging performance in complex scenes.

Linear array synthetic aperture radar (LASAR) is a promising radar 3-D imaging technique. In this paper, we address the problem of sparse recovery of LASAR image from under-sampled and phase errors interrupted echo data. It is shown that the unknown LASAR image and the nuisance phase errors can be constructed as a bilinear measurement model, and then the under-sampled LASAR imaging with phase errors can be mathematically transferred into sparse signal recovery by solving an ill-conditioned constant modulus linear program (ICCMLP) problem. Exploiting the prior sparse spatial feature of the observed targets, a new super-resolution sparse autofocus recovery algorithm is proposed for under-sampled LASAR 3-D imaging. The algorithm is an iterative minimize estimation procedure, wherein it converts the ICCMLP into two independent convex optimal problems, and joints l₁-norm reweights least square regularization and semi-definite relax to find the optimal solutions. Simulated and experimental results confirm that the proposed method outperforms the classical autofocus techniques in under-sampled LASAR imaging.

This paper presents that the extra passband with two transmission zeros can be obtained by adding shunt open stubs to the asymmetric half-wavelength resonators structure. By using this method, a fourth or even higher passband with good selectivity and compact size can be obtained. Dual-band, tri-band and quad-band bandpass filters are demonstrated by using this method. The measured bandwidth is 80/180 MHz for the dual-band, 60/180/180 MHz for the tri-band and 130/360/170/70MHz for the quad-band filter, respectively. The measured insertion loss for the dual-band, tri-band and quad-band filter is less than 2.7 dB, 2.5 dB and 2.9 dB at the center frequency. All the simulated results and the measured results agree well.

Cognitive radio technology proposes the utilisation of under-utilised spectrum resources which may include time, frequency, geographical location, direction, polarisation et cetera. Frequency is the conventional spectrum resource, considered to be exploited for cognitive radio, especially in the field of antenna design. We address the unconventional directional resource for cognitive radio, from antenna design perspective. The design concept of a multi-band compact array, capable of providing separate and simultaneous access to frequency and directional resources, is presented. The initial explorations are carried out for three frequency resources (bands) and three directional resources, providing nine degrees-of-freedom altogether. Laboratory version of the proposed antenna system is then used to gain proof-of-principle through line-of-sight measurements in an over-the-air test-bed, followed by static outdoor measurements in a multipath scenario. At the end, simulations are performed for arbitrary arrays in heterogeneous propagation scenarios to study the influence of antenna radiation pattern on the availability of directional opportunity. Recommendations are made for possible antenna design based on the simulation results.

A design and analysis of a novel proximity-fed printed slot antenna with 3.5/5.5 GHz dual band-notched characteristics are presented. To obtain an ultra-wideband (UWB) response, a circular patch with a rectangular conjunction arm is etched concentrically inside a ground plane aperture. The antenna is proximity-fed by a microstrip line with an open shunt stub on the other side of the substrate. The designed antenna satisfies a -10 dB return loss requirement in the frequency band from 2.7 to 17 GHz. In order to obtain dual band-notched properties at 3.5 and 5.5 GHz, an open ring slot is etched off the circular patch and a π-shaped slot is etched off the microstrip feeding line, respectively. A curve fitting formulation is obtained to describe the influences of the notched resonators on the corresponding notched frequencies. The proposed antenna is designed, simulated and fabricated. The measured data show a good agreement with the simulated results and the equivalent circuit results through the use of a modified Vector Fitting technique for a rational function approximation. The proposed antenna provides almost omnidirectional radiation patterns, relatively flat gain and high radiation efficiency over the entire UWB frequency excluding the two rejected bands.

This paper introduces a method for canceling the parasitic capacitance of integrated common mode (CM) filter by optimizing the layout of ground winding. Firstly, the CM filter with positive or negative coupling between the ground and inductor winding is researched, respectively. Then, the two coupling polarizes are combined to form the bi-directional coupling, simulation and measured results show bi-directional coupling ground can effectively improve the high frequency (HF) filtering performance. The equivalent circuits are given to demonstrate the cancellation mechanism, and modelling is derived for the design of ground winding. To further validate the application of proposed technique, CM noise and input/output signals for PFC (Power Factor Correction) converter with bi-directional coupling ground CM filter is simulated. The noise spectrums show conductive interference at high frequencies is effectively suppressed and meets the required electromagnetic interference (EMI) standard.

In recent years, active Radio Frequency Identification (RFID) tags have crossed into ultra low power domain. With obvious advantages over passive tags, a setback for active tag growth is the need for battery replacement and limited operational life. Battery life could be extended by scavenging surrounding Wi-Fi signals using rectenna architecture which consists of a receiving antenna attached to a rectifying circuit. A seven stage Cockroft-Walton voltage multiplier optimized for low input power (below 0 dBm) is proposed. Prototype was fabricated on RT/Duroid 5880 (RO5880) printed circuit board (PCB) substrate with dielectric constant and loss tangent of 2.2 and 0.0009 respectively. Experimental results show that 2 V output voltage can be harvested from an operating frequency of 2.48 GHz with -9 dBm (0.13 mW) sensitivity with 1.57 mm board thickness.

A rectangular slot antenna for UWB applications is proposed in this paper. The slot is designed in stepped configuration and is excited by an L-shaped microstrip line flared at the end. The measured impedance bandwidth (-10 dB) from 3 GHz to 27 GHz is achieved. The radiation patterns are bidirectional in the E plane and omnidirectional in the H plane with the measured peak gain around 5 dBi throughout the band. The experimental results are in good agreement with the simulated results. A detail parametric study is done for the flare angle and the flare width to axis ratio and their effect on the impedance bandwidth and the reflection coefficient is described.

This paper addresses the problem of direction-of-arrival (DOA) estimation of correlated and coherent signals, and two sparsity-inducing methods are proposed. In the first method named L1-EVD, the signal-subspace eigenvectors are represented jointly with well-chosen hard thresholds attached to the representation residue of each eigenvector. Then only the eigenvector corresponding to the largest eigenvalue is reserved for DOA estimation via sparse representation, which aims at highly correlated signals, and a method named L1-TEVD (TEVD: Truncated EVD) is proposed. Simulation results show that, L1-EVD and L1-TEVD both surpass L1-SVD in DOA estimation performance and computation efficiency for highly correlated and coherent signals.

A new balanced dual-band bandpass filter with strong commonmode rejection is presented in this paper. Common-mode rejection is provided by a section of a periodic microstrip differential line that behaves as a low-pass filter under common-mode operation. In contrast, the differential line exhibits very good all-pass behavior under differential mode operation. This structure is combined with a differential dual-band bandpass filter based on embedded resonators. Simulations and experiments confirm that the combined structure has good common-mode rejection within the passbands of the dual-band differential filter.

A new circuit and technique to extend bandwidth performance while preserving improvement on efficiency performance over the one attainable by conventional distributed amplifier (DA) is presented. The theoretical analysis is described in detail, and a test vehicle is realized to demonstrate the effectiveness of the proposed method. Output power of ~29 dBm, gain of 10 dB, covering a bandwidth from 100 to 800 MHz, PAE of 20-45% is experimentally demonstrated. The result is compared with measured result of conventional DA, a significant improvement of bandwidth and efficiency are achieved.

This paper presents a technique for the efficient and accurate determination of resonant frequencies and quality factors of Substrate Integrated Waveguide (SIW) resonators. To consider resonators of a general shape the SIW structure is modelled as a parallel plate waveguide populated with metalized via holes. The field into the SIW cavity is found solving the scattering problem for the set of vias into the parallel plate. Resonances are determined searching for the complex frequencies for which the determinant of the system of equations pertinent to the scattering is zero. To speed up the search, a first guess for the resonance frequency is found using an estimate of the minimum singular value of the system of equations. A Muller search in the complex plane is later used to accurately determine both frequencies and quality factors. Results relevant to resonators of various shapes are presented and compared with results obtained with a commercial code.

Based on the scattering theory and the Green function method, a dynamical theory is given for calculating the diffraction of deeply-etched gratings with a stratified structure substrate. The key of our method is that the patterned grating structure is considered as a perturbation to the unpatterned stratified structure rather than to vacuum. Using the first-order Born approximation and in the Fresnel diffraction region, we obtain a simple analytical expression, which can be used to calculating the scattering intensity of deeply-etched circular binary Fresnel zone plates with a stratified substrate (MDECBFZPs). The numerical results show that the focusing intensity at the foci of the MDCBFZP changes periodically with the etching depth and the thickness of the substrate film. Our results are in good agreement with FDTD simulations.

The analysis of an end-launcher type transition from coaxial to WR90 waveguides is presented. This transition is tuned to have the highest performance at the radar frequency of 9.375 GHz. The characteristics of the transducer are investigated comparatively in 30 cm aluminum and carbon fiber reinforced polymer waveguides. The advantage of the proposed feed is that it does not require grounding to the broad wall of the waveguide compared to the traditional end-launcher loop feeds. This departure from the current loop feeds makes the proposed feed suitable for carbon fiber reinforced polymer waveguides where a disruption in the broad wall would be undesirable.

This paper presents a multilevel Model Order Reduction technique for a 3-D electromagnetic Finite Element Method analysis. The reduction process is carried out in a hierarchical way and involves several steps which are repeated at each level. This approach brings about versatility and allows one to efficiently analyze complex electromagnetic structures. In the proposed multilevel reduction the entire computational domain is covered with macro-elements which are subsequently nested, in such a way that size of the problem which has to be reduced at each level is relatively small. In order to increase the speed of the reduction at each level, the electric field at the macro-elements' boundaries is projected onto the subspace spanned by Legendre polynomials and trigonometric functions. The results of the numerical experiments confirm the validity and efficiency of the presented approach.

This paper deals with the problem of constant false alarm rate (CFAR) target detection in high-resolution ground synthetic aperture radar (SAR) images based on KK distribution. For the parameter estimation of KK distribution, the semi-experiential algorithm is analyzed firstly. Then a new estimation algorithm based on the particle swarm optimization (PSO) is proposed, which takes the discrepancies between the histogram of the clutter data and probability density function (PDF) of KK distribution at some selected points as the cost function to search for the optimal parameter values using PSO algorithm. The performance of the two algorithms is compared using Monte-Carlo simulation using the simulated data sets generated under different conditions; and the estimation results validate the better performance of the new algorithm. Then the KK distribution, which is proposed for spiky sea clutter originally, is applied to model the real ground SAR clutter data. The goodness-of-fit test clearly show that the KK distribution is able to model the ground SAR clutter much better than some common used model, such as standard K-distribution and Gamma, etc. On this basis, a global CFAR target detection algorithm is presented. The detection threshold is calculated numerically through the cumulative density function (CDF) of KK distribution. Comparing the amplitude of every SAR image pixel with this threshold, the potential targets in ground SAR images can be located effectively. Then target clustering is implemented to eliminate the false alarm and obtain more accurate target regions. The detection results of the proposed algorithm in a typical ground SAR image show that it has better performance than the detector based on G⁰ distribution.

To analyze and to handle the radio frequency immunity of microcontrollers requires understanding the origins of the complex frequency response of the immunity. This paper assumes that the frequency response of the immunity can be characterized with a set of fingerprint features in the immunity curves. Positions and shapes of those fingerprint features are determined by certain components in the disturbance propagation network. In order to prove that assumption, a series of models are created and simulated. The roles of various model components on the immunity are analyzed by comparing the simulation results from different model structures. The fingerprint features on the immunity curves are identified. The paper shows how to treat a wide-range immunity curve with separated features. It also shows the responsible model components for those separated features. With the awareness of those features and their origins, researchers can concentrate on extracting the models of the most important components in the disturbance propagation network when modeling the immunity of the complex integrated circuits like microcontrollers.

This paper presents a novel artificial neural network (ANN) model estimating vehicle-level radiated magnetic emissions of an electric car as a function of the corresponding driving pattern. Real world electromagnetic interference (EMI) experiments have been realized in a semi-anechoic chamber using Renault Twizy. Time-domain electromagnetic interference (TDEMI) measurement techniques have been employed to record the radiated disturbances in the 150 kHz-30 MHz range. Interesting emissions have been found in the range 150 kHz-3.8 MHz approximately. The instantaneous vehicle speed and acceleration have been chosen to represent the vehicle operational modes. A comparative study of the prediction performance between different static and dynamic neural networks has been done. Results showed that a Multilayer Perceptron (MLP) model trained with extreme learning machines (ELM) has achieved the best prediction results. The proposed model has been used to estimate the radiated magnetic field levels of an urban trip carried out with a Think City electric car.

We analyze the performance of finite-difference time-domain (FDTD) method implementations for 2D and 3D problems. Implementations in Fortran, C and C++ (with Blitz++ library) languages and performance tests on several hardware setups (AMD, Intel i5, Intel Xeon) are considered. The performance of implementations using traditional FDTD algorithm for the largest size of test problem is limited by the bandwidth of computer random-accessed memory (RAM). Our implementations are compared with a commercial simulation software package Lumerical FDTD Solutions and an open source project Meep.