The aim of this paper is to present a frequency domain method for synthetic aperture radar (SAR) imaging. By using two consecutive linear mappings along Doppler and frequency domains, an azimuth-dependent SAR transfer function has been discovered. Based on this new transfer function, the SAR image can be reconstructed by the proposed azimuth stacking algorithm. The new algorithm can form SAR image at each azimuth position without DFT wrap around errors. If Chirp z-transform (CZT) is applied to carry out the two consecutive mappings (since they are linear mappings), the proposed algorithm will not require interpolations and thus its reconstructed image would be free of truncation errors. The new algorithm has been validated using both simulated and experimental ultrawideband/widebeam (UWB/WB) SAR data.

We design, characterize, and analyze a new kind of metamaterial (MTM) absorber (MA) in different frequency regions for the solar cell applications. This MTM based structure is particularly presented in a range of the solar spectrum in order to utilize the solar energy effectively. The proposed MTM based solar cell provides perfect absorption for both infrared and visible frequency ranges and can be used for the realization of more efficient new solar cells. The structure is also tested in terms of the polarization angle independency. The suggested MA has a simple configuration which introduces flexibility to adjust its MTM properties to be used in solar cells and can easily be re-scaled for other frequency ranges. Our experimental results in microwave frequencies confirm the perfect absorption for the resonance frequency and agree with the simulation results. This means that the developed MA for solar cells will offer perfect absorption in infrared and even in visible frequencies.

This paper presents a unified analysis of the three-parameter aperture distributions for both sum and difference antenna patterns, suitable for communications or telemetry applications with either a stationary or tracking antenna, and with the parameters automatically determined by Particle-Swarm Optimization (PSO). These distributions can be created, for example, by reflector, phased array, or other antenna systems. The optimizations involve multiple objectives, for which Pareto efficiency concepts apply, and are accelerated by compact, analytical closed-form equations for key metrics of the distributions, including the far-field radiation pattern and detection slope of the difference pattern. The limiting cases of the threeparameter distributions are discussed and shown to generalize other distributions in the literature. A derivation of the generalized vector far fields provides the background for the distribution study and helps clarify the definition of cross-polarization in the far-field. Examples are given to show that the three-parameter (3P) distributions meet a range of system-level constraints for various applications, including a sidelobe mask for satellite ground stations and maximizing pointing error detection sensitivity while minimizing clutter from sidelobes for tracking applications. The equations for the relative angle sensitivity for the difference pattern are derived. A study of the sensitivity of the 3P parameter values is presented.

A new spiral antenna is proposed in this paper. The developed antenna has improved axial ratio (AR) and shorted arm length. The function of the new spiral is given. The developed spiral antenna combines the low frequency property of power spiral antenna and high frequency property of Archimedean spiral antenna. That is, the growth rate of radial distance at large winding angle is close to power spiral for improved AR in low frequencies, and the growth rate at small winding angle is close to Archimedean spiral for good AR in high frequencies. The results reveal that the developed spiral antenna has noticeable improved axial ratio at low frequencies compared with Archimedean spiral antenna, and the problem of axial ratio degradation of power spiral antenna was also solved. The arm length is shorted by 46.2% compared to conventional Archimedean spiral antenna, and 63.5% compared to power spiral antenna.

A polarimetric radar system measures the complete scattering matrix of a target in the backscattered field that includes magnitudes of linearly polarized scattering amplitudes and the co-polarised and cross-polarised phase angles. Apart from backscattering intensity, the co-polarization phase difference (CPD) calculated from polarimetric synthetic aperture radar (SAR) data produces important information about target physical, geometrical and dielectric properties. In the present work, the distribution of CPD in C-band polarimetric SAR data corresponding to major kharif and rabi crops (denoting the monsoon and the winter season) and other land cover features have been studied over Central State Farm, Hisar, Haryana. The probability density functions (PDF) of CPD have been compared with dominant scattering contributions from these targets as obtained from polarimetric target decompositions. The results show that crops and other land cover features show characteristic CPD distributions, which relates well with crop physical and geometrical properties. An intuition of the rate of growth and plant vigour is indicative from the temporal PDF pattern.

In this paper, a dual-band high-gain antenna based on the split ring resonators (SRRs) and corrugated plate is presented. By combining the SRRs and corrugated plate, the presented antenna resonating at different frequencies with high performance is easily achieved based on the superposition of the electric fields radiated by the SRRs and the grooves. Both the simulated and measured results show that the gain is improved by 6 dB at 12.7 GHz and 6.5 dB at 14.2 GHz respectively compared with the conventional flat antenna without grooves. Moreover, half-power beam width (HPBW) of E-plane is reduced by more than 100 degrees at 12.7 GHz and 14.2 GHz.

In this paper, a simulation of ground penetrating radar ``GPR'' system on lossy and dispersive soil is investigated. The capability of the GPR system to detect buried targets is examined by evaluating and comparing the electromagnetic coupling between the transmitting and receiving antennas in two cases: (i) when the system is placed over an empty ground and(ii) when it is placed over a ground inside which a practical target is buried at a proper depth. Simulation software based on the finite difference time domain ``XFDTD'' is used for the electromagnetic simulations. The results concerning the coupling between the transmitting and receiving antennas are presented considering various practical parameters such as the operating frequency, the electric properties of the ground soil and the buried target, and the location at which the receiving element is placed. It is shown that the target detectability is strongly dependent on all of the above parameters. Also, the capability of target shape extraction and recognition are demonstrated through polarimetric ground penetrating radar.

In this article, a compact tri-band microstrip bandpass filter (BPF) using asymmetric stepped-impedance resonators (SIRs) is proposed. Only one set of asymmetric SIRs are used in designing this filter to achieve triple passband response with high selectivity and band-to-band isolation level. By properly selecting the impedance and electrical length ratios of the asymmetric SIRs, the tri-band BPF is designed. By using a cross-coupled configuration and 0˚ feed structure, high selectivity frequency responses with six transmission zeros are achieved. The three bands of the proposed tri-band filter are located at 1.57/3.9/7 GHz, respectively, and the circuit size is much smaller in comparison with previous works using the same substrate. Measured results are in good agreement with electromagnetic (EM) simulation.

To study electromagnetic scattering from dielectric rough surfaces, a hybrid finite element method (FEM) combined with boundary integral equations (BIE) is extended to the scattering problem with two half-open regions. Integral boundaries, as truncated boundaries of the FEM region, are employed as artificial boundaries of dielectric rough surfaces above and below the rough surface. In the hybrid method, conformal integral boundaries are introduced to reduce the computational region. The validity of our hybrid method is examined by available solutions got from the method of moment (MoM), which indicates the feasibility of our scheme in simulating the scattering from dielectric rough surfaces. Bistatic scattering coefficient from dielectric rough surfaces is studied in this paper for both polarizations, and functional dependence upon different parameters are numerically discussed.

Azimuthal Surface Waves (ASWs) are electromagnetic waves of the surface type, which propagate across an external steady magnetic field in plasma filled metal waveguides. The interaction between extraordinary ASWs and an electron beam that rotates along Larmor orbits in the gap between the plasma column and the metal wall is studied here. The initial stage of the ASW excitation is studied analytically and numerically. Growth rates of the ASW beam instability are analyzed as functions of the parameters of the plasma filled waveguide immersed in a steady magnetic field with toroidal nonuniformity. This nonuniformity leads also to the appearance of corrections to the ASW eigen frequencies. It is shown that the beam-wave interaction in a toroidally nonuniform steady magnetic field is not weaker than in the case of a uniform magnetic field. However, in the studied case, the efficiency of the power transfer from the beam into the excited waves becomes restricted due to the electron drift in the nonuniform magnetic field.

In various technological and scientific applications, different types of coil systems are being used to produce uniform alternating magnetic field. The dimensions of these coil systems are considerably larger than the volume of interest. There is a necessity to reduce the dimension of the coil system without sacrificing the extent of uniformity of the magnetic field. This problem has a wide audience and still remains as a topic of contemporary research in the development of miniaturized devices especially for calorimetric measurements of nano-particles, cancer therapy, and detection of minute surface defects by eddy current probes, etc. In this paper we present how we can modify the shape of a miniature solenoid to produce uniform magnetic field. A Genetic algorithm has been implemented to get the optimum dimension of the miniature solenoid. Our distinct shape design has achieved 97% uniformity for a 60% volume of interest.

The space-variant motion errors are specic to different targets and proportional to the beamwidth of a synthetic aperture radar (SAR) system, which makes them very difficult to be compensated for a SAR system with wide beamwidth. In this paper, a motion compensation (MoCo) algorithm that exploits the features of the geometry of near-range SAR applications is proposed. By dividing the whole range swath into several octave sub-swaths, the effects of space variant motion errors can be greatly reduced, especially for targets at nearer range, with low computational load.

As an emerging technique with a promising application prospect, the device-free passive localization (DFPL) technique has drawn considerable research efforts due to its ability of realizing wireless localization without the need of carrying any device and participating actively in the localization process. Recent technological achievements of the DFPL technique have made it feasible to realize location estimation using the received signal strength (RSS) information of wireless links. However, one major disadvantage of the RSS-based DFPL technique is that the RSS measurement is too sensitive to noise and environmental variations, which incur the misjudgment of shadowed links and degradation of localization performance. Based on the natural sparsity of location finding in the spatial domain, this paper proposes an environmental-adaptive sparsity-based localization method for the DFPL problem in the existence of model mismatch. The novel feature of this method is to adjust both the overcomplete basis (a.k.a. dictionary) and the sparse solution using a dictionary learning (DL) technology based on the quadratic programming approach so that the location solution can better match the changes of the RSS measurements between the node pairs to the spatial location of the target. Moreover, we propose a modified re-weighting l1 norm minimization algorithm to improve reconstruction performance for sparse signals. The effectiveness of the proposed scheme is demonstrated by experimental results where the proposed algorithm yields substantial improvement for localization performance.

Based on the principle of discone antenna a new UWB monocone antenna is presented. Instead of using traditional cone geometry as a radiator for discone, planar vertical cross strips of aluminum are used as an antenna radiator. This results in wide impedance characteristic and miniaturization of antenna. The simulated model has broadband impedance bandwidth 18:11 form 550 MHz to 18 GHz with Omni directional radiation pattern. The two different antenna models are presented in this paper. Design software CST Microwave Studio, HFSS and Solid works are used for designing and parametric analysis of antenna. Size reduction up to 45 percent is achieved as compared to tradition discone antenna. The N type panel mount connector is used for antenna feeding. As a result of a low profile structure, antenna can be easily mounted for portable application. The antenna radiation pattern is measured in anechoic test chamber. The measured results of antenna are found to be in good agreement with simulation results. The features make the antenna highly suitable for UWB applications.

Quantum properties of a modified Caldirola-Kanai oscillator model for propagating electromagnetic fields in plasma medium are investigated using invariant operator method. As a modification, ordinary exponential function in the Hamiltonian is replaced with a modified exponential function, so-called the q-exponential function. The system described in terms of q-exponential function exhibits nonextensivity. Characteristics of the quantized fields, such as quantum electromagnetic energy, quadrature fluctuations, and uncertainty relations are analyzed in detail in the Fock state, regarding the q-exponential function. We confirmed, from their illustrations, that these quantities oscillate with time in some cases. It is shown from the expectation value of energy operator that quantum energy of radiation fields dissipates with time, like a classical energy, on account of the existence of non-negligible conductivity in media.

A mathematical model of a spherical antenna excited by a slot cut in an impedance endwall of a semi-infinite rectangular waveguide was built using a rigorous solution of the problem. Control of energy characteristics is accomplished by changing impedance distributed on the end-wall of the waveguide section. If the waveguide is excited by the wave H₁₀, the wavelength tuning reaches (30-35)%, i.e. about a half of the wavelength range of single mode waveguide regime.

In the ongoing search for new materials for microwave absorption applications, Carbon Nanotubes deserve a special consideration due to their outstanding properties. In this paper, microwave absorbing properties of epoxy resin based composites containing commercial MultiWalled Carbon Nanotubes used as fillers have been analyzed. The complex permittivity of the composites was measured in a wide frequency band (3-18 GHz). The absorbing properties of a single-layer absorber backed by a metallic plate considering several concentration of CNTs was simulated taking into account the measured permittivity.

Various interference sources either intentional or unintentional can mask the synthetic aperture radar (SAR) signals and cause image degradation. With a novel data acquisition mode, a new method based on dual-channel SAR is applied to suppress the interference. Using the received dual-channel data, the two-dimensional location of the interference source can be estimated and then the interference can be removed via a Two-Channel Cancelation method. By establishing a linear model of the interference-removed signal, the SAR image is reconstructed based on compressed sensing (CS) theory. Our method requires only a minor change to the traditional SAR system hardware while obtains a higher resolution. Simulation results are shown to demonstrate the validity of the proposed method.

In this paper, frequency-tunable microstrip antennas, for cognitive radio applications, are proposed. The approach is based on electrically tuning the antenna's operating frequency by integrating reconfigurable band pass filters into wideband antenna structures. The design of an open loop resonator (OLR)-based bandstop filter, and its transformation to a bandpass filter, are investigated first. Then, the incorporation of the bandpass filter, with a wideband antenna, is detailed. The same methodology is employed to design cognitive radio pattern and polarization diversity tunable filter-antennas. A good agreement between the simulated and measured results for the different fabricated prototypes is attained.

In this paper, we derive a new geometrical blind corner scattering model for vehicle-to-infrastructure (V2I) communications. The proposed model takes into account single-bounce and double-bounce scattering stemming from fixed scatterers located on both sides of a curved street. Starting from the geometrical blind corner model, the exact expression of the angle of departure (AOD) is derived. Based on this expression, the probability density function (PDF) of the AOD and the Doppler power spectrum are determined. Analytical expressions for the channel gain and the temporal autocorrelation function (ACF) are provided under non-line-of-sight (NLOS) conditions. Additionally, we investigate the impact of the position of transmitting vehicle relatively to the receiving road-side unit on the channel statistics. Moreover, we study the performance of different digital modulations over a sum of singly and doubly scattered (SSDS) channel. Note that the proposed V2I channel model falls under the umbrella of SSDS channels since the transmitted signal undergoes a combination of single-bounce and double-bounce scattering. We study some characteristic quantities of SSDS channels and derive expressions for the average symbol error probability of several modulation schemes over SSDS channels with and without diversity combining. The validity of these analytical expressions is confirmed by computer-based simulations.