The calibration of the multistatic scattering matrix plays an important part in the construction of a quantitative microwave imaging system. For scattering measurement applications, the calibration must be performed on the amplitude and on the phase of the fields of interest. When the antennas are not completely identical, as for example with a multiplexed antennas array, a specific calibration procedure must be constructed. In the present work, we explain how a complex calibration matrix can be defined which takes advantage of the geometrical organization of the antennas. Indeed, for arrays of antennas positioned on a circle, the inherent symmetries of the configuration can be fully exploited by means of an adequate reorganization of the multistatic scattering matrix. In addition, the reorganization permits to detect antenna pairs which are not properly functioning and to estimate the signal-to-noise ratio. Experimental results obtained within a cylindrical cavity enclosed by a metallic casing are provided to assess the performance of the proposed calibration procedure.This calibration protocol, which is described here in detail, has already been applied to provide quantitative images of dielectric targets [1, 2].

A novel slot array antenna with two layers of substrate integrated waveguides (SIW) is presented for millimeter-wave wireless applications. Unlike conventional SIW-based slot arrays, in this structure a feed waveguide is placed underneath the main substrate layer containing the slot array and is coupled to the branches of the array via slanted slots. The proposed feeding structure results in a considerable reduction in size and eliminates unwanted radiations from the feed network. Experimental results for two slot arrays with 4×4 and 6×6 elements operating at 60 GHz are presented showing 14.8 dB and 18.5 dB gain, respectively. Furthermore, a novel doubly tapered transition between SIW and microstrip line is presented which is particularly useful in mm-wave applications.

Wireless Sensor Networks (WSNs) have attracted a great deal of research interest during the last few years. Potential applications make them ideal for the development of the envisioned world of ubiquitous and pervasive computing. Localization is a key aspect of such networks, since the knowledge of a sensor's location is critical in order to process information originating from this sensor, or to actuate responses to the environment, or to infer regarding an emerging situation etc. Indoor localization in the literature is based on various techniques, ranging from simple Received-Signal-Strength (RSS) to the more demanding Time-of-Arrival (ToA) or Direction-of-Arrival (DoA) of the incoming signals. In the context of several EU research projects, various WSN platforms for indoor localization have been developed, evaluated and tested within real-world emergency medical services applications. These platforms were selected in order to deal with all principal localization techniques, namely RSSI, ToA and DoA. Deployment and real-world considerations are discussed, measurements results are presented and overall system evaluation conclusions are drawn regarding indoor localization capabilities of WSNs.

A highly accurate, fast algorithm is proposed to evaluate the finite Fourier transform of both continuous and discontinues functions. As the discretization is conformal to the function discontinuities, this method is called the conformal Fourier transform (CFT) method. It is applied to computational electromagnetics to calculate the Fourier transform of induced electric current densities in a volume integral equation. The spectral discrimination in the CFT method can be arbitrary and the spectral range can be as large as needed. As no discretization for the Fourier exponential kernel is needed, the CFT method is not restricted by the Nyquist sampling theorem, thus avoiding the aliasing distortions that exist in other traditional methods. The accuracy of the CFT method is greatly improved since the method is based on high order interpolation and the closed-form Fourier transforms for polynomials partly reduce the error due to discretization. Assuming N_s and N are the numbers of sampling points in the spatial and frequency domain, respectively, the computational cost of the CFT method is O((M + 1)N log₂L), where M is the interpolation order and L=(N_s−1)/M. Applications in spectral analysis of electromagnetic fields are demonstrated.

The dipole impedance of an aperture in a plane conductor is obtained by modifying the general network formulation of electromagnetic apertures presented by Mautz and Harrington. The derived dipole impedances are combined in parallel to form an effective circuit description of low frequency aperture diffraction. Power transmitted into the aperture by an incident wave is determined by incorporating standard techniques for the transfer of wave power at an impedance mismatch. This transmitted power is divided into forward and backward scattered fields based upon the behavior of image currents surrounding the aperture, leading to a peak in forward scattered power above unity, consistent with known aperture behavior. The presented aperture circuit maintains an excellent correspondence with measurements of radiated power for an aperture excited by high energy electrons and with the numerically calculated impedance of a circular aperture using the finite element method.

A novel method of using bypass coupling SICC resonator to generate transmission zeros in filter stopband to improve stopband attenuation is presented. A SIW quasi-elliptic function filter for Satellite Communication application with bypass coupling SICC resonator is designed and fabricated to validate the method. The results show that the method is effective on improving the filter stopband performance.

This paper presents the high frequency electromagnetic field expressions for perfect electromagnetic conductor (PEMC) Gregorian system. In this Gregorian system both the reflectors are PEMC and are embedded in homogenous chiral medium. Depending upon the values of chirality parameter (kβ) two cases are analyzed. In the first case, chiral medium supports positive phase velocity (PPV) for both the left circularly polarized (LCP) and right circularly polarized (RCP) modes. In the second case, chiral medium supporting PPV for one mode and negative phase velocity (NPV) for the other mode is taken into account. Since geometrical optics (GO) fails at the focal point, so Maslov's method is used to find the field expressions at the focal point. Field plots for different values of admittance (M) of the PEMC and the chirality parameter (kβ) are given in the paper.

Recent studies have shown that the dielectric properties of normal breast tissue vary considerably. This dielectric heterogeneity may mean that the identification of tumours using Ultra Wideband Radar imaging alone may be quite difficult. Significantly, since the dielectric properties of benign tissue were shown to overlap with those of malignant, breast tumour classification using traditional UWB Radar imaging algorithms could be very problematic. Rather than simply examining the dielectric properties of scatterers within the breast, other features of scatterers must be used for classification. Radar Target Signatures have been previously used to classify tumours due to the significant difference in size, shape and surface texture between benign and malignant tumours. This paper investigates Spiking Neural Networks (SNNs) applied as a novel tumour classification method. This paper will describe the creation of 3D tumour models, the generation of representative backscatter, the application of a feature extraction method and the use of SNNs to classify tumours as either benign or malignant. The performance of the SNN classifier is shown to outperform existing UWB Radar classification algorithms.

This paper presents the theory, properties, types, and applications of high impedance wires (HIWs). The effective permeability of a transmission line that consists of an HIW and a second conductor has a resonating behavior. Consequently, slow-wave and stop-band regions appear in the dispersion relation. In the slow wave regions, a new implementation for dual-mode filter is presented. The proposed filter size is reduced by 33%. In the stop band region, a new application is presented; dual-band balun where the common mode is rejected by the HIW. The novel design has a total area of 4 x 2.4 cm² and exhibits reliable performances at 2.75 GHz with a 40% bandwidth (2.2--3.3 GHz) and at 4.75 GHz with a 15% bandwidth (4.4--5.1 GHz) with an amplitude imbalance less than 1 dB, a return loss better than 13 dB, and phase imbalance less than 5°. Theoretical expectations were confirmed by EM simulations and measurements.

A multilayer soil model for retrieving soil moisture content using the Integral Equation Method (IEM) is investigated in this paper. The total reflection coefficients of the natural soil are obtained using the multilayer model, and volumetric scattering is approximated by the internal reflections between layers. The surface reflection terms in IEM model are replaced by the total reflection coefficients from the multi-layer soil surface in retrieving the soil moisture content. The original IEM model includes only the surface scattering of the natural bare soil, while the multilayer soil - IEM model (MS-IEM) includes both the surface scattering and the volumetric scattering within the soil. Both the MS-IEM model and the original IEM model are compared in soil moisture retrieval using the experimental Synthetic Aperture Radar (SAR) backscattering coefficient data in the literature. It is noted that the mean square error between the measurement data and the values estimated by the modified IEM model is about 7.7%, while that between the measured and the estimated by the original IEM model is about 12%. The accuracy of estimating soil moisture by the IEM model is improved by 4.3%. In addition, the regression analysis between the measured and model-predicted soil moistures has been done.

In this contribution we propose the design of an inductive Frequency Selective Surface (FSS) with double resonant elements aimed at the achievement of a simple well-performing, dielectric-free, space filter screen able to separate the Ku band from the Ka band. The FSS performance is compared to that of a typical double ring FSS which major drawback is the use of a dielectric substrate that leads to unavoidable additional transmission losses and makes the dichroic mirror more complex with respect to a simple single perforated screen. For all applications in which the FSS is asked to be as simple as possible and the transmission losses specifications are severe, the Inductive FSS Double Resonant Elements here proposed turns out to be an interesting alternative to typical Double Ring FSS.

The structural and microwave properties of (y) Ni_1-xCd_xFe₂O₄ and (1-y) Ba_0.8Sr_0.2TiO₃ (x = 0.2, 0.4, 0.6 and y = 0.15, 0.30 and 0.45) composites synthesized by self propagating auto combustion route was studied. X-ray diffraction patterns reveal this method can produce two phases simultaneously. The porosity increases with increase in ferrite content in the composite. The SEM morphologies show the growth of cadmium substituted nickel ferrite grains which are well dispersed in barium strontium titanate (BST) matrix. The composite material shows microwave absorption of about 0.575 in a broad band from 8-12GHz. The permittivity varied from 7 to around 43 with increase in ferrite content .The microwave conductivity measurements reveal the loss of polaron conduction which supports the dielectric loss in the microwave region.

In this paper, a time domain analysis for ultra-wideband short pulse radiation from wire monopole antennas and their arrays is presented. The pulse travels along the monopole antenna and reflects from the open end; during the pulse reflection, the pulse gets compressed. The analysis presented in this paper accounts for the pulse compression and the radiated pulse is compared with the measured pulse. Measured energy patterns for different pulse excitations of the monopole and monopole arrays are presented and compared with theoretical patterns.

The frequency-domain finite-difference (FD-FD) methods have been successfully used to obtain numerical solutions of two-dimensional (2-D) Helmholtz equation. The standard second-order accurate FD-FD scheme is known to produce unwanted numerical spatial and temporal dispersions when the sampling is inadequate. Recently compact higher-order accurate FD-FD methods have been proposed to reduce the spatial sampling density. We present a semi-analytical solution of 2-D homogeneous Helmholtz equation by connecting overlapping square patches of local fields where each patch is expanded in a set of Fourier-Bessel (FB) series. These local FB coefficients are related to total eight points, four on the sides and four on the corners, on the square patch. The local field expansion (LFE) analysis leads to an improved, compact FD-like, nine-point stencil for the 2-D homogeneous Helmholtz equation. We show that LFE formulation possesses superior numerical properties of being low dispersive and nearly isotropic because this method of connecting local fields merely ties these overlapping EM field patches already satisfy the Helmholtz equation.

A computationally efficient surrogate-based framework for reliable simulation-driven design optimization of microwave structures is described. The key component of our algorithm is manifold mapping, a response correction technique that aligns the coarse model (computationally cheap representation of the structure under consideration) with the accurate but CPU-intensive (fine) model of the optimized device. The parameters of the manifold mapping surrogate are explicitly calculated based on the fine model data accumulated during the optimization process. Also, manifold mapping does not use any extractable parameters, which makes it easy to implement. Robustness and excellent convergence properties of the proposed algorithm are demonstrated through the design of several microwave devices including microstrip filters and a planar antenna.

A highly integrated up-converter MMIC is presented for low cost and high performance Ka-band transmitter module application. The multiple functions of the up-converter, such as local oscillator (LO) amplifier, single sideband subharmonic mixer, LO bandstop filter, and three-stage RF amplifier, are integrated into a single chip. A proper circuit topology for the complete integrated circuit is selected to achieve the miniature chip size. The combination of lumped and microstrip lines are used to realize the compact sub-circuits. The layout of the circuit is optimized using electromagnetic (EM) simulations. The chip is fabricated in WIN 0.15 μm PHEMT technology on 4-mil GaAs substrate with a layout area of only 2.8 mm×0.8 mm (2.24 mm²). Measured conversion gain is 12±1 dB over 28-37 GHz for the LO pumping power of 0 dBm. The sideband and 2×LO suppressions are above 20 dBc. The 1 dB gain compression output power (P-1dB) is 12 dBm. LO to RF isolation is about 35 dB.

A novel subharmonically pumped resistive mixer (SHPRM) with a chip dimension of 0.8×0.81 mm² is fabricated through a standard 0.18-μm CMOS process. An impedance-transforming active quasi-circulator is monolithically integrated with an nMOS field-effect transistor (FET) to perform up-converter mixing while simultaneously enhancing all port isolation through a broadband operation. The design analysis of impedance-transforming active quasi-circulator is also presented for matching between circulator and resistive transistor. As shown in the measured results, the mixer exhibits a 9-14.5 dB conversion loss. All port-to-port isolations better than 16.5\,dB over a radio frequency (RF) of 10-20 GHz can be achieved.

A realistic model of ground soil is developed for the electromagnetic simulation of Ground Penetrating Radar (GPR) systems. A three dimensional Finite Difference Time Domain (FDTD) algorithm is formulated to model dispersive media using N-term Debye permittivity function with static conductivity. The formulation of the algorithm is based on the concept of the Piecewise Linear Recursive Convolution (PLRC) in order to simulate the dispersion properties of soil as a two-term Debye medium. This approach of ground modeling enhances the accuracy and reliability of results obtained for GPR problems. The developed algorithm is validated when simulating practical GPR Systems used to detect different objects buried in Puerto-Rico and San Antonio clay loams. The proposed algorithm is employed to compare the impact of using two-term Debye model to simulate real soil on the coupling coefficient between transmitting and receiving antennas due to the absence and presence of buried targets to that of using non-dispersive soil model. The effect of soil moisture content on the performance of GPR system in detecting buried objects such as metallic and plastic pipes is investigated.

A fully integrated 5.5 GHz high-linearity low noise amplifier (LNA) using post-linearization technique, implemented in a 0.18 μm RF CMOS technology, is demonstrated. The proposed technique adopts an additional folded diode with a parallel RC circuit as an intermodulation distortion (IMD) sinker. The proposed LNA not only achieves high linearity, but also minimizes the degradation of gain, noise figure (NF) and power consumption. The LNA achieves an input third-order intercept point (IIP3) of +8.33 dBm, a power gain of 10.02 dB, and a NF of 3.05 dB at 5.5 GHz biased at 6 mA from a 1.8 V power supply.

This paper presents an efficient and accurate hybrid approach of method of moments (MoM) and physical optics (PO) for radiation problems such as antennas mounted on a large platform. The new method employs higher-order hierarchical Legendre basis functions in the MoM region and higher-order Nyström scheme in the PO region. The two regions are both discretized with large domains. The unknowns can be much less than those in the small-domain MoM-PO solutions, which will lead to a great reduction in computation complexity. Furthermore, with the Nyström scheme in the PO region, the higher-order accuracy is maintained, and the calculation of the impedances can be more efficient than that in the existing higher-order MoM-PO procedure. Numerical results show the validity of the proposed method.