The higher order method of moments (HMOM) has been proposed to calculate the bistatic scattering from two-dimensional (2D) perfectly electric conducting (PEC) rough surface in this paper. The electric field integral equation (EFIE) is solved through the HMOM with the hierarchical higher order basis functions which are the modified Legendre polynomials. The non-uniform rational B-spline (NURBS) surface is applied to model the plane surface related to the rough surface. Validity of this approach is shown by comparing the bistatic scattering coefficient (BSC) to that of lower order MOM (LMOM) with the Rao-Wilton-Glisson (RWG) or rooftop basis function. This approach has fewer segments in the parametric directions than the LMOM with rooftop basis, and is more efficient for the fewer unknowns and requires less memory than the LMOM with RWG basis. Properties of EM scattering from a 2D Gaussian rough surface are also exhibited and analyzed.

This paper proposes a new method to display microwave images of breast tissue, based on estimation of local microwave velocity from time of flight measurements. Its computational demands are low compared with tomography. It has two major components: 1) the estimation of the travel time of microwaves across the tissue between a set of antennae using a wavelet decomposition, and 2) the estimation of the microwave velocity field from the set of travel times using a low dimensional set of radial basis functions to model local velocity. The technique is evaluated in 2-D on clinical MR-based numerical breast phantoms incorporated in Finite-Difference Time-Domain simulations. The basis functions, used with a regularisation scheme to improve numerical stability, reduce the dimensionality of the inverse problem for computational efficiency and also to improve the robustness to error in velocity estimation. The results support previously published findings that the wavelet transform is suitable for robust measurement of time of flight even in clinically significant simulations, and shows that the velocity contrast images can be constructed so different regions of breast tissue type can be distinguished. In particular, the presence of a tumour is clearly detected, demonstrating the potential of this approach for breast screening. Keywords: Biomedical signal processing; Microwave imaging; Image reconstruction.

The paper describes a novel approach to the design of non-uniform planar circular antenna arrays for achieving maximal side lobe level suppression and directivity. The current excitation amplitudes and phase perturbations of the array elements are determined using an Adaptive Memetic algorithm resulting from a synergy of Differential Evolution (DE) and Learning Automata that is able to significantly outperform existing state-of-the-art approaches to the design problem. However, existing literature considers the design problem as a single-objective optimization task that is formulated as a linear sum of all the performance metrics. Due to the conflicting nature of the various design objectives, improvements in a certain design measure causes deterioration of the other measures. Following this observation, the single-objective design problem is reformulated as a constrained multi-objective optimization task. The proposed memetic algorithm is extended to the multi-objective framework to generate a set of nondominated solutions from which the best compromise solution is selected employing a fuzzy membership based approach. An instantiation of the design problem clearly depicts that the multi-objective approach provides simultaneous side lobe level suppression and directivity maximization in comparison to the single-objective scenario.

The design criteria of integrated optical biosensors based on the Mach-Zehnder Interferometer and on the Michelson Interferometer are proposed. Sensitive performance has been evaluated for different optical polymeric waveguiding structures such as channel, inverted-rib and strip waveguides. For all the configurations of the examined optical waveguiding interferometric biosensors maximum linearity and sensitivity have been obtained. In particular, the achieved sensitivity, expressed as the ratio between the normalized output power and the protein concentration, is about equal to 1.6 (g/ml)^-1 which, for a maximum variation of the output power equal to 100 mW, leads to a non-normalized sensitivity equal to 160 mW/(g/ml).

This paper presents a method of moments (MoM) solution for the problems of electromagnetic scattering by inhomogeneous three-dimensional bianisotropic scatterers of any shape. The electromagnetic response of bianisotropy has been described by the constitutive relations of the most general form composed of four 3 x 3 matrices or tensors. The volume equivalence principle is used to obtain a set of mixed potential formulations for a proper description of the original scattering problem. Here, the total fields are separated into the incident fields and the scattered fields. The scattered fields are related to the electric and magnetic potentials which are excited by electric and magnetic bound charges and polarization currents. The body of the scatterer is meshed through the use of tetrahedral cells with face-based functions used to expand unknown quantities. At last, the Galerkin test method is applied to create a method of moments (MoM) matrix from which the numerical solution is obtained. Implemented in a MATLAB program, the numerical formulation is evaluated and verified for various types of scatterers. The results are compared with those of previous work, and a good agreement is observed. Finally, a scattering from a two-layered dispersive chiroferrite sphere is presented as the most general example.

This paper presents an experimental performance comparison among three RF architectures that are very suitable for Software Defined Radio (SDR) implementation: zero-IF, low-IF, and six-port network. A six-port receiver and a dual zero-IF/low-IF receiver have been developed for this purpose. Six-port receiver is a very promising and flexible RF architecture for the low-cost implementation of integrated microwave and millimeter-wave systems. Competitive advantages such as ultra-broadband behavior, low-cost, reconfigurability, and low power consumption, point to the six-port architecture as a good candidate to implement a SDR. However, two issues on broadband six-port receivers require intensive research: dynamic range extension, and miniaturization. In this paper, two solutions are proposed to solve these problems: the use of biased detector diodes for dynamic range extension, and the use of low temperature co-fired ceramic (LTCC) technology for six-port reduction. The measurement results indicate that the six-port receiver shows high potential benefits and advantages compared to conventional zero-IF and low-IF receivers. In addition, the capability of the six-port architecture to operate as both zero-IF and low-IF receivers has been experimentally demonstrated for the first time.

This paper proposes an efficient microstrip isolator filter which suppresses the surface and lateral waves (SW and LW) in planar antenna arrays. The structure consists in a double or triple row of periodic and flipped array of subwavelength Complementary Split Ring Resonators (CSRRs). The array of CSRRs is etched on a dielectric substrate backed by a metallic ground plane. These structures can both block the electromagnetic (EM) energy in one direction and guide it along the other transverse direction. In particular, the flipped array of CSRRs presents wider bandgap characteristic (stopband ≥20%) than periodic array of CSRRs (~16%) and conventional array of SRRs (≥12%). Then, the metamaterial filter is inserted between two 6.1 GHz probe-fed patch antenna elements separated by a distance of 0.8 λ₀. Excellent agreements between the simulated and the experimental results are obtained. In fact, a significant reduction of the EM mutual coupling is achieved, more than 24 dB, over a wide frequency bandwidth. Moreover, the proposed CSRR structures are compact, low complex and, as printed antennas, are very easy to manufacture. They have numerous applications in MIMO systems and directive phased arrays.

In this paper, we propose a method based on evolutionary computations for joint estimation of amplitude, Direction of Arrival and range of near field sources. We use memetic computing in which the problem starts with a global optimizer and ends up with a local optimizer for fine tuning. For this, we use Genetic algorithm and Simulated annealing as a global optimizer while Interior Point Algorithm as a rapid local optimizer. We set up Mean Square Error as a fitness evaluation function which defines an error between actual and estimated signal. This fitness function is optimum and is derived from Maximum likelihood. It requires only single snapshot to converge and does not require any permutations to link it with the angles found in the previous snapshot as in some other methods. The efficiency and reliability of the proposed scheme is tested on the basis of Monte-Carlo simulations and its inclusive statistical analysis.

In this article, one realization version of quad-band filter is firstly proposed, and it is the cascaded structure composed of the shunt open-circuit DCRLH (dual composite right/left-handed) cell and the shunt short-circuit DCRLH cell. The above two cells are initially proposed here in order to improve the inherent limitations of the microstrip DCRLH cell. It is demonstrated that the matching performance and frequency selectivity of these two cells are both better than those of the microstrip DCRLH cell. What is more important, these two cells both exhibit three transmission zeros within the given frequency band and any of them is of great potential to be applied in the design of quad-band filters. In order to get sufficient design freedom, we utilize the cascade connection version based on the shunt open/short-circuit DCRLH cells. Whereas, only the first and second transmission zeros of both the shunt open/short-circuit DCRLH cells are explored. Both the simulated and measured results indicate that the proposed design method is right and effective.

A compact dual band notched Ultra-wideband (UWB) antenna with the multiple Hilbert curve slots is proposed that exhibits an impedance bandwidth from 2.5 GHz to 12 GHz. Hilbert curve slots result in band notch in the frequency range 5.15-5.5 GHz assigned to IEEE 802.11a and HYPERLAN/2 as well as 7.9-8.4 GHz band assigned to X-band uplink satellite communication systems. The antenna gain varies from 3 dBi to 5 dBi over the operating frequency. Stable radiation patterns throughout its operating frequency are obtained. Over all antenna size is 25 mm by 45.75 mm including the ground plane. Simulation and measured result of the proposed antenna are in good agreement.

This paper presents a frequency-tunable bandpass filter with constant absolute bandwidth and improved linearity. The proposed resonator is composed of an open-ended transmission line with back-to-back varactor diodes loaded at one end. The back-to-back varactor diodes are used to enhance the linearity of the filter, which is better than that of the single varactor counterparts. A mixed electric and magnetic coupling scheme is utilized to control the overall coupling coefficients so that the absolute bandwidth can be kept constant when the frequency is tuned. For validation, two frequency-tuning filters with 30-MHz and 44-MHz absolute bandwidth are implemented. The experimental and simulated results are presented to verify the proposed design.

A time-dependent nonlinear theory for complex cavity gyrotron is presented in this paper. The theory includes generalized telegrapher's equations and electron motion equations, which are deduced in detail. A calculation code for the self-consistent nonlinear beam-wave interaction is developed based on the presented theory. Using the code, a 94 GHz complex cavity gyrotron operating in TE₀₂₁-TE₀₃₁ modes is thoroughly studied. Numerical results show that an output power of 180 kW, about 36% efficiency is achieved with a 50 kV, 10 A electron beam at a focused magnetic field of 1.78 T and a beam velocity ratio of 1.65. The results from MAGIC simulation are also given and an output power of 192 kW, 38.4% efficiency is obtained. This tells the agreement with these two simulation codes.

A novel synthesis method for a class of time-domain passive filters that compensates for waveform distortion caused by frequency dependencies of the transmission properties of signal propagation paths, is formulated. The method is based on the linear response theory and mathematical properties of scattering matrices for passive circuits. This paper focuses on the formulation and theoretical consistency of the method. The causal transfer functions for the filters can be extracted by "regularizing" the inverse of a transfer function of the path. To fulfill the necessary restrictions imposed on the causal functions, regularization is realized by multiplying the function of linear phase filters comprising a sufficient number of resonators by the inverse. The filter circuits are easily derived from the regularized transfer functions through numerical optimization techniques and the coupling matrix synthesis method to determine transmission poles and extract each lumped element value, respectively. The method is then applied to practically designing a filter that compensates for the frequency dependencies of a two-port radio propagation path having a pair of wideband antennas. In addition, applications of the filter and the scope of further developments of this technology are discussed.

This paper presents a modified design of directional monopole antenna with parabolic-shaped ground plane. To increase the directivity, axis of parabola in the ground plane is rotated 45 degrees (in comparison with the previous antenna) to extend throughout the direction of the substrate's diagonal. Consequently, vertex of the parabola is placed at the optimum point in the corner of the substrate. The aim of this attempt is to design an extended and symmetrical ground plane around the patch, with more clarity, to maximize its capability as a reflector. Directivity is further improved by inserting parabolic-shaped slots at the corners of the ground plane. Simulation and measurements show that the proposed antenna has stable directional radiation pattern and higher gain compared to the previous directional monopole antennas. Impedance bandwidth of the antenna covers the frequency range of 4-9 GHz. Measured HPBW is among the degrees 54-22 between 4 and 9 GHz. Gain and HPBW of the antenna are improved 1.3-3.1 dB and 5-15 degrees, respectively among the bandwidth in comparison with previous antenna. Results confirm the good characteristics of the antenna for use in microwave imaging, where high resolution is required.

A design of coplanar waveguide (CPW)-fed circularly polarized slot antenna is presented. The proposed antenna consists of two orthogonal slots. By making use of the symmetric current and electric-field distributions of the two gaps of CPW-fed, a simple power divider is easily achieved. By adjusting the length of the two orthogonal slots and CPW-fed bent slot, a circularly polarized wave of two orthogonal modes with equal amplitude and phase difference of 90 degree is excited. The numerical results show that the 10 dB return loss bandwidth and 3 dB axial ratio (AR) bandwidth are 50.8 % and 11.2 % respectively. A prototype antenna is fabricated and measured, the measured results show that the proposed antenna achieves a good performance of circularly polarization.

Radar waveform synthesizer is a key component in radar system as it determines the best achievable resolution. A popular approach in radar waveform synthesis is the Direct Digital Synthesis approach where the signal is first generated in digital domain and converted into analog signal using a High Speed Digital-to-Analog Converter (HS-DAC). In this paper, a miniature and low cost radar waveform synthesizer is proposed. The synthesizer is targeted for Unmanned Aerial Vehicle (UAV) based radar system applications that require miniaturized equipment due to limited space in aircraft's fuselage. The signal synthesizer has been developed using Altera DE3 development board (Stratix III FPGA) and a custom made dual-channel 420 MSPS HS-DAC board. The proposed system is capable of generating various types of radar waveforms: a) Linear Frequency Modulated (LFM) or chirp pulse, b) Frequency Modulated Continuous Wave (FMCW), and c) Calibration Tone (Cal-Tone), for use in different types of radar applications. The distinguishing feature of the proposed synthesizer is its capability in reconfiguring the signal properties in real-time. The performance of the synthesizer has been benchmarked with commercially available radar waveform signal synthesizer and comparable performance has been observed.

A challenge faced by the information and communications technology (ICT) industry is the growing data volume and associated energy consumption. How to both meet a dynamic traffic demand at a consistently low energy consumption level is of importance from both commercial and climate change perspectives. This paper proposes a dynamic basestation concept that allows the number of active sectors to be adjusted in accordance with the traffic load. This is achieved through a novel switchable antenna design that can adjust the azimuth beam-width by using a tuneable reflector. Simulation and theoretical results show that the dynamic basestation can reduce the total operational energy of a cellular network by a peak of 75% and a mean of 38%.

This paper presents a compact microstrip stepped-impedance lowpass filter with ultra-wide stopband by using back-to-back C-shaped and triple C-shaped thin slots. The properties of several thin slots in the ground plane have been investigated in this paper. With the full-wave simulation results and a simplified equivalent model, the total equivalent inductance of the thin slots can be extracted at cutoff frequency for lowpass filter design purpose. On the other hand, the thin slots work as bandstop filter at the stopband of the lowpass filter for a better stopband rejection. The proposed lowpass filter with a cutoff frequency of 2 GHz shows a wide stopband with an over 25-dB attenuation up to 17.5 GHz. From dc to 2 GHz, the insertion loss is less than 0.3 dB and the return loss is greater than 20 dB. In comparison to the conventional stepped-impedance lowpass filter with the same passband performance, the proposed lowpass filter shows not only a 24.3% size reduction but also a better stopband rejection.

In this manuscript, a novel multiport matching method is devised to directly maximize the mean capacity with rigorous consideration of the mutual coupling effects of the matching network. In the RF front end of the real communication circuits, the mutual couplings always exist. In this paper, 1) a theoretical capacity upper bound of the 2-by-2 MIMO system with a matching network using the water-filling as the power allocation rule is analytically derived for the first time, 2) the Genetic Algorithm is employed to optimize the parameters of the matching network for the maximization of the mean capacity, 3) a coupled microstrip lines structure is devised to implement the matching network of the real MIMO receiving circuits by this matching method. The numerical results in the last section demonstrate that an optimized matching network obtained using our novel MPM method is capable to enhance the performance of the MIMO systems in a range of different indoor environments. This verifies that our method is not only effective but also practical.

In this paper, novel space-time adaptive processing algorithms based on sparse recovery (SR-STAP) that utilize weighted l₁-norm penalty are proposed to further enforce the sparsity and approximate the original l₀-norm. Because the amplitudes of the clutter components from different snapshots are random variables, we design the corresponding weights according to two different ways, i.e., the Capon's spectrum using limited snapshots and the Fourier spectrum using the current snapshot. Moreover, we apply the weighted idea to both the direct data domain (D3) SR-STAP and SR-STAP using multiple snapshots from adjacent target-free range bins. Simulation results illustrate that our proposed algorithms outperform the existing SR-STAP and D3SR-STAP algorithms.