A circular microstrip antenna (CMSA) cannot be fed directly with 50 Ω microstrip (MS) line, without an inset or an impedance transformer, as all around the periphery the impedance is equally high. The feeding technique such as inset fed or quarter wave transformer makes the antenna geometry asymmetrical. In this paper, a technique using single shorting post and a pair of shorting posts is proposed to match the peripheral impedance of the CMSA with that of the 50 Ω-MS-line feed for operation around 2.45 GHz. The shorting posts perturb the current distribution on the patch, altering the input impedance at the periphery. By selecting proper shorting posts positions a wide range of impedance has been adjusted without altering the patch geometry. Due to symmetric arrangement of the double shorting posts, the proposed antenna configuration has a very low cross-polarization ratio of better than -65 dB at the broadside direction for 2.45 GHz. The simulated results of the directly fed 50 Ω-MS-line CMSAs are experimentally validated with good agreement.

A new optimization algorithm for the Cylindrical Polarimetric Phased Array Radar (CPPAR) antenna pattern synthesis is presented to achieve multi-mission requirements. To allow accurate weather measurements, the CPPAR antenna needs to have matched co-polarization (H and V) patterns, low sidelobe levels and high cross-polarization purity. To achieve these goals, first, a high-performance dual-polarized hybrid-fed microstrip patch antenna is designed, and its embedded radiation pattern is extracted. Then, a pattern synthesis using a new optimization method is presented to find the optimal weights for each radiating element and each polarization. The modified particle swarm optimization (MPSO) with new features is used to optimize the current distribution of the CPPAR. The adaptive beamforming algorithm also has the capability to mitigate interference by steering nulls of the radiation pattern in the desired direction without aecting the main beam. The performance improvement is demonstrated through the simulation results.

This paper presents a direction of arrival (DOA) estimation method. Spectral-domain interferometer equation is first established based on integral transforms of spatial interferometer equations. The direction finding problem in the spatial domain is thereby mapped to that in the spectral domain, relating angular parameters to spatial spectrums. This method is then applied to DOA estimation with circular arrays and spherical arrays. As a result, the elevation angle and azimuth angle are decoupled, giving closed-form and analytical formulae for DOA estimations by discrete phase samples on a sampling aperture. Algebraic relations between angular parameters and phase samples are established, and this method is hence computationally efficient. The Cramer-Rao lower bound (CRLB) of the proposed method is derived, and accuracy analysis demonstrates that the proposed method approaches the CRLB. In addition, mathematical insights into accuracy enhancement by large number of samples are observed via Parseval's theorem. Finally, numerical simulations and experimental measurements are provided to verify the effectiveness and appealing performance of the proposed method.

This paper presents the performance of cylindrical plasma antenna. A plasma tube is used as radiating element. The antenna is designed and works at different frequencies. To couple electromagnetic signal from the coaxial probe to the plasma column, a coupling system is realized. It permits to excite the tube in order to have a monopole or dipole antenna. The performances of the cylindrical plasma antenna are given in terms of S₁₁, gain and radiations patterns.

This paper presents the design and evaluation of a compact antenna system with pattern reconfigurability at 2.6 GHz. The antenna is based on the concept of an electronically steerable parasitic array radiator (ESPAR), and its height is reduced by top loading. The antenna can generate 10 reconfigurable patterns with a maximal gain of 7.4 dBi. Furthermore, a multiple antenna system consisting of these antennas is proposed. The radiation patterns realized by this multiple-input-multiple-output (MIMO) system are optimized for automotive urban scenarios based on the results of previous research. The S-parameter measurement results of a fabricated prototype correlate with the simulation. Furthermore, 3D measurements of radiation patterns correspond very well with simulation and gain up to 8 dBi is obtained.

A miniaturized rat-race coupler with arbitrary power division ratio is proposed in this paper. The design formulas of the rat-race coupler with arbitrary power division ratio are derived using the even-odd decomposition analysis. The proposed structure demonstrates miniaturized size and perfect isolation due to adding phase inverter to the branch. For demonstration, a 20 dB rat-race coupler operating at 1 GHz with 81.34% size reduction is designed and fabricated. There is good agreement between measured and simulated results.

We study the electrical conductivity of three-dimensional (3D) nanocomposite with incorporated random carbon nanotubes (CNT). Large length of the remote nanotubes generates a lot of intersections that induce rather small percolating threshold of the global conductivity in this medium. We simulate such a system by random cylinders placed in a percolating parallelepiped with the use of Monte Carlo method. Conductivity of such structure is associated with the critical phenomena, where the main transition parameter is dened by the value of the percolation threshold. We calculate the minimal percolating threshold and determine the functional form of the conductivity by the global optimization technique. Such an approach allows studying the details of the electrical conductivity in nanocomposites even at signicant level of the percolating fluctuations.

The main objective of this article is to design, realize and measure the performance of a reconfigurable antenna for wireless applications. The designed antenna will be able to switch among several modes, from the ultra-wideband mode (UWB mode) to narrow band mode (NB mode) and then dual-band mode (Bi-bands mode) and vice versa in order to combine the maximum functionality. By incorporating two resonators into the octagonal antenna, the initial antenna can be covered by one wideband (UWB mode), one narrow sub-band (NB mode), or two narrow sub-bands (Bi-bands mode). The ultra-wideband mode is obtained by deactivating the two resonators (so the antenna operates as a classical octagonal antenna), while the one narrow band mode is obtained by activating just one resonator. In the bi-bands mode, the two resonators are activated at a time to be used as a coupling-bridge to very narrow frequency bands. To present the work, simulated and measured results are given and discussed.

We present a new equal power quadrature branch line coupler (BLC) for dual-band applications in this paper. A new topology of the dual-band quarter wavelength transmission lines (TL) with the derivation of design equations is also introduced. The proposed BLC is designed using Advanced Design System (ADS) and fabricated on Rogers 5870 at 0.9 GHz and 2.4 GHz center frequencies. The design approach for the proposed dual-band BLC is endorsed by the simulated and measured results. A comparative analysis of this BLC with the previous BLCs is also carried out.

Conventional multitarget tracking techniques assume that clutter density is known a priori and use it directly in the recursive processing. However, in practical surveillance systems, the spatial distribution density of measurements generated by clutter is unknown and time-variant. Therefore, in order to achieve better tracking performance as well as the ability to evaluate the surveillance environment, we propose a fully forward-backward probability hypothesis density (PHD) smoother integrated with clutter spatial density estimator in this paper. Details on the sequential Monte Carlo (SMC) implementation method are presented as well. Simulation results of tracking performance evaluation verify the effectiveness of the proposed PHD smoother.

A miniaturized serpentine patch antenna is presented for Industrial, Scientific and Medical band (2.4-2.48GHz) applications. The proposed antenna is fabricated on a Rogers RT/duroid5880 substrate having permittivity of 2.2 and loss tangent of 0.0009. In comparison with other traditional structures, this antenna has an electrical length of 0.961λ with 29.2% impedance bandwidth which is advantageous for higher data rate transmission. In order to test the performance, the proposed antenna is tested in a silicone feeding tube. The simulated and measured results show good agreement with each other. Defected ground structure is also incorporated to enhance the performance of the proposed structure. All the simulations have been carried out on FDTD based Empire XCcel tool.

The basic wave types of electromagnetic field propagation in anisotropic media are obtained. Based on the orthogonality relation between the vector wave functions and the orthogonality of trigonometric functions, etc., the expressions of zero order scattering fields and first-order scattered fields of arbitrary electromagnetic beam are presented. A stochastic system identification model for electromagnetic beam scattering by anisotropic particles is established. In the S wave band, the relationships respectively between the scattering field expansion coefficients, the basic wave types of the particle field and the tensor of dielectric constant are studied, and their validity of the model is verified. Taking the elliptical Gaussian beam as an example, the beam scattering characteristics of anisotropic media particles are investigated. The used method is simple, exploring a new approach of researching the electromagnetic beam scattering characteristics from anisotropic medium targets.

In this paper, a novel multiband microstrip patch antenna with small frequency ratio is designed and analysed. One can design a multiband antenna at any desired frequencies through these proposed methods. The proposed antenna shows six operating frequencies with very small frequency ratio between two consecutive resonant frequency 1.1248, 1.1123, 1.0792, 1.1469 and 1.3254 and can be used for various wireless applications i.e. 2.5 GHz for UMTS and Wi-Fi, 2.812 GHz for CCTV with wireless video links, 3.128 GHz and 3.376 GHz for WiMAX, 3.872 GHz for C-band applications and 5.132 GHz for Lower WLAN. Design procedure and formation of all six bands are presented and discussed. Analysis is done by Ansoft HFSS v.15 which is based on Finite Element Method (FEM), and simulated results are verified with experimental results of fabricated prototypes which are found in close agreement.

Diverse array processing methods with higher order statistics (HOS) have been developed in the last three decades. One of the main interests in using HOS relies on the increase of effective aperture and the number of sensors of the considered array. In this work, we further exploit space-time adaptive processing (STAP) using HOS based on the phased array radar with uniform linear array (ULA). We implement STAP with respect to signal powers instead of with respect to signal amplitudes as the convention. The purpose of this paper is to provide some important insights into the STAP with respect to signal powers (SP-STAP), such as the output response, output signal-to-interference-plus-noise ratio (SINR), minimum detectable velocity (MDV) performance and effect ofinternal clutter motion (ICM). Compared with the conventional STAP under the condition of the same number of array elements and transmitting pulses, the simulation results show that SP-STAP can gain narrower target main beam, lower side-lobe levels, better MDV performance and less deleterious effect of ICM.

This research article presents a compact planar antenna and a method for bandwidth improvement using parasitic resonant structure for UWB application with dual notch band performance, which are adjusted with an empirical formula. The radiating element of the microstrip square patch is slotted with two identical inverted J-shaped slots at the two non-radiating edges, a reversed F-shaped slot in the slotted radiating element, so that dual notch bands are excited. The bandwidth of the microstrip square patch radiator is improved with the help of a dumbbell-shaped parasitic resonant structure which is placed on the upper to partial ground plane for UWB application. The antenna, with size of (12×16 mm²), is fabricated on an epoxy FR-4 dielectric substrate of 1.6 mm thick and experimentally validated. The simulated and experimental results show that the invented radiator covers operating bandwidth from 2.8 to 13 GHz with VSWR < 2 and omnidirectional radiation characteristics. The two notch bands (3.3-4.2 and 5.1-5.4 GHz) are excited in the wide bandwidth by suppressing any interference from IEEE 802.16 WiMAX (3.3 GHz-3.6 GHz), C-band (3.7 GHz-4.2 GHz) and IEEE 802 11 a lower WLAN (5.15 GHz-5.482 GHz) with VSWR > 5.

In this paper, a folded slot active tag antenna for 5.8 GHz radio frequency identification (RFID) applications is presented. It consists of an inverted U-shaped monopole radiator fed by a coplanar waveguide (CPW) feed line and extended ground planes. A 10 dB return loss bandwidth of 5.65-6.55 GHz is achieved. The overall volume of the presented antenna is 10.7×11×1.6 mm³. A good agreement between the simulated and measured results is observed. The antenna has an omnidirectional radiation pattern at 5.8 GHz frequency which makes it suitable for RFID applications. It has advantages of compact dimensions and wider bandwidth than previously reported structures.

The deformation of antenna array due to external factors results in a significant degradation in the performance of the array direction of arrival (DOA) estimation. To solve this problem, an equivalent method based on the estimation of signal parameters by rotational invariance technique (ESPRIT) in single signal source for the array position errors is proposed in this paper. This method is mainly for the low-order deformation of the array and is based on the equivalent value of the position error. The DOA estimation of ESPRIT algorithm for single signal source was corrected. The simulation results show that the position error equivalent method can effectively equalize the position error caused by the vibration deformation of the array. When the equivalent position error is known, the orientation of the single signal source can be effectively corrected.

A frequency tunable multi-layer low cost microwave absorber is proposed for Ku and X bands of applications. The tunability is obtained with the cavity model design using two metallic layers; a frequency selective surface (FSS) layer and a metal backed substrate layer with the air gap between them. The change in air-gap results in variation of the effective substrate height, and as a consequences the resonant frequency is tuned. The coupling of LC resonance and cavity resonance at an air-gap of 7.5 mm results in a dual-band absorption of the design. The proposed absorber performance has been analyzed for both TE and TM polarizations of incident wave, and the results are found to be same. The studies on surface current distribution and incident angle variation are observed to get physical insight behind absorption. The waveguide measurement method is used to correlate the simulated results with the measured one. With this simple cost efficient design, the absorber appears well suited for EMI/ EMC application at X and Ku bands.

This paper presents an electronically tunable dual-band filtering power divider (TDFPD) with tuning diodes sharing technique. Two dual-mode tunable resonators (DMTRs) are embedded into a conventional power divider to achieve dual-band tunable bandpass filtering response. The two bands of the proposed TDFPD can be tuned independently. Tuning diodes sharing technique is utilized to reduce the number of tunable diodes. A prototype has been designed and fabricated to validate the proposed design as shown by the good agreement between the measured and simulated results. The measurement shows that the center frequencies of the lower and upper bands can be independently tuned from 1.31 to 1.62 GHz and 2.92 to 3.30 GHz, respectively. Within the passbands, isolation between the two output ports is higher than 16 dB with small phase and magnitude imbalance.

A multiple-arm dipoles antenna array based on magnetic coupling is proposed for ultra-high frequency (UHF) radio frequency identification (RFID) near-field applications. The design utilizes four multiple-arm dipoles to form a square region fed by a quarter-wave impedance transformer double-side parallel stripline (QDSPSL) structure. Broadband performance can be obtained for two different resonant frequencies caused by different dipole arm lengths. Moreover, in induction area, stronger and more uniform magnetic field distribution is generated for phases of currents on three dipole arms being kept in the same compared to conventional single-arm dipole. A 170 × 170 × 1.6 mm³ antenna has been fabricated on an FR-4 substrate to fit RFID near-field application. The measured 10-dB impedance bandwidth is 190 MHz (810-1000 MHz), which covers the entire UHF RFID frequency band (860-960 MHz). Measured tests on the antenna read range are carried out, exhibiting a reading region of 100 × 100 mm² and 100% reading rate within 200 mm for near-field tags.