This paper presents a new dual-mode stub-loaded resonator, which consists of a microstrip resonator with internal coupled lines and an open-circuit stub. Based on the odd- and even-mode equivalent circuits, the resonant characteristics of the proposed microstrip resonator are investigated. It is found that the fundamental even-mode resonant frequency of the proposed resonator can be flexibly controlled while the fundamental odd-mode resonant frequency remains unaffected. Then, based on the proposed resonator, three compact dual-mode bandpass filters, namely filer A, filter B and filter C, are designed, fabricated and measured to validate the design concept. Filters A and B demonstrate opposite asymmetric responses with two transmission poles in the passband and a transmission zero in the stopband. Filter C has three transmission poles in the passband and two transmission zeros respectively in the lower and upper stopbands to enhance selectivity. The experimental results show excellent agreement with the theoretical simulation results.

A 3D shape reconstruction algorithm for multiple PEC objects immersed in air is presented. The Hamilton-Jacobi PDE is solved in the entire computational domain with employing the marching cubes method to retrieve the evolving objects. The method of moment surface integral equation is used as the forward solver. An appropriate form of the deformation velocity, based on the forward and adjoint fields, is implemented to minimize the mismatch between the reference and evolving objects. The inversion algorithm showed good shape reconstruction results even using limited view data or noise corrupted data down to SNR of 5 dB.

In this paper a miniaturized branch-line coupler is proposed. The topology of the circuit is designed using novel design of T-model approach with open stubs with high-low impedances, which provides necessary bandwidth for WLAN band at 2.45GHz. The miniaturized branch-line coupler is designed and fabricated with a low-cost FR4 substrate as a platform in producing significantly reduction by more than 64.21% compared to the conventional coupler on inexpensive board. Furthermore, the coupler can equally divide the input signal with 90° phase of difference while maintaining the initial power from the source.

This paper presents a software defined radio six-port receiver for a novel broadband mobile communications system. The prototype covers the frequency range from 0.3 GHz to 6 GHz, and operates with up to 100 MHz-wide channels. The multi-band and multi-mode demodulation capabilities of the six-port architecture have been experimentally demonstrated. The six-port receiver has been satisfactorily proved for high data rates (up to 93.75 Mb/s, limited by the available test instruments). An efficient six-port auto-calibration method suitable for large instantaneous bandwidth systems is presented and validated.

HF-VHF Radars are used in oceanography and sea surveys [1] because they can cover a larger distance than other radars. We can use this kind of radar in sea and ground environments. In these bands, phenomena associated with clutter [2] interfere with radar performance for ship and terrestrial vehicle detection. To improve radar performance, a measure called Radar Cross Section is calculated. We have studied Radar Cross Section in HF-VHF bands with the objective of determining the influence of sea and ground clutter. There are two categories of Radar Cross Section: exact methods [3] and approximate methods [4-8]. We have studied approximate methods because they are faster than exact methods. A common radar configuration is the bistatic configuration where transmitter and receiver are dissociated. The aim of this paper is to study Radar Cross Sections of clutter estimated by approximate models in HF-VHF bands in a bistatic configuration.

A new type of waveguide based on the gap waveguide concept is here proposed and called gap-groove waveguide. Its design is based on the realization of a groove on a metal, facing an artificial surface which creates a high impedance surface (HIS) boundary condition. This condition is achieved here by employing a structure of closely packed metallic pins, known as bed of nails. The type of modes that can propagate in the gapgroove waveguide are similar to the ones of a standard waveguide but in this case there is no need of electrical connection. This is a potential advantage, especially when working at high frequencies. The dispersion characteristic of the gap-groove waveguide is derived by solving an eigenvalue problem, settled through a resonance condition at the interface between the groove and the bed of nails. The eigenvalues are associated with the modes propagating in the waveguide, and their dispersion characteristic is analyzed and compared with full wave simulations. A procedure to maximize the bandwidth is also provided, based on an appropriate choice of the geometrical parameters. Furthermore, the field distribution and the modal impedance of the fundamental mode are investigated.

A compact microstrip rat-race coupler is proposed with a new phase inverter which is realized by a modified Lange coupling structure with a slotted ground plane and a floating-potential conductor. Based on the evenand odd-mode theory, its parameters are generally synthesized. In order to further miniaturize the rat-race coupler, a T-shaped line is utilized. A prototype operating at 2.0 GHz is designed and fabricated for verification. The circumference of our proposed rat-race coupler is only 0.52λ. Its in-phase and out-of-phase bandwidths are also enhanced, with reasonable agreement obtained between its simulated and measured S-parameters.

An antenna and an array with photonic bandgap (PBG) structures, which are cylindrical conformal microstrip antennas, both operating in X-band (10.2 GHz) are proposed. As shown in the simulation, PBG structures could suppress the surface wave propagating on substrate and balance the influence of cylindrical curvature at resonance frequency on antennas. The simulation results indicate that they have a higher gain and better directivity over the conventional antenna without PBG structure. Both of the antenna and the array are designed and manufactured, and the measurement results agree well with the simulations.

A compact dual band-notched ultra-wideband slot antenna with sharp band-notched characteristics and controllable notched bandwidths is presented. The antenna is formed by a rectangular slot with chamfered corners on a printed circuit board ground plane, a T-shaped stub and two sets of compound band-notched structures. The compound band-notched structures are employed to generate desired lower and upper rejected bands with satisfactory skirt characteristics and sufficient rejection bandwidths. Moreover, the bandwidth of either the lower or upper rejected band can be independently adjusted by changing the size and location of the corresponding band-notched structure. Finally, an UWB slot antenna with two rejected bands at WiMAX/WLAN frequencies is successfully simulated, designed, and measured, showing good impedance matching, stable gain and near omnidirectional radiation patterns.

In this letter, a compact planer dual-band bandpass filter(BPF) using novel split-ring resonators (SRRs) is proposed. Compared with conventional SRRs, the stepped impedance split ring resonator (SIR-SRR) has better performance on miniaturization. To verify good characteristics of the novel structure, a new resonator-embedded cross-coupled filter, constructed by a pair of new resonators, is designed. This new filter has good characteristics of compact size and high selectivity. The improved SRR unit cell has a size of 0.108λ_g×0.108λ_g (where λ_g is the guided wavelength) at central frequency (2.25 GHz) of upper passband. Simulated results show that two central frequencies of the filter locate at 1.90 and 2.25 GHz with 3-dB fractional bandwidths of 1.0% and 7.7%, respectively. The lower passband band is generated by inner resonator with a via hole to gound plane, while the upper passband is created by outer resonator. Moreover, a good out-band performance is shown in this letter. Its stop-bands are extended 0-1.85 GHz at lower band and 2.4-5.8 GHz at upper band with a rejection level of about 20-dB. The measured and simulated results are well complied with each other.

For a cellular mobile communication system in narrow streets of urban areas, blind spots caused by shadowing of high buildings are a significant problem. In this research, a new dual-antenna system (DAS) is proposed, including a power transmission network, a receiving and a reradiating antenna to realize a broad-angle beam control. An equivalent bi-static radar cross section (BRCS) is deduced to present a theoretical explanation to the operating principles of the DAS. The main advantage of this design over ordinary reflectarray antenna as a passive RF booster is its flexible beam control capabilities. The simulated BRCS of the proposed DAS, composed of a microstrip patch array and a planar Yagi-Uda antenna, is given along with that of a metal plate of identical dimensions for comparison. purposes.

The corrected dispersion relation governing the linear interaction of a TE mode in a circular cylindrical wave guide with an annular beam of gyrating electrons in a gyro-TWT configuration is derived. The derivation of the correct dispersion relation no longer involves any integration with respect to the radial coordinate r_o. of the electron guiding center as the relevant equilibrium distribution function turns out to be independent of r_o. When the cyclotron resonance condition is satisfied by the TE mode for a positive s-number, the small-signal theory is shown to predict an initial exponential growth of the mode with interaction length over a small but finite band of frequencies around the design frequency.

In this paper spatial-band pass filters consisting of frequency selective surfaces (FSSs) are designed in order to realize both the desired transfer function of the filter in the frequency domain and drastic size reduction. Each FSS is made of aperture elements and patch elements. In this design method, the shape of each FSS is designed by a genetic algorithm (GA) so that the resonant curve of each FSS fits to the resonant curve which can be obtained from an equivalent circuit approach. By locating these designed FSSs at the intervals of quarter wavelength a spatial band pass filter is realized. Furthermore, a technique which controls the frequency response of each FSS has been applied to reduce the longitudinal size of filter. By this technique the FSSs are located at the intervals which are much shorter than a quarter wavelength, keeping the desired transfer function. Through a designed example it is shown that the half longitudinal length of a typical spatial filter can be obtained without any additional structure. Magnetic type spectral domain dyadic Green's functions are derived, and the characteristics of a spatial band-pass filter are calculated by means of the coupled magnetic filed integral equation which accurately takes higher order mode interactions. Derived linear matrix equations are solved using method of moment (MoM). The effectiveness of the proposed structure and its performance are verified and validated by designing and simulating an equal ripple spatial band pass filter at X-band.

In this paper we analyze the electromagnetic response of a metamaterial slab in the case of normal incidence using the point-dipole interaction model and an expansion of polarization by eigenmodes. The problem is simplified by assuming that the lattice dimensions are smaller than a half wavelength and invoking the nearest neighbor approximation. In this manner, we find the structure supports three modes: an ordinary mode and two extraordinary modes. In the long-wavelength limit, the ordinary mode propagates with the same wave number as that predicted using the classic Clausius-Mossotti relations, while, for most cases, the two extraordinary modes are confined to thin surface transition layers near the boundaries of the slab. A systematic method is presented to find the scattering from the slab, and the results are confirmed by full wave simulation using Ansoft HFSS.

In recent years, Wireless Sensor Networks (WSNs) have transitioned from being objects of academic research interest to a technology that is frequently being employed in real-life applications and rapidly being commercialized. The performance of a WSN is largely affected by high quality deployment and precise localization of sensor nodes. This article deliberates autonomous deployment of sensor nodes from an Unmanned Aerial Vehicle (UAV). This kind of deployment has importance in emergency applications, such as disaster monitoring and battlefield surveillance. The goal is to deploy the nodes only in the terrains of interest, which are distinguished by segmentation of the images captured by a camera on board the UAV. In this article we propose an improved variant of a very powerful real parameter optimizer, called Differential Evolution (DE) for image segmentation and for distributed localization of the deployed nodes. Image segmentation for autonomous deployment and distributed localization are designed as multidimensional optimization problems and are solved by the proposed algorithm. Performance of the proposed algorithm is compared with other prominent adaptive DE-variants like SaDE and JADE as well as a powerful variant of the Particle Swarm optimization (PSO) algorithm, called CLPSO. Simulation results indicate that the proposed algorithm performs image segmentation faster than both types of algorithm for optimal thresholds. Moreover in case of localization it gives more accurate results than the compared algorithms. So by using the proposed variant of Differential Evolution improvement has been achieved both in the case of speed and accuracy.

A broadband antenna integrated with the system ground plane of the Portable Media Player (PMP) device for digital television (DTV) signal reception is proposed. The antenna comprises of a quarter-wavelength monopole and a gaps-coupled open loop antenna that can generate two adjacent resonant modes to form a wide operation band. Result shows a wide bandwidth of 464-856 MHz to cover the DTV signal reception in 470-806 MHz band. Details of the proposed antenna designs and experimental results of the construct prototypes are presented.

In this paper, a tri-band metamaterial-inspired monopole antenna is proposed for multi-band wireless applications. A metamaterial consisting of three dual-band modified S-shaped resonators (MSRs) is directly connected to a regular monopole element, which can not only support the two WiFi bands but also bring the resonant frequency of monopole element down to the WiMAX band while the length of the antenna is maintained unchanged. The simulated and measured results verify our design for the wireless applications.

Arbitrarily polarized plane-wave diffraction equations for semiinfinite periodic rectangular grooves (RG) in a perfectly conducting plane are approximately proposed. To obtain diffraction equations for semi-infinite periodic RG, we utilize an overlapping T-block method as proposed for the analyses of finite and infinite numbers of RG, and the subtraction technique with infinite periodic solutions. The proposed semi-infinite solutions are then applied to finite periodic RG with very large number of diffracting elements. For verification of our approach, we performed numerical computations for finite periodic RG and compared our solutions based on semi-infinite equations with previously published analytic solutions, thus obtaining favorable agreement and proving computational efficiency.

The paper presents an analytical investigation of a tapered core optical fiber of which the outermost section is loaded with radially anisotropic liquid crystal. The analyses are dealt with transverse modes supported in the fiber structure followed by the relative distribution of power in the different fiber sections. Preliminary dispersion characteristics of the guide are also illustrated. The results demonstrate that the TE modes transport very large amount of power in the outermost liquid crystal region --- the criteria much useful for fiber optic sensing and field coupling devices.

The electromagnetic losses and shielding efficiency of shields for a buried three phase high voltage cable are studied for several shielding configurations. The shields are U-shaped gutters covered with plates, and the power cables are positioned either in trefoil or in flat configuration. The shielding efficiency and the losses are compared for shields with the same geometry but several shielding materials: aluminium, and two ferromagnetic steel grades. The numerical models are validated with experimental results. From the experiments, it is observed that the average reducing factor of the flux density is about 7 with the flat cable configuration while the average reducing factor of the flux density is about 5 with the trefoil cable configuration. But the power losses in the DX52 shield for trefoil configuration is about 40% lower compared to the flat configuration. In case of trefoil configuration, the losses are 12.41 W/m per meter length in the shield for a current of 750 A. Next to the shield material and the cable configuration, the paper investigates the influence of several parameters on both the shielding efficiency and the losses: the size of the shield, the current amplitude in the cable and the thickness of the shield.