In traditional over-the-horizon radar (OTHR), multipath propagation due to the multi-layer ionospheric structure always deteriorates the detection performance. The properties of multiple-input multiple-output (MIMO) radar technique, which transmits wide beams with low gain at the transmitter and achieves receiver beam-forming to obtain narrow beams with high gain, make it an ideal choice for OTHR to detect target through multi-layer ionosphere and suppress strong clutter. This paper investigates the assumption of a two-layer ionospheric model and proposes a two-step Max-Min algorithm based on the mutual information theory to optimize MIMO-OTHR waveform so as to suppress clutter, interference and noise. The first step is to maximize the mutual information between the echo and target response from the same direction of arrival (DOA) in order to reduce the impact of noise. The second step is to minimize the mutual information between the echoes from different DOAs, in order to suppress the clutter and interference by reducing the correlation of the echoes from the different DOAs. Numerical experiments validate that this algorithm can improve range resolution and detection probability significantly. Experiment results also demonstrate that the previously harmful multipath propagation can be utilized to enhance the detection performance in MIMO-OTHR.

The microwave scattering characteristics of a metamaterial (MTM) sphere and an MTM coated conducting sphere is compared to that of its DPS (Real (ε) > 0, Real (μ) > 0) counterpart in the presence of an infinite conducting plane using the multipole expansion method and is presented in this article. The DPS medium may be an artificial dielectric or natural dielectric. The differential scattering cross sections and the differential backscattering cross sections of the different types of spheres are presented for a circularly polarized (left or right) beam incident normally on the sphere. The results presented may be useful for maritime applications.

In this paper, a new de-embedding technique with Look-Up Table (LUT) is proposed for accurate and efficient characterization of interconnects, particularly printed circuit board (PCB) transmission lines including microstrip and stripline. LUT is pre-created to cover various fixture effects including the reference structures inside and/or outside test printed circuit boards (PCBs). The pre-established LUT is introduced to eliminate the errors of ``probing and launching fixtures'' in characterization of transmission lines. It is applied to characterization of loss of microstrip and stripline. Simulations and measurements are performed to verify its accuracy and feasibility. Results show it is in good agreement with conventional Delta-L like methods but significantly reduces the cost of characterization. It provides an accurate but cost-effective solution for characterization of high speed interconnects, in particular for high volume manufacturing environments.

This paper investigates the source reconstruction problem in underwater mediums using a compressive Near-Field Electromagnetic Holography (NEH) approach. More specifically we investigate the use of ℓ₁ regularization for the purpose of decomposing near-field magnetic and/or electric surface measurements into electric and magnetic dipole sources. Our study indicates that not only do ℓ₁ decompositions enable much higher resolution of sources than traditional ℓ₂ approaches, but important features of the dipoles are preserved in the reconstruction. Our hypothesis are supported by numerical experiments as well as underwater physical measurements obtained in an earth field simulator facility.

We present a Hilbert curve fractal antenna operating at 2.45 GHz ISM and 5.5 GHz WLAN bands. The proposed antenna employs a third-order Hilbert curve and two shorting vias for antenna miniaturization and dual-band/mode operation. At 2.45 GHz, the antenna exhibits a monopole-like radiation pattern, while at 5.5 GHz, it provides a broadside radiation pattern, suitable for simultaneous on- and off-body communication using two distinct frequency bands. The antenna foot print is as small as 25.5 mm×25.5 mm. Simulation and measurement results demonstrate that the antenna gain is more than 1.9 dBi if the antenna is mounted on a ground larger than 40 mm×40 mm. The effect of human body presence on antenna performance was investigated by means of full-wave simulations locating the antenna on a human body phantom. It is shown that the proposed antenna is capable of maintaining its free-space performance over the human body phantom except for the gain reduction of 2.5 dBi at 5.5 GHz band.

The measurement of far-field radiation patterns is time consuming and expensive. Therefore, a novel technique that reduces the samples required to measure radiation patterns is proposed where random far-field samples are measured to reconstruct two-dimensional (2D) or three-dimensional (3D) far-field radiation patterns. The proposed technique uses a compressive sensing algorithm to reconstruct radiation patterns. The discrete Fourier transform (DFT) or the discrete cosine transform (DCT) are used as the sparsity transforms. The algorithm was evaluated by using 3 antennas modeled with the High-Frequency Structural Simulator (HFSS) --- a half-wave dipole, a Vivaldi, and a pyramidal horn. The root mean square error (RMSE) and the number of measurements required to reconstruct the antenna pattern were used to evaluate the performance of the algorithm. An empirical test case was performed that validates the use of compressive sensing in 2D and 3D radiation pattern reconstruction. Numerical simulations and empirical tests verify that the compressive sensing algorithm can be used to reconstruct radiation patterns, reducing the time and number of measurements required for good antenna pattern measurements.

A novel uniplanar compact WLAN band-notched printed ultrawideband (UWB)-multiple-input-multiple-output (MIMO) antenna with dual polarization for high data-rate wireless communication is proposed. The antenna consists of two CPW-fed floral radiating elements along with a decoupling structure to ensure high isolation. The band notch at the WLAN frequency band is achieved by etching one single U-shaped slot on each antenna element. Results show that the proposed antenna gives impedance bandwidth from 2.7 GHz to 10.9 GHz with notched frequency band from 5.1 GHz to 5.9 GHz. The proposed antenna provides nearly omnidirectional radiation pattern, low envelope correction coefficient [ECC], moderate gain, efficiency, fidelity factor and pattern stability factor [PSF]. Furthermore, diversity characteristics such as mean effective gain [MEG] and diversity gain [DG] are also studied. Moreover, the time-domain analysis displays minimum dispersion to the radiated pulse. All these features make the proposed antenna a good candidate for future high data-rate wireless communication systems with polarization-diversity operation, where the challenge of multipath fading is a major concern.

We investigate optical bistability (OB) and optical multistability (OM) behaviors in a triply driven five-level atomic system. It is shown that the system has bistable behavior and can be controlled by intensity of applied fields. We find that OB switches to OM via interference induced among the Rabi-split resonance. We consider a superposed one-dimension standing wave, generated by two optical fields, and it is demonstrated that the OB and OM behaviors depend on the position of localized atoms as well as the relative phase of applied fields.

A beam-scanning partially reflective surface (PRS) antenna is presented in this paper. By employing a reconfigurable feed network to a two-element phased array source, the PRS antenna can realize beam steering between -10° and 10° with respect to the broadside direction across an overlapped frequency range from 5.35 GHz to 5.76 GHz. Good agreement between the simulated and measured results is achieved, which validates its capability to be a good candidate for the modern communication systems.

The light propagation through a one-dimensional symmetrical photonic structure, determined by the symmetric Silver mean Ag₄ distribution embedded between two Bragg structures Bg₂₇ (Bg₂₇/Ag₄/Bg₂₇), is studied using the transfer matrix method (TMM). The focus lies on the investigation of the influence of symmetry of the structure as well as the dependence of transmission on the frequency, angle of incidence of the light striking the structure and symmetrical deformation of the structure. The deformation was introduced by applying a power law, so that the coordinates y of the deformed object were determined through the coordinates x of the non-deformed structure in accordance with the following rule: y = x^1+k. Here, k is the degree of the law. A comparison will be made with a symmetrical periodic structure having the same number of layers. All results will be discussed in relation with the k values. Indeed, in the case of low k values close to zero a monochromatic filter was obtained, and in the case of relatively high values, an omnidirectional mirror is obtained.

In this paper, a development of compact wideband antenna for L-Band Applications is presented. The proposed antenna is developed based on Modified Sierpinski Based Fractal geometry for the antenna patch with additional meandered structure in the antenna transmission line. The designed antenna is printed on a 10 x 10 cm of substrate with a relative permittivity of 4.3 and thickness of 1.6 mm. The antenna is fed by a 50 Ω microstrip line. The proposed antenna is characterized both in numerical and experimental analysis. The antenna characteristics are analyzed in terms of return loss, bandwidth, antenna gain, radiation pattern and radiation efficiency. From the experimental analysis, the fabricated antenna exhibits reasonable agreement to numerical design. The proposed antenna has an operating frequency from 0.94 GHz to 2.25 GHz with the lowest return loss of -36dB and maximum gain around 5.49 dBi, as well as radiation efficiency of 97%, approximately.

A detailed study on the performance of square loop High impedance Surface (HIS) on lossy dielectric with its Artificial Magnetic Conductor (AMC) Property changing to narrow band absorber and then to Perfect Electric Conductor (PEC) depending on the loss in the dielectric is presented in this paper. An equivalent circuit modelling is used to theoretically explain how this transition is happening. This observed narrow band absorption (0.08 GHz) on the thin (0.016λ) lossy dielectric is scalable to different operating frequencies by varying the dimension of the geometry. The simulation studies on the effect of different geometrical, dielectric and incident wave parameters on the absorption property of this lossy HIS are also dealt with in this paper. Experimental investigation is in good agreement with simulated result and equivalent circuit modelling.

This paper presents compact dual/tri-band bandpass filters (BPFs) with controllable frequency and high selectivity for WLAN applications. A stepped impedance resonator with a shorting stub and a uniform impedance resonator with an open stub are applied in the designs. Several techniques that can generate transmission zeros are combined, to improve the frequency selectivity. The resonators and the proposed filters are characterized by full-wave simulations. To validate the design strategies, a dual-band BPF centered at 2.4 GHz and 5.2 GHz was first designed. With a minor modification, a tri-band BPF centered at 2.4 GHz, 5.2 GHz and 5.8 GHz was then developed. Both simulations and measurements were carried out to demonstrate the effectiveness of the designs. Good agreements are achieved.

A novel planar ultra-wideband (UWB) antenna with triple-notched bands using triple-mode stub loaded resonator (SLR) is presented in this paper. The basic UWB antenna consists of a circular-shaped radiating element, a 50 Ω microstrip feed line, and a partially truncated ground plane. Then, the resonance properties of the SLR are studied. Results reveal that the multiple-mode property of the SLR can be utilized in the UWB antenna design to achieve triple band-notched performance. To validate the design concept, a novel planar UWB monopole antenna with three notched bands respectively around the WiMAX band, WLAN band, and X-band satellite communication band is designed and fabricated. The results indicate that the proposed planar antenna not only retains an ultrawide bandwidth, but also owns triple band-rejections capability. The UWB antenna demonstrates omnidirectional radiation patterns across nearly whole operating bandwidth that is suitable for UWB communications.

This paper describes a method of measurement of miniaturized antenna gain in HF band based on a parallel plate cell. Compared to a free space outdoor approach this method offers two advantages: the use of a well defined environment and time efficiency. For the same external dimensions, it also has an advantage compared to TEM/GTEM cells designs in terms of useful antenna under test (AUT) space. This space is of a major importance in HF band since even miniature antennas can have considerable proportions. The proposed structure is composed of a parallel plate cell, whose construction is simple and not expensive. It offers a precision measurement with an error not exceeding 2.3 dB with respect to calibrated antenna gain and simulation results.

In modern information and communication technologies, manipulating focal length has been hot topic. Considering that the conductivity of graphene layer can effectively be tuned by purposely designing the thickness of the dielectric spacer underneath the graphene layer, a graphene-based lens with tunable focal length is proposed in this paper, and it can be used to collimate waves. The fabrication of the proposed graphene-based lens is purposed, and the performance of the lens is verified with finite-element method. The simulation results demonstrate that the graphene-based lens has excellent tunability and confinement. At the same time, the lens exhibits low loss in certain rang and large frequency bandwidth.

A compact triplet inline substrate integrated waveguide (SIW) bandpass filter is presented with sharp lower skirt and deep lower-stopband performance. The filter is composed of two SIW rectangular cavities and an embedded short-ended microstrip line on the top surface of two adjacent SIW cavities. A transmission zero can be generated by the cross coupling near the lower passband edge, which allows the filter implementation in inline with sharp lower skirt. Deep lower stopband performance is inherited from SIW. To validate the concept, a filter prototype with fractional bandwidth (FBW) of 4% at 5.75 GHz is designed, fabricated and measured. Good agreement can be obtained between the measured and simulated results.

This paper presents a compact, low-profile, wearable dual-band antenna operating in the Wireless WLAN band of 5.15~5.25 GHz and 5.72~5.83 GHz. The proposed antenna is composed of a planar monopole and underneath three by three array arrangement of Jerusalem Cross (JC) structure metasurface. The simulated results show that the integrated antenna express 4.09% and 4.14% impendence bandwidths, increased gain up to 7.9 dB and 8.2 dB, front to back (FB) ratio achieved to 20 dB and 18 dB at the two frequencies, respectively. The measured results agree well with simulations. In addition, the metasurface not only is equivalent to a ground plane for isolation, but also acts as the main radiator, which enables a great reduction in the specific absorption rate (SAR). Furthermore, because of a compact solution, the proposed integrated antenna can be a promising device for various wearable systems.

A maximum a posteriori (MAP) approach, based on the Bayesian criterion, is proposed to overcome the low cross-range resolution problem in forward-looking imaging. We adapt scanning radar system to record received data and exploit deconvolution method to enhance the real-aperture resolution because the received echo is the convolution of target scattering coefficient and antenna pattern. The Generalized Gaussian distribution is considered as the prior information of target scattering coefficient in MAP approach for the reason that it could express different target scattering coefficient properties with the control of statistic parameter. This constraint term makes the proposed algorithm useful in different applications. On the other hand, the reconstruction problem can also be viewed as the l_p-norm (0 < p ≤ 2) regularization. Simulation results show the robustness of the proposed algorithm against additive noise compared with other superresolution methods.

In this paper, the robust optimization shape and drive of switched reluctance motors (SRM) are discussed using robust particle swarm optimization (RPSO). The shape optimum goal of the algorithm was found for maximum torque value and minimum torque ripple, following changing the geometric parameters. The drive optimum aim of the algorithm was found minimum torque ripple, following changing the current profiles. The optimization process was carried out using a combination of RPSO and Finite Element Method (FEM). Fitness value was calculated by FEM analysis using COMSOL4.2, and the RPSO was realized by MATLAB 2011. The proposed method has been applied to two case studies and also compared with seeker optimization algorithm. The results show that the optimized SRM using RPSO has higher torque value, lower torque ripple and higher robustness, indicating the validity of this methodology for SRM design and implementation.