In low grazing angle scenario, target detection performance is seriously deteriorated due to multipath effect. This paper deals with moving target detection in low grazing angle with orthogonal frequency division multiplexing (OFDM) multi-input multi-output (MIMO) radar. We show that the detection performance can be improved through utilizing the multipath effect. Realistic physical and statistical effects such as refraction of the lower atmosphere and the Earth's curvature are incorporated into the multipath propagation model. Then, we derive a generalized likelihood ratio test (GLRT) detector by taking advantage of the frequency diversity of OFDM and MIMO configuration. Based on the fact that the target responses resonate at different frequencies and statistical characteristics of the test, we propose an algorithm which adaptively allocates the transmitted energy to improve the detection performance. The effectiveness of the GLRT detector as well as the adaptive design method is demonstrated via numerical examples.

In this paper, we report the design and evaluation of a compact 108-element base station antenna array for massive multi-input multi-output (MIMO) system using a 3-port multimode antenna as a unit element. Of these three ports, port 1 and port 2 have orthogonally polarized broadside radiation pattern with measured peak gain of 6.5 dBi and impedance bandwidth of 254 MHz (2.268 GHz-2.522 GHz) and 238 MHz (2.248 GHz-2.486 GHz), respectively, while port 3 has monopole-like radiation pattern having measured peak gain of 1.21 dBi and impedance bandwidth of 102 MHz (2.376 GHz-2.478 GHz). Mutual coupling among all the ports is kept as less than -14 dB. Design of 108 elements massive MIMO antenna array is evaluated as a base station antenna for multiuser urban street grid scenario in MIMO-OFDM downlink system, which is further modeled using Wireless World Initiative New Radio II (WINNER II) Channel models in MATLAB. Parameters like Singular value spread and Dirty Paper Coding (DPC) sum capacity was calculated and compared with i.i.d channel model. For 4 users case using same frequency and time resource, singular value spread and DPC sum capacity for presented antenna array converges to 7 dB and 11.6 bps/Hz at 10 dB SNR, respectively.

A low cost and easy fabrication multilayer antenna for wireless applications was presented to cover the industrial, scientific, and medical ISM band of (5.725-5.875) GHz with a gain of 11.7 dB. The antenna was composed of a feeding patch fabricated on a Rogers RT/Duroid 5880 substrate, and three superstrate layers of Rogers RO3006 were located above the feeding patch at a specific height for each layer. The superstrate layers were added to enhance the bandwidth and gain of the antenna and reduce its side-lobe level and return loss. The simulated and measured results of the operating frequency, return loss, bandwidth, and gain for the antenna were presented. CST Microwave Studio was used in this design's simulation.

As for the lack of the contribution by decision fusion in pose estimation and the demand for the combination of the feature fusion and the decision fusion in SAR ATR, in this paper, with the help of pose estimation, a new multi-look SAR ATR method is proposed in order to improve the performance, which is based on two-level decision fusion of neural network and sparse representation. The first-level decision fusion is acted for the combination of the pose estimation result by neural network and sparse representation. Based on the constraint of pose, these two models are exerted for the multi-look SAR ATR, and the second-level decision fusion is used to achieve the final recognition result. Several experiments based on MSTAR are conducted, and experimental results show that our method can achieve an acceptable result.

Within the framework of the finite-difference time-domain (FDTD) and the weighted Laguerre polynomials (WLPs), we derive an effective update equation of the electromagnetic in the dispersive media by introducing the factorization-splitting (FS) schemes and auxiliary differential equation (ADE). As two examples, we employ a 2-D parallel plate waveguide loaded with two dispersive medium columns and a thin grapheme sheet to calculate the plane wave propagation by using the FS-ADE-WLP-FDTD method. Compared with the ADE-FDTD and the ADE-WLP-FDTD methods, the results from our proposed method show its accuracy and efficiency for dispersive media simulation.

In this paper, an efficient lightweight double-layer absorber with impedance-matching structure at X-Ku bands was designed, optimized and implemented. First, genetic algorithm (GA) was considered to optimize the thicknesses and material properties for better absorption of the incident electromagnetic wave and reduction of radar cross section (RCS). Next, with the aid of the obtained dielectric and magnetic properties, the microwave absorber was fabricated from magnetodielectric composite materials besides a natural rubber. Finally, the analytical and numerical results were compared with the measurements to check the validity of the design. Experiments showed that the reflection coefficient for each layer backed with a metallic sheet was insufficient; however, for the double layer absorber, the reflectivity measurement values reached up to -28 dB in the case of normal incidence and -17 dB for oblique incidence.

Design and development of a novel dual-band microstrip patch array antenna suitable for WLAN and WiMAX applications are presented. The proposed array configuration is obtained by employing two parasitic patches gap coupled to the driven elements of a single layer proximity fed 2x1 microstrip patch array configuration. The proposed dual-band array has the advantages of enhanced bandwidth and gain. The feed patches are excited by proximity feeding method and the parasitic patches are excited by gap-coupling. This microstrip patch array provides resonances at two frequencies of 2.584 GHz (2.412-2.629 GHz) and 3.508 GHz (3.469-3.541 GHz). This novel configuration has a measured gain of 8.51 dBi and 5.8 dBi in lower and upper bands with an impedance bandwidth of 8.16% and 2.05% respectively. Additionally, to enhance the front to back ratio at the upper resonant frequency, a metal plate is placed at the back side of the array antenna. This modified proximity fed gap coupled array provides directional radiation patterns with improved gains. Re-configurability in the form of beam steering is obtained in the modified array configuration by varying the air gap between the ground plane and metal plate. The simulated results are in good agreement with the experimental ones.

A high-performance microstrip low-pass filter (LPF) with low cutoff frequency, negligible passband insertion loss, very sharp transition band, and deep ultra-wide stopband is designed, fabricated and measured. The presented filter is realized using three types of resonators which are coupled C-shape defected ground structure (C-CDGS), mirrored series-resonant branch loaded by radial stub, and high impedance line loaded by radial stub. A novel equivalent circuit model of the C-CDGS resonator is created, and its corresponding parameters are also extracted. The proposed filter is experimentally verified through the measured results which show good agreement with electromagnetic simulations.

In this paper, a novel broadband equalizer optimization technique is introduced for high-speed digital system designs. Through effectively compensating both conductor loss and dielectric loss, this technique provides a new solution to find optimal equalizer for high-speed signaling over printed circuit board (PCB) with continuous time linear equalizer (CTLE) as an application. The coefficients of CTLE are quickly identified through searching the minimum of the variation of total transfer functions over the low-mid frequency range. Channel simulations with different server interfaces of 12 Gbps and 25 Gbps are performed, respectively. Simulation results are presented to validate the technique.

In this paper, a miniaturized dipole antenna operating at 100 MHz frequency for Ground Penetrating Radar (GPR) application is presented. A conventional dipole antenna length is half of its lowest operating frequency wavelength. As low frequency GPR system is vital for high depth penetration, the size of the antenna used reduces its handling and portability. Therefore, the technique of miniaturizing a dipole antenna by adding extra radiating arms is presented here. The antenna design and analysis is carried out using Advanced Digital System (ADS) software, and a network analyser is used to validate antenna performance. The antenna of 66.5 cm × 22 cm dimension, fabricated on an FR4 substrate exhibits a frequency resonance at 104 MHz with 8 MHz -10 dB bandwidth. The proposed antenna radiates in omnidirectional pattern and features 55 % reduction in length compared to a conventional dipole antenna of same frequency operation.

This paper presents a compact tri-band dual-polarized planar monopole antenna, which is linearly polarized in the lower and middle bands and circularly polarized in the higher band. The antenna is printed on a substrate with an asymmetrical ground plane and a loaded vertical stub. The vertical stub and asymmetrical ground plane are mainly used to make the antenna obtain circular polarization performance in the higher band. The antenna has been built and tested. Its measured 10-dB impedance bandwidths are 2.39-2.54 GHz, 3.38-4.12 GHz, and 4.57-6.04 GHz, which can fully cover all the 2.4/5.2/5.8 GHz WLAN bands, all the 2.4/5.5 GHz Wi-Fi bands, and 3.5/5.5 GHz WiMAX bands. In the higher band, the measured 3-dB axial-ratio bandwidth is 5.4-5.83 GHz.

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.