With tens or an even larger number of antennas utilized, large-MIMO systems have many potential merits. However, there are also some difficulties with its practical realization. For example, the feedback overhead caused by sending back a large precoding matrix is heavy. In this paper, we propose a selective linear transceiver scheme to reduce the overwhelming feedback overhead in correlated large-MIMO systems. In line with the required reduced amount of feedback, antennas which can provide a potentially large diversity gain are firstly chosen independently of the actual channel realization. The transceiver is then designed over correlated MIMO channels in an iterative way to minimize the sum of detection errors under the transmit power constraint. Although optimal solutions for the case of full transceiver have been given under some special scenarios, we modify them to improve the BER performance of systems. Monte-Carlo simulation results verify that the proposed selective linear transceiver is a useful scheme in large-MIMO systems to provide a tradeoff between performance and feedback overhead.

An improved adaptive beamforming technique of antenna arrays is introduced. The technique is implemented by using a novel Invasive Weed Optimization (IWO) variant called Adaptive Dispersion Invasive Weed Optimization (ADIWO) where the seeds produced by a weed are dispersed in the search space with standard deviation specified by the fitness value of the weed. The adaptive seed dispersion makes the ADIWO converge faster than the conventional IWO. This behavior is verified by applying both the ADIWO and the conventional IWO on well-known test functions. The ADIWO method is utilized here as an adaptive beamformer that makes a uniform linear antenna array steer the main lobe towards the direction of arrival (DoA) of a desired signal, form nulls towards the respective DoA of several interference signals and achieve low side lobe level (SLL). The proposed ADIWO based beamformer is compared to a Particle Swarm Optimization (PSO) based beamformer and a well known beamforming method called Minimum Variance Distortionless Response (MVDR). Several cases have been studied with different number of interference signals and different power level of additive zero-mean Gaussian noise. The results show that the ADIWO provides sufficient steering ability regarding the main lobe and the nulls, works faster than the PSO and achieves better SLL than the PSO and MVDR.

A new triangular metamaterials (TMMs) is designed for electromagnetic (EM) absorption reduction at microwave frequencies in this paper. The reduction of EM absorption with a new TMMs attachment is investigated in this research. The finite-difference time-domain method with lossy-Drude model is adopted in this investigation. The method of EM reduction is presented and the effects of position, distance, and size of metamaterials are analyzed. TMMs have achieved a 1.0923 W/kg for SAR 1 gm which is 45.44% reduction of the initial SAR value for the case of 1 gm SAR.

This paper describes a subcell modeling technique for metallic resonators where the actual metal traces are replaced by a thin wire having equivalent magnetic and electric radii, as well as an impedance per unit length. The formulas for these quantities in the case of rectangular traces are given. In addition, the gap of a split-ring resonator is replaced by a lumped load. The response of the resonator can then be modeled using thin-wire algorithms in an integral equation code. It is demonstrated that the number of unknowns and runtime can be reduced by factors of a thousand using the subcell models. This is particularly important in cases where metamaterial designs with tapered properties are encountered and periodic boundary conditions are not applicable, because with this simplification larger numbers of resonator cells can be handled.

Several experimental time-domain EM induction instruments have recently been developed for unexploded ordnance (UXO) detection and characterization that use multiple transmitting and receiving coil combinations. One such system, the US Geological Survey's ALLTEM system, is unique in that it measures both the electro-dynamic response (i.e., induced eddy currents) and the magneto-static response (i.e., induced magnetization). This allows target characterization based on the dyadic polarizability of both responses. This paper examines the numerical response of the ALLTEM instrument due to spheroidal, conductive, and permeable UXO targets; and to conductive and optionally viscous magnetic earth. An inversion scheme is presented for spheroidal targets that incorporates fully polarimetric measurements for both magneto-static and electro-dynamic excitations. The performance of the inversion algorithm is evaluated using both simulated and surveyed data. The results are examined as a function of the number of coil combinations, number of instrument locations, and uncertainty in sensor location and orientation. Results from the specific cases tested (prolate spheroids lying horizontally) show that 1) that collecting data from more than 12 sensor locations or from more than four coil combinations reduced the chances that inversion solutions would be from a local minimum, and 2) that uncertainties in position greater than 3 cm or in orientation greater than 10 degrees cause errors in the estimated spheroid principal lengths of greater than 100%. Soil conductivities less than 1 S/m contribute negligible interference to the target response, but viscous magnetic soils with permeabilities greater than 10^-6 MKS units do cause detrimental interference.

Multi-pole permanent magnetic encoders are used for wheel speed sensing in automotive systems. This paper discusses rings and discs magnetized along axial direction. The vector field is calculated analytically in 3D as sums over all poles. For the case of discs with vanishing inner and infinite outer diameter the summation is done in closed form with a new summation formula. The results are discussed and several plots of field patterns are given in normalized form: At very small air-gap the field shows an overshoot. At moderate and large air-gaps it is a sine-function with exponentially decaying amplitude. The amplitude versus air gap, reading radius, thickness of the magnetic layer, and number of poles is studied and excellent agreement with measurements is found. The effect of a steel-back on the field is explained. It is also shown how to maximize the torque transmitted in axially magnetized couplings.

A simplified calibration procedure using T-matrix concept is presented for two-port vector network analyzer (VNA) with three measurement channels. Compared with Short-Open-Load-Thru (SOLT) calibration method based on 10-term error model where 10 error terms must be solved and saved at each frequency, the proposed method need define fewer characteristic variables. Moreover, a length-unknown 50Ω line can be used instead of a random single-port standard, for example, substituting Load standard with 50Ω line in SOLT calibration procedure. Via the simplified calibration procedure, the scattering parameters of a two-port device under test (DUT) can be finally obtained. Experimental verification is carried out, and good agreement is observed.

A novel S-band monopulse antenna with four conical helix antennas on a microstrip substrate comparator is designed, fabricated and measured. Conical helix antenna height is 3λ, and comparator size is 130mm×150mm. The bandwidth (SWR <2 dB) of the antenna is 21.3% with an operating frequency range of 2.7 GHz-3.35 GHz. The maximum gain of the sum pattern is 17.4 dB, and the null depths of the difference pattern are less than -30 dB.

This paper focuses on the interferometry phase of an active coherent jamming in InSAR (Interferometry Synthetic Aperture Radar) images. Based on the signal models of coherent jammer, the jamming's imaging results are derived by employing the Omega-K algorithm. By comparing the imaging results of InSAR's two channels, the jamming's interferometry phases for both working modes, the single-pass and repeat-pass modes, are proved to be constants. And the values of the interferometry phases are determined by the jammer's geometry position relative to InSAR baseline, but independent of the jamming's waveform modulation and its background terrain.

Efficient global optimization has been extensively used in problems with expensive cost functions. However, this method is not suitable for high-dimensional problems. In this paper, the radial basis function network is introduced into the efficient global optimization, to avoid local optima and achieve a fast convergence for high-dimensional optimization. Our algorithm is applied to a 12-dimensional optimization of a transmitting antenna. Compared to the genetic-algorithm-based efficient global optimization and the differential evolution strategy, our algorithm converges to the global optimal value more efficiently.

In this work, a theoretical analysis on the design of the beam splitter (BS) based on the frustrated total internal reflection (FTIR) is made. We consider a model structure made of a low-index gap layer bounded by two high-index layers. In the design of a 50/50 BS, we find that there exists a critical gap thickness which is a decreasing function of the angle of incidence for both TE and TM waves. There also exists a critical wavelength for the incident wave, and it increases with increasing angle of incidence. Finally, at a fixed gap thickness and wavelength of incident wave, the critical angle in $TE$ wave is slightly larger than that of $TM$ wave. The analysis provides some fundamental information that is of particular use to the design of a BS within the framework of FTIR.

The design, fabrication and measurement of a reconfigurable fishnet metamaterial based on a new method of tuning by changing unit cell geometry is reported. Retractable elements are added to the unit cell utilizing pneumatically actuated switching. It is shown that the pneumatic actuation approach can unite a number of metallic elements into a complex conducting structure. Experimental demonstration confirms that the structure operates at two different frequencies in the GHz range in distinct actuation states. The measured results also show good agreement with numerical simulations.

A planar triple-band monopole antenna with a U-shaped stripline and a L slot is presented. The antenna is very compact with a size of 20×30×1.5 mm³ and fed by a 50 Ω microstrip line with a defected ground. The measured -10dB impedance bandwidth of the proposed antenna covers 2.33 GHz-2.51 GHz, 3.25 GHz-3.82 GHz, and 4.83 GHz-8.4 GHz, respectively, which meets the specifications of WLAN 2.4/5.2/5.8GHz and WiMAX 3.5/5.5 GHz. The radiation characteristics shows a monopole-like pattern, and the measured results are in agreements with the simulated ones.

A novel phased array antenna with wide bandwidth and wide scan angle is presented. The radiating aperture of the phased array consists of periodically and closely spaced octagonal ring elements. Tight capacitive coupling between adjacent elements is realized by interdigitating the end portions of the ring elements. To improve the impedance matching of the individual antenna elements over wide frequency band, a novel impedance matching layer consists of periodic octagonal ring element is subtly designed and placed over the radiating aperture. Both of the radiating elements and impedance matching layer are printed on a flexible membrane substrate with a thickness of 0.04 mm. Measured results of a 16-element linear array demonstrate that good impedance matching over a 4.4:1 bandwidth can be obtained for beam scan angles within ±45° from broadside. As compared to conventional wideband phased array such as tapered slot antenna array, the proposed phased array has the features such as low cost, low profile, light weight, and ease of fabrication.

Millimeter-wave (MMW) imaging techniques have been used for the detection of concealed weapons and contraband carried on personnel at airports and other secure locations. The combination of frequency-modulated continuous-wave (FMCW) technology and MMW imaging techniques should lead to compact, light-weight, and low-cost systems which are especially suitable for security and detection application. However, the long signal duration time leads to the failure of the conventional stop-and-go approximation of the pulsed system. Therefore, the motion within the signal duration time needs to be taken into account. Analytical three-dimensional(3-D) backscattered signal model, without using the stop-and-go approximation, is developed in this paper. Then, a wavenumber domain algorithm, with motion compensation, is presented. In addition, conventional wavenumber domain methods use Stolt interpolation to obtain uniform wavenumber samples and compute the fast Fourier transform (FFT). This paper uses the 3-D nonuniform fast Fourier transform (NUFFT) instead of the Stolt interpolation and FFT. The NUFFT-based method is much faster than the Stolt interpolation-based method. Finally, point target simulations are performed to verify the algorithm.

This paper presents a new dual-band, dual-polarized 1 x 4 antenna array design for telecommunication base station. One of the bands covers global system for mobile communication (GSM) band, while the other covers both digital communication system (DCS) and universal mobile telecommunication system (UMTS) bands. The antenna is based upon an aperture stacked patch layout and incorporates a simple and novel dual-layered feeding technique to achieve dual polarized radiation. For feeding the array elements, a corporate feed network is used. In order to achieve appropriate matching in both bands, a three-section Chebyshev transformer has been designed. The proposed antenna shows good port decoupling, less than -30 dB for dual linear polarization over its operating bands. Peak antenna gains about 11 dBi and 11.6 dBi have been obtained for lower and upper bands, respectively. The effort was directed toward the design of a single standalone dual-polarized antenna to cover all three bands.

In this paper, a novel design method for a dual-band bandpass filter (BPF) with arbitrary controllable bandwidths based on a simple frequency mapping function is proposed and its analytical design equations are also derived. The circuit conversion techniques are employed for implementation with distributed transmission line. To validate the proposed dual-band BPF with controllable bandwidths, a low temperature co-fired ceramic (LTCC) transmission line as well as microstrip lines are used, respectively. The two types of design for the dual-band BPF have the same and significantly different fractional bandwidths (FBWs), respectively. The first type of dual-band BPF with same FBWs are implemented at 2.11-2.17 and 3.45-3.55 GHz. The second type of dual-band BPF with different FBWs are implemented at 3.40-3.60 and 5.15-5.25 GHz. The measured and theoretical results show good agreement, significantly validating the proposed frequency mapping function methodology.

In this paper, a recently improved SO-FDTD (shift-operator finite difference time-domain) method is proposed and applied to the numerical analysis of the anisotropic magnetized plasma with arbitrary magnetic declination. By using the constitutive relation between polarized current density vector J and electric vector E and bringing the shift operators, the difference iteration equations of field components for Maxwell equations are derived in detail. Furthermore, the memory requirement is decreased significantly through incorporating a memory-minimized algorithm into the FDTD iterative cycles. The reflection and transmission coefficients of electromagnetic wave through a magnetized plasma layer are calculated by using this method. It is shown that the new method not only improves accuracy but also produces speed and memory advantages over the SO-FDTD method in kDB coordinates system proposed in the recent reference. In addition, the recursion formulae of the improved SO-FDTD method are deduced and programmed easily and they involve no complex variables, so the computations for the magnetized plasma become very simple.

In this paper, the definition of the modal impedances of the electromagnetic field in a nonhomogeneously filled waveguide is discussed. The presence of TM modal impedances, which are functions of the transverse coordinate, does not permit us to obtain a unique Z matrix of these guides. Hence, the evaluation of the scattering matrix can be involved. The introduction of a {``natural" EM} expansion overcomes this problem leading to the definition of a unique modal impedance and a unique Z matrix. This approach is applied to the simulation of the effect of a block of dielectric in an empty waveguide by ``cascading" the $S$ matrices of the existing junctions. Finally, this {``natural" EM} expansion is applied to the junction between an empty waveguide and a completely filled waveguide, obtaining an equivalent circuit which better represents the physics of this problem, and to the optical fibers.

This paper mainly deals with the problem of detecting a target against spherically invariant random vector (SIRV) clutter in the presence of steering vector mismatches. Assuming that the mismatch of the steering vector satisfies the conic constraint, the generalized likelihood ratio test (GLRT) is devised, and the geometry description is proposed for the derived solution. Additionally, the fully adaptive GLRT is derived by replacing the exact covariance with fixed point estimate (FPE). Finally, several numerical results are provided and discussed.