Minimum Number Of Active Elements Research Articles

Distributed Convex Optimization Compressed Sensing Method for Sparse Planar Array Synthesis in 3-D Imaging Sonar Systems

Synthesis of sparse planar arrays can effectively reduce hardware costs and computational complexity in phased array 3-D imaging sonar systems. Traditional stochastic methods, such as simulated annealing, require multiple experiments and parameter adjustments to obtain optimal results. Methods based on compressed sensing (CS) can overcome this defect. However, when applied to large arrays, CS methods require vast computational complexity and may not obtain optimal sparse results because of violating the restricted isometry property. To make CS methods more practical, a distributed convex optimization CS method is proposed here for the sparse planar array synthesis in 3-D imaging sonar systems. This method is based on the CS theory, solving the minimum number of active elements under certain beam pattern constraints using the iterative reweighted l 1-norm minimization algorithm. Then, a multistage distributed framework is proposed to decompose the array into multistage subarrays, and the array synthesis is performed sequentially for each stage subarray to reduce computational complexity and obtain higher sparsity rates. Some applications of sparse planar array synthesis are employed to evaluate the efficiency of the proposed method.

A new ultra low-power, universal OTA-C filter in subthreshold region using bulk-drive technique

In this paper, a new ultra low-power universal OTA-C filter which can properly operate in all modes of operation (voltage, current, trans-resistance and trans-conductance) is presented. However, in order to reduce the power consumption effectively, the proposed circuit uses subthreshold transistors which are biased at Ia=50nA, Ib=150nA. Furthermore, using the bulk-drive technique leads to a reduced power consumption as well as the supply voltage of ±0.3V. Moreover, the grounded capacitors are used to effectively reduce the parasitic effects. However, the result of sensitivity analysis shows that the proposed circuit has a very low sensitivity to the values of active and passive circuit elements such as: trans-conductance (gm) and capacitance (C) values. Furthermore, the proposed circuit uses the minimum number of active elements to effectively reduce the power consumption as well as the chip area. Finally, the proposed filter is designed and simulated in HSPICE using 0.18µm CMOS technology parameters, while HSPICE simulation results have very close agreement with theoretical results obtained from MATLAB, which justifies the design accuracy and low-power performance of the proposed universal filter.

Thinning and weighting of planar arrays by modified teaching–learning-based optimization algorithm

Synthesizing antenna arrays with a minimum number of active elements is a problem of high importance in ultrasonic applications. This paper proposes a modified teaching–learning-based optimization (MTLBO) algorithm for thinning and weighting planar arrays to synthesize the desired antenna array factor. Not only the number of active elements and their corresponding excitation weights are optimized, but the peaks of side lobe level, main-lobe width, and current taper ratio are also minimized as objective functions in the multi-objective formulation. The optimization method for designing thinned planar arrays proposed in this work is easy to be implemented and requires few controlling parameters. The simulation cases demonstrate effectiveness of the proposed method, and it is proved that the MTLBO outperforms simulated annealing method and hybrid genetic algorithm through comparisons.

Efficient Combined Array Thinning and Weighting for Pattern Synthesis With a Nested Optimization Scheme

A novel procedure to thin an antenna array which synthesizes a desired pattern with the minimum number of active elements is introduced. The proposed method yields both the active elements and their corresponding excitations of a thinned array having the minimum number of active elements needed to meet several prescribed design specifications of the radiated far-field pattern. Specifications such as achieving a minimum gain, obtaining a pattern with a maximum allowable sidelobe level or synthesizing a shaped beam pattern confined into a mask are considered. Null field directions can also be added. In order to carry out the thinning, a genetic algorithm is used, while computing the excitations is carried out through linear or quadratic programming. The procedure incorporates the generalized scattering matrix analysis of an array made up of elements whose radiated field can be expressed as a spherical mode expansion, thus taking all electromagnetic effects inherently into account. Therefore, since the presence of an element can substantially alter the array features because of mutual coupling, two types of thinning are considered: removing elements or turning them off. Numerical results of arrays made up of isotropic sources, dielectric resonator antennas and microstrip patch antennas are presented.

Realization of current-mode high-order filters employing multiple output OTAs

Current-mode linear transformation (CMLT) high-order filters with minimum number of multiple output operational transconductance amplifiers (MOOTAs) are presented. Based on proposed design methods, we can synthesize current-mode high-order all-pole filters with minimum number of MOOTAs and all grounded capacitors efficiently. Moreover, high-frequency canonical CMLT elliptic filters with minimum number of MOOTAs and floating capacitors are also presented. Our proposed filters have the following merits: simplified design procedures, minimum number of active elements and simple design equations. Two design examples are demonstrated in this paper. Experimental results that confirm the theoretical analysis are provided.

New universal biquad filters using only two unity-gain cells

New current-mode and voltage-mode universal biquad filters are presented using only two unity-gain cells (one current follower and one voltage follower) in each configuration. The proposed filters employ one less follower than in the literature to date. The filters can realize highpass, bandpass, lowpass, notch and allpass responses without any changes in the circuit topology. The circuits enjoy the following advantages: minimum number of active elements, no component-matching condition and low active and passive sensitivities.

Optimum design of feed structures for high G/T passive and active antenna arrays

In this work, noise analysis of parallel feed structures is presented. Signal and noise behavior of the feed structures are signified by the newly introduced concepts of "coherent" and "incoherent" impedance match of power-combining structures. It is also shown that a feed structure can be redesigned for low-noise operation without affecting the radiation characteristics. Optimum design of parallel feed structures for low-noise operation is explained. Also an optimum use of active elements in such structures is investigated to have a low overall noise temperature of the antenna array with minimum number of active elements. In the analysis, a new method is introduced where a "noise-equivalent line length" (NELL) is defined. This definition, which unifies the contribution of noise from different array elements, is used in the design of a parallel feed structure and as an active circuit replacement criteria in passive arrays.

A chebyshev rational function with low Q‐factors

AbstractThe presented rational function is a modification of a recently published Chebyshev rational function defined by means of some orthogonal polynomials. the necessary conditions providing for the lowest pole Q‐factors for a given ripple are found. the function is a ratio of two similar Chebyshev polynomial transfer functions with multiple poles.The selectivity of the function can be increased by using the Chebyshev rational characteristic function instead of the characteristic polynomials. the minimum number of active elements in the cascade connection is obtained with third‐order elliptic characteristic functions.The function is compared with the Cauer (elliptic) and MCPER filters. the distinctive features of the presented function are small Q‐factors of the poles, almost ideal dynamic range, simple design and poles with the same multiplicity m, where m designates the number of cascaded blocks.