]Design of antenna lattices with optimization of their [/B]characteristics[/B]
On design data
M.A.Letajaf, the post-graduate student of faculty of RTS
At the design and optimization of an antenna array characteristics it is expedient to con-sider the available technical opportunities and an existing level of production. The theo-retical model of an antenna array which includes real construction parameters: number of conditions and discrete phases of phase switchers, a technological master cell which will be used in a construction of a divider. The further design problems are solved as a problem of numerical optimization, there is an optimum circuit of a divider and the law of control-ling phase switchers.
In practice was obtained an extended phased array antenna with the fixed amplitude distribution and a time quantized control phases of radiating element currents.
The amplitude radiation pattern of an array has the form:
,Where N – the number of radiating units in an array, - current amplitude of i-th radiating element, - a phase of a current of i-th radiating unit , - discrete phases, M – position number of the phase switcher, - coordinate of i-th radiating unit , d - a distance between elements
We consider a problem of finding an optimum phase distribution on the discrete set of phase conditions.
From a scanning array is required forming a beam in the given direction and a mini-mum values of radiation patterns in the directions of arrival of noise. It is clear, that the degree of suppression of noise depends both on array parameters, and mutual angular posi-tion of a beam and noise.
In figure is shown the radiation pattern obtained by optimization of phases. A direc-tion of arrival of a signal 20 deg. The noise comes under 32 deg.
At approximation of a noise to a real signal beam radiation pattern is displaced aside from a noise. Reception of a signal goes on a slope of a beam, but the pattern null on noise is kept. At very close angles of a signal and a noise the pattern null on a noise is formed, but the form of the radiation pattern will be strongly distorted.
Optimum dividing device of an antenna array should satisfy a number requirements: amplitudes of waves formed on its outputs should provide necessary antenna characteris-tics; out put channels are untied, undesirable intercommunications between radiating units of an array are eliminated; the construction of a divider is technological and simple.
The criterion of an optimality takes a side -lobe level , where the sector of determination of side lobes .
As an element phase is taken 3 db ring resistive power divider. At connection of such elements in the divider circuit it is possible to obtain various amplitude distributions on ra-diating units. However these distributions are those, that out put waves are the whole degrees , the Total transmitted power remains constant, i.e. .
The description way of such binary divider circuits is offered. For symmetrical an-tenna arrays with even number of radiating elements we enter a vector of divider structure P. Vector of structure has N-2 elements, its j-th element accepts values from 1 up to j+1. It orders construction process of the circuit of a binary divider, showing on a tree divider cir-cuits to what of branches to attach the following element.
At a variation of elements of a vector of structure of a divider the parameter of an op-timality construction is calculated and there is an optimum circuit of a divider
Let's carry out results for an array 20 radiating units. The minor-lobe level 0,1089 is obtained. In figures are represented the optimum circuit of a divider, amplitude distribu-tion and a radiation pattern.
At statement of a design problem of an antenna array as problems of optimization in a set of varied design parameters provides obtaining of optimum and structurally realized solution.[/LEFT]