Bandwidth of linear antenna arrays�

Abstract

Presented in this thesis are the following theoretical investigations on linear antenna arrays:

A generalised expression for the array factor of a linear antenna array has been derived, which can be applied to both equally and unequally spaced arrays.

An in?depth study of the beamwidth of a uniform linear array of equally spaced, isotropic radiators has been carried out. A new method involving representation of the array in the (u,v)(u, v)(u,v)-plane to study the effect of various array parameters on the formation of the beam of the array has been proposed. The beam may be said to be fully formed within the R?dB?down points if both the lower and the upper R?dB cross?over points exist. Extensive numerical computation of the beamwidth of several arrays has been carried out, and the data obtained has been presented in the form of tables and graphs suitable for use as design curves.

A study of the bandwidth of linear arrays, defined on the basis of the beamwidth of the array, has been carried out for the case of a uniform linear array of equally spaced, isotropic radiators (ULAEIR).

The effect of spacing the elements of the array unequally on the bandwidth of the array has been studied for the following element?spacing distributions: 1. Binomial distribution (thinned outwards): Spacings between adjacent elements are proportional to the binomial coefficients, increasing towards the extremities of the array. 2. Binomial distribution (thinned inwards): Spacings between adjacent elements are proportional to the binomial coefficients, decreasing towards the extremities of the array. 3. Sinusoidal distribution (thinned outwards): Spacings between adjacent elements are proportional to the sine of the distance from the centre of the array. 4. Sinusoidal distribution (thinned inwards): Spacings between adjacent elements are proportional to the cosine of the distance from the centre of the array. 5. Random distribution: Spacings between adjacent elements are chosen randomly.

In each of the above five cases of unequally spaced arrays, the results have been compared with those of the corresponding ULAEIRs. It is observed that there is an improvement in the bandwidth of the array in the case of the binomial distribution (thinned inwards) and also for the random distribution of element spacings.