The Study Of Reactively Loaded Directive Arrays

The radiation characteristics of an N-element antenna system can be controlled by impedance loading the ports and feeding only one or several of the ports. The resonance theory was proposed by R.F.Harrington, who got the resonated current by impedance loading the N ports in order to achieve a high directivity of the radiation pattern. Assuming sinusoidal current approximation, an optimization calculation was carried in this process above by using an optimum seeking univariate search method. Analysis and computation of reactively loaded directive arrays is done by using the Method of Moments(MOM) and an optimization procedure based on a quadratic interpolation method. The relationship between the characteristics of an N-element reactively loaded array and the spacing among the array elements, between that and the number, the thickness and the length of the array elements are given. The proper optimization of the gain and input impedance of an antenna is discussed in the view of practice. According to the symmetry of the circular array, the algorithm for solving the general impedance matrix assignment of MOM is presented to save computational time. The mutual impedance matrix of the circular array is also studied by using network theory and MOM . In the end, a seven-element circular array with six reactively loaded antenna elements equispaced on the circle and a central one to be fed is designed and constructed. The input impedance, radiation pattern and gain of the array are measured and the experimental results are in agreement with the computational values.