A.N. Tuvaev, A.O. Manichev

The possibility of flexible control of the radiation pattern shape is one of the basic requirements in design of phased array antennas (PAAs). For example, in order to increase the speed of search at shorter distances or communicate with an object having high angular speed, the PAA beam broadening can be used. Irregular element placement is desirable for the synthesis problem. At the same time, many known methods for beam broadening require the regular placement of PAA elements. Therefore, it is important to develop beam broadening methods for irregular PAAs. Two methods of this kind are studied in this paper. The first method for beam broadening is based on a hyperbolic phase distribution, which focuses the PAA beam to a point situated either before its aperture or behind it. The principle of operation of this method lies in determination of the focusing distance which provides the required beam width. This method was obtained experimentally. However, it is supposed to be applicable to all PAAs with axial symmetry in geometry and amplitude distribution. The second method for beam broadening uses geometrical properties of a spiral irregular PAA. In accordance with this method, the element phase is incrementally changed by a constant value from element to element along the PAA spirals. The resulting phase distribution is quite similar to the parabolic phase distribution frequently used for beam broadening. The beam width depends on the size of the phase difference between adjacent elements. It is important to note, that in the case of a series feed along PAA spirals the required distribution can simply be obtained changing the operating frequency. At first, the operation of the methods was tested through the use of a mathematical simulation of a spiral irregular PAA consisting of 384 elements, placed along six spirals. The beam width was increased by 20 and 250 times (in solid angle). The optimal parameters of the methods were determined in order to minimize the pattern ripples in the main beam region. The behavior of the optimal parameters with frequency change was also studied. The mathematical model used in the simulation was verified experimentally. The PAA radiation pattern was measured for a number of beam scanning angles and at different frequencies with an Agilent network analyzer in the collimator. The real PAA main beam was broadened using the proposed methods by 250 times (in solid angle) with a maximum ripples value of 7.5 dB. Simple analytical expressions for calculation of the optimal parameters of the methods at a given frequency in a 10% frequency band were obtained. Experimental results are in good agreement with the results of mathematical simulation.