Phase Array Antenna as a Prototype for LOFAR Project

INTRODUCTION

A small size, receiving, dual polarized phased array antenna as a prototype for the sub-sub-array of the Low Frequency Array Project (LOFAR) was simulated, designed and built. LOFAR is a proposed large radio telescope array that will operate in the 10-240 MHz frequency range. Multiple, simultaneous beams will be digitally formed and electronically steered allowing extreme agility in frequency and the ability to perform simultaneous observations on different targets in the sky. More information on LOFAR project could be found here.

The goal of this study was to design a working model of a small-size phased array with a low gain but wider scanning angle. This model could be used as a prototype for the sub-sub array - the primary building block of the LOFAR system. In order to realize the array prototype construction the original size of the antenna was scaled down for operation at a higher center frequency of 915 MHz. The phased array beam is steered electronically by changing relative phase shifts between antenna elements. This is accomplished via digital control and analog hardware. A user-friendly interface was created using MATLAB to control beam steering. Power of the received signal was evaluated as a function of beam position and made available to the computer interface. The initial design specifications were realized, including the resolution of 5 degrees close to zenith. The completed antenna was optimized for 915 MHz operation, and other frequencies were rejected.