Broad band antenna arrays and noise coupling for radio astronomy

In radio astronomy radio telescopes that use large spherical or parabolic reflector antennas are often used. They contain cryogenic cooling to lower the noise temperature of the antennas, which makes the antennas expensive to build and maintain. A next generation radio telescope that uses a phased array antenna instead of the reflector type antennas has been proposed. The collecting area of the telescope is proposed to be one square kilometer and the frequency range from 200 MHz to 2 GHz.; There are several advantages to a phased array radio telescope, as well as some potential difficulties that arise in its design. A phased array can have more than one beam, allowing astronomers to view multiple objects at the same time, and using analog and digital beam forming will allow for the active suppression of both mobile and stationary noise sources. Moreover, the large collecting area allows for higher noise temperature of the antenna, while still maintaining a high sensitivity. On the other hand, one disadvantage of the phased array is the potential for noise coupling that occurs when noise generated by LNAs in one antenna element is received by its neighboring elements, adding to the total noise of the telescope.; The first step in the design of the Square Kilometer Array (SKA) is the design of the sub-arrays. The sub-arrays are one square-meter dual polarized antenna arrays with an operating frequency from 200 MHz to 2 GHz. The sub-arrays elements must have broad beamwidth so that the array will have a large scan-angle and a low amount of coupling. The low coupling is important for the scan-impedance of the array, as well as its noise performance. In this thesis several antenna elements are studied, designed and built, including wire; log-periodic; slotline Vivaldi; and antipodal Vivaldi antennas. A twenty-element sub-array using the antipodal Vivaldi antenna element is designed and fabricated.; Noise coupling in antenna arrays was first observed in the Westerbork Radio Synthesis Telescope (WRST). A higher noise power than was predicted was measured when the antenna was directed at a cold region of the sky. This noise power was attributed to noise coupling between two elements in the feed of the antennas parabolic reflector. In a phased array where all the array elements are placed close together the coupling between them can be large, which will also increase the noise coupling in the array. A detailed analysis of the noise coupling of a phased array is performed. This analysis will lead to an analytical solution for the noise coupling in a phased array.