Mills CrossThe quest for good
resolution and large energy-collecting area has led to the development of several ingenious
radio telescope systems. One of the earliest was the Mills Cross, invented in 1953 by Bernard Mills of the University of Sydney, Australia. In the Mills Cross two antennas are used, each long and thin and fixed to the ground. Because of their shapes each antenna has good
resolution in one direction, the direction parallel to its long dimension, and poor resolution in the other direction. In a Mills Cross, the two antennas are arranged at right angles to one another, usually so that they look like a cross from above (hence the name), and the signals from the two antennas are multiplied together. The result is an overall response that gives good resolution in both directions. The largest Mills Cross is at Molonglo, Australia, where the antennas are each one mile long. Other large Mills Crosses are at Bologna, Italy, and Penticton, British Columbia. The configuration of a Mills Cross makes pointing the telescope's response pattern
difficult and following objects as the Earth moves impossible; the telescope is also difficult to operate at different radio frequencies. As a result new Mills Crosses are not being built.