How to point an antenna without moving it?

Foundations of Amateur Radio

The radio telescope at Dwingeloo in the Netherlands recently promoted an Open Day where visitors were treated to tours and live demonstrations. One video caught my eye, a 2.4m dish on a remote controlled azimuth and elevation mount that scanned the entire sky every fifteen minutes and afterwards created a map of the captured radio signals.

Having carried a dish that size around Australia for a couple of years, I was in awe. After I figured out how you'd create the map I was grinning. Essentially your program moves the dish through all the elevation and azimuth combinations while recording RF for each. Mapping becomes the process of drawing a representative dot at each location, and in doing so you have the basics of a radio telescope.

It gets better.

Imagine two identical antennas, side-by-side, receiving the same signal head-on. The combined antenna signals are said to be "in phase" and will reinforce each other, resulting in an amplified signal.

However, if the source is off-centre, its signal arrives at the closest antenna slightly before the other and that delay, or phase, between the two will cause their combined signal to appear weaker or attenuated, because they're no longer entirely reinforcing each other. These signals are said to be "out of phase".

If you were to add a slight delay to the earliest signal, or said differently, change its phase, the two would again appear to arrive at the same time, be in phase, and again reinforce each other.

In doing so, you've essentially modified the focus of the antenna toward the off-centre signal by adding this delay or phase shift, and so by modifying the phase, you can shift the antenna focus. Just so we're clear, there's no actual moving parts here, we're electronically adding a phase shift to adjust the delay between antenna signals.

In addition to changing the phase of any of the antenna signals, you can alter how much each antenna contributes to the combined signal and when you do that, you'll change the radiation pattern of the system.

You might ask: "Does all this apply to receive or transmit antennas?", to which I'll say: "Yes".

This arrangement of antennas is called a "phased array" and was first demonstrated as a three element array in 1905 by Nobel laureate Karl Ferdinand Braun, who shared the 1909 Nobel Prize in Physics with Guglielmo Marconi "in recognition of their contributions to the development of wireless telegraphy".

While I've been talking about tw