Friday, June 7, 2013

Testing an Antenna Array Inside an Anechoic Chamber

For the last couple of years, I have run tests on my anti-jamming antenna array inside an anechoic chamber. I have a picture of my antenna array inside the chamber below.

Figure 1: Antenna Array inside Anechoic Chamber

 The anechoic chamber is a special room designed specifically for testing antennas and antenna arrays (see Figure 2 below). The room is lined with blue absorbing foam and is meant to prevent stray electromagnetic (EM) energy from being reflected off walls and other objects. This makes sure that the signal coming from the horn antenna is the only signal received by the antenna array. Think of the horn antenna as a basketball player throwing foul shots into a hoop (represented by the antenna array). The shot should only count if the athlete throws the ball directly into the hoop. However, if the athlete were to throw the ball against a wall, the ball might bounce off and go into the hoop anyway. You could think of the blue absorbing foam as lines of referees to catch wildly thrown balls and make sure that the basketball player doesn't score points by cheating.

Figure 2: Test Setup Diagram Showing Antenna Array inside an Anechoic Chamber
When antenna engineers test antennas inside an antenna chamber, they are interested in the antennas' radiation patterns. Radiation patterns measure how well antennas focus EM energy in different directions. There are multiple names for the radiation patterns that they measure: Azimuth, Elevation, E cut, H cut. In my times, I was primarily interested in the Azimuth patterns with my antennas standing up (i.e., vertical) with the plane of measurement parallel to the ground. To get that pattern, I attached my antenna array to a rotary table with the array facing the horn antenna as shown in Figure 2. I then rotated the array 360 degrees in several degree increments and measured the power between the horn and the array at each step. I wrote a computer program that controlled both the turntable motor and the VNA to collect these measurements.

My computer program also included a genetic algorithm (GA) that optimized the radiation patterns to maximize EM energy towards the Signal of Interest (SOI) and minimized EM energy in jammer directions. I emulated SOI and jammers in the chamber by rotating the turntable in their respective directions and measured the power received in those directions with different hardware settings chosen by the GA. I'll explain more on how the GA works, but for now you can think of it as a computer program that emulates the concept of "Survival of the Fittest" mating in nature.

The antenna chamber is part of a previous project (led by Dr. Dan Stancil) called the Project Remote Educational Antenna Laboratory (PREAL for short). You can find more information about the PREAL project by visiting its webpage. Although you could see whatever antenna or antenna array is in the chamber via the PREAL webcam, I am sorry to say that it is not up at this time because the PREAL computer died. However, I am in the process of getting a new computer and hope to have PREAL up and running shortly.


Jonathan Becker
ECE PhD Candidate
Carnegie Mellon University