Okay, so it's really antenna radiation pattern testing - but that isn't as catchy.
Yes, there is modeling software and, yes, it is accurate. But nothing really beats a hard measurement.
My objective is to validate antenna radiation patterns. Because I'm going for pattern, not true power levels, I will use relative values; whatever the meter gives me. I will focus on the 2 meter band, 144 MHz to 148 MHz.
Before anyone freaks out, yes, I am a licensed amateur radio operator.
Phase 1 will be to verify my ability to measure RF signals. The antenna will be a vertical dipole. I should see roughly equal readings in all directions.
Phase 2 will be to test a 3-element yagi. After measuring the 8 compass points (N, NE, E, SE, S, SW, W, NW), I will try to verify the shape of the forward lobe.
Phase 3 will be to test a 2-element cardioid pattern. This is formed when two 1/4 wave antennas are placed 1/4 wavelength apart and one is fed 90 degrees out of phase. It's a test question on the Amateur Extra exam. I want to verify the single null to the rear.
The test equipment will basically be an RF detector circuit. Preliminary testing with a Baofeng UV-82 and a RF detector circuit built into a Harbor Freight multimeter have proven successful. It's at least at levels safe for an Arduino.
The RF detector was from QST magazine, "DMM Field Strength Meter", February 2015, page 71. I found a very similar item on Instructables.com. https://www.instructables.com/id/RF-Meter-for-Multimeter/
You can see that I took a few liberties with the DMM. It will only be a RF meter for the rest of its life. I will also be using this meter to "calibrate" the Arduino detector circuits to give similar readings. They'll all be wrong together.
Phase 1: Antenna Radiation - Phase 1
Phase 2: Antenna Radiation - Phase 2
Phase 3: Antenna Radiation - Phase 3