It starts with an oscillator circuit producing an alternating current sine wave at the desired frequency. The oscillator circuit often involves a crystal in ord

It starts with an oscillator circuit producing an alternating current sine wave at the desired frequency. The oscillator circuit often involves a crystal in order to generate an accurate and stable frequency. The alternating current is then feed down a transmission line, which in the most basic case is just 2 wires side by side. Being side-by-side, the current going "up" in one wire is balanced by the current coming "down" in the other so that at a distance from the transmission line, the radiation from the two wires (mostly) cancel each other out. Often instead of side-by-side, one wire is often wrapped around the other with an insulator separating them (coax), but the same principal applies. The transmission line then feeds into the antenna. A basic antenna is a piece of wire exactly 1/2 wavelength long. Electric pulses "bounce" off the wire's ends, sort of like how if you tether one end of a rope and then shake the other, the "waves" going down the rope will "bounce". The length of the wire being 1/2 wavelength is key because it takes a wave exactly one cycle to start from one end, bounce off the other, and return to the start. Just as the first wave is bouncing off the start end, it gets a new "bump" from the transmission line. This allows a lot of current to build up in the antenna, sort of like how a kid on a swing can use several small well timed kicks to swing himself much higher than just a single big one could. Of course, antennas can be much more complicated than just a dipole, for example, you could place several dipoles in a row and feed them in phase so that their transmitted signals add together at points perpendicular to the row, and cancel each other at points in line with the row. Or, you could use a parabolic dish to concentrate the signals in one direction. In radar, the radio waves travel out, bounce off objects in the their path, and a small fraction of the original signal comes back to the antenna. Depending on the design the radar might have a separate receiving antenna, or it might receive on the same antenna it used for transmitting. From a radio perspective, a receiving antenna is exactly the same as a transmitting antenna, only, it's the radio waves coming in through space that cause it to resonate instead of the other way around in a transmitting antenna. Finally, the signal comes down the transmission line and into a receiver circuit which analyzes and extracts whatever data (in the radar case, it deduces distance and speed by looking at the elapsed time and frequency shifts).