works by timing how long it takes for the radio
pulses it sends out at a particular angle take to return. These pulses need to be highly directional. Most recreational radar
units come in a dome and have a small transmitter surface and so do not produce a very directional signal.
A real radar system uses an open array, the longer the array is, the more focused (directional) the radar pulse is, and so the more accurate the radar system. Here, most fishing
boats, even small ones, rely on radar, and use open arrays.
Open array units are more expensive and not very good on sailing boats where ropes can get entangled with the array. Consequently, most recreational radars suitable for sail boats use a dome and hence aren't very good.
However fairly recently several techniques to improve the situation were commercialised. If the radar sends out more pulses per second you can get more precise information if the beam is tight. If the beam is not tight, the radar might get confused (you'd get a phantom image).
So these newer radar systems use variable frequencies instead. That way they can tell from the frequency of the return signal where the radar was pointed when it transmitted. This also reduces the power consumption
of the radar required considerably.
I have no idea how good the new system is but it might be worth investigating if you're either sailing, or you can't afford an open array radar.
A final note: in the old days, radar relied on a very long persistence phosphor green screen
to work. The physical persistence of the phosphor itself, the ability for it to keep glowing for a long time, is what made radar work by providing a "memory" of the return pulses. Modern radars use software
and memory to do this instead. Consequently, high speed pattern recognition is used for things like rain and sea clutter rejection, instead of tuning analogue equipment
. This can be very effective but it depends heavily on the quality of the software
and the digital processing electronics
. Tuning and using such software based radars is a black art. It takes a lot of practice, just as it did in the old days, to get the best out of your radar. So if you buy a radar, practice with it regularly!