im thinking you want a simple radar transponder. if you could have 2 inexpensive walkietalkie circuits. then you could simply narrow the bandwidth with a notch filter. then make a receiver and transmitter that would transmit on one frequency and receive on another frequency. there would be one transmitter and receiver in the car and one receiver transmitter pair outside the garage running off the exterior driveway light.. the car pair would revive on the same freq as the houses transmitter and the car transmitter would transmit on the house's receive freq.. the closer you get the higher the feedback freq.. the low-cost transmitters/receiver pair carrier frequency would be innately unstable so the frequency but the feedback frequency would be exact. infact. you could make simple high-pass filter that would only allow it to feedback on the target frequency or higher. mmmkay?
if you want any details on how to do that. i guess i assume your knowledge of basic electronics to be too high and i would be glad to make the circuit for you. but i would have to make a video to copyright it for patent.
love, jonathan
p.s. we used to get the walkietalkie pairs at the dime-store for 1$ for a pair of channel 14 citizens band walkietalkies. i think that was 29.245mhz. but i guess you would need 2 different frequencies.. yet same principal but todays cheep txrx devices are 433mhz arduino says they have a range. the receivers auto tune. i guess you would have to make a hibird mixersplitter by tuning the antenna like rabbit ears and spacing then correctly to keep it from tuning to itself, might be easier to use 29145 for one channel and 433 for the other channel. good luck
