RFID for car detection

Projects General Guidance
1

I'm working on a research project where I have to align a car with an RFID tag and reader. The reader is on the ground and the tag is on the bottom of the car. The distance between the car and the ground is approximately 25 cm.

I need a compact and inexpensive solution. I have looked into the 125kHz systems, but the antennas are huge and expensive with that range. I have also looked into 13.56MHz systems, but all the readers and antennas I found are expensive. For UHF, I'm worried about signal distortion because of all the metal beneath the car.

Do you know of any inexpensive solutions in the range of $10 to $50? Should I go with a DIY approach? All the DIY solutions I have read have huge ass antennas and I need something that is quite compact.

2

Unless you hav an active , powered transponder the read distance for tags is dependant on antenna size.
Look at the detector loops at you supermarket.

3

It seams to me to much distance and to much metal (but I'm not very sure). In the past I used UHF, and I read a lot of information about that. If you change the position of the tag and the antenna I believe that you will do that without trouble. But for that you will need a greater budget (a good UHF reader cost 1000USD a good UHF antenna cost more than 100USD).