I am currently in the process of building an RFID access system for my house + car. I've worked out the software side (I am using an arduino) but am having difficulty with the hardware side. I bought one of these for the transmitter but the read range is terrible – the access dongle has to be touching it for it to register.
I'm thinking about cutting the traces on the card and building a new antenna to amplify the read range. Unfortunately I don't know how to do this. I've read through the antenna cookbook and the antenna design notes from TI, but I'm a hobbyist and a lot of it seemed very general and went over my head – it would be great if I could get a more prescriptive answer.
I would like to have the antenna read from 5-10cm in most orientations if possible.
How important is material choice (wire/tape/tube)?
Do I need an additional power supply on the antenna end or is the 5V from arduino enough?
Can I build a square antenna into the flashing around the card window or will the metal create too much interference?
Best Answer
Unfortunately, it is not easy to design a good 13.56 MHz antenna. In general, a good antenna is at least 1/4 of the operating wavelength (of ~22m), so any practical 13.56 MHz antenna would be a bad antenna.
The main problem with electrically small antennas is that radiation resistance is tiny (less than 1 Ohm), making it almost impossible to match it to the 50 Ohm. One technique for matching would be to introduce a small series resistance (e.g. 2 Ohm) and then match to it with capacitors and inductors. However, this approach is difficult without access to a vector network analyzer.
I noticed that the module has a UFL connector. One way to improve the antenna would be to plug in another antenna you buy off the shelf and disable the current one (will probably need to cut traces of the old antenna)
To answer your questions: "How important is material choice (wire/tape/tube)?" - not important at 13.56 (as long as it is metallic)
"Do I need an additional power supply" - not if you are using the same chip
"Can I build a square antenna into the flashing around the card window" - would need more info on this.