Antenna ground plane 1

[chartman]

I have a large d/sided pcb with microcontroller and 433M Rx/TX module attached. I want a PCB track antenna of 16cm length along one edge.Track width is 60 thou ( 1.5 mm) . Do I/must I have a ground plane underneath it? I know about keeping other stuff 5mm away. I have a VCC plane on the topside. Does this have to be kept 5mm away from the aerial track as well?
Thanks.

 

[VEBill]

One small point, your Vcc plane should be effectively grounded at RF (via the bypass capacitors).

As to your larger question - perhaps someone here will have some recent hands-on experience. My guess is that you would want to keep your antenna away from everything else (including parallel surface ground planes).

 

[BrianR]

The simplest way to make a 433MHz antenna on a PCB is to construct it as a track, clear of the ground. It's length will be shortend by the velocity factor of the PCB dielectric, ie by 1/sqrt(Er). Er will be from 2.5 - 4.5 on common PCB materials, so you need to find out what yours is. Eg if Er = 3.5, then Vf = 0.534 and the length of your antenna element will be 53.4% of it's free space length which for a lamda/4 element @ 433MHz = 93mm.

You can further shorten the antenna by capacitively loading the far end to ground but this will need some more serious maths or modelling to get right.

 

[chartman]

Thanks guys, very useful. Appreciated.