Antenna efficiency and PCB impact

Question

I'm trying to improve the range on my 433 MHz radios and came across http://www.att.com/edo/en_US/pdf/AntennaFundamentals.pdf. (Geez, there's so much RF information in many bits and pieces, if only there were a more complete source somewhere)

Section 3.2 talks about antenna efficiency and defines it to be the amount of power that is radiated by the antenna (excluding the reflections to the signal source and the power absorbed by nearby objects).

Is this the reason why most PCB designs put the antenna at a corner of the board? So that less of the power will be absorbed by the board? The reason why I ask this is that our current board does something like this:

My initial thought is that the power absorbed by the board is directional. Or in other words, the size optimization that we did by putting the antenna directly behind the board should not affect the antenna efficiency in the directions away from the board. Does this theory make sense? If so, why does everyone isolate their antenna? Is it just for a more omnidirectional radiation pattern?

Answer 1

Putting the antenna behind the board affects its performance.

Your board seems to contain a ground plane directly below the antenna, this can also adversely affect its performance, the ground plane in this case stops part of the signal from reaching the antenna.

The board size and layout also affects the antenna performance. If I am not mistaken, you have a monopole antenna from Lynx technologies (Or Laird, or Antenna Factor, same company), This antenna requires large (>10cm) ground for optimal performance.

If you can rotate the jack 90 degrees counter clockwise, you might get a significant improvement in reception range.

Answer 2

Do you have an antenna jack?

If so, then this may help.

1] I bought a signal improver for my SW which is powered and is a small board arrangement. I'll try to get you some info if you like. It is plugged in-line with the antenna wire.

2] I had poor reception of a TV station for topological reasons. The directional antenna was not enough, so I took a ~3'x4' sheet of cardboard and put aluminum foil on one side, and placed it behind the antenna. First try didn't work so I moved it up against the read of the directional antenna. I do have very adequate reception now.

Hope this helps.