Ground plane/matching network of 915 Mhz antennas (chip,helical whip)

[kayoux1025]

Hi,

Our board has an SMA connector for antennas. The current design uses a 915 Mhz Xemics chip to transmist/receive. Following the design of their evaluation board, we did not add any impedance for the matching network. With a standard 1/4 wave antenna-- such as the CW monopole antenna from Linx Technologies -- it works fine. However, we tested, helical whip 1/4 wave antennas without success. Their performance on our board is the same as without any antenna. We assume the problem is due to the ground plane and the matching network. On the current design, there's no ground plane in the plane normal to the antenna axis. (the ground is made with the SMA connector only, which is connected to the PCB ground) Is this what we need? If so what size would you recommend?

It is crucial to know since I want to build a antenna test board, which will allow me to test with different matching network configurations with different antennas in order to assess their performance relative to each other. I want to do the same with chip antennas.

Any information on the ground plane/matching network would be greatly appreciated.

Thank you,

Yvan

 

[Higgler]

Did you test the 1/4 wave helical whip by itself? and compare it to the 1/4 wave monopole?. It sounds like either that helical antenna is broken or it isn't connected to your circuit board properly as you believe it is, maybe there's a crack in the antenna you can't see.

Another possibility is that the helical antenna results in antenna polarization different from vertical, it may be horizontal, though normally a helical is circular. If you are testing it with a vertical monopole antenna, maybe moving one of the antennas would help you determine if it's a polarization problem with the antennas.

kch