Reduction of a patch ground plane.

[toon]

Hi,
I'm designing a GPS receiver and I have a tricky size specification.
In order to meet this specification I have to use a patch antenna but the problem is that I will not be able to satisfy the groundplane size specification.
My question is do you know what kind of effect that will have on the patch ?
Detuning ?
Deformation of the radiation pattern ?
Modification of the input impedance ?
anything else ?

Thks for your help !

 

[bowmantenna]

Try serrating the edge of an electrically small groundplane. The serrations match the field's impedance to freespace effectively making the groundplane appear electrically larger to the attached antenna. The net effect is that the antenna pattern and impedance is restored.

 

[jbartos]

Suggestion: As an alternative to the above posting, go to the equation that you used for the patch antenna, and assess the equation potential variables for their modification to satisfy the ground plane size specification.

 

[bowmantenna]

Toon,

In general, as you reduce the size of a patch antenna's groundplane (or the ground of any antenna that is intended to operate against it) you will observe all of the effects you mention (detuning, pattern, impedance) as well as polarization. There are some exceptions. However, given your application is GPS and you have resorted to considering an electrically small groundplane area, then my guess is that you are stuffing this 'patch' antenna on some kind of handset. If that is the case, you might follow the lead of many of the other GPS handset manufacturers/designers who utilize a quadrifilar helix antenna. This type of antenna provides a superior hemispherical pattern and doesn't require driving against a groundplane. Yes, it isn't conformal and does take more space external to the electronics package. But the GPS mfrs have created some attractive packaging concepts that appear to be selling well. Moreover, you can model the quad helix fairly well with simple commercially available moment method analysis software. Alternatively you could contract the development of the antenna from one of the GPS antenna component mfrs out there such as MicroPulse or Tecom. If the quad helix is unsuitable, you may wish to consider other types of conformal printed antenna elements such as flared quad slots in the outer sheild of a triplate configuration. There are numerous ways to get the pattern/polarization/impedance/manufacturability/environmental features required for GPS reception.