Increasing Bandwidth of Patch-Antenna

I have designed a Patch-Antenna for a 868MHz System. Because the size
of this antenna was critical, I used a Printmaterial with a high er value
(Taconic CER-10 with er=10).
So it was possible to design an antenna with the dimension of about
35*80mm. The gain of this system is about -3dBi (better than by use of
a shortened patch).
This antenna has a very low bandwidth of about 5MHz. If this antenna is
used outside, the temperature-drift will be a problem (frequency-drift
is about 15MHz for 40°). So I have to increase the bandwith.
Which possibilities do I have? (It's not possible to use a multi-layer PCB,
so a slot feed is not possible).

Thanks

Normaly you can increase the bandwith by one of this wais:

- Decrease Er of material, a bigest patch
- Increase dielectrical heigh
- Some multi-dielectrical structures
- Some parasic in the patch, but you will lose polarization purity

I hope it can give you a clue

TaPa

mr_ghz,

your antenna is probe fed or edge fed?

If it is probe fed, I know a design which you can increase bandwidth to %20.

check this site out.

hxxp://www.ee.ucla.edu/antlab/ARAMHTML/Eshape/Eshape.html

regards,
Lkuzu

Hi Ikuzu

currently my antenna is edge fed, but it's change it to probe-fed. So
your link could be interesting for me, but it doesn't work (page removed).
Do you have a copy of the page content?

Thanks

just change hxxp with http. the link is smiling at my side.

Hi g86,

Next time, I will read the link a little bit more carefully... sorry
The idea with an E-shaped patch is good, but in my reality (using a
substrate with a high er) it doesn't work. I can increase the bandwith
from about 5MHz to 10MHz, and this is not enough. The advantage is
the (nearly) unchanged antenna-gain.
The best solution for my problem seems to be a resistor-loaded patch.
I can 'choose' my bandwith, but the gain is significant lower - that's life.

Thanks

Do u mean Gain Bandwidth or Impedance Bandwidth or both?
How much space do u have?
U could use planar parasitic elements.. u don't have decrease of Poplarization Purity.. Using other close patches u can improve your Gain.. In that case u have a larger antenna.....

Otherwise u can load your patch with slots to enlarge your Impedance Bandwidth but the Gain can decrease... it depends on your requirements...

For outdoor applications u should use some cover dielectric...(a superstate cen improve your Gain!) radome or something to avoid Temperature drift..

Be careful if you increase the thickness of your dieledtric.... higher order modes could be excited.

Regards
Lupin

Yes and we cannot get everything in our life. :( Anyway you are towards an optimum life with possibly -ve gain. :P Best wishes..