tunable antenna
Does anyone has an idea of how to make a
patch antenna with tunable resonance frequency?
I have read in research papers that by connecting a
capacitor, it can be done
I have done this but the return loss increases...
any idea why this happened?
My frequency was 2.4Ghz, capacitance of 100pf between
two patches of same dimensions
Thanks
Tunable resonance can be achieved as you mentioned, using capacitive loading
on the resonant side (the lambda/2 side.) The increase in return loss should be
an intuitive process - as you change the resonant frequency, the matching of your
feed mechanism is probably not as good at the new frequency as it was at the initial
design frequency. Next, be cautious of the size of the capacitance you're using.
In my experience 100pF is a huge load for a patch and I'm almost certain you
should drastically reduce it.
Thank you JJL
I reduced the capacitance to 1pf and 20pf
and the results were improved (s11 came down to -15dB)
You are right i guess about the size of capacitor, can u tell me
what should be the size of it?
Thanks
Actually it's impossible for me to tell you precisely what value you need. In your
simulation, begin with an almost negligible capacitance value (.01 or .1pF, lets say)
and begin to slowly adjust that value up. You should see the resonant frequency of
the antenna shift slowly downward as you do. Remember that similar effects come
in the patch design phase, due to fringing fields at the edges of the patch. These
fringing fields (parasitic capacitances) electrically extend the length of the patch,
altering the field distribution for a set frequency. The fundamentals here are the
same.
Play with the value until you reach the resonant frequency you want, then compare
the matching between the original F0 and the new one. At this point you can tune
your feed network appropriately.
I did what u said and by increasing the capacitance,
I got a decrease in the resonant freq. But now the problem
is of the direction of radiation. The directivity lobe has
inclined towards the capacitor and was decreased. I
want the directivity to atleast maintain its direction
regardless of its magnitude.
Thx
I would suggest reading up on antenna arrays. Wikipedia would be an easy place to start.
ok Thanks alot for your help
Why dont you try to insert a ferro/imagnetic material to your conventional dielectric substrate and try to tune it by magnetically biasing. I have been looking through it and it seems that it works
Understand that there are always consequences when introducing magnetic materials into a design. Primarily, in antenna circuits, you invite problems with reciprocity - the ability of antennas to receive exactly as they transmit. You could also have problems with nonlinearity for even the weakest transmitted signals. I would suggest avoiding that approach.