antenna-theory.com

[winson]

Hi everybody,

I'm trying to design a L probe microstrip patch antenna that resonate at 850MHz. Is it possible for the large antenna like what i'm build to have a return loss of -30dB? Currently i'm just getting return loss of less than -10dB.

Thanks.

[admin]

If you have no size constraints, 850 MHz should be no more difficult than 2GHz.

I know I've seen -20 dB in conference papers, but I'm not sure about -30 dB. Why do you need that low of a return loss?

[winson]

-30dB is just an example, actually what i desire is have a return loss of more than -10dB at the same time maintain the wide bandwidth. Currently, i have design the antenna to have a good "bandwidth", but it just have return loss of around -7dB(maximum) and no matter how i adjust the dimension of the antenna it does not increase the return loss much, so just post a question here to verify whether large antenna will having limit in its return loss.

Btw, i able to make the return loss become very low but the bandwidth will just become very narrow and this is not desire by the design specification.

[admin]

There are some things you can do to increase the bandwidth of a patch antenna:

a) Increase the substrate thickness
b) Keep the permittivity of the dielectric as low as possible
c) Add slots (like U-shaped slots to the top patch), or slots into the ground plane, which adds capacitance and tends to increase the bandwidth
d) Feed it off the center, and have slightly different W and L values that resonate at slightly different frequencies.

And so on, there are no doubt infinitely more ways than I can name

[winson]

Thanks for sharing your valuable experience.

[gelunmak]

Are you talking about L-probe feeding patch antenna? If yes, it's already a wideband design like using U-slot. Try to use air-substrate with thickness about 0.1 lambda.

Bty, so what is your bandwidth requirement (S11<-10dB) ?

[winson]

Hi,

I'm just aware that you leave a message here. Yes, it is a L-Probe Patch antenna and that project already finish.

Thanks for your suggestion. The BW requirement is about to cover 800MHz to 900MHz by using the teflon as the substrate but it fail to achieve that BW, then finally it is replaced by air substrate like what you suggested and we can achieve wider BW.

Thanks again.