microstrip antenna: inset feed vs L/4 trans.

[indiaco]

hi i´m designing an antenna for 802.11 and having some troubles with the feeding. The question is : are lambda/4 transformers as good as a microstrip inset feed ?
i think this is it, for a start...
thanks a lot.

 

[zubair]

The main thing is u have to know the i/p impedence of the patch e.g u can use transmissionline model for this purpose.Then both the impedence matching techniques i-e insetting or quarter wave will give the good results but If u use quarter wave it will increase the feedline length also there will be discontinuties involved so in my opinion inset feed is a better choice.

 

[indiaco]

thanks zubair for your answer.
The thing is i am following the balanis book to build my antenna, but it doesn´t have a formula (or pay attention at all) to the distance bettwen the inset feeding microstrip and the actual microstrip patch (if not clear let me know).
I do know the Z of the patch and the (i asume) correct Wo of the strip, althoug i don´t know how this distance i talked about before influences the impedance or radiation of the antenna.
That is why i came with the idea of matching with a L/4 transf.
If anybody has suggestions about this i´m happy to hear...
thanks a lot.

 

[mild-seven]

Please take a closer look at Balanis book.

There is indeed a formula for you to calculate the depth of inset.

Now I am using Ansoft Designer on the same 2.45G inset-feed square patch antenna.

The formula is quite good in Designer for the 50-ohm matching.

But the problem is its narrow-band matching.

2.45G is ok for 20DB RL, 2.4G and 2.5G are not good for 5dB RL.