microstrip fed patch antenna and quarterwave transformer

i am struggling to find out how we can design the microstrip line for feeding the patch antenna.

we can find its width using well known formulas so that its characteristic impedance is 50 ohm but what about the length?
is there any minimum or maximum length which we must use?

my second question is if we are using quarterwave transformer for matching the antenna to the 50 ohm transmission line . how much width we should use for the quarterwave trasformer. how we can calculate the required characteristic impedance
of quarterwave line ?
are there any equations or formulas for these?

regards

hi shahid78,

Z0=√(Zs*ZL)
For example if (50 ohm Transmission line)Zs=50 Ω and (Antenna impedance)ZL=35Ω
Then Chartersitic impedance of Quater wave transformer line = 41.83Ω.

Regards,
Balaguru.

hi Balaguru

well thanks for your answer. well i know the equation which you mentioned but my question was how do i know the antenna input impedance.
i can only find the characteristic impedance of quarterwave impedance if i know the impedance on the left side of the transformer which i know is 50 ohms
now i should know the impedance on the right side of the transformer which in this case is antenna input impedance which i dont know

so how can i find the input impedance of antenna if its edge fed.

regards

hi shahid,

You have to measure antenna input impedance from Vector Network Analyzer.
(just like measuring returnloss,format should be Smithchart).

We can match antenna impedance with the help of Quarterwave transformer if antenna input impedance has only real values but normally this is not the case, it also contains imaginary values.
So mostly lumped elements will be used for matching.

regards,
Balaguru.

How about using a recessed-line feed ?

Hi Shahid78,
From your questions, I would like to suggest some references.
For your first post:
Find solutions in Chapter 3 - Microwave Engineering (David M. Pozar), Microstrip section. You can calculate a desired characteristic impedance and λ/4 length for your microstrip line from given formulas and examples.

For your second post:
Take a look at chapter 6, "Modern Antenna Design" by Thomas A. Milligan.
There're some formulas which are useful.

Hope it helps!

why don't you use linecalc or appcad ?by choosing the substrate type and thickness you can find the appropriate width of the microstrip in order to be 50 Ω

well i think you havent read my question properly.
i have mentioned in my first post that i know how to find the microstrip width.
i am talking about the effect of the microstrip line length

i hope my question is clear now

regards