How to determine the input impedance of a patch antenna using ADS?

[theone23]

Hello,

I want to determine the input impedance of a patch microstrip antenna (W=49.41mm L=41.76mm, er=2.2) by using ADS Momentum, how can i achieve this?
i need it so i can match the antenna to a 1/4 wavelength transmission line.

I'v done a simulation in ADS Momentum and it shows that the impedance at my desired frequency (2.4GHZ) is - Zo*(5.733+4.43j), couple of questions:
1. as far as i know i can't match a complex impedance with a 1/4 wavelength TL, how do i turn it to a real value so i can match it? do i need to take only the real part?
2. I've used ADS's LineCalc and it calculated that the Z0 is 3.93 Ohm, is this the same Z0 that ADS momntum showed me ? - Z0*(5.733+4.43j) ?

attached is my mementum results.

THANKS guys.

 

[volker_muehlhaus]

Zo*(5.733+4.43j)

With Z0=50 Ohm, input impedance is 286 + j221 Ohm.

What feed method did you use? You should be able to change the feed position to achieve a lower impedance.

 

[theone23]

if that's my input impedance how do i match it to a 50 Ohm TL using a 1/4 waveguilde? (can only match it with a real impedance) do i need take only the real part (286 Ohm) for the matching
or do i need to find a spot on the antenna where my impedance is real and from this point do the matching?

and a final question, if Z0=50 (my TL impedance) what's the Z0 that ADS LineCalc is calculating - 3.93 Ohm? (attached to this a picture)

What feed method did you use? You should be able to change the feed position to achieve a lower impedance.

I'm using a regular Microstrip line feed of 50 Ohm which be latter connected to a 4:1 power divider - i'm building a 4 elements antenna array, but first i need to figure out how to match a singel patch to a 50 ohm TL... =/

 

[volker_muehlhaus]

if that's my input impedance how do i match it to a 50 Ohm TL using a 1/4 waveguilde?

Don't start external matching yet. Optimize your feed first (match by moving the feed position).

and a final question, if Z0=50 (my TL impedance) what's the Z0 that ADS LineCalc is calculating - 3.93 Ohm?

That is for a very wide line (not radiating, feed width = line width). You can't use linecalc for patch antenna calculation. You can only use if for lines.

 

[theone23]

after testing many feed positions the best i've got was -9 dB with a pure real Zin or 32 Ohm, and after i've matched it with a 1/4 wavelength TL i was able to get a -25 dB S11, (3.16e-3 unitless)
does such a result (-25dB) considered a good matching?
many thanks for the help.

 

[volker_muehlhaus]

Yes, 25dB matching is fine.

- - - Updated - - -

Yes, -25dB matching is fine.

 

[VIP_TEMAA]

You didn't indicate what is the value of matching ,is it 50 ohm
Can you show us you design
I am new ,also I am facing same problem
I need you help step by step how I can design one element with good matching to 50 ohm