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# Probe position, for patch antenna ?

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#### troyka_4484

##### Newbie level 3
How to determine the perfect probe position?
Is there any calculation to do?

trokya,

Why don´t you use an incremental rottary encoder ?

+++

In a rectangular patch the impedance present a sinusoidal variation with respect of the distance to the patch center. This helps in the optimization process: if you want to reduce the input impedance you have to approach the feed to the center; if you want to increase the impedance approach the feed to edge.
I think this rule alse applies for other patch geometries and the impedance variation depends on the dominant mode of the geometry.

troyka_4484

### troyka_4484

Points: 2
well I'm working on university project, i'm using HFSS and i need to get an exact fr of 2.45 GHz, and a minimum loss of -15db.
I calculated the patch dimension and every thing, but whenever i change the coax radius or the probe radius or its position the fr change, i managed to get 2.44 and 2.46 GHz, but not the 2.45 GHz
trokya,

Why don´t you use an incremental rottary encoder ?

+++

---------- Post added at 20:38 ---------- Previous post was at 20:35 ----------

whenever i change the position of the coax and the probe, the fr change and the loss too...trying to solve this problem, i need to get a 2.45GHz fr and a minimum of -15db loss..
In a rectangular patch the impedance present a sinusoidal variation with respect of the distance to the patch center. This helps in the optimization process: if you want to reduce the input impedance you have to approach the feed to the center; if you want to increase the impedance approach the feed to edge.
I think this rule alse applies for other patch geometries and the impedance variation depends on the dominant mode of the geometry.

I calculated the patch dimension and every thing, but whenever i change the coax radius or the probe radius or its position the fr change, i managed to get 2.44 and 2.46 GHz, but not the 2.45 GHz
...
whenever i change the position of the coax and the probe, the fr change and the loss too...trying to solve this problem, i need to get a 2.45GHz fr and a minimum of -15db loss..

Tune the frequency of resonance adjusting the patch size. Increase (or reduce) the resonant length if you get a higher (or lower) resonance, proportionally to the frequency. If this changes matching, shift the probe according to the desired impedance in the way eagle5 said.
Proceed in an iterative way. Quickly you will reach both conditions.

Regards

Z

troyka_4484

### troyka_4484

Points: 2
Tune the frequency of resonance adjusting the patch size. Increase (or reduce) the resonant length if you get a higher (or lower) resonance, proportionally to the frequency. If this changes matching, shift the probe according to the desired impedance in the way eagle5 said.
Proceed in an iterative way. Quickly you will reach both conditions.

Regards

Z

I tried adjusting the patch size, and i was also stuck between 2.44GHz and 2.46GHz (-25 db loss), finally my tutor told me that a 2.46 GHz and -25 db loss is an acceptable result for this project...
thank you all
regards

hi
PLS attach u design and why u use epsilon with 9.8??????????

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