impedance matching. Antenna simulation

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GVVIN

Joined: 11 Apr 2008
Posts: 112
Helped: 17

09 Jun 2008 2:20 impedance matching antenna

I need to match my antenna to an impedance of 48 - j 148 ohms. (microchip impedance). So the conjugate of that should be my antenna impedance. How to measure this ? Usually we have 50 ohm system and we use a 50 ohm port .

Can we use a 48 ohm port in series with around 1 PF capacitor (which has an impedance of approx -j150 ohms @950 MHz) and then connect my antenna for measurement. Is there any other technique . I am using CST for my simulations.

Thanks
GV

pankajdudulwar

Joined: 30 Mar 2006
Posts: 134
Helped: 2

09 Jun 2008 11:34 matching antenna

Is their any provision in your design for using LC circuits to transfer the impedance to 50ohm. This will solve your most of the problem. If not let me know .
Thanks,

tyassin

Joined: 22 Jul 2004
Posts: 340
Helped: 44
Location: Northern Hemisphere

09 Jun 2008 12:41 rf antenna impedance matching technique

Hi

Your impedance of 48-j148 ohms can be measured with a normal 50 ohm system. Normally you look at the center of the Smith chart(50 ohm), but now your match-"point" is just at another place(48+j148). It is the same matching technique as before and the same when you measure it.

Regards

GVVIN

Joined: 11 Apr 2008
Posts: 112
Helped: 17

09 Jun 2008 13:23 matching

thank you for your replies.

I am trying to design a UHF RFID Tag Antenna. The micro chip impedance is 48-j148 ohms. I cannot use LC matching in actual situation. for simulation I can.

Yes matching can be done but how to define a port, If I am using a loop antenna , I tried to represent the tag impedance using a series resistor and a capacitor and match the antenna to it . I couldnt find any complex port also in CST.

Hope I have explained my concern clearly

Thanks in advance
GV

zirtapoz

Joined: 25 Dec 2007
Posts: 167
Helped: 10
Location: finite space

10 Jun 2008 7:49 antenna impedence matching with lc

You can easily simulate ports with impedance having reactive parts on HFSS or ansoft designer. Try to use Ansoft designer(Studet version free) Easy to handle for UHF Rfid tag simulation.

byteptr

Joined: 29 Apr 2008
Posts: 112
Helped: 11
Location: Europe

10 Jun 2008 9:15 impedence matching in antenna

You can match complex impedance also with transmission lines instead of use LC circuits

GVVIN

Joined: 11 Apr 2008
Posts: 112
Helped: 17

10 Jun 2008 9:37 ansoft designer impedance matching

Explanation attached

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zirtapoz

Joined: 25 Dec 2007
Posts: 167
Helped: 10
Location: finite space

10 Jun 2008 12:59 lc matching for antenna

GVVIN wrote:

Explanation attached

What about the pattern u used on tag antenna??? if you modify the pattern on a simulation tool i have described before(transmission lines acts as capacitor, resistor or inductor), you ll not be on need of capacitor or resistor. So try to use ansoft designer(SV) draw your antenna pattern and use gap source. you can see whatever parameter u need with reports(S, VSWR, impedance etc.)

Good luck. Smile