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JulianCavinaugh AntennaTheory.com Newbie
Joined: 15 Oct 2010 Posts: 8 Location: US


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admin Site Admin
Joined: 03 Jan 2007 Posts: 205

Posted: Fri Oct 15, 2010 8:41 pm Post subject: 


I believe you have to request currents to be calculated in the solution.
Then you should be able to get the impedance (the source is assumed to be 1 volt, or whatever you specified in the sources tab). 

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JulianCavinaugh AntennaTheory.com Newbie
Joined: 15 Oct 2010 Posts: 8 Location: US

Posted: Fri Oct 15, 2010 9:00 pm Post subject: 


After I request the current and set the Voltage source, I get the input impedance for the patch antenna, which is approximately 150 ohms, but I still cannot get the impedance of the whole patch antenna, i.e input impedance + the patch itself 

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JulianCavinaugh AntennaTheory.com Newbie
Joined: 15 Oct 2010 Posts: 8 Location: US

Posted: Fri Oct 15, 2010 10:10 pm Post subject: 


What is reference impedance? how is it related to the input impedance? 

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bigSteve Antenna Wizard
Joined: 14 Mar 2009 Posts: 265

Posted: Fri Oct 15, 2010 10:21 pm Post subject: 


The reference impedance is the impedance of the transmission line used to connect the antenna. That is, the reflection coefficient is calculated from:
Gamma = (ZL  Z0)/(ZL + Z0), where ZL is the antenna impedance, and Z0 is the "reference impedance". That is, the reflection is a function of the transmission line that connects the antenna, not just a property of the antenna itself.
The impedance of the patch antenna is the input impedance. The patch has no "intrinsic impedance" associated with it. It varies based on where you feed it: i.e., it's input impedance. 

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JulianCavinaugh AntennaTheory.com Newbie
Joined: 15 Oct 2010 Posts: 8 Location: US

Posted: Fri Oct 15, 2010 10:46 pm Post subject: 


Thanks a lot BigSteve,
Your information is very helpful. Then the total ZL+Z0 gives me the total impedance of the patch antenna, am I correct? 

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bigSteve Antenna Wizard
Joined: 14 Mar 2009 Posts: 265

Posted: Sun Oct 17, 2010 12:33 am Post subject: 


There is no concept of total impedance.
The impedance of the path antenna is just the impedance ZL. It is independent of Z0, the transmission line. That is, if you change the transmission line that feeds the antenna to a new Z0 (Z0_2), the patch impedance does not change. 

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JulianCavinaugh AntennaTheory.com Newbie
Joined: 15 Oct 2010 Posts: 8 Location: US

Posted: Fri Oct 22, 2010 7:02 pm Post subject: 


So when I want to compute the impedance of the quarter wave length microstrip, which is between 50 ohms and patch antenna impedance, The quarter wavelength microstrip impedance = sqrt(50ohms*input impedance of the patch antenna), am I correct? 

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JulianCavinaugh AntennaTheory.com Newbie
Joined: 15 Oct 2010 Posts: 8 Location: US

Posted: Fri Oct 22, 2010 7:42 pm Post subject: 


In the case I have input feed into patch antenna is 150, the input impedance is equal to 150 ohms+ reference impedance, the reference impedance I set to be 150 ohms too because I noticed that whenever my reference is near to 150 ohms (the same impedance of input feed), the reflection coefficient lowest = 35 dB. Please let me know if my idea is correct
Many thanks 

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Schubert Antenna Wizard
Joined: 08 Apr 2009 Posts: 161

Posted: Sat Oct 23, 2010 2:02 am Post subject: 


I'm not sure where your equation on impedance comes from.
In regards to your last post, the reflection coefficient is given by:
Ref Cof = (ZA  Z0)/(ZA+Z0)
(ZA = antenna impedance, Z0 = reference impedance or characteristic impedance of transmission line feeding antenna)
So, if your antenna impedance is 150 Ohms, and you set the reference impedance to 150 Ohms, then the reflection coefficient will be very small (i.e. 35 dB). So yes, if you set the characteristic impedance to the antenna impedance, you will reduce the reflection coefficient. 

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JulianCavinaugh AntennaTheory.com Newbie
Joined: 15 Oct 2010 Posts: 8 Location: US


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