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positive values in returnLoss

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Shahar ben ezra
Shahar ben ezra on 31 Oct 2020
Commented: Shahar ben ezra on 4 Nov 2020
When I create an RL graph I get the positive graph
but it need to be negative
Why is my graph upside down?
my code:
C = 3*10^8;
F = 30*10^6 %hz
Z0 = 50
Lamda =C/F %m
ant_Half = dipole('Length', Lamda/2 );
figure(5) ; returnLoss(ant_Half,F-3e6:F/100:F+3e6,Z0)
my fig

Answers (1)

Dushyant Marathe
Dushyant Marathe on 4 Nov 2020
Hi Shahar,
It is my understanding that you are able to plot return loss in dB for dipole antenna. However, you are uncertain about sign of the values. The magnitude of s-parameter S11 for passive device like antenna is expected to be a negative number in dB. However, return loss |Tin| as defined below is always a positive number for passive device.
RL = −20 log |Tin|
For a matched load (|Tin| = 0) has a return loss of ∞ dB (no reflected power), while a total reflection (|Tin| = 1) has a return loss of 0 dB (all incident power is reflected). Note that return loss is a non-negative number for reflection from a passive network or device.
Example :
If |Tin| = 0.452
return loss is RL = −20 log |Tin|=−20 log (0.452) = 6.9 dB
Please, refer to the return loss documentation for more information. From above link, its seen that return loss for loopCircular antenna is positive.
  1 Comment
Shahar ben ezra
Shahar ben ezra on 4 Nov 2020
I can understand what you're saying
But that I do by Antenna designer
I get the right result (What I expect to get)
Look at the formula

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