positive values in returnLoss

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

Answer 1

[Dushyant Marathe]

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.

[Shahar ben ezra]

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