# Need to plot 10 db return loss fractional bandwidth of a dipole antenna

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Mounika Devarajan on 5 Oct 2019
Answered: Jyothis Gireesh on 9 Oct 2019
I am trying to plot 10 db return loss fractional bandwidth of a dipole antenna connected an charecteristic impedance of 75 ohms and resonant frequency is 72 Hz.
Please let me know how can I code this. I tried this below code:
d = dipole;
impedance(d,20e6:1e6:120e6)
S = sparameters(d,20e6:1e6:120e6,75)
rfplot(S)

Jyothis Gireesh on 9 Oct 2019
I am assuming that the value of resonant frequency is 72 MHz instead of 72 Hz since the range of frequencies specified is from 20 MHz to 120 MHz. Here are a few pointers which may be able of help in solving the above problem:
• The return loss of the dipole antenna can be calculated by using the function “returnLoss()” which takes the antenna, frequency range and the reference impedance as arguments. The syntax given below may be used to calculate the return loss:
antennaLoss = returnLoss(d, 20e6:1e6:120e6,75);
• Antenna bandwidth is the range of frequencies over which the value of “antennaLoss” variable is greater than 10dB. Fractional bandwidth is computed as Antenna bandwidth divided by center frequency(or resonant frequency)
clear;
d = dipole;
freqRange = 20e6:1e6:120e6;
resonantFreq = 72e6;
%impedance(d,20e6:1e6:120e6);
antennaLoss = returnLoss(d,freqRange,75);
%rfplot(S)
antennaBW = freqRange(antennaLoss>10);
fracBW = (antennaBW(end) - antennaBW(1))/resonantFreq;

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