MATLAB: Polarplot in dB.

polarplot

Hi, I am trying to plot a certain function (traveling wave) using polarplot(). However, the result isn't even close to that presented in the attachment, which is supposed to be the polar plot of the very same function! I have been trying for two days now to figure out what might be causing this visual discrepancy, to no avail. Below is my calling of polarplot:

theta=transpose(-1:0.01:1);
MagE=(cot(theta*pi/2).^2).*(sin(5*pi*(cos(theta*pi)-1))).^2;
polarplot(theta*pi,MagE,'Linewidth',1,'color',[.21 .81 .94]);

I also tried changing MagE to db(MagE), as the plot in the attachment appears to be in dB, yet it didn't do the trick. I hope someone here might be able to suggest a solution. I'd appreciate any assistance, advice, promptly if possible. Thanks

in advance.

Best Answer

You need to be careful about dB values as they might be negative. So you need to preprocess it to make it all positive before plotting and then fix the labeling. Here is an example

MagEdB = 10*log10(MagE);
MagEdB = MagEdB - max(MagEdB);
MagEdB(MagEdB<-40) = -40;
h = polarplot(theta*pi,MagEdB+40,'Linewidth',1,'color',[.21 .81 .94]);
haxes = get(h,'Parent');
haxes.RTickLabel = {'-40','-30','-20','-10','0'};

HTH

Related Solutions

MATLAB: How to draw a polar graph from r=0

Yuval, looks like you only need to increase the number of data points (theta):

 theta = 0:0.001:2*pi;

or something like this.

MATLAB: Polar plot draw line at -3dB opening

From your description, this seems to work:

angl = 0:10:360; 
pow = [-18.2 -18.5 -19.7 -21 -22.3 -23 -24.1 -28.1 -33 -37.8 -34 -32.4 -33.1 -32.8 -34.2 -36 -37.9 -39.2 -40 -40 -39.2 -36 -34.2 -32.8 -33.1 -32.4 -34 -37.8 -33 -28.1 -24.1 -23 -22.3 -21 -19.7 -18.5 -18.2];
R = deg2rad(angl);
powc = pow - max(pow);
powc(powc<-40) = -40;
hpp = -21.2;
db3(1) = interp1(pow(1:5), R(1:5), hpp);                        % Half-Power Angle 1
db3(2) = interp1(pow(end-4:end), R(end-4:end), hpp);            % Half-Power Angle 2
figure
h = polarplot(R, pow + 40, 'Linewidth', 1, 'color', [.21 .81 .94]);
hold on
polarplot([0 0; db3(1) db3(2)], [-40 -40; hpp hpp]+40, '-r')    % -3dB Opening’ Lines

hold off
haxes = get(h, 'Parent');
haxes.RTickLabel = {'-40 dB', '-30 dB', '-20 dB'};
title('Diagramme de rayonnement antenne TP-LINK TL-AN2409A');

producing:

Polar plot draw line at -3dB opening - 2019 03 09.png

If you want the lines to go to the edge of the plot, replace ‘hpp’ here:

polarplot([0 0; db3(1) db3(2)], [-40 -40; hpp hpp]+40, '-r')    % -3dB Opening’ Lines

with the radius of the edge of the plot, that being ‘max(rlim)’.

You could smoothe the plot with a cubic or similar interpolation, using the interp1 function, first using the linspace function to define ‘R’ with a larger number of grid points.

Experiment to get the result you want.

Best Answer

Related Solutions

MATLAB: How to draw a polar graph from r=0

MATLAB: Polar plot draw line at -3dB opening

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