radiation pattern with dB scale

can anyone help me to simulate the code below in Db scale(e.g -40, -30, -20, -10, 0) rather than linear.
the code below is in linear scale.
clc;
theta = 0:pi/100:2*pi;
N = input('enter number of elements:');
lambda = 2*pi;
beta = (2*pi)/lambda;
d = (lambda/4)*(1-(1/N));
alpha = (beta*d) + pi/N;
b = sin(((N/2)*(beta*d*cos(theta)+alpha)));
c = sin(((0.5)*(beta*d*cos(theta)+alpha)));
A = abs((1/N).*(b./c));
polar(theta,A)

just do the logscale prokection of the Y component.which is A ,depending on whether its a voltage or power value.it will be either 20 log or 10 log respectively.

Regards
Sajid Mohammed

you cannot use the polar function with dB-values. Check matlabcentral for a replacement.

Who said you cannot with dB values. you have to do a scaling of the dB scale in order to plot.like this i dont have matlab installed on my new puppy ,old one crashed otherwise i would've shown you how.but for time being consider this

polar(theta,40-10*log10(x)

and fit yours into the above .you do a 40 Db adjustment because log of negative value doesn't exist.

Hope it helps
Best regards
Sajid Mohammed.

I said it (and numerous others...).
If you do a radiation pattern plot in dB, you will get negative (dB-)values and polar() cannot plot negative values.
Rescaling is only a solution in rare cases. By the way: the scaling has nothing to do with the argument of the log-function and the argument can certainly get negative (irrelevant for radiation patterns).

Sebastian

sebastian

excuse my ignorance. i have never had a difficulty in plotting a polar plot with a log scale.i guess i never came across odd case.if you dont mind can you let me know what are the odd cases where its not valid.i will greatly appreciate your feedback

Best Regards
Sajid Mohammed.

Hi All,
Radiation pattern plot in dB scale is not possible using simple Polar function in Matlab.

@aroul.... you still need to plot radiation pattern in dB scale? I can upload the program which i once used in My thesis to do dB plotting of radiation patterns.

/SC

Hi sweetchoto,

can you upload the program for plotting radiation patterns?

Thanks

can you please upload it sweetchoto, so that i can get an idea how to do it.
Regards

Hi,
you can find the Matlab files in the attachment.1 file named 'Polarpat' is the one in which dB plotting has been programed. 2file named 'main' is used to call function 'polarplot' for dB plotting of radiation pattern. Both files are welldocumented and everything is clear. I hope it helps you guys.

thanks you everyone for your respond....... i will check it sweetchoto