Intersection plot of tangent function in waveguide condition

Hi,

I want to plot equation of waveguide condition. This happens when LHS = RHS where these are given as:

LHS = tand(k1*a*cosd(thetam) -m*90);
RHS = (sqrt((sind(thetam)).^2) - n*n)/cosd(thetam);

When these are plotted, I should get a figure similar to

Following is my script:

n1 = 1.455;
n2 = 1.44;
n=n2/n1;
lambda = 900e-6;
k1 = 2*pi*n1/lambda;
a = 10e-6;

thetam = 80:0.1:90;
LHS = tand(k1*a*cosd(thetam));
RHS = (sqrt((sind(thetam)).^2) - n*n)/cosd(thetam);
ezplot('LHS');
hold on
ezplot('RHS');
ylim([0 20]);

When script is executed, I don't get desired plots. How to plot LHS, and RHS, and mark their interesections?

[David Goodmanson]

HI CM,

whatever else is going on, I believe you need

LHS = tan(k1*a*cosd(thetam))

i.e tan and not tand. This does not fix things on its own, but it's a start.