Hi,
The 'Zin_res' is not calculated properly as the validation "if(fr(k)==fmn);" fails due to the mismatch in exact values. To get the input impedance at the resonant frequency find the index at which the difference between the current and the resonant frequency is minimum. Then index into the array.
Modified code:
%Parameters TE10
c= 299792458;
m=1;
n=0;
h= 0.0795e-2;
dm=2;
dn=1;
eps0= 8.85418782e-12;
epsR= 2.32;
eps= eps0*epsR;
a= 10e-2;
b= 1.5e-2;
theta1 =2e-2/(a+h);
z_p =-1.5e-2;
phi_p =1e-2/(a+h);
w= 5e-3;
Qf= 112.4;
del_eff= 1/Qf;
fr=[2349:1:2549]*1e+6;
fmn=c/(2*sqrt(epsR))*sqrt((m/(2*(a+h)*theta1)^2)+(n/(2*b))^2);
%fmn= 2449e+6;
befn= sin(m*pi*w/(4*a*theta1))/(m*pi*w/(4*a*theta1));
%Z= ((h*dm*dn)/(8*pi*a*b*theta1))*((cos (n*pi*z_p)/(2*b))^2)*((cos(m*pi*phi_p)/(2*theta1))^2)*((bessel(j0,m*pi*w)/(4*a*theta1)).^2)* ((del_eff^3)-i(freq)(freq^2-fmn^2))/(del_eff^4+)
Zin= h*dm*dn/(8*pi*eps*a*b*theta1)*cos(n*pi*z_p/(2*b))^2*cos(m*pi*phi_p/(2*theta1))^2*befn^2.*(del_eff*fr.^3-1i*fr.*(fr.^2-fmn^2))./(del_eff^2*fr.^4+(fr.^2-fmn^2).^2);
figure(1)
plot(fr*1e-6,real(Zin),'b','LineWidth',3);
hold on
plot(fr*1e-6,imag(Zin),'r','LineWidth',3);
set(gcf,'color',[1 1 1]);
set(gca,'fontsize',18);
xlabel('freq [MHz]')
ylabel('R and X [ohm]');
xlim([2349 2549]);
%ylim([1480 1560]);
legend('R','X');
% Find the index of the frequency closest to the resonant frequency fmn
[~, resonant_index] = min(abs(fr - fmn));
% Get the input impedance at the resonant frequency
Zin_res = Zin(resonant_index);
% Display the resonant frequency and the corresponding impedance
disp(['Resonant frequency index: ', num2str(resonant_index)]);
disp(['Resonant frequency (Hz): ', num2str(fr(resonant_index))]);
disp(['Zin at resonant frequency: ', num2str(Zin_res)]);
Glad to help!
