plotting dipole antenna far-field pattern, with multiple slices

i'm attempting to plot the far field pattern for multiple dipoles in a line, which make up one large one,

however, i need an input for current for each slice, so they can all be plotted on top of eachother so it appears as one dipole.

however, i am running into bugs in ths program, and i need it to ot only calculate the entire thing up at one point, but to do it in a circle so it can plot the field pattern

deltaL=.003366 %meters

beta=12.5664 %

eta=377

i=1.5 %current

betasq=157.914 %beta squared

addpath c:\antennas\ewa

l=.68

a=.001

ker='a'

basis='d'

R=1 %distance, one meter from dipole

E=[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,100/.001,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]

pfield(l,a,E,ker,basis)

%this spits out a large complex vector of many rows of the current

for k=0:1:49

i=abs(ans(k))%this will extract a different rom/value from the answer for each count

E=-x*(377*i*betasq*deltaL)/(2*pi)*e^(-sqrt(-1)*beta*R)*cos(theta)(1/(sqrt(-1)*beta*r)^2+1/(sqrt(-1)*beta*r)^3)-y*(377*i*betasq*deltaL)/(4*pi)*e^(-sqrt(-1)*beta)*R*sin(theta)*(1/(sqrt(-1)*beta*r)+1/(sqrt(-1)*beta*r)^2+1/(sqrt(-1)*beta*r)^3)

E=E*2 %second half of dipole

plot(x,y)

hold on

end

Answer 1

[Vinod Dwarapudi]

Hi Neil,

The following example approximates a dipole using multiple short dipoles. The current distribution of a reference dipole is sampled and applied as amplitude and phase excitations to the short dipoles, and the resulting pattern is compared with that of the original dipole.

%% Compare a physical dipole with an equivalent set of short dipoles

fc = 300e6;
c = physconst("lightspeed");
lambda = c/fc;

%% Reference dipole (designed at fc for proper half-wave behavior)
d = design(dipole, fc);

%% Discretize dipole into short dipoles
L = d.Length;
N = 21;                  % Number of segments
dL = L/N;

% Short dipole element (width must be < length)
elem = dipole;
elem.Length = dL;
elem.Width  = dL * 0.05;

% Segment locations along z-axis
z = linspace(-L/2, L/2, N);

% Build conformal array
ca = conformalArray;
ca.ElementPosition = [zeros(N,1), zeros(N,1), z'];
ca.Element = repmat({elem}, 1, N);

%% Sample current distribution from the large dipole
[I_ref, pos_ref] = current(d, fc);

% For z-oriented dipole, use z-component of current (row 3)
z_ref = pos_ref(3,:);
Iz = I_ref(3,:);

% Sort by z-position
[z_sorted, idx] = sort(z_ref);
Iz_sorted = Iz(idx);

% Interpolate amplitude and phase at segment centers
amp_weights = interp1(z_sorted, abs(Iz_sorted), z, 'linear', 0);
phase_weights = interp1(z_sorted, angle(Iz_sorted), z, 'linear', 0);

% Normalize amplitude
amp_weights = amp_weights / max(abs(amp_weights));

ca.AmplitudeTaper = amp_weights;
ca.PhaseShift = rad2deg(phase_weights);

%% Compare directivity patterns

theta = -180:180;

E_dipole = pattern(d, fc, 0, theta,...
    Type="directivity");

E_array = pattern(ca, fc, 0, theta,...
    Type="directivity");

figure
plot(theta, E_dipole, 'LineWidth', 2)
hold on
plot(theta, E_array, '--', 'LineWidth', 2)
grid on

xlabel('Elevation Angle (deg)')
ylabel('Directivity (dBi)')
title('Dipole vs Array of Short Dipoles (Current Sampled)')
legend('Single Dipole', 'Array of Short Dipoles')