The direction of current distribution on antenna surface isn't along the antenna surface, simulation mistake from MATHWORK?

I was trying the example provided by Mathwork (MATLAB, antenna toolbox)

 h = loopCircular;
 current(h,70e6,'Direction','on');  

This computes the current distribution on the loop. However the visual of the current vector isn't along the surface:

Is this a simulation error from MATLAB or the direction of the current on this conductive loop doesn't have to be along the surface(shouldn't the surface current always travel along the surface?)?

Answer 1

[Ashok]

Hey @Xingda Chen,

The current directions are being calculated correctly, but there seems to be a visual issue with the relative size of the quivers compared to the antenna loop’s thickness. Increasing the loop thickness resolves this visual discrepancy.

Additionally, at higher frequencies, the quiver size decreases, which improves the visualization of the current flow.

A potential workaround is to extract the current and position matrices using the ‘current’ function and manually create the plots. This provides additional control over the quiver size. For example, the following code can be used to produce a quiver plot of the current.

h = loopCircular; 
[i, p] = current(h,70e6,'Direction','on'); 

% Step 3: Extract Current Data 
% i contains the current components (Ix, Iy, Iz) 
% p contains the points (x, y, z) where current is calculated 
currentX = abs(i(1,:)); 
currentY = abs(i(2,:)); 
currentZ = abs(i(3,:)); 
xPos = p(1,:); 
yPos = p(2,:); 
zPos = p(3,:); 

% Plot the quiver plot for current vectors 
figure; 
quiver3(xPos, yPos, zPos, currentX, currentY, currentZ, 0.4); 

% Add labels and title 
xlabel('X Position'); 
ylabel('Y Position'); 
zlabel('Z Position'); 
title('Current Distribution on Circular Loop Antenna'); 
axis equal; 
grid on; 

The ‘surf’ function is also available for plotting the coloured surface. Here are the related documentation pages:

• quiver3: https://www.mathworks.com/help/releases/R2024b/matlab/ref/quiver3.html
• surf: https://www.mathworks.com/help/releases/R2024b/matlab/ref/surf.html

I believe this will assist you!