How does Matlab scale antenna fields?

Hi, I'm currently designing a loop antenna to produce microwaves at 6.8GHz. I'm interested in the magnitude of the magnetic field component at some distance along the loop's axis, but since I'm new to Antenna Toolbox I'm confused how the EHfields function obtains magnitudes of the electric and magnetic fields if I have not specified the power or current in the loop. Is there a way to determine the magnitude of the magnetic field for a given input current or power?

Thanks

Answer 1

[Govind KM]

Hi Matt,

The magnitudes of the electric and magnetic fields are calculated from the properties of the antenna or array object, as mentioned here:

https://www.mathworks.com/help/antenna/ref/cavity.ehfields.html?s_tid=doc_ta#buopyee-object:~:text=Antenna%20or%20array%20to%20calculate%20the%20field%20magnitudes

Based on the properties of the antenna/array object (such as voltage), the EHfields function determines the current, which is then used to calculate the field components. As an example, I used the EHfields function with two pcbStack antenna objects which differ only in their FeedVoltage parameter:

%Define pcbStack objects differing only in FeedVoltage
p1=pcbStack(FeedVoltage=1);
p2=pcbStack(FeedVoltage=100);
%Calculate electric and magnetic fields at points (0,0,1) and (0,1,0)
[e1,h1]=EHfields(p1,4e9,[0,0;0,1;1,0])

e1 = 
  -0.2125 + 0.0922i  -0.0418 - 0.0143i
  -0.0029 - 0.0005i  -0.0034 - 0.0070i
   0.0078 - 0.0004i  -0.0527 - 0.1168i

h1 = 
   1.0e-03 *

   0.0078 + 0.0014i  -0.1399 - 0.3099i
  -0.5647 + 0.2453i   0.0021 + 0.0038i
  -0.0001 - 0.0000i   0.1110 + 0.0381i

[e2,h2]=EHfields(p2,4e9,[0,0;0,1;1,0])

e2 = 
 -21.2452 + 9.2191i  -4.1832 - 1.4269i
  -0.2929 - 0.0510i  -0.3392 - 0.6982i
   0.7817 - 0.0447i  -5.2747 -11.6779i

h2 = 
   0.0008 + 0.0001i  -0.0140 - 0.0310i
  -0.0565 + 0.0245i   0.0002 + 0.0004i
  -0.0000 - 0.0000i   0.0111 + 0.0038i

We can see that scaling the voltage by 100 resulted in the field components being scaled by the same factor. The magnitudes of the fields can be determined using its components as follows:

%Calculating field magnitudes for p1 at each point
E1_magnitude = sqrt(abs(e1(1, :)).^2 + abs(e1(2, :)).^2 + abs(e1(3, :)).^2)

E1_magnitude = 1×2

0.2317 0.1358

<mw-icon class=""></mw-icon>

<mw-icon class=""></mw-icon>

H1_magnitude = sqrt(abs(h1(1, :)).^2 + abs(h1(2, :)).^2 + abs(h1(3, :)).^2)

H1_magnitude = 1×2

1.0e-03 * 0.6157 0.3598

<mw-icon class=""></mw-icon>

<mw-icon class=""></mw-icon>

The current function can be used to calculate the current on the surface of an antenna or array object. To determine the magnitude of the magnetic field for a specific current, you can adjust the properties of the antenna object such that the desired current is achieved. The EHfields function can then be used to detemine the magnetic field corresponding to this current.

More information about the current function can be found in the following documentation:

https://www.mathworks.com/help/antenna/ref/cavity.current.html

Hope this is helpful!