How to combine results for an antenna that uses multiple ports?

[general_custard]

Hi there, I have a quick query about how to combine results for an antenna that uses multiple ports, with a different phase excitation for each port. You see I've designed an open-ended waveguide antenna fed using balanced probes, which are excited with 1|0° and 1|180° signals, well in CST it's straighforward to excite each using a coaxial feed with a discrete port, and then use the 'results > combine results' function to provide the phase shift for port 2. However, I have experimental results from farfield measurements of the fabricated structure and I'm just wondering if I'm combining the results correctly. I have the gain in dBi and phase of the received signal at certain frequencies and I've been combining the results in the following way:

mag1 = 10^(gain1(dBi)/20)
real1 = mag1 * cos(phase1)
img1 = mag1 * sin(phase1)

mag2 = 10^(gain2(dBi)/20)
real2 = mag1 * cos(phase2+180°)
img2 = mag1 * sin(phase2+180°)

realsum = real1 + real2
imgsum = img1 + img2
magsum = √(realsum^2+imgsum^2)

gainsum(dBi) = 20*log(magsum)
phasesum = argument(realsum + j*imgsum)

I'm not sure if this is the method CST uses to combine results, it's hard to compare as CST doesn't give phase information for the farfield results I'm especially uncertain about whether the logs have a factor of 10 or 20, aside from that it's just a straightforward vector summation I know, could anyone shed any light on this? Thanks!

 

[alak]

Re: Combining results

I guess you are going the right way as we need to o vector sum of the fields for both the ports.

 

[general_custard]

Re: Combining results

Do you think it's correct to use a factor of 20 in the calculations though? I think since it's the electric field intensities of the farfield that are being summed (i.e. in V/m) it is correct to do so but I wasn't entirely sure, I know that when you apply 'linear scaling' to the farfield results in CST they use 10^(gain(dBi)/10), which I presume is because these values are related to the power of the farfield. Can anyone clarify this?