Hi, I am trying to design a monopole in CST to radiate at 28 GHz. I modeled my design after a monopole designed for 3 GHz (I scaled my antenna using the length to width ratio of the 3 GHz antenna). I got my monopole to be matched at 28 GHz (s-parameter), but it is not radiating well. I think its resonating, but not radiating.
The attached picture (Ant1 uncloaked gain) shows the farfield gain pattern of the 3 GHz monopole. I want my 28 GHz monopole to achieve similar results, but my farfield gain shown in the "28 GHz monopole farfield" attachement is not similar at all.
Is there some sort of optimization I can run to change the length and widths of the antenna to achieve good radiation? Maybe do an efficiency optimization? Also, do I have to change the length of the ground plane under the substrate too?
Any help would be greatly appreciated!
Did you scale everything? A monopole needs a ground. Often (like in a mobile phone) the ground is the other half of the dipole and is resonant.
To me the top diagram looks like radiation from a dipole, not a monopole.
Dear Sal Mastromatteo ,
What is the kind of port you used in your design?. for example, if you used a waveguide port, the extension coefficient of the waveguide port will vary with the width of the antenna feed transmission line, and also the height of the substrate material.
Regards.
I figured it out. I did not scale down the thickness of the substrate, and at 28 GHz, my substrate thickness was around 1/4 wavelength. The fields would travel through the substrate, reflect off the ground plate (phase shift of pi radians), and with a total distance traveled of 1/2 wavelength, another shift of pi radians resulting in a total shit 2*pi radians. This resulted in constructive interference.
I had to scale down the thickness of the substrate to make it deeply subwavelength to negate this, then change the rest of my dimensions accordingly. The waveguide port extension coefficient was tricky as Ahmed S. I. Amar pointed out, but through trial and error I got the right dimensions. Attached is the correct farfield gain. Thanks for the help!
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