I14R10
Full Member level 3
Hello
I'm trying to design a feedhorn for a parabolic dish. For frequency of 1420MHz. There are a bunch of questions about it, mainly about dimensions, but let me first ask some questions about related topic. Cantennas or coffee can antennas.
Trying to calculate the dimensions of a feedhorn I came across a cantenna. It's not useful for my design, but I went and tried to calculate her dimensions just to see if I get the same results. And I don't. Now, I know a bit about waveguide modes. TE11 mode is basic mode for a circular waveguide. Cutoff frequency for circular waveguide is 1.706*D, where D is diameter of the waveguide.
For comparing results I used this document https://pa3csg.nl/wp-content/uploads/2016/06/chapter-3.pdf , page 13. My results are:
\[ λ=23.13cm\\ D=7.5''=19.05cm\\ λ_c=1.706D=31.39cm\\ λ_g=\frac{λ}{\sqrt{1−\frac{λ}{λ_c}}}=32.93cm\\ λ_g/4=8.23cm \]λ=23.13cmD=7.5″=19.05cmλc=1.706D=31.39cmλg=λ1−λλc=32.93cmλg/4=8.23cm
But in that pdf file
But cantenna calculator on this page https://www.wikarekare.org/Antenna/WaveguideCan.html gives the same data as what I calculated.
Am I doing something wrong here?
I'm trying to design a feedhorn for a parabolic dish. For frequency of 1420MHz. There are a bunch of questions about it, mainly about dimensions, but let me first ask some questions about related topic. Cantennas or coffee can antennas.
Trying to calculate the dimensions of a feedhorn I came across a cantenna. It's not useful for my design, but I went and tried to calculate her dimensions just to see if I get the same results. And I don't. Now, I know a bit about waveguide modes. TE11 mode is basic mode for a circular waveguide. Cutoff frequency for circular waveguide is 1.706*D, where D is diameter of the waveguide.
For comparing results I used this document https://pa3csg.nl/wp-content/uploads/2016/06/chapter-3.pdf , page 13. My results are:
\[ λ=23.13cm\\ D=7.5''=19.05cm\\ λ_c=1.706D=31.39cm\\ λ_g=\frac{λ}{\sqrt{1−\frac{λ}{λ_c}}}=32.93cm\\ λ_g/4=8.23cm \]λ=23.13cmD=7.5″=19.05cmλc=1.706D=31.39cmλg=λ1−λλc=32.93cmλg/4=8.23cm
But in that pdf file
\( λ/4=3.75''=9.53cm \)
But cantenna calculator on this page https://www.wikarekare.org/Antenna/WaveguideCan.html gives the same data as what I calculated.
Am I doing something wrong here?
Last edited:
