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I am designing a microwave device in waveguide transmission line technology and I have to have an H-bend in it. But the bend brings me undesirable effects and I don't know in what radius the effects could be minimized? I searched and find some standards but they don't work.
H-bend compensation in WR-90 waveguide is well described in T.Moreno: Microwave Design Data, Dover 1948. On pages 162-166 you can find what you need. Instead of a single bend, two bends (double corner) are suggested to function without reflections.
I used this double corner many times and it works well over the full waveguide bandwidth.
The designed device is a directional coupler.
H-bend deviants directivity from what I expect
and this is what I mean from undesirable effects.
Design simulates in HFSS and by changing the radius
of bend, directivity alters.
In some radiuses can reach expected results but irrational thing
is that by increasing the radius of bend results do not approaches
to my expectations. Suppose results in r=15.4mm are ok but they're
not necessarily in r=20mm.
thank you for your time and attention.