S Like shape transmission line

yef smith

Joined Aug 2, 2020
348
Hello,I have desighed a transmissios line as shown bellow ,for matching i have used champhering at 45 degrees.
i got S11=-15dB.
I heard we can do a better line matching using "S" shape like continues line.
is it a true method?is there some article i could use to get guidelines for propely building this line.
what is the formal name of this method, so i coud try and read further to get S11 better then -15?
Thanks.

Ya’akov

Joined Jan 27, 2019
5,642
S shaped waveguides are widely used in optical circuits and there’s a lot of research on optimization for low loss. Maybe that would be a fruitful direction.

crutschow

Joined Mar 14, 2008
29,752

Tesla23

Joined May 10, 2009
510
There are two issues here, one is the performance of a single corner which is best studied in isolation. Plenty of books on microstrip give empirical formulas for good chamfering angles. The other is the interaction of the two bends. If you are only after narrow-band performance, then spacing the corners at odd multiples of λ/4 (ish) will tend the cancel the reflections.

yef smith

Joined Aug 2, 2020
348
Hello Tesla23 ,i will try your method very cool.
So is there a method for "S" like transmission line?
if you ever heard of such ,how its called? what is the guidelines for it?
thanks.

Tesla23

Joined May 10, 2009
510
No idea if it has a name. It is a good exercise to look at adding two equal shunt susceptances to a transmission line and determining the spacing where the reflections cancel (note that it is not exactly λ/4, but depends on the susceptance). Similarly for series reactances. All you need then is an approximate model of your bend.

sjsdorsay

Joined Dec 13, 2015
10
I'm guessing that by S like shape you mean using curves. Yes this can improve the matching/characteristic impedance of the section. The idea is that it removes or reduces the effects of the discontinuities in the line provided the radius is large enough. The rule of thumb, if I can remember correctly, is the radius should be greater than 3 x trace width.

The chamfer balances the inductive and capacitive parasitic components from the mitering to form a narrow band 90 degree which tends to be wide band enough for many applications.

Adding a quarter wave section can be difficult sometimes due to its large size but will work over narrow bandwidth. This may be shortened using a slow wave transmission line.