Performance differences between open and shorted stubs

Hi

Anybody has experience with open and shorted stubs? I'm am especially interested in the diffirence in performance,if you implement a stub as a short or as an open.

Did you microwave guys encounter great difference in performance?

Why I'am interrested in this? I'm currently designing microwave oscilators and for the matching network I use shorted stubs . But the resonant frequency differs from the one it is designed for.

So I am wondering if I implement the stubs as an open stub should it give better results?

As my PCB layout isn't very professional the vias for the shorted stubs are realised with a hole through the PCB an we soldered an wire to connect the capacitor,needed to create an short, with the ground plane.

Tell me your experience ............

Pro and contra......

Greetz E-goe

Hi

I am also designing an oscillator using microstip matching circuits.

I use open stubs for mine, simply for the reason that it decreases complexity. i spoke to a number of RF guys who have been in this field for a while, and they say the difference is negligible. There are certain advantages and disadvantages. Sometimes the lengths increase or decrease if you use open or short. Thats my experience.

What oscillator are you designing?

Open stubs are easier to fabricate when it comes to printing a circuit layout.
If a short stub cannot be traded with an open one, then a via (or vias) must be drilled through the PCB all the way down to the ground layer.

P.

It is easier to achieve a good short to ground than a good open (fringe effect on the end of the open).

Hi,

just to make difference in two possible cases of realizing short stubs. One way is to use via at the end of the shunt line to connest to the ground. Then, short stub doesn't have any significant advantage compared to open stub - open stub has open-end capacitance that is effectively making it longer than desired, short stub has via inductance that is effectively making it shorter than desired. Via can also have resistance, so it can lower resonator Q. The only advantage of short stub is than it can provide ground return if you need one. On the other hand, if you don't need ground return, it is in my experience more advantageous to use RF short (e.g. radial stub) instead of DC short (via) at the end of the line. This can be analized very accurately either with circuit simulators or EM simulators and discrepancy due to any parasitic effect will be minimized.

flyhigh

Hi,

you can use any stub either Open or short for matching but implementing short is easy as compare to open that's why most of the RF guys prefer short stub.

Thanks
Animesh

Hi,

open circuited stub, if too long becomes a radiating element? Not a good thing if the lenght is ~ 1/4 of the desired signals.

Depending on the fabrication capability, good vias may be difficult to implement.

Question voices back to the enigneering task of trading off the pros and cons :)

Hi.
Open stubs are easier to fabricate when it comes to printing a circuit layout.
If a short stub cannot be traded with an open one, then a via (or vias) must be drilled through the PCB all the way down to the ground layer.

Short stubs are far stable than open stub, let say mechanically at least not to mention the others. Yes open stub seems more flexible in fabricating