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X-Mailer: Mozilla 4.77 [en]C-CCK-MCD NSCPCD477 (Win98; U)
Subject: Re: Replacing two microstrip stubs with one
References: <3DD4F2ED.DD32B937@niobiumfive.co.uk> <3DE22B0F.77DD6FC4@niobiumfive.co.uk>
Date: Tue, 26 Nov 2002 03:03:28 GMT
NNTP-Posting-Date: Mon, 25 Nov 2002 19:03:28 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
The Technical Manager wrote:
> Lizard Blizzard wrote:
> > The Technical Manager wrote:
> > > I have a microstrip transmission line that has two short circuited stubs
> > > connected to it at the same point which radiate off in opposite
> > > directions to each other so that the interconnection point is a cross
> > > junction. Each stub has a different characteristic impedance and
> > > electrical length. I want to replace these two stubs with a single short
> > > circuited stub. How do I find the correct characteristic impedance and
> > > electrical length of the replacement stub ? Does a formula exist to
> > > calculate this ?
> > There are formulas, of course, found in Reference Data for Radio
> > Engineers, for example.
> Where ? Which page ?
> > But if you don't understand the reason why those were put there in the
> > first place, it would be very unwise to meddle with them.
> It is a concept, not some part of an an existing product.
I think you ahve to sue a Smith Chart to find the Impedances.
Are the Impedances... Resistive, Inductive, Capacitive ? Yes to all.
The Smith Chart will really help you out in finding Z = R +/- jX.
What will the signal do going into and reflecting back from the cross point?
There alot to be done.
A ----+---- B
The signal goes into A and comes back out of A. The signal goes out of B, and
reflects back into B. same goes for C and D. so you have 8 Reactance equations
to look at. You have to look at S parameters vs. frequencey of your circuit.
The stripline you design in will be 50 ohms? Most stripline will be 50 ohms.
If the stripline is thinner, then maybe it'll be 120 ohm? There's a ton of
engineering going on here. When you buy SMA and SMB connectors, semi-ridgid
coax cable, you'll be buying 50 ohm hardware.
But the way who sells 50 ohm SMB terminators? Pasternack ?
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