Microstrips operated in differential mode question

May 29, 2020 23 Replies

So true. BUT, measuring the coupling coefficient is the big issue. Please check

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for gory, full-blown treatment of odd, even mode impedances of two parallel coupled microstrip lines with frequency dispersion. No simplifyimg assumptions are used. Once frequency dependent even, odd impedances are calculated, the coupling coefficient is easily computed. That competes 85% of the work.

en

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tudes are sines and cosines of almost unit strength, so that if you drive o ne side only, the power will shift almost 100% to the other side, then back again sinusoidally.

Oh directional couplers! Now there's something I've never understood so well. The ones I sorta get are the waveguide with three ports and artfully chosen slots connecting top and bottom.

This type of thing

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So you can do similar tricks with coupled transmission lines?

George H.

Sure. One ham version uses a piece of coax with a bit of insulated wire sneaked in just inside the shield. Transmitted power comes out one end, reflected power comes out the other. It needs to be fairly long, of course.

Ordinary VSWR bridges work on a different principle, namely the phase relationship between the voltage and current in the line.

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com

Those are all approximate formulas, so yes, simplifying assumptions are used.

It shouldn't be that hard to do a full vector EM simulation--it's a 2D problem just like a mode solver.

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com

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