question about coplanar waveguide (CPW)

[Tisapphire]

usually for CPW, the middle metal line is used as the signal line and the other two on each side are grounded.

In my set up, I use one line on the side (say, the left one) to connect to the input signal, and ground the center line and the right line.

My question is, how should I analyze the modes in this configuration? should it be CPW with even mode? or should it be considered as two coupled transmission lines/slot lines?

Thank you so much!

 

[shmily0447]

Since your middle conductor and the right ground are all connected to ground, they are of the same potential. And only a small portion of parasitic modes could exist in the slot between the middle conductor and the right ground, which could be neglected.

The left ground is used as the signal line, I think the functional modes should exist in the slot between the left ground and the center conductor. You can study it as a slot line.

The above hypothesis just apply when your CPW is not grounded, meaning you do not have another ground plane on the other side of your CPW. If the CPW is grounded, you should study the proposed structure as a Microstrip line and aslo pay some attentions to the modes exist in the slot between the left ground and center conductor.

Otherwise, just study it as a slot line should be OK.

 

[Tisapphire]

Thank you so much for your analysis.

I still have a few more questions:

1. Although the center and right line are grounded, will it be possible that they are only DC grounded not for AC signal? For example if the right line is connected to ground through a meander shape line.

2. I am using Electro-Optical crystal to measure the E field between the left-center and center-right lines, the results shows that both fields have same polarity and similar amplitude.

3. The CPW was fabricated on a semiconductor chip (no metal on back side) and then clip mounted on a metal block. should I consider it grounded CPW or not?

Thanks again!