Coplanar vs. Microstrip

Are there any “rules of thumb” that folks go by when contemplating the use of coplanar vs microstrip? I’m well versed in both applications (how to design them), and understand the history a bit about coplanar, i.e. being able to terminate (or even pi/T networks)without vias, coplanar forces trace separation (limit crosstalk), certain “reasoning’s” for via stitching etc., but if microstrip is designed correctly, no close proximity parasitics within 3x trace width, proper gnd reference etc., when do folks lean towards coplanar, at what frequencies? I’ve design very clean boards out to 32Gbps performance with microstrip, no issues. I keep hearing coplanar is used for “high frequency applications”, stating contained E and M fields (via stitching) like a coax, eliminates crosstalk on and on, but I’ve had zero issues with these if proper design practices were followed with microstrip. TDR’s were all fine, no crosstalk issues, all good. I’ve also heard out beyond 30GHz is where coplanar really starts to be recommended. In a dielectric of ~3.3 for example, that’s a wavelength of 0.22", 1/10th(rule of thumb) stitching would be ~22mils. Typically, I use microstrip with dielectric height of 8mils. There’s plenty of dogma at my work regarding “high frequency”, I’d like to know folk’s thoughts on here.

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Hi Tom,

There are no “rules of thumb” for the use of Coplanar or Microstrip.
if you are satisfied with the results obtained by using a microstrip there is no need for you to switch to coplanar.

Coplanar ground definitely limits crosstalk and gives EM shielding, at higher frequencies the need to limit crosstalk and need for continuous reference became more necessary.
For RF antenna applications coplanar is recommended.
Coplanar is also required when you do not have a bottom ground reference or when it is very far from the signal trace, a closer coplanar reference is needed.
For Analog signals also use of coplanar traces is recommended.

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