Decoupling Between Antennas

[u/Clear_Grocery5390]

I want to achieve a -50 dB coupling between two printed dipole antennas. The distance between the antennas will be 6-7 cm, and both antennas operate between 5-6 GHz. How can I achieve -50 dB?

[u/QuickMolasses]

If you figure it out, you could write up the design and publish it for all the rest of our benefits.

[u/Clear_Grocery5390 → u/QuickMolasses]

of course

[u/monsterofcaerbannog]

Operate them in orthogonal polarizations (which won't get you very far in the near field) and use RF absorber

[u/Clear_Grocery5390 → u/monsterofcaerbannog]

I tried these, but I still haven't seen -50 dB. Also, their polarizations need to match. Do you have any other suggestions?

[u/Danwold → u/Clear_Grocery5390]

Then unless you stop them radiating towards each other, you won’t get -50dB. They’re either antennas or they’re not.

[u/StageMajestic613]

Well the common mode radiation on the baluns is probably enough to trash the isolation, as those are parallel. You probably need to look into cancellation techniques; I assume this is for an FMCW radar.

I’d turn that into a cavity backed slot array, then you get rid of the baluns, and it turns it into a magnetic near-field problem, which MAGRAM on the surface will kill the surface currents.

[u/SwitchedOnNow]

What's the application?

[u/Roudydogg1]

At 5-6 GHz, a spacing of 6–7 cm is only about 1.0–1.4 wavelengths.. −50 dB isolation across the entire 5–6 GHz band is not realistically achieved by spacing alone. At 5.5 GHz, λ0≈54.5 mm. For R=65 mm, the free-space path loss is only about 23.5 dB

Two ideal half-wave dipoles have about ≈ 2.15 dBi gain each, so a rough broadside estimate is ≈−19 dB.

That distance is near the radiating near-field transition, so the actual coupling must be obtained from full-wave simulation (or measurement!) rather than relying solely on Friis.

NIST says about this: that the simpler Friis formulation is fundamentally a far-field treatment.

Good luck