Cross Polarization Effect - Page 1
Forum section: electronics / rf-microwave

author: metrologist
author_rank: Super Contributor
timestamp: February 10, 2023, 11:01:58 pm
content: I read that with cross polarization of signal to antenna (horizontal/vertical) that there would be no power transfer, and with circular polarization to H/V there is 3dB signal loss.Our engineer set up a signal generator to a dipole and oriented the receive antenna in both vertical and horizontal and sees only ~4dB signal difference. I suspect he did this in his office cube at close range, so what is dominating here and how could this test be performed more adequately without chambers?

author: ahbushnell
author_rank: Frequent Contributor
timestamp: February 11, 2023, 03:46:54 am
content: Go out in an open field. Get the antennas up in the air to minimize ground interaction.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 11, 2023, 05:10:41 am
content: What antennas?If there was significant CM (feedline or mount) current, it could amount to capacitive or inductive coupling. The antennas must be adequately balanced for polarization to manifest.In the near field of course, it suffices to express the balance of E or H fields over the receiver's elements, but the same symmetry extends to far fields where we call it polarization specifically.Tim

author: Bud
author_rank: Super Contributor
timestamp: February 11, 2023, 05:54:55 am
content: As was suggested, try in open field with antennas suspended several Lamdas above ground. That means UHF or microwave antennas would be easier to set up. Still, radiation from the coax and reflections off of it may skew the results.

author: AFTORF
author_rank: Contributor
timestamp: February 11, 2023, 09:49:08 am
content: ...And another trick : Be careful of mast effect with yagi elements when you use V polarisation.

author: metrologist
author_rank: Super Contributor
timestamp: February 11, 2023, 10:38:10 am
content: Now I see the setup. The tx antenna was actually a whip antenna connected directly to the RF port of the signal generator. The receive antenna is a hand-held log periodic yagi connected to a SPA through about 2 feet of coax. The test was conducted at 1 GHz in a 2nd floor meeting room, about 15 feet apart.

author: AFTORF
author_rank: Contributor
timestamp: February 11, 2023, 11:23:57 am
content: I already tried this kind of trial in my office : forget it ! Outdoor only for antenna test at 1 GHz. There are too many reflections from desk, floor, wall in a building.

author: switchabl
author_rank: Frequent Contributor
timestamp: February 11, 2023, 01:39:30 pm
content: Quote from: metrologist on February 11, 2023, 10:38:10 amWell... that makes the actual TX antenna a combination of the whip antenna (monopole?) and the big metal box in its nearfield. The result is not exactly well-defined, even if you were to move it into a proper test chamber.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 11, 2023, 04:30:51 pm
content: Quote from: metrologist on February 10, 2023, 11:01:58 pmI am not sure what this test is or what the goal was. If you only want to see the effects, you can certainly do this in the comforts of your office as has been demonstrated.