Polarization of microwave door openers...

**MEM-TEK** · 03-31-2008, 04:20 PM

Originally Posted by Freebird

I did some more testing with the k-band speed sign with interesting results. Mounted vertically I get 30% or more alert distance on every pass. When I had it mounted horizontal I stopped when the alert was 3 lights on the meter and turned it vertical and it goes from 3 lights to full alert all lights. It is amazing how much differance on this speed sign how being vertical is much more sensative. I would assume the difference must be the polarization, circular to vertical. Too bad this does not work with police radar, would be nice to get 30% more sensativity

Its a good thing that it doesn't work with nearly all police radar guns. If police used polarized radar guns, all they would have to do is rotate their transmitters 90 degrees and our detection range would plummet.

**jimbonzzz** · 03-31-2008, 05:03 PM

Originally Posted by MEM-TEK

I don't think that you would see any change in distance in over-the-hill encounters since nearly all police radar guns are circularly polarized. I did also try my STi in the same test setup with the door opener and noted that the STi horn design for some reason was almost as good at picking up the polarized door opener radar compared to the 9500i when it was oriented vertically. I suspect the reason is that each STi horn uses a LNA. Jimbonzzz, what do you think?

The LNA only comes into play once the signal is coupled to microstrip, so I don't think it's a factor here, except for sensitivity.

**jimbonzzz** · 03-31-2008, 05:13 PM

Originally Posted by MEM-TEK

Its a good thing that it doesn't work with nearly all police radar guns. If police used polarized radar guns, all they would have to do is rotate their transmitters 90 degrees and our detection range would plummet.

I can see it now: a cop with a Stalker ATR, shooting it gangsta style

**TSi+WRX** · 03-31-2008, 06:21 PM

^

Yo, you gotz to pull ova!

**MEM-TEK** · 03-31-2008, 07:14 PM

Originally Posted by jimbonzzz

The LNA only comes into play once the signal is coupled to microstrip, so I don't think it's a factor here, except for sensitivity.

Judging by the way my single wave guide STi performs in comparison to my single wave guide 9500i, I strongly suspect that the LNAs in the STi are relatively immune to polarization. I suspect that it has to do with the architecture within the LNA chip itself. After all, the output of the STi's LNAs do indeed feed directly to microstrips for each of the radar horns, but that is the output from the LNAs. Just a thought, but this is the only way that I can explain why my STi is roughly as sensitive to the clearly polarized radar emanating from the K band door opener when oriented vertically, whereas my 9500i is all but dead to the door opener once I rotate the 9500i horn vertical.

Just a thought...

**asianfire** · 03-31-2008, 08:09 PM

Well, I learned something today...didn't even know what a LNA was until tonight.

**jimbonzzz** · 03-31-2008, 10:05 PM

Originally Posted by MEM-TEK

Judging by the way my single wave guide STi performs in comparison to my single wave guide 9500i, I strongly suspect that the LNAs in the STi are relatively immune to polarization. I suspect that it has to do with the architecture within the LNA chip itself. After all, the output of the STi's LNAs do indeed feed directly to microstrips for each of the radar horns, but that is the output from the LNAs. Just a thought, but this is the only way that I can explain why my STi is roughly as sensitive to the clearly polarized radar emanating from the K band door opener when oriented vertically, whereas my 9500i is all but dead to the door opener once I rotate the 9500i horn vertical.

Just a thought...

You're right, the LNA is immune to polarization. So, I'm not sure why you even thought to bring up the LNA up here at all as a possible reason for the differences you saw? Relatively speaking, if you're talking about polarization it won't act any differently if there is an LNA there or not.

The LNA is not part of the antenna, and is not responsible for the "receiving": The antenna feeds the microstrip, at which point the antenna (and polarization) no longer play a role in receiving the signal. The LNA only acts upon the signal that makes it into the microstrip transmission line, amplifying it before it goes to the mixer. It does NOT take a waveguide input and output to microstrip, the LNA input is microstrip and the LNA output is microstrip, I'm not sure why you would think otherwise?

I don't know why the STi might appear to be less susceptible to polarization mismatches in certain situations than other detectors, but the LNA shouldn't play any role here. IF it was determined that there actually was something to it, the thing look at for the reason is antenna design...

**KnightHawk** · 03-31-2008, 10:59 PM

Is this the reason why the X50 had a poor performance with this particular test I did in this thread?
http://www.radardetector.net/viewtop...282&highlight=
I have tested the RX65,V1,STi and the X50 and the later had poor performance with only less than half the distance in picking up the signal with radar antenna pointed up in the sky and the detector in horizontal position.

**jimbonzzz** · 03-31-2008, 11:19 PM

Originally Posted by Azonehits

Is this the reason why the X50 had a poor performance with this particular test I did in this thread?
http://www.radardetector.net/viewtop...282&highlight=
I have tested the RX65,V1,STi and the X50 and the later had poor performance with only less than half the distance in picking up the signal with radar antenna pointed up in the sky and the detector in horizontal position.

Polarization shouldn't have had an effect on your X50 35.5 results... for one, it's vertically polarized just like the rest of the detectors you tested, and for two, the 35.5 Gun is circular polarized so it wouldn't have made a difference anyway.