Chris:
The advantage of a full anechoic chamber is that you don’t have to worry about reflected signals messing up your pattern measurements. OTOH, full anechoic performance of a chamber is not easy to achieve, as you get reflections off the darndest little things. I think I might try to do a pattern test in nature’s own full anechoic chamber, a big open field. Remember that almost all the junk in your 2.45 & 5 GHz bands will be operating at very low power, so if you can put a few hundred feet between your test site and the rest of the electronic world, I think you might be able to do pretty good pattern testing. I just spent a couple of weeks in the desert on BLM land near Quartzite, Arizona. There are a lot of flat, wide open “antenna ranges” out there. <g> I recall that CKC Labs has an OATS near Yosemite, so that would make a great road trip for you. I think the biggest problem with trying to do 2 & 5 GHz antenna patterns in a typical commercial lab’s semi-anechoic chamber is simply that antenna patterns are a bit out of the ordinary job flow, so it will become a bit of a “science project” wherever you go. I think your accuracy will be influenced more by the lab’s technique than by stray chamber reflections. Ed Price El Cajon, CA USA From: Christopher [mailto:cksal...@yahoo.com] Sent: Friday, February 24, 2012 2:37 PM To: edpr...@cox.net Cc: Christopher Saleem Subject: Re: [PSES] Antenna Pattern for 2.4 GHz and 5GHz Hello Ed, Thanks for your fedback. You assumption is very correct about our AP. some of our products have internal 3x3and others have external 2x2 omni direction antenna. As I understand we need to use a full anechoic chamber that is required for antenna pattern testing? can you recommend any lab? regards Christopher From: Ed Price <edpr...@cox.net> To: emc-p...@ieee.org Sent: Thursday, February 23, 2012 10:15 PM Subject: RE: [PSES] Antenna Pattern for 2.4 GHz and 5GHz Chris: I would be very careful about the physical and electrical setup of the access point. Although you could feed the access point’s antennas with a low-level CW signal from a signal generator, I think that the coax cables (even if you use very small diameter and very flexible coax) will have nasty effects on the antenna patterns. I would try to not use any external devices, but rather use the real signal from the access point’s intentional radiators. Now, I’m imagining this “access point” to be like a conventional wireless router, so it will have perhaps an unshielded Ethernet cable and a 2-wire small DC power cable from a wall-wart power pack. Yep, these cables will also have effects on your antenna patterns, so you will have to define a cable positioning protocol and make sure the cables don’t move around when the access point is being rotated around its axes. I’m also imagining the access point will probably not have nice isolation of its antennas from the rest of the access point (that is, plastic cases and antenna stalks that may have multiple angles of deployment). Let’s at least hope that the case doesn’t flex or twist as the access point is rotated through your measurement arc. And I assume that you only want to measure with matched polarizations. If all goes well, an ordinary spectrum analyzer can be used to monitor the amplitude. You can start with the access point sitting on a plastic tripod, and do a measurement cut 360 degrees around the Z axis. Then, you tilt by maybe 18 degrees on the X axis, and then do another 360 degree cut around the Z axis. You can do this by walking into your test chamber and just manually moving the tripod, but be very careful to not move anything else. Obviously, an automated antenna range is best, but you can substitute time for facilities. BTW, sometimes you might get better amplitude readings by setting the spectrum analyzer to zero-span and using video triggering. Also, I would prefer using a very directional measurement antenna, like a horn, so that I didn’t have to worry about sidelobe responses from a typical Biconical or Yagi. You can also spend a lot of time playing with varying positions of cables connected to the access point. If you are conservative, you might want to use the position that gives you the worst gain. OTOH, if you intend to depend on that FCC style wording (move everything around until something finally works better), then maybe you will want to use the best performance positioning combination. If you have two or three intentional RF emitters running at the same time, so long as none overload your spectrum analyzer, then you can do multiple measurements at multiple frequencies each time you move the physical position by one increment. Be prepared with a nice matrix to keep you from getting confused about what angle of which cut and which frequency you are measuring. I have done one frequency with several cuts in a half-day, so if you have two frequencies and want relatively fine data increments, then a couple of days sounds reasonable. Ed Price El Cajon, CA USA From: Christopher [mailto:cksal...@yahoo.com] Sent: Thursday, February 23, 2012 1:23 PM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] Antenna Pattern for 2.4 GHz and 5GHz Folks, I would like to get the antenna patterns for our 802.11 Access point Antenna's. I am looking for a Test lab in Bay Area (preferably) that has the facility to provide antenna patterns and schedule some days of test time (that is my estimate, but, we may need more/less depending on various factors). For each AP, a signal generator is connected to the antenna’s and the unit I rotated in one axis and then turned and rotated is the other axis to get the antenna pattern at the receiving antenna. I think in MIMO all the antenna’s may be energized simultaneously?. Any help in this regard is appreceiated. regards Christopher 408-470-4915 www.Aerohive.com - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher <j.bac...@ieee.org> David Heald <dhe...@gmail.com> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@radiusnorth.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
