Co-locating GPS and GSM antennas - Page 1
Forum section: electronics / rf-microwave

author: angust_uk
author_rank: Regular Contributor
timestamp: January 10, 2019, 01:11:25 pm
content: Hi allI'm afraid it's an RF non-expert asking this, so go easy! I'm working on a design that includes a module with both GSM and GPS interfaces (Telit GE310), and am looking to implement antennas for both on the same board (cost is one of the biggest constraints). Unfortunately the board will be mounted vertically which means I'm a bit limited as to the orientation of the antennas I choose!My original plan was to use ceramic antennas for both GSM (https://www.molex.com/molex/products/datasheet.jsp?part=active/2047740001_ANTENNAS.xml) and GPS (https://lcsc.com/product-detail/Others_Rainsun-microwave-Tech-GPS1004_C239244.html) though the latter is designed to be mounted flat such that the sky is above it, not at 90 degrees!To make matters worse, board space is also fairly constrained, and I have an area of about 90mm x 65mm to play with (including space for the modules and power supplies).My question is: am I barking up the wrong tree completely hoping to get away with board-mount antennas? Ideally I'd put some co-ax connectors down and place the antennas more optimally but that's not really an option unfortunately.Also I'm struggling to find a GPS antenna that sits perpendicular to the PCB surface rather than parallel (apart from this one which is pricey:https://www.taoglas.com/product/ap-10h-gps-2-stage-smd-active-patch-10mm-2/). Has anyone here used such a thing?Help (please)!Angus

author: cdev
author_rank: Super Contributor
timestamp: January 11, 2019, 01:39:51 am
content: Is the top end of your device - presumably the edge of your PCB, in the clear or does your device live on a wall that continues upward past it where it cannot have a clear sky view?

author: angust_uk
author_rank: Regular Contributor
timestamp: January 11, 2019, 08:33:56 am
content: Quote from: cdev on January 11, 2019, 01:39:51 amHi cdev - unfortunately that is up to the end user as they will take care of installation. However we can advise them of the optimal position so we could (and likely will) state in the manual that it should have a clear view of the sky

author: cdev
author_rank: Super Contributor
timestamp: January 11, 2019, 03:49:39 pm
content: If you could slap an L shaped angle bracket on that end you can use that as a ground plane. But it may look a little squirrelly. Rounding its corners would pretty it up a bit. Another option for the GPS antenna would be a compact quadrifilar antenna like a geohelix from Sarantel, (There are other brands too that might be a lot cheaper)but they are typically fairly expensive compared to a patch antenna.They however, or any quadrifilar antenna should not need a ground plane and some work in almost any orientation, even upside down. (but don't put it on the bottom of a car where it will only see LHCP reflections, not RHCP direct signals.) QFH's are extraordinarily flexible in placement for that reason.The patch antennaalwaysneeds a ground plane and especially with the smallest ones, it should be fairly large!(50 mm if you want the device to appear to be sensitive, no less.)Manufacturers instructions should be followed.Want to see what I mean?Take one of those puck antennas, which is meant to be slapped on a car, stick it in a windowsill or better yet, on a stick or something, suspended in the air, but with nothing conductive, no ground plane underneath it, and compare it to when there is a piece of flat metal approximating a flat ground plane stuck to its bottom by the magnet underneath it and its top facing straight up. (how its meant to be used)You'll see a huge difference.