Prototyping an antenna array receiver - Page 1
Forum section: electronics / beginners

author: an_avid_brat
author_rank: Newbie
timestamp: December 17, 2013, 10:57:29 pm
content: (cross-posted at Electronics StackExchange and Edaboard)Disclaimer: I am decent with math/theory, but I have zero hardware knowledge (apart from some basic microcontrollers).I'm looking to build a (possibly crude, but functional) hardware prototype of a receiver with an antenna array. The application involves frequencies in the 2.4 GHz ISM band. I am experimenting with array processing algorithms and would like to be able to play around with the array geometry a bit. I would also like to do most of the processing in software. Given my background though, I have very little clue how to start. In particular, I've been trying to read data sheets for various types of components, but I can't figure out what the components expect as input and what they output.Here's what I've figured out so far:I'll need a couple of antennas, of course, close enough so that I don't get spatial aliasing. The antennas will need to be connected to an RF front end, which does the downconversion. At some point, I'll need an ADC for sampling, and then I'll need a 'bridge' into software.Assuming what I just described at least makes a little sense, here are my questions:1. How do I bridge the RF front end and the ADC?2. How do I bridge the ADC and the software part?3. Can I make things a bit simpler?, e.g. can I try oversampling the received antenna signals and then just doing everything in software from there?Additionally, is there a decent resource for learning about practical RF circuitry and prototyping? I think that is perhaps where I am weakest and need the most help.Thanks!

author: hagster
author_rank: Frequent Contributor
timestamp: December 18, 2013, 06:22:09 pm
content: This is pretty advanced stuff.1) There are lots of ways of doing it, but probably by filtering, mixing with a carrier frequency, filtering again and sampling near baseband.2) Never done it, but it probably depends on the bandwidth of your signal. If it's only a couple of KHz then its not too hard. If your after 20mHz WifI its probably somewhat harder.3) Buy a ready made receiver and use GNUradio. You can get a Dongle for a few dollars or something more capable like HackRF or Ettus stuff for more money. HackRF is open source if you want to see how it's done in that.What are you trying to do with the array? A fixed array is fairly simple to build, buy ff you want to do adaptive beamforming/steering in software I think you will be out of luck as these have to be done at the carrier frequency and you wont get an ADC that can do a direct digital conversion at that frequency. For this reason most adaptive arrays do the beamforming in the analogue or mechanical domain. Here is a good guidehttp://www.spectrumsignal.com/publications/beamform_primer.pdfIn my opinion the best way to experiment with arrays is by software simulation. I recommend using 4nec2 to build a simple dipole array that you can easily feed with any phasing you wish.

author: an_avid_brat
author_rank: Newbie
timestamp: December 19, 2013, 01:47:02 am
content: I basically want to use the array to do angle-of-arrival estimation. I've done the simulation part (MATLAB stuff, mostly), and would like to move on to a more realistic scenario, hence the question. My main concern is just being able to play around with the actual array geometry, which would rule out most of the off-the-shelf options.The HackRF and Ettus USRP stuff are interesting - I delved a bit deeper into some products that are designed to work with software-defined radio (e.g. bladeRF), and they seem promising (if slightly more expensive than I wished).Thank you for the advice and suggestions.

author: hagster
author_rank: Frequent Contributor
timestamp: December 19, 2013, 03:06:00 pm
content: The most important thing is the phase-coherence of your input channels. Normally by using the same LO.Alternately you could use one receiver and rapidly switch the antenna to do Pseudo-Doppler DF.

author: lorth
author_rank: Contributor
timestamp: December 20, 2013, 10:45:01 am
content: Check this course:http://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-system-capable-of-sensing-range-doppler-and-synthetic-aperture-radar-imaging-january-iap-2011/