I use GPS for the recovery of my model rockets. Often, I only use one GPS antenna, because its dead simple. Often, however, this is a ceramic antenna orientated "upwards" in the rocket, which does not get good reception after the rocket lands.
This projects aims to create an array of 5 GPS antennas around the circumference of the rocket. This will improve GPS reception when the rocket is on the pad, and when it hit the ground.
In order to do this, I am using 5 GPS chip antennas, each with their own low noise amplifier (LNA). The LNAs all connect to a SP5T RF switch. This switch allows me to select which antenna I would like to use, through the three address lines. I have also connected the three address lines to a 3-to-8 decoder that enables/disables the corresponding LNA to save power.
All of this is mounted on a 0.320" x 12.150" flexible PCB, which will be wrapped into a circle with the correct diameter to fit inside of a 4" cardboard rocket tube.
Files
GPS switcher.pdf
PDF of Schematic
Adobe Portable Document Format -
45.15 kB -
05/16/2019 at 05:36
I wasn't too happy with the original GPS chip antenna I chose for this board (1575AT43A40). It was really convenient though. It has a gain of -2.5 dBi and I was not too happy with the rf radiation pattern. (you can find the datasheet here: https://www.sparkfun.com/datasheets/GPS/JTI_Antenna-1575AT43A40_2006-09.pdf)
So I switched to a different ceramic chip antenna, the W3011A. This has a gain of +1.0 dBi and a return loss of -16 dB, which is much better than the -9.5 dB from the old antenna. In addtion, it doesn't need as much clear area around it, so I can make the board a little more narrow.
Also, here is a picture of the board layout for one of the 5 antennas + passives + LNAs. You can see the chip antenna in the upper right with the keepout layer to restrict the ground plane.