0 Replies Latest reply: Aug 18, 2012 12:44 PM by Harald Naumann RSS

Which GPS antenna shall be used for a tracking device?

Harald Naumann Expert

The sketch about GPS antennas was made during a training about wireless in Dortmund

GPS antenna how to use 229x300 Which GPS antenna shall be used for a tracking device?

Which GPS antenna to use and why?

      1. GPS chip antenna as PIFA

The  GPS module Fastrax UC430 and UC530 comes with integrated GPS chip  antenna. Such PIFA antennas are looking for 70 to 80 mm long PCBs. 35 to  40 mm left and 35 to 40 mm right is fine. The shorter the PCB length,  the worst the antenna efficiency will be. With 22.5 mm left and 22.5 mm  right, you still get a nice result. Please note that the evaluation PCB  of UC430 and UC530 has a length of 45 mm. X has to be at least 45 mm. In  Y direction the size does not matter. The form factor of UC430 and  UC530 is 9.6 x 14.0 x 1.95 mm. That means a PCB with 45 x 14 mm will  give a good result in the performance.
The centre frequency of this PIFA antenna can be tuned with the gap (ground less area) under the antenna plus matching circuit.

2. – 4. GPS chip antennas as monopole antenna

Option  2 and 3 are showing antennas on the corner of the PCB. Just take care  on the data sheets of the antennas. The distance to ground plane is  maybe different, by different types of antennas. This antenna type can  be tuned by making a stubby (small PCB track) on the open end of the  antenna and components in the matching circuit.

5. GPS patch antenna on PCB

Most  data sheets name a 70 x 70 mm or 35 x 35 mm ground plane. If you change  the size of the ground plane, then the centre frequency will shift. If  you put an antenna on top of the antenna, then the centre frequency will  shift again. If you change the thickness of the plastic or the type of  the plastic or the distance to the plastic – every change will interfere  with the antenna.

5.1 The way out of the GPS patch antenna jungle

Just  ask for an evaluation with GPS patch antennas, that comes with centre  frequencies of 2 MHz steps. One out of 10 antennas will fit to your  application. To limit the tuning trouble you shall select a 22×22x4 mm  GPS patch antenna. As bigger the GPS patch antenna is, as bigger the  bandwidth of the antenna. As bigger the bandwidth, as less the risk  to loose performance. 18×18x4mm is a good compromise. A 18×18x4mm GPS  patch antenna with tuning is on 20×20mm ground plane is in use with the  GPS module UP501.

6. – 7. GPS patch antenna on non symmetric PCB

GPS  patch antennas offers a circular polarisation. The circular polarisation you get by putting the feeding point not in the middle of the GPS patch antennas. The red round shaped lines on the sketch number 6 shows the floating current on your PCB. The current will float circular. Sketch number 6 shows a 40×40 mm PCB. This is OK. At sketch number 7 you see a non symmetric PCB. As soon, the PCB is not quadratic the circular polarisation will be destroyed and the loss will be 3 dB. If your PCB is not quadratic (what is common) then just take care, that the ground plane will be quadratic.

Conclusion

The  selection of the GPS antenna and the tuning plus selection of the GPS  module is a difficult task. The good news is that you can get advice on  PCB layout plus testing and tuning your PCB free of charge.

3 days training about wireless applications free of charge

  • Hotel Dorint Adlershof, Rudower Str. 15, 12489 Berlin
  • 25th. – 27th. of September
  • Registration  by email to harald.naumann (at) gsm-modem.de