Test process guide and overview
– Antenna Testing

All LabSat models can be used for antenna testing. The GNSS capabilities of the device under test (DUT) will determine which model is most suited.

If your DUT supports signals outside of the L1 frequency band, for example GPS L5, then LabSat 3 Wideband is the model required.
If your DUT only operates within the L1 frequency band, we recommend LabSat 3 for this test.
If your DUT requires a real time (current timestamp) RF signal, LabSat Real-Time or Real-Time+ would be the only suitable model.

Testing antennas, either internal or external, presents several challenges; the GNSS engine will get confused if it can see both the LabSat output and real GNSS signals, transmission of radio signals in the GNSS bands are very tightly restricted in most countries, and finally the surrounding environment can have a significant impact on the repeatability of the signals received by the antenna.

The simplest solution to these problems is to make use of a Radio Frequency (RF) Shielded Chamber by placing the signal output from the LabSat and the DUT/antenna within a sealed RF Chamber, shutting them off from the outside world.

This eliminates two of the difficulties:

• Live GNSS signals are prevented from reaching the DUT containing the antenna or antenna itself.
• The re-radiated signals from the LabSat are confined to the chamber, avoiding the issues with transmissions within the GNSS bands.

The third issue, ensuring a repeatable test, requires two further steps:

• Firstly the chamber should be lined with RF absorbent foam, this significantly reduces the reflections within the chamber and so reduces the potential risks of multipath interference.
• The final step to ensuring a repeatable test is remarkably simple, ensure the antenna under test is always placed in the same location. Ideally also lift it off the floor of the chamber in order to move the receiving antenna away from the RF absorbent lining. This could be as simple as a cardboard box with a line indicating unit location or it could involve a dock or mounting bracket fixed to the inside of the test chamber.

Ideally the DUT/antenna under test should not be placed too close to any of the chamber walls and should be as far as possible from the transmitting antenna. The use of metal within the chamber should be minimised and all cables should be as short as possible.

In practice, meeting these recommendations is not always possible. They may compromise the practicality of the test chamber and ultimately have only minimal impact on performance. Due to the nature of RF signals, every product will act slightly differently. When first setting up the chamber, some experimentation may be required to ascertain the best compromise between usability, test repeatability and GNSS performance.

The RF Test enclosure (RF shielded chamber) included in this test process is available for purchase from Sampson Technology – A selection of radiating antennas are also available to purchase from Sampson Technology.

Step 1)
Connect from the LabSat RF OUT port to the RF IN port on the outside of the RF test enclosure.

Step 2)
Fix your radiating antenna in location within the test enclosure and connect to the RF connector inside the enclosure (RF filtered pass through port from external RF connector).

Step 3)
Place the DUT/antenna under test in the test location within the enclosure – close and seal the enclosure.

Step 4)
Press the ‘play’ button to start the scenario replay.

To verify your results, we recommend completing this process with a ‘known good’ antenna and receiver combination to act as the baseline for expected results.