Timing is everything. So is location, especially in navigation. But both are nothing without reliable GNSS signals.
Achieving that reliability is particularly challenging in asset trackers, fitness wearables, drones, and other devices that must be compact, lightweight, oddly shaped, inexpensive, low power, or all of the above.
For starters, svelte form factors severely limit PCB space. This increases the likelihood that the GNSS receiver will be subject to RFI from the LTE transceiver and other nearby radios, as well as from the module’s power supply.
One potential solution is an active GNSS antenna, where an integrated Low-Noise Amplifier (LNA) boosts the signal before it goes to the receiver. Taoglas active GNSS antennas also have front-end filtering, which minimizes out-of-band signals and noise to improve signal quality.
How much of an improvement? One example is Basetime’s Locater One device, which construction and engineering companies use for ultra-precise measurements on job sites. Taoglas recommended the ADFGP.50A, an active GNSS antenna that includes an LNA and front-end Surface Acoustic Wave (SAW) filter. That was key for ensuring for sub-centimeter measurements. (For a closer look, see “Taoglas helps Basetime enable ultra-accurate geometric height measurement for construction application.”)
It’s also important to identify the source(s) of interference in order to pinpoint the most effective solution. Take the example of an asset tracker whose LTE radio is desensitizing the GNSS LNA. A GNSS antenna with an integrated LTE Band 13 notch filter will block those signals. (For more tips, see “Active vs Passive: Choosing a GNSS Antenna Solution”)
All of these factors highlight why it’s critical to consider the antenna early on in the device design process. For example, some GNSS receivers require an active antenna.
The Importance of Staying Grounded
A PCB that’s small, oddly shaped, or both also makes it difficult to put the GNSS antenna in a location where it has enough ground plane to optimize gain. For example, mounting a patch antenna in the corner of the PCB can destabilize its performance by disrupting the optimal ground plane currents.
To help overcome that challenge, consider the antenna early on in the device design process rather than toward the end, when the module and other components have been assigned PCB locations. This avoids the expense and delay of redesigning the board to make room for the antenna.
Similar challenges apply if the GNSS antenna is external. For example, in vehicular applications, the GNSS antenna usually is installed on the roof or trunk, whose metallic surface provides the ground plane. But that’s not an option for many other applications, such as a drone whose shell is plastic.
In those cases, choose a quad helix antenna that has an even gain across the hemisphere. For example, if the antenna needs to be embedded, consider the Taoglas EAHP.125. If it’s external, a good choice is the Taoglas Accura Series’ TS.125.0111W. (For more tips, see “Why Antenna Placement on PCBs is Critical for Chip Antenna Radiation Performance” and “Understanding Ground Planes for Cellular and GNSS Devices.”)
