How to Add High-Precision GNSS to Nearly Any Device

What do livestock, shipping containers and fitness wearables have in common? They’re three widely disparate examples of things that increasingly rely on GNSS. They’re also examples of why the global GNSS chip market is on track to grow from $2.7 billion in 2019 to nearly $3.8 billion by 2026, according to the research firm QYR.

GNSS today is like cellular a few years ago: Device OEMs recognize the business value of adding these technologies to their products, but they often lack the RF expertise necessary to select the right module and antenna, and then integrate them into their design to ensure reliable performance. For example, an OEM might be a leader in consumer electronics or construction equipment, but have no in-house RF engineering staff to develop and execute its GNSS strategy.

This causes a variety of challenges that directly affect their device’s performance, reliability and value in the customer’s eyes. For instance, GNSS received signal strengths are low power, which makes them vulnerable to interference — including the spurious signals generated by electronic equipment such as actuator motors and processors, as well as other wireless radios onboard the user device. That RFI noise can undermine the ability to get a highly precise location on a consistent basis.

The choice of constellation also affects accuracy. More constellations enable more precise location information and greater redundancy, which is why over 30 percent of GNSS chipsets now support the four majors: BeiDou, Galileo, GLONASS and GPS. (Some also support regional systems such as NAVIC and QZSS.) So, by choosing a module and antenna that can support multiple constellations, a device OEM can significantly increase its product’s reliability and precision. That performance could give its product a competitive edge — especially for mission-critical applications such as first responder devices — and even help justify a price premium.

Constellation choices also affect the spectrum that a GNSS solution must support. Figure 1 shows the bands that each constellation uses.

Figure 1: GNSS Constellation Types and Spectrum Bands

The Right Antenna in the Right Place

GNSS antenna systems are available in a variety of form factors. For OEMs, the choice depends partly on what their device can accommodate, such as a low-profile patch. Figure 2 summarizes the major types.

Figure 2: GNSS Antenna Types and Form Factors

Drones are helpful for understanding some of the challenges and considerations. Weight is a critical factor because it affects how long and how far a drone can fly, as well as the size of its payload capability. The PCB size (ground plane) directly affects GNSS antenna performance. A large ground plane would help maximize the GNSS patch antenna’s performance, but it also adds weight. And as Figure 3 shows, the position in that ground plane directly affects the amount of fine tuning that the OEM will need to do.

Figure 3: Ground Plane Location Affects Gain and Bandwidth

The catch is that mounting locations often are limited. The antenna must be far enough away from the drone’s motors and other electronic components that generate RFI, but those ideal locations often are unavailable because the additional weight in those spots would disrupt the delicate balance that drones require to fly safely and effectively.

Drone OEM Parrot considered all of these factors when choosing a GNSS antenna solution for its ANAFI USA model, which is designed for a professional applications including public safety, surveying, inspection, defense and more. Weighing a mere 500 grams, ANAFI USA is designed to withstand winds up to 52.92 km/h. Parrot chose Taoglas’ DSGP.1575.15.4.A.02, a passive patch antenna that supports GPS L1 and GALILEO E1.

At just 3.3 grams and 4 mm high, with a 15 mm² footprint, the DSGP.1575 is tuned on a 50 x 50 mm ground plane. Its ceramic architecture is ideal for drones because they spend most of their time flying parallel with the horizon. That position helps the DSGP.1575 collect enough quality GNSS signals to meet performance requirements.

Many GPS applications are devices designed to be worn, such as fitness trackers and medical wearables. A key consideration here is how the human body interacts and disturbs the GNSS received signal strength, regardless of whether the antenna technology used. As a result, systems designers should tune their antennas in the presence of a human body to determine how the antenna’s location and orientation affects the antenna’s radiation pattern, hence the overall system performance of the device.

This process can be daunting for OEMs that have no in-house RF engineering staff. Hence the importance of selecting an antenna vendor that offers tuning tricks and RF simulations to help its customers analyze body attenuation to optimize their designs. This kind of design support also helps OEMs reduce development costs and lead time, so they can get new products to market faster.

OEMs also should focus on antenna vendors that have decades of GNSS experience, which means they’ve faced and overcome a wide variety of challenging use cases and RF environments. This experience is reflected in the reference designs they’ve developed with radio partners, as well as a broad, deep portfolio of products that enable customers to choose the linear or circular polarized solution that best matches their application requirements.

For example, Taoglas’ ASGGB184.A and ASGGB254.A are single-band active GNSS patches whose hidden active circuitry is embedded between the ceramic patch and PCB base. This enables users to surface mount them directly onto their device PCB. It’s one more example of the kind of design flexibility that helps OEMs ensure that their products meet their customers’ expectations for performance, reliability and value.

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