The Internet of Things is in full swing and a top application is geolocation. After all, everyone needs to know where their device is located. (refer to “Where is my IoT Device” article). GNSS relies on triangulating RF signals received from orbiting satellites to precisely calculate a three-dimensional location on the face of the earth. It covers international protocols, like the Global Positioning System (GPS) deployed by the US government, Russia’s Globalnaya Navigazionnaya Sputnikovaya Sistema (GLONASS) and China’s BeiDou Navigation Satellite System (BDS).
The system also enables highly accurate calculation for time. Many applications including fitness trackers, watches, wearables, basestations (BTS), industrial controls, smart agriculture and transportation benefit from live assessment of geolocation and time of day. Selecting the proper antenna may be one of the most important design tradeoffs engineers can make given the wide array of protocols, form factors and received power from a satellite signal, which can be as low as -90dBm on the ground. Each antenna type offers advantages and disadvantages for GNSS applications.
1. Chip Antennas
Chip antennas offer a size advantage with form factors available from 3.0 x 1.6 x 0.55mm. These antennas work ideally for compact applications like wearable and fitness trackers, GPS/GLONASS/BeiDou modules, drones, AR/VR applications.
In RF design, everything comes at a price and chip antennas make no exception. Generally, smaller antennas provide lower gain. A second disadvantage is linear polarization. Polarization refers to the orientation of the electromagnetic field of the RF signal. Linearly polarized signals, which are typical for chip antennas, are more sensitive to the direction. Despite the constraint of linear polarization, chip antennas supporting high gain of 4dBi or higher represent an excellent tradeoff between sensitivity and size.
Examples: High Gain Chip Antenna (ACAG0301-1575) and Ultra Compact Global GNSS Chip Antenna (ACAR0301-SG3)
2. Right Hand Circular Polarization (RHCP) Patch Antennas
Different from linear polarization, circular polarization reduces directional sensitivity of the antenna and obtains a uniform performance at various angles. The increased size also enhances sensitivity. Overall, these two factors offer improved reception when using patch versus chip antennas.
These patches work best with larger systems that require an integrated design such as industrial sensors, larger robots and drones, shipping infrastructures, smart city and utility applications. Patch antennas supporting high gain may also integrate the ground plane and front-end low noise amplifier for more consistent performance and ease of use.
Example: GPS Patch Antenna with Integrated Low Noise Amplifier (APAM1866YA18)
3. External Antennas
External antennas provide the most consistent performance. However, they do not have the small form factor of patch and chip antennas. External antennas can outperform smaller embedded antennas because of their larger size.
External antennas provide flexible options for designers to consider when building their design and to help increase durability. They typically connect using standard RF connectors and don’t require a ground plane design, which offers engineers more flexibility when it comes to attaching the antenna. If the antenna features IP67 rating, it can also be attached in outdoor settings where it will receive a more consistent signal.
External antennas are ideal for high performance or mission critical applications such as tractors, smart agriculture, construction, marine, automotive, transportation, robotics, high performance drones and precision master clock systems used in networking, telecom and small cell gateways. Additional performance can be enhanced by using integrated low noise amplifiers.
Example: IP67 rated GNSS External Antenna (AEACBA050018-SG3)
The growth of GNSS in many applications requires the diversification of antenna technology to meet each device’s individual needs.
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