AN1195: Antenna Array Design Guidelines for Direction Finding
The purpose of this application note is to provide hardware design guidelines specific to the antenna arrays required for the direction finding implementations.
Note: This document applies to 2.4 GHz BLE standards for EFR32MG22 and EFR32BG22 devices.
●KEY POINTS:
■Describes general direction finding usecases
■Provides general antennarecommendations for a direction findingantenna array
■Details 4x4 antenna array properties andinsight into antenna tuning and itemswhich affect the antenna
AoA relies on a single-antenna transmit beacon with continuous tone extension appended to a Bluetooth packet transmission and a locator receiver device to measure the arrival angle of the signal using an array of antennas. Each antenna in the array sees phase differences due to different line of sight distances to the beacon device. The antennas in the array are switched during continuous tone extension, resulting in IQ samples with phase information for each antenna. This IQ-data is fed to an angle estimator algorithm. In this AoA use case, the receiving device tracks arrival angles for individual transmit beacon objects.
AoD is similar to AoA but the beacon and receiver roles are swapped. The AoD use case relies on a single-antenna mobile receiver and multi-antenna transmitter beacons. The mobile receiving device can calculate its own position in space using angles from multiple beacons and their positions.
Angle calculation is based on phase information from the individual antenna elements of the antenna array. The arrays utilized for this purpose are uniform rectangular arrays. The number of channels/antennas affects the overall angle estimation accuracy. A larger number of antennas also helps with multipath effects. Other types of arrays could be used for AoA/AoD, such as linear arrays, circular arrays, and non-uniform arrays. However, custom array development requires significant simulation and test efforts. For this reason, we recommend utilizing the array discussed in detail in this application note. The sections to follow outline general and specific recommendations related to the antenna array design.
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Application note & Design Guide |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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December 2020 |
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Rev. 0.3 |
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AN1195 |
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9 MB |
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