2 Angle of Arrival Antenna Design Considerations

To calculate the AoA, the incoming RF carrier phase must be measured with minimal impact to the signal phase of the carrier itself using two or more co-located antennas. Therefore, there are several considerations to understand when designing a Bluetooth Low Energy antenna array. First, to determine which antenna is closest to the transmitted signal, the antenna phase centers must be within ½ λ of each other, discussed in Section 2.1. Consequently, antenna spacing becomes a concern as undesired coupling can occur reducing the efficiency of the antenna array. Furthermore, to avoid additional phase measurement errors and any added calibration requirements, the phase centers of the antenna should be constant. If the phase center shifts due to the direction of the incoming signal, the phase center change must be accounted for in the AoA calculation. Finally, with any antenna design, other antenna basics such as grounding and efficiency should be understood to improve the overall effectiveness of the receiver and ensure minimal interference from reflections. Another aspect of the AoA hardware design is the RF switch required to switch between two or more antennas. It is important to understand the RF switching times to calculate the AoA measurement and meet the Bluetooth 5.1 specification as well as understand the RF switch specifications to ensure good performance while optimizing cost.