TIDA029A july   2019  – june 2023 CC2640R2F-Q1 , CC2642R , CC2642R-Q1

 

  1.   1
  2.   Bluetooth Angle of Arrival (AoA) Antenna Design
  3.   Trademarks
  4. 1Introduction
  5. 2Angle of Arrival Antenna Design Considerations
    1. 2.1 Antenna Spacing
    2. 2.2 RF Switch Considerations
  6. 3Dipole Antenna Array
    1. 3.1 Dipole Antenna Strengths and Weaknesses
    2. 3.2 Angle Measurement Plane
    3. 3.3 PCB Implementation
    4. 3.4 Two Dipole Array Test Results
      1. 3.4.1 Total Radiated Power (TRP)
      2. 3.4.2 Measuring Antenna 1 and 2 Phase Difference
        1. 3.4.2.1 Bare PCB
        2. 3.4.2.2 PCB + RF Absorbing Material
        3. 3.4.2.3 PCB + RF Absorbing Material + Tin-Plated Copper Foil
        4. 3.4.2.4 PCB + RF Absorbing Material + Tin-Plated Copper Foil + Metal
      3. 3.4.3 Phase Difference vs Distance
  7. 4Calculating AoA From IQ Measurements
    1. 4.1 Dipole Antenna Array Uncompensated Angle of Arrival Results
      1. 4.1.1 Bare PCB Uncompensated AoA
      2. 4.1.2 PCB + RF Absorbing Material Uncompensated AoA
      3. 4.1.3 PCB + RF Absorbing Material + Tin-Plated Copper Foil Uncompensated AoA
      4. 4.1.4 PCB + RF Absorbing Material + Tin-Plated Copper Foil + Metal Uncompensated AoA
    2. 4.2 Dipole Antenna Array Compensated AoA Results
      1. 4.2.1 Bare PCB AoA With Compensation
      2. 4.2.2 PCB + RF Absorbing Material + Tin-Plated Copper Foil Compensated AoA
      3. 4.2.3 PCB + RF Absorbing Material + Tin-Plated Copper Foil + Metal Compensated AoA
      4. 4.2.4 Hardware Setup Compensated Results Comparison
  8. 5References
  9. 6Revision History

4 Calculating AoA From IQ Measurements

In Section 3, the measured phases were used to calculate a phase difference between the two antennas with different hardware setups. The next step is to calculate AoA based on the measured phase difference. With a known spacing between the antennas (d), and phase difference between the two antennas measured (Φ), the AoA can be calculated using simple trigonometry as Figure 4-1 shows.

GUID-C8821ADF-F0B5-4663-94E8-7D3148983B86-low.png Figure 4-1 AoA Equations

The equations in Figure 4-1 can be simplified to Equation 4.

Equation 4. GUID-E34BE991-B027-4537-ACC1-4EA5DD6BC859-low.gif

Note that r is the distance to antenna 2 that the incident wave needs to travel after arriving at antenna 1. Because the phase difference is known (Φ), the extra distance r is equal to the wavelength of the incoming signal times Φ / (2π). For more information on the AoA calculation, see the SimpleLink Academy -> RTLS Toolbox -> Angle of Arrival (AoA). Performing the arcsin() function using the wavelength, known antenna phase center spacing, and calculated phase difference between the two antennas, the AoA is calculated.

After the AoA is calculated, the value may need to be compensated due to variation in results across frequency and antenna design. Therefore, a constant gain, an offset, or both may be used to improve the AoA results.

GUID-A6C15752-D3C3-4C5C-A357-028A04077EB9-low.png Figure 4-2 Compensation to Linear Plot

For more information on AoA compensation, see the Angle Compensation section of the SimpleLink™ CC2640R2 SDK BLE-Stack User’s Guide.