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

3.3 PCB Implementation

The ¼ λ dipole antennas were designed at the center of the Bluetooth Low Energy frequency spectrum (2.44 GHz) and therefore, have a length of about 30.8 mm. Notice that the phase centers are spaced 35 mm apart meeting the needed < ½ λ spacing requirement.

GUID-4449B38A-BE73-4C44-B675-A0B7F42811CD-low.png Figure 3-6 Layer 3 Dipole Spacing and Width

To transform the balanced (differential) signal to an unbalanced (single-ended) signal, a PCB Marchand balun was implemented on the layer below the dipole antenna (layer 4).

GUID-2E94169E-468B-4FC1-9DA6-FCDB0384D958-low.png Figure 3-7 Layer 4 Marchand Balun

The Marchand balun was designed, simulated, and tested to ensure proper performance. The top section of the balun routed to the RF switch is used to match the 50-Ω impedance transmission line. Additionally, the board stack-up ensures proper spacing between the 3rd layer (dipole antenna) and the 4th layer (Marchand balun) for the correct amount of capacitive coupling between the two layers. Because the single-ended trace from the RF switch requires ground, the Marchand balun and dipole antenna feed traces are sandwiched between two identical ground planes, one on the 2nd layer and one on the 5th layer, as Figure 3-8 shows.

GUID-A5AF2F7E-4DE4-4FEB-A037-97160EA93842-low.png Figure 3-8 Layer 2 and 5 Ground Planes

Figure 3-9 through Figure 3-12 show the dimensions for the dipole antennas, Marchand balun, and GND planes.

GUID-B2175265-A665-4D0F-81BC-ED56687CC57F-low.png Figure 3-9 Layer 3 Dipole Antenna Dimensions
GUID-C3C179ED-EC2E-4D37-872D-24B57363733D-low.png Figure 3-10 Layer 4 Marchand Balun Dimensions
GUID-3529AD00-2D16-462B-A08F-895B95D6E4BA-low.png Figure 3-11 Layer 2 and 4 Ground Plane Dimensions
GUID-7460E1AA-DE92-4BCF-AE9C-3CB1BAB536AD-low.png Figure 3-12 Dipole With Ground Plane Dimensions
Table 3-1 PCB Stack-up
Layer Name Type Material Thickness (mm) Dielectric Material Dielectric Constant
Top Solder Solder Mask/Coverlay Surface Material 0.01016 Solder Resist 3.5
Top Layer Signal Copper 0.035
Dielectric 1 Dielectric Core 0.1 FR-4 4.1
Layer 2 Signal Copper 0.01801
Dielectric 2 Dielectric Prepreg 0.2 FR-4 4.1
Layer 3 Signal Copper 0.01901
Dielectric 3 Dielectric Core 0.1 FR-4 4.1
Layer 4 Signal Copper 0.01801
Dielectric 4 Dielectric Prepreg 0.2 FR-4 4.1
Layer 5 Signal Copper 0.01801
Dielectric 5 Dielectric Core 0.1 FR-4 4.1
Bottom Layer Signal Copper 0.035
Bottom Solder Solder Mask/Coverlay Surface Material 0.01016 Solder Resist 3.5

See the TIDA-01632 Automotive Bluetooth® Low Energy car access satellite node reference design for more information on the design and for access to Gerber files, schematics, and more.