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Summary of Contents for Acconeer A111
- Page 1 Hardware and physical integration guideline PCR Sensor A111 User Guide...
- Page 2 Hardware and physical integration guideline PCR Sensor A111 Hardware and physical integration guideline PCR Sensor A111 User Guide Author: Acconeer Version 1.5: 2022-03-07 Acconeer AB Page 2 of 32 © 2022 by Acconeer – All rights reserved 2022-03-08...
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Page 3: Table Of Contents
Hardware and physical integration guideline PCR Sensor A111 Table of Contents Introduction ............................ 4 Radar loop equation ........................ 4 Radar loop radiation pattern ....................5 HW Integration - Schematics ......................6 Power ............................. 6 SPI Interface ........................... 7 PCB layout ............................. 8 Sensor ground plane size ...................... -
Page 4: Introduction
This document aims to provide general guidelines for the hardware and physical integration of the Acconeer A111 radar sensor. The A111 sensor is a fully integrated 60 GHz radar including the transmitter and receiver antenna. The Tx/Rx antenna is a folded-dipole type and the E-plane and H- plane of the antennas are indicated in Figure 1. -
Page 5: Radar Loop Radiation Pattern
Hardware and physical integration guideline PCR Sensor A111 1.2 Radar loop radiation pattern When characterizing the gain, we refer to the radar loop gain defined in the radar equation section. Figure 2 shows the radar setup configuration for the radar loop radiation pattern measurement. The reflector which in this case is a circular trihedral corner (radius of 3.8 cm) is located at the far-field... -
Page 6: Hw Integration - Schematics
SPI interface are pulled low during this time, otherwise reverse leakage will occur via the ESD diodes in the A111. If it is not possible to set the SPI interface in such a state (either via SW or by configuring any level-shifters that might be used in the design), the problem can be solved by adding a power switch only to VIO1 and VIO2. -
Page 7: Spi Interface
Hardware and physical integration guideline PCR Sensor A111 Figure 4. An example of how to connect a power switch to reduce the leakage current when A111 is powered off. 2.2 SPI Interface To optimize signal integrity of the SPI bus, it is recommended to route the SPI bus with as short as possible trace lengths with an adjacent ground plane. -
Page 8: Pcb Layout
In terms of regulatory compliance, any openings in the ground plane inside the A111 BGA footprint must be significantly smaller than the wavelength of the radiation that is being blocked, to effectively approximate an unbroken conducting surface. - Page 9 0.5 dB is seen when placing decoupling capacitors (metric 1005) as shown in (Figure 6b). Figure 6. A111 routing examples with vias placed close to sensor for maximizing ground plane size. (a) Without GND thermal reliefs, (b) with decoupling capacitors and without GND thermal reliefs, (c) with GND thermal reliefs.
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Page 10: Impact Of Conformal Coating
Hardware and physical integration guideline PCR Sensor A111 Example PCB designs can be found on the Acconeer developer page [1]. For designs requiring larger components close to the sensor, a tapered shielding wall can be designed as shown in Figure 8. -
Page 11: Sensor Underfill
Hardware and physical integration guideline PCR Sensor A111 Figure 9. Simulated impact of lossless dielectric conformal coating on radar loop gain (RLG) at center frequency (60.5 GHz). Figure 10. Simulated impact of conformal coating with ε =2 and ε =3 for different thicknesses. -
Page 12: Physical Integration
This chapter provides the integration guidelines for simplified sensor cover scenarios. In any case, it is important to carefully design and characterize the integration to ensure that the desired performance is obtained. The radiation pattern presented in the A111 datasheet (developer.acconeer.com), shows the sensor performance when integrated in free space. - Page 13 Hardware and physical integration guideline PCR Sensor A111 Figure 11. Placement of the radome in relation to the sensor. Figure 12. Measured reflected power from the target versus the radome to sensor distance for two different service profiles, Profile 2 (MaxSNR) and Profile 1(MaxDepth). Amplitude is nomalized by the maximum value of Free Space.
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Page 14: Radome Thickness
Hardware and physical integration guideline PCR Sensor A111 4.2 Radome thickness When an EM wave travels in a dielectric material, its effective propagation speed and the wavelength will change depending on the dielectric material: �� �� �� , �� √ ��... -
Page 15: Radome Distance
Hardware and physical integration guideline PCR Sensor A111 �� ������ ℎ = = 1.55 ���� Figure 15 shows the amplitude variation of the reflected wave from the radar target when the distance between the sensor and the radome is varied for different radome thicknesses. A thickness of 1.6 mm, which is very close to the thickness of half-a-wavelength, has the minimum impact on the amplitude variation. - Page 16 Hardware and physical integration guideline PCR Sensor A111 The optimum distance is valid if the thickness of the radome is optimum as well. Otherwise, to have a minimum insertion loss on the received signal, the distance to the sensor should follow the marginal criteria below: ��...
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Page 17: Impact On The Radiation Pattern
Hardware and physical integration guideline PCR Sensor A111 4.4 Impact on the radiation pattern The radar loop radiation pattern of the integrated antennas will be affected by the dome that is put on top of the sensor. Figure 16 shows the measured radar loop pattern for three different materials, ABS plastic, gorilla glass and free space. - Page 18 Hardware and physical integration guideline PCR Sensor A111 Figure 17. Impact of the radome-to-sensor distance on the radiation pattern (H-plane). Amplitude is stated in one direction (Tx or Rx side). For Radar Loop Gain (RLG) the values will be doubled.
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Page 19: Multi-Layer Radome Integration
Hardware and physical integration guideline PCR Sensor A111 4.5 Multi-layer radome integration Radomes can also be constructed from a multi-layer dielectric. Particularly, where the thickness of a single layer dielectric is fixed, thus additional layer can be added to the radome which can act as an anti-reflection layer. - Page 20 Hardware and physical integration guideline PCR Sensor A111 Figure 20. Simulation scenario: Sensor, air-gap, the matching layer and the screen. Figure 21. Normalized antenna gain (Tx or Rx antenna gain) where the matching layer dielectric constant is set to 1.1 and 3.
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Page 21: Physical Integration - Lens
Acconeer have designed two type of lens to narrow the beamwidth and improve the radar loop gain. First is the hyperbolic lens and the second is based on the phase correcting plate which is called Fresnel Zone Plate (FZP) lens. -
Page 22: Focal Distance
Hardware and physical integration guideline PCR Sensor A111 Figure 23. 3D-printed examples of the hyperbolic and FZP lenses. The material used for printing is ABS plastic. 5.1 Focal distance Radar measurement was done to characterize the focal point of the lens. The reflected power from a fixed radar target was captured for different sensor-to-lens distance. - Page 23 Hardware and physical integration guideline PCR Sensor A111 Figure 24. Gain variation of the lens versus the distance to the XM112 radome. The amplitude is normalized to Free Space (FS). Gain is stated in one direction (Tx or Rx side). For Radar Loop Gain (RLG) the values will be doubled.
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Page 24: Radiation Pattern
Hardware and physical integration guideline PCR Sensor A111 5.2 Radiation pattern Two focal distances, D = 2 and 8 mm, are chosen for characterizing the radar loop radiation sensor-lens pattern of the lenses. Figure 26 and Figure 27 show the measured radar loop pattern for free-space, HPL and FZP lenses for the selected focal distances. - Page 25 Hardware and physical integration guideline PCR Sensor A111 Figure 27. Radar loop radiation pattern of the sensor in Free Space and with lens. Distance from the lens to the sensor is set to 2 mm. Radius is in dB scale normalized to free space maximum gain. Gain value is stated in one direction (Tx or Rx side).
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Page 26: Fzp Lens Design
Hardware and physical integration guideline PCR Sensor A111 Figure 29. Gain of the FZP and hyperbolic lenses at E-plane for focal distances of 2 mm and 8 mm. Gain is stated in one direction (Tx or Rx side). For Radar Loop Gain (RLG) the values will be doubled. - Page 27 Hardware and physical integration guideline PCR Sensor A111 Figure 30. Detailed geometry of an FZP lens with quarter wavelength phase correction step. �� �� = √ (�� �� + 2���� �� = 1,2,3,4 �� �� �� �� �� = ��( √ ��...
- Page 28 Hardware and physical integration guideline PCR Sensor A111 For further details regarding FZP and hyperbolic lens design, see [2]. Page 28 of 32 © 2022 by Acconeer – All rights reserved 2022-03-08...
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Page 29: Appendix A: Materials
Hardware and physical integration guideline PCR Sensor A111 6 Appendix A: Materials Table 1. Measured dielectric constant and loss tangent of different materials at 60 GHz [3]. Page 29 of 32 © 2022 by Acconeer – All rights reserved 2022-03-08... -
Page 30: References
[4] "Acconeer Expolration Tool," [Online]. Available: https://acconeer-python- exploration.readthedocs.io/en/latest/sensor_introduction.html. [5] "Acconeer A111 datasheet," [Online]. Available: https://developer.acconeer.com/download/a111- datasheet-pdf. [6] "Acconeer PCR sensor A111 EVK hardware userguide," [Online]. Available: https://developer.acconeer.com/download/xc112_xr112-user-guide-pdf. Page 30 of 32 © 2022 by Acconeer – All rights reserved 2022-03-08... -
Page 31: Revision
Hardware and physical integration guideline PCR Sensor A111 8 Revision Date Version Changes 2019-11-13 Original version 2020-07-02 Comments on the gain values 2020-11-25 Added information about conformal coating. Updated pictures of GND planes in chapter 3. 2022-03-07 Updated chapter 3 on PCB routing. -
Page 32: Disclaimer
Hardware and physical integration guideline PCR Sensor A111 Disclaimer The information herein is believed to be correct as of the date issued. Acconeer AB (“Acconeer”) will not be responsible for damages of any nature resulting from the use or reliance upon the information contained herein.