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An Integrated Active Circulator for Radar Transceivers with Shared Tx/Rx Antenna

Masoumizadeh, Masoud | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56823 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Fotowat Ahmadi, Ali; Akbar, Fatemeh
  7. Abstract:
  8. The issue of automation has always been a concern for humans over the years. Replacing humans with machines or intelligent software to perform various tasks can significantly improve the accuracy and speed of those activities. One of the long-standing aspirations of humanity has been the automation of driving. In addition to freeing individuals from the time-consuming task of driving, automating vehicles can also dramatically reduce road accidents. To achieve this goal, vehicles need to be equipped with various sensors such as radar, cameras, lidar, and more. Each of these sensors has its advantages and disadvantages, and as a result, all of them must be used for safe driving. In this thesis, with a focus on the automotive radar sensor operating in the 77 GHz frequency band and utilizing Frequency Modulated Continuous Wave (FMCW) modulation, a new architecture for the receiver section has been introduced. Because of the increasing operating frequency for vehicle radar sensors, it is now possible to design all transmitter and receiver circuits, along with their antennas, in an integrated manner within a small area. To further minimize the form factor, the transmitter and receiver antennas can be shared. In such a case, blocks such as a circulator or directional coupler will be required to separate the transmission and reception paths. However, the fundamental challenge of self-interference signals in these systems is evident due to the simultaneous nature of transmission and reception in FMCW radars, and the similarity in frequency bands for these two paths. This challenge can potentially saturate and deviate the receiver section from its linear region. This thesis introduces a circuit for attenuating leakage signals using the property of circularly polarized wave propagation and creating a difference between the transmitted and received signals. In the proposed method, the transmitted and received signals behave as common mode and differential voltages, respectively. Exploiting this property and using low-noise and high common-mode rejection ratio (High-CMRR) differential amplifiers, isolation of up to approximately 75dB is achieved between the transmitter and receiver antennas in the frequency band of 77-81GHz. The proposed circuit is designed and simulated in the 65-nm CMOS process. All passive elements have been added to the circuit design after electromagnetic simulation and extraction of scattering parameters. The single-band (SSB) noise figure of the entire receiver chain and its conversion gain are obtained as 16dB and 18dB, respectively. The transmitted power can be increased up to 5.7dBm without saturating the receiver section. The S11 is also less than -15dB, and the overall power consumption of the receiver section is near to 35 mA. To eliminate the effects of insufficient antenna matching, a negative feedback loop has been employed to adjust the impedance of transmission lines, and system simulations have been investigated. In the presence of this loop, the level of isolation can be improved by up to approximately 14dB. A patch antenna required to achieve a beamwidth of less than ±20 in the desired frequency band has also been designed, and its performance has been reported. Finally, using the AWR1843 radar board, raw data were collected for radar processing, and parameters such as distance, speed, and angle of targets were extracted. By comparing various angle analysis methods, the best angular resolution was achieved with the Multiple Signal Classification (MUSIC) method using a Virtual Antenna Array (VAA). Furthermore, deep learning-based methods were introduced to fuse radar and camera data to enhance the reliability of autonomous vehicles. In addition to that, a method for mapping radar point clouds onto the camera sensor output and correcting the speed and distance of targets was proposed. The implementation of these algorithms on the nuScenes dataset showed an average improvement of 1.5% in mAP compared to the case where only a camera sensor is present
  9. Keywords:
  10. Frequency Modulated Continuous Wave (FMCW) ; Sensor Fusion ; Automotive Radar ; Simultaneous Transmit and Receive (STAR) ; Integrated Active Circulator ; Arrival Estimation Angle ; Self Interference Cancellation

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