Radar Front-End Architecture

The radar front-end is responsible for generating, transmitting, and receiving RF signals. It forms the first stage of the radar processing chain and largely determines the system’s performance: sensitivity, resolution, SNR, and robustness to interference.

Overview

This architecture describes an FMCW radar front-end commonly used in automotive and industrial systems.
Its main goals are:

• generate a stable and linear chirp
• transmit the signal through dedicated antennas
• receive echoes reflected by objects
• perform downconversion and analog filtering
• provide I/Q signals to the digital backend

Key constraints:

• high RF bandwidth (typically 76–81 GHz)
• low phase noise
• chirp linearity
• TX/RX isolation
• precise synchronization across channels

System Diagram

[Insert a block diagram here: PLL → Chirp Generator → PA → TX Antenna → RX Antenna → LNA → Mixer → LPF → ADC]

The diagram shows the signal path from RF generation to analog-to-digital conversion.
TX/RX separation can be achieved using separate antennas or a coupler/duplexer.

Key Components

Chirp Generator / PLL
Generates the FMCW signal with the required linearity. Chirp quality directly affects range resolution.

Power Amplifier (PA)
Amplifies the transmitted signal while maintaining linearity and stability.

TX Antenna Array
Defines the radiation pattern and contributes to angular resolution.

RX Antenna Array
Receives reflected echoes. The array geometry determines beamforming capability.

Low Noise Amplifier (LNA)
Amplifies the received signal while adding minimal noise.

Mixer / Downconverter
Converts the RF signal to baseband (I/Q).

Low-Pass Filter (LPF)
Removes unwanted components and limits the signal bandwidth.

ADC
Digitizes the I/Q signals for backend processing.

Data Flow / Control Flow

The FMCW signal generated by the PLL is amplified and transmitted through the TX antenna.
Reflected echoes are received by the RX antenna, amplified by the LNA, and mixed with the local oscillator to produce the beat frequency.
The resulting signal contains information about:

• distance (beat frequency)
• velocity (Doppler shift)
• angle (phase differences across RX channels)

Chirp control, frame sequencing, and channel synchronization are managed by a digital controller or integrated microcontroller.

Design Decisions

• FMCW vs Pulse Radar
  FMCW offers better integration and lower analog complexity for automotive applications.
• Separate TX/RX antennas
  Provides better isolation than a duplexer, at the cost of additional area.
• Number of RX channels
  Determines angular resolution and beamforming capability.
• Chirp linearity
  Critical for clean FFT range profiles.
• LO distribution
  Channel coherence is essential for MIMO processing.

Notes

• PLL thermal stability directly affects range profile quality.
• RF layout must minimize unwanted coupling between TX and RX paths.
• LPF characteristics define usable bandwidth and overall noise performance.
• The ADC must provide sufficient ENOB to preserve dynamic range.