In LiDAR systems, the terms monostatic and bistatic describe how the transmitter (Tx) and receiver (Rx) apertures are arranged. This architectural choice has a significant impact on system complexity, backscatter management, isolation requirements, and overall performance.
Monostatic LiDAR Configuration
In a monostatic LiDAR, the same optical aperture is used for both transmitting and receiving laser signals. A beamsplitter or circulator is typically employed to separate outgoing and incoming light within the shared optical path.
Key Characteristics
- Compact and space-efficient design
- Simplified mechanical alignment due to a single aperture
- Widely used in automotive, airborne, and compact LiDAR systems
Isolation Challenges
Because the transmitter and receiver share the same optics, optical isolation is critical. Without sufficient isolation, backscatter from the transmitted pulse—originating from internal optics, telescope surfaces, or nearby aerosols—can saturate or blind the receiver.
To mitigate this, monostatic systems rely on:
- Polarization-based isolation
- Temporal gating in pulsed systems
- High-quality anti-reflection coatings and wedged optics
Despite these challenges, monostatic LiDAR remains popular due to its simplicity, reduced size, and lower system cost.
Bistatic LiDAR Configuration
A bistatic LiDAR uses separate apertures for transmission and reception. By physically isolating the transmit and receive paths, internal optical backscatter is largely eliminated.
Key Characteristics
- Minimal transmitter-to-receiver optical coupling
- Improved immunity to internal backscatter
- Greater flexibility in optical design
In bistatic systems, the primary remaining backscatter typically originates from aerosols or particles near the LiDAR, rather than from the internal optics.
Design Flexibility
The transmit and receive apertures:
- Do not need to be the same size
- Do not need to be co-located
- Can be optimized independently for illumination and collection efficiency
This flexibility is particularly valuable in applications such as flash LiDAR, where:
- A small transmit aperture helps maintain phase coherence across the illuminated scene
- A larger receive aperture maximizes photon collection and signal-to-noise ratio
Advanced Architectures: MIMO LiDAR
Bistatic principles are also fundamental to multiple-input, multiple-output (MIMO) LiDAR systems, which employ multiple transmitters and receivers to improve angular resolution, coverage, and redundancy. In such systems, independent Tx/Rx paths simplify scaling and enable advanced signal processing techniques.
Monostatic vs Bistatic: Design Trade-Offs
| Aspect | Monostatic LiDAR | Bistatic LiDAR |
|---|---|---|
| Aperture Count | Single | Separate Tx/Rx |
| System Size | Compact | Larger footprint |
| Isolation Requirement | High | Low |
| Backscatter Sensitivity | Higher | Lower |
| Design Flexibility | Limited | High |
Summary
Monostatic LiDAR systems are favored for their compactness and simplicity, but they require careful isolation to manage internal backscatter. Bistatic LiDAR systems, while more complex in terms of alignment and packaging, offer superior isolation and design flexibility, making them well suited for flash LiDAR, MIMO architectures, and high-performance sensing applications.
Choosing between monostatic and bistatic configurations ultimately depends on system constraints, performance requirements, and application-specific priorities.