Difference between Active radar vs Passive radar
Active radar and passive radar are two distinct types of radar systems used in various fields, such as aviation, military, and communication systems. While active radar transmits its own electromagnetic signals to detect and track objects, passive radar relies on external sources like TV or radio signals to locate targets without emitting any signals. This page explores the unique working principles, advantages, disadvantages and applications of each radar system to help you better understand difference between active and passive radar systems.
Active Radar
Definition: Active radar systems emit their own electromagnetic waves, typically radio waves or microwaves, from a transmitter. The system then listens for reflections (echoes) of these waves from objects (targets). By analyzing the returned signals, active radar can determine the distance, speed, and direction of the target.
Figure-1 depicts active radar working operation.
Following are the features of active radar.
• It emits radio frequency pulse towards target and receives
reflected pulse from the target.
• In this radar system, transmitter and receiver are located at the same place. Hence it is known as
monostatic radar.
• Range of target (i.e. D) = c*t/2
Where, c = 3 x 108 meters/second
t = time delay between signal emission and reception from the target i.e. total time.
Example:
• AESA Radar (Active Electronically Scanned Array Radar)
Advantages of active radar
Following are the benefits of active radar.
1. Can detect objects at long distances.
2. Provides detailed information on target range, speed and angle.
3. Less affected by environmental factors such as ambient light or temperature.
Disadvantages of active radar
Following are the drawbacks of active radar.
1. Can be detected by enemy radar warning receivers.
2. Requires more power consumption compared to passive radar.
3. Susceptible to electronic counter measures (i.e. jamming).
Active Radar applications
• Military surveillance and target tracking
• Air traffic control
• Weather monitoring (e.g., detecting precipitation)
• Maritime navigation
Passive Radar
Definition: Passive radar systems do not emit their own signals. Instead, they rely on existing sources of electromagnetic energy (e.g., commercial broadcasts, cell towers, TV stations). The system uses the difference in signal arrival times between a direct path (transmitter to receiver) and a reflected path (transmitter to target to receiver) to detect and track targets.
Figure-2 depicts passive radar working operation.
Following are the features of passive radar.
• It also emits radio frequency pulse from transmitter and
receives pulse reflected from the target at the receiver.
• In this radar system,
transmitter and receiver are located at the different places.
Hence it is known as bistatic radar.
• In this passive radar system, range or distance is calculated based on time
delay between t1 and t2 where t1 is time from transmitter to receiver directly and
t2 is time from reflected signal to reach receiver.
• The system uses time difference of arrival (TDOA) and frequency difference of arrival (FDOA)
to analyze target properties.
Example:
PESA radar (Passive Electronically Scanned Array Radar)
Advantages of passive radar
Following are the benefits of passive radar.
1. Difficult to detect due to the absence of signal transmission.
2. Lower power consumption.
3. Can be deployed in regions where active transmission is restricted.
Disadvantages of passive radar
Following are the drawbacks of passive radar.
1. Dependent on availability of external electromagnetic sources.
2. Limited range compared to active radar.
3. Less accurate in range and speed measurements.
Passive Radar applications
• Covert surveillance and reconnaissance (low probability of detection)
• Monitoring air traffic without interference
• Border security and air defense
• Anti-stealth aircraft detection
Difference between active and passive radar
Following table compares active vs passive radar with respect to various features.
| Parameter | Active Radar | Passive Radar |
|---|---|---|
| Signal Transmission | Emits its own electromagnetic waves | Does not emit any signals, uses external sources |
| Detectability | Can be detected by other systems | Low probability of detection (stealthy) |
| Power Consumption | Higher (requires power for signal transmission) | Lower (no power needed for transmission) |
| Range and Accuracy | Typically has a longer range and higher accuracy | Shorter range and lower accuracy |
| Operational Mode | Active mode (transmits and receives) | Passive mode (receives only) |
| Susceptibility to ECM | More susceptible to jamming and interference | Less susceptible due to lack of transmission |
| Dependence on External Sources | Independent, can operate standalone | Dependent on external transmitters like TV or radio |
| Cost | More expensive | Less expensive |
| Complexity | More complex | simple architecture |
| Applications | Air traffic control, military tracking, weather radar | Covert surveillance, air traffic monitoring |
Conclusion
In summary, both active radar and passive radar serve different purposes based on specific operational needs. Active radar is known for its long-range detection and high accuracy, making it ideal for air traffic control, military surveillance, and weather monitoring. Conversely, passive radar is more suited for covert operations and low-detection scenarios due to its use of external signals. By analyzing their characteristics in terms of signal transmission, power consumption, and detectability, you can determine the most suitable radar system for your application.
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