RFActive vs. Passive Phased Array Antennas
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An array antenna is a structure comprised of a collection of radiating elements, each fed with a specific amplitude and phase. The electromagnetic (EM) fields from these individual elements combine to form a radiation pattern at a specific distance, typically in the far-field region.
In a phased array antenna, the main radiation beam can be electronically steered in any desired direction by varying the excitation phases of the individual EM waves fed to the radiating elements. Phased arrays can be classified into active and passive arrays based on the components used and their functionality. Understanding the difference between these types is essential for selecting the right one for specific applications in areas like aerospace, defense, and telecommunications.
Active Phased Array Antenna
Active phased array antennas utilize individual transmit/receive modules (TRMs) for each antenna element. These modules contain active components such as amplifiers, phase shifters, and digital control systems, allowing them to independently control the amplitude and phase of each antenna element. This makes active phased arrays highly versatile, enabling real-time electronic beam steering without mechanical movement.
Figure 1 illustrates an active phased array antenna:
Key features of active phased arrays include:
- Independent Control: Each antenna element has its own TRM, providing precise control.
- Beam Steering: The beam direction can be adjusted electronically.
- Power Amplification: Each element has its own amplifier, resulting in efficient power distribution across the array.
- Multi-Beam Capability: Active arrays can form multiple beams simultaneously, which is beneficial for radar and communication applications.
- Improved Reliability: Failure of individual elements doesn’t significantly affect overall performance due to the distributed nature of power and control.
Applications: Active phased arrays are widely used in advanced radar systems, military communication systems, electronic warfare, and satellite communication due to their high performance and flexibility.
The advantages of active phased array antennas are:
- Highest performance
- Effective radar resource management
- Low distribution loss
- Highest cost
Passive Phased Array Antenna
In a passive phased array antenna, the antenna elements are connected to a single (or a few) RF source(s) through a network of passive phase shifters and power dividers/combiners. The amplitude and phase of each element are adjusted using these passive components, without any active electronic devices in the antenna elements themselves.
Figure 2 depicts a passive phased array antenna:
Key features of passive phased arrays include:
- Simplified Design: Lacks individual TRMs, relying on centralized control.
- Limited Beam Control: Beam steering is achieved through phase shifters, but the flexibility is lower compared to active arrays.
- Centralized Power Amplification: Uses a common power amplifier for the entire array, making it less efficient in power distribution.
- Single Beam: Generally supports a single beam due to its limited phase-shifting capability.
- Lower Cost: Fewer components lead to reduced costs and lower power consumption.
Applications: Passive phased arrays are typically used in simpler radar systems, broadcast applications, and some communication systems where cost, size, and power efficiency are primary concerns.
The advantages of passive phased array antennas are:
- Beam agility
- Effective radar resource management
- High distribution loss
- Higher cost
Difference Between Active and Passive Phased Array Antennas
| Parameter | Active Phased Array Antenna | Passive Phased Array Antenna |
|---|---|---|
| Architecture | Contains individual TRMs for each element. | Elements are connected to a centralized RF source. |
| Beam Steering | Achieved electronically with high precision. | Achieved through phase shifters, with limited flexibility. |
| Power Amplification | Individual power amplifiers for each element. | Centralized power amplifier for the entire array. |
| Multi-Beam Capability | Supports multiple beams simultaneously. | Generally supports a single beam. |
| Cost and Complexity | Higher cost and complexity due to active components. | Lower cost and complexity, as it uses passive components. |
| Power Efficiency | Higher power efficiency due to distributed amplification. | Lower power efficiency due to centralized amplification. |
| Reliability | High reliability; failure of elements has minimal impact. | Lower reliability; failure of central components affects the system. |
| Applications | Advanced radar, military communication, satellite systems. | Basic radar, broadcast, and simple communication systems. |
Conclusion
Active and passive phased array systems serve distinct purposes depending on the application requirements. While active phased arrays offer greater flexibility, higher power output, and independent control of each element, they are more complex and expensive. Passive phased arrays, on the other hand, provide a cost-effective solution with shared power sources, but are limited in terms of performance and control. The choice between active and passive phased arrays should be made considering factors like cost, complexity, and operational efficiency.
