Active Vs passive phased array antenna types

The structure composed of collection of radiation elements which are fed with specific amplitude and phase is known as array antenna. The Electromagnetic (EM) fields from these individual radiation elements are combined to form radiation pattern at a specific distance from them. It forms radiation pattern in far field region. In Phased array antenna, main radiation beam can be altered electrically in any desired direction by varying excitation phases of individual EM waves fed to the radiation elements.

Phased arrays can be classified into active and passive arrays based on the nature of the components and their functionality. Understanding the difference between active and passive phased arrays is essential for choosing the right type for specific applications in areas such as aerospace, defense and telecommunications. Refer phased array basics and types >> for more information.

Active Phased Array antenna

Active phased array antennas use individual transmit/receive modules (TRMs) for each antenna element. These modules contain active components such as amplifiers, phase shifters, and digital control systems, enabling them to individually control the amplitude and phase of each antenna element. As a result, active phased arrays are highly versatile and can steer beams electronically in real time, without mechanical movement. The figure-1 depicts active phased array antenna.

The key features of active phased array are as follows.
➨Independent Control: Each antenna element has its own TRM, allowing for precise control.
➨Beam Steering: The direction of the beam can be adjusted electronically.
➨Power Amplification: Since each element has its own amplifier, power can be distributed efficiently across the array.
➨Multi-Beam Capability: Active arrays can form multiple beams simultaneously, which is advantageous 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 as follows.
1. Highest performance
2. Effective radar resource management
3. Low distribution loss
4. Highest cost

Passive Phased Array antenna

In a passive phased array antenna, the antenna elements are connected to a single or a few RF sources 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. The figure-2 depicts passive phased array antenna.

The key features of passive phased array are as follows.
➨Simplified Design: Lacks individual TRMs, relying on centralized control.
➨Limited Beam Control: Beam steering is achieved through phase shifters, but 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 as follows.
1. Beam agility
2. Effective radar resource management
3. High distribution loss
4. Higher cost

Difference between active and passive phased array antennas

Conclusion

Active and passive phased array systems serve distinct purposes depending on 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.

Antenna related links

Antenna Calculators

What is Difference between

RF and Wireless Terminologies