Active vs. Passive Beamforming: Differences and Comparisons

This article compares active and passive beamforming, outlining their differences, advantages, and disadvantages.

Introduction:

Beamforming is a technique used for directional signal transmission and reception using electrically steered antennas. Unlike mechanically steered dish antennas, these antennas can electronically change both the amplitude and phase of individual beams. Antenna arrays with provisions for amplitude/phase variation are used in beamforming for both transmission and reception. Beamforming is mainly categorized as analog and digital.

• Analog Beamforming: Amplitude and phase variation are applied to the analog signal before transmission.
• Digital Beamforming: Amplitude and phase variation are applied to the digital signal before DAC (Digital-to-Analog Conversion) at the transmitter side.

Beamforming can also be classified as active or passive, based on the placement of RF power amplifiers, RF LNAs (Low Noise Amplifiers), and radio transceivers.

Active Beamforming

Active beamforming refers to an architecture where RF amplifiers are integrated as internal elements within the antenna array.

Figure 1: Active Beamforming Architecture

Active beamforming can be further categorized into the following types:

• Active Analog Beamforming: Employs a single RF chain connecting the antenna element with amplifiers, phase shifters, and splitters/combiners.
• Active Digital Beamforming: Uses a dedicated RF-to-digital path from each antenna element, instead of the common RF chain used in analog beamforming. RF-to-baseband conversion is achieved using RF mixers, ADCs, and DACs. Phases and amplitudes are controlled digitally.
• Active Hybrid Beamforming: Combines both analog and digital beamforming architectures.

Passive Beamforming

Passive beamforming refers to an architecture where amplifiers or radios are used as external elements of an antenna array.

Figure 2: Passive Beamforming IC (ADAR1000 from Analog Devices Inc.)

The ADAR1000, for example, is a four-channel X/Ku-band Beamformer IC that functions as a vector modulator, using on-chip DACs for LNA and PA (Power Amplifier) bias. It operates from 8 GHz to 16 GHz and can interface with four external radio transceivers. The design allows for individual adjustment of amplitude and phase for all four channels. One ADAR1000 can interface with a maximum of four ADTR1107 front-end ICs, which consist of a PA, LNA, and SPDT switch.

Advantages of Passive Beamforming:

• Low DC Power Consumption: Consumes less DC power compared to active beamforming, as electronic amplifiers are not used.
• Simple Architecture: The antenna array architecture is simple and straightforward.

Disadvantages of Passive Beamforming:

• Larger Antenna Panel Size: The antenna panel is larger due to intrinsic losses of LC elements and PCB materials.
• Slower Beam Switching: Provides slower beam switching due to the higher time response of LC molecules. This can lead to temporary interruption of the user terminal-to-satellite radio link during handover processes.
• Temperature Sensitivity: Molecular response time depends on operating temperature. Therefore, this beamforming array may require an extra heater to maintain operating temperature and system performance under extreme environmental conditions.

Difference Between Active and Passive Beamforming

The following table highlights the key differences between active and passive beamforming:

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