Active beamforming is the mechanism used in WiFi access points and clients where the beamforming is done with different chains on a transmitting radio (usually using active components like transistors). Passive beamforming on the other hand is achieved by using passive components (resistors, capacitors, and inductors) to introduce phase and amplitude variations across different path such that we are able to achieve constructive addition in some cases which results in beamforming.
The main differences between these two mechanisms:
- Butler matrices are a passive beamforming and channel model rendering mechanism.
- Beamforming can be useful against jamming attacks to increase SNR at client.
- Passive beamforming networks are better because active components are more susceptible to change in temperature and other environmental factors.
- Compared to active beamforming networks, passive beamformers can be made electrically stable and reliable across a wide range of operating conditions, although a great deal of flexibility in the physical layout may be needed to accommodate a large variety of connector interfaces for different antenna arrays.
References
* Miscellaneous articles on butler matrices
* Understanding Passive Beamforming Networks http://defenseelectronicsmag.com/military-defense-electronics/understanding-passive-beamforming-networks
