Amazingly, you will find spatial filtering or beamforming everywhere. It’s used for wireless phones and networks, meeting rooms and even ultrasound.
Directional antennas are usually quite large. In fact, with normal antennas, the larger the aperture, the narrower the directional beam. Beamforming involves combining signals from a number of smaller, non-directional antennas to create a virtual single antenna with high directivity.
Other than AM broadcasting, the original “killer apps” for beamforming are radar and sonar.
In the early days, radar used large fixed or mechanically rotatable antennas. Not the easiest things to use, especially for tracking satellites and ballistic missiles. A new initiative in the 1950’s led to the use of rapid electronic phasing of the individual array antenna elements to steer the radar beam with the flexibility and speed of electronics rather than with much slower and less flexible mechanical steering. (Read the full story here.) So the new radars are essentially flat panels with hundreds of small dipoles that can be steered electronically as a phased array, as shown above, lower left.
At the same time, audio beamforming everywhere emerged, particularly for sonar. Even back in World War I, the French used directional microphone arrays to track approaching aircraft. But the real winner for audio spatial filtering was sonar, where digital steering was developed in the 1960’s.
Another popular use for acoustic beamforming is ultrasound imaging. As this video shows, ultrasonic imaging uses phased arrays of transducers.
Beamforming Everywhere – Including Your Home and Neighborhood
Spatial filtering is used in WiFi, cellular phones and meeting rooms.
If you have a wireless router with two or more antennas, odds are that it uses beamforming. Routers will try to figure out the direction of your device and adjust its antenna pattern accordingly. With the new 802.11ac specification, routers and devices measure and exchange their relative positions. MIMO or multiple input and output antennas allow beamforming to several devices at once.
Similarly, the cell tower in your neighborhood uses an antenna array to shape its beam towards your phone as it moves around. Beamforming of WiFi and mobile phones creates enough increased gain to enable faster speeds and better signal-to-noise ration. Here are some great demonstrations of beamforming in wireless communications and local WiFi devices.
If your meeting room at the office has one of those popular Polycomm phones, you have audio beamforming to track folks speaking on the conference call. Your neighborhood may also be covered by ShotSpotter, which uses acoustic spatial filtering to quickly identify the location of a gunshot.