Antenna phasing is used for ham radio beamforming and shortwave listening, especially on the lower bands where conventional beams are not feasible.
Most hams use Yagi antennas for beamforming across higher frequencies. Yagis are different than phased arrays. In a Yagi, only one element is driven. The rest of the elements are parasites that re-radiate the driven signal at different phases. In a true phased array, all the elements are driven directly at different phases.
At lower frequencies, a Yagi is not feasible because of size and height requirements. Hams use beamforming instead. A typical solution is the Four Square Array, shown above. With these, the operator installs four monopoles with λ/4 wavelength height and spacing. Each monopole is connected to variable length transmission line that introduces patterns depending on selection. Alternatively, a common RF matching network is used that provides -90° and +90° delays and relays are used to configure each element.
With the Four Square, the operator can select switched beamforming in four or eight directions.
Ham Radio Beamforming – Great for Listening, Too
Avid medium wave DXers always get excited about “phasing”. They will use directional loops and phasing devices to beamform in different directions. Spatial filtering creates very tight directional patterns. With these, medium wave listeners can tune in several different stations on the same frequency as long as they of not co-located.
Here is a great example of trans-Atlantic medium wave DX achieved by making a nearby AM station simply disappear. You can use beamforming with entirely different kinds of antenna elements, as demonstrated in this video.
Many shortwave listeners and hams are using beamforming with small active antennas. For example, the DX Engineering Receive Four Square works really well for directional listening across a wide range of frequencies.
Even if you cannot get a perfect design, some basic phasing of two or more antennas will produce useful directional effects. This is a technique we have already proven with “noise cancellers”. Now we have the opportunity to take Spatial Interference Filtering Techniques to the next level.