The HRS type antenna is an example of a curtain array antenna. It has Horizontal dipoles with a Reflector behind them, and the beam is Steerable. These antennas are also known as "HRRS" (for a Reversible Reflector), but the extra R is seldom used.
Curtain arrays were developed during the 1920s and 1930s when there was a lot of experimentation with long distance shortwave broadcasting. The underlying concept is to achieve gain over the simple dipole, possibly by folding one or more dipoles into a smaller physical space, or to arrange multiple dipoles such that their radiation patterns reinforce each other, thus concentrating more signal into a given target area.
The first curtain array to achieve popularity was the Sterba curtain, patented by Ernest J. Sterba in 1929 and this was used by Bell Labs and others during the 1930s and 1940s. The Sterba curtain is however a narrowband design and is only steerable by mechanical means. However, as far back as the mid-1930s, Radio Netherlands was using a rotatable HRS antenna for global coverage. Since the 1950s the HRS design has become more or less the standard for long distance high power shortwave broadcasting (> 1000 km).
Read more about HRS Antenna: Topology, Nomenclature, Steering, Notes On HRS Nomenclature, Azimuth Beamwidth, Vertical Launch Angle, Transmission System Optimization For Geopolitics, Cost Issues, Examples of HRS Antennas
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