HRS antenna

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 antenna, 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).

An HRS type antenna is basically a rectangular array of conventional dipole antennas strung between supporting towers. In the simplest case, each dipole separated from the next by λ/2 vertically, and the centres of each dipole are spaced 1λ apart horizontally. Again, in the simplest case (for a broadside beam), all dipoles are driven in phase with each other and with equal power. Radiation is concentrated broadside to the curtain.

Behind the array of dipoles, typically about 0.3λ away there will be a 'reflector' consisting of many parallel wires in the same orientation as the dipoles. If this was not present, the curtain would radiate equally forward and backward.

Since 1984 the CCIR have standardised the nomenclature for this family of curtain antennas as follows:

First symbol: Indicates the orientation of the dipoles in the array. Could be the letter "H" for horizontal or the letter "V" for vertical, however no vertical polarisation arrays of this kind have ever been built apparently.

Second symbol (if present): the single letter "R" indicates that there is a simple (passive) reflector on one side of the array. Alternatively the letters "RR" indicates that the array has some kind of "reversible reflector", i.e. can put its beam out at 0° or 180°. Very few of this type have ever been built - RCI Sackville may have 2 HRRS type antennas—perhaps the only ones in North America.

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Wikipedia