Nomenclature
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.
Third symbol (if present): "S" indicates that the array is steerable (see below).
Following the letters come three numbers "x/y/z" where 'x' (an integer) is the number of dipoles counting horizontally. 'y' (an integer) is the number of dipoles counting vertically and 'z' (a decimal fraction) is the height above ground (in wavelengths) of the lowest row of dipoles in the array.
So, a "HRS 4/5/0.5" antenna curtain is 4 dipoles wide, and 5 dipoles high with the lowest row being 0.5 wavelengths off the ground and with a standard reflector. An HRS 4/4/0.5 is one of the standard types of array seen at shortwave broadcast stations worldwide.
Read more about this topic: HRS Antenna