History
The HRS antenna type is said to have originated with RCA as an
experimental telecommunications antenna in the late 1920s. Its design
was almost immediately adopted by international broadcasters by the
mid-1930s, with rotateble versions of the antenna being pioneered
by
Radio Netherlands at its Huizen transmission site.
The curtain antenna is a dipole array,
consisting of
rows
and columns of dipoles
The fundamental structure of HRS antennas works like this
- The HR(S) notation is as follows: HR Rows / Columns
/ Wavelength(s) Above Ground
- A HR 4 / 4 / 1
means: 4 rows, 4 columns and 1 wavelength above ground.
- HRS : all the S means is that the antenna's pattern is
electrically
steerable (slewable), typically by ±15°.
- The number of rows can be 1, 2, 3, 4 or 6. [ - - ] to [ - - - -]
with multiples up to 12.
- The number of columns is usually 2, 3 or 4. [ | | ] to [ | | | |
| | ], with multiples up to 8.
- The curtain antenna is a high gain directional antenna, designed
for medium and long range communications.
- The dipoles are horizontally polarized (ALWAYS).
- A reflector screen is placed behind the dipole array to provide a
directive beam.
Curtain antennas are generally
available in two
sizes
HRS curtain array antenna variations
- A low band array typically covers the 6, 7, 9 and 11 MHz bands.
[larger, taller]
- A high band array typically covers the 11, 13, 15, 17 and 21 MHz
bands (or 13-26 MHz bands). [smaller, shorter]
- Occasionally an international broadcasters may use, for reasons
of geopolitical necessity -- a highband, midband as well as lowband HRS
curtain arrays.
- Using 3 HR curtain arrays to cover the HF broadcasting spectrum
creates a highly optimized HF transmission system.
- HF transmission systems using 3 curtain arrays can be costly to
build and maintain. Since the
1990s no new HF transmission systems like this have been built.
Existing systems will likely remain in use, with several rebuilds --
for
at least another 50 years.
- High priority target areas (Western Europe, Eastern Europe &
USA) -- were targeted by these optimized transmission systems when
duplexing and triplexing were not necessary for real estate reasons.
The number of dipole columns defines
the azimuth
beamwidth
The mathematical relationship between columns and directivity
- For a 2-wide dipole array, the beamwidth is around 50°
- For a 3-wide dipole array, the beamwidth is around 40°
- For a 4-wide dipole array, the beamwidth is around 30°
The main beam can be slewed by 15° or 30° so that a maximum
coverage
of 90° can be achieved.
The number of dipole rows and the height of the lowest element above
ground
determine the elevation angle and consequently the distance of the
service
area.
- A 2-row high array has a typical takeoff angle of 20° and is
used for medium range communications.
- A 4-row high array has a typical takeoff angle of 10° and is
used for long range communications.
- A 6-row array is similar to a 4-row, but can achieve 5° to
10° takeoff angles.
