- The document describes several large radio telescopes around the world, including their key design features and specifications. - Some of the telescopes discussed are the Big Ear radio telescope in Ohio with a curved reflector of 110x21m and flat reflector of 104x31m, the Five College Radio Astronomy Observatory with a 14m dish enclosed in a geodesic dome, and the Very Large Array in New Mexico consisting of 27 steerable 25m dishes. - The document also mentions the demolition of Big Ear in 1998 and a funding dispute around rebuilding the collapsed 91m Green Bank telescope.

1. UNIVERSIDAD MANUELA BELTRAN
ANTENAS Y PROPAGACION
(NOCTURNO)
MIGUEL PINEDA 79878418
(2006-2) 57

2. (P 696)
Island, Japan. It has 200 μm rms overall equivalent
surface deviation and a pointing accuracy of 2 arc
seconds. (Akabane-1). Maximum gain is almost 90 dBi
at 2- to 3-mm wavelengths. See the gain curve in Fig.
19-9. Thermal effects are minimized by covering the dish
structure with insulated panels and circulating air inside
he enclosure. Each of the. 600 rigid panels of the dish
has a surface accuracy of 60 m rms.
Ohio. The fixed-standing-curved reflector with tiltable -
flat reflector, dubbed “Big Ear”, of the Ohio State
University Radio Observatory is shown in Fig. 20-6. The
curved-standing reflector is a rectangular section of a
sphere with dimensions;; of 110 by 21 m. The tiltable
flat reflector dimensions are 104 by 31 m (Fig. 20-7).
Both reflectors are joined by a flat aluminum ground
plane (Kraus-1, 6).

3. (P696)
The basic design consideration of the antenna was that
of obtaining the maximum aperture per unit of cost. It
also had other advantages such as less than o ½ of 1
percent effective aperture blocking, reduced
susceptibility to terrestrial interference because of he
low profile of the feed (right at ground level) and
shielding by the large reflectors, and a spacious
underground receiver laboratory directly below the prime
focus where weigh restrictions were not a consideration.
Tilting the Hat reflector allows observations between
declinations of -36 and +46 (a range of 100°) whish
gave a coverage of 90 percent of the sky observable
from the site. Movement of the feed car permitted beam
steering of 15° in azimuth (or tracking of sources for an
hour or more in right ascension. The telescope (see Fig.
20-8a) has a very long focal length with F/D =1.17 in
azimuth (right ascensions) und F/D = 6.0in

4. (P696)

5. (P 697)

6. (P698)

7. elevation (declination) so that it was possible to
deploy many feed systems efficiently in the focal
region for .simultaneous operation. It is noteworthy
that because of long local length curved reflector
can be described as either a parabola or a sphere
since both are almost identical except at the
extreme E-W edges where they differ by only a few
millimeter. The antenna was operated routinely at
frequencies as low as 20 MHz, (15 m) and as high
as 3 GHz (10 cm). Incoming waves deflected off
the flat reflector into the parabola bringing them to
a focus at ground level near the base of the flat
reflector. Moving the flat reflector though 50° tilted
the antenna beam thought a 100º range in
elevation (or declination).
(P698)

8. Another important application off Big Ear was as the world's
largest compact range as M shown in Fig. 20-8b
In 1998, Big ear was demolished for a golf course.
Gorkí. Alberl Kislyakov has constructed a standing-
parabola tiltable -flat- reflector an-antenna near Gorki,
USSR, for operation al millimeter wavelengths, Although
the basic principle is the same as for Big liar, Kislyakov
has added a unique feature of self-calibration by
providing that the flat reflector can be set
vertically(Kislyakov-1). With flat reflector vertical and
with feed displaced literarily off-axis (and transmitting,
radiation is brought to a focus on the opposite side of the
axis where the signal can be received as suggested by
(P698)

9. • Fig. 20-9. By moving the receiving horn
sideways or up and down, the far-field pattern of
the antenna can be measured with an arbitrarily
high S/N ratio.
• With the same configuration (flat reflector
vertical), panels of the reflectors can be adjusted
lo maximize the gain, For example, with panels
1, 2, 3. 5, 6 and 7 covered with absorbing
material, only panels 4,4', 8 and 8' are
operational, and, with 4 and 4' as reference,
panels and S' can be adjusted for maximum
signal or gain. The same procedure is then
repeated with other pairs of panels until all
panels are adjusted.
(P699)

10. • Five College Observatory. The 14-m dish of
the Five College Radio Astronomy Observatory
is an example of a millimeter -wave antenna
enclosed in a Buckminster Fuller Triangular -
panel geodesic radome. Front and back views of
the dish are shown in Fig. 20-10. The reflector is
constructed of 72 panels contoured to a section
of a paraboloid with a 65μm rms surface
accuracy, or λ/20 at 1.3 mm. To set the panels
accurately a holographic technique was used in
which the amplitude and phase of a 38 GHz
satellite beacon signal was measured over an
angular extend much larger than the main beam
of the antenna. The amplitude and phase of the
antenna aperture field distribution was then
(P699)

11. (P 700)

12. obtained by a 2-dimensional Fourier transform.1 This
indicated a 90 μm rms residual panel position error with
the antenna at a 45° elevation angle. At 38 GHz (λ= 7.9
mm) the gain-loss factor from (19-2-3) is
0.09 mm
kg = cos ² 720 = 0.98
7.9 mm
or only 0.09 dB loss from surface error.
At 230 GHz (λ=1.3 mm) the loss is larger and irregular
lens behavior of the radome fabric becomes significant.
(P 701)

13. (P701)

14. • Nancay. A dual reflector antenna, shown in Fig. 20-11,
is located at Nancay, France. On completion in 1965, it
was dedicated by French President Charles DeGaulle.
The basic principle is the same as for the Ohio
telescope except that it operates without a ground
plane. It is 4 times larger than the Ohio telescope having
a 200 by 40 m tiltable flat reflector and a 300 by 35 m
standing curved reflector. A movable feed system
permits tracking sources for 2 hours or more. It was
upgraded in 2000 to work at shorter wavelengths.
RATAN-600. This radio telescope located near
Zelenchukbkaya, Russia, is shown in Fig. 20-12. it has
both tiliablc curved and flat reflectors. The curved
reflector is 600m in diameter and is constructed of
895 movable aluminum panels. Feed
(P 701-702)

15. • systems are situated near the center of the circle.
Operation can be as a flat reflector spherical -reflector
combination as in the Ohio and Nancay telescopes and
also in other modes where panels of the circular reflector
are used to bring the waves directly to a focus. Although
it does not have a filled aperture, the RATAN-600 has
the longest continuous aperture of any radio telescope.

16. • Parkes. This 64-m-diameter completely steerable alt-
azimuth mounted dish is situated at Parkes. New South
Wales. Australia, it is shown in Fig. 20-13. It has been
used for surveys of the southern skies and other radio
astronomy observations.
Manchester. The 76-m-diamcler alt-azimuth mounted
parabolic dish antenna shown in fig. 20-14 was the
world's first large fully steerable antenna, rotating azimuth
on circular track. It was completed in 1957 and is now
called "The Lovell Telescope" after Sir Bernard Lovell of
the University of Manchester Jodrell Bank Radio
Observatory. As of 2000 the "British Government Joint
infrastructure Fund" has provided £2 million for an
extensive upgrade that will permit observations al shorter
wavelengths.
(P 702)

17. VLA. This Very Large Aperture array of 27 steerable
reflector antennas each 25m in diameter, shown in part
in Fig. 15-14, is situated on the Plans of San Augustin,
New Mexico Operated by the National Radio Astronomy
Observatory, it is used for aperture –synthesis mapping
of the radio sky. The antennas are movable and can be
deployed at stations railroad tracks having a Y-shaped
configuration with each arm of [he Y = 21km long. The
page facing page 1 also has a photograph of the
VLA
(P 702)

18. (P 703)

19. The replacement is a 110 x 100 m completely steerable
dish (Figs.20-16 and 20-17) standing 40 stories tall West
Virginia mountaing valley near Green Bank. Name the
Robert C. Byrd telescope, it is the most sophisticade ,
complex and expensive antenna ever built with a cost as
of 2000 of well over $100 million (neck-and-neck) in cost
with Arecibo)
(P703)

20. • Nauen. This antenna system has two arrays, one for λ =
50 m and the other smaller array for λ= 25 m with a
reflector screen between which is held by outriggers set
at an angle. The antenna system can be turned 10 any
compass direction. Each array has 16 λ/2 dipoles.
example
Deutsche Welle Short Wave Antenna
(a) What is the gain of the Deulsche Welle λ = 50m
antenna array of Fig. 20-15a including the effect of
ground in the center of the array is 62.5 m above
ground?
(b) What is the ground bounce angle?
(P 703)

21. (P704)

22. (a) The gain of a single λ/2 dipole is 2.15 dBi and of 2
collinear in phase λ/2 dipole is 3.8 dBi. The array of 8
such collinear dipoles adds 3 + 3 + 3 = 9 dB.The reflector
screen adds 3 dB more and the ground bounce another
6 dB for a total gain ofr 3.8 + 9 + 3 + 6 =21.8 dbi or a
directivity of 151 approx.
Thus, for a power input of 10 KW to the antenna the ERP
(efective ardiation power) 10 ^ 4X 151 =1.5 Mw aprox.
(b) For 2 out-of-phase point sources separated by 2.5λ or
125 m the ground bounce angle α sin -¹ (0.5λ / 2.5λ)
= sin -¹ (25 m / 125m) = 11.5º.
ans (b) see sketch.
(P705)

23. • The pattern of the two point sources multiplied by the
pattern of the broadside array of stack dipoles results
in maximum radiation at a slightly lower angle α = 9º
approx.
(P705)

24. GREEN BANK. Jhon Findlay’s 91-m-diameter meridian
transit radio telescope of the National Radio Astronomy
Observatory at Green Bank, west Virginia, had been
several stressed for many years by rocking the dish
during right-ascension scans. On november 15 of 1998,
it collapsed. Senators Robert C. Byrd and Jay
Rockefeller of west Virginia inmediatately obteined a
Congressional appropriation of $75 million for a
replacement to be built a Green Bank. The national
science Foundation objected. The NSF wanted the
replacement constructed in the warmer, drier southwest.
U:S: Senator Byrd Rockefeller wanted in West Virginia
high-teeh.
(P705)