TVRO Antenna Introduction and Application
Antenna feed system can ensure high enough
gain and the lowest possible antenna noise. And it can effectively feedback
faint radio wave to low noise amplifier with high-frequency. Moreover, it shall
provide correct antenna pointing and polarization mode. Besides, antenna system
shall possess high enough capacity of bearing wind pressure.
Antenna type
Antenna is divided into two categories
which are rotated polarization and non-rotated polarization. Rotated
polarization antenna has two types which are spiral and parabolic. And
parabolic antenna has two basic forms. One is prime focus parabolic antenna of
feed forward with only one reflector. The other is Cassegrain antenna of feed
back, which processes main reflector (paraboloid) as well as sub-reflector (hyperboloid). And for
Cassegrain antenna, radio wave converges after reflecting twice. Primary focus
antenna is simple but its performance is worse. Low noise preamplifier of
Cassegrain antenna can be placed at the back of paraboloid so as to prevent
from sunlight. Cassegrain antenna is especially suitable for satellite TV
station in the tropics; however, the cost is higher.
Besides, there are flat panel antenna and
ring focus antenna. The former is portable, suitable for family receiving. The
latter decreases antenna sidelobe and improves receiving efficiency. To
flexibly receive TV program on different satellites, power-driven polar axis
antenna is produced. This type of antenna possesses the original antenna, feed;
moreover, it also possesses electric motor speed-reduction drive antenna
mechanism and antenna controller controlled by microcomputer.
Some cable television system adopts
multi-focus parabolic antenna, which uses fixed antenna to receive more
satellite’s television signal simultaneously. This type of antenna has more
feeds which receive signal from different satellites to form more beams. And
its reflector uses deformed sphere and paraboloid. For example, the reflector
consists of rectangle cut out from sphere or two kinds of curves. And its
horizontal direction is circular arc while vertical direction is a part of
paraboloid.
The diameter of parabolic antenna of large
satellite communication station is 15~
