1 Learn the words & word combinations:

antenna gain	коэффициент усиления антенны
envelope	огибающая (сигнала)
front-to-back ratio	коэффициент обратного излучения антенны
cross-polar discrimination	кросс - поперечная поляризация
dual polarization	двойная поляризация
magnitude	величина, значение
round-trip-echo	эхо-сигнал
radome	обтекатель
feeder	фидер
join	соединение, сочетание
shield	защитный экран, щит
baffle	экран, щиток
waveguide	волновод
circular waveguide	круглый волновод
vertex plate	вершина, точка пучка
near-in sidelobes sight radio	ближние боковые лепестки радиопеленгация

2 Read & translate the text (orally) 17.5.1 – 17.5.2:

3 Find Russian equivalents:

two axi-symmetric parabolic reflectors a high front-to-back ratio	sight path stable inevitably
near-in sidelobes	spillover noise
to maintain	loose joins
coded receivers	a beam waveguide feed system
the main feed horn	a high performance corrugated horn

4 Find English equivalents:

гарантировать	при любых природных условиях
потери (низкие)	возможность
относительно	удовлетворять
усилие	обнаружение
усовершенствовать	испытывать
доступный (имеющийся в наличии)

5Answer the questions:

1. What does a typical microwave relay system consist of?

2. What are important criteria for microwave radio antennas?

3. Where are earth station antennas used?

4. How many types are the antennas divided into?

5. What for are earth stations required?

6. Why is the axi-symmetric Cassegrain antenna the favorite choice?

7. What does the beam waveguide feed system consist of?

PART 5 (17.5.3 – 17.5.5)

17.5.3 Satellite antennas

17.5.3.1 Telemetry, tracking and command (TT&C)

The ideal TT&C antenna would give omnidirectional coverage so that the orientation of the satellite would be irrelevant. Wire an­tennas are used for VHF and UHF coverage but the spacecraft is a few wavelengths across at these frequencies and therefore consid­erable interaction between the antenna and the satellite distorts the radiation pattern. An alternative approach is to use a low gain horn antenna to provide full earth coverage. This is particularly useful for spin stabilised spacecraft. The earth subtends 17 degrees from a geostationary satellite which can be met with a small conical horn.

17.5.3.2 Spot beams

Spot beam antennas are required to produce a beam covering a small region of the earth's surface. The angular width of the beam is inversely proportional to the diameter of the antenna. Size consider­ations virtually dictate that some form of deployable mechanism is needed on the satellite and this leads to the use of offset reflectors with a dual-mode or corrugated feed horn. The constraints of the launcher mean that the maximum size for a solid reflector is about 3.5 metres. Larger reflectors can only be launched by using some form of unfurlable mesh or panel reflector. The trend towards smaller footprints on the earth can be met either by using a larger reflector or by using a higher frequency, both of which involve higher costs. To date most spot beam communication satellite have used two prime focus offset reflectors, one for transmit and one for receive, producing footprints on the earth's surface which are ellip­tical because of the curvature of the earth.