Communications: radio wave antennas – Antennas – With spaced or external radio wave refractor
Reexamination Certificate
2000-05-23
2002-08-27
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
With spaced or external radio wave refractor
C343S755000
Reexamination Certificate
active
06441793
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention relates generally to the field of wireless communications and, more particularly, to antenna systems.
2. Description of the Related Art
Satellite communication systems are commonly employed to globally transmit data signals from an originating destination to a receiving destination.
FIG. 1
shows a conventional satellite communication system. For an uplink operation, where communications signals are transmitted by a ground station
110
to a satellite
109
, a data signal is first sent to a modulator circuit
112
in the ground station
110
. From this data signal, modulator circuit
112
generates a modulated carrier signal with a frequency in one of the desired frequency bands. The modulated carrier signal is then sent to an input port on a waveguide assembly, commonly called an antenna feed
102
. Antenna feed
102
is typically positioned such that its radiated output is efficiently coupled to a system of one or more reflector units
100
. Antenna feed
102
acts as a transducer that converts the modulated carrier signal into radiated electromagnetic waves
114
that illuminate reflector unit
100
. The electromagnetic waves
114
are then directed by the reflector unit
100
to satellite
109
.
For a downlink operation, where communication signals are transmitted by satellite
109
to ground station
110
, the above process occurs in reverse. Radiated electromagnetic waves of a modulated carrier wave are transmitted from satellite
109
to reflectors
100
. The waves are redirected by reflectors
100
into antenna feed
102
. Antenna feed
102
then acts as a transducer to route the received signals to appropriate receiver ports. Waveguide may couple the receiver ports to a demodulator circuit
112
. Demodulator circuit
112
receives the carrier signal and recovers the data transmitted by satellite
109
by extracting the underlying data signal from the modulated carrier wave.
Satellite communication systems commonly employ more than one frequency band for electromagnetic signals radiated from a transmitting station to a receiving station through a satellite orbiting above the earth. These systems typically convey information on carrier signals in a number of different frequency bands approved by regulatory organizations and standards bodies (e.g., the Federal Communications Commission or FCC in the United States). Among the most widely implemented bands are the C band, X band and Ku band. These three bands together extend over two octaves of the communication frequency spectrum. The C band comprises frequencies in the range from 3.625 GHz to 6.425 GHz. The X band comprises frequencies in the range from 7.250 GHz to 8.40 GHz. The Ku band comprises frequencies in the range from 10.950 GHz to 14.500 GHz. The C, X and Ku bands are typically subdivided into many sub-bands wherein uplink and downlink data streams independently reside. Satellite communication systems employing single band communications are commonly referred to as narrow-band wireless signal communications. Multi-band communication systems are commonly referred to as broadband wireless signal communications.
FIG. 2
shows an antenna system
90
utilizing an antenna feed
102
. Antenna system
90
includes a main reflector
100
, a subreflector
101
and an antenna feed
102
. Support member
105
supports subreflector
101
and antenna feed
102
. Waveguides
107
connect antenna feed
102
to a plurality of transceivers
108
. While three transceivers are shown, other combinations of receivers are possible. The use of subreflector
101
may be optional in some configurations. The main reflector
100
, subreflector
101
and antenna feed
102
may be positioned in a prime focus, single offset, dual offset, Gregorian, Cassegrain, or Newtonian configuration. In the case of a prime focus configuration, subreflector
101
is removed. Main reflector
100
is typically paraboloidal, and subreflector
101
is typically hyperboloidal, but other shapes may also be used.
Prior art systems have typically relied on separate antenna feeds for transmission and/or reception of the C, X, and Ku frequency bands, i.e., a C-band antenna feed with its own input/output (I/O) port to transmit or receive in the C-band; a X-band antenna feed with its own I/O port to transmit or receive in the X-band; and a Ku-band antenna feed with its own I/O port to transmit or receive in the Ku-band. Since three separate antenna feed structures are needed, data transmission or reception in different frequency bands requires the physical removal of the first frequency antenna feed from the focal point of the reflector and the physical installation of a second frequency antenna feed into the focal point of the reflector. This movement is both a time consuming and tedious operation, in which improper alignment of the reflector and the antenna feed will cause distorted radiated patterns of the transmitted electromagnetic waves and may reduce transmission or reception efficiency. In addition, the distorted radiated patterns may be severe enough to violate FCC regulations. In order to prevent such problems, tests may be conducted after a switch is made from one antenna feed to another to obtain actual radiated patterns. This testing process may itself take several days to complete. Consequently, many ground stations limit their transmission or reception frequency to one of the three bands C, X and Ku. In addition, in the case of mobile satellite communications, there is a need for minimization of transportable payload weight in space or on earth. The use of multiple antenna feeds for communications at various frequencies may detrimentally increase payload weight and limit their usefulness on ground stations where size may be of highest importance.
Thus, a multi-band antenna feed structure capable of operating in two or more frequency bands simultaneously without the need for manual intervention is desirable. Such a feed structure may advantageously require fewer parts and consequently reduces depot supplies and training requirements. In the prior art, multi-band antenna feed structures have been recited. One such example is disclosed in co-pending U.S. patent application Ser. No. 09/183,355 filed on Oct. 30, 1998, entitled, “A Method and Apparatus for Transmitting and Receiving Multiple Frequency Bands Simultaneously” by Cavalier, et al., which is hereby incorporated herein by reference in its entirety. Cavalier, et al. teaches a multi-band antenna feed structure capable of simultaneous transmission and reception in the C, X, and Ku frequency bands. The structure, comprising coaxial waveguides and a subreflector, is preferably mated with parabolic reflectors.
FIG. 3
shows a cross-section of one embodiment of a multi-band antenna feed
102
capable of transmitting and receiving C, X, and Ku frequency bands as according to Cavalier, et al.
When an antenna feed is designed for a reflector system, the matching of the antenna pattern to the angular aperture of the reflector is of primary concern. If the antenna pattern is too wide, the radiated electromagnetic energy spills over the edge of the reflector, and may result in reduced efficiency of the antenna system. This is commonly referred to as over-illumination of the reflector system. In addition, the energy lost due to the over-illumination result in side lobes that interfere with other neighboring antenna systems. Thus, stringent rules about an antenna's spillover characteristics are enforced by the governmental agencies regulating the antenna systems. Conversely, if the antenna pattern is too narrow, the reflector is under-illuminated. This also results in reduced efficiency of the antenna system. The use of under-illuminated reflectors is generally avoided to minimize system cost and transportability. In addition, physical space constraints on the antenna system may prohibit the use of large reflectors. An ideally illuminated reflector matches the angular aperture of the reflector to the entire antenna radiation pattern being generated by th
Austin Information Systems, Inc.
Clinger James
Conley & Rose & Tayon P.C.
Meyertons Eric B.
Wong Don
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