Amplifiers – With distributed parameter-type coupling means
Reexamination Certificate
2000-03-20
2002-08-20
Lam, Tuan T. (Department: 2816)
Amplifiers
With distributed parameter-type coupling means
C330S12400D, C330S295000
Reexamination Certificate
active
06437642
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to paralleled amplifiers, and more particularly to paralleled amplifiers interconnected by hybrids to provide channelization, where the number of amplifiers in the paralleled arrangement can be other than 2
N
, where N is an integer.
BACKGROUND OF THE INVENTION
Multichannel spacecraft communications systems are now widely used.
Electronic amplifiers are used to boost signal strength at each end of an uplink and downlink. Power amplifiers are used to boost the power of the signal at the spacecraft before retransmission to earth. Amplifiers are basically nonlinear. If a single power amplifier were to be used to boost the signal power for all of a plurality of channels, the signals in the plural channels would become jumbled together, and, in addition to intermodulation problems attributable to the nonlinearity, the additional problem would exist that the signals could not be re-separated into separate channels without the use of frequency-sensitive filters. To avoid the need for large numbers of such filters, and also to reduce the amount of power which must be handled by a single amplifier, a number of amplifiers is used which is at least equal to the number of independent channels being transmitted. Phase-sensitive hybrid combining networks are coupled to the inputs of the amplifiers, and corresponding phase-sensitive separation hybrid networks are coupled to the outputs of the amplifiers to separate the amplified signals into the original channels. At the spacecraft, each separate channel appearing at the output of the phase-sensitive separation network may be designated, for example, for transmission over a separate antenna beam to a different portion of the Earth's surface.
It should be noted that the paralleling of amplifiers as described above is not done for purposes of redundancy or reliability, because, if a signal amplifier among the plurality of paralleled amplifiers fails, the phase-sensitive channelization is not accomplished.
FIG. 1
a
is a simplified block diagram of a spacecraft communication system
10
using a prior-art paralleled amplifier. In the arrangement of
FIG. 1
a
, communication system
10
includes a spacecraft
12
and first and second ground stations
14
and
16
, respectively.
The spacecraft
12
is illustrated as including a receiving antenna
12
ar
and a transmitting antenna
12
at
. Receiving antenna
12
ar
forms two separate receive antenna beams, designated
12
rb
1
and
12
rb
2
, directed toward ground stations
14
and
16
, respectively. The signals from ground station
14
are generated at a beamformer output port
12
aro
1
, and the signals from ground station
16
are generated at a beamformer output port
12
aro
2
. These signals are designated A and B, for ease of notation. Thus, the A signals are transmitted from ground station
14
to receive antenna
12
r
by way of beam
12
rb
1
, and the B signals are transmitted from ground station
16
by way of beam
12
rb
2
. The A and B signals are amplified in a paralleled amplifier
20
for application to beamformer ports
12
ati
2
and
12
ati
1
, respectively, of transmitting antenna
12
at
of spacecraft
12
. Paralleled amplifier
20
has first and second input ports
20
i
1
and
20
i
2
, and first and second output ports
20
o
1
and
20
o
2
. The A signals applied to input port
12
ati
2
are transmitted to ground station
16
by way of antenna beam
12
atb
2
, and the B signals applied to input port
12
ati
1
are transmitted to ground station
14
by way of beam
12
tb
1
. Consequently, in the simple system of
FIG. 1
a
, two separate locations on the Earth can communicate by way of pairs of antenna beams. The A and B signals may be viewed as being channels of information.
It will be clear in the arrangement of
FIG. 1
a
that, if the A and B signals are jumbled together in paralleled amplifier
20
, the signals applied from the paralleled amplifier output ports
20
o
1
and
20
o
2
to the beamformer input ports of the transmitting antenna
12
at
will include a mixture of both the A and B signals, and each transmit beam will transmit both A and B signals to both ground stations. This could be overcome by some method of channelization, such as by frequency division filters. However, such filters are heavy, bulky, and expensive, and therefore may not be desired. In amplifier
20
of
FIG. 1
a
, paralleled amplifiers
1
and
2
are connected to receive the A and B signals from antenna ports
12
aro
1
and
12
aro
2
at input ports
20
i
1
and
20
i
2
, respectively. The “paralleled” aspect of the amplifier
20
requires that there be some kind of cross-coupling of the A signals to amplifiers
1
and
2
, and of the B signals to amplifiers
1
and
2
. Within paralleled amplifier
20
, this cross-coupling is provided by hybrids. In amplifier
20
, ports
20
i
1
and
20
i
2
are coupled to the ports of a three-dB hybrid H
1
, well known in the art. Such hybrids are represented by crossed transmission lines in the form of the letter X, with the crossing representing the coupling between two transmission lines of the hybrid. As illustrated in
FIG. 1
a
, the ports of hybrid H
1
of
FIG. 1
a
are designated H
1
1
, H
1
2
, H
1
3
and H
1
4
, with ports H
1
and H
1
2
being equivalent to, or contiguous with, parallel amplifier ports
20
i
1
and
20
i
2
, respectively. In such three-dB hybrids, a transmission line, illustrated as a line designated T
1
, couples ports H
1
1
to port H
1
4
, and another transmission line, illustrated as a line designated T
2
, couples ports H
1
2
and H
1
3
. A salient characteristic of such hybrids is that, over a significant frequency band, the input signals applied to port H
1
1
appear at ports H
1
3
and H
1
4
with ½ power, and in mutual phase quadrature, and port H
1
2
is isolated from port H
1
1
. Similarly, signals applied to port H
1
2
appear at ports H
1
3
and H
1
4
with ½ power, and in mutual phase quadrature.
FIG. 1
b
illustrates a common way to designate these characteristics. In
FIG. 1
b
, the signal at port H
1
1
is designated as (1,0), representing full power and a reference phase of 0°. The signal at port H
1
2
resulting from application of (1,0) to port H
1
1
is (0,0) representing zero power or no signal. The signals appearing at ports H
1
3
and H
1
4
as a result of application of signal (1,0) to port H
1
1
are designated as (½,90) and (½,0), representing half-amplitude or half-power, with mutually quadrature phase shifts of 90° and 0° respectively. It should be noted that the terms “input” and “output” as applied to the ports of a hybrid refer only to its application, since the device is linear. A port termed an “input” port in one application may well be an “output” port in another application, or even in a different mode of operation of the same application.
In
FIG. 1
a
, half-power signal A at a phase shift of 90°, corresponding to (A/2,90), appears at port H
1
3
of hybrid H
1
, and half-power signal A at a phase shift of 0° (A/2,0) appears at port H
1
4
as a result of application of (A,0) to port H
1
1
. Similarly, half-power signal B at a phase shift of 0°, corresponding to (B/2,0), appears at port H
1
3
of hybrid H
1
, and half-power signal B at a phase shift of 90° (B/2,90) appears at port H
1
4
as a result of application of (B,0) to port H
1
2
. Thus, amplifier
1
receives for amplification the sum of (A/2,90) and (B/2,0), while amplifier
2
receives (A/2,0) and (B/2,90). These signals, which may be designated (A/2,90)+(B/2,0) and (A/2,0)+(B/2,90), respectively, appear in amplified form at the outputs of amplifiers
1
and
2
in the usual manner. While the amplifiers may invert phase, the amplification and phase inversion are not relevant to the end result, and are ignored in the discussion. Amplified summed signal (A/2,90)+(B/2,0) appears at the output of amplifier
1
for application to an input port H
2
1
of a 3dB hybrid H
2
, and amplified summed signal (A/2,0)+(B/2,90) appears at the output of am
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