Electric lamp and discharge devices: systems – Cathode ray tube circuits – Combined cathode ray tube and circuit element structure
Reexamination Certificate
1999-07-13
2001-03-27
Lee, Benny T. (Department: 2817)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Combined cathode ray tube and circuit element structure
C315S005380, C445S035000
Reexamination Certificate
active
06208079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Description of the Related Art
The present invention relates generally to travelling-wave tubes and more particularly to travelling-wave tube collectors.
2. Description of the Related Art
An exemplary traveling-wave tube (TWT)
20
is illustrated in FIG.
1
. The elements of the TWT
20
are generally coaxially-arranged along a TVVT axis
21
. They include an electron gun
22
, a slow-wave structure
24
(embodiments of which are shown in FIGS.
2
A and
2
B), a beam-focusing structure
26
which surrounds the slow-wave structure
24
, a signal input port
28
and a signal output port
30
which are coupled to opposite ends of the slow-wave structure
24
and a collector
32
. A housing
34
is typically provided to protect the TWT elements.
In operation, a beam of electrons is launched from the electron gun
22
into the slow-wave structure
24
and is guided through that structure by the beam-focusing structure
26
. A microwave input signal
36
is inserted at the input port
28
and moves along the slow-wave structure to the signal output port
30
. The slow-wave structure
24
causes the phase velocity (i.e., the axial velocity of the signal's phase front) of the microwave signal to approximate the velocity of the electron beam.
As a result, the beam's electrons are velocity-modulated into bunches which overtake and interact with the slower microwave signal. In this process, kinetic energy is transferred from the electrons to the microwave signal; the signal is amplified and is coupled from the signal output port
30
as an amplified signal
38
. After their passage through the slow-wave structure
24
, the beam's electrons are collected in the collector
32
.
The beam-focusing structure
26
is typically configured to develop an axial magnetic field. A first configuration includes a series of annular, coaxially arranged permanent magnets
40
which are separated by pole pieces
41
. The magnets
40
are typically arranged so that adjacent magnet faces have the same magnetic polarity. This beam-focusing structure is comparatively light weight and is generally referred to as a periodic permanent magnet (PPM). In TWTs in which output power is more important than size and weight, a second beam-focusing configuration often replaces the PPM with a solenoid
42
(partially shown adjacent the input port
28
) which carries a current supplied by a solenoid power supply (not shown).
As shown in
FIGS. 2A and 2B
, TWT slow-wave structures generally receive an electron beam
52
from the electron gun (
22
in
FIG. 1
) into an axially-repetitive structure. A first exemplary slow-wave structure is the helix
43
shown in
FIG. 2A. A
second exemplary slow-wave structure is the coupled-cavity circuit
44
shown in FIG.
2
B. The coupled-cavity circuit includes annular webs
46
which are axially spaced to form cavities
48
. Each of the webs
46
forms a coupling hole
50
which couples a pair of adjacent cavities. The helix
43
is especially suited for broad-band applications while the coupled-cavity circuit is especially suited for high-power applications.
In another conventional TWT configuration, (not shown) an oscillator is formed by replacing the output port
30
with a microwave load. Random, thermally generated noise interacts with the electron beam on the slow-wave structure
24
to generate a microwave signal. Energy is transferred to this signal as it moves along the slow-wave structure. This oscillator signal generally travels in an opposite direction from that of the electron beam (i.e., the TWT functions as a backward-wave oscillator) so that the oscillator signal is coupled from the port
28
.
TWTs are capable of amplifying and generating microwave signals over a considerable frequency range (e.g., 1-90 GHz). They can generate high output powers (e.g., >10 megawatts) and achieve large signal gains (e.g., 60 dB) over broad bandwidths (e.g., >10%).
The electron gun
22
, the signal input port
28
, the signal output port
30
and the collector
32
of FIG.
1
and the helix
43
of
FIG. 2A
, are again shown in the TWT schematic
20
of
FIG. 3
(for clarity of illustration, the slow-wave structure is not shown in the schematic). As described above with reference to
FIGS. 1 and 2A
, the helix
43
is an exemplary slow-wave structure and the signal input port
28
and signal output port
30
are coupled to opposite ends of this exemplary slow-wave structure, has a cathode
56
and an anode
58
and the collector
32
has a first annular stage
60
, a second annular stage
62
and a third stage
64
. Because the third stage
64
generally has a cup-like or bucket-like form, it is sometimes referred to as the “bucket” or “bucket stage”.
The helix
43
and a body
70
of the TWT are at ground potential. The cathode
56
is biased negatively by a voltage V
cath
from a cathode power supply
74
, as indicated by + and − potential indicators. An anode power supply
76
is referenced to the cathode
56
and applies a positive voltage to the anode
58
. This positive voltage establishes an acceleration region
78
between the cathode
56
and the anode
58
. Electrons are emitted by the cathode
56
and accelerated across the acceleration region
78
to form the electron beam
52
.
The electron beam
52
travels through the helix
43
and exchanges energy with a microwave signal which travels along the helix
43
from an input port
28
to an output port
30
. Only a portion of the kinetic energy of the electron beam
52
is lost in this energy exchange. Most of the kinetic energy remains in the electron beam
52
as it enters the collector
32
. A significant part of this kinetic energy can be recovered by decelerating the electrons before they are collected at the collector walls.
Because of their negative charge, the electrons of the electron beam
52
form a negative “space charge” which would radially disperse the electron beam
52
in the absence of any external restraint. Accordingly, the beam-focusing structure applies an axially-directed magnetic field which restrains the radial divergence of electrons by causing them to spiral about the beam.
However, the electron beam
52
is no longer under this restraint when it enters the collector
32
and, consequently, it begins to radially disperse. In addition, the interaction between the electron beam
52
and the microwave signal on the slow-wave structure
24
causes the beam's electrons to have a “velocity spread” as they enter the collector
32
, i.e., the electrons have a range of velocities and kinetic energies.
Electron deceleration is achieved by application of negative voltages to the collector. The potential of the collector is “depressed” from that of the TWT body
70
(i.e., made negative relative to the body
70
). The kinetic energy recovery is further enhanced by using a multistage collector, e.g., the collector
32
, in which each successive stage is further depressed from the body potential of V
B
. For example, if the first collector stage
60
has a potential V
1
, the second collector stage
62
a potential V
2
and the third collector stage
64
a potential of V
3
, these potentials are typically related by the equation V
B
=0>V
1
>V
2
>V
3
as indicated in FIG.
3
.
The voltage V
1
on the first stage
60
is depressed sufficiently to decelerate the slowest electrons
80
in the electron beam
52
and yet still collect them. If this voltage V
1
is depressed too far, the electrons
80
will be repelled from the first stage
60
rather than being collected by it. These repelled electrons may flow to the body
70
and this will reduce the TWT's efficiency. Alternatively, they may reenter the energy exchange area of the helix
43
. This undesirable feedback will reduce the TWT's stability.
Similar to the first stage
60
, successively depressed voltages are applied to successive collector stages to decelerate (but still collect) successively faster electrons in the electron beam
52
, e.g., electrons
82
are coll
Gudmestad T.
Hughes Electronics Corporation
Lee Benny T.
LandOfFree
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