Electric lamp and discharge devices: systems – Cathode ray tube circuits – Combined cathode ray tube and circuit element structure
Reexamination Certificate
1998-11-16
2001-12-04
Lee, Benny T. (Department: 2817)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Combined cathode ray tube and circuit element structure
C315S005380
Reexamination Certificate
active
06326730
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to linear beam electron devices, and more particularly, to a low-power depressed-collector klystron that provides high efficiency and wide bandwidth.
2. Description of Related Art
Linear beam electron devices are used in sophisticated communication and radar systems which require amplification of a radio frequency (RF) or microwave electromagnetic signal. A conventional klystron is an example of a linear beam electron device used as a microwave amplifier. In a klystron, an electron beam originating from an electron gun is caused to propagate through a drift tube that passes across a number of gaps, each gap being part of a resonant cavity of the klystron. The electron beam is velocity modulated by a RF input signal introduced into the first one of the resonant cavities. The velocity modulation of the electron beam results in electron bunching due to electrons, that have had their velocity increased, gradually overtaking the electrons that have had their velocity decreased. The traveling electron bunches represent a RF current in the electron beam, which induces electromagnetic energy into subsequent resonant cavities. The electromagnetic energy may then be extracted from the last of the subsequent resonant cavities as an amplified RF output signal.
The bandwidth and efficiency of a klystron are both of considerable importance in klystrons. For example, the information rate of the signal the klystron can amplify increases with the bandwidth. Also, the power consumed by the klystron decreases as the efficiency increases.
The bandwidth of a klystron increases as the ratio of beam current to beam voltage increases, or rather, as the beam conductance is increased. This occurs because both the load conductance across the output cavity and the loading conductances that the beam produces on the intermediate cavities are proportional to the beam conductance. Therefore the quality factor (Q) for these cavities, which is a measure of the energy stored to the energy lost per cycle, decreases as the beam conductance is increased. Accordingly, bandwidth is also inversely proportional to Q.
The beam conductance is determined by the perveance of the electron gun, which produces it, and by the voltage at which the electron gun is operated. The perveance (K) is defined by the relationship between the beam current (I) and the beam voltage (V) as I=K V
{fraction (3/2)}
. The perveance is generally 1×10
−6
to 3×10
−6
amperes per volt
{fraction (3/2)}
for the average klystron. The beam conductance (I/V) can thus be given by the expression I/V=K V
½
.
In low-power klystrons, the beam voltage is usually low and the corresponding power output is typically less than 1 kilowatt. One approach to increasing the bandwidth would be to increase the perveance because, as discussed above, increasing the perveance increases the beam conductance and thus the bandwidth. However, this approach has two disadvantages. First, if the perveance is made high, there is an adverse impact on the efficiency of the tube because the space charge forces in the beam increase and make it difficult to tightly bunch the electrons of the beam. Second, as the perveance is increased at constant electron beam power, the beam voltage must be decreased. This results in a decrease in the electron beam velocity because the electron beam velocity is proportional to the square root of beam voltage. Furthermore, the dimensions of the cavity gaps along the beam must be held constant in terms of electron transit time to maintain good coupling of the cavity gap fields to the electrons. Therefore, the dimensions of these cavity gaps may become extremely small in low voltage klystrons, which are designed to operate at very high frequencies, and this results in difficulties in constructing a suitable klystron.
Accordingly, it would be desirable to provide an efficient klystron for low-power wide-bandwidth applications that could be easily fabricated. Furthermore, it would be desirable to provide a design methodology that would allow construction of various low-power klystrons for specific applications having relatively low output power and high efficiency, but with a much wider bandwidth and utilizing larger, more easily fabricated parts than would be found in a klystron of standard design.
SUMMARY OF THE INVENTION
In accordance with the teachings of the present invention, a klystron that operates at low power levels but that provides high efficiency and wide bandwidth is provided. Furthermore, the klystron provides low power, high efficiency, and wide bandwidth to meet specific design specifications while utilizing more easily fabricated parts than klystrons of conventional construction.
In an embodiment of the present invention, a low-power wide-bandwidth klystron comprises a cathode that has an electron beam emitting surface capable of emitting an electron beam therefrom and a collector spaced from the cathode. The collector collects the electron beam emitted from the cathode. An anode, disposed between the cathode and the collector, channels the electron beam emitted from the cathode towards the collector and past an input cavity and an output cavity. A drift tube, disposed around the electron beam, couples the input cavity and the output cavity together and defines a path for the electron beam. At least one intermediate cavity may be disposed along the electron beam between the input cavity and the output cavity. The input cavity velocity modulates the electron beam while the output cavity extracts the amplified signal from the electron beam. The output cavity is overloaded by providing it with a load conductance that is at least twice that required for an optimal power output of the klystron.
More particularly, a first voltage, positive with respect to the cathode, is applied to the anode in order to draw the electron beam from the cathode emitting surface. A second voltage, positive with respect to the cathode, is applied to the collector in order for the electron beam to reach it for collection, but the cathode to collector voltage potential difference may be at most one half of the cathode to anode voltage potential difference so that increased efficiency is achieved. The anode voltage, higher than that required for the desired power output, along with the large output cavity load conductance, provide low-power wide-bandwidth klystron performance.
A more complete understanding of the low-power wide-bandwidth klystron will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings, which will first be described briefly.
REFERENCES:
patent: 3644778 (1972-02-01), Mihran et al.
patent: 3725721 (1973-04-01), Levin
patent: 3902098 (1975-08-01), Tanaka et al.
patent: 3904917 (1975-09-01), Ueda
patent: 4168451 (1979-09-01), Kageyama et al.
patent: 4558258 (1985-12-01), Miyake
“The Klystrode—An Unusual Transmitting Tube With Potential for UHF-TV” by Preist et al., Proceedings Of The IEEE, vol. 70, No. 11, Nov. 1982, pp. 1318-1325.
Lee Benny T.
Litton Systems, Inc
O'Melveny & Myers LLP
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