Electric lamp and discharge devices: systems – Combined load device or load device temperature modifying... – Distributed parameter resonator-type magnetron
Reexamination Certificate
1996-10-15
2001-01-23
Mis, David (Department: 2817)
Electric lamp and discharge devices: systems
Combined load device or load device temperature modifying...
Distributed parameter resonator-type magnetron
C315S307000
Reexamination Certificate
active
06177764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, generally, to a technique for controlling the RF output of a magnetron of a type employing a pulse-forming network to generate output pulses and, more particularly, to a closed-loop control system for controlling peak current through the magnetron using a peak current sense in a feedback loop.
2. Description of the Related Art
The use of magnetrons in radar systems is generally well known. Such radar systems are extensively used in military applications for detecting aircraft, projectiles, and the like. Magnetron-based radar systems are also routinely employed in weather systems to detect rain clouds, turbulence, and the like.
Presently known magnetrons typically comprise a diode encased in a vacuum tube. The diode essentially comprises a cathode and an anode, wherein a current source is fed to the cathode plate by a compatible current source. A pulse-forming network (PFN) may be utilized to condition a transmit pulse produced by the magnetron.
A PFN typically includes a group of coupled inductors and individual capacitors whose characteristic impedance is approximately matched to the static impedance of the magnetron. The resonant frequency of each LC section in the pulse-forming network and the number of such LC sections determine the pulse width of the RF pulse emitted by the magnetron. As a general rule, the ripple associated with the output pulse may be minimized and the squareness of the pulse enhanced by adding a larger number of LC sections to the PFN.
It is known that magnetron performance drifts as the magnetron ages. This is believed to be due in part to changes in the static and dynamic impedance of the magnetron with age. In addition temperature and other environmental factors can influence the performance of a magnetron. Attempts to control magnetron operation within its optimum operating range have met with limited success. This is due in part to the fact that although it may be possible to control magnetron voltage, the sensitivity of the magnetron output power to the magnetron voltage may be undesirably low. Although the magnetron output power is relatively sensitive to changes in the magnetron current, control of magnetron current has been difficult to achieve in prior art systems.
One known method for controlling magnetron current is to monitor magnetron power output and to manually adjust the magnetron current in the factory or a service center. Unfortunately, this process is time consuming, cumbersome, and expensive to perform.
Accordingly, a need exists for a magnetron current control configuration that overcomes the shortcomings of the prior art.
SUMMARY OF THE INVENTION
A control system is provided which maintains peak magnetron current at a desired predetermined level during the life of a magnetron.
In accordance with a preferred embodiment of the present invention, a closed-loop current control circuit is employed to monitor peak magnetron current, and to adjust PFN charge voltage to thereby control the peak current applied to the magnetron.
In accordance with one aspect of the present invention, a transformer assembly is employed in conjunction with a PFN to apply a peak current to the magnetron. The transformer assembly includes a current transformer configured to sample the peak current. The sampled peak current is applied to a sample and hold circuit that compares the measured peak current to a predetermined desired peak current. If the sampled peak current is higher or lower than the desired peak current, the charge voltage applied to the PFN is appropriately trimmed to thereby drive the peak current actually applied to the magnetron to the desired peak current.
In accordance with a further aspect of the present invention, a digital control circuit employs an up-down counter to incrementally increase or decrease the PFN charge voltage when the detected peak current is either too high or too low. By employing an up-down counter in this manner, the maximum change in PFN charge voltage may be limited to a predetermined range, e.g., a voltage change associated with one bit of resolution, during each correction cycle.
In accordance with a particularly preferred embodiment, the output of the up-down counter may be applied to a digital-to-analog converter (DAC), with the output of the DAC being applied to a PFN voltage trim circuit.
In accordance with an alternate embodiment of the present invention, an analog control scheme may be employed to adjust PFN charge voltage in response to the sampled peak current. In accordance with this alternate embodiment, the sampled peak current is compared to the desired peak current to produce a signal that is applied to the input of an integrator circuit. When the difference between the desired peak current and actual peak current exceeds a predetermined threshold, the integrator circuit is configured to apply an analog correction signal to the PFN charge circuit to adjust the PFN voltage and thereby drive the actual peak current to the desired level.
In accordance with a preferred aspect of the present invention, the control circuit operates with a dead band such that the PFN charge voltage is adjusted only when the sampled peak current differs from the desired peak current by a predetermined threshold amount.
REFERENCES:
patent: 2694149 (1954-11-01), Gross
patent: 3973145 (1976-08-01), Schmitt et al.
patent: 4755740 (1988-07-01), Loucks
patent: 0364040 (1989-10-01), None
patent: 0517226 (1992-06-01), None
patent: 1421195 (1973-01-01), None
patent: 2108734 (1982-10-01), None
patent: 2213613 (1988-12-01), None
patent: 2216688 (1989-03-01), None
patent: 2239330 (1990-11-01), None
Honeywell International , Inc.
Mis David
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