Abstract:
The invention is designed to employ one or a multitude of sensors designed to allow operational monitoring of any of a variety of electromagnetic radiating tubes. Monitoring is conducted to detect a degradation in performance which can be used as a factor in deciding whether tube replacement is justified. Contrary to some past approaches that focused on averaged tube outputs, the invention is designed to examine individual tube pulses.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/871,474 filed on May 31 2001, now U.S. Pat. No. 6,489,919 B1 incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Electromagnetic radiating devices, such as microwave tubes, are used in a large variety of communication, RADAR, and surveillance systems. Examples of microwave tubes include linear beam types such as traveling wave tubes (TWT) and cross-field amplifiers (XFA). Other microwave devices include the magnetron, klystron and solid state devices. The commonality for these devices is the emission of electromagnetic energy in the microwave, radio frequency (RF) or other band with wavelengths larger than the infrared region of the spectrum. Typically, microwave tubes are robust and very expensive, however since they are used in many critical systems they are routinely replaced prior to their failure to maximize system up-time. This approach increases the lifetime cost of the systems as full-life usage of the tubes is often not realized. Thus a need exists for a way of discerning microwave tube degradation so that useful microwave tubes are not replaced prematurely. 
     SUMMARY OF THE INVENTION 
     The invention is designed to employ one or a multitude of sensors designed to allow operational monitoring of any of a variety of electromagnetic radiating tubes. Monitoring is conducted to detect a degradation in performance which can be used as a factor in deciding whether tube replacement is justified. Contrary to some past approaches that focused on averaged tube outputs, the invention is designed to examine individual tube pulses. 
     An object of this invention is to provide a technique for testing electromagnetic radiating tubes. 
     A further object of this invention is to provide a technique for testing microwave radiating tubes. 
     Still a further object of the invention is to provide a technique that tests the transmitting tube of a radar system. 
     Still yet another object of this invention is to provide a technique that tests the transmitting tube of a radar system by exploiting a characteristic indicative of a degrading transmitting tube. 
     Still a further object of this invention is to provide a technique that tests the transmitting tube of a radar system by assessing acoustic emissions of the transmitting tube. 
     Still a another object of this invention is to provide a technique that tests the transmitting tube of a radar system by assessing current characteristics corresponding to the tube. 
    
    
     Other objects, advantages and new features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanied drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a general block diagram illustrating an electromagnetic radiating device wherein sensors are disposed to monitor the device in accordance with the invention. 
     FIG. 2 illustrates an exemplary acoustic emission technique for monitoring an electromagnetic radiating device according to an embodiment of the invention. 
     FIGS. 3A-3B illustrate acoustic emissions of a non-degraded and degraded electromagnetic radiating source, respectively. 
     FIG. 4 illustrates an exemplary current sensing technique for monitoring an electromagnetic radiating device according to an embodiment of the invention. 
     FIGS. 5A-5B illustrate current sensed of a non-degraded and degraded electromagnetic radiating source, respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 schematically illustrates an apparatus  10  as may be used for discerning degradation of an electromagnetic radiating device  12 . Apparatus  10  includes one or more sensors  14   1 ,  14   2 , . . . ,  14   N ) that are disposed in a manner to detect a characteristic signal or signals from electromagnetic device  12  that will be used to ascertain whether device  12  is degrading in performance. Such sensors may be physically attached to, incorporated within, or placed remotely about electromagnetic device  12 . The sensors are operably coupled to a data processor  16  as by connections  18 . Connections  18  may be any considered suitable such as for example electrical, mechanical, optical (e.g. infrared link), magnetic or electromagnetic (e.g. RF link). Processor  16  is used to compare a characteristic signal from one or more sensors to an algorithm to identify degradation of the electromagnetic device. 
     By way of example, acoustic emission sensor  14   1  is used to monitor a 2J56 magnetron. The acoustic sensors may be placed at a variety of positions so that a precise location of magnetron anomalies may be determined. FIG. 2 illustrates an embodiment of an acoustic emission sensing system  19  such as may be used in the invention. 
     System  19  uses a conventional acoustic sensor  20  that is disposed within, on, or near an electromagnetic energy generator desired to be monitored. In radar applications, such a generator may take the form of a magnetron, a traveling wave tube or a klystron, for example. Though these tubes are provided by way of example, the invention is considered useful with a great variety of tubes,.of radar type or otherwise. 
     Output  22  of acoustic sensor  20  is fed to a preamplifier  24  having three gain settings of 20 dB, 40 dB and 60 dB with a high input impedance. Preamplifier output  26  is then fed to an acoustic energy amplifier  28  having a total gain achievable of 41 dB in 3 dB steps. Suitably amplified signal  30  is then integrated over a preselected time period via integrator  32 , pulse output  34  having its pulse shape cleaned in low-pass filter  36 . The filtered output  38  has its peak voltage sampled in sample-and-hold element  40 . Sampled voltage  42  is then cleaned in low-pass filter  44  to provide a cleaned output signal  46 . 
     This output may be used directly for examination purposes however a preferred embodiment of the invention has output  46  go to a digital data processor  48 , which uses predetermined algorithms to assess the condition of the transmitting tube based upon an acoustic characteristic. These algorithms are considered within the purview of those skilled in the art and can be statistically and/or empirically derived. An output  50  of the processor is then sent to a data collection and storage system  52  whose files are then made available for observation by a radar system operator. 
     FIG. 3A shows a fast Fourier transform of output signal  52  (in volts) of an acoustic emission sensor when a good RF signal  54  is emitted. FIG. 3B shows a characteristic output signal  56  (fast Fourier transformed) of an acoustic emission sensor monitoring a 2J56 magnetron when a bad RF signal  58  is emitted. Output signal  56  has an anomalous intensity which can then be appropriately analyzed by the data processor  48 . In this case, a decrease in acoustic signal corresponds to a failed RF pulse. Examples of acoustic emission sensors include piezoelectric devices, surface acoustic wave devices, and microelectromechanical systems (MEMS) devices. 
     Another example of a sensor arrangement is illustrated in FIG. 4. A current sensor system  60  uses a conventional current sensor  62  that is applied directly to the cathode of a radar transmitting tube under test. Typical tubes used in high power radio frequency applications incorporate a pulse type microwave amplifier to amplify a radar signal. An example of this is a pulsed magnetron tube. Though this specific type of tube is provided as an example, the invention is considered useful with a great variety of tubes, pulsed and otherwise. 
     The output of sensor  62  is an analog voltage signal  64 . Signal  64  is fed to a high-pass filter  66  used to pass frequency components known to be indicative of faulty radar pulses. It has been observed that faulty radar pulses have a significantly increased content of undesired high frequency components that are directly related to the current sensed at the transmitting tube&#39;s cathode lead. 
     For microwave frequency radar transmissions of the previously cited pulsed magnetron tube, a suitable filter, for example, is a Chebyshev design that blocks frequency components below 8 MHZ and passing those above 8 MHz. Filtered analog voltage output  68  is fed to a detector  70 , wherein a rectified analog output voltage  72  is produced whose amplitude is proportional to the amplitude of the high frequency components passing through high-pass filter  66 . 
     A smoothing operation is next performed wherein rectified voltage  72  is fed to a low-pass smoothing filter  74  to take out undesired fluctuations generated by the rectified detection process. Selection of such a smoothing filter is considered within the discretion of one skilled in the art, however, for example, it is know that for microwave radar transmissions, a suitable filter is a 15 MHZ low-pass. 
     Though the output of filter  74  may be used directly for analysis purposes, a preferred embodiment of the invention employs a threshold operation to facilitate use of the test data. For example, smoothed analog output voltage  76  can be provided as an input to a threshold amplifier  78  having a logic output  80  of the TTL (transistor-transistor logic) type. 
     In this example, if the amplitude of the analog voltage going into amplifier  78  is less than 0.3 volts, the amplifier generates a TTL output  80  of 0 (voltage&lt;0.8 volts) indicating a good radar pulse. If the amplitude of a pulse going into amplifier  78  is greater than 0.3 volts, then the amplifier generates a TTL output  80  of 1 (voltage&gt;2.0 volts) indicating that the pulse from the radar was bad. 
     The TTL logic output  80  from threshold amplifier  78  then goes to a digital data processor  82 , which uses predetermined algorithms to assess the condition of the transmitting tube based upon the rate of occurrence of the bad radar pulses. These algorithms are considered within the purview of those skilled in the art and can be statistically and/or empirically derived. An output of the processor  84  is then sent to a data collection and storage system  86  whose files are then available for observation by a radar system operator. 
     FIG. 5A shows a characteristic output signal  88  (in amperes) of a cathode current sensor monitoring a 2J56 magnetron when a good RF signal  90  is emitted. FIG. 5B shows a characteristic output signal  92  of a cathode current sensor monitoring a 2J56 magnetron when a bad RF signal  94  is emitted. Output signal  92  has an anomalous temporal shape which can then be appropriately analyzed by data processor  82 . 
     The invention provides a method and apparatus for detecting and analyzing individual electromagnetic pulses (e.g. microwaves), not just an average of these pulses. It further provides the ability to discern degradation of the electromagnetic radiating devices by using individually identified pulses in a prognostic algorithm. This invention, when used in a RADAR system, will provide improvements in readiness, performance, maintainability and reliability by keeping personnel constantly apprized of the condition of the RADAR&#39;s high-power microwave tubes. The invention will reduce maintenance labor by reducing the time needed to locate and correct system malfunctions. It should reduce the number of required maintenance personnel, and their training requirements. 
     The invention may be applied to any electromagnetic emitting device, and may make use of any variety or plurality of sensors including but not limited to electrical, magnetic, electromagnetic, thermal, acoustic, optical, ionizing radiation and chemical sensors. The parameters used in the prognostic algorithm may be selected for optimized performance based on the specific device being monitored. Though the invention is considered highly usable with pulsed type transmitting tubes, other types of tubes are also considered usable with the invention, including a wide variety of electromagnetic radiating tubes. 
     Obviously, many modifications and variations of the invention are possible in light of the above description. It is therefore to be understood that within the scope of the claims the invention may be practiced otherwise than as has been specifically described.