Patent Publication Number: US-2015074984-A1

Title: Methods for Manufacturing Klystron Transmitters for Use in Weather Radar Systems

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of and claims priority to U.S. non-provisional patent application Ser. No. 13/223,942 entitled “Klystron Transmitters,” filed on Sep. 1, 2011, which is incorporated herein by reference in its entirety. 
    
    
     RELATED ART 
     A weather radar system transmits at a specific frequency, typically between 2.7 Giga-Hertz (GHz) and 3.0 GHz, pulses that reflect from various meteorological scatterers, such as rain, snow, hail, and/or sleet. The weather radar system receives and measures the pulse returns to provide weather data indicative of meteorological events within range of the system. Typically, the weather data is grouped into bins, and each bin is associated with a particular geographic region. In this regard, each bin indicates the measured reflectivity of pulses that are reflected from the associated region, and such measured reflectivity is indicative of the type of meteorological scatterers, if any, within such region. 
     Many weather radar systems use a Klystron transmitter to generate the pulses used for reflectivity measurements. As known in the art, a Klystron transmitter uses a linear-beam vacuum tube, referred to as a “Klystron,” that is used to amplify the pulses for transmission. In general, Klystron tubes allow precise control of output amplitude, frequency, and phase relative to other types of transmitters. In weather applications, Klystron tubes are operated at high power, and the Klystron tube, as well as the circuitry for driving the Klystron tube, is expensive. Techniques for improving performance and reducing the costs of weather radar systems are generally desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the disclosure. Furthermore, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a block diagram illustrating an exemplary embodiment of a weather radar system using a Klystron transmitter having universal core circuitry designed for a plurality of frequency ranges, such as a low S-band, a high S-band, and a C-band. 
         FIG. 2  is a block diagram illustrating an exemplary embodiment of processing circuitry, such as is depicted by  FIG. 1 . 
         FIG. 3  is a block diagram illustrating an exemplary embodiment of a transmitter module for a Klystron transmitter, such as is depicted by  FIG. 1 . 
         FIG. 4  is a block diagram illustrating an exemplary embodiment of splitter circuitry, such as is depicted by  FIG. 1 . 
         FIG. 5  is a flow chart illustrating an exemplary method of manufacturing a batch of Klystron transmitters for use in weather radar applications. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure generally relates to Klystron transmitters for use in weather radar systems. In one exemplary embodiment, a Klystron transmitter has a transmitter module for operating with any of various Klystron tubes designed for different frequency ranges, such as a low S-band between about 2.7 GHz and 3.0 GHz, a high S-band between about 3.4 GHz and 3.7 GHz, and a C-band between about 5.6 and 5.65 GHz. Each of the Klystron tubes is designed to have similar operating characteristics, such as output power and operating voltages. As an example, in one embodiment, each Klystron tube is designed to have the same output power (e.g., about 1 Mega-Watts (MW) or greater) and the same operating voltage (e.g., about 70 kilo-Volts (kV)). In addition, the transmitter module has driver circuitry for driving the Klystron tube of the transmitter, and such driver circuitry is operable over a wide frequency range so that the same driver circuitry can be used for any of the contemplated bands. Accordingly, the same core transmitter circuitry can be used for any of the Klystron tubes allowing a manufacturer to control which of the contemplated bands is implemented by selecting the appropriate Klystron tube and stable local oscillator (STALO) for the desired band. By using the same core design of the transmitter circuitry for all of the Klystron tubes, the overall manufacturing and implementation costs of Klystron transmitters can be significantly reduced. 
       FIG. 1  depicts an exemplary embodiment of a weather radar system  10  employing a Klystron transmitter  12  having universal core circuitry  14  for enabling the transmitter  12  to transmit pulses in any of a plurality of contemplated frequency ranges depending on the type of Klystron tube connected to the circuitry  14 , as will be described in more detail hereafter. In one exemplary embodiment, the Klystron transmitter  12  is designed to transmit at any frequency within a low S-band between about 2.7 GHz and 3.0 GHz, a high S-band between about 3.4 GHz and 3.7 GHz, and a C-band between about 5.6 and 5.65 GHz, depending on the type of Klystron tube connected to the circuitry  14 . 
     In this regard, if the transmitter  12  is to be used to transmit pulses in the low S-band, then the universal core circuitry  14  is connected, as shown, to a Klystron tube  15  and a STALO  25  that are both designed for communication in the low S-band. However, if the transmitter  12  is to be used to transmit pulses in the high S-band, then the universal core circuitry  14  is connected to a Klystron tube  16  and a STALO  26  that are both designed for communication in the high S-band in lieu of the Klystron tube  15  and STALO  25  shown by  FIG. 1 . If the transmitter  12  is to be used to transmit pulses in the C-band, then the universal core circuitry  14  is connected to a Klystron tube  17  and a STALO  27  that are both designed for communication in the C-band in lieu of the Klystron tube  15  and STALO  25  shown by  FIG. 1 . In other embodiments, other types of Klystron tubes and STALOs may be used to enable the transmitter  12  to transmit pulses in other frequency ranges. 
     Accordingly, to enable the transmitter  12  to transmit pulses in one of the contemplated frequency ranges (low S-band, high S-band, or C-band), a user connects the universal core circuitry  14  to the appropriate Klystron tube and STALO for communication in the desired frequency range. So connecting the appropriate Klystron tube and STALO configures the transmitter  12  for transmitting pulses in the desired frequency range without requiring the user to make further changes or adjustments to the universal core circuitry  14 . In this regard, each Klystron tube  15 - 17  is designed to have overlapping input characteristics relative to the other Klystron tubes  15 - 17  so that the universal core circuitry  14  can provide the same operational inputs to any of the Klystron tubes  15 - 17 . As an example, the universal core circuitry  14  may comprise driver circuitry  33  that drives the connected Klystron tube with pulses of the same amplitude and power regardless of which Klystron tube  15 - 17  and STALO  25 - 27  are actually connected to the circuitry  14 . The universal core circuitry  14  also may be configured to provide the same operating voltage (e.g., about 70 kV) to the connected Klystron tube regardless of which Klystron tube  15 - 17  and STALO  25 - 27  are actually connected to the circuitry  14 . Further, the universal core circuitry  14  is designed to drive the connected Klystron tube with pulses in any of the contemplated frequency ranges. Thus, a user may change the transmit frequency of the transmitter  12  merely by swapping the connected Klystron tube  15  and STALO  25  with a different Klystron tube ( 16  or  17 ) and STALO ( 26  or  27 ) designed to operate in a different band. 
     Referring to  FIG. 1 , the system  10  has processing circuitry  36  that is configured to generate pulses at a frequency based on the STALO  25  that is connected to the transmitter  12 . For example, when the STALO  25  is connected to the transmitter  12 , as shown by  FIG. 1 , the processing circuitry  36  transmits pulses in the low S-band. However, when the STALO  26  is connected to the transmitter  12  instead of the STALO  25 , the processing circuitry  36  transmits pulses in the high S-band. Further, when the STALO  27  is connected to the transmitter  12  instead of the STALO  25 , the processing circuitry  36  transmits pulses in the C-band. For illustrative purposes, it will be assumed hereafter unless otherwise indicated that the STALO  25  is connected to the transmitter  12 , as shown by  FIG. 1 , such that the processing circuitry  36  transmits pulses in the low S-band. 
     The pulses generated by the processing circuitry  36  are received and amplified by the driver circuitry  33 , which drives the connected Klystron tube  15  with the amplified pulses. In one exemplary embodiment, the Klystron tube  15  amplifies the pulses to a high power state, such as about 1 MW or greater, though other power ranges are possible in other embodiments. The amplified pulses pass through splitter circuitry  41  to antenna  44  from which the pulses wirelessly propagate. As the pulses propagate through the atmosphere, they reflect from objects, such as meteorological scatterers, and return to the antenna  44 . The splitter circuitry  41  separates such returns from the pulses output by the Klystron tube  15  and transmits the returns to a receiver  49 . Such returns are measured by the processing circuitry  36 , and the circuitry  36  processes the returns to define weather data  55  indicative of meteorological events within range of the system  10 . Such data is transmitted to a weather data processing system  52 , which uses the data for weather applications, such as displaying a radar weather map. Commonly-assigned U.S. Provisional Patent Application No. 61/472,773, entitled “Systems and Methods for Calibrating Dual Polarization Radar Systems” and filed on Apr. 7, 2011, which is incorporated herein by reference, describes exemplary techniques for processing returns and forming weather data. 
     Note that since the universal core circuitry  14  is operable for any of the contemplated frequency ranges, manufacturing of a large number of Klystron transmitters  12  is facilitated. In this regard, it is unnecessary for a manufacturer to match different Klystron tubes  15 - 17  with different versions of the core circuitry  14  during manufacturing since the same universal core circuitry  14  can be used with any of the Klystron tubes  15 - 17 . Further, since a larger number of manufactured units will utilize the same parts, better pricing of the parts for the circuitry  14  can likely be obtained. In addition, publishing an operator&#39;s manual for the circuitry  14  of the transmitter  12  is simplified since the same version of the core circuitry  14  is used for each transmitter  12 . Various other benefits and savings may be realized by using the same universal core circuitry  14  regardless of which contemplated frequency range is desired. 
       FIG. 2  depicts an exemplary embodiment of the processing circuitry  36 . The processing circuitry  36  comprises a coherent oscillator (COHO)  63  that generates pulses at a specific frequency. For illustrative purposes, assume that the desired transmit frequency for the transmitter  12  is about 3.0 GHz and that the COHO frequency is about 30 Mega-Hertz (MHz), though other frequencies may be used in other embodiments. As shown by  FIG. 2 , the COHO  63  is coupled to a pulse modulator  66  that receives the pulses generated by the COHO  63 . The pulse modulator  66  is configured to perform pulse code modulation to provide a conditioned pulse at the COHO frequency, which is 30 MHz in the current example. 
     The pulse modulator  66  is coupled to a STALO socket  69 , which is configured to receive the STALO  25  ( FIG. 1 ) after the universal core circuitry  14  has been manufactured. Thus, a user may select which STALO  25 - 27  he or she desires to use based on the desired transmit frequency for the transmitter  12  and plug the selected STALO  25 - 27  into the socket  69 , thereby electrically coupling such selected STALO  25 - 27  to the universal core circuitry  14 , receiver  49 , and other components of the processing circuitry  36 . The pulse modulator  66  is coupled to a mixer  71  ( FIG. 3 ). 
       FIG. 3  depicts an exemplary embodiment of a transmitter module  72  on which the universal core circuitry  14  resides. Referring to  FIG. 3 , the mixer  71  mixes the pulses from the modulator  66  ( FIG. 2 ) with pulses generated by the STALO  25  ( FIG. 1 ), which as described above is selected to provide the desired transmit frequency for the transmitter  12 . In the current example in which the COHO frequency is about 30 MHz and the desired transmit frequency for the transmitter  12  is about 3.0 GHz, the STALO frequency may be about 2970 MHz. The pulses output by the mixer  71  are at the desired transmit frequency for the transmitter  12  (i.e., 3.0 GHz in the current example). 
     As shown by  FIG. 3 , the mixer  71  is coupled to a bandpass filter  74 , which filters the pulses output by the mixer  71 . In one exemplary embodiment, the filter  74  has a relatively narrow passband, such as about 30 MHz or less centered around the desired transmit frequency (e.g., 3.0 GHz in the current example), but other passbands are possible in other embodiments. 
     The bandpass filter  74  is coupled to a broadband attenuator  77  of the driver circuitry  33 , and the broadband attenuator  77  attenuates the pulses for input to a driver amplifier  79 . In one exemplary embodiment, the broadband attenuator  77  is a high-power radio frequency (RF) resistor, but other types of attenuators are possible. The driver amplifier  79  is a broadband device capable of amplifying pulses at least in the contemplated frequency ranges (e.g., at least between 2.7 GHz and 5.65 GHz in the instant embodiment) with sufficient power to drive the Klystron tubes  15 - 17 . 
     The driver amplifier  79  is coupled via a control line  81  ( FIG. 1 ) to a signal processor  82  ( FIG. 2 ) of the processing circuitry  36 , which controls the on/off state of the amplifier  79 . In this regard, the signal processor  82  turns on the amplifier  79  just before a pulse arrives at the input of the amplifier  79  and turns off the amplifier  79  just after the pulse leaves the amplifier  79 . Accordingly, while a pulse is at the input of the amplifier  79 , the amplifier  79  is turned on and amplifies the pulse. However, shortly after a pulse leaves the driver amplifier  79 , the amplifier  79  is turned off until just before the arrival of the next pulse. Thus, between pulses, the driver amplifier  79  is prevented from outputting electrical energy. 
     The output of the driver amplifier  79  is coupled to a broadband attenuator  85 , which attenuates the pulses output by such amplifier  79 . In one exemplary embodiment, during the time period that a pulse is at the input of the amplifier  79 , the amplifier  79  saturates such that the output is at a precise voltage (i.e., the amplifier&#39;s saturation voltage). Further, the broadband attenuator  85  attenuates the output of the amplifier  79  such that the output voltage is lowered to a particular voltage within a desired input range for the Klystron tube  15 . Note that this voltage is the same regardless of which Klystron tube  15 - 17  is actually connected to the driver circuitry  33 . In one exemplary embodiment, the broadband attenuator  85  is a high-power RF resistor, but other types of attenuators are possible. 
     As shown by  FIG. 3 , the broadband attenuator  85  is coupled to a Klystron tube socket  89 , which is configured to receive the Klystron tube  15  ( FIG. 1 ) after the universal core circuitry  14  has been manufactured. Thus, a user may select which Klystron tube  15 - 17  he or she desires to use based on the desired transmit frequency for the transmitter  12  and plug the selected Klystron tube  15 - 17  into the socket  89 , thereby electrically coupling such selected Klystron tube  15 - 17  to the universal core circuitry  14  and, specifically to at least to the broadband attenuator  85 , as well as other components of the transmitter module  72 , as will be described in more detail hereafter. 
     The Klystron tube  15  is configured to amplify the pulse provided by the driver circuitry  33 , thereby significantly increasing the pulse&#39;s power. As an example, in one exemplary embodiment, the pulse provided by the driver circuitry  33  is about 50 Watts (W), and the Klystron transmitter  15  amplifies the pulse to about 1.0 MW or greater. The other Klystron tubes  16  and  17  are configured to similarly amplify pulses from the driver circuitry  33  to the same power level when either such tube  16  or  17  is used in lieu of the Klystron tube  15 . 
     The Klystron tube socket  89  is coupled to an arc detector  90 , which is configured to detect whether there is an arc present in the output of the Klystron tube  15 . If such an arc is present, the arc detector  90  turns off the Klystron tube  15  such that it is prevented from operating at least temporarily. The presence of an arc in the tube&#39;s output is indicative of an abnormal condition that could damage the Klystron tube  15  or other equipment, and the detector  90  may be configured to provide a warning, such as an audio or visual message, in response to an arc detection. 
     As shown by  FIG. 3 , pulse generation circuitry  91  is coupled to the Klystron tube socket  89  and provides electrical power to the Klystron tube  15  through the socket  89 . In one exemplary embodiment, the voltage of the power signal supplied by the circuitry  91  is about 70 kV, but other voltages are possible in other embodiments. To provide such a high voltage, the circuitry  91  comprises a direct current (DC) power supply  94  that provides a DC power signal at a specific voltage, such as about 15 kV. The DC power supply  94  is coupled to a high power modulator  96 , which modulates the power signal to provide a series of pulses at approximately the same frequency as those amplified by the Klystron tube  15 , as will be described in more detail hereafter. The modulator  96  is coupled to a transformer  99 , which increases the voltage of the pulses to the desired operating voltage of the Klystron tube  15  (e.g., 70 kV in the instant example). 
     The modulator  96  is coupled via a control line  101  ( FIG. 1 ) to the signal processor  82  ( FIG. 2 ) of the processing circuitry  36 , which controls the modulation performed by the modulator  96 . In this regard, the signal processor  82  controls the timing and frequency of the pulses output by the modulator  96  such that these pulses, which control the on/off state of the Klystron tube  15 , arrive at the Klystron tube  15  at about the same time as the pulses from the driver amplifier  79 . Specifically, a high power pulse from the modulator  96  arrives at and turns on the Klystron tube  15  just before a pulse arrives at the Klystron tube  15  from the driver amplifier  79 . Further, the Klystron tube  15  stops receiving the high power pulse from the modulator  96 , thereby turning off the Klystron tube  15 , just after the Klystron tube  15  stops receiving the pulse from the driver amplifier  79 . Accordingly, while a pulse from the driver amplifier  79  is at the input of the Klystron tube  15 , the Klystron tube  15  is turned on and amplifies the pulse. However, shortly after a pulse from the driver amplifier  79  leaves the Klystron tube  15 , the Klystron tube  15  is turned off until just before the arrival of the next pulse from the driver amplifier  79 . Thus, between pulses from the driver amplifier  79 , the Klystron tube  15  is prevented from outputting electrical energy. 
     As shown by  FIG. 3 , the Klystron tube socket  89  is coupled to a heat supply  111 , a vac-ion supply  112 , and a solenoid supply  113 . The heat supply  111  is configured to provide heat for the Klystron tube  15 , and the vac-ion supply  112  is configured to provide a vacuum for the Klystron tube  15 . Further, the solenoid supply  113  has an electromagnet  114  that is used to focus the beam of the Klystron tube  15 , and the electromagnet  114  operates under the control of a solenoid  115  within the supply  113 . In one exemplary embodiment, the power, heat, vacuum, and electromagnetic field respectively provided by the pulse generation circuitry  91 , the heat supply  111 , the vac-ion supply  112 , and the solenoid supply  113  are not dependent on which Klystron tube  15 - 17  is plugged into the socket  89 . Accordingly, any of the Klystron tubes  15 - 17  may be plugged into the socket  89  without having to adjust the configuration or operation of the pulse generation circuitry  91 , the heat supply  111 , the vac-ion supply  112 , and the solenoid supply  113 . In other embodiments, other configurations are possible. 
       FIG. 4  depicts an exemplary embodiment of the splitter circuitry  41 . The splitter circuitry  41  comprises a circulator  122  that is coupled to the Klystron tube socket  89  and receives the pulses output by the Klystron tube  15  that is plugged into the socket  89 . The pulses pass through the circulator  122  to a tuner  126 , a bandpass filter  127 , and a harmonic filter  128  before being wirelessly transmitted via the antenna  44  ( FIG. 1 ). 
     Reflections of the pulses are received by the antenna  44  and pass through the harmonic filter  128 , the bandpass filter  127 , and the tuner  126  to the circulator  122 . The circulator  122  separates the reflections from the pulses output by the Klystron tube  15 . Such reflections are transmitted to the receiver  49 , which filters and processes the reflections before they are received by the signal processor  82  ( FIG. 2 ). The signal processor  82  then uses the received reflections to define the weather data  55 . 
     As described above, either of the Klystron tubes  16  or  17  may be used in lieu of the Klystron tube  15 . Further if the Klystron tube  16  is used, the STALO  26  associated with such tube  16  is preferably used in lieu of the STALO  25 . If the Klystron tube  17  is used, the STALO  27  associated with such tube  17  is preferably used in lieu of the STALO  27 . In such embodiments, the operation of the transmitter  12  is the same as that described above except that pulses are generated at a different frequency. For example, if the Klystron tube  16  and STALO  26  are used, then pulses in the high S-band are generated. If the Klystron tube  17  and STALO  27  are used, then pulses in the C-band are generated. 
     In the embodiments described above, the Klystron tubes  15 - 17  (and associated STALOs  25 - 27 ) are configured for operation in the bands of 2.7 to 3.0 GHz (low S-band), 3.4 to 3.7 GHz (high S-band), and 5.6 to 5.65 GHz (C-band), respectively. In other embodiments, other frequency ranges are possible. As a mere example, in one exemplary embodiment, the Klystron tubes  15 - 17  (and associated STALOs  25 - 27 ) are configured for operation in the bands of 2.7 to 2.9 GHz (low S-band), 3.6 to 3.7 GHz (high S-band), and 5.6 to 5.65 (C-band), respectively. Such bands may be less susceptible to interference and, thus, provide better overall performance. 
     In this regard, the band from about 3.0 GHz to about 3.7 GHz is generally reserved for military operation. However, the band from about 3.4 GHz to about 3.7 GHz is not currently used by the military at least to a significant extent, and it is possible that the military would grant a petition to use such band for weather radar applications. However, limiting the low S-band to less than 2.9 GHz and the high S-band to greater than 3.6 GHz provides guard-bands that help to separate the pulses generated by the transmitter  12  from the signals currently used by the military from about 3.0 GHz to about 3.4 GHz. Accordingly, the pulses generated by the transmitter  12  are less susceptible to interference by the military signals and also less likely to interfere with the military signals. Yet other bands are possible in other embodiments. 
     An exemplary method of manufacturing a batch of Klystron transmitters  12  for use in weather radar systems will be described in more detail below with reference to  FIG. 5 . For illustrative purposes, assume that each Klystron transmitter  12  in the manufactured batch is to be manufactured for transmission in a respective band selected from three contemplated frequency ranges: low S-band between 2.7 and 2.9 GHz, a high S-band between 3.6 and 3.7 GHz, and C-band between 5.6 and 5.65 GHz. In other embodiments, other frequency ranges are possible. 
     As shown by block  212  of  FIG. 5 , a batch of Klystron transmitter modules  72  are manufactured without a Klystron tube for the socket  89  or a STALO for the socket  69 . Each such module  72 , however, has the universal core circuitry  14  shown by  FIG. 3 . 
     As shown by block  215  of  FIG. 5 , one of the transmitter modules  72  is selected for completion. In block  218 , a determination is made whether the selected transmitter module  72  is to transmit pulses in the low S-band. If so, a Klystron tube  15  and STALO  25 , which are designed for communication in the low S-band, are selected as shown by block  222 . If the transmission band of the selected transmitter module  72  is not the low S-band, then a determination is made whether the selected transmitter module  72  is to transmit pulses in the high S-band, as shown by block  219 . If so, a Klystron tube  16  and STALO  26 , which are designed for communication in the high S-band, are selected as shown by block  225 . If the transmission band of the selected transmitter module  72  is not the low S-band or the high S-band, then the selected transmitter module  72  is to transmit pulses in the C-band since the other contemplated bands have been eliminated in the selection process. In such case, a Klystron tube  17  and STALO  27 , which are designed for communication in the C-band, are selected as shown by block  227 . Note that the determinations in blocks  218  and  219  may be based on a customer order specifying the desired transmission band for a completed transmitter  12 . 
     As shown by blocks  235  and  238 , the selected Klystron tube is inserted into the Klystron tube socket  89  of the selected transmitter module  72 , and the selected STALO is inserted into the STALO socket  69  of the selected transmitter module  72 . At this point, the manufacturing of a Klystron transmitter  12  is complete, and a determination is made whether there are any more transmitter modules  72  in the batch that have yet to complete the manufacturing process, as shown by block  241 . If so, another transmitter module  72  in the batch is selected for completion, and the process of selecting a suitable Klystron tube and STALO for this other transmitter module  72  is repeated.