JP2005339892A - Traveling-wave tube and array antenna using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small/thin traveling-wave tube capable of reducing the weight and cost of an array antenna. <P>SOLUTION: Multiple-stage iris coupling is formed in a waveguide of an output circuit 123 to provide functions of a band-pass filter and a band-reject filter for the output circuit 123, whereby spuriousness generated by nonlinear distortion of this small/thin traveling-wave tube 1 is removed, and the need of a filter conventionally installed in a subsequent stage of the small/thin traveling-wave tube 1 for removing the spuriousness is obviated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a traveling wave tube, and more particularly to a traveling wave tube that is required to be reduced in size and diameter.

  Conventionally, in a broadcasting / communication satellite system that uses the Ka band (21 GHz band) where rainfall attenuation increases, high power is radiated only in areas where severe rain attenuation occurs, and normal power is radiated in other areas. An array antenna is used to reduce the power consumption of the satellite repeater by forming such a radiation pattern.

  FIG. 9 is a diagram showing a conventional array antenna. As shown in FIG. 9, the array antenna includes a beam forming device (BFN: Beam Forming Network) 2 that forms and controls a beam, a traveling wave tube 4 that amplifies a microwave output from the beam forming device, and a traveling wave tube. Are provided with a filter 5 for filtering the output microwave and a horn 3 for outputting the filtered microwave.

  In this array antenna, by controlling the output power and the output phase from the horn 3 by the beam forming device 2, the distribution (radiation pattern) of the radiation power from the satellite can be freely formed.

  In this case, in order to form a radiation pattern more freely, a large number (for example, several hundreds) of horns 3 need to be two-dimensionally densely arranged at intervals of about 1.0 to 1.5λ. A small-sized and small-diameter traveling wave tube in which the cross-sectional dimension of the traveling wave tube 4 that is a high-power and high-efficiency amplifier is miniaturized is required (for example, see Non-Patent Document 1).

  The traveling wave tube 4 as the final stage amplifier is desirably used in a saturation region where the power efficiency is high in order to increase the power efficiency of the transponder. On the other hand, when the traveling wave tube 4 is operated in the saturation region, non-linear distortion of output power and output phase occurs, and generally spurious out of band occurs in digital modulation.

  That is, as shown in FIG. 10, the input spectrum as shown in FIG. 10A becomes a spectrum having a desired out-of-band spurious as shown in FIG. 10B due to the nonlinear distortion of the traveling wave tube.

For this reason, a bandpass filter (BPF: Band Pass Filter) that passes the output signal spectrum of only a desired band as a filter 5 after the traveling wave tube 4 or a band rejection filter that removes spurious out of the desired band. (BEF: Band Eliminate Filter) needs to be installed separately to obtain a signal spectrum as shown in FIG.
Jin Nakagawa and Takao Murata, “Current Status and Prospects of 21 GHz Band Satellite Broadcasting Research”, IEICE Technical Report, IEICE, June 17, 2003, IEICE Tech. 103No. 139, p. 1-4

  However, when the traveling wave tube 4, the filter 5, and the horn 3 are connected in this way, the array antenna described above requires a large number (for example, several hundreds) of the filters 5, which increases the weight and costs. The problem of rising will arise.

  Therefore, the present invention provides a small-sized and small-diameter traveling wave tube that can eliminate the filter and reduce the weight and cost of the array antenna by providing a filter function in the output circuit of the small-sized and small-diameter traveling wave tube. The purpose is to provide.

  In a traveling wave tube having an output circuit that uses a waveguide installed in parallel with the axial direction of the low-speed wave circuit, the first invention for solving the above-mentioned problem has a filter characteristic in the output circuit. It is characterized by.

  In the present invention, the microwave is filtered by the output circuit. Therefore, it is not necessary to provide a filter after the traveling wave tube.

  According to the present invention, since the filter function is provided in the output circuit, it is not necessary to provide a filter in the subsequent stage, and the configuration can be simplified.

  Further, if the traveling wave tube of the present invention is mounted on an array antenna, it is not necessary to provide a filter after the output circuit, and the array antenna can be reduced in weight and cost.

  The present invention will be described below with reference to the drawings.

  FIGS. 1-8 is a figure which shows the small and small diameter traveling wave tube of one Embodiment of this invention.

  In FIG. 1, a small and narrow traveling wave tube 1 of the present embodiment includes an electron gun unit 11 that emits electrons, a high-frequency circuit unit 12 that processes microwaves, a collector unit 13 that captures electrons, and an electron beam. And a package 15 for supporting the main body and radiating heat.

  The electron gun unit 11 includes a cathode 111 that emits electrons, a heater 112 that heats the cathode 111, and an insulating ceramic 113 around the cathode 111 and the heater 112.

  The high-frequency circuit unit 12 includes an input circuit 121 that inputs a microwave, a helix delay circuit 122 that interacts the microwave and an electron beam, and an output circuit 123 that outputs an amplified microwave.

  The focusing device section 14 includes a plurality of magnets 141 and magnetic poles 142 that generate a magnetic field in the electron beam path.

  The electrons emitted from the cathode 111 in the vacuum of the electron gun unit 11 are accelerated by a high voltage of several kV or more, and at the same time, the electrons are focused by the magnetic field formed by the focusing device unit 14, and the focused electrons are thin electrons. A beam is formed and passes inside the helix of the helix delay circuit 122.

  On the other hand, the microwave is guided from the input circuit 121 to the helix delay circuit 122 and travels along the helical helix delay circuit 122 from the upstream side (cathode 111 side) of the electron beam, and its axial velocity is the electron beam velocity. When almost synchronized, an interaction between the electron beam and the microwave occurs, and the microwave power is amplified. The amplified microwave is extracted from the output circuit 123 connected to the helix delay circuit 122.

  The electron beam that has finished the interaction with the microwave collides with the collector 13 and is captured, and the kinetic energy of the electrons is converted into thermal energy.

  In order to reduce the size and diameter of the small-sized and small-diameter traveling wave tube 1, in a general traveling-wave tube, a cross section of an input circuit 121 and an output circuit 123 that are installed perpendicular to the electron beam emission direction is shown. In order to reduce the size, the microwave is placed in parallel with the radiation direction of the electron beam, and the amplified microwave is taken out from the output part at the extreme end of the traveling wave tube.

  Moreover, the waveguide which comprises the input circuit 121 and the output circuit 123 uses the flat waveguide whose height is lower than a normal waveguide, and is aiming at size reduction and diameter reduction.

  Furthermore, in the small-sized and small-diameter traveling wave tube 1 of the present embodiment, the output circuit 123 is provided with functions of a band rejection filter and a band pass filter depending on the purpose.

  FIG. 2A shows an example of a band rejection filter in which one inductive window is provided in a waveguide like the output circuit 123, and FIG. 2B shows an example of a band pass filter.

  When a window is provided in the waveguide, it is considered that a lumped constant jB is connected in parallel to the transmission line, and therefore the equivalent circuit is as shown in FIG.

In that case, the susceptance B of the inductive window of FIG.
In the case of BEF, B = −λg / a · cot ² πd / 2a (1 + cosec ² πd / 2a)
In the case of BPF, B = −λg / a · cot ² πd / 2a
And the reflection coefficient γ is γ = −jB / (jB + 2).
It can be calculated by

  Here, λg is the guide wavelength, a is the waveguide width of the input / output section, and d is the waveguide width of the inductive window section.

  From these two equations, it is shown that the filter characteristics can be designed only by the combination of a and d, which are elements in the width direction of the waveguide, and even in a waveguide with a reduced height like an output circuit. It is considered possible to have filter characteristics.

  FIG. 4 shows an example in which a band-pass filter is configured by 5-stage iris coupling. The height of this bandpass filter (the length of A in the figure) is configured with a conventional waveguide (height: 4.318 mm) and a flat waveguide with a reduced height, such as an output circuit. FIG. 5 shows a comparison of filter characteristics in the case of the above (height 1.318 mm).

  In FIG. 5, S11 indicates the reflection characteristic of the filter, and S21 indicates the pass characteristic of the filter.

  As shown in FIG. 5, the filter characteristics are exactly the same even when the height is changed, and the same filter characteristics can be obtained even in a waveguide with a reduced height as when designed with a waveguide of normal dimensions. I understand. The same applies to the band rejection filter.

  For this reason, in this embodiment, a 5-stage iris coupling as shown in FIG. 4 is provided in the waveguide of the output circuit, and the output circuit has the function of a band-pass filter.

  When a waveguide type filter is used in the 21 GHz band, a length of about 10 mm per stage is required. Since the output circuit of the small-sized and small-diameter traveling wave tube of this embodiment has a length of about 80 mm, this output circuit can have a steep filter function of 7 to 8 stages.

  If the small-sized and small-diameter traveling wave tube 1 of this embodiment is used, the satellite-mounted array antenna can be configured as shown in FIG. 6 and the conventionally required filter can be omitted. The development cost for reducing the diameter of the filter can be reduced, the weight of the array antenna can be reduced, and the manufacturing cost of the array antenna can be reduced.

  Further, when the horn 3 having a normal waveguide size is connected to the small-sized and small-diameter traveling wave tube 1 of the present embodiment, the height of the flat waveguide is obtained by using a step structure as shown in FIG. (1.418mm) can be converted to normal waveguide height (4.148mm).

  Even in such a configuration, as shown in FIG. 8, the filter characteristics are generally maintained, and the desired filter characteristics can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the small-sized and small diameter traveling wave tube of one Embodiment of this invention, and is the sectional drawing. It is a figure which shows the example of the waveguide filter which provided the inductive window. It is a figure which shows the equivalent circuit of the waveguide filter which provided the inductive window. It is a figure which shows the example of the bandpass filter by a 5-stage iris coupling. It is a figure which shows the filter characteristic at the time of changing height. It is a figure which shows the structure of the array antenna using the small and small diameter traveling wave tube of one Embodiment of this invention. It is a perspective view which shows an output circuit when connecting the horn of a normal waveguide dimension to the small-sized and small diameter traveling wave tube of one Embodiment of this invention. It is a figure which shows the filter characteristic. It is a figure which shows the structure of the conventional array antenna. It is a figure of the signal spectrum which shows the spurious by the nonlinear distortion of the conventional traveling wave tube.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Small and thin traveling wave tube 11 Electron gun part 111 Cathode 112 Heater 113 Insulating ceramic 12 High frequency circuit part 121 Input circuit 122 Helix delay circuit 123 Output circuit 13 Collector part 14 Focusing part 141 Magnet 142 Magnetic pole 15 Package 2 Beam forming apparatus 3 Horn 4 Traveling wave tube 5 Filter

Claims (2)

In a traveling wave tube with an output circuit that uses a waveguide installed parallel to the axial direction of the slow wave circuit,
A traveling wave tube characterized in that the output circuit has a filter characteristic.   An array antenna comprising the traveling wave tube according to claim 1.

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