GB2392004A

GB2392004A - Magnetron device

Info

Publication number: GB2392004A
Application number: GB0229357A
Authority: GB
Inventors: Naoki Tsuji; Yasujirou Minamitani
Original assignee: New Japan Radio Co Ltd
Current assignee: New Japan Radio Co Ltd
Priority date: 2002-05-13
Filing date: 2002-12-17
Publication date: 2004-02-18
Anticipated expiration: 2022-12-17
Also published as: GB0229357D0; GB2392004B; JP4004850B2; JP2003331746A

Abstract

A magnetron device in which a magnetron 1 and a filter 3 for blocking an electromagnetic wave in a, predetermined frequency band are coupled to each other through a transmission line L. At least one of resonant frequencies of a circuit system constituted by the magnetron, the transmission line and the filter is caused to be approximately coincident with a frequency of at least one of spurious components radiated from the magnetron which is included in a stop frequency band of the filter. The resonant frequencies of the circuit systems from the magnetron to the filter are adapted to a frequency to suppress a radiation. Consequently, The Q value of The frequency can be decreased so that a magnetron device having a high stability can be implemented.

Description

( - 1 MAGNETRON DEVICE

The present invention relates to a magnetron device including a filter in order to reduce a spurious radiation, and more particularly to a magnetron device having a good stability of oscillation.

Since a magnetron is inexpensive and easy to handle, it has 5 widely been used for a transmitter of a radar device or the like.

However, the magnetron is one of devices which are hard to suppress a spurious radiation in respect of an oscillating mechanism thereof. On the other hand, recently, the spurious radiation has been limited more strictly for a device for radiating a microwave and a magnetron device lo including a filter to reduce the spurious radiation has been developed.

In general, a magnetron is oscillated in a main mode referred to as a n mode and various other spurious radiations are generated. A spurious radiation in a mode referred to as a - 1 mode which is caused by the resonant circuit of a magnetron gives the highest radiation power.

In a magnetron of a vane strap type in which the arc mode is oscillated in a 9.4 GHz band, for example, the arc - 1 mode is present in the vicinity of 10.5 GHz and has a higher frequency band than the mode. By using a filter having a frequency in the mode in a pass band and a frequency in the - 1 mode in a stop band, the spurious radiation can be suppressed 20 Fig. 7 is a block diagram showing a conventional example. A microwave oscillated from a magnetron 1 is transmitted to a load such as an antenna of a radar device through an isolator 6 and a filter 3. The filter 3 is a band pass filter for setting a frequency in the mode to be a pass band and for setting a frequency in the - 1 mode to be a stop band, 25 a low pass filter, a band stop filter or me like. The isolator 6 is provided

- 2 for preventing the microwave oscillated by the magnetron 1 from influencing on the oscillation of a magnetron due to a reflected wave from the filter 3. In the magnetron device having such a structure, the spurious suppressing effect can be exactly produced based on a s characteristic peculiar to a filter and a design can also be carried out easily. In the magnetron device using the isolator 6, however, the cost of the isolator is high so that the cost of the device is hard to reduce.

Fig. 8 is a diagram showing another conventional example in which the magnetron 1 and the filter 3 are directly coupled to each other lo through a transmission line 7. In this case, a microwave reflected by the filter 3 is directly incident on the magnetron 1. For this reason, the reflected wave directly influences the oscillation of the magnetron 1.

Therefore, the line length of the transmission line 7 cannot be i determined arbitrarily and is to be set to a required length.

IS Conventionally, the line length of the transmission line has been settled to have a phase with which an output power in the mode can be led most effectively. In the magnetron device in which the line length is thus set, however, an oscillation in the mode is not stabilized and an operation is often carried out in the - 1 mode, that is, a frequency of a 20 so-called missing pulse rate is increased. Consequently, there is a problem that the stability of the oscillation is poor. Moreover, there is a problem that a spurious suppressing effect peculiar to the filter cannot be obtained.

25 As described above, in such a structure that the isolator is used, there is a problem that the cost of the isolator is high and the cost of the device is hard to reduce. With such a structure that the filter for

- 3 spurious suppression is directly coupled to the magnetron through the transmission line, moreover, there is a problem that the stability of the oscillation of the magnetron is poor and the spurious suppressing effect of the filter cannot be obtained sufficiently. The present invention 5 solves the problems described above and has an object to provide a magnetron device having such a structure that a magnetron and a filter are directly coupled to each other through a transmission line in which the stability of an oscillation is good.

In order to attain the object, a first aspect of the present lo invention is directed to a magnetron device in which a magnetron and a filter for blocking an electromagnetic wave in a predetermined frequency band are coupled to each other through a transmission line, wherein at least one of resonant frequencies of a circuit system constituted by the i magnetron, the transmission line and the filter is caused to be 5 approximately coincident with a frequency of at least one of spurious components radiated from the magnetron which is included in a stop frequency band of the filter.

A second aspect of the present invention is directed to the magnetron device according to the first aspect of the present invention, so wherein an adjusting mechanism for the resonant frequency is provided on the transmission line.

A third aspect of the present invention is directed to the magnetron device according to the first or second aspect of the present invention, wherein another transmission line is coupled to a load side of 25 the filter to which the magnetron and the transmission line are coupled and an adjusting mechanism for adjusting an output to be transmitted is provided on the another transmission line.

A forth aspect of the present invention is directed to the magnetron device according to the first, second or third aspect of the present invention, wherein at least one of resonant frequencies of a circuit system constituted by the magnetron, the transmission line and s the filter is caused to be approximately coincident with a frequency of 1 mode radiated form the magnetron.

Fig. 1 is a block diagram showing a magnetron device according to an embodiment of the present invention; 0 Fig. 2 is a diagram showing the measured result of an impedance of a magnetron shown in Fig. 1; Fig. 3 is a diagram showing the result of measurement of an impedance of a filter shown in Fig. 1; Fig. 4 is a chart showing the relationship between a is transmission line length and a missing pulse rate; Fig. 5 is a view for explaining a method of adjusting the resonant frequency of a transmission line according to the present invention; Fig. 6 is a view for explaining a method of adjusting an output 20 power to be transmitted according to the present invention; Fig. 7 is a block diagram showing a conventional example; and Fig. 8 is a block diagram showing another conventional example.

An embodiment according to the present invention will be described below. Fig. 1 shows an embodiment according to the present

- 5 invention in which a magnetron 1 is of a vane strap type, and a frequency in a n mode to be a main mode is 9.441 GHz and a frequency in a arc - 1 mode to be one of spurious components is 10.464 GHz.

Fig. 2 shows the measured result of an impedance Zm of the 5 magnetron 1 according to the present invention. Resonances corresponding to the mode and the - 1 mode are indicated as a marker 1 (ok) and a marker 2 (a), respectively. On the other hand, a filter 3 is a low pass filter for causing a frequency in the rr mode of the magnetron 1 to pass and for stopping a frequency in the - 1 mode, and lo has an impedance Zf shown in Fig. 3 The marker 1 (ok) and the marker 2 (of) are set to have frequencies which are equal to those in Fig. 2 (9.441 GHz and 10.464 GHz respectively). It is apparent from Fig. 3 that a reflection is hardly carried out in the microwave of a; mode and an almost complete reflection is carried out in the microwave of Tc - 1 mode. In 5 such a device, if the line length of a transmission line 2 is determined such that an output to be transmitted in the mode can be sent well, the resonance in the - 1 mode of the magnetron 1 has a Q value increased since the filter 3 is blocked in the same frequency band, that is, an almost complete reflection state is brought. For this reason, the so magnetron device in which the magnetron and the filter are coupled to each other through the transmission line according to the conventional example is not operated stably. In the present invention, therefore, a resonant frequency in a circuit system constituted by the magnetron 1, the transmission line 2 and the filter 3 is caused to be coincident with 25 the frequency in the - 1 mode in order to decrease the Q value of the resonance in the arc - 1 mode. By such a structure, a microwave energy in the If - 1 mode is subjected to a resistance loss by the resonance of the

- 6 transmission line so that the Q value is decreased.

A method of setting a length L of the transmission line 2 will be described as a method of adapting the resonant frequency in the circuit system constituted by the magnetron 1, the transmission line 2 5 and the filter 3 to the frequency in the - 1 mode. This method can be implemented by setting the sum of imaginary number components of an admittance in the circuit system to be zero. An impedance counting on the magnetron 1 is Zm = 0.786 + 0.205j in the - 1 mode as shown in Fig. 2, and a phase angle is 128 degrees. An impedance counting on the 10 filter 3 is Zf = 0.033 - 1. 149j as shown in Fig. 3, and a phase angle is 82 degrees. In order to set the imaginary number component of an admittance counting on the magnetron to be zero, therefore, it is preferable that a transmission line having a line length of 128 degrees should be added to the magnetron. On the other hand, in order to set 5 the imaginary number component of an admittance counting on the filter to be zero, it is preferable that a transmission line having a line length of -82 degrees should be added to the filter. Accordingly, it is preferable that the line length of the transmission line 2 should be set to 46 degrees (128 - 82 degrees). An effective wavelength Ag at a frequency 20 of 10.464 GHz in the - 1 mode is 36.76 mm since the used waveguide is a rectangular waveguide having a size of 22.9 mm x 10.2 mm.

Accordingly, the line length L of the transmission line is set to be L = 36.76 mm x (46/720) = 2.35 mm. Even if a line having a length which is integral times as great as Ag/2 is added to the transmission line, 25 equivalency can be obtained. Therefore, it is preferable that the line length It should be set to 2.35 mm, 20.73 mm, 39 11 mm or the like.

Fig. 4 shows the relationship between the line length of the

- 7 transmission line and the missing pulse. It is apparent from Fig. 4 that a range in which the magnetron is oscillated stably is L \/16. A value obtained by fixing the transmission line length and converting the dimensional allowable value into the allowable value of a frequency is set 5 to be the allowable value of a frequency when the resonant frequency of the transmission line is caused to be coincident with the frequency in the - 1 mode.

With reference to Fig. 5, next, description will be given to the

case where an adjusting mechanism for adjusting the resonant lo frequency of the transmission line is added. In Fig. 5, a rectangular waveguide 4 is used as a transmission line between the magnetron 1 and the filter 3, and the rectangular waveguide 4 is provided with a screw stub 8 for resonant frequency adjustment as a mechanism for adjusting a resonant frequency. The screw stub 8 is provided in order to compensate for a variation in the impedance in the - 1 mode of the magnetron. By adjusting such a length as to insert the screw stub 8 into the rectangular waveguide 8, a capacity value at a tip thereof can be adjusted to set the resonant frequency to have a desirable value.

In Fig. 6, another rectangular waveguide 5 is coupled to the to load side of the filter 3 and a screw stub 9 for transmitted output power adjustment in the n mode is added to the rectangular waveguide 5 as a mechanism for adjusting the transmitted output power in the embodiment shown in Fig. 5. In the case where the resonant frequency of the circuit system is caused to be approximately coincident with the 25 frequency in the - 1 mode, consequently, the oscillation in the mode is also influenced so that an output power is reduced. Therefore, the adjusting mechanism is provided to compensate for the reduction.

( - 8 Moreover, it is also possible to obtain the effect of compensating for a variation in the impedance in the TC mode of the magnetron 1. As shown in Fig. 6, accordingly, in the case where the length of the rectangular waveguide 4 is simply set to be a predetermined length and the screw 5 stub 8 for resonant frequency adjustment is not provided as well as the case where the rectangular waveguide 4 is provided with the screw stub 8 for resonant frequency adjustment, it is possible to obtain the effect of adjusting the oscillated output power in the mode. It is desirable that the screw stub 9 for transmitted output power adjustment should be lo provided from the filter 3 toward the load side. If the screw stub 9 is provided from the filter 3 toward the rectangular waveguide 4 on the magnetron 1 side, the impedance of the magnetron in the - 1 mode is influenced by the adjustment of the output power to be transmitted.

Consequently, the stability of the magnetron operation is reduced.

s While the case where the rectangular waveguide is used as the transmission line has been described in the above explanation, the present invention can also be implemented even if the transmission line is a coaxial line or a planar circuit. Moreover, there has been described the case where the filter is the low pass filter for causing the mode to go pass and for blocking the - 1 mode, the present invention can also be implemented by using a band pass filter or a band stop filter with such a structure that a main mode is passed and a spurious component is blocked. While there has been described the case where the main mode of the oscillation of the magnetron is set to be the mode and the 25 spurious component is set to be the n - 1 mode, it is a matter of course that the present invention is not restricted thereto.

As described above, in the present invention, the resonant

- 9 - frequencies of the circuit systems from the magnetron to the filter are made coincide with a frequency to suppress a radiation. Consequently, the Q value of the frequency can be decreased so that a magnetron device having a high stability can be implemented.

5 Moreover, the screw stub for resonant frequency adjustment or the screw stub for transmitted output adjustment is provided on the transmission line. Consequently, it is possible to compensate for a variation in the impedance of the magnetron. Thus, it is possible to obtain an advantage that the magnetron device can be manufactured lo with high yield.

Claims

l - 10 CLAIMS:

1. A magnetron device in which a magnetron and a filter for blocking an electromagnetic wave in a predetermined frequency band 5 are coupled to each other through a transmission line, wherein at least one of resonant frequencies of a circuit system constituted by the magnetron, the transmission line and the filter is caused to be approximately coincident with a frequency of at least one of spurious components radiated from the magnetron which is included in a stop lo frequency band of the filter.

2. The magnetron device of Claim 1, wherein an adjusting

mechanism for the resonant frequency is provided on the transmission line.

3. The magnetron device of any one of Claims 1 to 2, wherein another transmission line is coupled to a load side of the filter to which the magnetron and the transmission line are coupled and an adjusting mechanism for adjusting an output to be transmitted is provided on the 20 another transmission line.

4. The magnetron device of any one of Claims 1 to 3, wherein at least one of resonant frequencies of a circuit system constituted by the magnetron, the transmission line and the filter is caused to be 25 approximately coincident with a frequency of - 1 mode radiated from the magnetron.