rus
Issue #7-8/2022
N.I. Skripkin, A.V. Shmelev, A.I. Pronikov, I.M. Ivanov
COMPLEXED UHF-MODULE WITH SYNCHRONIZED M-TYPE GENERATORS
COMPLEXED UHF-MODULE WITH SYNCHRONIZED M-TYPE GENERATORS
INTRODUCTION
Modern microwave technology is characterised by a wide variety of generator types. Among these, the magnetron has established itself as a reliable, simple to operate and economical vacuum appliance of high efficiency.
In the 2-centimetre wavelength range, the nomenclature of developed magnetrons is quite large and depends on specific tasks. The pursuit to develop super-power magnetron designs (0.5 MW or more) [1] is a relevant but not easy task.
In the late 80’s the experimental design bureau at the Pluton factory developed unique single samples of magnetrons in the 2-centimeter wavelength range with a pulse power up to 1 MW. These magnetrons presented inverted-coaxial designs that had both advantages and disadvantages. Special exhaust units and modulator benches were built for them, the pumping was performed for several days and training for up to two months. The device was produced with an integrated technological magnetic electrodischarge pump (MEDP), which allowed of continuous pumping during operation of the magnetron in the generator mode. The magnetrons needed a long training period because it was necessary to get rid of sparks and stabilise the electrical parameters.
In the 1990s, after the economic downturn, many companies in the electronics industry suffered. This situation also affected the experimental design bureau at the Pluton factory. It was disbanded, and the number of employees decreased sharply. The range of products was also sharply reduced. It was not possible to retain all technological processes for production of single magnetrons.
Nowadays, super-power magnetrons are beginning to be in demand for specific tasks, such as generating high-power pulsed signals for probing. The production of magnetrons that have not been in manufacturing for more than 30 years is a challenge, both in terms of time and in terms of the cost of developing the processes.
This paper describes a "microwave module" installation which uses the coherent power summation method of two magnetrons in a power summator. The magnetrons are powered by a high voltage dual channel modulator. Series-produced magnetrons in the 2-centimeter wavelength range with a pulsed power of 270-300 kW allow of obtaining a pulsed power at the output of the summator at least 500 kW.
Based on previous studies [2, 3], in our opinion, it is found that the most efficient and simple in design method for coherent summation of power of two generators with a waveguide output is to use a waveguide 3-decibel bridge as summator. In this case the output power of the synchronised device within the synchronisation bandwidth can reach 95% of the total power of the generators. The synchronisation scheme is shown in Fig.1.
Mutual phasing (synchronisation) of two magnetrons (M1 and M2) is provided by the phase shifter (F), matching is provided by the short-circuit plunger (P). The summed signal is sent to the output (antenna) path of the radar or to the input of the hot measurement device (HMD). Precise selection of the plunger position ensures maximum summation factor. The UHF generator module is designed to generate probing pulse signals in a multifunctional transceiver radar measurement complex.
SELECTION OF A SUMMATOR
Classic waveguide bridges are divided into three groups [4]:
slotted waveguide bridge with wide or narrow wall coupling;
waveguide bridge based on a 2nd waveguide tee (E and H);
ring-type waveguide bridges.
Narrow-wall bridges are characterised by the best coordination and electrical strength. The waveguide bridge with narrow wall coupling (Fig.2) was selected for further work. Electrical strength has been achieved due to excess pressure of sulphur hexafluoride (sulphur hexafluoride gas) in the waveguide path. The computational model of such a summing device in the software for three-dimensional modelling of microwave processes is shown in Fig.2.
Figure 3 shows equal summation of the signals from shoulder 1 and shoulder 2 to shoulder 4.
The calculation was carried out in the frequency range 14.5 to 15.6 GHz. The gain (S-parameters) for different positions of the tuning (matching) pin are shown in Fig.4–7. The tuning pin can be moved between 2.5 and 4.0 mm in the waveguide path of the power combiner.
Figure 8 shows a simplified diagram of the bridge. Numbering of the arms is: 1, 2 – input, 4 – output.
The dissipation matrix of an ideal summator can be represented as
[S]=[0 jd f jg jd 0 jg f f jg 0 jd jg f jd 0],
where d characterises directivity of the slotted bridge; f and g are the levels of the branching signals. Based on the power balance, we have:
d2 + f2 + g2 = 1.
In this case, ideally the elements S11 = S22 = S33 = S44 = 0.
The S-parameters were measured for the fabricated summer on a four-arm (eight-pole) transmission ratio meter.
At 15GHz, the position (length) of the adjusting pin was ~3mm, ensuring perfect matching, directivity and branching balance of the signals.
Measurement of S-parameter modules:
S11 ≈ S22 ≈ S33 ≈ S44 ≈ 0.1 ± 0.05
S12 ≈ S21 ≈ S34 ≈ S43 ≈ 0.1 ± 0.05
S13 ≈ S31 ≈ S24 ≈ S42 ≈ 0.7 ± 0.05
S14 ≈ S41 ≈ S23 ≈ S32 ≈ 0.7 ± 0.05.
Measured power balance:
(S11)2 + (S12)2 + (S13)2 + (S14)2 ≈ 1 ± 0.04.
By changing the length of the adjusting pin, the symmetry of the bridge is broken and the balance between the inputs (outputs) is missing. Accordingly, the bridge is fully compliant with the requirements for summing and synchronising signals when correctly adjusted.
COHERENT SUMMING MODE
The coherent power summation mode of the two magnetrons was tested in the microwave module setup shown in Fig.9.
The following operating parameters are obtained:
The modulating pulse, current pulse, HF envelope and output signal spectrum (phase-synchronised mode) are shown in Figs.10 and 11. Cooling modes with integrated high efficiency coolers ensured smooth operation of the module. The overpressure in the waveguide path was created by sulphur hexafluoride (sulphur hexafluoride) and was equal to 2 atm.
Figure 12 shows the oscillograms of the modulating pulse, the current pulse and the HF envelope for a non-synchronised magnetron operating mode. The HF envelope is a beat oscillogram.
The developed microwave module is a device consisting of two magnetrons, powered from two-channel, high-voltage, pulse modulator and power summator placed in a special 750 × 550 × 800 mm cabinet in one of the walls of which the waveguide path for its further connection through the necessary elements to the antenna (Fig.13, 14). The mass of the UHF module device is ~ 150 kg.
The microwave module is controlled by a remote computer using special programmes that allow of adjusting in each channel: power supply, amplitude and duration of the modulating pulse, pulse repetition frequency, magnetron incandescence current (Fig.15, 16).
CONCLUSIONS
Pluton JSC was the first in Russia to create a microwave module installation in the 2-centimeter wavelength range which made use of the principle of coherent summation of the power of two commercially available magnetrons. The cost of the installation and manufacturing time is many times less than the magnetron being newly developed with the parameters presented in this article.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Modern microwave technology is characterised by a wide variety of generator types. Among these, the magnetron has established itself as a reliable, simple to operate and economical vacuum appliance of high efficiency.
In the 2-centimetre wavelength range, the nomenclature of developed magnetrons is quite large and depends on specific tasks. The pursuit to develop super-power magnetron designs (0.5 MW or more) [1] is a relevant but not easy task.
In the late 80’s the experimental design bureau at the Pluton factory developed unique single samples of magnetrons in the 2-centimeter wavelength range with a pulse power up to 1 MW. These magnetrons presented inverted-coaxial designs that had both advantages and disadvantages. Special exhaust units and modulator benches were built for them, the pumping was performed for several days and training for up to two months. The device was produced with an integrated technological magnetic electrodischarge pump (MEDP), which allowed of continuous pumping during operation of the magnetron in the generator mode. The magnetrons needed a long training period because it was necessary to get rid of sparks and stabilise the electrical parameters.
In the 1990s, after the economic downturn, many companies in the electronics industry suffered. This situation also affected the experimental design bureau at the Pluton factory. It was disbanded, and the number of employees decreased sharply. The range of products was also sharply reduced. It was not possible to retain all technological processes for production of single magnetrons.
Nowadays, super-power magnetrons are beginning to be in demand for specific tasks, such as generating high-power pulsed signals for probing. The production of magnetrons that have not been in manufacturing for more than 30 years is a challenge, both in terms of time and in terms of the cost of developing the processes.
This paper describes a "microwave module" installation which uses the coherent power summation method of two magnetrons in a power summator. The magnetrons are powered by a high voltage dual channel modulator. Series-produced magnetrons in the 2-centimeter wavelength range with a pulsed power of 270-300 kW allow of obtaining a pulsed power at the output of the summator at least 500 kW.
Based on previous studies [2, 3], in our opinion, it is found that the most efficient and simple in design method for coherent summation of power of two generators with a waveguide output is to use a waveguide 3-decibel bridge as summator. In this case the output power of the synchronised device within the synchronisation bandwidth can reach 95% of the total power of the generators. The synchronisation scheme is shown in Fig.1.
Mutual phasing (synchronisation) of two magnetrons (M1 and M2) is provided by the phase shifter (F), matching is provided by the short-circuit plunger (P). The summed signal is sent to the output (antenna) path of the radar or to the input of the hot measurement device (HMD). Precise selection of the plunger position ensures maximum summation factor. The UHF generator module is designed to generate probing pulse signals in a multifunctional transceiver radar measurement complex.
SELECTION OF A SUMMATOR
Classic waveguide bridges are divided into three groups [4]:
slotted waveguide bridge with wide or narrow wall coupling;
waveguide bridge based on a 2nd waveguide tee (E and H);
ring-type waveguide bridges.
Narrow-wall bridges are characterised by the best coordination and electrical strength. The waveguide bridge with narrow wall coupling (Fig.2) was selected for further work. Electrical strength has been achieved due to excess pressure of sulphur hexafluoride (sulphur hexafluoride gas) in the waveguide path. The computational model of such a summing device in the software for three-dimensional modelling of microwave processes is shown in Fig.2.
Figure 3 shows equal summation of the signals from shoulder 1 and shoulder 2 to shoulder 4.
The calculation was carried out in the frequency range 14.5 to 15.6 GHz. The gain (S-parameters) for different positions of the tuning (matching) pin are shown in Fig.4–7. The tuning pin can be moved between 2.5 and 4.0 mm in the waveguide path of the power combiner.
Figure 8 shows a simplified diagram of the bridge. Numbering of the arms is: 1, 2 – input, 4 – output.
The dissipation matrix of an ideal summator can be represented as
[S]=[0 jd f jg jd 0 jg f f jg 0 jd jg f jd 0],
where d characterises directivity of the slotted bridge; f and g are the levels of the branching signals. Based on the power balance, we have:
d2 + f2 + g2 = 1.
In this case, ideally the elements S11 = S22 = S33 = S44 = 0.
The S-parameters were measured for the fabricated summer on a four-arm (eight-pole) transmission ratio meter.
At 15GHz, the position (length) of the adjusting pin was ~3mm, ensuring perfect matching, directivity and branching balance of the signals.
Measurement of S-parameter modules:
S11 ≈ S22 ≈ S33 ≈ S44 ≈ 0.1 ± 0.05
S12 ≈ S21 ≈ S34 ≈ S43 ≈ 0.1 ± 0.05
S13 ≈ S31 ≈ S24 ≈ S42 ≈ 0.7 ± 0.05
S14 ≈ S41 ≈ S23 ≈ S32 ≈ 0.7 ± 0.05.
Measured power balance:
(S11)2 + (S12)2 + (S13)2 + (S14)2 ≈ 1 ± 0.04.
By changing the length of the adjusting pin, the symmetry of the bridge is broken and the balance between the inputs (outputs) is missing. Accordingly, the bridge is fully compliant with the requirements for summing and synchronising signals when correctly adjusted.
COHERENT SUMMING MODE
The coherent power summation mode of the two magnetrons was tested in the microwave module setup shown in Fig.9.
The following operating parameters are obtained:
The modulating pulse, current pulse, HF envelope and output signal spectrum (phase-synchronised mode) are shown in Figs.10 and 11. Cooling modes with integrated high efficiency coolers ensured smooth operation of the module. The overpressure in the waveguide path was created by sulphur hexafluoride (sulphur hexafluoride) and was equal to 2 atm.
Figure 12 shows the oscillograms of the modulating pulse, the current pulse and the HF envelope for a non-synchronised magnetron operating mode. The HF envelope is a beat oscillogram.
The developed microwave module is a device consisting of two magnetrons, powered from two-channel, high-voltage, pulse modulator and power summator placed in a special 750 × 550 × 800 mm cabinet in one of the walls of which the waveguide path for its further connection through the necessary elements to the antenna (Fig.13, 14). The mass of the UHF module device is ~ 150 kg.
The microwave module is controlled by a remote computer using special programmes that allow of adjusting in each channel: power supply, amplitude and duration of the modulating pulse, pulse repetition frequency, magnetron incandescence current (Fig.15, 16).
CONCLUSIONS
Pluton JSC was the first in Russia to create a microwave module installation in the 2-centimeter wavelength range which made use of the principle of coherent summation of the power of two commercially available magnetrons. The cost of the installation and manufacturing time is many times less than the magnetron being newly developed with the parameters presented in this article.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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