Research of low frequency components of a magnetron oscillator spectrum

In this article the resonant properties of the plant for the investigation of Ku-band magnetrons’ operation in the low-frequency domain from 100 kHz to 35 MHz were experimentally investigated. Improving the electronic devices’ quality is an important task for Ukrainian scientists. It will increase the duration and reliability of sophisticated equipment based on electronic devices, as well as improve the production economic efficiency in the electronics industry. The M-type device, the magnetron, was selected as the studied object. Low-frequency oscillation modes were influenced to the magnetrons’ output spectrum quality. Theses modes can occur in the device itself, as well as in the power supply circuits or be induced from the ether. It is hypothesized that spurious oscillations which may impair the electronic devices output spectrum quality, in particular magnetrons, will be amplified at frequencies which the resonances in the device, the supply circuits, and the system as a whole are observed. The experimental study is aimed to determine the frequency domain of the possible occurrence of these spurious oscillations. The measuring plant for magnetron research consists of a magnetron, a wave type transducer, an absorbent power meter, and a spectrum analyzer. The total error of this setup does not exceed ±4 dB. The resonant properties study of this plant in the low-frequency domain was performed according to the classical scheme of the resonant properties study of oscillating circuits. The total relative error of resonance properties measurements did not exceed ±8 %. As a result of research, it was discovered a pronounced resonant peak of the magnetron supply circuits in the 30 MHz band, magnetron filament circuits have a pronounced resonant peak in the 20 MHz band, the magnetron has two pronounced peaks in the 5 and 20 MHz band and two peaks in the 15 and 35 MHz band, the system as a whole has two pronounced peaks in the 10 and 30 MHz band.


Introduction
In the context of the rapid development of electronic devices and the continuous industry expansion the quality improvement is of particular importance, both to ensure the duration and reliability of the operation of sophisticated electronic devices, and to increase rapidly the economic efficiency of production in the electronics industry. Therefore, the quality improvement, operation duration and reliability of electronic devices are constantly given special attention [1].
The most important conditions for improving the electronic devices' quality, the duration and reliability of their operation are the standardization of general requirements for the electronic devices (ED) quality assurance, the study and standardization of the various factors parameters influencing on the devices, and the creation of appropriate test methods.
The electronic devices' quality is the set of electronic devices properties that determine their ability to perform specified functions under certain operating conditions.

Analysis of recent research and publications
These properties are characterized by the following indicators: the electronic devices' mission, their reliability, adaptability, operation safety, service convenience, transportability, etc., as well as the properties determined by the ergonomic, aesthetic and environmental properties of the device, the degree of standard and unified products in it.
Depending on the type, design and operating conditions of the ED, some indicators may be missing. The list of required indicators for certain devices types is set out in the relevant regulatory documents.
The electronic devices' quality control includes input inspection, technological process accuracy inspection and acceptance inspection. Input inspection is carried out to ensure the electron devices' production by raw materials and semi-finished products that meet the requirements of regulatory and technical documentation for such devices manufacture. The results of the technological processes accuracy inspection are used to purposefully regulate the process itself. This inspection type is subjected to both technological operations and devices or devices that produce as an operations result; such inspection is also called operational. During the operational inspection the reasons are identified that lead to the violation of the technological operations accuracy, the limits of regulation of the technological process parameters are determined. Ready electron devices are subject to acceptance inspection. Based on the results of acceptance inspection, the possibility of industrial production of these devices is decided. Such inspection includes qualifying acceptance, periodic electron devices' tests, as well as durability, safety and (if necessary) type tests. If the test results are unsatisfactory, the defects' causes are analyzed and remedial measures are taken.
In the electronic industry of Ukraine, the electronic devices' quality management is carried out by improving the quality of both raw materials, semi-finished products and components, and the equipment production and work culture. The set of controls and management facilities and their connections, which ensure the industrial release of the desired quality ED in a timely manner with minimal material cost, is called the quality management system [2]. Electronic devices quality management involves the quality planning (forecasting, normalization), its accounting and control, analysis and estimation, the decision production to perform planned tasks.
Electronic device quality planning involves ensuring that quality assurance is fulfilled through the development of scientifically based tasks to improve (or maintain the achieved level) quality based on the best use of available resources, and the implementation of organizational measures, research and development activities.
Consideration covers the collection, accumulation and information processing about the actual quality level of electronic devices and the factors that affect it at the stages of development, production and electronic devices operation, as well as the implementation of the planned measures to ensure the assigned tasks. Inspection consists of checking that the results meet the intended standards or requirements. Assessment of the achieved level of electronic devices quality and detection of actual values deviations of quality indicators from the planned ones allow to evaluate more correctly the quality work of the industries, the team and individual performers. Solutions aimed at eliminating the detected deviations in the electronic devices quality, which require the obligatory development of measures to ensure these solutions implementation and the conditions to stimulate the production, teams and individual workers to improve the quality of the products they produce.
In addition to the factors discussed earlier [3,4], the magnetrons output spectrum quality is influenced by the low-frequency oscillation modes which can occur in the device itself, as well as in the power circuits or be induced from the ether.
Thus, it is relevant to determine the frequency domains of possible occurrence of spurious oscillations, which will impair the output spectrum quality of the electron devices, in particular the most common M-type device -the magnetron.
It is suggested that spurious oscillations can be amplified at frequencies where resonances in the device, supply circuits, and the system as a whole are observed.
Thus this work purpose is experimental investigation of amplitude-frequency resonance magnetron performances, circuit supply and whole system in low frequency domain.

Experimental plant
No theoretical studies of the M-type devices behavior in the low-frequency domain have been performed.
Due to the fact that the magnetron power supplies have various constructive and schematic embodiments, theoretical studies on this matter do not seem possible.
The results of such circuits experimental studies are considered here because of their such system theoretical description is impossible.
An industrial Ku-band magnetron was selected for a study. In addition, measurements were made in the such devices power circuits and in the whole system.
The experimental studies were performed on the plant according to the scheme shown in Fig. 1. Unfortunately, for each specific this scheme embodiment ( Fig. 1) such studies need to be repeated. The measuring system contains a standard signal generator AFG-3051 with absolute error in setting the frequency ±10 -6 Hz, oscilloscope GDS-3000, which I. Moshchenko, O. Nikitenko, Chen Xin allows to measure the signal amplitude with a relative error ±2 %, the magnetron power supply, the valve, the spectrum analyzer C4-27, the wattmeter.

Results of the experimental investigation
The procedure is as follows: to the object being investigated (device, power circuits, and system as a whole), the standard signal generator AFG-3051 provides a calibrated signal in the frequency band 100 kHz -35 MHz with a rms amplitude 1 V.
Using the GDS-3000 oscilloscope, the signal passed through the object being examined was observed and measured.
The measurement results are shown in Fig. 2.
The y-axis in the Figure (Fig. 2) shows the amplitude relative to the resonance amplitude. Fig. 2 shows that the magnetron supply circuits have a pronounced resonance peak in the 30 MHz band.
The magnetron filament circuits have a pronounced resonance peak in the 20 MHz band.
In fact, the magnetron has two pronounced peaks in the 5 and 20 MHz band and two much smaller amplitude peaks in the 15 and 35 MHz band.
The system as a whole has two pronounced peaks in the 10 and 30 MHz band.

Conclusion
Experimental studies of high-voltage power circuits on the part of the connector separately from the device, and the system on "cold measurements" revealed spurious resonant modes, which are located in the 0.1-35 MHz frequency domain. Spectral power, measured in the same range on "hot measurements" through the cathode junction, has a distribution that repeats by the form the output circuits amplitude-frequency response of the devices on the cathode input.
Undoubtedly, the power circuits resonances will create low-frequency modulation of the anode voltage, which may result in lateral components and combining components, which in turn leads to a deterioration in the magnetron output quality.
It is clear that appropriate measures must be taken to attenuate and suppress the spurious resonances in the power circuits.