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In principle, autodynes (AD) represent a totality of the microwave oscillator and registration (extraction) means for the autodyne signals. The AD signals are usually extracted according to variations of currents or voltages in the power source circuit of the active element (AE) of the microwave (or mm-wave) oscillator. Practically, in this case, any microwave oscillator without essential variations of its design can be used as AD. The special autodyne modules, which signals are detected on variations of the amplitude or the oscillation frequency, are developed and manufactured in a series of applications. At that, slight complication of the oscillator design is quite defensible since it provides improvement of autodyne system parameters (sensitivity, the radar potential characteristics, the dynamic range, etc.) and expansion of its functional possibilities (measurement of a velocity, the passed path, a distance, etc.). In this review, the analysis of construction principles of autodyne reception-transmission modules and various oscillators as well as circuit solutions of registration means for autodyne response is described. In addition, some results of original authors’ investigations are presented. In the first section of the paper, the functional diagrams of autodyne sensors, which provide the measurement possibilities of the target velocity, the passed path, an acceleration, and direction of movement, are considered. At first, the circuit of the simplest radar sensor, which uses the traditional microwave oscillator as the transceiver and may be made on the Gunn diodes, IMPATT diodes, or BARRIT diodes, is discussed. The autodyne signal extraction in it is fulfilled in the power source circuit of the oscillating diode with the help of the specific circuit of the registration unit (RU). One of distinctive features of autodyne short-range radar systems compared to the systems with the homodyne transceiver architecture is the presence of anharmonic distortions of the radar signal. At that, we should note that the signal distortion degree is defined by the feedback parameter of Cfb value, which depends on the reflection signal amplitude and on the distance to the target. In the case negligible values of this parameter (when Cfb<<1), autodyne signals have practically the harmonic shape, as in the homodyne systems. With increase of reflected signal level and the distance to the target, the Cfb value grows and, accordingly, the signal distortion degree increases. This phenomenon, which is caused by nonlinearity of the phase incursion of reflected emission due to autodyne frequency variations, is mainly manifested in the mm-wave range, especially, in its shorter part. Factually, this phenomenon restricts the dynamic range of autodynes short-range radars and creates problems for signal processing. To reduce autodyne signal distortions it is offered to stabilize the autodyne frequency, for instance, by means of additional high-Q cavity application in the oscillator of the feedback on frequency. In this paper we describe the engineering solutions of autodyne modules, which can realize these suggestions. Then, the description on construction principles of transceivers is presented, in which autodyne signals are registered not only in the power source circuit but on variation of oscillation amplitude and frequency. At that, amplitude variations are registered with the help of one or two detector diodes embedded additionally in the module. The frequency variations are transformed from the microwave oscillator in the low-frequency region with the help of additional AD, which operates as the autodyne frequency converter and after them are detected. Signals obtained have the relative phase displacements (offsets), which provide a possibility of reliable determination of movement direction of the reflecting targets owing to the sign change of its phase difference depending on the sign of the radial components of the relative movement velocity. At the end of this section, the description of the so-called double-diode autodyne transceiver module is presented. Constructively, it represents two in series-connected oscillating modules realized in the «passage» manner in chambers of the flange type. The comparative advantages of the double-diode autodyne are shown. In the second section of this review, at first, we consider the general principles of registration circuits design for autodyne signal in the AD bias circuits. At that, we show that the current for devices with the volt-ampere curve of N-type (the Gunn diode) and the voltage for devices of S-types (IMPATT and BARITT diodes) are optimal registered parameters of the autodyne response from the point of view of the best stability of the transfer functions. Then for the autodyne on the Gunn diode, at first, the traditional principle of voltage signal extraction with the help of the one-port connected in series into the power source circuit. Such one-ports are usually made on the resistor, the choke (inductance) or the transformer base. Circuits on the base of transistors and op-amps are described, which under some conditions provide the autodyne signal selectivity in the required frequency band and improvement of some AD parameters. Nevertheless, we must note that all above-considered registration devices have the common drawback, which relates to the presence of the low-frequency load reaction on the AD operation mode in the microwave area. This reaction degrades the AD operation stability and causes variations of its mode when changing the Gunn diode specimen. Besides, the simplest registration circuits do not provide the AD output protection against penetration of the power source noise. After that, the implementation principle is examined and description of specific RU circuit solution is given for autodynes on Gunn diodes, which provide the optimal conditions of transformation of Gunn diode current variations into the output signal voltage in the short-circuit mode at output. This mode is provided under condition of the voltage source application. At that, improvement of AD noise characteristics occurs as well.
投稿的翻译标题Modern hybrid-integrated autodyne oscillators of microwave and mm-wave ranges and its’ application. Part 11. Fundamentals of autodyne implementation
期刊Успехи современной радиоэлектроники
Published - 2019



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