V. Ya. Noskov, S. M. Smolskiy
In the 6th part of the review the operation principle description of homodyne and autodyne intro-pulse short-range radar (SRR) systems is given. In such systems, the time delay of the reflected signal is less than radio-pulse duration, and therefore the reflected signal reception is performed simultaneously with the transmission of probing radio-pulse. Under the condition that radiated and received radio-pulses do not overlap, the output is absent. It allows the possibility of forming the far limit of detection zone on a range.
The research results for an autodyne response transients, at switching-on the oscillator in different operation modes, both in the case of without the frequency modulation (FM) (i.e., Doppler systems) and in slow and fast FM modes are discussed. The problem of determination of oscillation amplitude and frequency as well as the bias voltage, under influence of reflected signal is solved by means of «step» method according to which the separate solutions at each time interval were determined with the account of the previous step results.
In result of researches it was stated that the transient initiated by the first reflected pulse causes firstly the variations in oscillation’s amplitude and frequency on sine law. At this step the autodyne SRRs are similar to the homodyne systems keeping the linear transform of own oscillations. The transient duration and the peculiarities of autodyne partial response formation under affects of the further reflected pulses essentially depends on an distortion parameter.
Under influence of the first set of reflected radiation from the ensemble of bright points of the distributed object, the autodyne response spectrum is a linear superposition of single-frequency components. The following influences cause the combination interaction of all spectral components. It can be explained by autodyne frequency variations, which lead to the non-linearity of the reflected phase shift. The level of this non-linearity is defined by the distortion parameter value, that depends on both the reflected signal level and the time of two-way propagation.
The equality of the distortion parameter to unity is the boundary of principally different autodyne responses. When less than unity, the autodyne response transient is completed by steady-state values. When more than unity, the transient may accompany by steak-slip and hysteresis variations. This phenomenon may cause, even for movement with constant speed, the non-periodicity of an autodyne signal.
Using the synchronization of radio-pulse autodyne be low-level signal provides the improvement of its radar energy potential up to 10-15 dB due to decreasing of phase fluctuations. This engineering solution allows the reduction of transient time and widening of dynamic range of autodyne SRR. As such a signal source in the promising autodyne module of hybrid-integrated technology we can recommend the additional FM oscillator made on the small-current mesa-planar Gunn diode