The operating principle of the channel bearing the phase measurement method

The antenna system has APM pict (a) horizontal beam shape close to a circle which is offset with respect to the center of APM. Rotation of the diagram at an angular velocity = 30 rev / s results in amplitude modulation of the received signal with a frequency =30 Hz (pict (b)).At point with an arbitrary azimuth azimuth phase envelope of the received AM signal lags the phase of the AM signal received in a northerly direction (point 1) for (3.2) where - the time required to rotate through an angle of NAM.

Figure 3.2 The radiation pattern of the antenna phase ARM

(a); azimuth signals received at points 1 and 2

(b); spectrum of the received signal (in and

On board equipment block diagram)

The basic equation of ARM that implements phase method of determining azimuth, has the form

By measuring the phase of the envelope of the received signal, it is possible to directly determine the azimuth of the point of reception. It follows that the determination of the azimuth error is numerically equal to the phase measurement error.

For phase measurement on LA with APM transmit a reference signal which is frequency-modulated subcarriers with an average frequency oscillations kHz. Modulating voltage signal is at a frequency of 30 Hz at a constant phase corresponding to the phase of the signal received at the workstation from a northerly direction. Thus, the signal at the point of APM with the azimuth is given by

(3.3)

where - the amplitude of the signal; and - ratios AM azimuth and a reference signal; - An index of frequency modulation

The onboard equipment of aircraft detected, ARM signal Rx receiver divided filters F30 and F10, respectively tuned to the frequency and. From the reference signal after the frequency detector BH stands constant phase signal with a frequency that is supplied to the IF phase meter, which served as the azimuth signal of the same frequency.

Accuracy azimuth phase channel. Accuracy of the channel depends mainly on the change in the azimuthal phase of the signal at its interference with signals reflected from surrounding objects APM. Assuming that only one such object with a complex coefficient

reflection

(3.4),

where , using the above formula to the direct and reflected signals and carrying out appropriate transformations, we can find the error azimuth

(3.5)

where - the delay of the reflected signal relative to the direct and - azimuth of the reflecting object. The maximum value of this error

.(3.6)

For example, if = 0.1, the = 5, 63 °, which does not meet the current requirements to the means of navigation.