RU2626405C2 - Homodyne radar - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: homodyne radar contains a receiving and transmitting antenna, a sounding signal generator, a circulator, a mixer, an amplifier, an amplitude modulator, a time window function generator, and an amplifier with a quadrature amplitude-frequency characteristic that are connected in a certain way.

EFFECT: reduction of the dynamic range of received signals, simplification of the radar.

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Description

The invention relates to the field of radar, and in particular to homodyne radar.

Known homodyne radar containing a probe signal generator, the output of which is connected through a circulator to the transmit-receive antenna, a mixer, one input of which is connected to the transmit-receive antenna, and the second to the output of the probe signal.

A disadvantage of the known radar are: the extremely large dynamic range of the output signals of the radar, in which the analog-to-digital converter (ADC) will not work; low speed, narrow functionality.

In order to eliminate these drawbacks, the proposed radar further comprises an amplifier, an amplitude modulator, the second input of which is connected to the output of the generator of the time window function, and an amplifier with a quadratic amplitude-frequency characteristic whose output is connected to the output of the radar.

Using the invention will reduce the dynamic range of the output signals of the radar, minimize the "blind" zone of the radar, compress (2 or more orders of magnitude) the frequency band of the broadband sounding signal (ZS) and thereby simplify the analog and digital parts of the structure of the radar, minimize its cost.

The essence of the invention is illustrated by Figures 1-6.

In FIG. 1 shows a structural diagram of a homodyne radar, where the following notation:

1. The probe signal generator

2. The circulator

3. Transmitting antenna

4. Mixer

5. Amplifier

6. Amplitude modulator

7. Amplifier with quadratic amplitude-frequency characteristic

8. Time window function generator

Figure 2 presents the law of change in the frequency of the probing and received signals.

In Figure 2 is indicated:

ƒ ₀ - carrier frequency of the AP, ƒ - frequency, t - time,

ƒ _b - beat frequency, directly proportional to the distance to the object R,

ƒ _min and ƒ _max - the minimum and maximum frequency of the chirp of the probing signal,

Δƒ _D is the frequency deviation of the ES,

t _R - time delay of the reflected signal, proportional to the distance to the object R,

T _m - period of modulation of ZS.

The Figure 3 presents the spectrum of the beat signal without S ₁ (f) and taking into account S ₂ (f) frequency correction.

Figure 4 shows the spectrum of the beat signal S (f) and the spectrum of the beat signal modulated by the time window function S _mod (f).

The Figure 5 presents the spectrum of the beat signal without S ₃ (f) taking into account S ₁ (f) transformations.

Homodyne radar operates as follows.

The output signal of the generator ZS 1 (Fig. 1), the frequency of which is controlled by the law of continuous linear frequency modulation (LFM) using the frequency modulator and the modulating signal generator (Fig. 2), is connected to the input of the first arm of the circulator 2. From the output of the second arm of the circulator 2, the signal is supplied to the transmit-receive antenna 3 and is radiated into space.

The signal reflected from the object is received by the transmitting and receiving antenna 3, from the output of which through the second and third arms of the circulator 2, this signal is fed to the first input of the mixer 4. The leakage signal of the probe signal generator 1 through the first and third arms of the circulator 2 is fed to the second input of the mixer 4. The mixer 4 multiplies the input signal reflected from the object with the reference signal of the probe signal generator 1 (leakage signal), which passed in the opposite direction from the first to the third arm of the circulator 2.

Given the low level of signals reflected from objects with a small effective scattering surface (EPR) - S _eff , the output signal of the mixer 4 (beat signal) is first amplified in a low-noise amplifier 5 (an amplifier with a small noise figure).

To implement the frequency expansion and decrease the dynamic range of the beat signal in a homodyne radar, the dependence of the received signal intensity on the distance (proportional to the beat frequency) is used by applying the nonlinear amplitude-frequency characteristic (AFC) of amplifier 7. The quadratic (in amplitude) frequency response is most easily implemented. Therefore, the use of a beating signal amplifier 7 with a quadratic frequency response equalizes the power of signals received from objects located at different distances and having the same value of S _eff . In this case, the dynamic range of all signals narrows to the dynamic range of the observed scene (Fig. 3).

However, in addition to the noted positive effect of narrowing the dynamic range, a problem arises of increasing the level of the side lobes of the uncertainty function of the chirp of the probing signal. This increase creates significant interference in the radar image of the scene - the spatial illumination of the screen in range, following the signal that corresponds to the reflection from the object.

.To eliminate this effect, as well as parasitic amplitude modulation of the probe signal generator in the homodyne radar, an amplitude modulator 6 is used, in which the beat signal (Fig. 4) is modulated in amplitude by the “time window” function as a function:

.

It is easy to show that in this case the envelope of the spectrum of the beat signal at the output of the amplitude modulator 6 will have the form of a function:

,

,

where: ω _b - beat frequency,

S (ω) is the spectral density of the beat signal.

, огибающая спектра сигнала биений, модулированная функцией «временного окна» S_mod(ω), на выходе усилителя с квадратичной АЧХ 7 (Фиг. 4) имеет более широкий основной лепесток и боковые лепестки, которые спадают обратно пропорционально третьей степени частоты.Unlike function

, the envelope of the spectrum of the beat signal, modulated by the “time window” function S _mod (ω), at the output of the amplifier with a quadratic frequency response 7 (Fig. 4) has a wider main lobe and side lobes that fall inversely with the third power of the frequency.

, и, следовательно, спектр огибающей сигнала биений будет иметь вид функции:Thus, the multiplication of the signal in the amplitude modulator 6 by the window function leads to compensation of the factor

, and, therefore, the envelope spectrum of the beat signal will have the form of a function:

As a result, an undesired increase in the level of the side lobes of the uncertainty function of the LFM signal will not be observed in the homodyne radar (Fig. 5).

Thus, the technical result from the use of the proposed technical solution is to simplify the radar, increase its functionality and reduce cost.

The inventive step of the proposed technical solution is confirmed by the distinctive part of the claims.

Literature

1. Transceiver homodyne radar. Koshurinov E.I. RF patent №2189055 from 01.20.2000, IPC G01S 13/08, prototype.

Claims (1)

A homodyne radar containing a transmit-receive antenna 3 and serially connected a probe signal generator 1, a circulator 2 and a mixer 4, the output of a transmit-receive antenna 3 is connected through a circulator 2 to the second input of the mixer 4, and the third output of the circulator 2 is connected to the input of the transmit-receive antenna 3, characterized in that it further comprises an amplifier 5, an amplitude modulator 6, the second input of which is connected to the output of the generator of the function of the time window 8 in series with the output of the mixer 4, and amplify v is a quadratic amplitude-frequency characteristic 7, whose output is connected to the output of the radar.

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