JPH0372286A - Doppler radar apparatus of delay-type frequency-modulated continuous wave system - Google Patents

Abstract

PURPOSE:To enable accurate detection of a speed of an airplane by giving an offset delay of radio wave propagation between modulation signals of transmission and reception systems. CONSTITUTION:A phase modulator 13 for transmission generates a continuous wave signal from an output oscillated by a radio-frequency oscillator 11 and a first phase modulation signal of a delayed phase generator 15, and the signal is emitted as a radio wave from a transmission antenna 21 on the output side thereof. The signal wave which is reflected and comes back is received by an antenna 22 for reception, and a single-sideband mixer 17 generates a single- sideband Doppler frequency signal from the output oscillated by the oscillator 11 and a continuous wave signal which a phase modulator 16 for reception generates from a second phase modulation signal of the generator 15. In this way, an offset delay of radio wave propagation is given between the phase modulation signals for transmission and reception and thereby a reception modulation index in a reception device is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a delayed frequency modulation continuous wave type Doppler radar device.

The device according to the present invention is used in a Doppler radar mounted on an aircraft and used for detecting the aircraft's own speed.

[Prior art and problems to be solved by the invention] The conventional frequency modulation continuous wave type Doppler radar device
This will be explained using diagrams. In the device shown in FIG. 6, microwaves generated by a radio frequency oscillator 11 are frequency modulated by an FM signal from an FM signal generator 19. The FM signal generator 19 receives an FM synchronization signal from the timer 5 and shapes the waveform of the FM signal in order to synchronize it with the signal received by the frequency tracker 4. The modulated microwave is branched by a coupler 12 into a transmission system and a reception system. The receiving microwave is used as a local signal.

The branched transmission system microwave is amplified by the power amplifier 14 and emitted to the outside from the transmission antenna 21.

A reflected microwave that has undergone a Doppler frequency shift from the ground surface R is taken in from the receiving antenna 22, amplified by an amplifier 18, and supplied to a single sideband mixer (SSB mixer) 17. The single sideband mixer mixes the local signal supplied from the coupler 12 and the reflected microwave with a Doppler frequency shift from the amplifier 18, and generates a frequency signal in the audio domain as a single sideband Doppler frequency shift. Output.

The S/N of this frequency signal is It can be obtained from the general radar equation as follows.

16π2・h2・NF・KT-B-THPt: Transmission power G: Antenna gain W: Antenna factor λ2: Wavelength δ1. Reflection coefficient of a two-reflecting object E: Frequency modulation loss L: Microwave loss (loss inside the transmitter/receiver) cosψ: Cosine of the beam incidence angle h: Altitude NF: Noise figure KT: Thermal noise B: Bandwidth of the received Doppler signal TK: Signal Acquisition Level of Frequency Tracker Here, the frequency modulation loss E is caused by the frequency modulation continuous wave type Doppler radar device.

In the device shown in FIG. 6, when the altitude of the aircraft carrying the Doppler radar device is low, frequency modulation loss increases and the received signal strength decreases.

That is, when the altitude of the aircraft is h, the single side wave '+lF
The S/N ratio of the mixer output signal has the following relationship, and the frequency modulation loss E is expressed as follows.

E = J-(M) ・
... (3) Therefore, when the propagation time τ of the radio wave is small, M approaches 0, and sufficient signal strength cannot be obtained, especially on calm sea or lake surfaces where reflection is small, and the S/N becomes low. worsened,
It would be impossible to detect the aircraft speed.

where J, (M) is the first-order Bessel function, m is the transmit modulation index, and M is the receive modulation index.

An object of the present invention is to provide a radio wave propagation offset delay between the modulated and demodulated signals of the transmitting system and the receiving system in a frequency modulated continuous wave type Doppler radar device, so that when the altitude of the aircraft on which the Doppler radar is mounted is low, The object of the present invention is to improve the received signal level, increase the S/N ratio, prevent the situation in which the aircraft speed cannot be detected, and accurately detect the aircraft speed.

Regarding the theoretical formula, as shown in FIG. 2 (2), the offset delay τ. θ (leading phase component in terms of phase) corresponding to (
4) By adding to the equation, the following equation is obtained.

(5) Therefore, the frequency modulation loss E of the delayed frequency modulation continuous wave system of the present invention can be expressed by the following equation from equations (3) and (5).

E=10 log J, ” (M) [dB] [Means for solving the problem] In the present invention, an oscillator that oscillates a radio frequency continuous wave, and first and second phase modulation signals having delayed phases. a transmission phase modulator that receives the output of the oscillator and the first phase modulation signal and generates a phase-modulated continuous wave signal; a phase modulator that receives the output of the oscillator and the second phase modulation signal and receives the phase A receiving phase modulator that generates a modulated continuous wave signal, a transmitting antenna that is connected to the output side of the transmitting phase modulator and emits a phase modulated continuous wave signal, and a phase modulator that is reflected and arrives. a receiving antenna that receives a radio wave of a continuous wave signal, and a single sideband Doppler frequency signal that receives the phase modulated continuous wave signal supplied through the receiving antenna and the output of the receiving phase modulator. A single sideband signal that generates
, whereby an offset delay of radio wave propagation is given between the transmitting phase modulated signal and the receiving phase modulated signal, and the receiving modulation index in the receiving device is increased. A delayed frequency modulation continuous wave type Doppler radar device is provided.

〔Example〕

FIG. 1 shows a schematic configuration of a delayed frequency modulation continuous wave type Doppler radar device as an embodiment of the present invention.

Figure 1: To explain the operation of the device in comparison with the operation of conventional devices, Figure 2 shows the first-order Bessel function curve, altitude and radio wave propagation distance, and the relationship between altitude, reception modulation index, and frequency modulation loss. , first-order Bessel function J for altitude
, (M), frequency modulation loss, and S/H characteristics are the third
As shown in FIG.

The device shown in FIG. 1 includes an oscillator 11 that oscillates a radio frequency continuous wave;
a delayed phase generator 15 that generates first and second phase modulated signals with delayed phases; a transmitting phase modulator that receives the output of the oscillator and the first phase modulated signal and generates a phase modulated continuous wave signal; 13. A reception phase modulator 16 that receives the output of the oscillator and the second phase modulation signal and generates a phase-modulated continuous wave signal, and a phase-modulated continuous wave connected to the output side of the transmission phase modulator. A transmitting antenna 21 that emits a signal radio wave, a receiving antenna 22 that receives reflected and arriving phase modulated continuous wave signal radio waves, and a phase modulated continuous wave signal supplied through the receiving antenna and the corresponding radio wave. It has a single sideband mixer 17 that receives the output of the reception phase modulator and generates a single sideband Doppler frequency signal.

The microwave oscillated by the radio frequency oscillator 11 is
It is a continuous wave (CW), and the power is divided into a transmitting system and a receiving system at a coupler 12, and each radio frequency phase modulator 1
3 and 16 are phase modulated. Its output becomes a phase modulated continuous wave (PM-CW).

The delayed phase generator 15 receives the frequency synchronization signal from the timer 5, performs waveform shaping, and generates two types of phase modulation signals 515 (ω=1θ), S+s(
ωt) is generated and supplied to the radio frequency phase modulators 13 and 16 of the transmitting system and the receiving system, respectively. The microwaves modulated by the radio frequency phase modulators 13 and 16 of the transmission system and the reception system have a delayed phase, that is, a delay time.

Microwaves output from the transmission system radio frequency phase modulator 13 are amplified in the power amplifier 14 and emitted from the transmission antenna 21. The emitted radio waves are reflected on the ground surface R, and the reflected radio waves are received by the receiving antenna 22, amplified by the low-noise FET amplifier 18, and supplied to the single sideband mixer 17.

In the single sideband mixer 17, the local signal is mixed with a received signal, which is a reflected microwave, which includes a delay time given in advance by the transmission phase modulator 13 in addition to the delay time due to Doppler frequency deviation and radio wave propagation. , a single sideband Doppler frequency signal, that is, a frequency signal in the audio domain is output.

The characteristics of the received modulation index M with respect to altitude are shown in FIG. In the device shown in FIG. 1, τ is added to the M curve shown in FIG. 2 in advance. Just give the offset delay. That is, by lengthening the radio wave propagation time at low altitude, the reception signal from the ground surface R is processed in the receiving device as an apparently high-altitude signal.

In this case, as a signal processing method, the phase modulation signal of the reception system in the transmitting/receiving device is used as a reference, and the phase modulation signal of the transmission system is delayed.

Frequency modulation loss and S/H characteristics with respect to altitude, which is the radio wave propagation distance, are shown in FIGS. 3 (1) to (4). Figure 3 (1) shows the altitude measure first-order Bessel function J, (M),
Figure 3 (2) shows the height vs. modulation loss, Figure 3 (3) shows the height vs. S/N in continuous wave method, and Figure 3 (4) shows the height vs. frequency modulated continuous wave (FM-CW). S/N in method
, is shown.

In the conventional device, as shown by the solid lines in Fig. 3 (2) and (4), the frequency modulation loss increases as the altitude decreases, so the S/N deteriorates. In the device, good characteristics as shown by the broken lines in FIG. 3 (2) and (4) can be obtained.

The frequency modulation loss and S/N characteristics with respect to altitude in the device shown in FIG. 1 are shown in FIGS. 4 (1) and (2).

In the device shown in FIG. 1, the increase in frequency modulation loss is suppressed by the phase delay, resulting in an improvement in S/N.

Regarding the operation of the apparatus shown in FIG. 1, the degree of improvement in the reception modulation index M, frequency modulation loss Loss (FM), and S/N with respect to the delay time determined by the Bessel function of the first kind and the theoretical formula will be described.

Altitude h=12.2m (40 feet), modulation frequency f
.

= 30 kHz, beam incidence angle m = 24.4°, and transmission modulation index m = 1. According to equation (6), the frequency modulation loss E is -41.5 when the delay time is 0 IIS.
0dB, delay time 1.856 sec (delay phase θ=
20°), it becomes -14.95dB, and the difference between the two (-1
4,95dB) -(-41,50dB) =26.5
5 dB corresponds to the degree of improvement in S/N.

Further, under the above conditions, the relationship between the delay phase θ and the frequency modulation loss E is as follows.

This relationship is expressed by the S/N points at 40 feet in FIG.

In addition, it can be seen that the S/N received by the frequency tracker of the delayed frequency modulation continuous wave method and Doppler radar device shown in Fig. 1 is improved as shown in the following table from equations (1) and (6). .

In the above description of the apparatus shown in FIG. 1, the delay time was considered to be fixed, but the delay time is not limited to this, and it is also possible to change it stepwise or continuously in accordance with the altitude.

Regarding the modulation index switching type frequency modulation continuous wave type Doppler radar related to the device shown in FIG.
(Japanese application) can be referred to.

[Effects of the Invention] According to the present invention, in a frequency modulated continuous wave type Doppler radar device, an offset delay of radio wave propagation is given between the modulated signals of the transmitting system and the receiving system, so that the altitude of the aircraft on which the Doppler radar is mounted is low. The received signal level at altitude increases, the S/N ratio increases, a situation in which the aircraft speed cannot be detected is prevented, and the aircraft speed is accurately detected.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a schematic configuration of a delayed frequency modulation continuous wave type Doppler radar device as an embodiment of the present invention, and Fig. 2 shows the first-order Bencel function, offset delay, modulation loss, altitude, and radio wave propagation. Figures 3 and 4, which explain the distance relationship, show modulation loss and S/S versus altitude.
Figure 5 is a diagram explaining the characteristics of the N ratio. Figure 5 is a diagram explaining the degree of S/N improvement at low altitude (40 feet). Figure 6 is a circuit diagram of a conventional frequency modulation continuous wave Doppler radar. are shown respectively. Further, in FIG. 1, the correspondence between numbers and devices is as follows. 1... Radio frequency oscillator, 12... Coupler, 13... Radio frequency phase modulator for transmission, 14... Power amplifier, 15... Delay phase generator, 16...
- Receiving radio frequency modulator, 17... Single sidewave IF mixer, 18... FET amplifier, 21... Transmitting antenna, 22... Receiving antenna, 3... Preamplifier, 4...・Frequency tracker, 5...Timer, R...Ground surface.

Claims (1)

[Claims] An oscillator that oscillates a radio frequency continuous wave; a delayed phase generator that generates first and second phase modulated signals having delayed phases; a transmitting phase modulator that generates a modulated continuous wave signal; a receiving phase modulator that receives the output of the oscillator and a second phase modulated signal and generates a phase modulated continuous wave signal; and the transmitting phase modulator A transmitting antenna that emits phase-modulated continuous-wave signal radio waves, a receiving antenna that receives reflected phase-modulated continuous-wave signal radio waves, and a receiving antenna connected to the output side of the receiver. a single sideband mixer that receives the supplied phase modulated continuous wave signal and the output of the receiving phase modulator and generates a single sideband Doppler frequency signal;
, thereby providing a radio wave propagation offset delay between the transmitting phase modulated signal and the receiving phase modulated signal,
A delayed frequency modulation continuous wave type Doppler radar device, characterized in that the reception modulation index in the receiving device is increased.