JPH0472588A - Radar transmit modulation signal generating method and its radar device - Google Patents

Abstract

PURPOSE:To substantially reduce generation of spurious component in a transmit radio wave by switching a hourly smoothly repeated signal as a modulation signal of the transmit radio wave to a short form wave signal synchronized with the repeated signal. CONSTITUTION:A sine wave (a) outputted from a sine wave generator 1, a clock pulse (b) synchronized with this, and a logical product (f) of a first transition detection signal (k) having delay of half-clock for driving a one bit random number generator and a last transition detection signal (e), control a switch circuit 7 to select the sine wave and one bit random number signal. When the output signal (g) is used as a modulation signal of transmit signal, the amplitude is changed smoothly at the time of transmission-receiving switching. When the one bit random number signal having delay of half-clock is used as a transmission-receiving switching signal (i), the previously obtained transmit radio wave is not outputted in a period of receiving. Thus, any spurious component in the transmit radio wave generated by modulation can be substantially reduced.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method of generating a radar transmission modulation signal and a radar device thereof, and in particular to a method for generating a radar transmission modulation signal, and particularly to a method for generating a radar transmission modulation signal. The present invention relates to a method for generating a radar transmission modulation signal that reduces unnecessary radiation (unwanted radiation) and makes radar sensitivity uniform over distance, and a radar device for the same.

(Prior Art) One of the radar systems is the FMCW system, which has the advantage of requiring less peak value of transmission power compared to the pulse system with the same average transmission power. If this radar is implemented in the medium/short wave band, the transmitted radio waves will go directly to the receiver, suppressing the reflected signal from the target. Transmit and receive at the same point by changing the time. The latter is called a pulsed chirp radar (also called a transmission/reception switching type FMCW radar or FMICW radar).

FMCW radar transmits observation radio waves while changing the frequency over time, and the scattered signal from the target is received with a time delay depending on the distance, so the distance to the target is calculated from the frequency difference with the transmitted radio wave at that time. do. Since the pulsed chirp radar switches between transmission and reception, scattered signals are effectively input to the receiver only while the radar is in the receiving state, and scattered signals that arrive during the period of transmission are invalid. The rate at which scattered radio waves from the target are effectively received is called the reception time rate, and in order to obtain a uniform reception time rate with respect to distance, transmission and reception are switched using, for example, a 1-bit random number.

, generally the scattered signal from a radar target is at a distance of 4
Since the signal strength decreases in proportion to the power of For example, a frequency amplifier may be given a frequency characteristic, or frequency modulation may be performed using a sine wave to select a higher-order mode for reception.

(Problem to be Solved by the Invention) Since the pulse charcoal radar intermittents the transmission radio waves, the spectrum of the transmission radio waves is expanded in accordance with the spectrum of the modulation signal corresponding to the transmission/reception switching signal.

The spectral components necessary for measuring the distance to the target as an FMCW radar are only the carrier wave, in other words, the DC component of the modulation signal, and all other spectral components become spurious. When a 1-bit random number with a rectangular wave as the basic waveform is used for the modulation signal, the power spectrum W (f) at a frequency f apart from the carrier wave is expressed by A as the amplitude,
It is expressed as where T is the clock period, the first term on the right side corresponds to the spurious component, and the second term corresponds to the necessary DC (carrier wave) component. As can be seen from the above equation, the spurious component decreases at a rate of 6 dB per octave of f. In a pulsed char radar, the transmitted signal must not be output during the reception period, so this method uses a rectangular wave smoothed by passing it through a low-pass filter as a modulation signal to reduce the spurious intensity and narrow the occupied bandwidth. cannot be used. There are many radio stations in a narrow band,
In the medium and short wave bands, where radio waves are intertwined internationally, there is a strong need to prevent interference between radio stations, making it difficult to install radio stations that require wide occupied bandwidth.

To reduce spurious components, a waveform smoothing circuit that uses the time constant of resistors and capacitors and the nonlinearity of diodes smoothes the rise and fall portions of the rectangular wave so that they do not overlap during the reception period, and generates a modulation signal. There is a method, but it is difficult to adjust the time constant and the circuit reproducibility is poor. Additionally, there is a difficulty in responding to changes in clock frequency.

It is difficult to obtain the necessary frequency characteristics of the receiver intermediate frequency amplifier for correcting the received signal strength that changes in response to changes in the distance to the target. Furthermore, in a method in which frequency modulation is performed using a sine wave and the higher-order mode is selected for reception, the signal strength is weaker than in the fundamental mode.

This invention overcomes the above-mentioned difficulties (disadvantages, problems), and reduces to the utmost the generation of spurious components associated with modulation of a pulsed char blade, and also makes it possible to change the clock frequency during random number generation. It is an object of the present invention to provide a method for generating a radar transmission modulation signal that can be used without any adjustment and that can uniformly correct the strength of a received signal that changes depending on the distance to a target.

Another object of the invention is to provide a radar device that generates the above modulated signal.

(Means for Solving the Problems) In order to achieve the above object, the method for generating a radar transmission modulation signal of the present invention is a method for generating a radar transmission modulation signal in a pulsed chirp radar. The outline of the method is to form a radar transmission modulation signal by switching between a repetitive signal and an edge portion of a rectangular wave signal synchronized with the repetitive signal.

Further, in order to achieve the above object, the radar device of the present invention is a pulsed chirp type radar device, and includes a repetitive signal generating means for generating a temporally smooth repetitive signal, and a timing synchronized with the repetitive signal. square wave signal generating means for generating a square wave signal whose level changes;
The outline of the present invention is to include a signal switching means for detecting an edge portion of the rectangular wave signal and replacing the signal of the edge portion with the smooth repeating signal.

(Function) In such a configuration, the signal generating means generates a temporally smooth repetitive signal such as a sine wave signal, and the level of the rectangular wave signal generating means changes at a timing synchronized with the repetitive signal. Generates a square wave signal. The signal switching means detects an edge portion of the rectangular wave signal and replaces the signal of the edge portion with the smooth repetitive signal, so that the received signal has reduced spurious components and corresponds to the distance to the target. This is to obtain radar transmission modulation signals of varying intensities.

(Description of Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a block diagram of the pulsed chirp radar of the embodiment, and FIG. 4 is a schematic diagram of the operation of the pulsed chirp radar of FIG. 3.

In FIG. 3, a sweep signal generator 9 generates a frequency sweep signal whose frequency increases linearly with time. The modulator 11 amplitude modulates the frequency sweep signal according to the modulation signal g supplied by the transmission/reception switching signal generator 10. The transmission signal is amplified to the required power by the transmission amplifier 12 and output to the transmission/reception antenna 14 through the transmission/reception changeover switch 13 . The transmission/reception switching switch 13 switches the antenna 14 between the transmission amplifier 12 and the receiver 1 according to the transmission/reception switching signal i.
Switch to 5. The receiver 15 outputs a signal representing the difference in frequency between the frequency spread signal and the received signal as a baseband signal.

As shown in FIG. 4, the transmission signal whose frequency changes over time is interrupted in accordance with the transmission/reception switching signal i. The received signal scattered from the target is received with a time delay proportional to the distance to the target, and the difference in frequency from the transmitted signal at that time is proportional to the distance. The FCMW radar calculates the distance to the target from the frequency difference between the transmitted signal and the received signal. The received signal is effectively input to the receiver only during the period when the transmission/reception changeover switch 13 shown in FIG. 3 is on the receiver side, and the scattered signal from the target that arrives during the transmission period becomes invalid.

FIG. 1(a) is a block diagram of the transmission switching signal generator of the embodiment, and FIG. 1(b) is a timing chart of the circuit of FIG. 1(a). In FIG. 1(a), from the sine wave a output from the sine wave oscillator 1, the clock generator 2 generates a clock pulse b synchronized with the sine wave as shown in FIG. 1(b), and generates one bit. , /) drives the random number generator 3. Such a lock generator 2 can be easily constructed by, for example, a comparator circuit (not shown) and a flip-flop circuit (not shown) that detect the peak and bottom of the sine wave a. The rising edge detection circuit 4 outputs a half clock pulse d in response to the rising edge of the random number signal pulse C, and the falling edge detection circuit 5 similarly outputs a half clock length pulse d in response to the falling edge of the random number signal pulse C.

outputs a pulse e with a longer length. Half clock delay circuit 6 delays pulse d by a further half clock. The sine wave signal a and the 1-bit random number signal i delayed by half a clock by the half clock delay circuit 8 are supplied to the input of the switch circuit 7. The logical sum f of the rising detection signal delayed by half a clock and the falling detection signal e becomes a control signal for the switch circuit 7, and a sine wave or a 1-bit random number signal is selected as the output g of the switch circuit 7 depending on the detection signal. If this signal is used as the modulation signal g of the transmitted radio wave, the amplitude will change smoothly when switching between transmission and reception, and a transmitted radio wave with less spurious will be obtained. Also,
If the l-bit random number signal delayed by half a clock is used as the transmission/reception switching signal i, the transmission radio wave obtained as described above will not be output during the reception period.

In the block diagram of FIG. 1(a), each component other than the sine wave oscillator l does not include a time constant circuit. Therefore, even if the frequency of the sine wave a is changed, the timing relationship between each signal is maintained.

A longest sequence pseudorandom code (hereinafter referred to as M sequence) pulse with a clock frequency of 200kHz as a 1-bit random number,
The spectra of the signal whose rising and falling edges are smoothly connected as described above are shown in FIGS. 2(a) and 2(b), respectively. The M-sequence pulse has an overall reduction rate of 6 [dB/octave], whereas the smoothed signal has a reduction rate of 1
The reduction is 1 by 5 [dB/octave], and the effect of the present invention in reducing spurious signals is obvious. For your reference,
The signal reduction rate by a smoothing circuit that combines resistors, capacitors, and diodes is 11°5 [dB/octave]
Met.

Generally, the received fg signal strength p (d) from a target at distance d is expressed as PtG2λ2 p(d)'' (4x)・6・ where pt is the transmission power, G is the antenna gain, and λ is the wavelength of the radio wave. In a pulsed chirp radar, the average received signal strength Pr(d) input to the receiver is Pr(d) = RTR(cl) ・ p(d)
It is expressed as Here, RTR(d) is the reception time rate due to switching between transmission and reception, the modulation waveform of the transmission signal for time t is T(t), and the reception weighting is the waveform of the function R(t).
It is expressed as .

A sine wave can be approximated by a curve of the square of the phase angle when the phase angle is small, so if we use a smooth 1-bit random number waveform connected to T (t) and R (t) with the above sine wave, RTR (
cl) is a function proportional to the fourth power of the distance d, and the average received signal strength Pr(d) takes a negative value with respect to the distance at short distances.

In the above embodiment, a sine wave is used as a temporally smooth repetitive signal, but it is possible to select an appropriate waveform depending on the characteristics of the modulator, etc.

Furthermore, although a 1-bit random number waveform was used as the rectangular wave signal synchronized with the signal, the present invention is not limited to this, and a pulse signal synchronized with a temporally smooth repetitive signal may be appropriately selected according to the characteristics required by the radar. is possible.

In the above embodiment, a signal whose frequency increases over time is used as the frequency sweep signal, but a signal whose frequency decreases over time may also be used.

(Effects of the Invention) As described above, according to the present invention, by switching between a temporally smooth repetitive signal and a rectangular wave signal synchronized with the signal as a transmission modulation signal of a pulsed chirp radar, the signal is included in radar transmission radio waves. This makes it possible to significantly reduce spurious signals caused by noise and make effective use of frequency resources.

In addition, it is possible to correct the distance sensitivity characteristics of the radar without using equivalent additional equipment or data processing, and eliminate differences in scattered signal intensity due to distance from the target.

Further, according to the present invention, since the circuit of the modulation waveform generation part does not include a time constant, the clock of the rectangular wave signal synchronized with the signal can be easily changed by simply changing the frequency of the temporally smooth repetitive signal. It is possible to change Leda's characteristics.

[Brief explanation of drawings]

FIG. 1(a) is a block diagram of a transmission switching signal generator according to an embodiment of the present invention, FIG. 1(b) is a timing chart of the circuit of FIG. 1(a), and FIG. 2(a) is a 1-bit The power spectrum of the random number pulse, Figure 2 (b) is shown in Figure 2 (
The power spectrum of a waveform in which the rising and falling pulses are connected to a smooth repeating signal using the method described in the present invention at the same clock frequency as in a). Figure 3 is a block diagram of the Wald chirped radar of the embodiment. Figure 4 3 is a schematic diagram of transmission and reception signals of the pulsed chirp radar in FIG. 3. FIG. In the figure, 1 is a sine wave oscillator, 2 is a clock generator, 3 is a 1-bit random number generator, 4 is a rising edge detection circuit, 5 is a falling edge detection circuit, 6 is a half clock delay circuit, 7 is a switch circuit, and 8 is a half clock delay circuit. clock delay circuit, 9 a sweep signal generator, 10
1 is a transmitting/receiving switching signal generator, 11 is a modulator, 12 is a transmitting amplifier, 13 is a transmitting/receiving switch, 14 is a transmitting/receiving antenna, and 15 is a receiver. In the figure, a is a sine wave signal, b is a clock pulse, c is a 1
Bit random number pulse, d is a rising detection signal, e is a falling detection signal, f is the logical sum of d and e, g is a modulation signal,
h is a frequency sweep signal, i is a transmission/reception switching signal, j is a transmission signal, and k is a baseband signal. Patent Applicant: Director, Telecommunications Research Institute, Ministry of Posts and Telecommunications Figure 1a) Figure 2(b) Figure 11!1 (bl Figure 3)

Claims (2)

[Claims] (1) In a method of generating a radar transmission modulation signal in a pulsed chirp radar, a radar transmission modulation signal is formed by switching between a temporally smooth repetitive signal and an edge portion of a rectangular wave signal synchronized with the signal. A method of generating a radar transmission modulation signal, characterized in that: (2) In a pulsed chirp type radar device, a repetitive signal generating means that generates a temporally smooth repetitive signal, and a rectangular wave signal that generates a rectangular wave signal whose level changes at a timing synchronized with the repetitive signal. A radar device comprising: a wave signal generating means; and a signal switching means for detecting an edge portion of the rectangular wave signal and replacing the signal of the edge portion with the repetitive signal.