JPH01102382A - Pulse radar - Google Patents

Abstract

PURPOSE:To separate a weak signal from an unnecessary strong signal, by providing a detector for detecting the output signal of a filter and a low band- pass filter inputting the output signal of the detector to output a gain control signal to an amplifier so as to make a signal level constant. CONSTITUTION:The signal generated by a charp signal generator 1 is amplified by a high frequency power amplifier 2 and subsequently emitted to the space as a radio wave through a transmitting and receiving wave divider 3 and antenna 4. Next, the reflected wave from an object to be observed is again returned to the antenna 4 with time delay corresponding to the distance from the antenna 4 to the object to be observed, and amplified and covered in frequency by a high frequency receiver 5 through the wave divider 3 and amplified by an intermediate frequency amplifier 6. This output signal is distributed into two signals and one of them is inputted to a ground reflection timing detector 10 to extract only the strong signal from the ground and the start timing signal of the charp signal is formed at the front edge thereof. This timing signal becomes the stopping frequency sweep start signal (a) of a narrow beand-pass variable frequency filter 11 and the frequency of the charp signal generator is changed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a microwave pulse radar that is mounted on an aircraft or two artificial satellites to observe the state of the upper atmosphere and rain areas.

[Conventional technology]

FIG. 5 shows an example of the configuration of a conventional pulse radar using microwaves. In the figure, (1) is a chirp signal generator, (21 is a high frequency power amplifier).

(3) C transmitter/receiver splitter, (41fl antenna, (5) is a high frequency receiver, (6) is an intermediate frequency amplifier, (7) is a detector, (8) is a low pass filter, (9) is an output terminal It is.

Next, the operation will be explained. Chirp signal generator (11
As shown in FIG. 3(a), the generated signal is a signal whose frequency changes linearly between the transmission and reception pulse widths τp. This signal is amplified by a high frequency power amplifier (2) and radiated into space as a radio wave via a transmitting/receiving duplexer (3) and an antenna (4). The radio waves reflected by the observation target are received again by the antenna (4) with a time delay depending on the distance from the antenna to the observation target, and are then transmitted via the transmitter/receiver splitter (31) to the high-frequency receiver (5).

Amplification 9 Frequency conversion is performed, and after further amplification by an intermediate frequency amplifier (6), the wave is detected by a detector (7), and the output terminal (9
) for subsequent signal processing.

This output is passed through a low-pass filter (8) to remove components that change at high speed, and then passed through the intermediate frequency amplifier (
6). This causes the average level of the output signal to remain at a constant level.

[Problem that the invention seeks to solve]

Conventional equipment was configured as 9 or more, so if a strong signal from the ground surface and a weak signal from the upper atmosphere are received without a time difference, the strong signal and weak signal overlap. Therefore, there was a problem that it became impossible to identify weak signals.

This invention was made with the aim of eliminating the above-mentioned problems that conventional devices have, and utilizes the difference in instantaneous frequencies of signals. It provides a means for identifying signals.

[Means for solving problems]

In the pulse radar according to the present invention, the instantaneous transmission frequency changes over time within the transmission pulse, and a narrowband variable frequency filter is inserted in the reception frequency band in the receiver, and the rejection frequency of this filter changes with the change in the transmission frequency. The frequency changes at the same speed, and the start time of the frequency change can be set to any time from the transmission timing of the transmission signal.

[Effect]

In this invention, by using a variable frequency narrow band filter in the receiving circuit, it is possible to accurately measure the strength of the weak signal even if the strong signal and the weak signal are close in time. It is.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention.

113 to (9) are the same functional elements as the conventional pulse radar. αQ is a ground reflected wave timing detector, and 圓 is a narrow band variable frequency filter.

Further, FIG. 2 is a diagram showing an example of the configuration of the variable frequency filter in FIG. A down converter, which outputs a signal with a difference frequency of
Q4) is an up-converter that outputs a signal with a frequency equal to the sum of the two input signal sources; (19 is a high-pass filter; and (19 is an intermediate frequency amplifier).

In the above configuration, the signal generated by the chirp signal generator (1) has a time waveform as shown in FIG. 3(a), and a frequency within the pulse width τp as shown in FIG. 3(b). is a signal that changes linearly. Similar to conventional pulse radar, this signal is amplified by a high-frequency power amplifier (2) and then radiated into space as a radio wave via a transmitting/receiving splitter (3) and an antenna (4). As shown in Fig. 4(a), the reflected waves of 9, for example, ■～■(
■~0 is reflection from the upper rigid area, ■ is reflection from the ground surface). (5) Amplify and.

Frequency conversion is performed and amplified by a first intermediate frequency amplifier (6). This output signal is divided into two, and one signal is input to the ground reflection timing detector aα.

Only strong signals from the earth's surface are extracted, and a chirp start timing signal is generated at the leading edge of the signals. This timing signal becomes the stop frequency sweep start signal A of the narrowband variable frequency filter circle, and changes the frequency of the chirp signal generator (2) in FIG. 2 as shown in FIG. 4(b). Using this signal as a local oscillator, an intermediate frequency amplifier (to) inserted between the down converter αJ and the up converter (141), and a high-pass filter (to)
Due to the function of , the pass band of the input signal changes with time as shown in FIG. 4(C), and only the ground surface reflection component (2) is removed from the signal shown in FIG. 4(a). Therefore, it is possible to easily distinguish weak signals from the upper layer from strong signals reflected from the ground surface.

In the above explanation, the receiver is of a superheterodyne type using an intermediate frequency amplifier.

The method of the present invention is not limited to this, and can be implemented in any receiver in exactly the same way. Furthermore, it is clear that the narrow band variable frequency filter can be constructed in the same manner by using a variable frequency band rejection filter using a variable capacitance capacitor instead of the above-mentioned combination of an up converter and a down converter.

〔Effect of the invention〕

As described above, according to the present invention, the frequency is variable.

Since weak signals can be separated from strong unnecessary signals using a narrow band rejection filter, it is extremely effective when applied to observation purposes such as detecting the amount of rain on the sea surface from atop an aircraft or artificial satellite.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a pulse radar according to an embodiment of the present invention, FIG. 2 is a diagram showing the configuration of a variable frequency band rejection filter according to an embodiment of the present invention, and FIGS. 3 and 4 is a diagram for explaining signal waveforms, and FIG. 5 is a diagram showing a conventional pulse radar. In the figure, tll is a chirp signal generator, (4) is an antenna, (61t: C intermediate frequency amplifier, α1 is a ground reflection timing detector, and αυ is a narrow band variable frequency filter. In Figure 9, the same symbols are the same. , or the equivalent part.

Claims (1)

[Claims] A chirp signal generator generates a chirp signal whose instantaneous transmission frequency changes over time within a transmission pulse, and the output signal of this chirp signal generator is radiated into space as a radio wave via a power amplifier, and reflected waves from the observation target are generated. an antenna that receives the signal, an amplifier with adjustable sensitivity that inputs the received signal of this antenna, and a ground reflection that inputs the output signal of this amplifier and extracts the strong signal from the ground surface to generate the start timing signal of the chirp signal. The output signals of the timing detector, the amplifier, and the ground reflection timing detector are input, and the rejection frequency of the filter changes depending on the start timing signal, and the passband of the input signal changes with time to remove the ground reflection component. A variable band frequency filter to be used, a detector to detect the output signal of this filter, and an output signal of this detector to be input,
A pulse radar comprising: a low-pass filter that outputs a gain control signal to the amplifier to keep the signal level constant.