JP2006266788A - Radio altimeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio altimeter capable of accurately measuring altitude even if the distance between a transmission antenna and a ground surface is short. <P>SOLUTION: A delay line 7 for delaying a reflected wave signal R3 from a reception circuit 6 by a prescribed time and outputting it is arranged between the reception circuit 6 and an intermediate frequency amplifier 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radio altimeter, and more particularly to a radio altimeter that is mounted on an aircraft or the like and measures a distance such as a ground altitude.

  As a conventional technique, there is a radio rangefinder described in JP-A-11-304908.

  This radio rangefinder includes a reference pulse generator, a pulse transmission circuit, a transmission antenna, a reception antenna, a reception circuit, an amplification circuit, a first pulse generation circuit (reflection wave capturing means), and a differential circuit (time detection means). .

  The reference pulse generator generates a reference pulse.

  The pulse transmission circuit generates a transmission pulse in synchronization with the reference pulse.

  The transmitting antenna converts transmission pulses into radio waves and transmits them to the ground surface or the like.

  The receiving antenna receives radio waves reflected from the ground surface or the like.

  The receiving circuit converts the output of the receiving antenna into an intermediate frequency signal and detects it.

  The amplifier circuit amplifies the output of the receiving circuit.

  The first pulse generation circuit includes a capture pulse generation circuit and a comparator. The capture pulse generation circuit generates a capture pulse that partially overlaps the reflected wave signal output from the amplifier circuit. The comparator advances or delays the output timing of the capture pulse so that the overlap area of the reflected wave signal and the capture pulse is the same as the reference overlap area. The first pulse generation circuit outputs a reflected wave capturing pulse when the two areas become the same.

The differential circuit detects a time difference between the reference pulse and the reflected wave capturing pulse, and outputs a voltage corresponding to the time difference. Based on this voltage, the distance to the ground surface or the like is obtained.
Japanese Patent Laid-Open No. 11-304908

  In this radio altimeter, when the pulse transmission circuit oscillates a transmission pulse, a large current flows and potential fluctuation occurs. This potential variation is amplified by the amplifier, and as a result, noise is generated at almost the same timing as the oscillation of the transmission pulse.

  This noise enters the first pulse generation circuit. When the distance between the transmitting antenna and the ground surface is long, the reflected wave signal and noise do not overlap in the first pulse generation circuit, and no special problem occurs. However, when the distance between the transmitting antenna and the ground surface is short, the reflected wave signal and noise overlap in the first pulse generation circuit. The comparator cannot distinguish the overlap between the reflected wave signal and noise and the overlap between the reflected wave signal and the captured pulse. For this reason, the comparator determines that the overlap between the reflected wave signal and the noise is an overlap between the reflected wave signal and the captured pulse, and outputs the reflected wave captured pulse. As a result, the time difference between the reflected wave capturing pulse and the reference pulse does not correspond to the distance between the transmitting antenna and the ground surface, and the altitude cannot be measured accurately.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a radio altimeter capable of accurately measuring altitude even when the distance between the transmitting antenna and the ground surface is short.

  In order to solve the above-mentioned problems, a radio altimeter according to claim 1 is a reference pulse generating means for generating a reference pulse, a pulse transmitting means for generating a transmission pulse in synchronism with the reference pulse, and the transmission pulse as a radio wave. A transmitting antenna for converting to a ground surface and transmitting to the ground surface, a receiving antenna for receiving radio waves reflected from the ground surface, a receiving means for converting the output of the receiving antenna into an intermediate frequency signal and detecting, and from the receiving means An intermediate frequency amplifier for amplifying the reflected wave signal, a reflected wave capturing means for capturing the reflected wave signal from the intermediate frequency amplifying means and outputting a reflected wave capturing pulse, and the reference from the reference pulse generating means A time detecting means for detecting a time difference between the pulse and the reflected wave capturing pulse from the reflected wave capturing means, and outputting an altitude signal corresponding to the time difference; and Characterized in that it comprises a delay means for delaying the force.

  As described above, since this radio altimeter includes delay means for delaying the output of the receiving means, even if the distance between the transmitting antenna and the ground surface is short, noise and reflected wave signals are input to the intermediate frequency amplifying means. The timing is off.

  According to a second aspect of the present invention, in the radio altimeter according to the first aspect, the delay means is connected between the receiving means and the intermediate frequency amplifying means.

  According to the present invention, the altitude can be accurately measured even if the distance between the transmitting antenna and the ground surface is short.

  Embodiments of the present invention will be described with reference to the drawings.

  1 is a block diagram showing a radio altimeter according to an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of a delay line of the radio altimeter shown in FIG. 1, and FIG. 3 is a timing chart showing the operation of the radio altimeter shown in FIG. It is.

  As shown in FIGS. 1 and 3, a reference pulse generator (reference pulse generating means) 1 generates a reference pulse P. A pulse transmission circuit (pulse transmission means) 2 generates a transmission pulse S in synchronization with the reference pulse P. The transmission antenna 3 converts the transmission pulse S into a radio wave R1 and transmits it to the ground surface 4.

  The receiving antenna 5 receives the radio wave (reflected wave) R2 reflected by the ground surface 4. The reflected wave R2 is input to the receiving circuit (receiving means) 6.

  The receiving circuit 6 converts the reflected wave R2 from the receiving antenna 5 into an intermediate frequency signal, detects it, and outputs a reflected wave signal R3.

  The delay line (delay means) 7 delays the reflected wave signal R3 from the receiving circuit 6 for a predetermined time and outputs it. The delay line 7 is composed of two coils 71 and two capacitors 72 (see FIG. 2).

  An intermediate frequency amplifier (intermediate frequency amplification means) 8 amplifies the reflected wave signal R3 from the delay line 7 and outputs a reflected wave signal R4.

  The reflected wave acquisition circuit 9 includes an acquisition pulse generation circuit (not shown), a comparator (not shown), and the like. The acquisition pulse generation circuit generates an acquisition pulse based on the reference pulse P of the reference pulse generator 1 and the altitude signal A from the time detection circuit 10. A part (rear edge) of the acquisition pulse overlaps a part (front edge) of the reflected wave signal R4. The comparator outputs a feedback signal for advancing or delaying the output timing of the capture pulse to the capture pulse generation circuit so that the overlap area of the reflected wave signal R4 and the capture pulse is the same as the reference overlap area.

  The time detection circuit (time detection means) 10 detects the time difference between the reference pulse P from the reference pulse generator 1 and the reflected wave acquisition pulse C from the reflected wave acquisition circuit 9, and outputs an altitude signal A corresponding to the time difference. To do.

  Next, the operation of this radio altimeter will be described.

  As shown in FIGS. 1 and 3, a transmission pulse S is transmitted from the pulse transmission circuit 2 in synchronization with the reference pulse P generated by the reference pulse generator 1, and a radio wave R 1 corresponding to the transmission pulse S is transmitted from the transmission antenna 3. It is transmitted to the ground surface 4. The transmission pulse S is output from the pulse transmission circuit 2 when the time Ta elapses after the reference pulse P is output from the reference pulse generator 1 (see FIGS. 3A and 3B). The reference pulse P is output at a predetermined repetition period tf. When the transmission pulse S is transmitted, noise N is generated almost simultaneously (see FIG. 3C), and this noise N directly enters the intermediate frequency amplifier 8.

  The radio wave R1 transmitted from the transmitting antenna 3 is reflected by the ground surface 4 and reaches the receiving antenna 5 as a reflected wave R2. Tb in FIG. 3F represents the time from transmission to reception. The reflected wave R2 is input to the receiving circuit 6, converted into an intermediate frequency signal, and output as a reflected wave signal R3. Tc in FIG. 3F represents the time from when the reflected wave R2 is input to the receiving circuit 6 until the reflected wave signal R3 is output from the receiving circuit 6.

  The reflected wave signal R3 passes through the delay line 7. At this time, the reflected wave signal R3 is delayed from the delay line 7 by a predetermined time Td. Therefore, the noise N enters the intermediate frequency amplifier 8 long before the intermediate frequency signal R 3 is input to the intermediate frequency amplifier 8. The noise N is amplified and output from the intermediate frequency amplifier 8. The reflected wave signal R3 is also amplified and output from the intermediate frequency amplifier 8 as the reflected wave signal R4. The noise N is input to the intermediate frequency amplifier 8 and output when the time Te elapses. Similarly, the reflected wave signal R3 is input to the intermediate frequency amplifier 8 and output as the reflected wave signal R4 when the time Te elapses. Is done.

  In the conventional radio altimeter, when the flight altitude is low, the noise N and the reflected wave signal R4 are output from the intermediate frequency amplifier 8 in a superimposed state (see R4 of the imaginary line in FIG. 3). However, in the radio altimeter according to this embodiment, the timing at which the reflected wave signal R3 enters the intermediate frequency amplifier 8 by the delay line 7 is delayed by the time Td as compared with the noise N, so the reflected wave signal R4 is delayed from the noise N. Is output (see FIG. 3D). Therefore, in the radio altimeter according to this embodiment, even if the flight altitude is low, the noise N and the reflected wave signal R4 do not overlap with each other, or the noise N and the reflected wave signal R4 do not approach each other so much that they cannot be distinguished. When the flight altitude is high, the reflected wave signal R4 is sufficiently separated from the noise N in time.

  The reflected wave signal R4 is input to the reflected wave capturing circuit 9. Based on the reference pulse P and the altitude signal A, the capture pulse generation circuit of the reflected wave capture circuit 9 outputs a capture pulse so that the trailing edge of the capture pulse overlaps the front edge of the reflected wave signal R4. The reflected wave signal R4 and the captured pulse are input to the comparator. The comparator compares the overlap area of the reflected wave signal R4 and the capture pulse with the reference overlap area, and the overlap area of the capture pulse is the same as the overlap area of the reflected wave signal R4 and the capture pulse. A feedback signal that advances or delays the output timing is output to the capture pulse generation circuit of the reflected wave supplement circuit 9. When the overlap area of the reflected wave signal R4 and the capture pulse becomes the same as the reference overlap area, the reflected wave capture circuit 9 outputs the reflected wave capture pulse C to the time detection circuit 10 (FIG. 3 (e), ( f)).

  The reflected wave capture pulse C from the reflected wave capture circuit 9 and the reference pulse P from the reference pulse generator 1 are input to the time detection circuit 10 to detect a time difference ΔT between the two pulses, and an altitude signal corresponding to the time difference ΔT. A is output. This time difference ΔT is obtained by the following equation.

  ΔT = Ta + Tb + Tc + Td + Te

  The altitude signal A is output to a display device (not shown) via a buffer (not shown).

  According to this embodiment, since the noise N and the reflected wave signal R4 do not overlap even when the airplane is flying low, the reflected wave capture pulse C is output at the correct timing. Accurately measured.

  In the above-described embodiment, the delay line is used as the delay unit, but an ultrasonic delay element or the like may be used instead.

FIG. 1 is a block diagram showing a radio altimeter according to an embodiment of the present invention. FIG. 2 is an equivalent circuit diagram of the delay line of the radio altimeter shown in FIG. FIG. 3 is a timing chart showing the operation of the radio altimeter shown in FIG.

Explanation of symbols

1 Reference pulse generator (reference pulse generator)
2 Pulse transmission circuit (pulse transmission means)
3 transmitting antenna 5 receiving antenna 6 receiving circuit (receiving means)
7 Delay line (delay means)
8 Intermediate frequency amplifier (Intermediate frequency amplification means)
9 Reflected wave capture circuit (reflected wave capture means)
10 Time detection circuit (time detection means)

Claims (2)

A reference pulse generating means for generating a reference pulse;
Pulse transmission means for generating a transmission pulse in synchronization with the reference pulse;
A transmission antenna for converting the transmission pulse into a radio wave and transmitting it to the ground surface;
A receiving antenna for receiving radio waves reflected from the ground surface;
Receiving means for converting and detecting the output of the receiving antenna into an intermediate frequency signal and outputting a reflected wave signal;
An intermediate frequency amplifier for amplifying the reflected wave signal from the receiving means;
Reflected wave capturing means for capturing the reflected wave signal from the intermediate frequency amplification means and outputting a reflected wave capturing pulse;
Time detection means for detecting a time difference between the reference pulse from the reference pulse generation means and the reflected wave acquisition pulse from the reflected wave acquisition means, and outputting an altitude signal corresponding to the time difference;
A radio altimeter comprising: delay means for delaying the output of the receiving means.   2. A radio altimeter according to claim 1, wherein said delay means is connected between said receiving means and said intermediate frequency amplifying means.

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