JP3341711B2 - Radar altimeter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar altimeter, and more particularly to a radar altimeter for measuring an altitude of an aircraft by sequentially switching a plurality of antennas.

[0002]

2. Description of the Related Art A conventional radar altimeter is shown in FIGS.
Shown in

FIG. 8 is a block diagram showing a conventional radar altimeter using a dual antenna, and FIG. 9 is a block diagram showing a conventional radar altimeter using a single antenna.

Next, FIGS. 8 and 9 will be described.

[0005] Referring to FIG. 8, the ranging signal output by the signal processing unit 29 is transmitted from the transmitting antenna 25 as a transmission radio wave 40 by the transmitter 27, and the transmission radio wave 40 is reflected on the ground surface 30. This reflected radio wave 41 is transmitted to the receiving antenna 2
6, the ranging signal is detected by the receiver 28 and output to the signal processing unit 29. The signal processing unit 29 calculates the altitude to the ground surface 30 from the delay time between the transmitted ranging signal and the received ranging signal.

Referring to FIG. 9, a ranging signal output from a signal processing unit 35 is transmitted as a transmission radio wave 40 from a transmission / reception antenna 31 via a circulator 32 by a transmitter 33, and the transmission radio wave 40 is reflected on the ground surface 30. You. The reflected radio wave 41 is received by the transmission / reception antenna 31, detected by the receiver 34 via the circulator 32, and output to the signal processing unit 35 after being detected.

The signal processor 35 calculates the altitude to the ground surface 30 from the delay time between the transmitted ranging signal and the received ranging signal.

Generally, as a feature of the radar altimeter, a radio wave is transmitted from an airframe, a reflected wave from the ground is received, and a distance is measured from a propagation time of a signal. As the radio wave at this time, a microwave with good straightness is used. Therefore,
The antenna used must have directivity and high gain, and generally the antenna beam width (directivity) is ± 15.
Using degrees around. It is better if it is wider, but there is a disadvantage that the antenna shape becomes larger. Usually, the antenna is mounted so that the directivity is centered in the vertical direction of the body, so that if the body is tilted, radio waves from the ground cannot be received. For this reason, by installing a tilted antenna, it is possible to receive radio waves in the vertical direction even when the aircraft is tilted.

An example of such a technique is disclosed in
A “radio altimeter” described in US Pat. No. 66923 is known.

This publication describes a technique in which a plurality of antennas are radially installed around the fuselage of an aircraft such that the antenna directivity covers the entire sphere, and these antennas are sequentially connected by a switching control unit.

[0011]

Since the above-mentioned conventional radar altimeter is mounted so that the center of the directivity of the antenna is in the vertical direction of the airframe, if the airplane is tilted, radio waves in the vertical direction of the ground surface cannot be received, and the altitude is low. Has the disadvantage that it cannot be measured.

Further, since a plurality of antennas are radially installed so that the directional directions of the antennas cover the whole sphere, there is a disadvantage that the scale of the antennas and the switching control becomes large.

An object of the present invention is to provide a radar capable of switching the minimum number of antennas having an angle in a certain direction from the vertical direction of the airframe to measure the actual altitude from a high altitude to a low altitude even when the airplane is tilted. To provide an altimeter.

[0014]

[0015]

SUMMARY OF THE INVENTION A radar altimeter according to the present invention.
Is a radar altimeter equipped with a transmitting and receiving antenna,
In order to change the radiation angle of the transmission antenna, a plurality of transmission / reception shared transmission antennas are attached to the body at an angle, and a reception antenna dedicated for reception is mounted in the vertical direction of the body, and when the body is at a high altitude, the plurality of transmission antennas are used. Measuring the altitude by sequentially switching the number of transmitting antennas, wherein when the aircraft is at a low altitude, the transmitting antenna is fixed to a transmitting antenna perpendicular to the aircraft, and the altitude is measured with the receiving antenna. I have.

In a radar altimeter provided with a transmitting and receiving antenna, a first transmitting antenna oriented in the vertical direction of the fuselage in the z-axis; a second transmitting antenna inclined by +30 degrees in the x-axis; A third transmitting antenna tilted by 30 degrees; a fourth transmitting antenna tilted by +30 degrees on the y-axis;
A fifth transmitting antenna inclined at -30 degrees with respect to the y-axis; a first switching device for sequentially switching these transmitting antennas according to a first switching signal; and a receiving antenna facing the z-axis in a vertical direction of the aircraft; A second switch that is connected to the receiving antenna and switches the receiving antenna according to a second switching signal output according to the altitude of the aircraft; the first and second switches;
Circulator for both transmission and reception connected to a switcher of
A transmitter that outputs the distance measurement signal as a transmission signal to the circulator; a receiver that receives a reception signal from the reception antenna via the second switch, and outputs the signal as a second distance measurement signal; Outputting the first and second switching signals,
A signal processing unit that calculates an altitude to the ground from a delay time between the transmitted first ranging signal and the received second ranging signal.

At a low altitude of the airframe, a transmitting antenna is fixed to the first transmitting antenna, and a connection with the receiver is switched to the receiving antenna.

The present invention is characterized in that the first to fifth transmitting antennas are sequentially switched at a high altitude of the airframe, and the transmitting antenna is used as a transmitting / receiving antenna.

[0019] Even if the body is tilted back and forth and right and left, the first
The distance between the airframe and the ground surface can be measured by sequentially switching the first to fifth transmission antennas.

[0020]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a radar altimeter according to the present invention.

The present embodiment shown in FIG. 1 has a transmitting antenna 2 oriented in the vertical direction of the body, a transmitting antenna 3 inclined at +30 degrees with respect to the x-axis, and a transmitting antenna 4 inclined at -30 degrees with the x-axis. , A transmitting antenna 5 tilted at +30 degrees in the y-axis, a transmitting antenna 6 tilted at −30 degrees in the y-axis, and a switch 7 for sequentially switching these transmitting antennas by a switching signal 13.
And the receiving antenna 1 oriented in the vertical direction of the aircraft, and the receiving antenna 1 connected to the receiving antenna 1 by the altitude switching signal 14.
, A transmission / reception circulator 9 connected to the switching unit 7 and the switching unit 8, a transmitter 10 for outputting the distance measurement signal 21 to the circulator 9 as a transmission signal 23, and a reception signal from the reception antenna 1. 24 switches 8
Receiver 12 which receives the signal via a relay and outputs it as a distance measurement signal 22
And a signal processing unit 11 that calculates an altitude to the ground surface 30 from a delay time between the transmitted ranging signal 21 and the received ranging signal 22.

Here, the x and y axes indicate a Cartesian coordinate system in which the vertical direction of the body is the z axis.

FIG. 2 is an explanatory diagram showing the antenna arrangement on the x-axis of the radar altimeter.

FIG. 3 is an explanatory diagram showing the antenna arrangement on the y-axis of the radar altimeter.

Next, the operation of the present embodiment will be described in more detail with reference to FIGS. 1, 2 and 3.

As a radar altimeter, an antenna having a high gain and a wide beam width is required. An array antenna using a patch antenna as a radiation element can obtain a relatively high gain and a wide beam, but the usable range is up to about 30 °.
The gain in the 45 ° direction is about 15 to about 0 °.
Decrease by 20 dB. A single antenna with a peak gain of 15 dBi cannot satisfy the range of ± 45 °. Therefore, in order to satisfy the range of ± 45 ° when the attitude of the body changes, it is necessary to further arrange an antenna (peak gain 15 dBi) tilted with respect to the attitude change of 15 °.

At high altitudes, the propagation time of the reflected wave is long, so that the transmission signal and the reflected signal can be separated even when the antenna is used as a transmission / reception antenna for transmission and reception. In this case, the signal cannot be separated, so that it is necessary to identify the signal separately from the transmitting and receiving antennas. Also, at low altitudes, since the change in attitude is small, measurement is performed using only the antenna in the vertical direction. Accordingly, an increase in the number of antennas can be suppressed as much as possible by switching the antenna between high altitude and low altitude.

Therefore, at high altitude, one single antenna for both transmission and reception is used in the vertical direction, and the single antenna is used in both the positive and negative directions of the x and y axes.
At two degrees, two axes are mounted in a tilted state, and a total of five are mounted, and the antennas are sequentially switched to transmit and receive radio waves.

On the other hand, at low altitude, only the transmitting antenna 2 and the receiving antenna 1 in the vertical direction are used as dual antennas for transmission and reception. The switching altitude between high altitude and low altitude is determined under the following conditions. That is, the switching altitude is determined based on the altitude immediately before the propagation time becomes short and the transmission and reception signals cannot be separated.

The transmission signal 23 output from the transmitter 10 shown in FIG. 1 passes through the circulator 9 and the switch 7 and is transmitted from the transmission antenna 2 to the ground 30 as a transmission radio wave 40. The transmission radio wave 40 is reflected on the ground surface 30 and then reflected radio wave 41
Is received by the transmitted transmitting antenna 2, passes through the circulator 9, and is input to the receiver 12 through the switch 8 as a received signal 18. The signal processing unit 11 measures the altitude from the ground based on the propagation times of the transmission signal 23 and the reception signal 18.

Since the transmitting antennas 2 to 6 are sequentially switched by the switch 7, the altitude to the ground can be measured by selecting the signals of the switched transmitting antennas 2 to 6 even if the body attitude is inclined. Also, the inclination angle can be calculated.

Next, when the altitude is low, the time required for receiving the transmission signal 23 transmitted from the transmission antenna 2 is shortened, so that it is difficult to separate transmission and reception signals using the same antenna for transmission and reception. Therefore, at low altitude, the transmission antenna is fixed to the transmission antenna 2 in the vertical direction, and the switch 8 is switched so that the connection with the receiver 12 is selected to the reception antenna 1 dedicated to reception. By using a separate antenna for the transmitting and receiving antennas, transmission and reception signals can be separated even at a low altitude (altitude zero).

The radar altimeter has five transmitting antennas 2 to 6 and one receiving antenna 1.
It is composed of Referring to FIGS. 2 and 3, the transmitting antennas 3 to 6 are arranged at an angle of ± 30 degrees with respect to the transmitting antenna 2 in the vertical direction of the fuselage in each of the x and y axes. There is only one receiving antenna 1 in the vertical direction.

FIG. 4 is an explanatory diagram showing the antenna arrangement on the x-axis and the y-axis.

The transmission antennas 5 and 6 are arranged in the y-axis direction with respect to the transmission antenna 2 in the vertical direction,
Transmitting antennas 3 and 4 (not shown by the back) are arranged in the axial direction.

FIG. 5 is a time chart showing an example of the transmission antenna switching operation.

As shown in FIG. 5, the antenna selection is sequentially switched from the transmission antenna 2 at 0 °, and the five transmission antennas 3
After switching from # 6 to # 6, the switching is repeated in the same order. A transmission radio wave 40 is transmitted from each of the transmission antennas 2 to 6 to the ground surface 30, and a reflection radio wave 41 from the ground surface 30 is received by the reception antenna 1 and altitude calculation is performed by the signal processing unit 11.
Since the directions of 1 are different by 30 °, the reflected radio waves 41 are received at different signal levels depending on the attitude of the body. The signal reflected perpendicular to the ground surface 30 will be received as the strongest signal. Therefore, when five antennas are switched in one cycle, the highest signal among the received signals is used for the calculation as the actual altitude. Even if the aircraft is tilted, the presence of the antenna whose beam is directed in the vertical direction makes it possible to receive the reflected signal and measure the altitude.

At high altitude, the signal can be identified by the transmitting / receiving antennas of the transmitting antennas 2 to 6 and the circulator 9. However, in a low altitude region, the time until the transmission radio wave 40 transmitted from the transmitting antennas 2 to 6 is received is reduced. Shorter,
In the transmitting / receiving antenna, the transmission signal 23 is transmitted to the circulator 9.
From the receiver 12 and cannot be distinguished from the reception signal 24 obtained from the reflected radio wave 41, so that it becomes difficult to separate the signal.

Therefore, at low altitude, it is necessary to distinguish between the reception signal 24 and the reception signal 24 by the reflected radio wave 41 by using a separate antenna for transmission and reception. The altitude change is sequentially calculated by the signal processing unit 11, and when the area changes from a high altitude to a low altitude, the signal processing unit 1
The switching device 7 is fixed to the transmission antenna 2 at 0 ° by the sequential switching signal 13 from 1, and the switching device 8 is switched by the altitude switching signal 14 so as to select the reception antenna 1 at 0 °.

FIG. 6 is a diagram showing the mounting relationship between the body and the x-axis of the antenna. FIG. 6A shows a case where the body is not tilted, and FIG. 6B shows a case where the body is tilted.

FIG. 7 is a diagram showing the mounting relationship between the body and the antenna on the y-axis. FIG. 7A shows a case where the airframe is not tilted, and FIG. 7B shows a case where the airframe is tilted.

Referring to FIG. 6A, the transmission radio wave 40 from the transmission antenna 2 installed on the body 20 is reflected on the ground surface 30, and the reflection radio wave 41 is received by the transmission antenna 2.

Referring to FIG. 6B, since the airframe 20 is inclined, the transmitting antenna 3 is perpendicular to the ground surface 30, and the transmitting radio wave 40 from the transmitting antenna 3 is reflected on the ground surface 30, and the reflected radio wave 41 Is received by the transmitting antenna 3.

Next, referring to FIG.
The transmission radio wave 40 from the transmission antenna 2 installed in the antenna is reflected by the ground surface 30, and the reflection radio wave 41 is received by the transmission antenna 2.

Referring to FIG. 7B, since the fuselage 20 is inclined forward and downward, the transmitting antenna 5 is perpendicular to the ground surface 30, and the transmitting radio wave 40 from the transmitting antenna 5 is reflected on the ground surface 30. The reflected radio wave 41 is received by the transmitting antenna 5.

In any case, even if the body 20 is tilted, x
Since transmission and reception can be performed by any of the transmission antennas for the axis and the y axis, altitude measurement can be performed.

At high altitudes, it is considered that the attitude of the body 20 changes. However, at low altitudes, control is usually performed to stabilize the attitude of the body 20, so that the attitude of the body 20 is stable. Therefore, at low altitude, the transmission antenna is fixed to the transmission antenna 2 in the vertical direction, and the switch 8 is switched so that the connection with the receiver 12 is selected to the reception antenna 1 dedicated to reception. This makes it possible to separate transmission and reception signals even in a low altitude region by using a separate antenna for transmission and reception. When the altitude changes and enters the high altitude region, control is performed by switching the switches 7 and 8 and sequentially switching the transmitting antennas 2 to 6 as described above.

The switching unit 7 always performs switching periodically and sequentially switches the five transmitting antennas 2 to 6.

A reflected radio wave 41 is obtained for each of the transmitting antennas 2 to 6, but the signal direction of the reflected radio wave 41 differs by 30 degrees, so that the level of the received signal of the reflected radio wave 41 also differs. The altitude calculation is performed using the largest received signal. The altitude information is monitored by the signal processing unit 11, and when the altitude changes from a high altitude to a low altitude (set to about 50 m), the switch 7 is fixed at a position where the transmission antenna 2 of 0 ° is selected. When the altitude changes and the altitude changes from low altitude to high altitude, the switch 7
Switches the five transmitting antennas 2 to 6 sequentially.

The switch 8 selects the circulator 9 when the altitude is higher than 50 m and the receiving antenna 1 when the altitude is lower than 50 m from the altitude information of the signal processor 11.

Here, the reason why the antenna is switched depending on the altitude will be described below.

As the altitude increases, the propagation distance of the signal increases, and there is a time difference between the transmission signal 23 and the reception signal 24 as a reflection signal. Therefore, the transmission signal 23 leaks from the circulator 9 and the reception signal 24 Can be identified. At low altitude, in order to separate and identify the leaked signal of the transmitted signal 23 and the received signal 24 as a reflected signal,
The switch 8 is switched to the side of the receiving antenna 1 so that the transmission signal 2
3 prevents the leaked signal from entering the receiver 12 (measurement cannot be made at low altitude without antenna separation).

In this configuration, there are five transmitting antennas (also used as receiving antennas at high altitude) and one receiving-only antenna.
It may be provided individually. However, there is a disadvantage that the number of antennas increases.
It is made into pieces.

This is based on the premise that the attitude of the body 20 is stable at low altitude. Therefore, when the altitude is low, only the transmitting antenna 2 in the vertical direction among the five transmitting antennas is selected and used by the switch 7, and the receiving antenna 1 is arranged in the vertical direction so that the reflected radio wave 41 is transmitted. Can be caught.

As described above, the transmitting and receiving antenna portions of the radar altimeter mounted on the airframe 20 include a plurality of antennas whose radiation angles are changed for transmission, one antenna for reception, a circulator shared for transmission and reception, and each antenna. By providing the high-frequency switch for switching the circulator, the altitude from the ground surface 30 can be measured regardless of the inclination of the body 20.

It is possible to simultaneously measure the inclination angle of the aircraft using the transmitting antenna used.

[0058]

As described above, the radar altimeter according to the present invention can sequentially switch a plurality of antennas whose radiation angles are changed for transmission, so that the attitude angle of the airframe greatly changes with the minimum antenna configuration. However, there is an effect that the altitude to the ground can be measured and the attitude angle can also be measured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a radar altimeter of the present invention.

FIG. 2 is an explanatory diagram showing an antenna arrangement on the x-axis of a radar altimeter.

FIG. 3 is an explanatory diagram showing a y-axis antenna arrangement of the radar altimeter.

FIG. 4 is an explanatory diagram showing an antenna arrangement on the x axis and the y axis.

FIG. 5 is a time chart illustrating an example of a transmission antenna switching operation.

FIG. 6 is a diagram showing an x-axis mounting relationship between a body and an antenna.

FIG. 7 is a diagram illustrating a mounting relationship between a body and an y-axis of an antenna.

FIG. 8 is a block diagram showing a conventional radar altimeter using dual antennas.

FIG. 9 is a block diagram showing a conventional radar altimeter using a single antenna.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 reception antenna 2 to 6 transmission antenna 7 switch 8 switch 9 circulator 10 transmitter 11 signal processing unit 12 receiver 13 sequential switching signal 14 altitude switching signal 18 reception signal 20 fuselage 21 ranging signal 22 ranging signal 23 transmission signal Reference Signs List 24 reception signal 25 transmission antenna 26 reception antenna 27 transmitter 28 receiver 29 signal processing unit 30 ground surface 31 transmission and reception antenna 32 circulator 33 transmitter 34 receiver 35 signal processing unit 40 transmission radio wave 41 reflected radio wave

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01S ⁷ /00-7/42 G01S 13/00-13/95 H01Q 1/28 H01Q 3/24

Claims (5)

(57) [Claims] In a radar altimeter provided with a transmitting / receiving antenna, a plurality of transmitting / receiving transmitting antennas are attached to the body at different angles in order to change the radiation angle of the transmitting antenna, and a receiving-only receiving antenna is mounted vertically on the body. Direction, when the aircraft is at a high altitude, the altitude is measured by sequentially switching the plurality of transmitting antennas, and when the aircraft is at a low altitude, the transmitting antenna is fixed to a transmitting antenna perpendicular to the aircraft, And a radar altimeter for measuring altitude with the receiving antenna. 2. A radar altimeter provided with a transmitting / receiving antenna, a first transmitting antenna oriented in the z-axis in a vertical direction of the aircraft; a second transmitting antenna inclined by +30 degrees with respect to the x-axis; A third transmitting antenna inclined at -30 degrees in the y-axis; a fourth transmitting antenna inclined at +30 degrees in the y-axis; a fifth transmitting antenna inclined at -30 degrees in the y-axis; A first switching device that sequentially switches according to a switching signal; a receiving antenna oriented in the z-axis in a vertical direction of the aircraft; a second switching signal connected to the receiving antenna and output according to the altitude of the aircraft, A second switch for switching a receiving antenna; a circulator for both transmission and reception connected to the first and second switches; and a transmission for outputting the first distance measurement signal as a transmission signal to the circulator. And a receiver that receives a reception signal from the reception antenna via the second switch and outputs the signal as a second ranging signal; and outputs and transmits the first and second switching signals. The first
A signal processing unit for calculating an altitude to the surface of the ground from a delay time between the distance measurement signal and the received second distance measurement signal. 3. a low altitude of the aircraft, the claims of the transmitting antenna is fixed to the first transmitting antenna, and switches the connection between the receiver to the receiving antenna
The radar altimeter described in 2 . 4. a high altitude of the aircraft, the transmitting antenna as a transceiving antenna, radar altimeter of claim 2, wherein sequentially switching the fifth transmission antenna from the first. 5. be inclined to the right and left the aircraft longitudinal, the sequential switching operation of the fifth transmission antenna from the first, wherein the distance between the aircraft and ground, characterized in that the measurable
The radar altimeter according to claim 2 or 4 .