RADIO ALTIMETER

Abstract

A radio altimeter includes a voltage controlled oscillator outputting a radio frequency signal through a forward path in a direction from the voltage controlled oscillator to a radio frequency antenna, a path extending unit positioned in the forward path to receive the radio frequency signal to delay the radio frequency signal to generate a delayed radio frequency signal. The radio frequency antenna transmits the delayed radio frequency signal to ground and receives the delayed radio frequency signal reflected from the ground. The radio altimeter also includes a mixer that receives the reflected delayed radio frequency signal through a signal reception path from the radio frequency antenna and the radio frequency signal from the voltage controlled oscillator and mixes the radio frequency signal and the reflected delayed radio frequency signal to output a beat frequency signal which is used to calculate altitude with respect to the ground.

Claims

1. A radio altimeter including: a voltage controlled oscillator outputting a radio frequency signal through a forward path, the forward path being a signal transmission path for transmitting the radio frequency signal in a direction from the voltage controlled oscillator to a radio frequency antenna; a path extending unit that is positioned in the forward path and receives the radio frequency signal through the forward path to delay the radio frequency signal and generate a delayed radio frequency signal, wherein the path extending unit comprises: an electro-optical (E/O) converter converting the radio frequency signal into an optical signal; an optical cable delaying the optical signal; and a photoelectric (O/E) converter re-converting the delayed optical signal into the delayed radio frequency signal; and the radio frequency antenna that transmits the delayed radio frequency signal to ground and receives the delayed radio frequency signal reflected from the ground; and a mixer that receives the reflected delayed radio frequency signal through a signal reception path from the radio frequency antenna and the radio frequency signal from the voltage controlled oscillator and mixes the radio frequency signal and the reflected delayed radio frequency signal to output a beat frequency signal which is used to calculate altitude with respect to the ground.

2. The radio altimeter of claim 1, further comprising: a directional coupler that divides the radio frequency signal output from the voltage controlled oscillator; and a power amplifier of which out put signal is provided to the radio frequency antenna, wherein the path extending unit is positioned between the directional coupler and the power amplifier.

3. The radio altimeter of claim 1, wherein the path extending unit is positioned only in the forward path.

Description

DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is a block diagram illustrating a configuration of a general frequency modulated-continuous wave (FM-CW) radio altimeter;

[0027] FIG. 2 is a view illustrating the principle of calculating altitude using the FM-CW radio altimeter of FIG. 3.

[0028] FIG. 3 is a block diagram illustrating a configuration of a pulse limited altimeter according to an exemplary embodiment of the present disclosure.

[0029] FIG. 4 is a block diagram illustrating a configuration of an FM-CW radio altimeter according to an exemplary embodiment of the present disclosure.

BEST MODE

[0030] Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

[0031] First, characteristic concepts of the present disclosure common to two embodiments will be described as follows.

[0032] As described above, in a case in which a wide range of altitude measurement, from a very short distance to a long distance, is required, for example, a range of measurement altitude from 1 m to 10,000 m, when a path having a predetermined distance is added to a transmission (or reception) path of radio waves, a dynamic measurement range may be reduced.

[0033] For example, when a path equal to a distance of 200 m (since this is a round-trip distance, an altitude of 100 m) is inserted into a transmission or reception path, a range of actual measurement altitude ranges from 101 m to 10,100 m, obtaining an effect that a dynamic range of a maximum altitude with respect to a minimum altitude is reduced to 100 times (20 dB) from that of the related art 10,000 times (40 dB).

[0034] In this regard, in the case of using an optical cable included as an embodiment of a path extending unit, even when the optical cable is considerably long, a loss thereof is 1 dB/km or less, substantially small, and since there is no burden of size, an optical cable having a length of tens of kilometers may be inserted. In addition, in the case of using an optical cable having a length of 200 meters, a dynamic range of measurement altitude is reduced to the 20 dB level. Hereinafter, effective advantages of altitude measurement according to the insertion of an optical cable will be described with reference to a specific exemplary embodiment.

MODE FOR INVENTION

[0035] FIG. 3 is a block diagram illustrating a configuration of a pulse limited altimeter according to an exemplary embodiment of the present disclosure.

[0036] In the exemplary embodiment of FIG. 3 the path extending unit 700 is installed between the modulation switch 510 and the power amplifier 515 to extend an optical path between transmission and reception of a pulse signal. In the case in which the extended optical path is 200 meters, a minimum measurement altitude is 101 meters, whereby a width of a maximum transmission pulse may be increased from the conventional 6.67 ns to 670 ns, and thus, a bandwidth of a receiving end may be reduced to 1/100, which also reduces MDS of the receiver to 1/100 (=20 dB).

[0037] The path extending unit 700 includes an electro-optical (E/O) converter converting an RF pulse signal input from the modulation switch 510 into an optical signal, an optical cable 720 inserted into the path by a length required for extending the optical path, and a photoelectric (O/E) converter 730 converting an optical signal output from the optical cable 720 into an RF signal.

[0038] Here, the E/O converter 710 may employ an analog modulation scheme of amplitude-modulating an output from a laser diode by using an RF signal, and the O/E converter 730 may employ an analog amplitude modulation/demodulation scheme of detecting an amount of input light by using an optical sensor such as a photodiode, or the like, and outputting a corresponding signal.

[0039] As for the E/O converter 710 and the O/E converter 730, it is important to use an element or a component capable of providing a sufficient bandwidth according to a dynamic range of measurement altitude.

[0040] In FIG. 3, it is illustrated that the path extending unit 700 is inserted between the modulation switch 510 and the power amplifier 515, namely, in the transmitting end, but it may also be inserted into the receiving end, for example, into the portion indicated by {circle around (a)}.

[0041] In addition, the path extending unit 700 may also be installed to be inserted into a certain point in a signal transmission path.

[0042] FIG. 4 is a block diagram illustrating a configuration of an FM-CW radio altimeter according to an exemplary embodiment of the present disclosure.

[0043] Referring to FIG. 4, the FM-CW radio altimeter according to an exemplary embodiment of the present disclosure may include a path extending unit 700 inserted between a directional coupler 610 and a power amplifier 615, and here, the path extending unit 700 may include an optical cable 720.

[0044] The path extending unit 700 may be positioned between transmission and reception to serve to delay a signal provided from the outside to reduce a dynamic range of the radio altimeter. Here, since the path extending unit 700 includes the optical cable 720, in the case in which the extended optical path is 200 meters, a minimum measurement altitude is 101 meters, whereby, in the FM-CW radar scheme, the beat frequency Fb according to altitude is changed 100 times, and this degree of frequency range may allow for sufficiently accurate measurement and, in actual implementation, a bandwidth of the receiving end can be considerably reduced. Namely, the path extending unit 700 may reduce the dynamic range of the radio altimeter to 1/10 to 1/1,000, and in this case, the optical cable 720 may be formed to have a length sufficient for reducing a frequency band of transceiver components of the radio altimeter to 1/10 to 1/1,000.

[0045] In the case of uniformly maintaining the beat frequency Fb according to altitude through feedback, the beat frequency Fb may be uniformly maintained when it is designed such that frequency variations f (or fm) is changed about only 100 times, and thus, an actual implementation is non-problematic.

[0046] In addition to the optical cable 720, the path extending unit 700 further includes an electrooptic (E/O) converter 710 and a photoelectric (O/E) converter 730. Here, the E/O converter 710 may employ an analog modulation scheme of amplitude-modulating an output from a laser diode by using an RF signal, and the O/E converter 730 may employ an analog amplitude modulation/demodulation scheme of detecting an amount of input light by using an optical sensor such as a photodiode, or the like, and outputting a corresponding signal.

[0047] In FIG. 4 it is illustrated that the case in which the path extending unit 700 is inserted between the directional coupler 610 and the power amplifier 615, namely, in the transmitting end, but it may also be inserted into the receiving end, for example, into the portion indicated by {circle around (a)}. In addition, naturally, the path extending unit 700 may also be installed to be inserted into a certain point in a signal transmission path.

[0048] While the present invention has been shown and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

INDUSTRIAL APPLICABILITY

[0049] The present invention provides a radio altimeter effectively coping with a wide measurement range from a short range to a medium and long range, and thus, it may be very useful for the aviation industry or defense industry.