Frequency modulation radio altimeter

• US 4,739,330 A
• Filed: 06/19/1985
• Issued: 04/19/1988
• Est. Priority Date: 06/29/1984
• Status: Expired due to Fees

• Current Assignee: Thomson-CSF (Thales SA)
• Original Assignee: Thomson-CSF (Thales SA)
• Inventors: Lazarus, Michel
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): Sotomayor, John B.
• Application Number:
  US06/746,328
• Time in Patent Office: 1,035 Days
• Field of Search: 343/12 A, 343/14, 342/120, 342/122, 342/123, 342/128, 342/129, 342/130, 342/74, 342/85, 342/86, 342/87
• US Class Current: 342/122
• CPC Class Codes: G01S 13/343 using sawtooth modulation
• CPC Class Codes: G01S 13/70 for range tracking only
• CPC Class Codes: G01S 13/882 for altimeters measuring height using barometric means G01C5/06
• CPC Class Codes: G01S 7/034 Duplexers switching devices for waveguides H01P1/10; transmit-receive switching in transceivers H04B1/44

Abstract

A frequency modulation radio altimeter has a directional antenna which is connected to a transmission-reception switch controlled by a signal generator. The generator delivers periodic signals whose recurrence period is proportional to the delay time of the ground echo. The transmitter includes a radio frequency modulator modulated in frequency by a saw tooth signal whose recurrence period is proportional to the delay time of the ground echo. A homodyne receiver includes circuits for acquiring and tracking the ground echo signal, and supplies an output signal representative of the altitude and a control signal which is supplied to the inputs controlling the recurrence period of the transmission modulator and of the generator controlling the transmission-reception switch.

Claims

1. Frequency modulation, radio altimeter apparatus for use with a single antenna which emits transmission signals and receives echo signals, comprising:

modulation means, having a control input, for providing periodic modulation signals having a recurrence period which is proportional to a delay time of said echo signal;

radio frequency oscillator means, coupled to said modulation means, for providing said transmission signal modulated in accordance with said modulation signals;

generator means, having a control input, for providing a periodic signal having a recurrence period which is proportional to said delay time of said echo signal;

switch means, coupled to said oscillator means and said generator means and adapted to be coupled to said single antenna, adapted for switching said single antenna between a transmission mode and a reception mode, said switch means being controlled by said periodic signal from said generator means;

RF mixer means, coupled to said switch means and to said oscillator means, for mixing said echo signals with said transmission signals to provide a mixed signal;

RF bandpass amplifier means, coupled to said RF mixer means, for amplifying said mixed signal; and

processing means, coupled to said bandpass amplifier means and to said modulation means and to said generator means, for acquiring and tracking said echo signals from the amplified mixed signal, and for supplying a control signal to the control inputs of said modulation means and said generator means, and for supplying an output signal corresponding to said delay time of said echo signal.

2. Apparatus according to claim 1, wherein said modulation means includes a saw tooth signal generator.

3. Apparatus according to claim 2 wherein said saw tooth generator includes a generator of analog signals.

4. Apparatus according to claim 2 wherein said saw tooth generator includes a digital generator having a pulse counter and a digital-to-analog converter coupled in series.

5. Frequency modulation, radio altimeter apparatus for use with a single antenna which emits transmission signals and receives echo signals, comprising:

modulation means, having a control input, for providing periodic modulation signals having a recurrence period which is proportional to a delay time of said echo signal;

radio frequency oscillator means, coupled to said modulation means, for providing said transmission signal modulated in accordance with said modulation signals;

generator means, having a control input, for providing a periodic signal having a recurrence period which is proportional to said delay time of said echo signal;

switch means, coupled to said oscillator means and said generator means and adapted to be coupled to said single antenna, adapted for switching said single antenna between a transmission mode and a reception mode, said switch means being controlled by said periodic signal from said generator means, and said switch means including;

(i) a circulator adapted to be coupled to said single antenna, and having an input and an output;

(ii) a first unidirectional isolator coupled to the input of said circulator;

(iii) a second unidirectional isolator coupled to the output of said circulator;

(iv) a first gate having a first input coupled to said oscillator means, a second input coupled to said generator means, and an output coupled to said first unidirectional isolator;

(v) an inverter having an input coupled to said generator means, and an output; and

(vi) a second gate having a first input connected to the inverter output, a second input coupled to said second unidirectional isolator, and an output coupled to said mixer means;

RF mixer means, coupled to said switch means and to said oscillator means, for mixing said echo signals with said transmission signals to provide a mixed signal;

RF bandpass amplifier means, coupled to said RF mixer means, for amplifier means, coupled to said RF mixer means, for amplifying said mixed signal; and

processing means, coupled to said bandpass amplifier means and to said modulation means and to said generator means for acquiring and tracking said echo signals from the amplified mixed signal, and for supplying a control signal to the control inputs of said modulation means and said generator means, and for supplying an output signal corresponding to said delay time of said echo signal.

6. Apparatus according to claim 5 wherein said first gate includes:

a first blocking element coupled to said generator means;

a capacitor coupled to said oscillator means and to said first blocking element;

a diode-impedance circuit coupled between ground and said capacitor;

a diode coupled between said first blocking element and said first unidirectional isolator; and

a second blocking element coupled between ground and said first unidirectional isolator.

7. Frequency modulation, radio altimeter apparatus for use with a single antenna which emits transmission signals and receives echo signals, comprising:

modulation means, having a control input, for providing periodic modulation signals having a recurrence period which is proportional to a delay time of said echo signal;

radio frequency oscillator means, coupled to said modulation means, for providing said transmission signal modulated in accordance with said modulation signals;

generator means, having a control input, for providing a periodic signal having a recurrence period which is proportional to said delay time of said echo signal;

switch means, coupled to said oscillator means and said generator means and adapted to be coupled to said single antenna, adapted for switching said single antenna between a transmission mode and a reception mode, said switch means being controlled by said periodic signal from said generator means, and said switch means including;

(i) first, second and third nodes, said second node being adapted to be coupled to said single antenna;

(ii) a first blocking element coupled between said generator means and said first node;

(iii) a first capacitor coupled between said oscillator means and said first node;

(iv) a first diode-impedance circuit coupled between ground and said first node;

(v) a first diode coupled between said first and second nodes;

(vi) a blocking element coupled between ground and said second node;

(vii) a second diode coupled between said second and third nodes;

(viii) a second blocking element coupled between said generator means and said third node;

(ix) a second capacitor coupled between said mixer means and said third node; and

(x) a second diode-impedance circuit coupled between ground and said third node;

RF mixer means, coupled to said switch means and to said oscillator means, for mixing said echo signals with said transmission signals to provide a mixed signal;

RF bandpass amplifier means, coupled to said RF mixer means, for amplifying said mixed signal; and

processing means, coupled to said bandpass amplifier means and to said modulation means and to said generator means, for acquiring and tracking said echo signals from the amplified mixed signal, and for supplying a control signal to the control inputs of said modulation means and said generator means, and for supplying an output signal corresponding to said delay time of said echo signal.

8. Frequency modulation, radio altimeter apparatus for use with a single antenna which emits transmission signals and receives echo signals, comprising:

modulation means, having a control input, for providing periodic modulation signals having a recurrence period which is proportional to a delay time of said echo signal;

radio frequency oscillator means, coupled to said modulation means, for providing said transmission signal modulated in accordance with said modulation signals;

generator means, having a control input, for providing a periodic signal having a recurrence period which is proportional to said delay time of said echo signal;

RF mixer means, coupled to said switch means and to said oscillator means, for mixing said echo signals with said transmission signals to provide a mixed signal, said mixer means also being coupled to said generator means and including;

(i) an inverter having an input coupled to said generator means, and an output;

(ii) a preamplifier having an input coupled to said mixer means, and an output;

(iii) a gate coupled to the outputs of said inverter and said preamplifier, and having an output;

(iv) a bandpass filter coupled to the output of said gate, and having an output;

(v) an amplifier having an input coupled to the output of said bandpass filter;

RF bandpass amplifier means, coupled to said RF mixer means, for amplifying said mixed signal; and

processing means, coupled to said bandpass amplifier means and to said modulation means and to said generator means, for acquiring and tracking said echo signals from the amplified mixed signal, and for supplying a control signal to the control inputs of said modulation means and said generator means, and for supplying an output signal corresponding to said delay time of said echo signal.

9. Frequency modulation, radio altimeter apparatus for use with a single antenna which emits transmission signals and receives echo signals, comprising:

modulation means, having a control input, for providing periodic modulation signals having a recurrence period which is proportional to a delay time of said echo signal;

radio frequency oscillator means, coupled to said modulation means, for providing said transmission signal modulated in accordance with said modulation signals;

generator means, having a control input, for providing a periodic signal having a recurrence period which is proportional to said delay time of said echo signal;

switch means, coupled to said oscillator means and said generator means and adapted to be coupled to said single antenna, adapted for switching said single antenna between a transmission mode and a reception mode, said switch means being controlled by said periodic signal from said generator means;

said generator means including;

(i) a voltage frequency converter having an output; and

(ii) a divide-by-two divider coupled to said voltage frequency converter output, an output of said divide-by-two divider being provided to said switch means;

said modulation means including;

(i) a modulo 2^D counter coupled to said voltage frequency converter output; and

(ii) a digital-to-analog converter coupled to an output of said modulo 2^D counter;

RF mixer means, coupled to said switch means and to said oscillator means, for mixing said echo signals with said transmission signals to provide a mixed signal;

RF bandpass amplifier means, coupled to said RF mixer means, for amplifying said mixed signal; and

processing means, coupled to said bandpass amplifier means and to said modulation means and to said generator means, for acquiring and tracking said echo signals from the amplified mixed signal, and for supplying a control signal to the control inputs of said modulation means and said generator means, and for supplying an output signal corresponding to said delay time of said echo signal.

10. Frequency modulation, radio altimeter apparatus for use with a single antenna which emits transmission signals and receives echo signals, comprising:

modulation means, having a control input, for providing periodic modulation signals having a recurrence period which is proportional to a delay time of said echo signal;

radio frequency oscillator means, coupled to said modulation means, for providing said transmission signal modulated in accordance with said modulation signals;

generator means, having a control input, for providing a periodic signal having a recurrence period which is proportional to said delay time of said echo signal, said generator means including;

(i) a voltage frequency converter having an output; and

(ii) a divide-by-two divider coupler to said voltage frequency converter output, and having an output;

said modulation means including;

(i) a modulo 2^N-1 counter coupled to said divide-by-two divider output; and

(ii) a digital-to-analog converter coupled to an output of said modulo 2^N-1 counter;

switch means, coupled to said oscillator means and said generator means and adapted to be coupled to said single antenna;

adapted for switching said single antenna between a transmission mode and a reception mode, said switch means being controlled by said periodic signal from said generator means;

RF mixer means, coupled to said switch means and to said oscillator means, for mixing said echo signals with said transmission signals to provide a mixed signal;

RF bandpass amplifier means, coupled to said RF mixer means, for amplifying said mixed signal; and

processing means, coupled to said bandpass amplifier means and to said modulation means and to said switch means, for acquiring and tracking said echo signals from the amplified mixed signal, and for supplying a control signal to the control inputs of said modulation means and said generator means, and for supplying an output signal corresponding to said delay time of said echo signal.