Compatible split-band distance measuring method and apparatus

Claim 2

An improved radio distance measuring method comprising the steps of transmitting a distance measurement interrogation signal from an aircraft in a channel of a first frequency band, receiving said interrogation signal at a ground station, transmitting a response signal from the ground station in a channel of a second frequency band, receiving said second frequency band response signal at the aircraft, converting the second frequency band response signal to a frequency within said first frequency band for processing for thE distance measurement determination, and concurrently preventing the utilization of response signals received from ground stations by direct radiation in said first frequency band.

Claim 3

A method as claimed in claim 1 wherein said first frequency band is the L-band, and said second frequency band is the C-band.

Claim 4

A method as claimed in claim 1 wherein utilization of response signals received from ground stations by direct radiations in said first frequency band is prevented by interposing a duplexing circuit.

Claim 5

A method as claimed in claim 1 wherein the utilization of response signals received from ground stations by direct radiation in said first frequency band is prevented by providing a non-standard interrogation signal from the aircraft in said first frequency band in which said interrogation signal consists of two pulses of carrier energy spaced apart by a non-standard spacing so that the ground stations are prevented from recognizing the interrogation signals as signals calling for direct radiation response signals in said first frequency band.

Claim 6

A split-band distance measuring apparatus comprising airborne equipment including an L-band DME aircraft transmitter operable to transmit DME interrogation signals to a ground station and an L-band receiver for receiving and processing L-band response signals from a ground station and operable to measure distance therewith, a ground station operable to receive the L-band DME interrogation signals, said ground station including a C-band transmitter operable in response to the L-band interrogation signals to transmit DME response signals at a C-band frequency, said airborne equipment including a C-band receiver operable to receive the C-band DME response signals and comprised of frequency conversion means operable to convert the C-band response signals to L-band signals, means connecting said frequency conversion means to said L-band receiver to measure distance with the converted L-band signals, and means to prevent the reception by said L-band receiver of L-band response signals transmitted from a ground station by direct radiation at L-band frequencies.

Claim 7

A split-band distance measuring apparatus comprising airborne equipment including an L-band DME aircraft transmitter operable to transmit DME interrogation signals to a ground station and an L-band receiver for receiving and processing L-band response signals from a ground station and operable to measure distance therewith, a ground station operable to receive the L-band DME interrogation signals, said ground station including a C-band transmitter operable in response to the L-band interrogation signals to transmit DME response signals at a C-band frequency, said airborne equipment including a C-band receiver operable to receive the C-band DME response signals and comprised of frequency conversion means operable to convert the C-band response signals to L-band signals, means connecting said frequency conversion means to said L-band receiver to measure distance with the converted L-band signals, and means to prevent the reception by said L-band receiver of L-band response signals transmitted from a ground station by direct radiation at L-band frequencies.

Claim 8

Apparatus as claimed in claim 5 wherein said means to prevent the reception of direct radiation L-band response signals by the airborne equipment comprises means contained within said L-band aircraft transmitter for causing the L-band interrogation signals to be issued in a plurality of pulses of carrier having a unique spacing so as to prevent L-band response distance measurement equipment ground stations from responding to the interrogation signals to thereby prevent the transmission of direct radiation L-band response signals, said ground station including a C-band transmitter and said ground station being operable only in response to L-band interrogation signals issued in said plurality of pulses of carrier having said unique spacing to transmit DME response signals at C-band frequency.

Claim 9

Apparatus as claimed in claim 6 wherein said ground station includes both a C-band transmitter and an L-band transmitter, said ground station being operable to receive and distinguish both the interrogation signals issued in a plurality of pulses having a unique spacing which is used when C-band responses are desired and L-band interrogation signals issued in a conventional form when L-band responses are desired, said ground station including an L-band response transmitter as well as a C-band response transmitter, said ground station being operable to actuate said L-band response transmitter in response to L-band interrogation signals indicating a request for L-band responses, and said ground station being operable to actuate said C-band transmitter in response to L-band interrogation signals indicating a request for C-band responses.

Claim 10

A split-band distance measuring apparatus as claiMed in claim 5 wherein said ground station includes an L-band distance measuring equipment receiver operable to receive distance measurement interrogation signals in the form of two bursts of carrier energy having a predetermined spacing therebetween, said receiver including a directional L-band antenna providing a high signal receptivity in a predetermined direction from which aircraft interrogation signals are expected, a pulse spacing recognition circuit connected to said receiver and operable to detect when said predetermined spacing of said interrogation bursts of carrier have been received by said receiver and to provide an output signal in response thereto, said C-band transmitter being connected to receive the output signal from said pulse spacing recognition circuit and operable to generate distance measurement signal responses at C-band frequencies, a C-band antenna connected to said C-band transmitter and operable to transmit the C-band response signals, said C-band antenna having a directional characteristic to provide substantially stronger transmission of signals in said predetermined direction from which interrogation signals are expected.

Claim 11

Apparatus as claimed in claim 8 wherein there is provided a second pulse spacing recognition circuit operable to respond to a different spacing of transmitted pulses and to provide an output signal therefrom, an L-band transmitter connected to receive and to respond to output signals from said second pulse spacing recognition circuit to provide L-band response signals, said L-band transmitter being connected to said L-band antenna for transmission of said L-band response signals from said L-band antenna.

Claim 12

A split-band distance measuring apparatus comprising airborne equipment including an L-band DME aircraft transmitter operable to transmit DME interrogation signals to a ground station and an L-band receiver for receiving and processing L-band response signals from a ground station and operable to measure distance therewith, said airborne equipment also including a C-band receiver operable to receive C-band DME response signals in response to L-band interrogation signals and comprised of frequency conversion means operable to convert the C-band response signals to L-band signals, means connecting said frequency conversion means to said L-band receiver to measure distance with the converted L-band signals, and means to prevent the reception by said L-band receiver of L-band response signals transmitted from a ground station by direct radiation at L-band frequencies.

Claim 13

A split-band distance measuring apparatus comprising airborne equipment including an L-band DME aircraft transmitter operable to transmit DME interrogation signals to a ground station and an L-band receiver for receiving and processing L-band response signals from a ground station and operable to measure distance therewith, said airborne equipment also including a C-band receiver operable to receive C-band DME response signals in response to L-band interrogation signals and comprised of frequency conversion means operable to convert the C-band response signals to L-band signals, means connecting said frequency conversion means to said L-band receiver to measure distance with the converted L-band signals, and means to prevent the reception by said L-band receiver of L-band response signals transmitted from a ground station by direct radiation at L-band frequencies.

Claim 14

Apparatus as claimed in claim 10 wherein said airborne equipment includes UHF-VHF instrument landing system equipment, said C-band receiver and frequency conversion means comprising means for converting the C-band responses to UHF-VHF frequencies corresponding to the conventional instrument landing system frequency requirements so as to provide for a C-band instrument landing system function by means of said C-band receiver, and a separate frequency converter means connected to further convert DME signals included in the converted C-band signals at instrument landing system frequencies to L-band frequencies for processing by said L-band DME receiver.

Claim 15

Apparatus as claimed in claim 10 wherein said means to prevent the reception of direct radiation L-band response signals comprises means contained within said L-band transmitter for causing the L-band interrogation signals to be issued in a plurality of pulses of carrier having a unique spacing different from the spacing used when L-band responses are requested so as to prevent L-band response distance measurement equipment ground stations from responding to the interrogation signals to thereby prevent the transmission of direct radiation L-band response signals.

Claim 16

Apparatus as claimed in claim 10 wherein said means to pRevent the reception of direct radiation L-band response signals is operable only when C-band response signals are expected, and wherein there is provided a common L-band antenna which is operable for both transmission of L-band interrogation signals and reception of direct radiation L-band response signals, said L-band antenna being connected to said L-band receiver and said L-band transmitter through said connecting means for said frequency conversion means.

Claim 17

Apparatus as claimed in claim 13 wherein said connecting means comprises a duplexing circuit which is operable to permit L-band interrogation signals to be fed to said L-band antenna for transmission, and which is operable to block any substantial dissipation of the L-band interrogation signals in said frequency conversion means.

Claim 18

Apparatus as claimed in claim 13 wherein said connecting means comprises a duplexing circuit and wherein said means to prevent the reception of direct radiation L-band response signals is combined in said duplexing circuit, said duplexing circuit being operable to at least substantially attenuate direct radiation L-band response signals received at said L-band antenna before any part of the direct radiation L-band response signals reaches said L-band receiver.

Claim 19

Apparatus as claimed in claim 15 wherein a circuit means is provided which is operable in conjunction with said duplexing circuit for selectively eliminating the attenuation of direct radiation L-band response signals whenever said direct radiation L-band response signals are desired.

Claim 20

Apparatus as claimed in claim 15 wherein said duplexing circuit is operable to block any substantial dissipation of L-band interrogation signals in said frequency conversion means.

Claim 21

Apparatus as claimed in claim 17 wherein said duplexing circuit comprises at least one circulator having a first port connected in circuit with a common connection to the output of said L-band transmitter and the input of said L-band receiver and having a second port connected in circuit with said L-band antenna and having a third port connected to a non-reflective matched load and having a fourth port connected to said frequency conversion means, the direction of circulation of said circulator corresponding to the progressive numbering of said first, second, third, and fourth ports.

Claim 22

Apparatus as claimed in claim 18 wherein said duplexing circuit further comprises a second circulator connected in circuit between said second port of said first-mentioned circulator and said L-band antenna, said second circulator having a first port connected to said second port of said first-mentioned circulator and a second port connected to said L-band antenna and a third port connected to a non-reflective matched load, the direction of circulation of said second circulator being in the direction of the numbering of said first, second, and third ports.

Claim 23

Apparatus as claimed in claim 17 wherein said duplexing circuit comprises a directional coupler operable to detect the initiation of outgoing L-band interrogation signals from said L-band transmitter, a first switching means connected in circuit with said directional coupler and operable in response to the initiation of the outgoing L-band transmission signal to close a circuit from said transmitter to said L-band antenna, a second switching means connected for operation only in response to a signal from said directional coupler for opening a circuit from said frequency conversion means to said transmitter.

Claim 24

Apparatus as claimed in claim 20 wherein a monostable multivibrator is connected in circuit between said directional coupler and said first and second switching means for maintaining said first and second switching means in the switched condition for a period of time determined by the operating period of said monostable multivibrator whenever operAtion is first initiated, said first and second switching means comprising PIN microwave switches.