Beacon interrogator beamwidth control using sidelobe signal integration in transponders

• US 5,218,365 A
• Filed: 07/02/1992
• Issued: 06/08/1993
• Est. Priority Date: 07/02/1992
• Status: Expired due to Term

• Current Assignee: OL Security LLC (Intellectual Ventures LLC)
• Original Assignee: Alliedsignal Inc. (Honeywell International Inc.)
• Inventors: Woodall, Phillip J.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US07/907,945
• Time in Patent Office: 341 Days
• Field of Search: 342/32, 342/37, 342/39, 342/40
• US Class Current: 342/39
• CPC Class Codes: G01S 13/762 with special measures concerning the radiation pattern, e.g. S.L.S. aerials or aerial systems providing at least two radiation patterns, e.g. providing sum and difference patterns, H01Q25/00

Abstract

A method for inhibiting responses by transponders to interrogation signals originating in the side lobes of an interrogating radar of a secondary radar system. The interrogating radar first transmits a reference signal with the highest power level of the reference signal being directed into a zone of interest to the interrogating radar. The interrogating radar then transmits a control signal having a higher power level than the reference signal in all regions of space except within the zone of interest. The control signal is of substantially longer duration than the reference signal. A transponder receives, detects and measures the peak amplitude of the reference signal and establishes a minimum trigger level (MTL) at a predetermined level below the reference signal peak. The control signal is received, detected and integrated. The peak amplitude of the integrated control signal is compared with the MTL. A transponder response is inhibited if the peak amplitude of the integrated control signal is greater than the MTL. The peak amplitude of the integrated control signal may be amplified before comparison with the MTL to increase the amount of synthetic beam sharpening provided by the method and the amount of synthetic beam sharpening provided may be controlled by the interrogating radar by delaying the start of transmission of the control signal.

Claims

1. A method for inhibiting response to interrogation signals by certain transponders in a secondary radar system having a plurality of transponders and an interrogating radar, where the transponders whose responses are to be inhibited are locate outside of a zone of interest to the interrogating radar, comprising the steps of:

transmitting a reference signal P_ref by said interrogating radar, said P_ref signal being transmitted into said zone of interest at a power level that exceeds the power level of said P_ref signal in all regions of space outside said zone of interest;

transmitting a control signal I₁ by said interrogating radar at a predetermined time after transmission of said P_ref signal, said I₁ signal being transmitted at a power level that exceeds the power level of said P_ref signal in all regions of space outside said zone of interest but that is lower than the power level of said P_ref signal within said zone of interest;

receiving and detecting said P_ref signal at a transponder;

measuring the peak amplitude of said detected P_ref signal;

establishing a minimum trigger level at a predetermined value below said measured peak amplitude of said detected P_ref signal;

receiving and detecting said I₁ signal at said transponder;

integrating with respect to time said detected I₁ signal over the period of said detected I₁ signal;

measuring the peak amplitude of said integrated I₁ signal;

comparing said peak amplitude of said integrated I₁ signal with said minimum triggering level; and

inhibiting a response by said transponder to an interrogation signal transmitted by said interrogating radar

whenever said peak amplitude of said integrated I₁ signal is greater than said minimum triggering level.

2. A method as claimed in claim 1, wherein said control signal I₁ is transmitted by said interrogating radar for a substantially longer period than the period of transmission of said reference signal P_ref.

3. A method as claimed in claim 2, wherein a directive antenna is used in performing said step of transmitting a reference signal P_ref and an omnidirectional antenna is used in performing said step of transmitting a control signal I₁.

4. A method as claimed in claim 2, wherein said interrogating radar is a monopulse radar having sum and difference antenna patterns, and wherein said step of transmitting a reference signal P_ref is performed using said sum antenna pattern and said step of transmitting a control signal I₁ is performed using said difference antenna pattern.

5. A method as claimed in claim 2, wherein said step of integrating with respect to time said detected I₁ signal includes the steps of:

,

applying said detected I₁ signal to an integrator circuit having a transfer function in the form of;

##EQU7## where;

A is the amplification factor of said integrator circuit, τ

is the time constant of said integrator circuit, and s is the differential operator d/dt;

enabling operation of said integrator circuit at the expected arrival time at said transponder of said I₁ signal; and

terminating operation of said integrating circuit at a predetermined time after said integrating circuit is enabled, the value of the output of said integrator circuit at the time of said termination being said peak value of said integrated I₁ signal.

6. A method as claimed in claim 5 wherein the value of the amplification factor A of said integrator circuit is selected so that said peak value of said integrated I₁ signal is greater than the peak value of said detected I₁ signal.

7. A method as claimed in claim 6 wherein the volume of space occupied by said zone of interest to said interrogating radar can been enlarged a controllable amount by modifying said step of transmitting a control signal I₁, said modification comprising:

delaying the start of transmitting a control signal I₁ until a selected amount of time after said predetermined time after transmission of said P_ref signal, the extent of said enlargement of said zone of interest being proportional to the length of said selected amount of time.

8. A method for inhibiting response to interrogation signals by certain transponders in a secondary radar system having a plurality of transponders and an interrogating radar, where the transponders whose responses are to be inhibited are located outside of a zone of interest to the interrogating radar, comprising the steps of:

transmitting a reference signal P_ref by said interrogating radar, said P_ref signal being transmitted into said zone of interest at a power level that exceeds the power level of said P_ref signal in all regions of space outside said zone of interest;

transmitting a first control signal I₁ by said interrogating radar at a first predetermined time after transmission of said P_ref signal, said I₁ signal being transmitted at a power level that exceeds the power level of said P_ref signal in all regions of space outside said zone of interest but that is lower than the power level of said P_ref signal within said zone of interest;

transmitting a second control signal I₂ by said interrogating radar at a second predetermined time after transmission of said P_ref signal, said I₂ signal being transmitted at a power level that exceeds the power level of said P_ref signal in all regions of space outside said zone of interest but that is lower than the power level of said P_ref signal within said zone of interest;

receiving and detecting said P_ref signal at a transponder;

measuring the peak amplitude of said detected P_ref signal;

establishing a minimum trigger level at a predetermined value below said measured peak amplitude of said detected P_ref signal;

receiving and detecting said I₁ signal at said transponder;

integrating with respect to time said detected I₁ signal over the period of said detected I₁ signal;

receiving and detecting said I₂ signal at said transponder;

integrating with respect to time said detected I₂ signal over the period of said detected I₂ signal;

measuring the peak amplitude of said integrated I₂ signal;

individually comparing said peak amplitudes of said integrated I₁ signal and said integrated I₂ signal with said minimum triggering level; and

inhibiting a response by said transponder to an interrogation signal transmitted by said interrogating radar whenever said peak amplitude of either said integrated I₁ signal or said integrated I₂ signal is greater than said minimum triggering level.

9. A method as claimed in claim 8 wherein said interrogating radar is a monopulse radar that transmits a conical beam, said interrogating radar having an antenna producing a sum antenna pattern and a difference antenna pattern in the azimuth plane and a sum antenna pattern and a difference in the elevation plane, wherein:

said step of transmitting a reference signal P_ref is performed using simultaneously said sum antenna pattern in the azimuth plane and said sum antenna pattern in the elevation plane;

said step of transmitting a first control signal I₁ is performed using simultaneously said difference antenna pattern in the azimuth plane and said difference antenna pattern in the elevation plane; and

said step of transmitting a second control signal I₂ is performed using simultaneously said difference antenna pattern in the azimuth plane and said difference antenna pattern in the elevation plane.

10. A method as claimed in claim 8 wherein said interrogating radar is a monopulse radar that transmits a conical beam, said interrogating radar having an antenna producing a sum antenna pattern and a difference antenna pattern in the azimuth plane and a sum antenna pattern and a difference in the elevation plane, wherein:

said step of transmitting a reference signal P_ref is performed using simultaneously said sum antenna pattern in the azimuth plane and said sum antenna pattern in the elevation plane;

said step of transmitting a first control signal I₁ is performed using one of said difference antenna patterns in one of said planes; and

said step of transmitting a second control signal I₂ is performed using the other of said difference antenna patterns in the other of said planes.