Radar transponder apparatus and signal processing technique
First Claim
1. A transponding apparatus comprising:
- a) signal receiving means for receiving an illuminating signal from a radar source located on an airborne platform;
b) frequency conditioning means coupled to said receiving means for phase-shifting said illuminating signal into a phase-shifted transponder signal; and
c) transmitting means coupled to said frequency conditioning means for transmitting said phase-shifted transponder signal to an rf receiving means at said airborne platform;
wherein said transponding apparatus is capable of amplitude-gating and phase-coding said phase-shifted transponder signal with a number of prescribed and/or informational pulse sequences for retransmission to said rf receiving means at said airborne platform.
2 Assignments
0 Petitions
Accused Products
Abstract
An active, phase-coded, time-grating transponder and a synthetic-aperture radar (SAR) and signal processor means, in combination, allow the recognition and location of the transponder (tag) in the SAR image and allow communication of information messages from the transponder to the SAR. The SAR is an illuminating radar having special processing modifications in an image-formation processor to receive an echo from a remote transponder, after the transponder receives and retransmits the SAR illuminations, and to enhance the transponder'"'"'s echo relative to surrounding ground clutter by recognizing special transponder modulations from phase-shifted from the transponder retransmissions. The remote radio-frequency tag also transmits information to the SAR through a single antenna that also serves to receive the SAR illuminations. Unique tag-modulation and SAR signal processing techniques, in combination, allow the detection and precise geographical location of the tag through the reduction of interfering signals from ground clutter, and allow communication of environmental and status information from said tag to be communicated to said SAR.
113 Citations
33 Claims
-
1. A transponding apparatus comprising:
-
a) signal receiving means for receiving an illuminating signal from a radar source located on an airborne platform; b) frequency conditioning means coupled to said receiving means for phase-shifting said illuminating signal into a phase-shifted transponder signal; and c) transmitting means coupled to said frequency conditioning means for transmitting said phase-shifted transponder signal to an rf receiving means at said airborne platform; wherein said transponding apparatus is capable of amplitude-gating and phase-coding said phase-shifted transponder signal with a number of prescribed and/or informational pulse sequences for retransmission to said rf receiving means at said airborne platform. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
-
-
9. A transponder apparatus comprising:
-
a) illuminating radar signal receiving means for receiving an illuminating signal from a radar source; b) frequency conditioning means coupled to said illuminating radar signal receiving means for modulating said illuminating signal into a phase-shifted tag signal; c) code generator means for generating a prescribed code sequence in response to said illuminating signal; d) transponder status means coupled to said code generator means for providing status information unique to said transponder apparatus to an airborne-based platform through a transmitting means; e) mixing means, incorporated as part of said code generator means, for combining said prescribed code sequence with said status information to produce a sequence having a combination of prescribed and information content to be sent to said airborne platform by a transmitting means; and f) transmitting means for transmitting said identifying code signal and said identifying information to said airborne platform. - View Dependent Claims (10, 11, 12, 13)
-
-
14. An rf transponder recognition and identification system comprising:
-
a) an rf transponder (tag) for receiving, modulating, and retransmitting rf pulses transmitted to said tag by a synthetic-aperture radar means, wherein said tag means is capable of amplitude-gating and phase-coding its echo with a number of prescribed and/or informational pulse sequences for retransmission to said synthetic-aperture radar means, said tag further comprising; i) radar signal receiving means for receiving an illuminating signal from said SAR; ii) frequency conditioning means coupled to said radar signal receiving means for phase-shifting said illuminating signal into a phase-shifted tag signal; iii) transmitting means for transmitting rf signals to said SAR; iv) code generator means for generating a prescribed code sequence for transmission to said SAR through said transmitting means; v) tag status means coupled to said code generator means for providing identifying, environmental and '"'"'status information of said tag to said SAR through said transmitting means; and vi) mixing means, incorporated as part of said code generator means, for combining said prescribed sequence with said status information to produce a sequence having a combination of prescribed and informational content to be sent by said transmitting means to said airborne SAR; and b) a synthetic-aperture radar (SAR) located on an airborne platform said SAR comprising; i) illumination signal means for transmitting illuminating signals toward a ground surface from an airborne platform; ii) rf receiving means for receiving radio frequency echo signals after said SAR transmits said illuminating signals to said surface; iii) first signal-processing means coupled to said rf receiving means wherein echo signals are processed and demodulated using prescribed modulation sequences stored in a code-memory means and wherein prescribed modulation sequences, stored in a code memory means, identical to that used by said tag are mixed against echoes received by said rf receiving means providing processing of incoming tag echoes also received by said receiving means with said radio frequency echo signals reflected from said surface; and iv) code memory means coupled to said first signal processing means for storing said modulation sequences; wherein the total echo signal returned to said synthetic-aperture radar is processed by said processing in combination with additional standard image-formation processing of the echoes of at least one transponder apparatus, and resulting in the significant suppression of unwanted echoes due to clutter echo from stationary, natural or cultural targets located in proximity to said at least one transponder apparatus. - View Dependent Claims (15, 16, 17, 18)
-
-
19. A method of detecting and locating a transponding apparatus comprising the steps:
-
a) an airborne platform-based synthetic-aperture radar transmits illuminating radar signals towards the earth'"'"'s surface for receipt by ground-based transponder devices; b) at least one transponding apparatus receives the illuminating signals through a receiving means; c) said transponding apparatus filters and amplifies said illuminating signals; d) said illuminating signals are decoded to identify downlink commands from said SAR wherein said commands contain information that allow said SAR and said transponder to obtain a common pulse index; e) the illuminating signals pass through a time-gating circuit within said tag and into a time-delay device wherein said signals are delayed in time by an amount equal to a function of the duration of the pulse transmitted by the SAR; f) the signals are provided to a transponder transmitter through a bi-phase modulator which impresses on the signals a prescribed phase code and changes the phase of the signals; g) the signals are amplified at the transponder transmitter and are retransmitted back to the SAR in a phase-shifted state to identify the transponder'"'"'s location; h) the SAR receives the phase-shifted signals retransmitted by the transponder; i) the signals received by the SAR are processed and filtered at a signal processing means; and j) a pseudo-image is formed on a screen allowing the transponder'"'"'s location to be determined on said screen wherein clutter energy which is not phase-shifted appear at Doppler frequencies outside the frequency passband of the pre-filter and are not shown within said screen. - View Dependent Claims (20, 21, 22, 23)
-
-
24. A method of communicating identifying information and status information from a transponding apparatus to a synthetic aperture radar (SAR) following detection and location of said tag by said SAR, wherein:
-
a) an airborne platform-based SAR transmits illuminating radar signals toward the earth'"'"'s surface for receipt by at least one ground-based transponding apparatus; b) at least one transponding apparatus (tag) receives the illuminating signals through a receiving means; c) said tag filters and amplifies the illuminating signals through a receiving means; d) said illuminating signals are decoded to identify downlink commands from said SAR wherein said commands contain information that allows said SAR and said tag to obtain a common pulse index; e) said illuminating signals pass through a time-gating circuit within said tag and into a time-delay device wherein said signals are delayed in time by an amount equal to a fraction of the duration of the pulse transmitted by the SAR; f) said signals are provided to a tag transmitter through a bi-phase modulator which impresses on the signals a phase code containing both prescribed and informational content; g) said signals are amplified at the tag transmitter and are retransmitted back to the SAR in a phase-shifted state; h) said SAR receives said phase-shifted signals retransmitted by said tag; i) said phase-shifted signals are processed and filtered by a signal processing means wherein the said prescribed-code portion of said phase-shifted signal is removed; and j) said phase-shifted signals are further processed to determine the information code sequence sent by the transponder. - View Dependent Claims (25)
-
-
26. A method of recognizing a remote transponder on a display comprising the steps of:
-
a) sending an illuminating radar signal from a radar source on an airborne platform towards the earth'"'"'s surface; b) the illuminating radar signal is received at a remote transponder wherein the signal is filtered and processed by the remote transponder'"'"'s signal processing means; c) the illuminating signal is modulated within said signal processing means such that said illuminating signal is phase-shifted; d) the phase-shifted signal is amplified and transmitted back to the airborne platform where the signal is received; e) the phase-shifted signal is amplified and filtered at the airborne platform after it is received by a receiving means; f) the phase-shifted signal is displayed on a screen means wherein the location of the transponder is indicated on said screen and clutter and noise that is not phase-shifted is not displayed on said screen after said filtering. - View Dependent Claims (27, 28, 29, 30)
-
-
31. A method of communicating identifying information from a transponding means to an airborne-based monitor, comprising:
-
a) a transponding apparatus receives an illuminating signal through a receiving means; b) the illuminating signal is filtered and amplified by said transponding apparatus; c) the illuminating signal is decoded to identify commands from said airborne-based monitor which allow said transponding apparatus and said airborne-based monitor to obtain a common pulse index; and d) identification signals unique to said transponding apparatus are amplified and retransmitted by said transponding apparatus using said common pulse index to said airborne-based monitor in a phase-shifted state. - View Dependent Claims (32, 33)
-
Specification