Abstract: A transponder lock provides allows an aircraft transponder to continue transmitting an alerting code for the duration of an emergency. The transponder lock thereby enables the aircraft transponder to continue to provide crucial information to ground tracking stations. Installation of the transponder lock results in very little aircraft downtime because the transponder lock connects in-line with existing aircraft wiring.

Abstract: SAW devices such as interdigital transducers (IDTs) have been widely used in RADAR applications and as filters. An IDT produces a SAW when excited by a single electrical pulse and can be fabricated to embody a code, which code provides for a passive autocorrelation of a SAW input to the IDT and thereby lends itself to further application as a signal generator in a communication device. However, internal dimensions of IDTs are inversely proportional to operating frequency, such that high frequency IDTs present significant manufacturing difficulties. Fabrication of IDTs for high frequency applications is simplified by exploiting a harmonic frequency SAW generated by IDTs. An IDT may therefore be designed according to fundamental frequency internal dimension criteria but can operate at a multiple of the fundamental frequency, thereby providing much higher frequency operation than conventional SAW systems.

Abstract: A radio frequency identification device comprises an integrated circuit including a receiver, a transmitter, and a microprocessor. The receiver and transmitter together define an active transponder. The integrated circuit is preferably a monolithic single die integrated circuit including the receiver, the transmitter, and the microprocessor. Because the device includes an active transponder, instead of a transponder which relies on magnetic coupling for power, the device has a much greater range.

Abstract: A transceiver or transponder particularly for synthetic aperture radar, or SAR, systems, operating in a frequency band having a central frequency, the transponder comprising a receiver (1) and a transmitter (2) both thermally stable and made by microstrip technology, the receiver (1) and the transmitter (2) being adapted to receive and to transmit, respectively, an electromagnetic wave provided with at least one linear polarisation, the receiver (1) being connected to the transmitter (2) by amplifier means comprising an amplifier unit (5) for each linear polarisation of the wave received by the receiver (1), each amplifier unit (5) including at least two amplifier stages (7, 9, 11) cascade arranged along a single microstrip and interconnected to one another and to an input and to an output of the corresponding amplifier unit (5) by means of coupling or matching stages (6, 8, 10, 12), the output signal of each amplifier unit (5) having substantially the same frequency as the input signal thereto, the amplifier

Abstract: An airline distress system is provided for an airplane. The airplane includes a pilot cockpit and a transponder for transmitting signals to an air traffic controller. The airline distress system includes an auxiliary transponder (10) that transmits auxiliary signals to the air traffic controller. The auxiliary transponder is preferably disposed outside of the pilot cockpit and inaccessible to airplane crew and passengers. In one embodiment, a sensor (16) is operatively coupled with the cockpit door, and a switch (20) communicates with the sensor (16) and the auxiliary transponder (10). The auxiliary transponder (10) is configured to be automatically activated by the switch (20) according to a signal from the sensor that the cockpit door has been opened.

Abstract: An access control system for an object, particularly a motor vehicle, comprises at least one base station with a transceiver device that transmits a wideband modulated interrogation signal, at least one transponder that has a modulation device, in order to modulate an auxiliary carrier signal, the frequency of which is changed between an infinite number of frequency positions, onto an interrogation signal received at a distance from the base station and reflect it as a code-modulated response signal, and an evaluation device that is connected after the transceiver device and that evaluates the response signal in sidebands of the changed frequency positions, with respect code and distance.

Abstract: An RFID system using encoded digital information utilizing pulsed linear frequency modulation (LFM). The LFM waveform is sent from an24 aircraft or satellite and is received by a transponder. The LFM waveform is demodulated using both, an AM and an FM receiver. The demodulated data is compared to preprogrammed criteria tables, and after validation is decoded and utilized. Algorithms in the transponder are used to determine the frequency deviation and for calculating the direction of the slope of the LFM input signal. The valid RF signal is stored in a delay element, encoded with the transponder data using phase modulation (PM), and frequency modulation (FM). The tag transmission is synchronized to the input LFM waveform. The transmit/receive chopping signal prevents unwanted oscillations and is capable of randomization.

Abstract: An RFID system using encoded digital information utilizing pulsed linear frequency modulation (LFM). The LFM waveform is sent from an aircraft or satellite and is received by a transponder. The LFM waveform is demodulated using both, an AM and an FM receiver. The demodulated data is compared to preprogrammed criteria tables, and after validation is decoded and utilized. Algorithms in the transponder are used to determine the frequency deviation and for calculating the direction of the slope of the LFM input signal. The valid RF signal is stored in a delay element, encoded with the transponder data using phase modulation (PM), and frequency modulation (FM). The tag transmission is synchronized to the input LFM waveform. The transmit/receive chopping signal prevents unwanted oscillations and is capable of randomization.

Abstract: A method and system for identifying a plurality of transponders in an interrogation involves transmitting an interrogation signal to the transponders and receiving, at a reader, response signals from the transponders. Each transponder period, and alters the maximum length of the waiting period during the interrogation process.

Abstract: The invention relates to a system for determining a position of a moving transponder adapted to receive a substantially stationary magnetic field signal and to transmit a further signal. The system comprises a signal generating arrangement adapted to generate said stationary magnetic field signal for said transponder, said transponder being adapted to determine a plurality of signal strengths of said received magnetic field signal; at least one signal receiving arrangement, adapted to receive said further signal of said transponder, said transponder being adapted to insert at least one message portion in said further signal indicative of at least one of said plurality of signal received signal strengths and processing means adapted to determine said position in accordance with a plurality of said received signal strengths determined by said moving transponder. This further signal can e.g.

Abstract: An integrated circuit having an identification code of M bits includes a communication interface circuit for receiving a selective identification request and a selection code, and a processing circuit connected thereto. The processing circuit includes a logic comparator having a first input for receiving the selection code and a second input for receiving the identification code, and an output for delivering an equal signal if the selection and identification codes are equal. A shift register has an output coupled to the first input of the logic comparator. A serial memory stores the identification code, and has a serial output coupled to the second input of the logic comparator and to a serial input of the shift register. A controller is connected to the shift register and to the serial memory for loading the selection code into the shift register, and for applying M shift pulses to the shift register and M read pulses to the serial memory.

Abstract: A Write Broadcast system and method uses a base station to write sent data to all or some selected number (sub group) of tags in a base station field simultaneously. By unselecting the tags that have been successfully written to, and requesting a response from the remaining tags in the field (or sub group), the system determines, by receiving a response to the request, that there are tags in the field (sub group) that were unsuccessfully written to. Another Write Broadcast signal is sent to these tags. The system is useful for quickly (simultaneously) “stamping” information on the tag memory of a large number of tags in the field of the base station.

Abstract: A multi-frequency RFID remote communication system is provided that includes a plurality of RFID tags configured to receive a first signal and to return a second signal, the second signal having a first frequency component and a second frequency component, the second frequency component including data unique to each remote RFID tag. The system further includes a reader configured to transmit an interrogation signal and to receive remote signals from the tags. A first signal processor, preferably a mixer, removes an intermediate frequency component from the received signal, and a second processor, preferably a second mixer, analyzes the IF frequency component to output data that is unique to each remote tag.

Abstract: A radio frequency identification device comprises an integrated circuit including a receiver, a transmitter, and a microprocessor. The receiver and transmitter together define an active transponder. The integrated circuit is preferably a monolithic single die integrated circuit including the receiver, the transmitter, and the microprocessor. Because the device includes an active transponder, instead of a transponder which relies on magnetic coupling for power, the device has a much greater range.

Abstract: A wireless network transmits digital data. The network includes an active transceiver to transmit carrier waves at a succession of preselected frequencies and a transponder. The transponder transmits digital data to the active transceiver by partially reflecting the carrier waves.

Abstract: Apparatus for processing a signal of a predetermined intermediate frequency (IF) to generate in-phase (I) and quadrature (Q) components thereof comprises: an analog-to digital converter circuit for sampling and digitizing the IF signal to generate digitized data samples thereof at a sampling rate that produces consecutive digitized data samples that are separated in phase by a substantially fixed phase angle 2&pgr;/n, where n is an integer greater than zero; first digital circuitry coupled to the analog-to digital converter circuit for demodulating the digitized data samples by multiplying every n consecutive digitized data samples with n respectively corresponding digital reference samples; and second digital circuitry coupled to the first digital circuitry for combining selected ones of the demodulated samples based on the substantially fixed phase angle to generate digital data samples of the I and Q components of the IF signal.

Abstract: A radio frequency identification device comprises an integrated circuit including a receiver, a transmitter, and a microprocessor. The receiver and transmitter together define an active transponder. The integrated circuit is preferably a monolithic single die integrated circuit including the receiver, the transmitter, and the microprocessor. Because the device includes an active transponder, instead of a transponder which relies on magnetic coupling for power, the device has a much greater range.

Abstract: Disclosed herein is a critical band encoding technology (CBET) system having at least one portable people meter (PPM) and a home base station and/or household hub, the CBET system containing a radio frequency (RF) proximity detection and identification system, comprising at least one RF transmitter for receiving a control signal, modulating an RF signal to a present modulation frequency upon receipt of the control signal, and wireless transmitting the modulated signal; and an RF receiver for receiving the wirelessly transmitted modulated signal, determining the modulation frequency, and transmitting the modulation frequency to a remote location, wherein the transmission power of the RF transmitter is preset to transmit the modulated data within a predetermined range.

Abstract: The output to the antenna of an RFID tag or label is disconnected from the balance of the RFID chip by means of a series switch activated in response to a logic command, CLOAK, generated by the RFID chip. Activation of the switch disconnects the output to the antenna of the RFID tag without disconnecting its input. The output to the antenna is thus disconnected for a time sufficient to allow the remaining RFID tags in an RF interrogation field to be identified. However, the input of the antenna remains connected and is capable of receiving at any time, including during the cloaking period commands which can lift the tag out of cloaking and allow it to then selectively output its signal.

Abstract: A security system which is suitable for use in a vehicle. The security system is a passive entry and passive re-mobilization system in which a security controller transmits a command signal LCs to a remote transponder, which replies with a LF response signal LRs. If an LF response signal is not received in response to the transmission of a command signal LCs, the security controller re-transmits the command signal, again as an LF command signal LCs. On determining that a command signal is a re-transmitted command signal, the remote transponder re-transmits the response signal as an UHF response signal URs.

Abstract: A method and apparatus that permit military aircraft operators to use the civilian Aircraft Addressing and Reporting System (ACARS) technology while ensuring data security.

Abstract: Transponders present in an interrogation zone can be identified by an interrogator by it sending an RF interrogation signal into the interrogation zone, the RF interrogation signal containing a code string prompting the transponders to generate partial addresses. As soon as one transponder “sees” that the generated partial address agrees with part of its own address, it responds by sending its full address which can then be read by the interrogator. Immediately after having received a full address the interrogator sends a code string characterizing the address of the transponder having responded before so that this transponder is thereby addressable. The signal sent by the interrogator to the transponder with this code string also contains an instruction which prompts the transponder to assume the condition in which it no longer responds to receiving its address or partial address.

Abstract: A system containing a navigational marker, the navigational marker having the ability to reflect radar in such a manner that the navigational marker is identified. In one embodiment, a polarized radar-reflective material is affixed to the navigational marker. A radar signal is reflected by the polarized radar-reflective material, causing the reflected radar signal to be polarized. The reflected radar signal is received and the navigational marker is identified. The radar system contains a detector/decoder capable of distinguishing the type of navigational marker based on the reflected radar signal. The detector/decoder relays information about the navigational marker to a display. In another embodiment, a navigational marker contains a radio responder. When a radar signal illuminates the navigational marker, the radio responder transmits a signal containing encoded data. A receiver detects the signal from the responder and decodes the encoded data. The decoded data is relayed to a display.

Abstract: A method and an identification system us for communicating between a reader and a plurality of transponders. The reader has a transmitter for transmitting a signal and each transponder includes a receiver for receiving the reader signal and a transmitter for generating a transponder signal. When the reader recognises a transponder signal from one of the transponders it immediately issues a mute instruction, muting all other active transponders and passing control to the said transponder, without the need for a specifically timed acknowledgement to the said controlling transponder. The reader may issue a single disable/wakeup instruction which disables the controlling transponder returning control to the reader and reactivated all muted (but not disabled) transponders.

Abstract: A transponder comprises a retro-reflective antenna array in which the length of the transmission lines is given by I=±A n&lgr; where: A is an arbitrary length; n is zero, or an integer, &lgr; is the wavelength of the retro-reflected signal. The array is fabricated on a board (71) of insulating material, using microstrip techniques. Rectangular patches (not shown) form the individual antennae and these are interconnected by transmission lines (75 to 82), each of which pass through a respective modulation device (43) whereby the retro-reflected signal is modulated. A positioning/tracking system incorporating one or more modulated transponders is also disclosed.

Abstract: A modulated backscatter communication system (e.g., an Electronic Shelf Label (ESL) system) includes a central node (e.g., a ceiling node) and one or more remote nodes (e.g., ESL tags). The central node transmits a downlink radio signal which is reflectively modulated at a remote node to produce a modulated reflected radio signal. At the remote node, a precise-frequency subcarrier signal is modulated with an uplink information signal to produce a modulated signal which is used to produce the modulated reflected radio signal. At the central node, the modulated reflected radio signal is received, detected and narrowband filtered to obtain the modulated subcarrier signal which is then demodulated to obtain the uplink information signal, with great immunity to close to carrier downlink radio noise and fluorescent light backscatter interference.

Abstract: A wireless network transmits digital data. The network includes an active transceiver to transmit carrier waves at a succession of preselected frequencies and a transponder. The transponder transmits digital data to the active transceiver by partially reflecting the carrier waves.

Abstract: A method for identifying and determining the position of rolling stock within a railyard using a system that includes an AEI reader, a plurality of elevated electronic imaging devices and a tracking computer. The rolling stock includes a plurality of railcars and a plurality of locomotives. The method includes recording an identification pattern for each piece of rolling stock as each piece enters the railyard, compiling tracking data of the rolling stock as the rolling stock moves within the railyard using the respective identification patterns, and mapping the position of each piece of rolling stock as the rolling stock moves within the railyard.

Abstract: The invention relates to a system suitable for a remote interrogation of passive transponders using chirp signals for interrogation. The transponder preferably has an encoding unit (11), a calibrating unit (12) and a measuring unit (13) each with a plurality of parallel channels (11.1 to 11.5, 12.1 and 13.1 to 13.2). The encoding unit and the calibrating unit are preferably jointly incorporated with a common delay line (14) on the same SAW chip. The interrogation signals received in the transponder via an antenna (10) are delayed characteristically and code-specifically, in particular in the encoding and calibrating unit. Decoding in the interrogation station is preformed by discrete Fourier transformation of the response signal and subsequent evaluation of the spectrum. To correct general disturbing influences on the delay of the response signal, said signal is calibrated using a single calibrating component in the response signal.

Abstract: The present invention provides a system for locating lost golf balls which includes a golf ball that incorporates an array of passive transponders and a radio frequency (“RF”) transmitter/receiver capable of energizing the passive transponder array and of detecting a signal emitted by the array. Each passive transponder functions as a tuned LC circuit that is charged by the RF transponder/receiver and emits an RF signal, detectable by the RF transmitter/receiver, for a finite period of time after the RF transmitter/receiver is turned off.

Abstract: A police activity transponder utilizes data available through a vehicle on-board diagnostic system or a intelligent vehicle data bus to adjust the sensitivity of the police activity transponder to law enforcement signals based on speed data. A police activity transponder is configured to read speed data available through an on-board diagnostic system or an intelligent vehicle data bus and using an internal clock, calculate a 0 to 60 mile per hour or a quarter mile time for display and function as a speedometer. A police activity transponder is configured to read engine revolutions per minute (rpm) data and function as a tachometer. A police activity transponder is configured to allow a user to input shift points, read engine rpm data, and provide a user indication.

Abstract: A device for data transmission in a motor vehicle and/or from a motor vehicle in its vicinity has a first transceiver unit (1) in or on the motor vehicle and a second transceiver unit (2) which is provided in at least one transponder unit whose spatial position relative to the vehicle may be variable or any desired position; it is characterized in that the first transceiver unit (1) is a radar unit equipped for distance measurement, expanded by adding a two-channel data transmission system; the second transceiver unit (2) is also a two-channel data transmission unit, and the microwave frequencies (f1, f2) for two-channel communication of the data transmission system are selected so that their difference |f1-f2| yields an intermediate frequency (fIF) which is processable using conventional components in a heterodyne receiver in the reception part of each of the first and second transceiver units (1, 2).

Abstract: In a transponder (19) for amplification of a received signal (60) into an antenna (1), to a signal (61) for retransmission, and where the retransmitted signal (61) possibly may have information superimposed, a quenched oscillator (5) is incorporated as amplifying element. The oscillator (5) is preferably of superregenerative type and exhibits negative resistance (30) for the received signal (60). Transponders according to the present invention may be introduced as system elements in a wireless or wire based network to work as intelligent or unintelligent connections in the network. The transponders can also be used in positioning systems.

Abstract: An active RF transponder is provided with a wake-up circuit that wakes the RF transponder from a sleep state upon detection of an RF interrogating signal. The active RF transponder includes a battery, an antenna adapted to receive RF signals from an interrogator, and electronic circuitry providing the various RF transponder functions of sending/receiving signals and storing data. A first embodiment of the invention includes a wake-up circuit that periodically checks for the presence of an RF signal at the antenna. The wake-up circuit is coupled to the antenna and includes a switch adapted to selectively couple the battery to the electronic circuitry and provide electrical power thereto upon detection of the RF signals by the antenna. The wake-up circuit further comprises an oscillator providing a clock signal having a low duty cycle that defines intervals during which the antenna is sampled for presence of the RF signals (e.g., approximately 20 ns every 100 &mgr;s).

Abstract: A transmitter and method for transmitting transponder or TCAS signals uses linear amplification to save on circuit component weight, cost and size while enabling precise amplification and control of the transmitted signal.

Abstract: An enhanced backscatter RF-ID tag reader system and multiprotocol RF tag reader system is provided. In a multiprotocol mode, the system emits a non-stationary interrogation signal, and decodes a phase modulated backscatter signal by detecting a stronger phase component from quadrature phase representations or determining phase transition edges in a phase of a received signal. The RF tag reader system predicts or follows the phase of the backscatter signal, thereby avoiding interference from nulls in the received signal waveform due to the non-stationary in terrogation signal, relative movement or environmental effects. An acoustic RF-ID tag detection system detects the reradiated signal corresponding to respective transformation of a signal in the tag. Detection of either type of RF-ID tags therefore is possible, and the absence of any tag or absence of any valid tag also determined.

Abstract: A method for identifying a person authorized to enter into a secured transaction, including implementing a security system to receive a coded signal that purports to identify as an authorized person the wearer of a device generating the coded signal through a transmission link constituting the body of the wearer, upon physical contact between an input terminal of the security system and the body of the wearer. After purported identification of the wearer as an authorized person for the transaction, data stored in a memory of the device is delivered to assist in processing the transaction by access through the security system. Data stemming from the transaction is retrieved for updating data stored in the memory, usable in a subsequent transaction by the wearer.

Abstract: This invention is a radar/tag system where pulses from a radar cause a tag (or transponder) to respond to the radar. The radar, along with its conventional pulse transmissions, sends a reference signal to the tag. The tag recovers the reference signal and uses it to shift the center frequency of the received radar pulse to a different frequency. This shift causes the frequencies of the tag response pulses to be disjoint from those of the transmit pulse. In this way, radar clutter can be eliminated from the tag responses. The radar predicts, to within a small Doppler offset, the center frequency of tag response pulses. The radar can create synthetic-aperture-radar-like images and moving-target-indicator-radar-like maps containing the signature of the tag against a background of thermal noise and greatly attenuated radar clutter. The radar can geolocate the tag precisely and accurately (to within better than one meter of error).

Abstract: A method and apparatus are provided that determine a frequency dependent calibration vector for a set of transmit or receive chains of a radio communications system using only differential phase and amplitude between the transmit chains and the receive chains, respectively. In one embodiment, the invention includes an antenna array adapted to transmit and receive radio communications signals with a plurality of other terminals, a transmit chain to transmit a calibration signal through the antenna array to a transponder on at least two different frequency bands, and a receive chain to receive through the antenna array a transponder signal from the transponder, the transponder signal being received on at least two different frequency bands and being based on the calibration signal.

Abstract: In a method and device for the encoding/decoding of power distribution at outputs of a system, a distribution encoder includes an element that receives a useful input signal and a piece of distribution information, and that superposes the piece of distribution information received on the input signal. The piece of information is used for the subsequent distribution of the total power of the input signal at an output or outputs of the system. A distribution decoder includes one or more inputs that receive an encoded signal or an encoded signal divided into several signals including the useful signal and the piece of distribution information. Further, one or more outputs are connected to the outputs of the system to which the useful signal is transmitted by distributing the total power received according to the piece of distribution information. The method and device enable, for example, fast, low-power switching of the outputs of a high-power system and the programming of a system with variable power outputs.

Abstract: A passive remote control device (20, 50) is powered remotely by a radio frequency exciter/receiver (14, 42) and used in a remote control system (100, 200) to control operation of a controlled device (10, 40), such as, for example, a television, video game controller, VCR, or CD player. The remote control device and the exciter/receiver communicate without wires via electrostatic or electromagnetic radiation. No line of sight connection to the passive remote control unit is required. No power source is integrated with the remote control device. The remote control device has a plurality of keys (22, 24, 25, 26, 27, 28, 29, 30, 31, 32) or control members that are manually actuated. Depression of a key or button, or other actuation of a control member, causes a response signal associated with that key to be generated. The response signal relates to an operation for the controlled device.

Abstract: An enhanced backscatter RF-ID tag reader system and multiprotocol RF tag reader system is provided. In a multiprotocol mode, the system emits a non-stationary interrogation signal, and decodes a phase modulated backscatter signal by detecting a stronger phase component from quadrature phase representations or determining phase transition edges in a phase of a received signal. The RF tag reader system predicts or follows the phase of the backscatter signal, thereby avoiding interference from nulls in the received signal waveform due to the non-stationary interrogation signal, relative movement or environmental effects. An acoustic RF-ID tag detection system detects the reradiated signal corresponding to respective transformation of a signal in the tag. Detection of either type of RF-ID tags therefore is possible, and the absence of any tag or absence of any valid tag also determined.

Abstract: A method and apparatus are provided for sensing two-dimensional identification marks provided on a substrate or embedded within a substrate below a surface of the substrate. Micropower impulse radar is used to transmit a high risetime, short duration pulse to a focussed radar target area of the substrate having the two dimensional identification marks. The method further includes the steps of listening for radar echoes returned from the identification marks during a short listening period window occurring a predetermined time after transmission of the radar pulse. If radar echoes are detected, an image processing step is carried out. If no radar echoes are detected, the method further includes sequentially transmitting further high risetime, short duration pulses, and listening for radar echoes from each of said further pulses after different elapsed times for each of the further pulses until radar echoes are detected.

Abstract: A method and apparatus is provided for remotely and constantly calibrating a transponder by using the ring around phenomenon. A number of different time varying physical quantities, such as for example temperature, signal level, noise, transmission line flex, frequency, and general operational effects, affect the inherent delay in transponders on a time varying basis. The invention relies on a the ring around phenomenon to produce pulse doublets, wherein the distance between the pulses in the pulse doublets correspond to the instantaneous delay in the transponder. The system is configured so that instantaneous variation in the transmission delay is detected and recognized on a pulse by pulse basis and transmitted to the interrogation device, which then functions to calculate the actual delay. Normal operation of the transponder is not affected by the continuous calibration method, and therefore a special calibration mode is not required.

Abstract: A method and apparatus for transponding pulsed RF signals is provided. The method comprises receiving, with a receiver, pulsed RF signals having a plurality of PRIs. Further the method includes generating, with a PRI tracker, control signals from the received pulsed RF signals. The method then filters the received pulsed RF signals with the control signals to thereby obtain enable signals, which in turn control a transmitter permitting retransmission without clock jitter.

Abstract: A radio frequency transponder device in an integrated circuit package requires only one dedicated pin for connection to a parallel resonant tuned circuit for receiving a remote signal. The one dedicated pin has a capacitor which blocks direct current (DC) flow and allows independent DC biasing of a radio frequency amplifier for increased signal amplification gain. Another package pin used for common power or ground connections supplies the second connection to the resonant tuned circuit. Multiple transponder inputs may be implemented in a single integrated circuit package using only one dedicated pin per input plus one common pin which may be used for another purpose, such as a power or a ground connection.

Abstract: Apparatus for the identification of articles (5) endowed with device for changing the polarization properties of the radiation, comprising a source (1) of non-randomly polarized microwave radiation, and a detector (3) for detecting the change in polarization properties of the radiation. The microwave radiation may have a first plane of polarization and, in use, the device for changing the plane of polarization properties of radiation may change the first plane of polarization to a second plane of polarization. The detector (3) for detecting the change in polarization properties of radiation may comprise a receiving antenna (4c) connected to suitable microwave detector (3), where the receiving antenna (4c) is arranged to favour reception of radiation having the second plane of polarization. For example, the transmitting (4b) and receiving (4c) antennas may be waveguide antennas.

Abstract: A data communication apparatus according to the present invention can be used both in one-wave mode and two-wave mode, and includes: first and second tuning circuits (1, 2); a power supply circuit (3) connected to first tuning circuit (1) for generating power by a signal received by first tuning circuit (1); an information processing circuit (15) connected to first tuning circuit (1) or second tuning circuit (2) through a switching circuit (6) and including a detection circuit (7), a decoder (8), an encoder (10) and the like. Information processing circuit (15) includes a switch control circuit (14) detecting if the mode of the received radio wave is one-wave mode or two-wave mode in accordance with an output from first tuning circuit (1) and controlling switching circuit (6) such that detection circuit (7) is connected to one of first and second tuning circuits (1, 2).

Abstract: A method and apparatus is provided for remotely and constantly calibrating a transponder by using the ring around phenomenon. A number of different time varying physical quantities, such as for example temperature, signal level, noise, transmission line flex, frequency, and general operational effects, affect the inherent delay in transponders on a time varying basis. The invention relies on a the ring around phenomenon to produce pulse doublets, wherein the distance between the pulses in the pulse doublets correspond to the instantaneous delay in the transponder. The system is configured so that instantaneous variation in the transmission delay is detected and recognized on a pulse by pulse basis and transmitted to the interrogation device, which then functions to calculate the actual delay. Normal operation of the transponder is not affected by the continuous calibration method, and therefore a special calibration mode is not required.

Abstract: A method and apparatus for transponding pulsed RF signals is provided. The method comprises receiving, with a receiver, pulsed RF signals having a plurality of PRIs. Further the method includes generating, with a PRI tracker, control signals from the received pulsed RF signals. The method then filters the received pulsed RF signals with the control signals to thereby obtain enable signals, which in turn control a transmitter permitting retransmission without clock jitter.