AU785098B2 - A transmitter and a method for transmitting data - Google Patents

Description

WO 99/34526 PCT/AU98/01077 TITLE: A TRANSMITTER AND A METHOD FOR TRANSMITTING DATA Field of Invention The invention relates to a transmitter and a method for transmitting data.

The invention has been developed primarily for the field of radio frequency identification (RFID), and more particularly to a method for transmitting data to a transponder with a single antenna, and will be described hereinafter with reference to that application. This invention has particular merit when applied to passive transponders where high speed data transmission is desirable.

Background of the Invention Hitherto, high speed data has been transmitted to RFID transponders by modulation of the excitation field. Generally pulse position modulation with 100% depth amplitude modulation of the excitation field is used. The excitation field is turned off for short intervals which are detected by the transponder's processing circuitry. To achieve high data rates while maintaining the transmission of power the intervals must be short and the duty cycle low. Typically a duty cycle of 10% is used and the intervals are 1 ps long and the average time between intervals is I 0ps. Short intervals such as these have a wide bandwidth. Accordingly, both the interrogator and the transponder require low Q factor, wide bandwidth antennae to transmit and receive the data. Low Q factor antennae are not energy efficient and, as such, the interrogator antenna will consume more power than a high Q factor antenna. Moreover, for passive transponders a stronger excitation field is required to compensate for the less efficient antenna.

17/05 2006 WED 12:04 FAX Smoorenburg Attorneys 4 IP AUSTRALIA 1004/027 2 Additionally, regulations governing the magnitude of electromagnetic emissions place upper limits on the strength of excitation fields that can be used and the allowable bandwidth of an excitation field. The wide bandwidth of the prior art pulse, modulation data results in limitations being placed on the maximum excitation field strength.

Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein.

Disclosure of the Invention It is an object of the invention, at least in the preferred embodiment, to overcome or substantially ameliorate at least one of the disadvantages of the prior art.

According to one aspect of the invention there is provided a method for transmitting data from a first antenna, said method including the steps of: providing a carrier signal; imposing a low level phase modulation on the carrier signal in accordance with a data signal to create a modulated signal; providing the modulated signal to said first antenna for transmission.

According to a second aspect of the invention there is provided a :i ""transmitter including: a first antenna; oscillator means for providing a carrier signal; and mixing means for imposing a low level phase modulation on the carrier signal in accordance with a data signal to create a modulated signal, the mixing means also providing the modulated signal to the first antenna for transmission.

Preferably, the modulated signal is received by second antenna which in response thereto, produces a first signal which is provided to receiver means, the 30 receiver means deriving a second signal indicative of the data signal. Even more preferably, the first signal is used to power the receiver means.

In a preferred form, the modulated signal includes the sum of the carrier signal and an attenuated quadrature signal which is modulated with the data COMS ID No: SBMI-03615697 Received by IP Australia: Time 12:17 Date 2006-05-17 05/07 2006 WED 12:57 FAX Smoorenburg Attorneys IP AIJSTKAI.IA 3 signal. This form of modulation is described herein as phase jitter modulation

(PJM).

In a preferred form the antenna is a tunable coil. Preferably also, both the first and second antennas have a high Q factor.

According to another aspect of the invention there is provided an identification system including a transmitter as described above.

Preferably, the system is for identifying luggage.

According to another aspect of invention, there is provided a radio frequency identification device (RFID) adapted for interrogation by a device as herein disclosed, the RFID comprising: a second antenna, and receiver means, adapted to derive a second signal indicative of a data signal from a first signal provided by the second antenna in response to receiving the modulated signal.

15 According to another aspect of invention, there is provided a method for transmitting data from a first antenna, said method including the steps of: providing a carrier signal; imposing a phase modulation of less than 900 on the carrier signal in accordance with a data signal to create a modulated signal having a carrier frequency and sidebands, the sidebands being substantially lower in amplitude than the carrier frequency; and providing the modulated signal to said first antenna for transmission.

According to another aspect of invention, there is provided a transmitter including: a first antenna; oscillator means for providing a carrier signal; and mixing means for imposing a phase modulation of less than 90° on the carrier signal in accordance with a data signal to create a modulated signal, the mixing means also providing the modulated signal to the first antenna for transmission, wherein the modulated signal has a carrier frequency and sidebands, the sidebands being substantially lower in amplitude than the carrier frequency.

COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 12:57 FAX Smoorenburg Attorneys IP AjUS'TRALIA iaOU4/36 3a According to another aspect of invention, there is provided a method for transmitting data from a device having a first antenna, said method comprising the steps of: providing a carrier signal; imposing a phase modulation on the carrier signal in accordance with a data signal to create a modulated signal having a carrier and sidebands, the amount of phase modulation being selected such that the amplitude of the sidebands is substantially lower than that of the carrier; and providing the modulated signal to the first antenna for transmission.

According to another aspect of invention, there is provided a method of imposing a low level signal having a modulated quadrature component on a carrier signal, the method comprising the steps of: providing a carrier signal; and "imposing on the low level signal, a data signal to create a modulated signal.

According to another aspect of invention, there is provided a method of transmitting data from a first antenna, said method comprising the steps of: providing a modulated signal as herein disclosed, and providing the modulated signal to said first antenna for transmission.

According to another aspect of invention, there is provided a device comprising: a first antenna; *oscillator means for providing a carrier signal; and mixing means for imposing a low level phase modulation on the carrier signal in accordance with the method as claimed in claim 68, the mixing means also providing the modulated signal to the first antenna for transmission.

According to another aspect of invention, there is provided a method of demodulating a modulated signal received by a device and deriving there from a data signal, the method comprising the steps of: receiving the modulated signal producing a first signal being a local oscillator signal, COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 12:57 FAX Smoorenburg Attorneys IP AUSTRALIA M005/038 3b demodulating the modulated signal using the local oscillator signal to obtain an indicative data signal.

According to another aspect of invention, there is provided a method of demodulating a modulated signal received by a device and deriving there from a data signal, the method comprising the steps of: receiving the modulated signal and inducing into an antenna of the device, an antenna voltage signal, amplifying the antenna signal providing a portion of the amplified signal to a phase locked loop to filter off sidebands and creating a first signal passing another portion of the amplified signal through a delay means and creating a second signal XORing the first and second signals to provide indicative data.

According to another aspect of invention, there is provided a transmitter including: a first antenna; oscillator means for providing a carrier signal; and mixing means for imposing a phase modulation on the carrier signal in accordance with a data signal to create a modulated signal having a carrier and sidebands, the amount of phase modulation being selected such that the amplitude of the sidebands is substantially lower than that of the carrier, the mixing means also providing the modulated signal to the first antenna for transmission.

According to another aspect of invention, there is provided a transmitter including: a first antenna; an oscillator for providing a carrier signal; and a mixer for imposing a phase modulation of less than 900 on the carrier signal in accordance with a data signal to create a modulated signal, the mixer also providing the modulated signal to the first antenna for transmission, wherein the modulated signal has a carrier frequency and sidebands, the sidebands being substantially lower in amplitude than the carrier frequency.

COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 12:58 FAX Smoorenburg Attorneys IP AIJSTRALIA oo000/038 3c According to another aspect of invention, there is provided a transmitter including: a first antenna; an oscillator for providing a carrier signal; and a mixer for imposing a phase modulation on the carrier signal in accordance with a data signal to create a modulated signal having a carrier and sidebands, the amount of phase modulation being selected such that the amplitude of the sidebands is substantially lower than that of the carrier, the mixer also providing the modulated signal to the first antenna for transmission.

Other aspects and preferred aspects are disclosed in the specification and/or defined in the appended claims, forming a part of the description of the invention.

Description of the Drawings Further disclosure, objects, advantages and aspects of the present application may be better understood by those skilled in the relevant art by reference to the following description of preferred embodiments taken in conjunction with the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the present invention, and in which: Figure 1 is a schematic illustration of a prior art transponder circuit; 20 Figure 2 illustrates representative waveforms associated with the prior art circuit of Figure 1; Figures 3(a) to 3(c) are frequency spectra associated with the waveforms of the prior art circuit of Figure 1; Figures 4(a) and 4(b) are phasor diagrams for waveforms produced in accordance with the invention; Figures 5(a) to 5(c) are frequency spectra associated with the invention; COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 WO 99/34526 PCT/AU98/01077 -4- Figures 6(a) and 6(b) respectively illustrate methods of encoding and decoding data in accordance with the invention; Figure 7 is a schematic illustration of a preferred circuit for encoding the data signal for transmission; and Figure 8 is a schematic illustration of a preferred circuit for decoding the data signal in the transponder.

Detailed Description of a Preferred Embodiment of the Invention Passive RFID transponders that incorporate a single antenna are interrogated by an interrogator using an excitation field. This field is received by the transponder's antenna and the voltage induced on the antenna is rectified and used to power the transponder. Often it is necessary for the transponder to receive data transmitted from its interrogator. For single antenna transponders the received messages must be received by the same antenna that is used to receive the excitation signal used to power the transponder. In prior art systems the excitation signal is amplitude modulated to convey messages from the interrogator to the transponder.

Figure 1 shows a prior art transponder where the antenna L is tuned by a capacitor C and data is transmitted to the transponder by amplitude modulation. The voltage V1 induced in the transponder's antenna coil is magnified by the antenna's tuning, rectified by the rectifiers and stored on the DC storage capacitor Cdc for use by the transponder's electronic circuits. The antenna voltage is peak level detected by the diode envelope detector D1, C1 and RI to give the envelope voltage V2.

Figures 2(a) and 2(b) illustrate waveforms associated with the prior art circuit of Figure 1. More particularly, Figure 2(a) shows the excitation voltage V1 with WO 99/34526 PCT/AU98/01077 amplitude intervals to giving pulse position modulation. To deliver the maximum power to the transponder, a low duty cycle is used, typically 10:1. Figure 2(b) shows the envelope of the voltage V2 induced in the antenna. The antenna's transient response results in a finite rise and fall time for V2. The transient time of the antenna must be sufficiently short to allow narrow pulses to pass without significant distortion.

The antenna's transient response time constant Ts and bandwidth BW are related by Accordingly, to pass short pulses the bandwidth of the antenna must be broad. For example, to pass l4s pulses a bandwidth of at least 1 MHz is required.

Figures 3(a) to 3(c) are frequency spectra associated with the prior art circuit of Figure 1. Figure 3(a) shows a typical data spectrum. For data at 100 kbps the first zero of the frequency spectrum occurs at 100 kHz. Figure 3(b) shows the data spectrum when encoded as pulse position modulation PPM where narrow low duty cycle pulses are used. The spectrum for this type of encoding is much broader than the original data spectrum. For I ps pulses with a 10:1 duty cycle the first amplitude zero of the frequency spectrum occurs at 1 MHz. Figure 3(c) shows the spectrum of the excitation signal when modulated with the PPM signal whose spectrum is shown at Figure The modulated spectrum is double sided and accordingly, for 1 [is pulses with a 10:1 duty cycle the width of the main spectral lobe is 2 MHz. Clearly the bandwidth of the PPM modulated excitation signal is much broader than the original data spectrum.

To pass the inherently broad band PPM excitation signal both the interrogator and transponder antenna must have a wide bandwidth. Consequently the interrogator and transponder antennae must have a low Q and will operate with a low efficiency. In WO 99/34526 PCT/AU98/01077 -6the interrogator the generation of 100% amplitude modulated PPM requires that excitation signal be completely quenched for each pulse. This requires a wide band low efficiency antenna. Narrow band antennae would operate with high efficiency but are unable to respond to the narrow amplitude pulses of PPM. Similarly the transponder antenna bandwidth must be broad band enough to pass the modulated excitation signal. Broad band antennae are inherently low Q and are poor collectors of energy from an excitation field.

In this preferred embodiment of the invention data is imposed as a low level signal having a modulated quadrature component. Most preferably this modulation is phase modulation although in other embodiments use is made of amplitude modulation. In the present embodiment the low level signal appears as a tiny phase jitter in the excitation field. There is no change in the amplitude of the excitation field and hence the transmission of power to the transponder is unaffected. This form of modulation will be termed phase jitter modulation or, for convenience, PJM.

There are many methods of producing small modulated phase shifts. For example, by passing the signal through a phase shifter such as an RC or tuned circuit, or through a variable length delay line.

In this embodiment, to produce the signal at the interrogator, a small portion of the excitation signal is phase shifted 90 degrees to give a quadrature signal. This is then PRK modulated with the data signal and added back onto the original excitation signal before being transmitted to the transponder. The resultant signal can be amplitude limited to remove any residual amplitude component. At the transponder these tiny phase shifts in the excitation induce corresponding antenna voltage phase WO 99/34526 PCT/AU98/01 077 -7shifts that are unaltered by any circuit impedances or power regulation circuitry connected to the transponder's antenna.

Figure 4(a) is a phasor diagram of the excitation signal Fc and the modulated quadrature signal PRK. The amplitude of the respective signals are given by their phasor lengths. The phase deviation THETA caused by the modulated quadrature signal is, for low level signals, extremely small and is given by: THETA arctan (2xMag(PRK)/Mag(Fc)) For a 40 dB attenuated PRK signal THETA 1.2 degrees and for a 60 dB attenuated PRK signal THETA 0.12 degrees. Both of these are extremely small phase deviations of the excitation signal.

Phase quadrature modulation is recovered using a local oscillator (LO) signal, with a fixed phase with respect to the excitation signal, to down convert the modulated data to baseband in a mixer or multiplier. In the transponder the LO signal must be derived from the modulated excitation signal. The preferred method of extracting a LO signal from the modulated excitation signal uses a Phase Locked Loop PLL in the transponder to generate the LO signal. The LO signal is generated by a low loop bandwidth PLL which locks to the original excitation signal's phase but is unable to track the high speed modulated phase shifts. The quadrature data signal is down converted and detected in a mixer or multiplier driven with the LO signal. Depending upon the type of phase detector used in the PLL, and the propagation delays through the circuit, the phase of the LO with respect to the excitation signal can be anywhere between 0' and 360'. Ifa conventional XOR phase detector is used in the PLL then the output of the PLL oscillator will be at nominally 90 degrees to the excitation signal WO 99/34526 PCT/AU98/01077 -8and will be in phase with the data modulated phase quadrature signal. A 900 phase between the LO and the excitation signal is not necessary for the effective detection of quadrature phase modulation. An XOR mixer has a linear phase to voltage conversion characteristic from 0' to 1800 and 1800 to 3600. Hence it gives the same output amplitude irrespective of the phase angle except around 00 and 1800 where there is a gain sign change.

The average output voltage DC level from a mixer is a function of the average phase difference between its inputs. It is more convenient for circuit operation for the average output to be around midspan and hence an LO with a phase angle of around 90' is more convenient. The phase of the LO signal can be simply adjusted using fixed phase delay elements. Hence a 00 or 1800 phase detector can be used and a further 900 (roughly) of phase shift can be achieved with a fixed delay element.

Figure 4(b) is a phasor diagram of the modulated excitation signal and a quadrature local oscillator signal in the transponder used to demodulate the data signal. The local oscillator signals phase is at 90 degrees with respect to the excitation signal's phase.

For phase modulation the data bandwidth is no broader than the original double sided data bandwidth. When attenuated the level of the modulated data spectrum is extremely low with respect to the excitation signal amplitude making conformance to regulatory emission limits significantly easier than with the prior art.

Figures 5(a) to 5(c) are representative frequency spectra that explain the operation of the invention. More particularly, Figure 5(a) is a typical data spectrum.

For data at 100 kbps the first zero of the frequency spectrum occurs at 100 kHz. Figure WO 99/34526 PCT/AU98/01077 -9is a representative frequency spectrum of the data when modulated onto a quadrature version of the excitation signal. The spectrum for this type of modulation is the same as the double sided spectrum of the original data spectrum. In the invention the modulated quadrature signal is attenuated and added to the original excitation signal. Figure 5(c) shows the spectrum of the excitation signal Fc plus the attenuated modulated quadrature signal whose spectrum is shown in Figure The attenuation level is given by the difference between the amplitude of the excitation signal and the amplitude of the data sidebands.

Since the spectrum of the transmitted excitation signal is equal to the original to double sided data spectrum, narrow band high Q interrogator and transponder antennae are used to respectively transmit and receive the modulated excitation signal.

Consequently, the interrogator's excitation antenna operates with high efficiency and the transponder's antenna likewise receives energy with high efficiency. In other embodiments use is made of low Q antennae.

Figures 6(a) and 6(b) show methods of modulating and demodulating according to this invention. Turning first to Figure the portion of the main excitation signal is phase shifted 90 degrees to produce a quadrature signal. The quadrature signal is then modulated with data. The preferred form of modulation is phase reverse keying PRK. The PRK modulated quadrature signal is attenuated and then added back to the main excitation signal. Although shown in a particular order the sequence phase shift, modulation and attenuation are done in other orders in alternative embodiments. This method of modulation produces low level data side bands on the excitation signal where the sidebands are in phase quadrature to the WO 99/34526 PCT/AU98/01077 excitation signal. The data signal appears as a low amplitude phase jitter on the excitation signal. In some embodiment the signal is further amplitude limited to remove any residual amplitude component.

Figure 6(b) illustrates a method for demodulating the data modulated on to the excitation signal. A LO signal is generated by a low loop bandwidth phase lock loop PLL. The PLL locks on to the excitation signals phase and is unable to follow the high speed phase jitter caused by the data modulation. For the standard PLL phase detector the PLL oscillator will lock at a fixed phase with respect to the excitation signal's phase. This oscillator signal is then used as a LO to demodulate the quadrature sideband data signal in the multiplier. A low pass filter LPF filters out high frequency mixer products and passes the demodulated data signal.

Figure 7 shows an example circuit for encoding the data signal for transmission. An excitation reference source Fc is split through a 90 degree splitter.

One output from the splitter is fed to the LO port of a mixer. Data is fed to the mixer's IF port and causes PRK modulation of the LO port's signal. The output of the mixer at the RF port is a PRK modulated quadrature signal. This is attenuated and added back onto the reference by a zero degree combiner ready for transmission to the transponder.

Figure 8 shows an example circuit for decoding the data signal in the transponder. The transponder antenna voltage is squared up by a schmitt trigger, the output of which feeds a type 3 PLL. A type 3 phase detector is a positive edge triggered sequence phase detector which will drive the PLL oscillator to lock at 1800 with respect to the input phase. With a low loop bandwidth the PLL is able to easily 17/05 2006 WED 12:06 FAX Smoorenburg Attorneys IP AUSTRALIA 1010/027 11 filter off the sidebands on the input signal. The output of the Schmitt is passed through a chain of invertors designed to add a fixed delay to the input signal. The delay is approximately chosen so that the phase of the output from the delay chain is not 00 or 1800 with respect to the LO. A preferred phase value is 90* for circuit convenience. The output of the VCO acts as the LO to demodulate the Phase Jitter Modulated data. The data is demodulated in an exclusive OR gate, the output of which is low pass filtered and detected with a floating comparator.

Although the invention has been described with reference to a specific example it will be appreciated by those skilled In the art that it may be embodied in many other forms.

While this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification(s). This application is intended to cover any variations uses or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth.

As the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that the above described embodiments are not to limit the present invention unless otherwise specified, but rather should be construed broadly within the spirit and scope of the invention as defined in the appended claims.

-Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the invention and appended claims. Therefore, the 25 specific embodiments are to be understood to be illustrative of the many ways in which the principles of the present invention may be practiced. In the following claims, means-plus-function clauses are intended to cover structures as performing the defined function and not only structural equivalents, but also equivalent structures. For example, although a nail and a screw may not be 30 structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface to secure o wooden parts together, in the environment of fastening wooden parts, a nail and a screw are equivalent structures.

COMS ID No: SBMI-03615697 Received by IP Australia: Time 12:17 Date 2006-05-17 17/05 2006 WED 12:07 FAX Smoorenburg Attorneys -44 IP AUSTKALIA ij UII/UZI 11a "Comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof." Thus, unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, In the sense of "including, but not limited to".

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COMS ID No: SBMI-03615697 Received by IP Australia: Time 12:17 Date 2006-05-17

Claims (89)

1. A method for transmitting data from a first antenna, said method including the steps of: providing a carrier signal; imposing a low level phase modulation on the carrier signal in accordance with a data signal to create a modulated signal; and providing the modulated signal to said first antenna for transmission.

2. A method according to claim 1 including the step of receiving the modulated signal with a second antenna which, in response thereto, produces a first signal which is provided to receiver means, the receiver means deriving a second signal indicative of the data signal. 15

3. A method according to claim 2, wherein the first signal is used to power the receiver means.

4. A method according to claim 2 or claim 3, wherein both the first and second antennas have a high Q factor.

5. A method according to claim 1 including the step of deriving the modulated signal from the sum of the carrier signal and an attenuated quadrature carrier signal which is modulated with the data signal.

6. A transmitter including: a first antenna oscillator means for providing a carrier signal; and mixing means for imposing a low level phase modulation on the carrier signal in accordance with a data signal to create a modulated signal, the mixing means also providing the modulated signal to the first antenna for transmission. COMS ID No: SBMI-01471472 Received by IP Australia: Time 15:45 Date 2005-09-06 05/07 2006 WED 12:58 FAX Smoorenburg Attorneys IP AUSTRALIA IgUU7/UJo 13

7. A transmitter according to claim 6, wherein the modulated signal is received by a second antenna which, in response thereto, produces a first signal which is provided to receiver means, the receiver means deriving a second signal indicative of the data signal.

8. A transmitter according to claim 7, wherein the first signal is used to power the receiver means.

9. A transmitter according to any one of claims 6 to 8, wherein both the first and second antennas have a high Q factor.

*10. A transmitter according to claim 6, wherein the modulated signal includes the sum of the carrier signal and an attenuated quadrature carrier signal which is S. modulated with the data signal.

11. A transmitter according to claim 6, wherein the antenna is a tunable coil.

12. A method for transmitting data from a first antenna, said method including the steps of: providing a carrier signal; imposing a phase modulation of less than 900 on the carrier signal in accordance with a data signal to create a modulated signal having a carrier 00* frequency and sidebands, the sidebands being substantially lower in amplitude than the carrier frequency; and providing the modulated signal to said first antenna for transmission.

13. A method according to claim 12 including the step of receiving the modulated signal with a second antenna which, in response thereto, produces a first signal which is provided to receiver means, the receiver means deriving a second signal indicative of the data signal. COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 12:59 FAX Smoorenburg Attorneys IP AUSTAI..IA 1008/038 14

14. A method according to claim 13, wherein the first signal is used to power the receiver means.

A method according to claim 13, wherein both the first and second antennas have a high Q factor.

16. A method according to claim 12 including the step of deriving the modulated signal from the sum of the carrier signal and an attenuated quadrature carrier signal which is modulated with the data signal.

17. A transmitter including: S.:a first antenna; oscillator means for providing a carrier signal; and mixing means for imposing a phase modulation of less than 90° on the carrier signal in accordance with a data signal to create a modulated signal, the mixing means also providing the modulated signal to the first antenna for transmission, wherein the modulated signal has a carrier frequency and sidebands, the sidebands being substantially lower in amplitude than the carrier frequency.

18. A transmitter according to claim 17, wherein the modulated signal is received by a second antenna which, in response thereto, produces a first signal which is provided to receiver means, the receiver means deriving a second signal indicative of the data signal.

19. A transmitter according to claim 18, wherein the first signal is used to power the receiver means.

A transmitter according to claim 17, 18 and 19, wherein at least one of the first and second antennas have a high Q factor.

21. A transmitter as claimed in any one of claims 17 to 20, wherein at least one of the first and second antennas have a low Q factor. COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 12:59 FAX Smoorenburg Attorneys IP AUSTRALIA UgjuV/uJa

22. A transmitter according to any one of claims 17 to 21, wherein the modulated signal includes the sum of the carrier signal and an attenuated quadrature carrier signal which is modulated with the data signal.

23. A transmitter according to any one of claims 6 to 11 or 17 to 22, wherein the antenna is a tunable coil.

24. A transmitter as claimed in any one of claims 17 to receiver means is a Radio Frequency Identification Device.

A transmitter as claimed in any one of claims 17 to receiver means is a passive device.

26. A transmitter as claimed in any one of claims 17 to receiver means is a transponder.

27. A device including a transmitter as claimed in any one of 17 to 26. 24, wherein the 25, wherein the 23, wherein the claims 6 to 11 or

28. An identification system including the device of claim 27.

29. A method for transmitting data from a device having a first antenna, said method comprising the steps of: providing a carrier signal; imposing a phase modulation on the carrier signal in accordance with a data signal to create a modulated signal having a carrier and sidebands, the amount of phase modulation being selected such that the amplitude of the sidebands is substantially lower than that of the carrier; and providing the modulated signal to the first antenna for transmission. A method according to claim 29, wherein the phase modulation is selected such that the sidebands are greater than 10 dB below the carrier amplitude.

COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 12:59 FAX Smoorenburg Attorneys IP AIJS'IRAI.IA 10010/038 16

31. A method according to claim 29, wherein the phase modulation is selected such that the sidebands are greater than 40 dB below the carrier amplitude.

32. A method according to claim 29, wherein the phase modulation is selected such that the sidebands are greater than 60 dB below the carrier amplitude.

33. A method according to claim 29 including the step of receiving the modulated signal with a second antenna which, in response thereto, produces a first signal which is provided to receiver means, the receiver means deriving a second signal indicative of the data signal.

34. A method according to claim 33, wherein the first signal is used to power the receiver means.

35. A method according to claim 33, wherein both the first and second antennas have a high Q factor.

36. A method according to claim 29, including the step of deriving the modulated signal from the sum of the carrier signal and an attenuated quadrature carrier signal which is modulated with the data signal.

37. A method as claimed in claim 29, wherein the modulation is phase quadrature modulation.

38. A method as claimed in claim 29, wherein the phase modulation is attenuated.

39. A method according to claim 29, further comprising the step of deriving the modulated signal from the sum of the carrier signal and an attenuated quadrature carrier signal which is modulated with the data signal. A method as claimed in claim 39, further comprising the step of phase shifting the carrier signal 900 to produce the quadrature signal.

COMS ID No: SBMI-04065200 Received by IP Australia: Time (H m) 13:12 Date 2006-07-05 05/07 2006 WED 13:00 FAX Smoorenburg Attorneys I AUSTKALIA CUI/uo0

41. A method as claimed in claim 40 further comprising the step of modulating the quadrature signal with data.

42. A method as claimed in claim 41, wherein the modulation is phase reverse keying PRK.

43. A method of imposing a low level signal having a modulated quadrature component of a carrier signal, the method comprising the steps of: providing a carrier signal; and imposing on the low level signal, a data signal to create a modulated signal.

44. A method as claimed in claim 43, wherein the modulated signal has a carrier and sidebands, the amount of phase modulation being selected such that 15 the amplitude of the sidebands is substantially lower than that of the carrier.

A method as claimed in claim 43, wherein the modulation is phase quadrature modulation.

46. A method as claimed in claim 43, wherein the phase modulation is attenuated.

47. A method according to claim 43, further comprising the step of deriving a modulated signal for transmission from the sum of the carrier signal and an attenuated quadrature carrier signal which is modulated with the data signal.

48. A method as claimed in claim 47, further comprising step of phase shifting the carrier signal 900 to produce the quadrature signal.

49. A method as claimed in claim 48, further comprising the step of modulating the quadrature signal with data.

COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 13:00 FAX Smoorenburg Attorneys IP AISTRA..IA 1s012/038 21 A method as claimed in claim 49, wherein the modulation is phase reverse keying PRK.

51. A method of transmitting data from a first antenna, said method comprising the steps of: providing a modulated signal as claimed in claim 43, and providing the modulated signal to said first antenna for transmission.

52. A method as claimed in claim 51, wherein the modulated signal is phase modulation.

53. A method as claimed in claim 51, wherein the modulated signal is amplitude modulation.

54. A method as claimed in claim 51, wherein the low level signal is phase jitter. 0 0 *000 *0*0 0 0 *0 0

55. A method as claimed in claim 51, modulation.

56. A method as claimed in claim 51, the signal through a phase shifter. wherein the modulation is phase jitter further comprising the step of passing

57. A method as claimed in claim 51, further comprising the step of passing the signal through an RC filter.

58. A method as claimed in claim 51, further comprising the step of passing the signal through a tuned circuit.

59. A method as claimed in claim 51, further comprising the step of passing the signal through a variable length delay means.

COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 13:00 FAX Smoorenburg Attorneys IP AUSTRALIA 10013/038 22 A method as claimed in claim 51, wherein the step of imposing a low level phase modulation includes the step of imposing a phase modulation of less than on the carrier signal in accordance with a data signal to create a modulated signal having a carrier frequency and sidebands.

61. A method as claimed in claim 51, wherein the signal provided to the first antenna is amplitude limited.

62. A method as claimed in claim 51, wherein the phase deviation caused by the low level signal is arctan (2xMag(PRK)/Mag(Fc)), where PRK is the modulated quadrature component, and Fc is the excitation signal.

63. A method as claimed in claim 62, wherein for a 40 dB attenuated PRK 15 signal, the phase deviation is 1.2 degrees.

64. A method as claimed in claim 62, wherein for a 60 dB attenuated PRK signal, the phase deviation is 0.12 degrees.

65. A device comprising: a first antenna; oscillator means for providing a carrier signal; and mixing means for imposing a low level phase modulation on the carrier signal in accordance with the method as claimed in claim 43, the mixing means also providing the modulated signal to the first antenna for transmission.

66. The transmitter of claim 65, wherein the low level phase modulation is less than 90' and wherein the modulated signal has a carrier frequency and sidebands.

67. A device as claimed in claim 65, operatively adapted to transmit data from the first antenna in accordance with the method of any of claims 51 to 64. COMS ID No: SBMI-04065200 Received by IP Australia: Time 13.12 Date 2006-07-05 05/07 2006 WED 13:01 FAX Smoorenburg Attorneys IP AUSTRALIA 1o114/u36 23

68. A method of demodulating a modulated signal received by a device and deriving there from a data signal, the method comprising the steps of: receiving the modulated signal and inducing into an antenna of the device, an antenna voltage signal, amplifying the antenna signal providing a portion of the amplified signal to a phase locked loop to filter off sidebands and creating a first signal passing another portion of the amplified signal through a delay means and creating a second signal XORing the first and second signals to provide indicative data. 0

69. A method as claimed in claim 68, wherein the antenna signal is amplified by squaring the signal by a Schmitt trigger device. S S 15

70. A method as claimed in claim 68, wherein the phase locked loop is a low bandwidth phase locked loop device.

71. A method as claimed in claim 68, wherein the data is detected using a floating point comparator device.

72. A transmitter including: a first antenna; oscillator means for providing a carrier signal; and mixing means for imposing a phase modulation on the carrier signal in accordance with a data signal to create a modulated signal having a carrier and sidebands, the amount of phase modulation being selected such that the amplitude of the sidebands is substantially lower than that of the carrier, the mixing means also providing the modulated signal to the first antenna for transmission.

73. A transmitter according to claim 72, wherein the phase modulation is selected such that the sidebands are greater than 10 dB below the carrier amplitude. COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 13:01 FAX Smoorenburg Attorneys IP AUSTRALIA tols/uU3 24

74. A transmitter according to claim 73, wherein the phase modulation is selected such that the sidebands are greater than 40 dB below the carrier amplitude.

75. A transmitter according to claim 74, wherein the phase modulation is selected such that the sidebands are greater than 60 dB below the carrier amplitude.

76. A transmitter according to claim 72, wherein the modulated signal is received by a second antenna which, in response thereto, produces a first signal which is provided to receiver means, the receiver means deriving a second signal indicative of the data signal.

77. A transmitter according to claim 76, wherein the first signal is used to 15 power the receiver means.

78. A transmitter according to claim 72, wherein both the first and second antennas have a high Q factor.

79. A transmitter according to claim 72, wherein the modulated signal includes the sum of the carrier signal and an attenuated quadrature carrier signal which is modulated with the data signal.

A transmitter according to claim 72, wherein the antenna is a tunable coil.

81. An identification system including a transmitter according to any one of claims 72 to

82. A system according to claim 81, configured for identifying luggage.

83. A transmitter including: a first antenna; an oscillator for providing a carrier signal; and COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 13:02 FAX Smoorenburg Attorneys IP AIJSTRALLA 1o016/038 a mixer for imposing a phase modulation of less than 90° on the carrier signal in accordance with a data signal to create a modulated signal, the mixer also providing the modulated signal to the first antenna for transmission, wherein the modulated signal has a carrier frequency and sidebands, the sidebands being substantially lower in amplitude than the carrier frequency.

84. A transmitter including: a first antenna; an oscillator for providing a carrier signal; and a mixer for imposing a phase modulation on the carrier signal in accordance with a data signal to create a modulated signal having a carrier and sidebands, the amount of phase modulation being selected such that the amplitude of the sidebands is substantially lower than that of the carrier, the mixer also providing the modulated signal to the first antenna for transmission. S.

85. A system as claimed in claim 28 adapted to identify luggage.

86. A method substantially as herein described with reference to Figure 3a to Figure 8 of the accompanying drawings.

87. A transmitter substantially as herein described with reference to Figure 3a to Figure 8 of the accompanying drawings.

88. A device substantially as herein described with reference to Figure 3a to Figure 8 of the accompanying drawings. COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05 05/07 2006 WED 33:02 FAX Smoorenburg Attorneys IP AiisTrRAI.IA ij070 LO 017/038 26

89. A system substantially as herein described with reference to Figure 3a to Figure 8 of the accompanying drawings. DATED this 5th day of July 2006 Magellan Technology Pty Ltd SMOORENBURG PATENT TRADE MARK ATTORNEYS P0 BOX 515 RINGWOOD VIC 3134 AUSTRALIA S. COMS ID No: SBMI-04065200 Received by IP Australia: Time 13:12 Date 2006-07-05