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A system and method are useful for conducting an exhibition at which visitors visit a plurality of booths or stations. A smart tag issued each visitor includes at least an electronic memory from which information from the memory may be provided and/or information may be received and stored in the me

A system and method are useful for conducting an exhibition at which visitors visit a plurality of booths or stations. A smart tag issued each visitor includes at least an electronic memory from which information from the memory may be provided and/or information may be received and stored in the memory. Stored information may include visitor information, exhibitor information, visit information, product/service information and data items. Smart tag control units and antenna arrays at the stations communicate with the smart tags and communicate directly or indirectly with one or more processors that process the information.

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A system and method are useful for conducting an exhibition at which visitors visit a plurality of booths or stations. A smart tag issued each visitor includes at least an electronic memory from which information from the memory may be provided and/or information may be received and stored in the me

A system and method are useful for conducting an exhibition at which visitors visit a plurality of booths or stations. A smart tag issued each visitor includes at least an electronic memory from which information from the memory may be provided and/or information may be received and stored in the memory. Stored information may include visitor information, exhibitor information, visit information, product/service information and data items. Smart tag control units and antenna arrays at the stations communicate with the smart tags and communicate directly or indirectly with one or more processors that process the information. in order to receive an attachment cover. 4. Filter according to claim 1, characterized in that the base of the cylinder is a rectangle. 5. Filter according to claim 1, characterized in that the support (1) is made of a conducting material. 6. Filter according to claim 1, characterized in that the discs are made in metal or a metal alloy. 7. Filter according to claim 4, characterized in that the base of the cylinder is a square. er signal by a predetermined amount. 8. The method of claim 7 wherein the predetermined amount is approximately 90° C. 9. The method of claim 8 wherein the step of modifying the quadrature amplitude modulated signal includes applying the error signal to the phase shifting circuit so as to adjust the amount of the phase shift applied to the first carrier signal in the production of the second carrier signal as a function of the magnitude of the error signal. 10. The method of claim 9 wherein the first carrier signal and the second carrier signal are radio frequency signals. 11. The method of claim 9 wherein the quadrature amplitude modulated signal is an M-QAM signal. 12. A phase corrected quadrature amplitude modulator comprising: first circuit means for producing a first carrier signal; second circuit means for producing a second carrier signal shifted in phase approximately 90° from said first carrier signal; first combining means for modulating said first carrier signal with a first input signal to thereby produce a first component signal; second combining means for modulating said second carrier signal with a second input signal to thereby produce a second component signal; first summing means for combining said first component signal and said second component signal to thereby produce a quadrature amplitude modulated signal; second summing means for combining said first input signal and said second input signal to thereby produce a combined signal; and error producing means foil producing an error signal responsive to the difference between the phase relationship of the first and second component signals and the phase relationship of the first and second input signals, whereby said error signal is applied to said second circuit means so as to maintain a quadrature phase relationship between said first carrier signal and said second carrier signal. 13. The modulator of claim 12 wherein said first carrier signal and said second carrier signal are radio frequency signals. 14. The modulator of claim 12 wherein the first input signal and the second input signal include digitized data. 15. The modulator of claim 12 wherein the quadrature amplitude modulated signal is an M-QAM signal. 16. The modulator of claim 12 wherein said first circuit means is an oscillator. 17. The modulator of claim 12 wherein said second circuit means is a phase shifting circuit adapted to receive said first carrier signal and capable of producing said second carrier signal from said first carrier signal. 18. The modulator of claim 17 wherein said phase shifting circuit includes a plurality of phase shifting circuits arranged in a cascaded series. 19. The modulator of claim 12 wherein the first summing means includes: a first summing circuit for combining said first and second component signals to thereby produce said quadrature amplitude modulated signal; a first squarer circuit for producing a squared signal proportional to the square of said quadrature amplitude modulated signal; and a low pass filter for filtering out the components of said squared signal that are at a frequency higher than a predetermined frequency to thereby produce a first correlation signal. 20. The modulator of claim 19 wherein the value of said predetermined frequency is such that said first and second carrier signals and all harmonics related thereto are filtered out. 21. The modulator of claim 19 wherein the second summing means includes: a second summing circuit for combining said first and second input signals to thereby produce a combined signal; and a second squarer circuit to thereby produce a second correlation signal proportional to the square of said combined signal. 22. The modulator of claim 21 wherein said error producing means includes a correlator for comparing the phase difference between the phase relationship of the first and second component signals and the phase relationship of the first and second input signals to thereby produce said error signal for applying to said second circuit means to maintain the quadrature phase relationship between said first carrier signal and said second carrier signal. 23. In a modulator for producing a quadrature amplitude modulated signal representative of a first input signal and a second input signal where a first carrier signal is modulated by the first input signal to thereby produce a first component signal and a second carrier signal is modulated by the second input signal to thereby produce a second component signal, and where said first and second carrier signals are substantially in a quadrature phase relationship, the improvement comprising a feedback loop for dynamically adjusting the phase relationship between said first and second carrier signals as a function of the difference between the phase relationship of the first and second component signals and the phase relationship of the first and second input signals. 24. The modulator of claim 23 wherein said first carrier signal and said second carrier signal are radio frequency signals. 25. The modulator of claim 23 wherein the first input signal and the second input signal include digitized data. 26. The modulator of claim 23 wherein the quadrature amplitude modulated output signal is an M-QAM signal. 27. A method for producing a quadrature amplitude modulated signal comprising the steps of: providing a first and a second input signal producing a first and a second carrier signals substantially in a quadrature phase relationship with each other; modulating the first carrier signal with the first input signal to thereby produce a first component signal; modulating the second carrier signal with the second input signal to thereby produce a second component signal; combining the first and the second component signals; providing a feedback loop to dynamically adjust the phase relationship between the first and the second carrier signals so as to maintain the first and the second carrier signals in a substantially quadrature phase relationship; wherein the step of providing a feedback loop includes the step of determining the difference between the phase relationship of the first and second component signals and the phase relationship of the first and second input signals: and, wherein the step of determining the difference in phase relationships includes the steps of: producing a first correlation signal representative of the phase relationship of the first and second component signals; producing a second correlation signal representative of the phase relationship of the first and second input signals; producing an error signal responsive to the difference between the first and second correlation signals. 28. The method of claim 27 wherein the step of producing the first and the second carrier signals includes the steps of: producing the first carrier signal by an oscillator; and producing the second carrier signal by applying the first carrier signal to a phase shifting circuit so as to shift the phase of the first carrier signal by approximately 90°. 29. The method of claim 28 wherein the error signal is applied to the phase shifting circuit so as to adjust the amount of the phase shift applied to the first carrier signal in the production of the second carrier signal as a function of the magnitude of the error signal. 30. The method of claim 29, wherein the first carrier signal and the second carrier signal are radio frequency signals. 31. The method of claim 29, wherein the quadrature amplitude modulated signal is an M-QAM signal. 32. In a method for generating a phase-compensated quadrature amplitude modulated signal responsive to a first input signal and a second input signal, including the steps of: producing a first component signal by modulating a first carrier signal with the C first input signal; producing a second component signal by modulating a second carrier signal with the second input signal, where the first carrier signal and the second carrier signal are substantially in quadrature phase relationship; and combining the first component signal and the second component signal to thereby produce a quadrature amplitude modulated signal, the improvement comprising the step of: dynamically adjusting the phase of the second carrier signal via closed-loop feedback control as a function of the difference between the phase relationship of the first and second component signals and the phase relationship of the first and second input signals. 33. In a method for generating a phase-compensated quadrature amplitude modulated signal responsive to a first input signal and a second input signal, including the steps of: producing a first component signal by modulating a first carrier signal with the first input signal; producing a second component signal by modulating a second carrier signal with the second input signal, where the first carrier signal and the second carrier signal are substantially in quadrature phase relationship; and combining the first component signal and the second component signal to thereby produce a quadrature amplitude modulated signal, the improvement comprising the step of: dynamically adjusting the level of one of the two input signals as a function of the difference between the phase relationship of the first and second component signals and the phase relationship of the first and second input signals. 34. In a method for generating a phase-compensated quadrature amplitude modulated signal responsive to a first input signal and a second input signal, including the steps of: producing a first component signal by modulating a first carrier signal with the first input signal; producing a second component signal by modulating a second carrier signal with the second input signal, where the first carrier signal and the second carrier signal are substantially in quadrature phase relationship; and combining the first component signal and the second component signal to thereby produce a quadrature amplitude modulated signal, the improvement comprising the step of: dynamically adjusting the level of each of the two input signals via closed loop feedback control as a function of the difference between the phase relationship of the first and second component signals and the phase relationship of the first and second input signals. ght line. 4. The microwave waveguide filter of claim 1, wherein the main-line cavity structure is folded and the main propagation path is not substantially a straight line. 5. The microwave waveguide filter of claim 1, wherein each of the main-line cavities and the first feedback cavity have a base wall that lies in a common filter plane. 6. The microwave waveguide filter of claim 1, wherein a first-cavity sidewall of the first main-line cavity and a second-cavity sidewall of the second main-line cavity are both of a first-sidewall length, and the first feedback cavity has a first-feedback cavity sidewall length of about the first-sidewall length. 7. The microwave waveguide filter of claim 1, wherein a first-cavity sidewall of the first main-line cavity and a second-cavity sidewall of the second main-line cavity are both of a first-sidewall length, and the first feedback cavity has a first-feedback cavity sidewall length of about two times the first-sidewall length. 8. The microwave waveguide filter of claim 1, wherein the main-line cavity structure and the first feedback cavity are formed in a single filter block of material. 9. The microwave waveguide filter of claim 8, further including a second microwave waveguide filter in a back-to-back relation to the microwave waveguide filter. 10. The microwave waveguide filter of claim 8, further including a single cover overlying and affixed to the single filter block of material. 11. The microwave waveguide filter of claim 1, wherein the main-line cavity structure includes a third main-line cavity and a fourth main-line cavity. 12. The microwave waveguide filter of claim 11, further including a rectangular second feedback cavity in microwave communication with each of the third main-line cavity and the fourth main-line cavity through the respective sidewall of the third main-line cavity and the fourth main-line cavity, there being a third-cavity feedback aperture between the second feedback cavity and the third main-line cavity, and a fourth-cavity feedback aperture between the second feedback cavity and the fourth main-line cavity. 13. The microwave waveguide filter of claim 12, wherein each of the main-line cavities, the first feedback cavity, and the second feedback cavity have a base wall that lies in a common filter plane. 14. The microwave waveguide filter of claim 12, wherein a third-cavity sidewall of the third main-line cavity and a fourth cavity sidewall of the fourth main-line cavity are both of a third-sidewall length, the first feedback cavity has a first-feedback-cavity-sidewall length of about the first-sidewall length, and the second feedback cavity has a second-feedback-cavity-sidewall length of about the third-sidewall length. 15. The microwave waveguide filter of claim 12, wherein the main-line cavity structure, the first feedback cavity, and the second feedback cavity are formed in a single filter block of material. 16. A microwave waveguide filter comprising a main-line cavity structure comprising a group of at least two rectangular main-line cavities arrayed along a main propagation path and including a first main-line cavity and a second main-line cavity, wherein each main-line cavity includes a sidewall, and wherein each pair of adjacent main-line cavities has a common transverse wall therebetween perpendicular to the main propagation path and a main-line aperture in the common transverse wall; and a rectangular first feedback cavity in microwave communication with each of the first main-line cavity and the second main-line cavity through the respective sidewall of the first main-line cavity and the second main-line cavity, there being a first-cavity feedback aperture between the first feedback cavity and the first main-line cavity, and a second-cavity feedback aperture between the first feedback cavity and the second main-line cavity, wherein each of the main-line cavities and the first feedback cavity have a base wall that lies in a common filter plane, and wherein a first-cavity sidewall of the first main-line cavity and a second-cavity sidewall of the second main-line cavity are parallel and both of a first-sidewall length, and the first feedback cavity has a length measured parallel to the first-cavity sidewall selected from the group consisting of about the first-sidewall length and about twice the first-sidewall length. 17. A method for fabricating a microwave waveguide filter, comprising the steps of providing a single filter block of material; and fabricating the single filter block of material to have therein a main-line cavity structure comprising a group of at least two rectangular main-line cavities arrayed along a main propagation path and including a first main-line cavity and a second main-line cavity, wherein each main-line cavity includes a sidewall, and wherein each pair of adjacent main-line cavities has a common transverse wall therebetween transverse to the main propagation path and a main-line aperture in the common transverse wall, and a rectangular first feedback cavity in microwave communication with each of the first main-line cavity and the second main-line cavity through the respective sidewall of the first main-line cavity and the second main-line cavity, there being a first-cavity feedback aperture between the first feedback cavity and the first main-line cavity, and a second-cavity feedback aperture between the first feedback cavity and the second main-line cavity. 18. The method of claim 17, wherein the step of fabricating includes the step of machining the main-line cavity structure and the first feedback cavity into the single filter block of material.