1. Field of the Invention
The present invention relates generally to radio frequency signal processing. More specifically, the present invention relates to a method and system which prevents the loss of RF signal phase and amplitude information when the data is being processed by a countermeasure system or the like.
2. Description of the Prior Art
In the past, transmission of RF signal amplitude and phase information from a receiver antenna to an RF signal processing device always occurred by utilizing RF electrical cables to transfer the amplitude and phase information from the receiving antenna to the processing device. The RF signal is an electro-magnetic waveform received by the antenna and then converted to an equivalent RF electrical signal. Phase and amplitude information can easily change during the transfer due to cable problems and other deficiencies in an RF system. Cable leakage, temperature variations, amplifier stability and phase compilation problems are representative of the types of problems that can cause substantial variations in the transfer of RF signal amplitude and phase data using RF cables and RF electrical equipment.
Accordingly there is a need to develop an electrical RF signal transfer device which insures that phase and amplitude information are not compromised during transfer and processing of the RF signal by an RF signal device such an electronic countermeasure device.
The present invention overcomes some of the disadvantages of the past including those mentioned above in that it comprises a relatively simple, yet highly effective system and method which prevents the loss of RF signal phase and amplitude information when the data is being transferred and then processed by a countermeasure system or the like.
According to the method comprising the present invention, when an incoming RF signal is received by an antenna for processing by an electronic countermeasure system of the like, the RF signal is first converted to an equivalent optical RF signal for transmission through a first fiber optic cable. The optical RF signal is transmitted through the first fiber optic cable to a controller. The controller converts the RF optical signal to an equivalent RF digital signal.
The RF digital signal is manipulated by the controller and a countermeasure set using RF countermeasure techniques. When processing of the RF digital signal by the controller and countermeasure set is complete the signal is converted to an RF analog output signal and then transmitted to a transmit antenna via an RF electrical signal cable.
A feedback loop comprising a second fiber optic cable is included on the signal output side of the controller. The amplitude and phase for the RF analog output signal to be transmitted by the transmit antenna is monitored by the feedback loop. Phase and amplitude information for the RF analog output signal is transmitted back to the controller via the feedback loop.
The feedback loop by providing feedback of the amplitude and phase information for the transmitted signal allows the M and S controller to make adjustments to the signal to be transmitted to insure that there is a 90° phase shift between the received RF signal and the transmitted RF signal. The feedback loop allows for instantaneous re-calibration of the RF signal to be transmitted by a transmit antenna.
The controller first converts the optical signal from the second fiber optic cable to a digital equivalent signal. The controller then adjust the amplitude and phase of the RF digital output signal to compensate for amplitude and phase errors which are caused by transmission of the RF analog output signal through the RF electrical cables. The controller makes minor adjustments to the RF analog output signal to insure that phase and amplitude error are minimal operating as a self-calibrating system.
Referring first to
Transmission of amplitude and phase data for the horizontally polarized radiation of the RF input signal from antenna element 22 to M and S controller 30 is by a signal transmission line 26. Transmission of amplitude and phase data for the vertically polarized radiation of the RF signal from antenna element 24 to M and S controller 30 is by a signal transmission line 28.
By eliminating conventional electrically conductive RF cables for signal transmission from antenna elements 22 and 24 to M and S controller 30, the transmission problems associated with these cables are substantially reduced. For example, changes in phase and amplitude data which normally occur using conventional RF cables are almost completely eliminated when the data is converted from an RF signal to an optical format for transmission through an fiber optic cable.
Referring to
A fiber optic cable 52 connects the optical signal output from detector 70 to an optical signal input of M and S controller 30. The fiber optic cable 52 prevents degradation of the RF signals amplitude and phase information while phase and amplitude data is being transferred from the antenna 50 to the M and S controller 30. Only one fiber optic cable is required since one cable can transmit multiple signals simultaneously, that is one fiber optic cable can transmit both the horizontally polarized and vertically polarized RF components of the incoming RF signal.
An adjustable attenuator 72 is also included within receive antenna 50. The attenuator 72 allows a user to adjust and reduce the power level of the incoming RF signal to match the power level of RF detector 70 preventing damage to the RF detector 70.
Connected to Measure and Set detector 30 via an electrical signal transmission line 32 is an AN/ULQ-21 (V) Electronic Countermeasure set 34, which is an electronic attack suite used in aerial and surface targets for specific mission requirements. The AN/ULQ-21(V) Electronic Countermeasure set 34 is configured to provide multiple Electronic Countermeasure (ECM) techniques including the capability to produce both noise and deception techniques across the 850 MHz to 18 GHz frequency range.
The M and S controller 34 receives one or more countermeasure signals from the AN/ULQ-21 (V) Electronic Countermeasure set 34 and then combines the phase shifted RF signal with the countermeasure signals. The processor 90 within controller 34 generates the 90° phase shaft and also combines the phase shifted RF signal with the countermeasure signals providing the RF signal to be transmitted. The countermeasure signals received from the AN/ULQ-21 (V) Electronic Countermeasure set 34 are jammer type signals.
The optical signal including the incoming RF signal's phase and amplitude information is transmitted to the M and S Controller via fiber optic cable 52. M and S controller 30 converts the optical signal to a digital equivalent signal for processing by controller 30 and Countermeasure set 34.
Referring again to
The feedback loop 60 by providing accurate feedback of the amplitude and phase information for the transmitted signal allows the M and S controller 30 to make adjustments to the signal to be transmitted to insure that there is a 90° phase shift between the received RF signal and the transmitted RF signal. The feedback loop 60 allows for instantaneous re-calibration of the RF signal by controller 30, which is to be transmitted by transmit antenna 62. The use a fiber optic cable insures the accuracy of the phase and amplitude information provided to processor 90 by allowing for data feedback using optical signals which will not degrade during transmission.
At this time it should be noted that the 90° phase shift between the received RF signal and the transmitted RF signal is a jamming technique. The phase shift provides a null which makes the return signal appear void of any objects.
The feedback loop 60 also compensates for non-linearity in the power amplifier 60 which can cause the transmitted signal to become out of calibration.
As shown in
The controller 30 first converts the optical signal from the fiber optic cable 60 to a digital equivalent signal. The controller 30 then adjust the amplitude and phase of the RF digital equivalent signal to compensate for amplitude and phase errors which are caused by transmission of the RF analog output signal through the RF electrical cables. The controller 30 makes minor adjustments to the RF analog output signal to insure that phase and amplitude error are minimal operating as a self-calibrating system. The transmit antenna 62 also has an adjustable attenuator 76. The attenuator 76 allows a user to adjust and reduce the power level of the RF electrical output signal to match the power level for RF detector 74 preventing damage to the RF detector 74.
Referring to
Referring to
When the processor 90 completes the corrections to the amplitude and phase data for the signal to be transmitted by transmit antenna 62, a digital equivalent RF signal is supplied to a signal/RF amplifier 92 which converts the signal to an analog RF format and amplifies the RF signal. The signal is then supplied to a VM1/VM2 vector modulator circuit 100. The VM1/VM2 circuit 100 allows for any correction of errors introduced by the amplifiers 40 and 42. VM1/VM2 circuit 100 is controlled by the processor 90.
From the foregoing, it is readily apparent that the present invention comprises a new, unique and exceedingly useful method and system for phase and amplitude error occurring in an RF transmitted signal, which constitutes a considerable improvement over the known prior art. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims that the invention may be practiced otherwise than as specifically described.
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Number | Date | Country | |
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20100056040 A1 | Mar 2010 | US |