Mobile digital communications using phase -conjugating arrays.

Abstract

A phase conjugation based method for full duplex digital communications and position sensing is presented. The method has been used to demonstrate that it is possible to maintain a spatially confined, highly directive, and hence overt antenna pattern while the overall system is engaged in a digital communications link between moving platforms that contain the transceivers. The antenna patterns of the linked phase conjugating arrays self-phase and therefore automatically track each others position in space without the use of traditional RF phase shifters and their computer control or any explicit phase measurements and associated overhead in hardware and software. As a result a large effective processing gain can be realized by using the high gains of each of the adaptive antennas in the link. The technique can also produce relative position information of the transmitter and receivers. This relative position location feature might be useful in supplementing GPS position data or as a final-approach-to-landing aid for aircraft in difficult IFR flight conditions. The communications and position sensing features would be obtained by the use of a microwave phase conjugating array and phase processing electronics. To achieve this functionality nonlinear devices and phase filtering techniques are employed. The communications ability of the array is based on phase separation techniques. The phase of the electromagnetic energy transferred between platforms can be broken into two parts: (1) geometry-phase which is due to position, velocity, and acceleration, and (2) message-phase which is due to the phase modulation of digital data which is being impressed on the electromagnetic carrier. It has been found that the power spectrum of the geometry-phase and digital message phase may be separated, thereby making it possible to phase conjugate geometry phase and extract message phase simultaneously. It will be shown that this allows simultaneous tracking and full duplex communications functions to be implemented.