Current Research Projects:
Digital Communications Using Retrodirective Arrays (Phase Conjugation)

A new technique for full duplex digital communications using adaptive phase conjugation is presented. The technique is based on mixing the RF signal to an intermediate frequency where it can be easily processed, and filtering the phase of the IF signal to separate the geometry phase and the message phase. The retro-directive array automatically tracks communicating platforms and transmits a directive return signal without the use of phase shifters. A 6 GHz microstrip retrodirective antenna array was built, together with the signal IF processing needed for full duplex operation. The measured RCS values of a linear 6-element array are in good agreement with theory and results in a 0 to ­5 dB RCS for angles up to +/- 60°. The measured RCS values of a circular array are much flatter and are 0 to -5 dB up to +/- 80°. Two way digital communications at a baud rate of 78 KBits/sec was also demonstrated with a BER < 10-6 for a SNR around 10 dB. The application areas are in high-performance digital mobile telecommunications for commercial and military applications.

Graduate Student: Leo DiDomenico (now at Jet Propulsion Laboratory)
Sponsor: Army Research Labs/Federated-Lab Program.

More details can be found in these papers:

- L.D. DiDomenico and G.M. Rebeiz, "Digital communications using self-phased arrays," Accepted for publication in the IEEE Trans. Microwave Theory Tech. To appear Oct. 2000. (File: pdf 540 K)

- L.D. DiDomenico and G.M. Rebeiz, "Frequency stability in adaptive retrodirective arrays," Accepted for publication in the IEEE Trans. Aerospace and Electronic Systems. To appear June 2000. (File: pdf 1.4 MB)

Figure 1: A retrodirective array using a phase conjugating cell.

Figure 2: A phase conjugating cell using two mixers and an IF processing network for digital communications.

Fig. 3: A 6-element circular retrodirective array with the IF processing for retro-directive communications.

Fig 4: Measured RCS of the retrodirective array, with and without modulation. Also shown is the array response with no phase conjugation.