Retrodirective Techniques Research Articles

A Time-Modulated Array With Digitally Preprocessed Rectangular Pulses for Wireless Power Transmission

A cooperative design of the advanced time-modulated array (TMA) and the retrodirective (RD) array is introduced to act as a transmitting array for multiuser wireless power transmission (WPT) applications. The conventional rectangular-pulse based TMA is lack of harmonic beamforming flexibility limited by its frequency spectral properties. By preprocessing the rectangular pulses with the sinusoid-based control signal, harmonic beams are independently steerable. The proposed array is enabled with self-phasing capability by taking advantage of the RD technique. Besides, to avoid the unexploited radiation caused by unscannable fundamental beam and specular harmonic beams, the single sideband (SSB) modulator is utilized to enable the transmitting array with high-efficiency beamforming capacity. The numerical results verify that the presented array performs well in various charging scenarios, which brings a highly potential insight for far-field WPT.

4-D Retro-Directive Antenna Arrays for Secure Communication Based on Improved Directional Modulation

The 4-D antenna arrays combined with retro-directive technique based on an improved directional modulation technique are proposed for physical layer secure communications. The optimized time sequence is designed, which improves the security performance of 4-D antenna arrays greatly. By introducing the retro-directive technique into 4-D antenna arrays, secure communication can be realized without any prior knowledge of the legitimate receiver's location. Moreover, the proposed approach avoids both the heavy computational burden and complex hardware implementation, benefiting from the inherent advantages of retro-directive antenna arrays in automatic target tracking. The numerical and experimental results demonstrate that the proposed transmitter architecture of 4-D retro-directive arrays provides an effective way to achieve wireless secure communication in the scenario with multiple legitimate receivers and under multipath environment.

Study on Reconfigurable Coaperture Antenna Arrays Based on Time-Modulation and Retrodirective Techniques

Time-modulation (TM) technique for array design is opening the way for the development of easy-reconfiguration, low-complexity, and high-accuracy antenna systems for modern wireless applications. In this study, four different scenarios of TM-based reconfigurable coaperture antenna arrays are introduced. The aims are to make use of the common antenna elements for the coaperture and to share the RF switches needed in TM technique to form the reconfiguration. For the reconfigurable functionality, the retrodirective (RD) technique is involved, and for the reconfigurable band, the synthesized transmission line (STL) technology is involved. Four proposed arrays are single-band time-modulated retrodirective and self-null-steering array (i.e., single-band TM-RDNA), single-band time-modulated/retrodirective/time-modulated retrodirective array (i.e., single-band TM-RDA), dual-band TM-RDA, and triband TM-RDA. In the single-band TM-RDNA, a frequency offset, which is equal to the TM frequency, between two time-modulated phase conjugators is introduced to realize the array capable of RD and self-null steering simultaneously at retransmitted frequency. In the single-, dual-, and triband TM-RDAs, the introduced TM-RDA functions as a low sidelobe RDA at carrier frequency, and as an extra benefit, it can function as a low sidelobe RDA at harmonic frequencies. The features, superiority, and inferiority of these TM-based reconfigurable coaperture arrays are discussed and summarized. To experimentally verify the feasibility of the proposed schemes, a four-element single-band TM-RDNA and single-band TM-RDA structures are constructed and tested.

A satellite data transmission antenna

A retrodirective satellite antenna for a broad bandwidth, satellite-to-ground data transmission link, is described. An information-collecting satellite which transmits its data in the direction of the ground receiver upon command, is considered. The satellite antenna described for this system is an active retrodirective antenna which utilizes the beam-forming characteristics of a phasing matrix. A signal from the ground station is received on a particular beam port of the matrix which corresponds to a particular beam-pointing direction. Control circuitry in the satellite activates a switching matrix and a transmitter so that the data-carrying signal is transmitted in the same direction from which the satellite is interrogated. Other retrodirective techniques in addition to the phasing-matrix antenna are evaluated in terms of their relative merit. The systems considered include the active Van Atta array, the automatic three-dimensional electronic scanning, antenna (ATHESA), the Luneberg lens and various other antenna array techniques.