Ultracompact Retrodirective Antenna Arrays With Superdirective Radiation Patterns

Abstract

It is shown that the Direction-of-Arrival (DoA) information carried by an incident electromagnetic wave can be encoded into the evanescent near field of an electrically small antenna array with a spatial rate higher than that of the incident field oscillation rate in free space. Phase conjugation of the received signal leads to the retrodirection of the near field in the antenna array environment which in turn generates a retrodirected far-field beam towards the original DoA. This electromagnetic phenomenon enables electrically small retrodirective antenna arrays with superdirective, angular superresolution, auto-pointing properties for an arbitrary DoA. Theoretical explanation of the phenomenon based on first principle observations is given and full-wave simulations demonstrate a realisability route for the proposed retrodirective terminal that is comprised of resonance dipole antenna elements. Specifically it is shown that a 3-element disk-loaded retrodirective dipole array with 0.15λ spacings can achieve 3.4dBi maximal gain, 3dBi front-to-back ratio and 13% return loss fractional bandwidth (at 10dB level). Next it is demonstrated that the radiation gain of a 3-element array can be improved to approximately 6dBi at expense of the return loss fractional bandwidth reduction (2%).

Analog/Digital Hybrid Delay-Locked-Loop for K/Ka Band Satellite Retrodirective Arrays

“…RETRODIRECTIVE array (RDA) has the capability to re-transmit a signal back along the spatial direction(s) Manuscript along which the array was illuminated by the incoming signals without the need for a-priori knowledge of their points of origin [1], [2]. This automatic tracking characteristic makes RDA technology useful in many applications, including long-range radio frequency identification (RFID) [3], microwave power transmission [4], physical-layer wireless spatial encryption [5]- [7], and mobile satellite communications (SATCOM) [8], [9], etc.…”

Experimental Study of Electrically Compact Retrodirective Monopole Antenna Arrays

“…The design of electrically small antenna arrays with relatively high gain and practically useful bandwidth [3] represents a more challenging task than designing a single electrically small antenna, since the known rules for standard, half-wavelength spaced antenna arrays cannot be routinely applied due to complex near field EM coupling mechanisms [1], [3], [15].…”

“…It has been shown in [3], [15] that the spacings between the array elements cannot be made arbitrarily small due to accompanying significant radiation resistance drop, consequent antenna feeding mismatch and eventual antenna array efficiency reduction.…”

“…In our previous companion paper [15] we proposed a fundamentally new class of electrically compact antenna terminals with omnidirectional radiation pattern in receive mode and auto-pointing superdirective radiation pattern in transmit mode, with auto-pointing requiring dedicated electronic circuitry performing EM signal phase conjugation, [20]- [22]. The EM phenomena enabling electrically compact retrodirective antenna array (RDA) operation are theoretically considered in full detail in [15].…”

“…The EM phenomena enabling electrically compact retrodirective antenna array (RDA) operation are theoretically considered in full detail in [15]. Particularly, it has been demonstrated that the DoA information carried by an incident EM wave can be encoded into the array excitation vector in the receive mode with a spatial rate higher than the incident field spatial oscillation rate in free space.…”