Investigation on retrodirective arrays : novel component developments and system constructions

Abstract

Phased arrays with control circuitries are favorably employed in many wireless applications in both military and commercial communication systems. The demands of high performance communication systems directly impact design issues at both system and component levels; phased arrays are no exception. Retrodirective arrays belong to the family of phased arrays but have self-controlled circuitries. These arrays are of particular interest to various applications because of their simple structure and cost effectiveness. They offer simple ways to retransmit a signal toward the signal source. This function is performance automatically without relying on digital signal processing and control algorithms. In recent years, retrodirective arrays have received consideration attention in the community. This dissertation is accordingly intended to provide a comprehensive investigation of performance enhancements of various retrodirective arrays which can be devoted to antenna arrays to achieve retrodirectivity with different or additional features. There are two main categories of antenna arrays that achieve retrodirectivity, namely, the Van Atta array and the phase conjugated array. Several newly proposed techniques that lead to higher performances are applied to these arrays. First, an active wideband circularly polarized Van Atta array with full utilizations of both antennas and amplifiers is proposed. The dual-fed microstrip patch combines the two techniques of stacked patch and aperture coupling excitation such that the axial-ratio bandwidth is successfully enhanced. The active array is implemented by inserting ordinary unilateral amplifiers to increase the effective isotropic radiated power. The circular polarization enables a full utilization of all elements. Each antenna with unidirectional amplifier services for both signal receiving and signal transmitting. Second, a 2-D Van Atta cross-shaped array using star-shaped patches with information carrying ability are proposed. Star-shaped patches with lower mutual coupling are proposed as the antenna elements in the 2-D array. With a similar arrangement as in the first design extended to a 2-D array, 2-D retrodirectivity is created; an 8-element prototype with cross-shaped arrangement with a fewer number of elements in than an m × m array is realized. Several 2-stage amplifiers biased by a DC-DC boost converter are applied and integrated with the 2-D Van Atta array. The DC-DC converter provides not only a stable active bias but also serves as an information carrier with the amplitude modulation for the outputs of amplifiers. Without the need of external signals and digital circuitries, the proposed array can so directly modulate the information source, such that information carrying ability is firstly introduced to the Van Atta array with simpler configuration than that of the phase conjugated array. Third, both 1-D and 2-D phase conjugated arrays employing low conversion-loss mixers and star-shaped patches are proposed. The non-linear optimization techniques, named multi-harmonic loads, as a systematic way are employed to realize low conversion-loss resistive field effect transistor (FET) mixers for phase conjugation. Both the 1-D linear and the 2-D cross-shaped phase conjugated arrays are designed to support linear polarization and both linear and circular polarizations respectively. The retrodirectivities of both the 1-D array and the 2-D array are compared. The graceful degradations are observed though the linearly polarized 1-D phase conjugated array still works even there are small deflections in polarization which may be caused, for example, by improper hardware installation. Fourth, a balanced phase conjugated array using the proposed dual-fed patch is proposed for direct conversion transmitters. The dual-fed patch is proposed as a passive integrated antenna which combines the functions of both radiation and Wilkinson power divider/combiner. Different from the conventional square patch antenna, the proposed dual-fed patch operates in the first higher order resonance mode. This makes the two feeding ports possess very good isolation so that it can be employed for balanced circuitries. The proposed balanced phase conjugated array supports a dual-channel transmission which obviously has lower costs and is more compact than that using two separated and identical phase conjugated arrays. Two different waves at base-band frequencies serve as different information sources which are both modulated by the proposed array and successfully demodulated by a direct conversion receiver. Finally, the circular phase conjugated array providing a planar solution for 360° scannable arrays in the single printed circuit board is proposed. A simple Yagi antenna with end-fire radiation is proposed and integrated with low conversion-loss phase conjugating mixers to form a circular phase conjugated array. A planar design with 12 elements arranged circularly with a single external signal is realized. The full range retrodirectivity is experimentally confirmed. A circular phase conjugated array for the applications, which need the full range or angular independently scan array, is proposed with saving in both the cost and element number.