SUMMARYThe electronically steerable parasitic array radiator antenna consists of one feed radiating element and parasitic radiating elements placed in the near field of the active radiator. A beam is formed due to spatial electromagnetic field coupling among radiating elements. The radiation pattern is electronically controlled by means of the variable capacitance devices (varactors) loading the parasitic elements. Unlike a conventional phased array, only one transmitter and receiver are needed for system configuration. Therefore, adaptive beamforming of low dissipation power and low fabrication cost can be achieved. On the other hand, there is only one output port to observe the signal and the weights can be controlled indirectly via reactors instead of direct control. In addition, due to interelement mutual coupling and the parasitic element being directly connected to the reactive device, the linear adaptive array theory developed to date cannot be applied straightforward. In this paper, the configuration of this antenna, its operating principle and formulation, and its measurement method, control scheme, and applications to signal processing are presented. We describe a mathematical model to simulate the radio frequency behavior of the antenna, the equivalent weight vector used for formulation of the characteristics, the admittance matrix including varactors, the effective element length, the equivalent steering vector method, the method for effectively extending the variable range of the capacitance of the varactor, the reactance circuit to cancel nonlinear distortions, the method for calibration of varactors and radiation pattern by measurement of near field of the radiating element, the learning criteria used to control radiation patterns autonomously in adaptation to the electromagnetic environment, the reactance optimization algorithm, the concept of the reactance domain signal processing and the direction of arrival estimation based on such a process, and diversity reception and spatial correlation.

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SUMMARYIn this paper, we show that the current distribution along the parasitic dipole elements loaded by variable reactors varies greatly depending on the variable reactor value. Thus, when the directionality of an Electronically Steerable Passive Array Radiator (ESPAR) antenna constructed from parasitic dipoles is calculated, we must consider the changes in the current distribution along these elements. Therefore, we propose a method where the current weight is the value of the vector effective length of each element multiplied by the current value at the port. We also show that when the dipole length is less than approximately the half wavelength, the vector effective length is calculated for the most part by the ratio of the port voltage to the port current. From this relationship, even if the current distribution along an element is not determined, the vector effective length of a parasitic element can be calculated from the value of the variable reactor loading the element. Thus, the current distribution along the elements can be easily considered when calculating the directionality of the ESPAR antenna. We present a method that calculates the directionality of the feed dipole array antenna having mutual coupling among the elements that considers the current distribution along the element where not only the port current but also the port voltage are set as the weights.

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We propose a millimeter-wave antenna to serve as an element antenna for a multi-sector switched-beam antenna, which can be fed by a post-wall waveguide. Several tapered slot antennas are connected to an aperture of an H-plane sectoral post-wall horn antenna whose radiation pattern is narrowed in the H-plane to further narrow the pattern in the E-plane. Moreover, the aperture of each tapered slot antenna is loaded with a dielectric to increase the gain. We designed an antenna whose gain is over 16 dBi in the frequency band of 57-66 GHz. The wideband property is experimentally examined.Index Terms-Millimeter wave, post-wall, horn antenna, tapered slot, wideband

A new mathematical model of Electronically Steerable Parasitic Array Radiator (ESPAR) antennas is proposed. The ESPAR antenna is a kind of adaptive array antenna expected to spread as a terminal antenna for home LANs or wireless ad-hoc networks. Parasitic elements loaded with variable-reactance terminations are excited by mutual-coupling, so the current distributions along each wire element are not in the ideal sinusoidal function. To consider the current distributions, an equivalent weight vector (EWV) model is modified by introducing a vector effective length (VEL) for each wire element. The vector effective length of a parasitic dipole can be calculated by the reactance value of the variable reactor loading the dipole. The directivity of ESPAR antennas can be calculated simply and accurately by the EWV-VEL model. 0-7803-8145-9/04/$17.00 ©2004 IEEE.

This paper reports the first experiment on binary reactance diversity. A prototype of a 3-element 5-GHz band ESPAR antenna is designed and fabricated in a planar printed circuit. It consists of one radiator and two parasitic elements with loading varactor diodes. It functions as a diversity antenna. The diversity scheme that employs a simple binary reactance control based on the criterion of received power. In an indoor multipathfading environment, the ESPAR antenna exhibits a performance of diversity with 7-dB gain at CDF 99% in spite of its simplified mechanics.