Varactor-loaded inverted-F multiport parasitic array radiator antenna

In order to realize a compact low-profile antenna that can steer beam/null continuously in full azimuthal directions, this paper proposes a new configuration of beam-steering antenna with mutual coupling between inverted-F antenna (IFA) elements. The antenna array consists of two active and two passive IFA elements loading variable reactors, thereby realizing a low-profile antenna array within a small space. It is expected that the antenna possesses a high ability to form beam and/or null, since it behaves as both Yagi-Uda array and phased array. Furthermore, we derive here a general expression of equivalent weight [1] for multiport parasitic IFA arrays. Finally, the beam steering of the proposed antenna is demonstrated by the numerical simulation.

Introduction

Frequency spectrum below 6 GHz, which is suitable for mobile radio systems, is used very densely by a lot of radio systems, and the spectrum resource become scarce. One of the approaches to solve the problem is “System-to-system SDM (Space Division Multiplexing) technologies,” which improves spectrum efficiency in a unit area by cooperative communication between transmitters and receivers using beam-steering antennas. To achieve beam steering, some array configurations of single port have been proposed, for example parasitic arrays [1], [2] and switched element arrays [3]. However, monopole or dipole antennas of the former ones are not so low-profile, and the latter ones are difficult to control beam and null directions simultaneously. Also, multi-fed-port antennas as the extended version have been presented in [4], but have the same restrictions as antennas in [1]–[3] yet.