Simulation Analysis of LC-Based Array Antenna Operation and Its Radiation Pattern

Abstract

An liquid crystal(LC)-based array antenna is of increasing interest in academy and industry because of many advantages over conventional antennas in various aspects. While conventionol antennas show fixed radiation pattern for a given frequency, the array antenna induces various radiation patterns by controling amplitude and phase of individual antenna elements. In an LC-based array antenna, LCs manipulate the phase of the RF signal while the amplitude can be set by signal input circuits. If the RF signal penetrates through the LC layer as the incident light does inside the traditional liquid crystal displays (LCDs), the thickness becomes beyond acceptable limit of reasonable material cost. Therefore, we made the RF signal propagate on the substrate in our LC antenna simulation so that the thickness of the LC layer and LC response time decreases. The LC array antenna consists of N by N microstrip unit antennas, tunable delay lines on the substrate, RF feeding and biasing networks. The RF phase shift is determined by the length of the delay lines and the effective permittivity of LCs around the delay lines. To obtain an appropriate phase shift, the vector components of LC directors around the delay lines are extracted by using a commercial LCD simulation package. And an effective permittivity profile is calculated by using the three dimensional LC director alignment. From the effective permittivity profile, we can create a waveguide model in RF signal simulation programs, and the phase shift can be estimated, which is used for the radiation pattern calculation. Figure 1. (a) shows the schematic design of the LC-based array antenna with rectangular microstrip patches and Figure 1. (b) shows the radiation pattern of the array antenna. The suggested simulation process connecting the LC simulation program and the RF simulation tools can be a good basis for analysing and designing the LC-based array antennas.