Despite the economical and technical problems with the current Iridium and GlobalStar and proposed Teledesic satellite systems, it is expected that a high-speed satellite-based internet will become practical in the near future. Iridium and GlobalStar do not have sufficient bandwidth to accommodate high-speed transmission of data. It is undeniable that the future anywhere-anytime high-speed internet access requires low-earth-orbit K or Ka-band satellite systems similar to the one proposed by Teledesic.
One of the major problems with the proposed Teledesic system is the cost of the ground station antenna and control system. Unlike a geo-synchronous satellite, the low-orbit satellites move from horizon to horizon in 10 to 20 minutes. The antenna must be able to keep track of one or more satellite locations in order to obtain an uninterrupted connection. This is usually performed using phased array or mechanically steerable antennas. Unfortunately, the mechanically steerable antennas which use electro-mechanical actuators are usually bulky and prone to mechanical failures. The electronic phased array antennas are fast and no moving parts are involved, but they are very expensive.
Their objective is to develop a low-cost steerable antenna using a novel phase shifter and electro-active polymer (EAP) actuators. In order to achieve this objective, the PIs propose the following four tasks. Task 1: Develop a low-cost phase shifter for a phased-array antenna using EAP. Task 2: Design a practical, low-cost phased-array antenna. Task 3: Develop a variable reflector surface antenna with EAP actuators. Task 4: Develop reliable and practical EAP materials and actuators.
The phase shifter consists of a tiny mechanically movable dielectric element on transmission lines. To move the dielectric block, they will use a newly developed EAP actuator which requires only 1-2V. An EAP actuator can also be used as a microwave switch to create a controllable delay line. The whole unit can be integrated with the patch antennas on a multi-layer PCB. The proposed antenna does not contain any solid state microwave switches or electromechanical devices. It can be fabricated inexpensively. They have already conducted the numerical simulations and results were obtained for several TL configurations. Another application of the EAP actuator is for a mechanically steerable antenna. A profile of a flexible membrane or plates can be controlled accurately with an array of EAP actuators. A desired radiation pattern can be quickly created by adjusting the surface profile. There are many technical challenges to realize the EAP-based antenna. To achieve their objective, they must develop reliable EAP materials and actuators.
The PIs believe that the proposed low-cost antenna will be one of the key components to realize the "Internet-in-the-Sky". Although many aspects of this antenna have been tested and verified, they still need to work on several details. An EAP actuator is still in an infant state. To design the proposed antenna, they need a close collaboration between a material scientist who can design the EAP actuator and electrical engineers who can utilize the EAP actuator for the antenna applications.
