Power Amplifier Linearization for Lmds from High Altitude Aeronautical Platforms

Introduction. Broadband LMDS (Local Multi-Point Distribution Systems) is a wireless point-to-multipoint communication system operating above 20GHz (usually around 26− 31GHz) that can be used to provide digital voice, data, Internet, and video services. One possible solution for LMDS is to use High-Altitude Aeronautical Platforms (HAAPs), which are situated in the stratosphere, 20− 22km above the ground [1]. The High Altitude Platforms (HAPs) [2][3] work like pseudo-stationary satellites giving coverage to a large number of users, situated over a large geographical area, and offer some advantages in front of satellite or terrestrial platforms for broadband communications with direct contact and without intermediate relays or signal delays. Such platforms require considerably less communications infrastructure than that required if delivered by a terrestrial network. The High Altitude Long Endurance (HALE) platforms are cost effective and no pollution alternatives powered by solar panels. Nowadays several projects are developed abroad, such as the HELINET project, achieved by a European Union team from Italy, UK, Spain, Switzerland, Slovenia and Hungary [4]. The use of a HALE like a node of a LMDS system need high linearity in the RF power amplifiers, so much for signal quality considerations as to avoid interference with other communication systems working inside the same geographical area. In this paper the behaviour of a 28 GHz power amplifier linearized by using the Cartesian feedback structure is assessed. The studied power amplifier is the combination of the Agilent-HMMC-5040 (driver) and AgilentHMMC-5033 (Power Amplifier).