الفهرس | Only 14 pages are availabe for public view |
Abstract The aim of this thesis is to study the design procedures of a broadband quadriphase shift keying ( QPSK ) digital modulator, using finline techniques so as to be applied in spread spectrum systems. Two biphase shift keying modulators, one 1T and the other 11/2 areconnected in cascade to achieve the requi red modulation. The obtained modulator has a bandwidth of about O.5GHz centered at lOGHz with phase deviation o less than ~ 7 and a reflection loss variation not more than O.8db. The thesis discusses the different spread spectrum modulating techniques, their advantages and disadvantages. A survey is also given about the two main classes of high speed codes used in spread spectrum systems. This survey studies the properties and capabilities of these codes as well as the coders/decoders used for their generation/regeneration. An introduction is then presented to the design of broadband QPSK reflection type modulators used in spread spectrum systems. A modulator is realized with circulators, switching PIN diodes and impedance matching networks having filter structures. Finally,the practical realization of the QPSK modulator using finline techniques is given. The measurements and results of the modulator circuit using a network analyzer are obtained. It is noticed from the design performance that it agrees quite well with the obtained measured results . |