Poboljšanje performansi pojačavača i mešača primopredajnika za širokopojasnu i dvokanalnu primenu u mikrotalasnim komunikacionim sistemima

Abstract

Modern wireless communication systems should provide certain performances of the power amplifier (PA), which is their component, where high energy efficiency, high gain and linearity of the system stand out as the most important. In the area of maximum output power (saturation of power gain characteristic), the amplifiers have a satisfactory efficiency, but express non-linear characteristics. If the amplifier works in the lower power range, it can be characterized by good linearity, but on the other hand, high efficiency will not be achieved. The best solution to this problem is to design the amplifier to operate near the saturation of the power gain characteristic, where it has good efficiency, but operates in a non-linear mode, and then perform its linearization by using appropriate linearization method. The research in this dissertation includes the development and application of certain methods for the design of non-linear circuits of the transceiver part of the communication system, such as the PA and the mixer, with the aim of improving their efficiency and linearity. In the dissertation, the analog linearization method was modified for application on broadband PA and a digital linearization method was developed. In the transmitting part of the system, broadband and dual-band amplifiers were designed, which with the application of the linearization methods ensure high output power, high efficiency, and linear operation of the PA. In the receiving part, the linearization of the Gilbert mixer, which has a good conversion gain characteristic in a wider frequency range, was performed. The linearization method that uses nonlinear signals of the 2nd and 4th order (NI2 and NI4 signals) at frequencies around the 2nd harmonic of the fundamental carrier was modified in the analog domain for application on broadband single-stage and two-stage amplifiers (Doherty topology), as well as on the amplifiers that operate in two frequency bands. Moreover, a digital linearization method was developed, which includes the four different approaches, where the processing of appropriate nonlinear (NI) signals generated for linearization purposes is achieved in the digital domain. The first digital method uses NI signals in the baseband, while in the other three adequately processed NI signals modulate the 2nd harmonic of the fundamental carrier and are applied to the circuit that should be linearized. The effects of the application of linearization methods on amplifiers and mixers were validated through the simulation procedure in the ADS software (Advanced Design System), as well as through the experimental verification of one of the proposed digital linearization approaches on a practically manufactured asymmetrical two-stage Doherty amplifier.