Design and nonlinear analysis of a dual-band Doherty power amplifier for ISM and LMDS applications

Abstract — In this paper, the design and nonlinear analysis of a dual-band mm-wave Doherty power amplifier is presented. The Doherty power amplifier has been designed to operate simultaneously at 24GHz for ISM band and 28 GHz for LMDS applications with 1 GHz bandwidth at each band, using Large-signal model of 0. 15µm GaAs PHEMT transistor with 6 dB of output power back off at both frequencies. Analysis results show that DPA improves both efficiency and linearity in a wide power ranges for these two frequency bands. Keywords- dual-band; millimeter wave; Doherty power amplifier; GaAS PHEMT; ISM band; LMDS; I. I NTRODUCTION Recently, the research for radio frequency power amplifiers in 24 GHz band has been accelerated because of the potential Industrial, Scientific and Medical (ISM) band [1] and the wireless vehicular radar applications and with the emergence of Local Multipoint Communication Service (LMDS), there is considerable activity in ka-band. In order to provide communication services such as television, video-on-demand, distance learning, Internet access, interactive games, as well as a host of other services to homes [2]. This tremendous need has created considerable interest in the development of ka-band, linear, high power and high efficiency power amplifiers. In these applications, power amplifiers play an important role in high frequency transmitter front-end circuits. Beside, requirements for the support of multi standards in communication systems have emerged. These requirements necessitates the design of multi-band PAs. A straightforward way is to use multiple power amplifiers in parallel which operate at different bands. However, the space in a transceiver is usually too small to integrate many power amplifiers. Thus, the design of a PA that concurrently supports multiple bands is a challenge. In fact, besides to be the main responsible of the transmitted signal linearity, the PA efficiency is heavily correlated to battery autonomy as well as the heat generated and associated thermal issues. As a consequence, new design methods are needed to realize RF PA able to work simultaneously in a multi-band, multi-mode wireless environment. Also, A power amplifier (PA) must have an acceptable linear performance and high power efficiency. For achieving these objectives, different linearization and efficiency enhancement technique such as Doherty, envelope elimination and restoration, predistortion, etc have been developed[3]. Among these techniques Doherty power amplifier (DPA) is very popular, since it enhances both linearity and efficiency and is specially suitable for signals with high PAPR. Up to now a number of power amplifiers have been reported with good performance for ISM band or for LMDS application [4], But most pervious works have been focused on one of these bands and these amplifiers are not suitable for modulated signals with high PAPR such as OFDM. In this paper, a dual-band Doherty power amplifier with good linearity and performance to work simultaneously in two frequency bands (ISM band and LMDS application) is designed, using 0. 15µm GaAS PHEMT as active device. II. D