Experimental optimization of the 2ND loop configuration for feedforward amplifiers in terms of their efficiency and linearity

In this paper, we report the results of the experimental optimization of the 2(nd)-loop configuration for feedforward amplifiers in terms of their efficiency and linearity. We consider two parameters in the 2(nd)-loop of a feedforward amplifier: (i) the size ratio between the main and error amplifiers and (ii) the coupling factor of the error signal coupler. Experiments are performed using a multicarrier down-link WC-DMA signal under various configurations. The measured data, which are normalized with respect to the overall power capacity of the main and error amplifiers, show that, among the different 2(nd)-loop configurations, the best compromised efficiency (13.4%) at a given adjacent channel leakage ratio (ACLR) level (-50 dBc) is observed for a size ratio of around 3.0 and a coupling factor of around 7.2 dB. (c) 2006 Wiley Periodicals, Inc.