Experimental optimization of the 2^ND 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.