The advent of fourth generation (4G) wireless communication with available modulation bandwidth ranging from 1 MHz to 20 MHz is starting to emerge. The linear modulation technique being employed means that the power amplifiers that support the standards need to have high degree of linearity. By nature, however, all power amplifiers are non-linear. Load-pull measurement system provides anindispensable non-linear tool for the characterization of power amplifier and transistor for linearity enhancement. Conventional passive or active load-pull has delay problem that get worse as the modulation frequency is increased beyond few MHz. Furthermore in order to provide robust non-linear measurement, load-pull system needs to provide bandwidth at least five times the modulation bandwidth by including the fifth-order inter-modulation (IMD5). This thesis presents, for the first time, delay compensation on the unique active envelope load-pull architecture providing constant impedance for bandwidth up to 20 MHz. In doing so, it provides a superior load-pull measurement and also the ability to directly control in-band impedances. Artificial variations imposed on the in-band impedances offer further insight on power amplifier and transistor behaviours under wideband multi-tone stimulus.