The new generation wireless communication technologies are adopting more complex modulation schemes in order to satisfy the increasing demands of high data rate. As the modulation schemes have evolved from 4-QPSK to OFDM, the peak to average power ratios (PAPRs) have risen from 3.3 dB to 9.6 dB. From the view of RF Power Amplifier (RFPA) designer, high PAPR translates to a challenge of maintaining high efficiency and linearity over wide dynamic range. In a conventional RFPA designs, when the power is backed off from its maximum level, the efficiency drops significantly. Therefore, to maintain the efficiency even when the power is backed-off, it has become necessary to include efficiency enhancement technique with conventional RFPA designs.;The outphasing technique is one of the most prominent technique which can deal with challenges created by high PAPRs, in other words high power back-offs. This technique allows the PAs to perform linear amplification and operate at high efficiency even when the power is significantly backed off. This work explores the different ways of improvement in previously established four-way outphasing combiner. First, a new microstrip line based implementation method is demonstrated that reduces the area of the original combiner by 83%. Second, a new experimental control law is introduced which improves the deviation in input impedances by 10% in the mid-power range, and by a factor of 2 at the high power range. Above that, a novel design methodology of dual-band Chireix outphasing combiner, tuned to two arbitrary frequencies, is introduced and the practicality of the network is demonstrated by a microstrip-based implementation, operating at 4.4 GHz and 5.2 GHz.;In addition, a CAD based design of two-stage Base station PA is presented. This PA is designed to fit into Envelope Tracking (ET) architecture. The drain supply is made to vary from 20 V to 50 V with the step-size of 10 V. This base station PA produces 150 watt of output power and operates from 1.99 GHz to 2.29 GHz. At the highest drain voltage and at center frequency, the efficiency is observed to be 60.2% with the total gain of >35.8 dB.
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