In this paper, we present a design method for a compact inverted Doherty power amplifier (IDPA), which has high-efficiency and high-power characteristics. An optimum load matching network and an additional offset line, after the matching network of the carrier amplifier, dynamically modulate the load impedance according to the input power drive, while the conventional Doherty power amplifier uses a quarter-wave line to do it. The operational principles and design guide are provided. For experimental verification, a 50-W Doherty amplifier was designed for the 4 differential quadrature phase-shift keying application at the 860-MHz band. The measured performance of the IDPA was compared with that of the balanced class-AB amplifier with the same output matching network. At an output power of 50 W, the IDPA performs with 3.16 dB better adjacent channel power ratio ( 28 versus 24.84 dBc) and 6.15% higher power-added efficiency (59.02 versus 52.87%) than the class-AB amplifier does.Index Terms-Doherty power amplifier, inverted Doherty power amplifier (IDPA), load modulation, offset line, 4 differential quadrature phase-shift keying (DQPSK).

No abstract

frequency increases, the half-power beam-width reduces. In addition, the cross-polarization level is lower in the H-plane than the E-plane, and is about Ϫ22 dB for H cross-polar and Ϫ12 dB for E cross-polar at 4 GHz. CONCLUSIONA new spatial power combiner with EBG has been realized. From the measured results, the prototype can provide more than 90% impedance bandwidth and with good out-of-band suppression. A system gain of about 17 dB has been realized. ACKNOWLEDGMENTSThe authors would like to acknowledge the funding support received from both the Conicyt, Chile, Bicentenario Project ATC-11, and the A*Star Singapore-Poland Joint Collaboration Project. Both linearity and efficiency performances have been very important selection criteria for high-power RF amplifiers. There are many well-known techniques for the enhanced linearity and efficiency performance [1][2][3][4][5][6]. The Doherty power amplifier, employing a very simple load impedance modulation technique, has provided a powerful solution for an efficiency improvement without loss of linearity [4 -6].Kim et al. proposed an uneven power drive for the Doherty amplifier which drives a little more input power to the peaking amplifier to compensate for its lower gain due to a lower bias point [5]. However, they put an attenuator to an input of the carrier amplifier in order to drive relatively more input power to the peaking amplifier, which degrades the gain of the Doherty power amplifier. Hence, the power-added efficiency (PAE) improvement can be limited by the gain degradation.In this study, we adopted an unequal quadrature input splitter for better performance of the Doherty amplifier. An optimized uneven power drive using an unequal splitter allowed the proposed Doherty amplifier to have higher gain than the unevenly driven Doherty amplifier using an attenuator. The efficiency performance at a given linearity of the Doherty power amplifier was experimentally optimized for a down-link wideband code division multiple access (WCDMA) signal through the power splitters having varied unequal power split characteristics and the optimized bias conditions of the amplifier. The experimental results of the Doherty amplifiers using unequal splitters were compared with those of the conventional Doherty and class-AB amplifiers. Figure 1 shows a schematic diagram of the Doherty power amplifier using an unequal quadrature input splitter. In general, the peaking amplifier has a class-B or -C bias point to use its low gain at a low power level, while the carrier amplifier is biased for class-AB operation. A large gain expansion of the peaking amplifier can be used as an on/off transition for load impedance modulation. However, the fully expanded gain of the peaking amplifier, at a high power level, is still lower than that of the carrier amplifier which can be compensated by the unequal input power drive. CIRCUIT CONFIGURATIONThe unequal input power splitters were designed based on a modified branch-line hybrid coupler which also compensated for the phase offset due to a /4...

No abstract

No abstract