This paper presents a generalized expression of the modified load networks (MLNs) for Doherty power amplifiers (DPAs) with an extended output power back-off (OBO) range. Based on the analysis using this new expression, a new circuit structure generally applicable to any combination of the multiple MLNs is proposed. The load network has a simple structure including impedance matching circuits and offset lines for the carrier and peaking amplifiers. A design procedure for the proposed load network is presented. A DPA using any optimized combination of the multiple MLNs can be easily designed using the proposed load network. For verification, a GaN-HEMT symmetrical DPA based on a combination of the virtual open-stub (VOS) and out-phased current combining (OCC) methods was designed and implemented for the frequency band of 3.4 - 3.7 GHz. The reversed uneven power splitting method is adopted in the design for higher power gain. Using the 5G New Radio (NR) signal with a peak-to average power ratio (PAPR) of 7.9 dB and a signal bandwidth of 100 MHz, the proposed DPA exhibited DE of 55.3 - 60.9% with a power gain of 11.9 - 12.7 dB at an average output power of 33.7 dBm. An adjacent channel leakage power ratio (ACLR) of −42.6 - −44.8 dBc was achieved at the average power level by using a digital predistortion (DPD) technique across the band.

A simplified all-in-one load network of Doherty power amplifier (DPA) was proposed for extended back-off range and broadband operation in this study. Although the proposed load network was simplified to just have a postmatching network (PMN) and compact $L$ -section matching networks for both carriers and peaking amplifiers, it could fully incorporate previously known back-off range extending methods, such as asymmetric structure, virtual stub (VS), out-phased current combining (OCC) method, and complex combining load (CCL). Accurate closed-form expressions for the elements and impedances of the load network based on the back-off range extending methods were derived and used to design the structure of the load network. Among available configurations of synthesized load networks, a structure suited for broadband operation was derived. To verify the proposed load network and its closed-form expression, an asymmetric DPA based on GaN-HEMT with an extended back-off range of 8 dB was designed and implemented for a frequency band of 2.9–4.0 GHz, which includes the N78 5G frequency band. Lumped inductors for the initial configuration were transformed using transmission lines for a quasi-lumped structure which was optimized to have a frequency response similar to the original inductor. Implemented DPA exhibited a drain efficiency (DE) of 50%–56% under an output power back-off (OBO) of 8.0 dB from a saturated output power of about 43 dBm, while it showed a DE of 62%–76% over a frequency range of 2.9–4.0 GHz using a continuous-wave (CW) signal. An efficiency of as high as 50.6%–58.0% and an adjacent channel leakage power ratio (ACLR) of under $-$ 46.0 dBc after a digital predistortion (DPD) based on a memory polynomial were achieved at an average output power of 35 dBm using a 5G new radio (NR) signal with a signal bandwidth of 100 MHz and a peak-to-average power ratio (PAPR) of 7.8 dB.

The load networks of advanced Doherty power amplifiers (DPAs) have traditionally been designed according to the ABCD parameters. In this paper, design conditions as an impedance transformation condition and an effective electrical length were used to design the output matching networks (OMNs) for the carrier and peaking amplifiers of the virtual-stub DPAs (VS-DPAs). An optimization method for the effective electrical length was proposed that was specifically constructed for the load impedances of the carrier amplifier at the low power level to have broadband characteristics through the load-pull simulation. Using the optimized design conditions for broadband design, compact OMNs for the carrier and peaking amplifiers were designed using quasi-lumped components. Moreover, an asymmetric structure with an increased power capacity of the peaking amplifier for the VS-DPA was proposed to compensate for a relatively low peak fundamental current of the peaking amplifier due to its deep class-C operation as well as the extended output back-off (OBO) range of the VS-DPA. To verify the proposed load network, a broadband asymmetric VS-DPA for the 3.3 - 4.2 GHz band was designed and implemented using GaN HEMTs with power capacities of 6 and 10 W. Using a 5G new radio (5G NR) signal with a signal bandwidth of 100 MHz and a peak-to-average power ratio (PAPR) of 7.8 dB, power gain of 8.2 - 9.1 dB, DE of 46.0 - 57.0%, ACLR of better than -45 dBc after DPD linearization at an average power of 35.0 dBm were achieved at the broad frequency range of 3.3 - 4.2 GHz.

We propose a coupled transmission line (CTL)-based load network structure for the Doherty power amplifier (DPA) with an extended output power back-off (OBO) range, designed to achieve high efficiency and broad bandwidth. This load network features a highly simplified structure, consisting of a CTL and a post-matching network (PMN) with only two additional shunt elements. We also propose a novel approach to comprehensively analyze the CTL using its equivalent circuit model, which facilitates the comparison of various CTL-based load network structures suitable for DPA applications. By searching for 2-D closed-form parameters derived from the equivalent circuit models, we can determine the most suitable load network structure and its design parameters for optimal performance across a wide bandwidth. For implementation, a new method is proposed to ascertain the initial dimensions of a CTL based on analyzing the half-circuits as either a coplanar waveguide (CPW) or a CPW with a lower ground plane (CPWG), under even-mode and odd-mode conditions. To validate the proposed CTL-based load network and its equivalent circuit model, a DPA featuring an asymmetric structure using GaN-high electron mobility transistors (HEMTs) was designed and implemented, extending the back-off range to 8 dB for the broad frequency band, including the sub-6 5G (N78) band. The chosen load network, including the CTL, was fabricated on a two-layer printed circuit board (PCB). Measurement results show a drain efficiency (DE) of 44%–52.3% at an OBO of 8.0 dB from the saturated output power of approximately 43 dBm across the frequency range of 2.9–4.1 GHz under continuous wave (CW) signal excitation. With a 5G new radio (NR) signal featuring a bandwidth of 100 MHz and a peak-to-average power ratio (PAPR) of 7.8 dB, efficiencies of 48.0%–55.3% were achieved at an output power of 35.5 dBm, while maintaining an adjacent channel leakage power ratio (ACLR) of under -47.0 dBc across the frequency band after linearization using a digital pre-distortion (DPD) based on a memory polynomial.

A new load modulation combiner (LMC) having the capability of back-off control is proposed for a Doherty power amplifier (DPA). The proposed LMC consists of two transmission lines tied at the combining node, and a shunt element across the other ends of the transmission lines. The shunt element of the LMC becomes virtually open-circuited at the peak power level and allows the carrier amplifier to have an arbitrary load impedance at the low power level. The operating principle and circuit structure of the DPA based on the proposed LMC are presented in detail. The proposed DPA was implemented using GaN-HEMT for the 3.5 - 4.0 GHz band. Using a 5G NR signal with a peak-to-average power ratio (PAPR) of 7.9 dB and signal bandwidth of 100 MHz, the implemented DPA showed drain efficiency (DE) of 49.6 - 54.4% and power gain of 11.1 - 13.0 dB at an average output power of 34.5 dBm. An adjacent channel leakage power ratio (ACLR) was obtained as -50.4 - -45.0 dBc at the average power level with a digital pre-distortion (DPD) technique.

The microwave power transfer (MPT) system requires a massive Tx array for building a focused radio wave to efficiently transfer power to the Rx. Beamforming IC is one of the core elements for the massive Tx array. This paper presents a 5.8 GHz 4-channel beamforming Tx IC based on a CMOS process. The beamforming Tx IC includes a resistive 4-way power splitter, 5-bit differential phase shifters, drive amplifiers, and power amplifiers. Each channel is designed to transmit a power of no less than 100mW. To verify the Tx IC, a 16-channel beamforming Tx module based on 16 patch antennas and four 4-channel Tx ICs was designed. The module also includes a PLL, a frequency doubler, and a 4-way Wilkinson power divider. MPT experiments to verify the beamforming IC and module were carried out using the implemented 16-channel Tx module at 5.8 GHz. Received power levels of 13 dBm and 2.1 dBm were achieved at distances of 0.4 and 1.4 m, respectively. The results are almost similar to the values acquired from the calculation using the Friis equation.