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The load network of the carrier amplifier for the conventional Doherty power amplifier (DPA) consists of an impedance matching circuit, an offset line, and a <inline-formula> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula>/4 transmission line (TL), so that the overall electrical length of the network can easily exceed the minimum value of 90&#x00B0;. Then for appropriate impedance modulation, it should be 270&#x00B0; with an additional 180&#x00B0;. This excessive electrical length of the load matching network limits the bandwidth at either the low-power or peak-power level. In this paper, a compact quasi-lumped <inline-formula> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula>/4 impedance transformer (ITF) having simultaneous multiple functions of impedance matching and load impedance modulation with a controlled electrical length of 90&#x00B0; is presented. The proposed load network includes the internal components of the transistor, the simplest high-pass network using a shunt inductor, and a low-pass L-C network. Using the optimized value of the shunt inductor, the electrical length of the load network can be adjusted to 90&#x00B0;, while other components are accordingly changed to match the optimum load impedance. To verify the proposed load network, a DPA was designed and implemented using 10 W GaN-HEMTs for both carrier and peaking amplifiers. Using a 5G New Radio (NR) signal with signal bandwidth of 100 MHz and peak-to-average power ratio (PAPR) of 7.8 dB, a drain efficiency (DE) of 47 - 54.2&#x0025;, and adjacent channel leakage power ratio (ACLR) of &#x2212;27.9 - &#x2212;23 dBc were achieved at an average output power level of 35.8 - 36.3 dBm for the frequency band of 3.4 - 3.8 GHz.

Compact Load Network Having a Controlled Electrical Length for Doherty Power Amplifier