This article presents a novel method to design the multiband Doherty power amplifier (DPA). It is illustrated that phase periodic matching networks (PPMNs) can be used as multiband impedance inverters, off-set elements, and phase compensators to realize multiband DPAs. Moreover, the number of Doherty operation bands can be further increased by employing the reciprocal gate biases. A six-band dual-mode DPA with 1.8-2.2-/3.9-4.3-GHz operation bands in Mode I and 1.52-1.72-/2.38-2.53-/3.67-3.82-/4.53-4.68-GHz operation bands in Mode II using commercial GaN transistors is designed and implemented to validate the proposed method. The fabricated DPA achieves 8.7-13.5-dB gain and 39.6-41.5-dBm peak output power at all the designed bands. Drain efficiency of 49.2%-54.5% and 42.2%-56.7% is measured at a 6-dB output back-off in Mode I and Mode II, respectively. When stimulated by a five-carrier 100-MHz OFDM signal with a 7.7-dB peak-to-average power ratio (PAPR), adjacent channel power ratio (ACPR) of better than -48.9 dBc can be obtained by the proposed DPA after digital predistortion with 35.5%-50.1% average drain efficiency at 1.65/1.95/2.45/3.75/4.1/4.6 GHz, respectively.