| At present,the wireless communication system is developing to the direction of multi-band and high transmission rate.As an important component of wireless communication system,the performance of power amplifier plays a decisive role in the overall performance of the whole communication system.Under such a background,the broadband power amplifier with dual-band capability applied in the base station transmitter has gradually become a research hotspot.Due to the design structure of traditional dual-band Doherty power amplifier,the further expansion of bandwidth is limited.In addition,the peak-to-average power ratio of modulated signals in modern wireless communication systems is getting higher and higher,and the traditional Doherty power amplifier with a 6dB back-off range can no longer meet the design requirements.Therefore,in order to expand the working bandwidth,this paper combines the continuous power amplifier technology with the impedance inverter network with a specific phase shift,which provides a theoretical basis for Doherty power amplifier to realize the broadband operation in the dual-band mode.Furthermore,based on the theory of dual-band,it uses asymmetric Doherty power amplifier technology to achieve its work in a higher back-off range.The main work of this article is divided into the following three parts:First,the classification,specifications,linearization technology of the power amplifier and the working principle of the Doherty power amplifier are introduced.At the same time,the passive foundation of the traditional power amplifier to achieve dual-band operation is analyzed,and the shortage of narrow bandwidth is pointed out.Second,in order to realize the broadband high-efficiency operation of Doherty power amplifier in dual-band mode,a design method of continuous class dual-band Doherty amplifier based on specific phase shift matching is studied.The traditional design method mainly uses the matching network that composed of a dual-band impedance converter of a T-type or ?-type structure and a dual-band Stub Loaded Line to achieve dual-band operation.Although this method can achieve impedance matching at any two frequencies,due to its parallel resonance characteristics,it cannot achieve matching in a wide range,and its operating bandwidth is usually less than 100 MHz.To solve the above problems.In this paper,the principle of phase shift period repeatability is adopted.By determining the specific phase shift required in the two target frequency bands and combines the Chebyshev low-pass filter matching method to design the matching network to solve the problem of traditional dual-band Doherty power amplifier bandwidth limitation.Designed and implemented a dual-band Doherty power amplifier operating at 2.2-2.7GHz and 3.1-3.4GHz.The test results show that the saturation efficiency of the two frequency bands of the power amplifier are 60.8%-71% and 63.1%-66.3%,respectively,and the 6dB backoff efficiency reaches 47.2%-58.7% and 44.9%-53.8%.It meets the needs of multi-band simultaneous operation of future mobile wireless communication systems.At last,in order to realize the high-efficiency operation of the power amplifier in the higher back-off range on two frequency bands,a dual-band asymmetric Doherty power amplifier using a combined output network is proposed.By combining the impedance inverter network of the two peaking amplifiers,and combining the specially designed dual-band impedance conversion line,it can generate the Peaking output impedance required by the carrier amplifier for broadband operation in two frequency bands at the combining point,which improves the Broadband performance in dual-band.At the same time,it further analyzes the fundamental and harmonic impedance requirements of the Carrier amplifier to meet the requirements of continuous inverse Class F in dual-band,and the required post-matching network is designed to make its fundamental and harmonic load impedance better meet the requirements of continuous inverse Class F power amplifiers.Finally,a dual-band asymmetric Doherty power amplifier is designed to operate in the 2.35-2.75 GHz and 3.2-3.6GHz frequency bands.The saturation efficiency of the two frequency bands is 53.6%-64.3% and 48%-67.8%,and the 9dB back-off efficiency Reached 41.5%-53.3% and 40.5%-52.8%,respectively.It satisfies the requirements of future mobile wireless communication systems for high back-off. |
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