A novel digital predistortion (DPD) technique is proposed to linearize ultra-broadband millimeter wave (mmWave) power amplifiers (PAs) by only employing very limited bandwidth resources for the Tx, feedback loop (FB), and baseband (BB). Compared to the conventional methods, the proposed method will comprehensively reduce the bandwidth requirements for the whole system, which will make the linearization affordable for mmWave PAs. To validate the proposed idea, a 4-carrier 320 MHz modulated signal was employed to excite a mmWave PA with the center frequency of 41 GHz. Experimental results have proven that the proposed method can effectively realize the PA linearization with very narrow Tx/FB/BB bandwidth, which largely extends the capability of DPD to the forthcoming 5G era.
The waveguide traveling-wave power combiner (WTWPC) falls into the category of asymmetrical non-isolated power combiners, and, therefore, the active load modulation occurring within the combiner was investigated. Proper manipulation of active load modulation gave rise to a two-step design method for the combiner. The first step formulated the specifications of the combiner in terms of active load impedance at its input ports, which determined the objective scattering parameters of the combiner, as well as the desired coherent excitation signals. The second step established a versatile equivalent circuit model to provide a mapping relation between the scattering parameters and the physical dimensions of the combiner. The proposed equivalent circuit method not only offered a close-to-reality description of the existing type of traveling-wave power combiners but also broke new ground for combiner variants that accommodate the more general driving amplifiers. A Q-band quasi-planar traveling-wave waveguide spatial combined amplifier was built to demonstrate the proposed method. The measured P −1dB bandwidth of the prototype was 6 GHz (33-39 GHz). INDEX TERMS Equivalent circuit, load modulation, traveling wave, mm-wave power amplifier, rectangular waveguide, waveguide probe, waveguide iris window.
A near-band digital predistortion technique is proposed to linearise a wideband power amplifier (PA) with millimetre wave (mmWave) non-contiguous carrier aggregation (CA). The proposed method employs low-bandwidth linearisation architecture to only focus on the in-band compensation and part of the out-of-band (OOB) distortion suppression, which largely alleviate the bandwidth limitation for baseband operation. Experiments have been carried out on an mmWave PA with the centre frequency of 41 GHz. Good measurement results can be achieved when the PA is excited by a very wideband modulated signal with 1001 CA configuration and the total bandwidth of 640 MHz.
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