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A novel memory-grouped method is proposed for digital predistortion (DPD) of power amplifiers (PAs) with constrained acquisition bandwidth (BW) and extremely low sampling rate. By grouping the basis functions with different memory delays, a two-step algorithm can reduce overfitting in the constrained-BW technique. As a result, excellent DPD performance can be achieved even when the acquisition BW is constrained to several times narrower than the BW of the original input signal. Thus, using the memory-grouped method, a very low-speed analog-to-digital converter (ADC) can be used to sample the constrained feedback signal without aliasing, significantly reducing the cost of configuring a high-speed ADC. The performance of the proposed method is compared with the existing methods in different scenarios. Experimental results show that when the feedback BW is less than the BW of the original input signal, the proposed method can still achieve good performance, while the traditional methods fail to work. The experiment results also imply that the memory-grouped method can reduce the sampling rate by more than ten times. [ABSTRACT FROM AUTHOR]

In this letter, a modified band-limited digital predistortion (DPD) technique is proposed to improve the performance of the conventional band-limited DPD method in wideband systems. The power amplifier’s (PA’s) spectral regrowth outside the passband of bandpass filter is unable to be compensated using the traditional band-limited DPD. To increase the overall linearized bandwidth and reduce the requirement for feedback signal path, this new technique introduced two modules of full-band model extraction and coefficient iteration based on the conventional structures of band-limited DPD. It provides higher linearization performance and also reduces the sampling rate of analog-to-digital converter. The experimental results for 30-W Class F PA and 40-W GaN Doherty PA with 40-MHz orthogonal frequency division multiplexing signal and 60-MHz long-term evolution signal, respectively, have shown the superiority of the modified band-limited DPD. [ABSTRACT FROM PUBLISHER]

In this paper, a novel closed-form design method of generalized Wilkinson power dividers is proposed. By using this method, the power divider could be designed to be arbitrary-way (N-way) with arbitrary power division, and arbitrary dual-band operations in a pure planar structure. A previous dual-band unequal Wilkinson power divider is extended to arbitrary terminal impedances case, thus, it can be used to construct multiway planar power dividers through the combination of the two-section dual-frequency transformers. To obtain three-way (or any odd-way) power dividers with dual-band and unequal power division features, a new developed recombinant structure is employed. This recombinant structure consists of a two-way dual-band unequal power divider/combiner without any isolation structures. Furthermore, the complete design procedures and analytical equations of these proposed generalized power dividers are presented. To verify our proposed design approach in theory, several three-way and four-way power dividers with different dual-band applications and various power divisions are designed and simulated. Finally, a practical three-way power divider operating at both 0.6 and 2.45 GHz with a power dividing ratio of 3:5:1 is fabricated in microstrip technology as a typical example. The measured results of the fabricated power divider verify our proposed idea. [ABSTRACT FROM AUTHOR]

This letter proposes a novel design approach of wideband 90^\circ phase shifter, which comprises a stepped impedance open stub (SIOS) and a coupled-line with weak coupling. The result of analyses demonstrates that the bandwidths of return loss (RL) and phase deviation (PD) can be expanded by increasing the impedance ratio of the SIOS and the coupling strength of the coupled-line. For RL>10\ dB, insertion loss (IL) <1.1 dB, and PD of \pm 5^\circ, the fabricated microstrip single-layer phase shifter exhibits bandwidth of 105% from 0.75 to 2.4 GHz. [ABSTRACT FROM PUBLISHER]

The Gysel power divider (PD) is modified to achieve unequal or equal power division and suitability for three arbitrary real terminated impedances without any transmission losses in this letter. The calculation of electrical parameters in this asymmetrical structure is flexible. Meanwhile, this modified Gysel PD maintains high power-handling advantage over Wilkinson PD. By using the transmission line theory, the simple closed-form design equations are available for evaluation of these circuit parameters. For verification, two microstrip examples, which include an equal Gysel PD with three different output-port impedances and an unequal one for three standard 50-\Omega ports without additional output-port transformers, are given. It can be observed that there is excellent agreement between the simulated and measured results. [ABSTRACT FROM PUBLISHER]