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University of Oulu

1. Karhu, A. (Anssi). Behavior of the RF power amplifier under a varying load condition in 5G mMIMO base station.

Degree: 2018, University of Oulu

RF power amplifier is located at the backend of the transmitter before the filter and the antenna. To ensure ideal operation, known output impedance of the power amplifier is matched to the load impedance with help of matching network. Load impedance is traditionally provided by the circulator which has good isolation properties and stable load property. Higher frequencies are investigated in future 5G technology to obtain wider available bandwidths and meet increased capacity requirements. Higher frequencies have shorter wavelength which leads to smaller cell sizes due to their poorer propagation capability. As many RF components, also antennas have properties that are relative to wavelength. Higher frequency thus enables to integrate more antenna elements to base station structure, which is called massive MIMO (mMIMO) structure. By adjusting excitation signals of each element, wanted beam forms and beam directions are achieved. The possibility for the removal of the circulator from the power amplifier output was investigated in this thesis. In mMIMO structure number of transmitting branches is huge, so there is potential to achieve cost savings and increase the integration level if the removal is feasible. However, transistor output would be then altered to highly frequency and power dependent load, because the antenna input impedance is affected by the coupling effects from neighboring elements as a function of beam steering functionality. Thanks to good isolation properties of the circulator, power amplifier is not altered to that in traditional base station design. Additionally, circulator protects the transistor from reflecting waves, as they are routed to the termination. The device under test was optimized to 3.4 GHz-3.6 GHz frequency band and was connected as a balanced structure. The goal in this thesis was to investigate how the removal is changing the behavior of the power amplifier compared to the design where the circulator exists. Investigation was carried out by examining the basic RF performance parameters and quality of the feedback response for the digital pre-distorter (DPD). Simulation models turned out to be inadequate to simulate the performance under a varying load condition properly and accurate correlation between simulations and hardware measurements was not achieved. However, hardware implementation and measurement results showed up a potential, but there also occurred a big variation over the operation bandwidth. There occurred 8.3% unit variation in the efficiency figures in the circulatorless design over the bandwidth while it was just 2% units in the design where circulator existed. Peak power quantities varied 1.5 dB and. 0.5 dB respectively. Also, the effect on the DPD feedback response was more severe than expected as the ripple in the response was 4 dB in the circulatorless design while it was within acceptable limits in the design where the circulator existed. Therefore, more investigation would be needed in the future to ensure the proper performance over the…

Subjects/Keywords: Electrical Engineering

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Karhu, A. (. (2018). Behavior of the RF power amplifier under a varying load condition in 5G mMIMO base station. (Masters Thesis). University of Oulu. Retrieved from http://urn.fi/URN:NBN:fi:oulu-201809122771

Chicago Manual of Style (16th Edition):

Karhu, A (Anssi). “Behavior of the RF power amplifier under a varying load condition in 5G mMIMO base station.” 2018. Masters Thesis, University of Oulu. Accessed November 21, 2018. http://urn.fi/URN:NBN:fi:oulu-201809122771.

MLA Handbook (7th Edition):

Karhu, A (Anssi). “Behavior of the RF power amplifier under a varying load condition in 5G mMIMO base station.” 2018. Web. 21 Nov 2018.

Vancouver:

Karhu A(. Behavior of the RF power amplifier under a varying load condition in 5G mMIMO base station. [Internet] [Masters thesis]. University of Oulu; 2018. [cited 2018 Nov 21]. Available from: http://urn.fi/URN:NBN:fi:oulu-201809122771.

Council of Science Editors:

Karhu A(. Behavior of the RF power amplifier under a varying load condition in 5G mMIMO base station. [Masters Thesis]. University of Oulu; 2018. Available from: http://urn.fi/URN:NBN:fi:oulu-201809122771

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