Design and analysis of MOSFET based absorber for 5G massive MIMO base station.
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Date
2021
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Abstract
The Fifth Generation (5G) technology suffers from a series of drawbacks ranging from the high cost of infrastructure development, replacement of old devices that may not be compatible with 5G, and losses within the 5G base station construct. During transmission, these losses have a negative effect on the overall performance and efficiency of transmission systems. The 5G massive-Multiple Input Multiple Output (MIMO) base station structure suffers from these losses. In addition, a loss experienced in the 5G technology is due to the reflection of signals from the receiver (Rx) branch connected to the circulators in the 5G massive-MIMO base station. Operators often specify that the worst-case reflections (return loss) over the system's operating frequency range must be 18 dB lower than the signal transmitted into the system.
As feed systems become shorter and antenna systems are required to operate over broader frequency ranges, achieving an 18 dB return loss may not be practical, most especially at a 5G frequency regime. This reflection loss experienced in the 5G massive-MIMO base station results from the Rx branch's unmatched load impedance with the source impedance of the Transceiver (TX) branch.
However, this problem can be solved by designing a matched circuit between the TX and RX branch of the base station. But Engineers are often faced with the challenge of designing a matching network for impedance mismatch, most especially at high frequency. For this reason, an N-channel Metal Oxide Field Effect Transistor (MOSFET) connected to a circulator has been proposed as an alternative solution to the performance and efficiency reducing effects of reflected radio frequency signal. The proposed model has been presented by connecting the Tx branch, antenna, Rx branch, and the MOSFET to each of the assumed four-port circulator ports.
Two comparisons have been made between the source current and drain current of the MOSFET whenever there is a reflection from the base station's Rx branch, In this research, four case of reflection from the RX branch of the base station have been examined at 28 Ghz to analyse the model's performance. Various performance parameters (Insertion loss, Reflection coefficient, Total Power Absorbed by MOSFET (TPAM), Total Power Lost to Rectifier (TPLR), S-parameter, efficiency, etc.) have been analyzed for the validity, stability, and reliability of the proposed model. At worst case reflection from port-3 of the circulator, TPAM, TPLR and reflection coefficient have been observed to be 0.64 mW, 2.95 mW, and 0.0001179.
Comparisons have been made with existing RF absorber models using efficiency, insertion loss, frequency, RF power absorption level, and ease of implementation as a standard. The model has been observed to have an efficiency greater than 90 %, an insertion loss more significant than 38 dBm at a frequency of 28 GHz.
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Masters Degree. University of KwaZulu-Natal, Durban.