Performance measurement of 4x4 butler matrix
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Date
2019-06
Authors
Loo, Bo Yuan
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Abstract
Beam Forming Networking is a network to process signal and forms beam at outputs in a specific or predetermined direction. This network plays an important role in wireless transmission especially in the field of Wireless Local Area Network (WLAN) as it helps to direct the transmission beam towards a specific direction. There is some Beam Forming Network in this field now, for instance, the Blass Matrix, Rotman Lens and Butler Matrix. Butler Matrix is chosen in this project for its simplicity for design, lossless network and able to fabricate with PCB. 4×4 Butler Matrix is a network with 4 input ports and 4 output ports. It is a combination of the Branchline coupler, Crossover and Phase Shifter. In this study, the Butler Matrix is designed and simulated using ADS 2006A software with operating frequency at 2.4 GHz for WLAN application. The design also fabricated with Rogers RO4003C with a dielectric constant of 3.38 and 0.813 mm thick. The simulation results show there is only 0.05 dB to 0.15 dB amplitude imbalance at the output ports while the input port is excited respectively and the phase is at four different direction. The return loss of Port 1 is 35.164 dB and Port 2 is 33.370 dB at 2.4 GHz, which indicates the design is well-matched. The fabricated prototype is measured for the S-parameters using network analyzer. The measured results show there is 1.6 dB to 2.3 dB of amplitude imbalance and the phase also in four different degrees but differ with simulated results. The measured return loss is relatively low compared to simulated results, which only about 15 dB and 29 dB for Port 1 and Port 2. Low return loss is due to poor soldering of SMA connectors at ports. Besides, the difference in measured phase with simulated is due to the extra transmission length is induced due to the SMA connectors does not solder exactly at the edge of the microstrip transmission line.