| Summary: | The paper proposes a four-directional beamforming switched antenna system based on Butler matrix for 28 GHz mmWave. It is made up of a 90-degree coupler, a crossover, and a 45-degree phase shifter. A <inline-formula> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> Butler matrix is combined with a 28 GHz patch antenna to form a Butler network antenna. Four directions of the radiation beam can be changed when the input position is changed. From the simulation and measurement results, the measured reflection coefficients cover 27.9-29.3 GHz at all four ports with a standard reflection coefficient of -10 dB and four different angles of 15°, -46°, +44° and -13° for switching beam direction. The antenna’s compact size of <inline-formula> <tex-math notation="LaTeX">$39.1\times 45.6\,\,{\mathrm {mm}}^{2}$ </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">$3.65\lambda _{0}\times 4.26\lambda _{0}$ </tex-math></inline-formula>) makes it ideal for use in millimeter wave bands for 5G NR n258, and n261 applications, while also providing a high gain of 11.5 dBi.
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