A Six-Port Dual-Function RF Device With Four-Element MIMO Antenna Array and Bandpass Filter Operations

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This article presents a dual-function RF device, with four antenna ports and two filter ports, which behaves either as a multiple-input multiple-output (MIMO) antenna array or a bandpass filter. It consists of four parallel-coupled microstrip lines as the dual-function part and two feed parts for the two channels. The former part simultaneously performs wideband array radiator and fourth-order filter resonator characteristics. For MIMO antenna array operation, the parallel-coupled microstrip line structure is equivalent to a traditional patch, which is divided into four strips with three slots. Based on such a configuration, wide antenna impedance bandwidth is achieved. With regard to the filter operation, it features a conventional fourth-order microstrip parallel-coupled filter typology. As a result, high circuit integration is achieved, and although the two channels share the common part, the bandwidth improvement for both the channels is realized. For demonstration, the proposed dual-function device is implemented and fabricated. As an MIMO antenna array, the center frequency and the measured impedance bandwidth is 4.5 GHz and 27.3%, respectively. The isolation between the two channels in this band is more than 23.6 dB. In addition, it features ±45° continuous beam scanning capacity with less than 3 dB gain reduction. With respect to the bandpass filter operation, the center frequency and measured impedance bandwidth is 0.55 GHz and 15.6%, respectively. The measured in-band insertion loss is 2.12 dB and channel isolation is more than 58 dB.