A novel integrated Tx-Rx diplexer for dual-band WiMAX system

In this paper, a novel integrated Tx-Rx diplexer for dual-band Worldwide Interoperability for Microwave Access (WiMAX) application is realized by low temperature co-fired ceramic (LTCC) technology. The proposed Tx-Rx diplexer has 5 ports and consists of two lowpass filters, two bandpass filters, and one common matching network, which are fully embedded in the LTCC substrate. This novel structure can be applied for either Tx or Rx path by simply making two ports to be shorted to the ground. The fabricated Tx-Rx diplexer has 9 pattern layers including 3 ground layers and it occupies less than 3.0 mm × 2.5 mm × 0.528 mm. In case of Tx operation, the measured insertion losses at 2-GHz and 5-GHz band are less than 0.9 dB and 2.5 dB, respectively, with a return loss of more than 19.4 dB and 10 dB. Furthermore, it provides a more than 32-dB and 19.2-dB second harmonic suppression at 2-GHz and 5-GHz bands is obtained. In case of Rx operation, the insertion losses are less than 1.4 dB and 2.4 dB in 2-GHz and 5-GHz bands. It provides a more than 30-dB and 32-dB attenuation at 2-GHz and 5-GHz band. The measured results of the implemented Tx-Rx diplexer are in good agreement with the simulated results. The RF FEM was realized by the proposed Tx-Rx diplexer and 4 PIN diodes at each port except antenna port for shortening to the ground or not. It can be low-loss and low-cost solution by removing MMIC SPDT switch in series connection.