Efficient Microstrip Diplexer Employing a New Structure of Dual-Mode Bandpass Filter

In this paper, a highly efficient design for microstrip diplexer employing a new configuration of dual-mode squared shape bandpass filters is introduced. The proposed diplexer consists of two dual-mode bandpass filters (BPFs), a matching network, which is utilized to ensure that the two BPFs and the antenna port are properly matched resulting in good isolation between the transmitter (Tx) and the receiver (Rx) branches. For the proposed BPFs, the transmission zeros of each BPF are adjusted to the nearest passband center frequency, which makes them very selective to achieve high isolation between the Tx and Rx frequencies. This also provides a low-frequency space ratio and low insertion loss. The proposed diplexer improves the channel isolation, bandwidth with compact size of . Based on this structure, the proposed diplexer has good insertion losses of about  and  at transmit frequency  and receive frequency , respectively. The achieved fractional bandwidth is  at  and  at . The achieved simulated isolation levels are  and  for Tx and Rx frequencies, respectively. The proposed diplexer is useful for several wireless communication applications such as WLAN, GPS and global mobile system (GMS)