A broadband diplexer-integrated double-pole single-throw switch for FDD/TDD operations

A broadband diplexer-integrated double-pole single-throw (DPST) switch is proposed to realize frequency division duplexing (FDD) and time division duplexing (TDD). It consists of a lowpass filter (LPF) and a bandpass filter (BPF). The series LC resonators are used in both channels to create transmission zeros (TZs) in the stopband to ensure high selectivity. The diplexer is realized by inter-digital capacitors and microstrip section inductors, which can achieve low cost and compact size. Besides, this diplexer does not require a T-junction, achieving a compact size. For demonstration, a diplexer operating in DC-1.78/3.29–4.42 GHz has been designed, fabricated, and measured. The diplexer has four operating modes. And it has a compact size of 24.67 mm × 21.4 mm. The measured results show that the diplexer exhibits broadband, low insertion losses, high isolation, and high selectivity.