Flexible Design Method for Multifunctional Filtering Diplexers Integrated With Single-Pole Double-Throw Switches

This paper presents a novel design method for multifunctional filtering diplexers integrated with single-pole double-throw switches having three operating modes: Modes 1–3. Modes 1 and 2 involve the operation of switchable filters with different frequencies, which are suitable for time-division duplexing (TDD) systems. Mode 3 involves the operation of switchable diplexers, which are suitable for TDD and frequency-division duplexing (FDD) systems. The proposed design method is based on distributed coupling technology and can thus offer a high degree of design flexibility, particularly in terms of controlling the filter order, bandwidth, and number of channels. To demonstrate the feasibility and design flexibility of the proposed method, it was used to design and fabricate second- and fourth-order multifunctional diplexers; the designed diplexers were then assessed through electromagnetic simulations and experimental measurements. The simulation results were in good agreement with the experimental results, thereby validating the feasibility and design flexibility of the proposed method. The results indicated that the second- and fourth-order multifunctional diplexers occupied small circuit areas (approximately
$0.098 {\lambda }_{g}^{2}$
and
$0.198 {\lambda }_{g}^{2}$
, respectively). In addition to their multifunctional characteristics and high design flexibility, the multifunctional diplexers exhibited satisfactory performance, including an in-band insertion loss of < 2.5 dB in the ON state, an in-band attenuation of >42 dB in the OFF state, and a port-to-port isolation of >48 dB.