Switchable and High-Isolation Diplexer With Wide Stopband

This letter presents a switchable diplexer composed of a stepped-impedance distributed coupling feeding line, four different quarter-wavelength stepped-impedance resonators (SIRs), two shunt open stubs, two p-i-n diodes, and bias circuitry. Compared with previous works, the proposed circuit features compactness, wide stopband, high selectivity, and independently switchable channels. To suppress harmonics, various quarter-wavelength SIRs with the same fundamental frequency but harmonic frequencies in stagger are used. Open stubs are also adopted to achieve an optimal stopband response. To meet the demands of reconfigurable application in wireless communication systems, switching circuit is integrated into the proposed diplexer to develop a switchable diplexer. In this way, mismatch losses during integration and circuit size are both further reduced. Simulations and measurements have been carried out to verify the design concept with good agreement.