Design of compact microwave diplexer for system-in-a-package applications

A compact-size and high-isolation microwave diplexer for system-in-a-package has been proposed. By employing the folded stepped-impedance resonators (SIRs), the overall circuit size can be significant reduced. For demonstration, a diplexer operating at 0.5 GHz and 0.86 GHz with third-order Chebyshev bandpass response has been designed and fabricated with microstrip technology. As a result, the diplexer occupies a small size, i.e., 0.14 λg by 0.12 λg. The measured results are in good agreement with the simulation. The output isolation and out-of-band rejection better than 60 dB are achieved.