Integration Design of Filtering Balun Diplexer with Improved Output Isolation Performance

A novel integration design of filtering balun diplexer with improved output isolation performance has been investigated in this research. The functions of bandpass filter (BPF), balun, and diplexer were successfully integrated into one component, which significantly decreased the system area, mismatch loss, and cost. The high output isolation was realized due to the cancellations of the electric and magnetic couplings. For validation, a filtering balun diplexer with second-order Chebyshev bandpass response was designed and fabricated in microstrip technology. The size of the designed diplexer is only 0.52 × 0.22 λ
g
²
. Moreover, multifunctional operations with an output isolation of 20 dB over the whole channel passbands are achieved.