A Multiharmonic Absorption Circuit Using Quasi-Multilayered Striplines for RF Power Amplifiers

A multiharmonic absorption circuit utilizing the quasi-multilayered striplines is presented. The circuit consists of a multiharmonic reflection filter, a broadband bandpass filter, and a termination. The novel quasi-multilayered striplines, which consist of alumina substrates stacked using solder balls, provide flexibility in the filter structure and realize low insertion loss at the fundamental frequency. The measured results of the fabricated filter exhibit an insertion loss of less than 0.47 dB at the fundamental operation frequency in C-band, as well as high absorption of the second, third, and fourth harmonics, thus outperforming existing solutions. In addition, the device is compact, with a size of only 0.21 λ
₀
× 0.39 λ
₀
, where λ
₀
is the free space wavelength at C-band.