Multi-harmonic absorption filter using quasi-multilayered striplines

A novel multi-harmonic absorption filter that uses quasi-multilayered striplines is presented. The filter circuit consists of a multi-harmonic reflection filter, a broadband band-pass filter, and a terminator. The quasi-multilayered striplines, which consist of alumina substrates stacked using solder balls, improve the flexibility of layout for the resonator and offer low insertion loss at the basic band. The measurement results of the fabricated filter demonstrate an insertion loss of less than 0.47 dB at point frequency of the C-band and good absorption at the 2nd, 3rd, and 4th harmonics. In addition, these devices are compact, with a size of just 0.21 λ₀ × 0.39 λ₀, where λ₀ is the wavelength in free space at the C-band.