Design of a Compact High-Rejection Bandpass Filter for K-band Downconverters in Satellite Communication Systems

This paper proposes a miniaturized bandpass filter featuring ultra-high stopband rejection, specifically designed for K-band ($17-22 \mathrm{GHz}$) downconverters in satellite communication systems. To meet the increasingly stringent requirements for out-of-band suppression, this work employs two distinct types of resonator structures and introduces out-of-band transmission zeros through a cascaded configuration. This significantly enhances the filter’s rejection performance within the $27-31 \mathrm{GHz}$ stopband, achieving an out-of-band suppression level exceeding 45 dB. To address constraints on circuit area while simultaneously ensuring low in-band insertion loss and a flat passband response, a capacitively coupled tuning structure is adopted to optimize the transmission characteristics. The filter is implemented using a gallium arsenide-based Integrated Passive Device (IPD) process, enabling a highly compact layout with an overall footprint of only $\mathbf{0. 8 9 ~ m m} \times \mathbf{0. 8 5 ~ m m}$. Post-fabrication measurements reveal a center frequency of 19.5 GHz, a 5 GHz bandwidth, and an in-band insertion loss of less than 2 dB, along with superior out-of-band suppression of over 45 dB across the $27-31 \mathrm{GHz}$ range. When integrated into the down-conversion module of a Low Earth Orbit (LEO) satellite user terminal, the filter effectively suppresses interfering signals and improves receiver sensitivity. This design presents an effective solution for high-performance radio frequency front-end modules for K-band downconverters in Satellite Communication Systems.