Surface Mount Ultra-Thin Millimeter-Wave Bandpass Filter Chip Based on Lithium Niobate With Ultralow Loss and Sharp Roll Off

This is the authors' abstract. We don't add key points for this paper.

A millimeter-wave (mmWave) coplanar waveguide (CPW) bandpass filter (BPF) chip based on lithium niobate (LN) is presented, and its surface mount on a printed circuit board (PCB) is demonstrated. LN is a cost-effective multifunctional crystal with a high dielectric constant and a low loss tangent. While the high dielectric constant enables size reduction, it introduces higher-order modes. To mitigate this issue, the LN thickness is optimized to elevate the cutoff frequencies of higher-order modes beyond the desired passband. The proposed dual-mode cross-shaped CPW resonator with embedded slots can introduce an intrinsic transmission zero (TZ), thereby enhancing upper-stopband suppression and reducing size. Meanwhile, an additional TZ in the lower stopband is generated through four folded stubs. After surface mount, a sharp 30-dB roll-off rate of 26.21dB/GHz in the lower stopband is achieved. The measured center frequency is 30.44GHz with a minimum insertion loss (IL) of 0.53dB, and a shape factor (SF) of 1.5. Furthermore, temperature characterizations from - 100 °C to 150 °C indicate stable frequency responses. The overall dimension is 2.61 × 1.7 × 0.16 mm3, and the weight is 3.346mg. The surface-mountable LN-based mmWave BPF chip features small size, ultralow loss, sharp roll off, and lightweight, offering a promising solution for future 5G/6G mmWave mobile terminals.