Generalized Synthesis of Double-Ladder Acoustic Filters with Demonstration of a High-Performance Dual-Band Duplexer on LTOI

This work presents a generalized synthesis framework for double-ladder acoustic filters with a validation through a high-performance dual-band duplexer on a LiTaO3-on-insulator (LTOI) platform. The method decouples the two passbands through independent single-band syntheses based on reduced Chebyshev polynomials, followed by systematic resonator combination that preserves positive static capacitance and converges the electromechanical coupling coefficients (K2) to process-defined values. The framework reduces structural constraints of prior dual-band approaches, supporting flexible zero/pole placement, uneven passband orders, bounded return loss, and pseudo-resonator implementation for out-of-band poles. A compact dual-band duplexer (1.96  1.44 mm2) is developed, covering 1518–1525/2170–2200 MHz for RX and 1668–1675/1980–2010 MHz for TX, with minimum insertion losses of 0.85/1.89 dB (RX) and 0.81/0.93 dB (TX), high in-band selectivity, and full-band isolation better than 43 dB. The results confirm the flexibility of the generalized synthesis and the excellent performance achievable on LTOI.