Compact tunable bandpass filter with improved stopband rejection and wide tuning range

Abstract

A compact tunable bandpass filter (BPF) with wide tuning range and improved stopband rejection based on low-temperature co-fired ceramic (LTCC) technique is presented. The axial coupling structure is employed to achieve a wide tuning range and increase resonator Q. To improve the stopband characteristics, Multiple transmission zeros (TZs) are introduced near the passband. A new tunable BPF with a 100% tuning range from 480 to 960MHz has been designed and fabricated to verify the proposed method. The measured results are in good agreement with the electromagnetic (EM) simulation. The circuit only occupies 3.5×3.0×1.7mm³.