LTCC Ultra‐Wideband Bandpass Filter With Wide Out‐Of‐Band Suppression Based on Composite Independent‐Filters Topology

ABSTRACT A miniaturized ultra‐wideband band‐pass filter with wide out‐of‐band suppression based on low‐temperature cofired ceramic (LTCC) technology is presented, which works from 0.74 GHz to 6.5 GHz, consisting of a highpass filter and a lowpass filter. Because of utilizing advanced LTCC technology, the big multilayer capacitors and helical‐shape inductors can be realized in multiple thin layers to overcome the large circuit size, so the size of the proposed filter is miniaturized with 6 mm × 4 mm × 2 mm (0.19λ g × 0.12λ g × 0.06λ g ). The high frequency interferences are able to be eliminated by introducing small capacitors in the lowpass part of the proposed filter to realize wide stopband performance. Therefore, the fractional bandwidth of the proposed passband filter is 160% with return loss better than 10 dB, insertion loss less than 2 dB, and 20 dB out‐of‐band suppression arrival at 4.4 f 0 ( f 0 is the center frequency 3.6 GHz). The measured results have a good agreement with simulated results to verify the design theory.