Design of Multi-layer Ceramic LTCC Bandpass Filter

The paper provides a design method of multi-layer ceramic microwave bandpass filter based on LTCC(low temperature co_fired ceramic)technology. First, the circuit model is built by ADS software, and the resonant structure in the circuit model is designed by using 4 UIR structure to realize a band-pass filter with a center frequency of 625 MHz and bandwidth of 50MHz. The Ansoft HFSS software is then used to design a new coupling structure that enhance the coupling between the resonat stages, thereby reducing the insertion loss(S21)and passband fluctuation in the passhand band enhancing out-of-band rejection. The final dimensions are 5.0 mm × 5.0 mm × 1.5 mm, the insertion loss less than 3.5 dB, the bandwidth is 50MHz, the suppression is greater than 40 dB at out-of-band 70 MHz, the in-band ripple is less than 1.0 dB, and the voltage standing wave ratio(VSWR)is less than 1.5, and there is no parasitic passband in 3GHz, and the center frequency is 625 MHz lower frequency bandpass filter.