The Principles, Design And Simulation Of LTCC Interdigital Filter

With the rapid development of wireless communication and the popularization of personal consumer electronics, demand has been made on high performance, miniaturization, low power electronics devices. Utilizing the technology of Low Temperature Co-fired Ceramic (LTCC), the microwave filter has great potential on miniaturization, so researchers at home and abroad pay more attention to it.The general procedures were concluded to design microwave ceramic filter by combining the circuit synthesis method and electromagnetism digitally computing technique, and the theoretical formulae of special transmission lines'and coupling lines'characteristic impedance were deduced. The accuracy of the theoretical formulae was proved by comparing the result of theoretical calculation with EM simulation. Basing on the theoretical calculation of odd- and even-mode characteristic impedance, the practicality of using the theoretical formulae to calculation the coupling coefficient was proved by comparing the result of theoretical calculation with EM simulation.Combining the structure of the interdigital and broadside-coupled transmission line, a new structure of microwave filter which has small volume was designed. Different form ordinary uniform interdigital filter, the resonators of the filter was placed on different layers of the medium, and constructed the structure of the interdigital. If the resonator of this filter transform to SIR andгform, the volume of the filter could become more smaller. In order to guide the debug of the filter, the rules between the structural parameters and performance parameters were laid out. According as the same performance requirements, this kind of filter was designed. Especially, by using theoretical formulae, the total structural parameters of the middle-slot coupling filter were calculated. By comparing, it was found that the theoretical formulae gave guidance to filter design. To the filter that using the SIR andгform resonator, the dimension on the axis X could be reduce about 20% and 50%, respectively. At the same time, a five-pole and a for-pole filter were designed, respectively. It is found that the four-poleгform filter has more small volume and great performance.