Design Of The Ltcc Balanced Bandpass Filter With 2.45ghz Center Frequency

Balanced filter is a very important component in wireless communication systems. With the rapid development of wireless communication, the demand of compact microwave components is increased. The LTCC technology is a good candidate for size reduction. This thesis presents the design method of a LTCC balanced filter with 2.45GHz center frequency which is widely used for Bluetooth and wireless LAN.In this thesis, the theory analyses and the magnetic-electronics simulation software are used to analyze and design the LTCC balanced filter. It contains three parts, and the contents are as follows:1. Filter design. It includes two kinds of filter design methods. One is designed by coupled microstrip lines, and the other bases on the principle of the transversal filter. They are both derived from lumped circuits, and calculated the stripline dimensions according to the relationship between lumped circuits and the striplines. Then the initial model could be optimized by the high-frequency simulation software (HFSS). At last, a balanced filter with 2.45GHz center frequency and 100MHz bandwidth has been designed. There are differences between the two design methods. The lumped circuit of the first filter bases on the design method of a normalized Chebyshev lowpass filter. Through transformation, a second order bandpass filter using quarter-wave-length SIR is designed. While the lumped circuit of the transversal bandpss filter is composed of a lowpass filter and highpass filter. Then according as the classic transmission line theory, striplines are used instead of each lumped element.2. Balun design. Firstly, by using the analytical methods of odd and even mode, the impedance of coupled lines could be calculated. Secondly, use the Transmission line software to calculate transmission line parameters. At last, a three-line balun using spiral structure for size reduction has been designed. The amplitude difference between two balanced ports in the passband was less than 2dB, and the phase was on the contrary.3. Design of the LTCC balanced filter. When the hole is used to interconnect the filter and balun in RF circuits, it will affect the performances of the filter and balun. So the model must be adjusted after the interconnection. In this thesis, by using the HFSS, a LTCC balanced bandpass filter with two transmission zeros was designed. Its size was 2.5×2.0×0.9mm3, and the center frequency of was 2.45 GHz with 100 MHz bandwidth.