Compact LTCC balanced multicoupled line bandpass filter with enhanced stopband characteristic

This paper proposes a compact balanced multicoupled line bandpass filter that is widely used in Bluetooth and wireless LAN transceiver system with enhanced stopband characteristic. The device works as a balun as well as a bandpass filter at the same time. The proposed filter is configured by using modified resonators which provide a transmission zero located at upper stopband frequency. A parallel resonator is used at input port to produce a transmission zero at the lower stopband. Thus, traditional coupled-resonator filter theory can be used to design and analyze such the device, which can obtain excellent bandpass transmission characteristic. A 2.45GHz balanced multicoupled bandpass filter with a size of 1.8mm×1.25mm×0.9mm has been implemented in a multilayered low-temperature co-fired ceramic (LTCC) substrate. The simulated results are that the maximum of 0.4 dB amplitude imbalance and maximum 3.2° of phase imbalance are achieved in the passband, respectively. The zeros are located in the 1.7 GHz and 4.8 GHz, provided suppressions more than 40 dB.