Fully embedded LTCC bandpass filter for 40GHz BMWS applications

Abstract

This thesis proposes and implements a low-loss fully embedded BPF using low-temperature co-fired ceramic (LTCC) technology for 3-dimensional radio integration of 40 GHz broadband multimedia wireless system (BMWS). The main research issue in this thesis is to implement the BPF which can be easily embedded within multilayer circuit space-efficiently, has low insertion loss, high out-of-stopband rejection, and good flatness. The transmission line structure composing the BPF is the stripline, which is especially well suited for the implementation of the millimeter-wave passive components because upper and lower ground planes make the even- and odd-mode phase velocities equal, the line has less radiation loss and dispersion than other transmission line structures. The CPW-to-stripline transitions allow the interconnection between the embedded stripline BPF and active components such as power amplifier and mixer on top of the LTCC circuit. Also, they allow on-wafer characterization of the stripline LTCC filter using GSG probes. Both CPW and stripline have 50 Ohm characteristic impedance. And, the CPW-to-stripline transition has been designed and evaluated, which allows the transition loss to be decreased by controlling the space between CPW signal line and upper ground of the stripline and makes the resonance response to be suppressed by placing the ground vias near stripline and CPW. The stripline structure needs the ground vias which make both top and bottom ground planes equalize the electric potential. However, the structure of the ground vias can generate the spurious resonances, or rectangular waveguide modes which affect heavily the performance of the filters such as the flatness and the rejection of out-of-stopband. This thesis reports the modified embedded LTCC BPF, which suppresses spurious responses by controlling the placement of the ground vias. The overall size is 6.1 mm $\times$ 5.3 mm $\times$ 0.6 mm including the ground vias and CPW pads. The num...