| Summary: | 碩士 === 國立中央大學 === 電機工程學系 === 103 === The target of this work is the design of wideband dual-band bandpass filter, and the circuit size can be largely reduced by using the bridged-T coils to substitute transmission line sections, such that the advantages of compact size and wide frequency bandwidth can both be achieved simultaneously. The bridged-T coil can be designed as a wideband transmission-line equivalent. It can be realized by a balanced inductor and metal-insulator-metal (MIM) capacitors in the integrated passive device (IPD) process with very compact circuit size. The bridged-T coil can be used to replace the required transmission line sections in wideband dual-band bandpass filter designs to achieve wideband using the IPD process.
First of all, the test kits of bridge-T coils in IPD are implemented to demonstrate the design procedure and performance. They are applied to wideband dual-band bandpass filter designs to achieve compact size with no bandwidth reduction. The center frequency of the wideband dual-band bandpass filter designs are designed at f0 = 1.5 GHz, so that they can be applied to long term evolution (LTE) system of wireless communication devices. While the wideband dual-band bandpass filter is fabricated in printed circuit board (PCB), the circuit size of 0.52 λ0×0.475 λ0 at f0 = 1.5 GHz. The measured insertion loss at center frequency of passband is 0.36 dB and 1.01 dB (return loss > 16 dB), and the fractional bandwidth is 106.5 % and 33.8 %. While the wideband dual-band bandpass filter is fabricated in the integrated passive device (IPD) process, the circuit size of 0.015 λ0×0.024 λ0 at f0 = 1.5 GHz. The measured insertion loss at center frequency of passband is 2.14 dB and 3.64 dB (return loss > 15 dB), and the fractional bandwidth is 100.7 % and 32.1 %. While the wideband dual-band bandpass filter is fabricated in PCB and IPD, the circuit size of 0.26 λ0×0.265 λ0 at f0 = 1.5 GHz. The measured insertion loss at center frequency of passband is 0.95 dB and 1.97 dB (return loss > 13 dB), and the fractional bandwidth is 101.7 % and 27.01 %.
Compared with conventional designs, the circuits are smaller in size with no bandwidth reduction by using bridged-T coils to implement transmission lines. The proposed wideband dual-band bandpass filter designs feature very compact size and wide bandwidth, and can be implemented in handheld wireless communication devices for mobile communication applications.
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