| dc.description.abstract | In this thesis, very compact integrated passive circuits with high performance are presented. The major bottleneck of the size reduction of active and passive microwave circuits is the requirement of multiple transmission lines with given electrical length. Traditionally, lump elements are used to replace the transmission line, e.g. the equivalent T or π model. Although the size can be reduced, the bandwidth of the resulted microwave circuit is also reduced. This is due to the fact that those lumped T or π networks are equivalent to transmission line at single frequency only. In this work, the bridged T-coil is used to replace the conventional T model, such that the advantages of compact size and wide frequency bandwidth can both be achieved. The bridged T-coil can be implemented using balance inductor and metal-insulator-metal (MIM) capacitor in GaAs semiconductor IC process or Glass Integrated Passive Device (GIPD) process to achieve very compact size. It is then applied to the design of wideband four-way Wilkinson power divider, ultra-wideband multimode resonator Bandpass filter, and a switch beamforming network.
First of all, the proposed wideband four-way Wilkinson power divider is fabricated in GIPD process with a circuit size of 0.0245λ0 × 0.0245λ0 at 1.6 GHz. The measured minimum insertion loss is 1.18 dB, the fractional bandwidth is 117% with a return loss of greater than 20 dB, and the phase error is less than 0.269°. Then, by implementing the stepped-impedance resonator using the proposed bridged T-coil structure, several novel wideband multimode resonator Bandpass filters for ultra-wideband application are proposed. Specifically, the proposed triple-mode Bandpass filter fabricated in GaAs has a circuit size of only 0.0376λ0 × 0.0292λ0 at 6.85 GHz, a minimum insertion loss of 0.895 dB and a bandwidth of 86.6% for a return loss of greater than 10 dB. Another triple-mode Bandpass filter in GIPD process exhibits a circuits size of 0.02λ0 × 0.02λ0 at 6.85 GHz, a minimum insertion loss of 0.644 dB, and a fractional bandwidth of 89% for a return loss of greater than 15 dB. In order to improve the selectivity, a five-mode Bandpass filter is also designed using the GIPD process. Its circuit size is 0.0548λ0 × 0.0351λ0 at 6.85 GHz, the minimum insertion loss is 1.327 dB, and the fractional bandwidth is 96.6% for a return loss of greater than 10 dB. Finally, a compact GIPD beamforming network including a 4×4 Butler matrix and a SP4T switch is demonstrated, and the circuit size is only 0.037λ0 × 0.037λ0 at the center frequency of 2.4 GHz. The measured insertion losses are within -12.13±1.605dB (±45°path) and -12.25±1.12dB(±135°path), phase error are -6.7°~-0.3°(±45°path) and 2.5°~11.3°(±135°path), and the DC power consumption is 4.5 mW.
Compared with conventional designs, the above circuits are smaller in size with no bandwidth reduction as compared with their transmission-line based counterparts. The effectiveness of bridged T-coil on the design of miniaturized on-chip passive microwave circuit is also validated through proposed design examples.
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