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This study presents a novel planar coupled-line directional coupler with tunable both power division ratio and operating frequency, which is achieved using microstrip technology for the first time. Its tunability of the operating frequency and the power division ratio, or coupling ratio, can be independently controlled by the bias voltages. Moreover, it can simultaneously maintain perfect port match and isolation. On the basis of the even-odd mode analysis method, both the closed-form analytical equations and parameter discussions are provided to facilitate the practical design. An experimental prototype of the tunable coupler is simulated, fabricated, and measured to demonstrate how it works. The measured results indicate that power division ratio can vary from 0.35 (9 dB) to 0.71 (3 dB) when operating frequency ranges from 0.55 to 1.48 GHz (91.63%) while power division ratio varies from 0.35 (9 dB) to 1 (0 dB) when operating frequency is fixed at 1 GHz, which validated the reliability of the proposed model. [ABSTRACT FROM AUTHOR]

A novel dual-band bandpass filter with a compact structure and a wide stopband is proposed. The total structure includes coupled-line stubs and coupled-line connected sections, leading to a compact circuit. This proposed filter can be implemented easily by using single-layer microstrip technology. The measured results of a prototype filter show that it can operate at both 1.32 and 2.67 GHz and up to the 8 GHz 15 dB stopband. [ABSTRACT FROM AUTHOR]