Yusuke Kitsukawa

Tunable MEMS hybrid coupler and L-band tunable filter

Simultaneous control of frequency and coupling coefficient of a directional coupler provides a wide band tunable hybrid coupler. This hybrid coupler is combined with identical two tunable band rejection filters (BRF), to achieve a small-size wide-band tunable band pass filter (BPF). The BPF is called a reflection-type BPF and has a feature of converting rejection frequency bands of the BRF to pass frequency bands.

A CPW hybrid coupler with an enhanced coupling microstructure

A new micromachined coplanar waveguide (CPW) 3-dB hybrid coupler has been demonstrated. A micromachined enhanced coupling structure at the middle of two coupled transmission lines is employed to obtain high directivity. The coupling structure is composed of alternately overlapping plated conductors employing micromachined air-gap structures. This structure relaxes the tolerance of the gap between the coupled transmission lines, and mitigates production error. Moreover, this coupling structure enhances the coupler directivity by equalizing phase velocities of both even- and odd modes. We fabricate the CPW hybrid coupler with the enhanced coupling structure on a silicon substrate to verify the performance. The results showed the return loss of better than 28 dB, the isolation of more than 25 dB over 11 to 15 GHz.

An RFMEMS based reflection type C-Ku band tunable band pass filter

In this paper, we present a novel band reflection type C-Ku band tunable band pass filter (BPF), which has been developed by surface micromachining technology for wireless applications. Our BPF consists of two identical band rejection filters (BRF) and a coplanar waveguide (CPW) 90-degree hybrid coupler. The BRF is composed of metal contact type RFMEMS switches, inductors and capacitors. In the fabrication, a sacrificial layer is applied to not only RFMEMS switch but also inductor, capacitor and CPW 90-degree hybrid coupler to form air bridge, short avoidable structure and enhanced capacitive coupling, respectively. Each tuning state in C- to Ku-band is achieved by RFMEMS switch operation, which selects adequate capacitors or inductors designed corresponding to each tuning state. The insertion losses of the BPF were 3.2dB, 3.6dB and 3.5dB at 8GHz, 12GHz and 16GHz, respectively.