Contents I. Introduction
Single-Pole multithrow (SPMT) RF switches are widely applied to switching systems, multiband selectors, and filter banks, which consist mainly of GaAs MESFETs [1] or GaAs pseudomorphic high electron-mobility transistors (pHEMTs) [2]. The SPMT RF switches are easily integrated with other modules so they have been effectively used for a variety of the monolithic microwave integrated circuits (MMICs). Up to 2 GHz, the GaAs MESFET switches present good RF performances for an insertion loss of 0.7 dB and isolation of . GaAs pHEMTs show an insertion loss of 0.6 dB and isolation loss of Schematic for the SP6T MEMS switch based on metal-contact RF MEMS series switches. . However, as the frequency range increases, it is difficult that the RF switch module is directly applied to high-frequency applications due to their inherent parasitic parameters, which may be junction capacitances, parasitic capacitances, or pad resistances. Instead, the RF switch module has to be revised completely for the applications. Therefore, the SPMT switches composed of solid-state devices can be limited to RF performances at a high frequency in spite of their compact size and compatibility with other RF modules. One of the promising components is an RF microelectromechanical systems (MEMS) switch. Recently, many researchers have studied metal-contact MEMS switches [3], [4], which have a much lower insertion loss and higher isolation characteristic than solid-state devices. For better RF performance, the RF MEMS switches have been successfully applied to dual-path power amplifiers for wireless communication systems [5], to 4-bit true time delay (TTD) phase shifters in phased-array antennas [6], to a -band single-pole double-throw (SPDT) circuit [7], and to a single-pole four-throw (SP4T) switch using lateral switches [8]. Although the RF MEMS switches show excellent RF performances at higher frequency, they may have some limitations with respect to application in communication systems because their active area is 2–4 times larger than that of the RF switch. Therefore, to overcome the bottleneck for both RF performances and the area issue, it is necessary to design an SPMT switch based on compact RF MEMS switches. Schematic views about each part dimension and the switching part for the metal-contact RF MEMS series switch. In this paper, we present a low-loss single-pole six-throw (SP6T) switch with a total area of 1 using small metal-contact RF MEMS switches, each of which has an area of 0.4 mm ×0.3 mm. The SP6T MEMS switch is comprised of a transmission line and six MEMS switches, as shown in Fig. 1, and its dc and RF characteristics have previously been presented [9]. In order to evaluate RF performances of the fabricated MEMS switch, we have performed small-signal modeling. Conventional small-signal models for on-state modeling are generally inaccurate because the fringing capacitances are not expected to occur at the front end of each broken signal line. On account of this inaccuracy, we adapted a physically based parameter-extraction method to the small-signal modeling [10], which has been used for modeling solid-state devices [11] [12] [13], where we can more accurately find the on-state resistance and off-state upper capacitance from measured data. Subsequently, coplanar waveguide (CPW) lines were also modeled to lumped RLC equivalent circuits by the extraction method so each section of the transmission line in the SP6T switch can be modeled to “T-shape” equivalent circuits. The modeled -parameters indicate that the modeling is valid in the whole range of frequency.
