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Uniplanar 180[degrees] hybrids are basic building blocks in uniplanar technology. In this paper, a new rigorous analysis of a uniplanar 180[degrees] magic-T hybrid based on an air-bridged coplanar cross is performed. The analysis proposed is multimodal since it takes into account the coplanar even and odd fundamental modes simultaneously. From this analysis, a complete circuit model for the hybrid is extracted, and the conditions for ideal performance are derived. This new multimodal model is necessary for the design of the hybrid, and allows a quantitative analysis of its performance, notably bandwidth, isolation, and return loss under any actual loading condition. It has been used to design and implement a 180[degrees] hybrid on alumina with a working frequency of 15 GHz. A very good agreement between simulation and measurement is obtained. The experimental results prove a frequency-independent phase-shift behavior with a measured phase error less than [+ or -] 2[degrees]. Index Terms--Coplanar waveguide (CPW) cross, magic T, multimodal models, 180[degrees] hybrid, uniplanar circuit.

Radio frequency identification (RFID) applications are growing rapidly, especially in the UHF frequency band, which is being used in inventory management. Passive UHF tags are preferred for this application. However, the read range is often overestimated using free space calculations. This paper presents a method to estimate the read range in multipath environments. Other effects with a direct impact on read range as the effect of materials on tag performance are also addressed. Using the proposed model and the ray trace method a RFID system simulator is presented. Index Terms--Link budget, material properties, propagation, Radio frequency identification (RFID).

This paper presents an electrothermally actuated lateral resistive-contact switch for application to low-gigahertz-band communication systems. It was manufactured on a standard low-resistivity substrate, and its RF performance was improved by suspending the structures 25 [micro]m from the substrate, which is a strategy for future integration with active devices in the system-on-chip concept. Measured insertion losses are -0.26 dB at 1 GHz and -0.65 dB at 6 GHz, return losses are -29 dB at 1 GHz and -25 dB at 6 GHz, and isolations are -52 dB at 1 GHz and -26 dB at 6 GHz. The device is driven by a metal electrothermal actuator, which achieves large displacements and contact forces at much lower temperatures than traditional polysilicon electrothermal actuators. The RF power handling characteristics are also addressed and measured. [2007-0051] Index Terms--Electrothermal actuator, low-resistivity substrate, microelectromechanical systems (MEMS) switch, system on chip.

This paper proposes a new vertical electrothermal actuator. It can be considered as a hybrid between the traditional in-plane buckle-beam actuator and the vertical hot-cold actuator. it is here referred to as vertical buckle beam. At identical dimensional and bias conditions, it features a displacement larger than that of other vertical electrothermal actuators proposed so far in the literature. The actuator performance is demonstrated by means of an analytical model along with finite-element analysis. It is applied as a driving element in parallel-plate capacitors, where it is validated and its advantages in terms of power consumption are demonstrated empirically. [2006-0115] Index Terms--Buckle-beam actuator, out-of-plane (vertical) and in-plane electrothermal actuators.

This paper provides a rigorous study of the causes and physical origins of intermodulation distortion (IMD) in RF microelectromechanical systems (MEMS) capacitors, its analytical dependence on the MEMS device design parameters, and its effects in RF systems. It is shown that not only third-order products exist, but also fifth order and higher. The high-order terms are mainly originated by the nonlinear membrane displacement versus applied voltage and, in the case considered in this study, with an additional contribution from the nonlinear dependence of the reflection coefficient phase on the displacement. It is also shown that the displacement nonlinear behavior also contributes to the total mean position of the membrane. In order to study these effects in depth, an analytical frequency-dependent IMD model for RF MEMS based on a mobile membrane is proposed and particularized to the case of a MEMS varactor--a device for which IMD can be significant. The model is validated, up to the fifth order, theoretically (using harmonic balance) and empirically (the IMD of a MEMS varactor is measured). To this end, a two-tone IMD reflection measurement system for MEMS is proposed. Index Terms--Intermodulation distortion (IMD), microelectromechanical systems (MEMS), MEMS varactor, self-actuation, two-tone IMD measurement.

This paper proposes a new method to measure dynamics and power handling of RF microelectromechanical systems (MEMS) devices based on a mobile membrane. The method uses in-phase/quadrature demodulation of an RF signal proportional to the reflection coefficient of the measured device, which contains information of its mechanical properties, such as actuation and release times and instantaneous position of the mobile membrane. Both one-port (capacitors) and two-port devices (switches and extended tuning-range capacitors) can be measured. Its main advantage is the capability of obtaining information from both magnitude and phase variations of the device reflection coefficient to characterize its dynamics and power handling. It is shown that detecting phase is advantageous in high quality factor capacitors, where the magnitude of the reflection coefficient is nearly constant for any position of the mobile membrane. Open-short-load calibration of the system is provided in order to obtain absolute measurements, which are necessary for power-handling characterization. The performances of the proposed method are demonstrated by comparison to systems based on detection of the magnitude of the reflection coefficient. A MEMS capacitor is characterized in terms of dynamics--actuation and release times, and mechanical resonance frequency--and in terms of power handling--membrane instantaneous position and phase and tuning range variation. Index Terms--Dynamics, in-phase/quadrature (I/Q) demodulator, microwave microelectromechanical systems (MEMS) variable capacitor, MEMS switch, self-actuation.