An Interferometric Modulator (IMod) is a microelectromechanical device for modulating light using interference. The colors of these devices may be determined in a spatial fashion, and their inherent color shift may be compensated for using several optical compensation mechanisms. Brightness, addressing, and driving of IMods may be accomplished in a variety of ways with appropriate packaging, and peripheral electronics which can be attached and/or fabricated using one of many techniques. The devices may be used in both embedded and directly perceived applications, the latter providing multiple viewing modes as well as a multitude of product concepts ranging in size from microscopic to architectural in scope.

Interferometric modulation of radiation

RF MEMS technology was initially developed as a replacement for GaAs HEMT switches and p-i-n diodes for low-loss switching networks and X-band to mm-wave phase shifters. However, we have found that its very low loss properties (high device Q), its simple microwave circuit model and zero power consumption, its high power (voltage/current) handling capabilities, and its very low distortion properties, all make it the ideal tuning device for reconfigurable filters, antennas and impedance matching networks. In fact, reconfigurable networks are currently being funded at the same level-if not higher-than RF MEMS phase shifters, and in our opinion, are much more challenging for high-Q designs.

Tuning in to RF MEMS

The design is presented of aperture-coupled microstrip line-fed patch antennas (ACMPAs) and 4times4 planar arrays on Ferro A6-S low-temperature cofired ceramic (LTCC) substrate operating in the 60-GHz frequency band. In addition to the traditional ACMPA design, air cavities processed inside the LTCC substrate are used to improve the bandwidth and gain of the antennas. The arrays are excited through the microstrip-line feed networks using quarter-wave matched T-junctions and using Wilkinson power dividers. The results show that ACMPAs and arrays can be fabricated with a standard LTCC process even for the millimeter-wave region. Good agreement is achieved between simulations and measurements. The measured S-parameters indicate impedance bandwidths of 9.5% and 5.8% for the array elements with and without an embedded cavity. The measured maximum gains for the 16-element patch arrays (with and without cavity) are 18.2 and 15.7 dBi, respectively.

60-GHz Patch Antennas and Arrays on LTCC With Embedded-Cavity Substrates

This paper presents a state-of-the-art RF microelectromechanical systems wide-band miniature tunable filter designed for 6.5-10-GHz frequency range. The differential filter, fabricated on a glass substrate using digital capacitor banks and microstrip lines, results in a tuning range of 44% with very fine resolution, and return loss better than 16 dB for the whole tuning range. The relative bandwidth of the filter is 5.1 /spl plusmn/ 0.4% over the tuning range and the size of the filter is 5 mm /spl times/ 4 mm. The insertion loss is 4.1 and 5.6 dB at 9.8 and 6.5 GHz, respectively, for a 1-k/spl Omega//sq fabricated bias line. The simulations show that, for a bias line with 10-k/spl Omega//sq resistance or more, the insertion loss improves to 3 dB at 9.8 GHz and 4 dB at 6.5 GHz. The measured IIP/sub 3/ level is > 45 dBm for /spl Delta/f > 500 kHz, and the filter can handle 250 mW of RF power for hot and cold switching.

A differential 4-bit 6.5-10-GHz RF MEMS tunable filter

This paper presents a multi-band multi-mode class-AB power amplifier, which utilizes continuously tunable input and output matching networks integrated in a low-loss silicon-on-glass technology. The tunable matching networks make use of very high Q varactor diodes (Q>100 @ 2 GHz) in a low distortion anti-series configuration to achieve the desired source and load impedance tunability. A QUBIC4G (SiGe, ft=50 GHz) high voltage breakdown transistor (VCBO=14 V, VCEO>3.6 V) is used as active device. The realized adaptive amplifier provides 13 dB gain, 27-28 dBm output power at the 900, 1800, 1900 and 2100 MHz bands. For the communication bands above 1 GHz optimum load adaptation is facilitated resulting in efficiencies between 30%-55% over a 10 dB output power control range. The total chip area (including matching networks) of the amplifier is 8 mm2

Adaptive Multi-Band Multi-Mode Power Amplifier Using Integrated Varactor-Based Tunable Matching Networks

The radio-frequency identification (RFID) concept is expanded to millimeter-wave frequencies and millimeter-wave identification (MMID) in this paper. The MMID concept and a comparison with UHF RFID are presented, showing the limitations and benefits of MMID. Three feasible applications are suggested for MMID, which are: (1) wireless mass memory; (2) an automatic identification system with pointing functionality; and (3) transponder communication with automotive radar. To demonstrate the feasibility of the MMID system, experimental results for both downlink and backscattering-based uplink are presented at 60 GHz.

Millimeter-Wave Identification—A New Short-Range Radio System for Low-Power High Data-Rate Applications

We have developed a novel reconfigurable matching network based on the loaded-line technique. The network is composed of N-switched capacitors (N = 4–8) with a capacitance ratio of 4–5:1 and is suitable for power amplifiers at 4–18 GHz, or as an impedance tuner for noise parameter and load-pull measurements at 10–28 GHz. The networks are very small, and offer better performance than double or triple stub matching networks. Extensive loss analysis indicates that the 8-element network has a loss of 0.5 dB at 4–12 GHz, and less than 1.5 dB at 18 GHz, even when matching a 10Ω output impedance to a 50Ω load. As expected, the 4-element matching network has about half the loss of the 8-element network, but with much less impedance coverage. Both networks were simulated and measured in high VSWR conditions and can handle at least 500 mW of RF power at 4–18 GHz. The application areas are in phased array antennas, reconfigurable power amplifiers, and wideband noise-parameter and load-pull measurement systems. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 356–372, 2004.

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A 4–18-GHz reconfigurable RF MEMS matching network for power amplifier applications

A reconfigurable matching network has been developed and it is based on loaded line techniques. It consists of 8 switched MEMS capacitors producing 256 (2/sup 8/) different impedances and is only 1/spl times/2.5 mm in size on a glass substrate. The network is ideally suited to match power amplifiers with 10-20 /spl Omega/ output impedance to 50-60 /spl Omega/ systems at 20-50 GHz. The estimated loss of the network is only 1-1.5 dB at 40 GHz while matching a 10-20 /spl Omega/ load to a 50 /spl Omega/ load. The reconfigurable network can also be used as an impedance tuner in noise parameter and load-pull measurements of active devices at 30-65 GHz.

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A 20-50 GHz reconfigurable matching network for power amplifier applications

A novel radio-frequency (RF) microelectromechanical system (MEMS) single-stub impedance tuner has been developed. The design is based on combining the loaded line technique with the single-stub topology to obtain wide impedance coverage with high |/spl Gamma//sub MAX/|. The tuner consist of ten switched MEMS capacitors producing 1024(2/sup 10/) different impedances. The design has been optimized for noise parameter and load-pull measurements of active devices and shows excellent measured impedance coverage over the 20-50 GHz frequency range.

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A 20-50 GHz RF MEMS single-stub impedance tuner

A 6-20 GHz reconfigurable triple-stub impedance tuner has been developed. It is based on a 11-switched MEMS capacitor network producing 2/sup 11/ different impedances. The measured and simulated impedance coverage is the widest ever measured to-date from any RF MEMS tuner. This network is most suitable for noise parameters and load-pull measurements of transistors at 6-20 GHz.

Tauno Vähä-Heikkilä

Papers

Millimeter-Wave Identification—A New Short-Range Radio System for Low-Power High Data-Rate Applications

A 4–18-GHz reconfigurable RF MEMS matching network for power amplifier applications

A 20-50 GHz reconfigurable matching network for power amplifier applications

A 20-50 GHz RF MEMS single-stub impedance tuner

A reconfigurable 6-20 GHz RF MEMS impedance tuner