Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

In this paper, an overview of recently reported low-noise amplifiers (LNAs), designed, and fabricated in GaN technology is provided, highlighting their noise performance together with high-linearity and high-robustness capabilities. Several SELEX-ES GaN monolithic technologies are detailed, providing the results of the noise characterization and modeling on sample devices. An in-depth review of three LNAs based on the 0.25- μm GaN HEMT process, marginally described in previous publications, is then presented. In particular, two robust and broadband 2-18-GHz monolithic microwave integrated circuit (MMIC) LNAs are designed, fabricated, and tested, exhibiting robustness to over 40-dBm input power levels; an X-band MMIC LNA, suitable for synthetic aperture radar systems, is also designed and realized, for which measurement results show a noise figure ~ 2.2 dB with an associated gain and robustness up to 41-dBm input power level.

GaN-Based Robust Low-Noise Amplifiers

Microelectromechanical systems (MEMS) technology has the potential of replacing many of the radio frequency (RF) components used in to day's satellite communication systems. In many cases, such RF MEMS components would not only substantially reduce size, weight, and power consumption, but also promise superior performance when compared to that of current technologies. The benefits of MEMS technology be come more pronounced for switch matrices because there is a large number of switching elements and, therefore, any size and mass reduction would have large overall impact. Though there has been some controversy on the reliability and lifetime of RF MEMS switches, significant improvements have been made and RF switches with billions of switching cycles have been demonstrated. This article describes the potential applications of RF MEMS switch matrices in the satellite industry, where mass reduction and performance improvement is crucial.

RF MEMS Satellite Switch Matrices

We demonstrate an on-wafer liquid crystal phase shifter which has a tunable 0–300°/cm phase shift at 110 GHz. The results show no dispersion over the entire frequency range indicating a tunable “true time delay” of up to 2.5 ps/cm at all frequencies. The inherent losses in the liquid crystal are small, less than 1 dB/cm over the range of 1–110 GHz. The full tunability is achieved using small voltages, close to 10 V. We anticipate that one could achieve a phase shift of 600°/cm at 220 GHz.

Liquid crystal phase shifters at millimeter wave frequencies

This paper presents a novel frequency-agile filtering power divider with constant absolute bandwidth and high selectivity. The proposed design utilizes four coupled resonators to obtain the two functions of power division and filtering. Synthesis of the filtering power divider is carried out and the design guidelines are given. Varactors are then loaded to the resonators to enable frequency tuning. By using capacitors as well as magnetic and electric coupling to obtain required external quality factors and coupling coefficients, a constant absolute bandwidth is maintained when tuning the frequency. To demonstrate the validity of the proposed design, a circuit was fabricated. Experimental results show that the operating frequency can be changed from 0.62 to 0.85 GHz with the 3-dB absolute bandwidth of 60 $\pm$ 2.5 MHz. Moreover, transmission zeros are generated near the passband, resulting in high selectivity for each tuning state. Comparisons between the measured and simulated results are presented and good agreement is observed.

Compact Tunable Filtering Power Divider With Constant Absolute Bandwidth

To reduce the complexity and cost of future telecommunication systems, electrically tunable or reconfigurable filters based on radio frequency microelectromechanical systems (RF MEMS) and waveguide technology constitute a very promising solution, since they allow for very high $Q$ and good tunability. Three concepts for tunable waveguide filters using ohmic RF MEMS switches are described in this paper, and compared in terms of performance and manufacturing complexity. Quality factors of the order of 1000 and frequency tunability of the order of 5% are shown both by High-Frequency Structure Simulator simulations and experimental results in $K$ -band.

High- $Q$ Tunable Waveguide Filters Using Ohmic RF MEMS Switches

This paper presents a MEMS-reconfigurable power divider on high resistivity silicon substrate with variable power ratio. The circuit is based on two cascaded hybrid couplers connected through a tunable phase shifter that produces the required power ratio. A 5 state prototype has been fabricated on a 525 m high resistivity silicon substrate employing two 3 dB branch line couplers and a reflection-line MEMS phase shifter. The latter is reconfigured through two MEMS-switched open ended lines, whose lengths can be varied through the actuation of eight ohmic contact MEMS switches. Measurements of the MEMS switch show an isolation and an insertion loss better than 15 dB and 0.2 dB, respectively, with a contact resistance lower than 1 Ohm in the entire power divider bandwidth. RF measurements of the power divider exhibit a return loss better than 16 dB and an isolation better than 17 dB in the bandwidth [11.8-12.2] GHz with nominal power ratios of 1:0, 6:1,1:1,1:6, and 0:1.

A MEMS-Reconfigurable Power Divider on High Resistivity Silicon Substrate

In this paper a novel MEMS-tunable hairpin line filter is presented. The circuit has been realized on a 525 ?m high resistivity silicon substrate using a well established micromachining process at ITC-irst in Trento, Italy. The tunability of the device is obtained by line sections added to the U-line branches of the resonators of the hairpin filter through 10 identical MEMS ohmic contact cantilever switches. Measurements of the MEMS switch show an isolation and an insertion loss better than 20 dB and 0.3 dB, respectively, in the filter frequency range. Measured S-parameters of the MEMS-filter exhibit an insertion loss and a return loss better than 4.5 dB and 17 dB respectively, with a 15% passband at 6.2 GHz and 10% tuning range.

A Novel MEMS-Tunable Hairpin Line Filter on Silicon Substrate

A broadband single pole double throw (SPDT) switch has been developed for use in the range of 0 to 30 GHz. The switch consists of a cascade of a MEMS ohmic series and a capacitive shunt switch with floating electrode in each branch. It is manufactured on high-resistive silicon using surface micro-machining technology. The SPDT switch provides an insertion loss better than ?0.6 dB, return loss smaller than ?20dB, and isolation better than ?40 dB in nearly the whole band. A switching voltage around 50 V is needed. The switch is used as a building block for more complex switching networks. The fabrication process is described and the measured RF-performances are reported and discussed. A failure analysis exhibits a lifetime up to 109 actuations.

Broadband RF-MEMS Based SPDT

This paper presents a novel wide tuning range MEMS varactor based on a toggle push - pull mechanism for high RF power applications and improved reliability. The device anchoring utilizes a torsion spring mechanism which virtually allows for a full capacitance tuning range. Improved mechanical stability is also provided by the actively controlled pull-out implementation that is realized without increasing the MEMS manufacturing complexity. As a proof of concept, a toggle MEMS varactor has been modeled, designed and manufactured in shunt configuration on a 50 Omega coplanar transmission line. Analytical and full wave electromechanical models are provided as well as electromagnetic characterization. The device has been manufactured on HR Silicon substrate by using the standard FBK-irst RF MEMS process. Optical profile, DC and RF measurements are presented in the 0-40 GHz frequency band. Excellent RF performance as well as a capacitance tuning ratio of 2.5 has been obtained.

Paola Farinelli

Papers

High- $Q$ Tunable Waveguide Filters Using Ohmic RF MEMS Switches

A MEMS-Reconfigurable Power Divider on High Resistivity Silicon Substrate

A Novel MEMS-Tunable Hairpin Line Filter on Silicon Substrate

Broadband RF-MEMS Based SPDT

A Wide Tuning Range MEMS Varactor Based on a Toggle Push-Pull Mechanism