Fabrizio Cacciamani

High-

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.

Q

The design of a Ku-band reconfigurable reflectarray antenna for emergency satellite communications is presented. Bidirectional high data rate satellite links are needed in emergency conditions where other telecommunication infrastructures are not available. In order to operate in this type of scenario, an antenna should be deployable, transportable, and easily repointable. The need of an automatic and fast satellite location and pointing system leads to a completely electronic reconfigurable antenna. The operative bandwidth is from 10.7 to 12.5 GHz for reception and from 14 up to 14.5 GHz for transmission (30% of relative bandwidth). The selected antenna architecture is based on a dual reflectarray system comprising a passive subreflectarray and an active main reflectarray made of reconfigurable 1-bit elementary cells based on PIN diodes.

Tunable Waveguide Filters Using Ohmic RF MEMS Switches

This paper presents ultra-compact dual-mode dielectric-loaded waveguide bandpass filters with Nth-order pseudoelliptic filtering function and asymmetric positioning of N transmission zeros. A waveguide cavity is loaded with a very high-permittivity rod (εr>30). Two degenerate resonant TM modes are employed along with nonresonating modes. In contrast to previous works, that are limited to structures with a symmetric response, in the proposed solution both modes are directly coupled to the input and output interconnections. Nonresonating modes are exploited to produce a direct source-load coupling. In this way, a single cavity generates two transmission poles and two transmission zeros located either below or above the two poles, thus realising a basic building block for N-pole and N-zero filters with asymmetric response. The dimensions of a 3% FBW 4th-order filter with 4 zeros at 4.35 GHz are 40×40×12 mm3 (using εr=34). A preliminary prototype has been fabricated and measured showing an unloaded Q of 1750 and good agreement with HFSS® simulations.

A Transportable Reflectarray Antenna for Satellite Ku-band Emergency Communications

A new approach to bandwidth-reconfigurable planar filter is proposed. RF MEMS switches are used to modify the intra-resonator coupling in hairpin band pass filters so as to control the bandwidth while keeping constant the centre frequency. The design and full-wave simulation of a 2nd order hairpin-line filter is reported to demonstrate the feasibility of the proposed approach. The measurement of the device will be soon carried out.

Ultra-compact filters using TM dual-mode dielectric-loaded cavities with asymmetric transmission zeros

This paper presents the modeling, manufacturing, and testing of a micro-electromechanical system (MEMS)-based LC tank resonator suitable for low phase-noise voltage-controlled oscillators (VCOs). The device is based on a variable MEMS varactor in series with an inductive coplanar waveguide line. Two additional parallel stubs controlled by two ohmic MEMS switches have been introduced in order to increase the resonator tunability. The device was fabricated using the FBK-irst MEMS process on high resistivity (HR) silicon substrate. Samples were manufactured with and without a 0-level quartz cap. The radio frequency characterization of the devices without 0-level cap has shown a continuous tuning range of 11.7% and a quality factor in the range of 33–38. The repeatability was also tested on four samples and the continuous tuning is 11.7 ± 2%. Experimental results on the device with a 0-level cap, show a frequency downshift of about 200 MHz and a degradation of the quality factor of about 20%. This is, most likely, due to the polymeric sealing ring as well as to a contamination of the ohmic contacts introduced by the capping procedure. A preliminary design of a MEMS-based VCO was performed using Advanced Design System and a hardwired prototype was fabricated on Surface Mount Technology on RO4350 laminate. The prototype was tested resulting in a resonance frequency of 5 GHz with a phase noise of −105 and −126 dBc at 100 KHz and 1 MHz, respectively, and a measured output power of −1 dBm.

RF MEMS bandwidth-reconfigurable hairpin filters

This paper presents the design, manufacturing and validation of Land Sband filters based on TM010 mode dielectric resonators. This work has been developed in the framework of the PETIT project (“compact highPErformance filters for space applicaTIon based on dielectric resonator Technology”), funded by ESA. Goal of the project is to reduce mass and volume of Land S-band input filters using dielectric resonator technology. Large and bulky coaxial resonators are currently used in the realization of filters for such applications. While dielectric resonators can reduce the filter footprint up to 50%, an optimum trade-off in terms of spurious performance, temperature stability and unloaded Q-factor (Q) must be found. High dielectric permittivity (er > 30) dielectric resonators operating with TM010 mode represent the best trade-off in terms of volume, spuriousfree range and Q-factor. A dielectric 4 order bandpass filter has been designed in S-band to achieve this objective. The fractional bandwidth is 1.5% and the IL is 0.25-0.3 dB, corresponding to an unloaded Q above 4000. The filter dimensions are approximately 50x50x40 mm (including connectors). A stable response over a temperature variation between -10°C and +65°C has been demonstrated.

MEMS-based LC tank with extended tuning range for low phase-noise VCO

This paper presents the design of a compact ultra-wideband (UWB) bandpass planar filter with a tunable notched band within the bandwidth. The filter can be used for wireless communications within the unlicensed UWB range (3.1-10.6 GHz). The UWB filter is based on external interdigitated quarter-wavelength microstrip resonators and a central half-wave microstrip resonator embedding a reconfigurable open-circuited stub. The stub introduces a narrow rejection band inside the UWB filter bandwidth. The frequency tuning of the notched band is obtained by sequentially activating three RF MEMS ohmic switches placed in series along the embedded stub. HFSS® simulations of a 5th order UWB filter show very low return (>;13dB) and insertion losses (<;0.3dB) in all stub states and good selectivity performance of the notched bands (up to -18dB of rejection). The device has been fabricating at FBK on quartz substrate; experimental results will be available soon.