A. Ocera

A novel technique for complex permittivity measurement based on a planar four-port device

A novel technique for the measurement of the complex permittivity of materials is presented that overcomes many limitations of the conventional measurement methods. The RF signal transmitted through a transmission line loaded with the material under test is combined with a reference signal using a quadrature hybrid in such a way that the complex permittivity can be measured by simply detecting the two output amplitudes. This technique requires a simple calibration procedure, provides good accuracy, and avoids expensive vector measurements, thus combining the advantages of transmission methods, in terms of good accuracy, with those of resonant methods, in terms of scalar measurements. Two microstrip implementations have been realized for measurements at 2.35 and 10 GHz, showing very good accuracy to be achieved in both frequency ranges. The measured permittivities have been compared with those obtained with a resonant and transmission method and with data from literature, resulting in a very good agreement for both epsivr and tandelta

A Novel MEMS-Tunable Hairpin Line Filter on Silicon Substrate

In this paper a novel MEMS-tunable hairpin line filter is presented. The circuit has been realized on a 525 mum 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 MEMS-Reconfigurable Power Divider on High Resistivity Silicon Substrate

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 Novel Compact Dual Band Reconfigurable Power Divider for Smart Antenna Systems

This paper presents a novel compact dual band reconfigurable power divider for smart antenna systems. The circuit employs two cascaded dual band hybrid couplers connected through two dual band discontinuities. The dual band discontinuities, consisting of a diplexer and two varactor diodes, can be tuned through two different biasing voltages thus allowing an independent and arbitrary choice of the power ratio in the two frequency bands. A prototype has been designed to operate in the dual band WLAN frequency range, and fabricated in microstrip technology on a 25 mils CER10 substrate. Measured scattering parameters exhibit good performance in terms of return loss, insertion loss and isolation in both WLAN bands, confirming the feasibility of the proposed architecture. The compactness of the circuit makes it suitable for employment in array configurations.

Development of different K-band MEMS phase shifter designs for satellite COTM terminals

This work presents the design, manufacturing and testing of three 5-bit K-band MEMS phase shifters based on similar architectures (combination of switched line and loaded line) but employing different MEMS switch typologies (cantilevers & air-bridges) and RF junctions (SP2T & SP4T). All devices have been monolithically manufactured on 200 μm thick high resistivity silicon substrate (4”) by using the FBK MEMS process. The performance of the different devices have been compared in order to identify the best configuration to be implemented in electronically steerable phased arrays antennas for Satellite COTM (Communication On The Move) Terminals. Excellent performances were measured for the dielectric-free pad MEMS switches as well as the single bits constituting the phase shifter. The three 5-bit devices show return loss better than 15 dB for all states, with average insertion loss of 3.5dB for the clamped-clamped, SP2T-based design, 2.2 dB for the cantilever, SP2T-based device and 2.1 dB for the cantilever, SP4T-based design. The measurements of the packaged devices are on-going.

A novel technique for complex permittivity measurement based on a planar four port device

A novel four port device for complex permittivity measurement is presented consisting of the cascade of two 3 dB branch line directional couplers connected through two U-shaped transmission line lengths. The material under test (MUT) is brought into contact with one U-shaped section. The complex dielectric permittivity of the MUT is evaluated by simply measuring the amplitudes of the two outputs, thus obtaining a simple and cheap measurement procedure. A prototype has been fabricated and experimentally tested exhibiting very good accuracy.

Novel RF-MEMS widely-reconfigurable directional coupler

This paper presents an innovative widely reconfigurable directional coupler based on concentric selectable squares. The device can be reconfigured by simply addressing the RF signal to the selected square through independent sets of MEMS switches. A very wide tuning range of the operating frequency can be attained, still maintaining good performance in terms of both return loss and isolation in the all states. A 2-state MEMS prototype has been designed on a 525 mum high resistivity silicon substrate, employing a well-established eight-mask surface micro-machining process developed at Fondazione Bruno Kessler, Trento, Italy. A 41% tuning range has been achieved ranging from C to X band with a return loss and isolation better than 25 dB in both states. Two test circuits have been realized in microstrip technology confirming the feasibility of the proposed architecture.

An Innovative Reconfigurable Reflection-Type Phase Shifter for Dual Band WLAN Applications

This paper presents an innovative reconfigurable reflection-type phase shifter for dual band WLAN applications. The device allows an independent choice of the phase shifts for both the two WLAN bands, employing a quadrature hybrid dual band coupler, two diplexers and four reflective loads. A full 360deg phase shifter prototype has been realized in microstrip technology, the reflective loads being realized through eight varactors, whose capacitances are varied through two different biasing networks. Measured results show good performance in terms of return loss, insertion loss and excellent isolation between the two WLAN bands, confirming the feasibility of the proposed architecture and its applications to dual band smart antenna systems

A Novel Technique for Measuring One-Dimensional Permittivity Profiles Using a Simple Non-Commensurate Planar Structure

A novel technique is presented for measuring one-dimensional permittivity profiles based on a simple planar structure. The measuring device consists of a transmission line loaded with open-ended stubs of non-commensurate lengths. The permittivity profile of the material under test is evaluated by simply measuring the attenuation pole frequencies in the transmitted RF signal due to the different loaded stubs. The proposed technique provides reliable results for both continuous and discontinuous permittivity profiles without requiring any a priori information of the unknown profile. Measurements using different materials have been performed resulting in good agreement with data from the literature.

A MEMS programmable power divider/combiner for reconfigurable antenna systems

A programmable power divider/combiner is proposed for applications to low-cost reconfigurable antenna systems. The circuit employs two 3dB branch line couplers and a programmable reflection-type phase shifter that produces the required power ratio. A 5-state programmable power divider has been designed using microstrip technology and 8 RF MEMS devices. The circuit has been designed on a 525 /spl mu/m high resistivity silicon substrate using a well established micromachining process at ITC-irst in Trento, Italy. The circuit is presently being fabricated; the simulated results show return loss better than 25 dB and isolation better than 20 dB with power ratios of 1:0, 4:1, 1:1, 1:4, and 0:1 with a maximum error in the power ratio lower than 4.5%. An example of reconfigurable antenna system based on the proposed device is shown.