Current Issue : January - March Volume : 2012 Issue Number : 1 Articles : 8 Articles
A novel technological method to improve the quality factor (Q) of RF-integrated inductors for wireless applications is presented in this paper. A serious reduction of substrate losses caused by capacitive coupling is provided. This is realised by removing the oxide layers below the coils with optimized underetching techniques. This special etching procedure is used to establish an environment in the inductor substructure with very low permittivity. A set of solid oxide-metal-columns placed below the metal windings stabilize the coil and prevent the hollowed out structure from mechanical collapse. The oxide capacitance is lowered significantly by the reduction of the permittivity er from values around 4 to nearly 1. Capacitive coupling losses into substrate are decreasing in the same ratio. The resulting maximum Q-factors of the new designs are up to 100% higher compared to the same devices including the oxide layers but shifted significantly to higher frequencies. Improvements of Q from 10 up to 15 have been obtained at a frequency of 3?GHz for a 2.2?nH inductor with an outer diameter of 213?�µm. The resonance frequency (f res) and frequency at maximum Q( f(Qmax)) are shifted to higher frequencies, caused by the shrunk total capacitance of the structure. This enables the circuit designer to use the inductors for applications working at higher frequencies. Coils with different layouts and values for inductance (L) were verified and showed similar results....
Three patch antennas suitable for integration and operation in a compact 24?GHz wireless sensor node with radar and communication functions are designed, characterized, and compared. The antennas are manufactured on a low loss glass wafer using thin film (BCB/Cu) wafer level processing (WLP) technologies. This process is well suited for 3D stacking. The antennas are fed through a microstrip line underneath a ground plane coupling into the patch resonator through a slot aperture. Linear polarization (LP), dual mode (DM) operation, and circular polarization (CP) are achieved through the layout of the slot aperture and rectangular patch dimensions. Antenna gain values of ~5.5?dBi are obtained in addition to the 10 dB impedance bandwidths of 900?MHz and 1.3?GHz as well as 500?MHz CP bandwidth with a 3?dB axial ratio for the LP, DM, and CP patch antennas, respectively....
This paper presents simulation and measurement results of fully distributed tunable coplanar bandpass filters (BPFs) with center frequencies around 6?GHz that make use of ferroelectric Barium Strontium Titanate (BaxSr1-xTiO3 or BST-x) thin film as tunable material. The two experimental bandpass filters tested are based on a novel frequency-agile structure composed of cascaded half wavelength slow-wave resonators (2 poles) and three coupled interdigital capacitors (IDCs) optimized for bias voltage application. Devices with gap dimensions of 10 and 3?�µm are designed and fabricated with a two-step process on polycrystalline Ba0.5Sr0.5TiO3 thin films deposited on alumina substrate. A frequency tunability of 9% is obtained for the 10?�µm gap structure at �±30?V with 7?dB insertion loss (the BST dielectric tunability being 26% with 0.04 loss tangent for this gap size). When the structure gap is reduced to 3?�µm the center frequency shifts with a constant 9?dB insertion loss from 6.95?GHz at 0?V to 9.05?GHz at �±30?V, thus yielding a filter tunability of 30% (the BST dielectric tunability being 60% with 0.04 loss tangent for this gap size), a performance comparable to some extent to localized or lumped element BPFs operating at microwave frequency (>2?GHz)....
Physical principles for designing a multipurpose set of high Q-factor quasioptical and corrugated resonators with automatic frequency tuning (Q > 6 Ã?â?? 104, VSWR < 1.6) that can operate in the frequency band from 37.5 to 400?GHz are presented. The electrodynamical calculation methods of resonators, the constructive particularities of resonators, the methods and results of the experimental researches are considered. This set of resonators can be used as a universal measuring resonator for measuring radio-signal fluctuations and parameters of different media, in particular, nanotube composites and high-temperature superconductors....
Radio Frequency (RF) modules have been miniaturized to meet the demand for smaller and more enhanced handsets for wireless applications such as cellular phones. However, area for passive devices used in RF modules has made further miniaturization difficult. Passives embedded in substrates are now being studied intensively. In addition, circuit simulation technology has been developed that enables efficient designing of RF module circuits. Circuit designers, however, have limited database of organic substrates and embedded passives. Further, optimized thermal designs are required to prevent thermal resistance increase due to miniaturization of substrates. In this paper, we describe the high-frequency properties of the capacitors embedded in the organic substrates and present the equivalent circuit models of the embedded capacitors. We also present the thermal design of organic substrates applicable to RF modules....
A domestic microwave oven (1000?W) was modified to permit the continuous flow of liquids run through a helical coil centrally located inside the oven cavity. Heating characteristics were evaluated by measuring inlet and outlet temperatures of coil as a function of system variables. The influence of number of turns, coil diameter, tube diameter, pitch and initial temperature were evaluated at different flow rates. The average residence time of water was computed by dividing the coil volume by the volumetric flow rate. The influence of Dean number was evaluated. Results from this study showed that (1) higher number of turns resulted in lower heating rate, lower temperature fluctuations, higher exit temperature and longer time to achieve temperature equilibrium; (2) larger tube or coil diameter gave larger coil volume causing the heating rate to decrease; (3) faster flow rates resulted in lower exit temperatures, lower temperature fluctuation, higher Dean number and slightly higher heating rate; (4) higher initial temperatures resulted in higher exit temperatures; (5) higher Dean number resulted in more uniform heating and slightly higher heating rate. Overall, the coil volume was the more dominant factor affecting heating rate as compared with flow rate and Dean number....
This study presents the temperature dependence of small signal parameters of GaN/SiC HEMTs across the 0ââ?¬â??150?C range. The changes with temperature for transconductance (gm), output impedance (Cds and Rds), feedback capacitance (Cdg), input capacitance (Cgs), and gate resistance (Rg) are measured. The variations with temperature are established for gm, Cds, Rds, Cdg, Cgs, and Rg in the GaN technology. This information is useful for MMIC designs....
Time reversal is a physical concept that can focus waves both spatially and temporally regardless of the complexity of the propagation medium. Time reversal mirrors have been demonstrated first in acoustics, then with electromagnetic waves, and are being intensively studied in many fields ranging from underwater communications to sensing. In this paper, we will review the principles of time reversal and in particular its ability to focus waves in complex media. We will show that this focusing effect depends on the complexity of the propagation medium rather than on the time reversal mirror itself. A modal approach will be utilized to explain the physical mechanism underlying the concept. A particular focus will be given on the possibility to break the diffraction barrier from the far field using time reversal. We will show that finite size media made out of coupled subwavelength resonators support modes which can radiate efficiently in the far field spatial information of the near field of a source. We will show through various examples that such a process, due to reversibility, permits to beat the diffraction limit using far field time reversal, and especially that this result occurs owing to the broadband inherent nature of time reversal....
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