OPTIMIZED MECHANICAL DESIGN OF CAPACITIVE MICROMACHINED SWITCH: A CAD-BASED NEURAL MODEL

In this paper, the authors propose the neural modeling of optimized design for pull-in instability reduction of micromachined capacitive shunt radio frequency (RF) micro electro mechanical system (MEMS) switch. Prediction of effective dielectric constant and hence the critical collapse voltage that represents the bridge position instability for two typical bridge geometrics have been derived using artificial neural network (ANN). The effects of residual stress, length of center conductor and the gap between the bridge and center conductor of switch in lowering the driving voltage have been studied. Based on the neural model results, we have observed the reduction of 3 V in critical collapse voltage for an increase of 10 μm in length of center conductor. We have also noted the strong variation in voltage (reduction of 0.8 V for 1 MPa residual stress reduction) with respect to residual stress change. We achieved the reduction of 1.5 V in collapse voltage by reducing the gap between the bridge and the center conductor by 0.1 μm. Among the two structures considered, the structure with lower width of the center conductor proved as an optimum in achieving low critical collapse voltage. Further, the performance of trained neural network with the training datasets derived from MATLAB simulation has been evaluated in terms of convergence speed and mean square error.

Miniature single-sideband subharmonically-pumped 60 GHz direct upconverter in a uniplanar GaAs pHEMT technology using inductive and capacitive loading techniques

This paper presents a novel, compact, single-sideband (SSB) subharmonically-pumped (SHP) direct upconverter developed in a uniplanar 0.18 μm GaAs technology. A total of 100 MHz in-phase and quadrature signals directly modulate the second harmonic of a 30 GHz carrier signal, producing a 60.1 GHz output. Two pairs of antiparallel diodes reduce feed-through of the 30 GHz local oscillator (LO) signal to the mixer's RF output. Novel structures patterned in the center conductor of a coplanar waveguide (CPW) provide matching and size-reduction simultaneously. The 2.1mm2 circuit also uses a miniaturized Wilkinson divider based on asymmetric coplanar stripline and a standard CPW 90° coupler. The SSB SHP direct upconverter exhibits a conversion loss of 10 dB, a lower-sideband rejection of 15 dB and 2fLO suppression of approximately 25 dB over a wide frequency range from 52–61 GHz.

Experimental Multiport Bicone Antenna

A practical, easily manufactured multiport bicone antenna suitable for many receiving tasks such as direction finding systems can be made by using sharp-edged metal fins on the feeding coax center conductor to provide a tapered transition and connection path to coaxial probes. This construction resembles an arrow's tail. Already four mutually orthogonal fins can give full 360 degree azimuth coverage with suitable −3 dB port pattern overlap. Five experimental constructions working at Ku and Ka bands, each with fractional bandwidths of 23 to 31 per cent, are shown with full dimensional details. Suitable fin tapering is close to the full air gap in the coax and fin thickness should be less than 1/16th of the outer conductor diameter.

Polymer-based micromachined rectangular coaxial filters for millimeter-wave applications

In this paper, micromachined devices for millimeter-wave applications at U- and V-bands are presented. These structures are designed using a rectangular coaxial line built of gold-coated SU-8 photoresist layers, where the coaxial center conductor is suspended in air by stubs. The designs include a stepped coplanar waveguide (CPW)-to-coaxial transition at 63 GHz, with an insertion loss of 0.39 dB at 67.75 GHz and a return loss better than −10 dB across the band of operation between 54.7 and 70.3 GHz. Two filters have been designed; one centered at 42 GHz with a 10% bandwidth, and another at 63 GHz with a 5% bandwidth. Measured insertion losses of 0.77 and 2.59 dB were obtained for these filters, respectively. Measured return loss lower than 13.8 dB over the passband was achieved for both designs. The structures presented in this paper involve a low-cost manufacturing process suitable to produce integrated subsystems at millimeter waves.

New class of SiGe reduced-size loaded slow wave 60 GHz CPW series/shunt stubs and its applications to the design of slow wave bandpass filters

This paper proposes a practical approach for developing a new class of compact slow-wave coplanar waveguide (CPW) series/shunt stubs, which offer 40% reduction in size relative to a conventional design. It demonstrates that the technique using interdigitated capacitive loading can provide size and cost reductions, while also providing performance enhancements such as better return loss. The experimental prototypes presented in this paper demonstrate the validity of the design method and the ability to print interdigitated capacitors inside the center conductor of the series/shunt stubs. The principle of achieving such high-quality circuits is detailed and is also confirmed by theoretical and experimental results, which are in reasonable agreement up to at least 70 GHz. The paper also presents a family of novel topologies of slow wave bandpass filters based on the proposed capacitively loaded CPW series/shunt stubs.

High Isolation X-Band RF MEMS Shunt Switches on Groove Etched Substrates

Developments in RF MEMS switches have demonstrated great potential at low-loss microwave application. MEMS shunt switches have a few advantages compared to the FET or p-i-n diode counterparts due to their characteristics of low intermodulation distortion or harmonics, low DC power consumption, low insertion losses and high isolation [1][2]. RF MEMS shunt capacitive switches has shown excellent performance from Ka-band to W-band, however, they fail to perform the same in X-band for the low isolation in this frequency range. Various approaches have been introduced to address this shortcoming, such as applying high-impedance transmission line [3], using strontium titanate oxide (SrTiO3) as high relative dielectric constant material [2], etc. Aimed at X-band applications, this paper reports a novel design of a high isolation RF MEMS shunt capacitive switch which is fabricated on a groove etched substrate. Fig. 1(a) and Fig. 2(a) show the schematics of the MEMS capacitive switch. The switch is constructed on a coplanar waveguide (CPW) transmission line. When the switch is up, the switch presents a small shunt capacitance to ground, presenting an RF open. When the switch is pulled down to the center conductor by electrostatic force, the shunt capacitance increases remarkably, presenting an RF short. In this work, a short high-impedance section of transmission line is designed between the MEMS bridge and the ground plane. This increases the series inductance of the switch so as to lower the resonant frequency. The length of this line is designed to put the series resonant frequency into the frequency range of X-band. Two grooves are etched into the substrate along the center conductor between the transmission line and the ground plane. For the desired characteristic impedance, a wider center conductor width can be obtained by increasing the groove depth accordingly. Thus the CPW with grooves potentially has a lower attenuation due to conductor losses [4]. Moreover, as center conductor gets wider, the down-state shorting-circuit capacitance increases which helps to gain a higher isolation. The mechanical and RF performances of this switch have been analyzed by FEA software, IntelliSuite and HFSS. As shown in Fig. 1(b), the actuation voltage of the planar switches is 26V. The RF characteristics of the switch at down state are obtained through HFSS. In Fig. 1(c), the down state isolation reaches −54.6dB at its self-resonate frequency of 13.5GHz. Compared with the non-grooves counterpart, the designed grooves optimize the isolation performance by 7dB. The insertion loss is less than 0.2 dB from 5 to 30 GHz. Fig. 2(a) shows the serpentine folded suspension switch, its actuation voltage is 14V, shown as in Fig. 2(b). The RF response in Fig. 2(c) demonstrates that the series resonant frequency is down to 11GHz due to the inductance introduced by serpentine folded suspensions. The down state isolation is −42.8dB at 11GHz. However, it is demonstrated that the substrate grooves did not help to optimize isolation performance. This is due to the higher resistance and inductance introduced by serpentine folded suspension. This research is supported by “Hundreds Scholar Program”, Chinese Academy of Sciences.