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Design Approach for Return-Loss Optimisation of Multi-Stage Millimetre-Wave MEMS Dielectric-Block Phase Shifters
KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201). (RF MEMS)
KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
2012 (English)In: IET Microwaves, Antennas & Propagation, ISSN 1751-8725, E-ISSN 1751-8733, Vol. 6, 1429-1436 p.Article in journal (Refereed) Published
Abstract [en]

This study reports on the radiofrequency (RF) performance optimisation of a novel multi-stage microelectromechanical system (MEMS) dielectric-block phase-shifter concept. The objective is to minimise the average return loss for all possible operation states of a multi-stage phase shifter, without substantially compromising the overall insertion loss or in phase-shift performance. The optimisation method presented in this study is generally applicable to any type of multi-stage RF MEMS devices that are operated in all possible state combinations of the different stages. The return loss is optimized for a seven-stage MEMS dielectric-block phase shifter by adjusting the individual distances between the phase shifter stages, for the nominal frequency of 75 GHz as well as for 500 MHz and 1 GHz bandwidth. A total of seven different designs following different optimisation approaches are investigated by simulations and measurements of fabricated devices. The best concept was found for exponentially increasing distances between the stages that takes into account the proper actuation sequence for all possible phase-shift combinations. As compared with a non-optimised device previously published by the authors, the design offering the best compromise between return loss and insertion loss, achieved by this optimisation method, results in a significant return loss improvement of 11.8 dB (simulated) and 6.98 dB (measured), whereas compromising the insertion loss by only 0.75 dB (simulated) and 0.92 dB (measured). In contrast to that all other investigated concepts, including intuitive optimisation methods such as λ/4 distances or optimisation of equidistant concepts result in a much smaller or no return-loss improvement and some even in a drastic worsening of the insertion loss.

Place, publisher, year, edition, pages
2012. Vol. 6, 1429-1436 p.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-79407DOI: 10.1049/iet-map.2012.0299ISI: 000318230200005Scopus ID: 2-s2.0-84880032164OAI: oai:DiVA.org:kth-79407DiVA: diva2:495463
Note

QC 20160504

Available from: 2012-02-08 Created: 2012-02-08 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Novel RF MEMS Devices for W-Band Beam-Steering Front-Ends
Open this publication in new window or tab >>Novel RF MEMS Devices for W-Band Beam-Steering Front-Ends
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents novel millimeter-wave microelectromechanical-systems (MEMS) components for W-band reconfigurable beam-steering front-ends. The proposed MEMS components are novel monocrystalline-silicon dielectric-block phase shifters, and substrate-integrated three-dimensional (3D) micromachined helical antennas designed for the nominal frequency of 75 GHz.

The novel monocrystalline-silicon dielectric-block phase shifters are comprised of multi-stages of a tailor-made monocrystalline-silicon block suspended on top of a 3D micromachined coplanar-waveguide transmission line. The relative phase-shift is obtained by vertically pulling the suspended monocrystalline-silicon block down with an electrostatic actuator, resulting in a phase difference between the up and downstate of the silicon block. The phase-shifter prototypes were successfully implemented on a high-resistivity silicon substrate using standard cleanroom fabrication processes. The RF and non-linearity measurements indicate that this novel phase-shifter design has an excellent figure of merit that offers the best RF performance reported to date in terms of loss/bit at the nominal frequency, and maximum return and insertion loss over the whole W-band, as compared to other state-of-the-art MEMS phase shifters. Moreover, this novel design offers high power handling capability and superior mechanical stability compared to the conventional MEMS phase-shifter designs, since no thin moving metallic membranes are employed in the MEMS structures. This feature allows MEMS phase-shifter technology to be utilized in high-power applications. Furthermore, the return loss of the dielectric-block phase shifter can be minimized by appropriately varying the individual distance between each phase-shifting stage.

This thesis also investigates 3D micromachined substrate-integrated W-band helical antennas. In contrast to conventional on-chip antenna designs that only utilize the surface of the wafer, the novel helical radiator is fully embedded into the substrate, thereby utilizing the whole volume of the wafer and resulting in a compact high-gain antenna design. The performance of the antenna is substantially enhanced by properly etching the substrate, tailor making the antenna core, and by modifying size and geometry of the substrate-integrated ground plane. A linear line antenna array is composed of eight radiating elements and is demonstrated by simulations. Each antenna is connected to the input port through a multi-stage 3-dB power divider. The input and output of the single-stage 3-dB power divider is well matched to the 50-Ω impedance by four-section Chebyshev transformers. The simulation results indicate that the novel helical antenna arrays offer a narrow radiation beam with an excellent radiation gain that result in high-resolution scan angles on the azimuth plane. The proposed helical antenna structures can be fabricated by employing standard cleanroom micromachining processes.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xii, 84 p.
Series
Trita-EE, ISSN 1653-5146 ; 2012:011
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-93507 (URN)978-91-7501-296-4 (ISBN)
Public defence
2012-05-25, Q1, Osquldas väg 4, entréplan, KTH, Stockholm, 09:30 (English)
Opponent
Supervisors
Note
QC 20120427Available from: 2012-04-27 Created: 2012-04-19 Last updated: 2012-04-27Bibliographically approved

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