Browsing by Author "Sekar, Vikram"
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Item Advances in Filter Miniaturization and Design/Analysis of RF MEMS Tunable Filters(2012-10-19) Sekar, VikramThe main purpose of this dissertation was to address key issues in the design and analysis of RF/microwave filters for wireless applications. Since RF/microwave filters are one of the bulkiest parts of communication systems, their miniaturization is one of the most important technological challenges for the development of compact transceivers. In this work, novel miniaturization techniques were investigated for single-band, dual-band, ultra-wideband and tunable bandpass filters. In single-band filters, the use of cross-shaped fractals in half-mode substrate-integrated-waveguide bandpass filters resulted in a 37 percent size reduction. A compact bandpass filter that occupies an area of 0.315 mm2 is implemented in 90-nm CMOS technology for 20 GHz applications. For dual-band filters, using half-mode substrate-integrated-waveguides resulted in a filter that is six times smaller than its full-mode counterpart. For ultra-wideband filters, using slow-wave capacitively-loaded coplanar-waveguides resulted in a filter with improved stopband performance and frequency notch, while being 25 percent smaller in size. A major part of this work also dealt with the concept of 'hybrid' RF MEMS tunable filters where packaged, off-the-shelf RF MEMS switches were used to implement high-performance tunable filters using substrate-integrated-waveguide technology. These 'hybrid' filters are very easily fabricated compared to current state-of-the-art RF MEMS tunable filters because they do not require a clean-room facility. Both the full-mode and half-mode substrate-integrated waveguide tunable filters reported in this work have the best Q-factors (93 - 132 and 75 - 140, respectively) compared to any 'hybrid' RF MEMS tunable filter reported in current literature. Also, the half-mode substrate-integrated waveguide tunable filter is 2.5 times smaller than its full-mode counterpart while having similar performance. This dissertation also presented detailed analytical and simulation-based studies of nonlinear noise phenomena induced by Brownian motion in all-pole RF MEMS tunable filters. Two independent mathematical methods are proposed to calculate phase noise in RF MEMS tunable filters: (1) pole-perturbation approach, and (2) admittance-approach. These methods are compared to each other and to harmonic balance noise simulations using the CAD-model of the RF MEMS switch. To account for the switch nonlinearity in the mathematical methods, a nonlinear nodal analysis technique for tunable filters is also presented. In summary, it is shown that output signal-to-noise ratio degradation due to Brownian motion is maximum for low fractional bandwidth, high order and high quality factor RF MEMS tunable filters. Finally, a self-sustained microwave platform to detect the dielectric constant of organic liquids is presented in this dissertation. The main idea is to use a voltage- controlled negative-resistance oscillator whose frequency of oscillation varies according to the organic liquid under test. To make the system self-sustained, the oscillator is embedded in a frequency synthesizer system, which is then digitally interfaced to a computer for calculation of dielectric constant. Such a system has potential uses in a variety of applications in medicine, agriculture and pharmaceuticals.Item Novel rf mems tunable filters with adjustable spurious suppression(2009-05-15) Sekar, VikramThis thesis presents the theory and design of fixed and Radio Frequency (RF) Microelectromechanical Systems (MEMS) -based tunable microwave filters for RF and microwave applications. The methodology for the design of coupled resonator filters is explained in detail and is used to design an end-coupled microstrip filter at 1.5 GHz with inductive loading using a stepped microstrip discontinuity to lower the resonance frequency of the half-wavelength microstrip resonator. The fabricated endcoupled filter shows center frequencies of 1.36 GHz and 1.03 GHz in the unloaded and loaded state respectively, with insertion losses between 1.2-1.5 dB and return loss better than 10 dB in both states. The filter response shows spurious passbands at approximately twice the filter center frequencies. To overcome this problem and improve the upper rejection skirt of the filter, microstrip resonators with tapped input/output coupling and mixed inter-resonator coupling are used to suppress the spurious passband by introducing a transmission zero at spurious resonance frequency. Measurement results for the fabricated tapped-resonator filters show an improvement of the upper rejection skirt due to spurious suppression to a level of -40 dB, with insertion loss of 1.2-1.5 dB for the same center frequencies. The concepts developed from fabrication and measurement of fixed-tuned microstrip filters are used to design an inductively-loaded RF MEMS tunable filter with adjustable spurious suppression implemented using packaged metal-contact switches. The two-pole 5% filter has a tuning range of 17% from 1.06 GHz to 1.23 GHz with an insertion loss of 1.56-2.28 dB and return loss better than 13 dB over the tuning range. The inductive loading mechanism is used to tune the open-ended quarter wavelength stub such that a tunable transmission zero supresses the spurious resonance as the filter center frequency is tuned. The spurious passband response in both states is suppressed below -20 dB. The unloaded quality factor (Q) of the filter varies from 127 to 75 as the filter is tuned. The equivalent circuit model for the series metalcontact packaged RF MEMS switch used in the tunable filter is derived from full-wave electromagnetic simulations and used to predict the effect of MEMS switch parasitics on the overall performance of the tunable filter.