Novel Electromagnetic Structure, Circuit, and Material for Microwave Applications

Abstract

This dissertation presents the investigation of novel electromagnetic structure, circuit, and material for microwave engineering. There are four topics covered in this work: the study of a waveguide filter at W-band frequencies using electromagnetic crystal (EMXT) surfaces, the design of a dual-band amplifier with flexible frequency ratio, the analysis and testing of a compact 4:1 planar combiner with complex matching, and the investigation of a dielectric nanostructured material using a mixture of polymer and silver nanoparticles. First, a rectangular waveguide band-stop filter using electromagnetic crystal EMXT surfaces is presented. A waveguide is loaded on the top and/or the bottom walls with EMXT surface, which has a propagating band gap. An equivalent circuit is developed to model the filter behavior and to predict its stop band. A W-band prototype based on the proposed filter architecture is designed and tested. The experimental results show a rejection band centered at 97 GHz and a rejection level of 16 dB. Second, a dual-band amplifier is demonstrated with flexible frequency ratios. The proposed amplifier features novel dual-band Wilkinson power divider/combiner that allows large frequency ratios between the first and second bands (2.16 to 4.9) between the first and second operating frequencies. The stand-alone combiner has maximum potential combining efficiency of 95% and 75% at the first and second frequency bands, respectively. A 2.4 / 5.8 GHz prototype amplifier is tested to verify its dual-band functionality. Measured linear gains are 12.85 dB and 11.09 dB at the first and second frequency bands, respectively. Third, a “spatial” combiner inspired power combiner / divider for solid-state amplifier application is presented. The proposed “one-stage” combining is realized by a single port tapered to an oversized microstrip connecting to parallel multiport microstrip sections. Uniform amplitude/phase and complex impedance matching at the parallel multiport microstrips are simultaneously achieved by adjusting the geometry of the structure. A prototype 5 GHz 1-to-4 divider/combiner designed using ADS co-simulation is characterized. The measured combining efficiency of 82.4% is achieved at 5 GHz. Lastly, a nanostructure thin film with giant dielectric response is proposed by strategically dispersing silver nano-particles inside a Tropropylene glycol diacrylate (TRPGDA) polymer. The dielectric properties of the proposed thin film are experimentally extracted at the microwave frequencies. The measurement sample is prepared by laying a coplanar waveguide (CPW) line on the thin film that is supported by a glass substrate. Two-port S-parameter measurements on the CPW are performed. Dispersion mechanism due to internal inductance of the CPW line when calculating the effective dielectric constant is investigated. The extraction involves conformal mapping approximation that uses closed-form equations to calculate the dielectric constant and the loss tangent of each layer based on the effective dielectric constant and loss tangent of the entire structure. Alternatively, direct fitting technique using simulation to model the experiment is studied. The results of the two techniques are compared and discussed. The measured dielectric constant ranges from 30000 to 4600 from 1 to 20 GHz with a loss tangent of 0.55 to 1.75 from 1 to 20 GHz.