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Tunable RF Antennas and Filters for Advanced Communication Systems and Wideband Quasi-Optical Network Analyzer for Millimeter-Wave and Terahertz Applications

  • Author(s): Alazemi, Abdullah J.
  • Advisor(s): Rebeiz, Gabriel M
  • et al.
Abstract

The dissertation comprises of four projects; double bow-tie slot antennas for wideband millimeter-wave and terahertz applications, a 100 − 300 GHz free-space scalar network analyzer using compact Tx and Rx modules, a tunable dual-band quadruple-pole antenna for carrier aggregation systems, and RF MEMS tunable 4-pole bandpass filters with bandwidth control and improved stopband rejection. The dissertation first presents millimeter-wave and THz double bow-tie slot antennas on a synthesized elliptical silicon lens. Two different antennas are designed to cover 0.1 − 0.3 THz and 0.2 − 0.6 THz, respectively. The double bow-tie slot antenna results in a wide impedance bandwidth and 78-97% Gaussian coupling efficiency over a 3:1 frequency range. A wideband CPW low-pass filter is designed using slow-wave techniques, and the measured filter response shows an S21 < -25 dB over a 3:1 frequency range. Absolute gain measurements done at 100 – 300 GHz and 200 − 600 GHz confirm the wideband operation of this design. The double bow-tie slot antenna is intended to fill the gap between standard double-slot antennas and log periodic and sinuous antennas, with applications areas in radio astronomy and imaging systems.

In chapter 3, the dissertation presents a 100 − 300 GHz quasi-optical network analyzer using compact transmitter and receiver modules. The transmitter includes a wideband double bow-tie slot antenna and employs a Schottky diode as a frequency harmonic multiplier. The receiver includes a similar antenna, a Schottky diode used as a sub-harmonic mixer, and an LO/IF diplexer. The 100 − 300 GHz RF signals are the 5th to 11th harmonics generated by the frequency multiplier when an 18 − 27 GHz LO signal is applied. The measured transmitter conversion gain with Pin = 18 dBm is -35 to -59 dB for the 5th to 11th harmonic, respectively, and results in a transmitter EIRP of +3 dBm to -20 dBm up to 300 GHz. The measured mixer conversion gain is -30 to -47 dB at the 5th to 11th harmonic, respectively. The system has a dynamic range > 60 dB at 200 GHz in a 100 Hz bandwidth for a transmit and receive system based on 12 mm lenses and spaced 60 cm from each other. Frequency-selective surfaces at 150 and 200 GHz are tested by the proposed design and their measured results agree with the simulations. Application areas are low-cost scalar network analyzers for wideband quasi-optical 100 GHz to 1 THz measurements.

In chapter 4, the dissertation presents a tunable dual-feed, dual-band, quadruple-pole antenna for carrier aggregation and mobile communication systems. The dual-feed PIFA (planar inverted F-antenna) has four operating frequencies which are independently tunable within the long-term evolution frequency range (LTE) from 0.7 to 2.7 GHz. Tuning is obtained using varactor diodes: two at low-band (0.7 − 1 GHz) and two at high-band (1.6 − 2.6 GHz). The antenna is well matched at both feeds (S11, S22 < -10 dB) and the isolation between the feeds is < -20 dB at low-band and < -13 dB at high-band. The antenna volume is 66 × 100 × 3.15 mm3 and is placed on RO4003C ("r = 3.55) printed-circuit board (PCB). The measured radiation efficiency is 25-50% at low-band and 30-62% at high-band with varactor diodes and it can be improved to > 50% using high Q devices such as RF-MEMS (Q > 200). A new concept to achieve tunable wideband performance is demonstrated using an extra shunt variable capacitor.

In chapter 5, 0.7 − 1 GHz and 1.7 − 2.4 GHz tunable 4-pole bandpass filters with bandwidth control and improved stopband rejection using RF-MEMS capacitors and varactor diodes have been demonstrated. The MEMS capacitors are fabricated and fully packaged using a 0.18 μm CMOS standard process with integrated high voltage drivers and SPI/RFFE control logic and with reliability in the billions of cycles. The 0.7 − 1 GHz filter results in insertion loss < 2.9 dB with controllable 1-dB bandwidth of 30-76% and IIP3 > 25.2 dBm with varactors and = 52 dBm with MEMS only. The measured ACPR (adjacent channel power ratio) for a 5-MHz Wideband CDMA signal is at least 49 dB at 10 dBm input power with varactors and at least 58.3 dB at 26 dBm input power with MEMS only. The 1.7 − 2.4 GHz filter results in insertion loss < 3.7 dB with controllable 1-dB bandwidth of 70-178% and IIP3 > 20 dBm with varactors and = 48 dBm with MEMS only. The measured ACPR for a 5-MHz Wideband CDMA signal is at least 37 dB at 10 dBm input power with varactors and at least 57.8 dB at 26 dBm input power with MEMS only. This paper also discusses the requirements of RF-MEMS capacitors with SPI and RFFE digital control for wireless communication systems.

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