Time-Domain Antenna and Scattering Analysis for Micro- and Millimeter-Wave Applications
Abstract: Telecommunications industries are investing tremendously to meet the ever-increasing demands for higher data rates and capacity. In particular to develop standardization for 5G, which is expected around 2020. The existing spectrum for traditional mobile networks is limited to highly occupied bands at microwave frequencies below 6 GHz. It is expected that 5G will use millimeter-waves to enable higher data rates. Even though losses at millimeter-waves are higher, higher data rates for short range applications can be achieved due to the available wide bandwidth. The radio channel between a transmitter and a receiver has a great impact on the quality of the received signals. The channel includes everything between the transmitter and receiver that may impact the signals, such as buildings, walls, windows, etc. High data rate transmission at millimeter-wave frequencies requires size- and cost-efficient circuitry. The recent advances in nanotechnology and semiconductor devices enable the signal generation at millimeter-waves. The existence of the available extreme bandwidth at millimeter-wave frequencies enables the application of impulse radio using high frequency ultra-short pulses. Transmission of a short pulse through antennas and a free-space radio channel without significant distortion requires a wideband antenna with high fidelity. In this thesis a time-domain antenna system with ultra-short pulse transmission and reception at millimeter-waves is presented. The antenna system consists of wideband and non-dispersive leaky lens antennas and a high frequency short pulse (wavelet) generator based on III-V technology. The time-domain system is presented in Paper I. The transmission of 100 ps long pulses at 60 GHz produced by the wavelet generator through different antennas is investigated. It is shown that the leaky lens antennas have negligible pulse distortion and preserve the shape of the generated high frequency short pulses. Further characterizations of the leaky lens antennas for the 60 GHz band, using a time-domain gating method is presented in Paper III. The results show that the antenna has a low dispersion and can thereby transmit short pulses with high fidelity. A time-domain characterization method at millimeter-waves using the antenna system is presented in Paper II. The complex permittivity of low loss non-magnetic materials with low dispersion are estimated directly from the received time-domain pulses. The wide bandwidth of the wavelet is also used to determine the frequency dependence of dispersive materials. Time-domain scattering analysis of periodic structures is presented in Paper IV and Paper V. A sum rule for scattering in parallel-plate waveguides based on energy conservation and the optical theorem is derived in Paper IV. A parallel-plate waveguide with wideband TEM horn antennas and a parallel-plate capacitor are used for dynamic and low frequency (static) measurements, respectively. The results show that the all waveleghts electromagnetic interaction introduced by the object is given by the static polarizability. The broad bandwidth and high resolution of the time-domain system is utilized for radar imaging application in Sec. 6 of the Research Overview. The images are obtained through gridding method which is a classical Fourier reconstruction and l1-minimization problem. It is shown that the resolution achieved by the time-domain system is similar to the frequency-domain measurements using a vector network analyzer.
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