Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 1992. / Thesis Advisor: Jenn, David C. "March 1992." Includes bibliographical references (p. 71). Also available in print.

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Thesis (M.S.)--Ohio University, August, 1998. / Title from PDF t.p.

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In this thesis, the concept of multi-phase centre virtual antenna is thoroughly investigated when a dual-mode primary feed is placed at the focal point of an offset reflector antenna. The virtual antenna requires that the antenna have multiple phase centre locations with identical radiation patterns. It is shown that different polarizations and mode content factors of a dual-mode circular waveguide can displace the phase centre location of an offset reflector antenna without changing its radiation patterns in any direction. This novel idea has promising applications in modern satellite, remote sensing, global positioning systems, and radars with moving platform. The concept is well matched for the modern Displaced Phase Centre Antenna technique, in which a simple signal processing technique is employed to electronically displace the phase centre locations. To avoid mechanically rotating the primary feed, a novel dual-mode feed is also proposed and implemented. It is capable of generating two perpendicular polarized TE11 modes with a fixed aligned TE21 mode. The antenna such developed has a potential application as a transceiver in ground moving target indicator radars. All numerical results are successfully validated by fabricating and testing a prototype antenna in practice. As known, an offset reflector fed by a conventional linear polarized feed suffers from high cross polarization level. This property is also investigated for single-phase centre antenna applications along with sidelobe level and aperture efficiencies. A simplified feed model is proposed utilizing the TE11 and TE21 type modes to reduce the cross polarization at both asymmetry and inter-cardinal planes. It is shown that an asymmetric dominant TE11 mode with the presence of the TE21 mode is sufficient in order to reduce the unwanted cross polarization. The results of this investigation are used to design practical dual-mode feeds using simple circular waveguide geometries. To complete the study, the effects of linear and quadratic phase errors associated with the optimized primary feed are also investigated on the cross polarization of the offset reflector antennas. In particular, the phase errors resulting in separate phase centre locations of each mode produce broadside-shape cross polarized patterns instead of boresight-null ones.

In this thesis, the concept of multi-phase centre virtual antenna is thoroughly investigated when a dual-mode primary feed is placed at the focal point of an offset reflector antenna. The virtual antenna requires that the antenna have multiple phase centre locations with identical radiation patterns. It is shown that different polarizations and mode content factors of a dual-mode circular waveguide can displace the phase centre location of an offset reflector antenna without changing its radiation patterns in any direction. This novel idea has promising applications in modern satellite, remote sensing, global positioning systems, and radars with moving platform. The concept is well matched for the modern Displaced Phase Centre Antenna technique, in which a simple signal processing technique is employed to electronically displace the phase centre locations. To avoid mechanically rotating the primary feed, a novel dual-mode feed is also proposed and implemented. It is capable of generating two perpendicular polarized TE11 modes with a fixed aligned TE21 mode. The antenna such developed has a potential application as a transceiver in ground moving target indicator radars. All numerical results are successfully validated by fabricating and testing a prototype antenna in practice. As known, an offset reflector fed by a conventional linear polarized feed suffers from high cross polarization level. This property is also investigated for single-phase centre antenna applications along with sidelobe level and aperture efficiencies. A simplified feed model is proposed utilizing the TE11 and TE21 type modes to reduce the cross polarization at both asymmetry and inter-cardinal planes. It is shown that an asymmetric dominant TE11 mode with the presence of the TE21 mode is sufficient in order to reduce the unwanted cross polarization. The results of this investigation are used to design practical dual-mode feeds using simple circular waveguide geometries. To complete the study, the effects of linear and quadratic phase errors associated with the optimized primary feed are also investigated on the cross polarization of the offset reflector antennas. In particular, the phase errors resulting in separate phase centre locations of each mode produce broadside-shape cross polarized patterns instead of boresight-null ones.

This thesis presents a new approach to the hardware test environment for a twist reflector monopulse antenna system with a radome extending current measurement practice. New research is presented on the optimisation of the design of a twist reflector monopulse antenna system with a radome, significantly improving the design and the design process. A unique extension to current measurement practice, for single channel antennas, is presented to determine the best practice method on phase stable measurements of a multi-channel antenna on a moving positioner. A novel axis transform for a 3 axis positioner system located within an anechoic chamber is derived. It allows for true performance measurement of a twist reflector antenna with a radome. This progresses the field of antenna measurement as, uniquely, this axis transform allows the aberration caused by the antenna radome to be measured and included. Design improvements have been made on polarisation selective grids, the matched thickness of the radome and a new software method that removes the need for a comparator and increases the robustness of the antenna system. Polarisation selective grids, constructed from a set of parallel conductors, have a wide range of uses in antenna systems. This thesis shows that the depth of a copper grid line can be reduced to 15 m and still provide better than -25 dB cross-polar isolation. This is contrary to current understanding at 30 times the skin depth. A new combined approach to radome thickness optimisation is presented that reduces the time taken to calculate the optimal thickness by over 3 orders of magnitude and the computer memory by over 2 orders of magnitude without compromising accuracy. The use of a digital comparator is described and leads to a novel method to compensate for a failed feed element, verifified in both simulation and anechoic chamber measurements.

In this study, 1/2 £f mode SMR filters on Si substrates by reactive RF magnetron sputtering method were fabricated. In addition, the thermal annealing process was adopted to improve the insertion loss of SMR filter. The Bragg reflector in SMR is alternately mounted by high and low acoustic impedance materials, with low acoustic impedance material of SiO2 and high acoustic impedance material of W. We could obtained three kinds of crystal structures of W, £\ - phase W¡B£] - phase W and £\ & £] - mixed phase W, respectively, it could be obtained by modulating the sputtering recipe. £\ - phase W possesses higher acoustic impedance and is suitable for high acoustic impedance material in bragg reflector. The piezoelectric layer of ZnO is sputtered by a 2-step deposition method on Si substrates with different temperature. The ZnO film with stronger C-axis (002) orientation and lower surface roughness value could be obtained at substrate temperature of 200 ¢J, which is suitable for fabricating SMR device. After the SMR filter had completed, the device is thermal annealed with CTA¡BRTA and RTA in O2 ambient. After thermal treatment, the properties of filters are improved. The properties could be optimized with RTA in O2 ambient condition. The insertion loss was improved from -12.03 dB to -6.96 dB. The film characteristics of ZnO changes after the SMR processed thermal treatment. The strongest C-axis (002) intensity with the lowest surface roughness value at 400 ¢J annealing temperature could be obtained, in that, approximate equal Zn:O ratio could be achieved by XPS examination. The central frequency of SMR filter drifted to higher value as the temperature of thermal treatment increased, which is attributed to the changes of the ZnO acoustic velocity(£o) after thermal treatment.

As the world continues to adopt the next generation of mobile technology, dual-band 5G wireless communications are becoming increasingly significant. 5G technology operates on two different frequency bands, the sub-6 GHz Frequency Range (FR1) and the millimeter wave (MMW) Frequency Range (FR2). The special features in each band enable 5G dual-band communication to provide better coverage and capacity than previous generations of wireless networks. This is especially essential for applications that need high-bandwidth and low-latency connections, such as virtual and augmented reality, autonomous vehicles, and industrial automation. Furthermore, dual-band 5G can help alleviate network congestion in urban areas by redirecting traffic to the MMW band, which has considerably greater capacity. As a result, dual-band 5G is expected to play a critical role in facilitating the next wave of technological innovation and revolutionizing the way we live and work. A dual-band antenna with a large frequency ratio (FR) is required due to the significant difference between each frequency band in 5G. Research on dual-band antennas is facing challenges such as low FR and a lack of a specific design methodology. Despite attempts to develop dual-band antennas with large FRs, there are still issues with low performance and limited bandwidth. This study introduces a novel approach for designing a dual-band antenna with a large FR. The proposed solution draws inspiration from a hybrid design of a dual-band antenna to achieve a large FR, and from the parabolic reflector antenna design to significantly enhance gain in the upper band. The lower band antenna in this design serves as both a radiator for the lower band and a reflector to align the beam in the upper band. This approach can be used to design dual-band antennas for various frequencies. In this thesis, we present a comprehensive model and framework for designing an antenna integrated reflector that offers a large FR. The proposed model is capable of producing an antenna that meets the requirements of the targeted application, namely 5G. This antenna exhibits wideband characteristics and high gain. Two different antenna integrated reflectors, named AIR-I and AIR-II, were designed based on the proposed model. AIR-I has a FR of 10.1. As for AIR-II, due to the presence of dual-band upper antennas, it has a lower band at 1.35 GHz and two upper bands at 13 GHz and 24 GHz thus, a FR of 9.5 and 18, respectively. The above design followed a specific purpose. It uses a 24 GHz/1.35 GHz frequency ratio of 18 to showcase the antenna performance in the context of dual-band 5G. However, the measurement facilities being limited to 20 GHz, a frequency ratio of 9.5 at 13 GHz/1.35 GHz was measured for the AIR-II, as proof of concept. Then, two prototypes were fabricated from AIR-II namely, Prototype-I and Prototype-II. While it would have been possible to demonstrate a proof of concept from a single prototype, it has been decided to produce and test two samples to enable a more exhaustive examination of the subject and obtain additional data that would lend greater support to the model outlined in this thesis. Prototype-I had the same structure as AIR-II and had an operational bandwidth of 0.69 GHz-1.74 GHz / 6 GHz-18 GHz and a FR of 9.9. On the other hand, Prototype-II had an operational bandwidth of 0.69 GHz-1.74 GHz / 13 GHz-18 GHz and a FR of 12.8. These prototypes exhibited maximum bandwidths of 100% and 86%, respectively. Furthermore, at the upper band, Prototype-I achieved a peak gain improvement of 12.6 dB, while Prototype-II achieved an improvement of 8.7 dB. These results demonstrated the significant advantages of our proposed methodology in dual-band antenna design.

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