Synthesis of multi-layer frequency selective surfaces of quasi-optical systems

This thesis investigate design techniques for multilayer Frequency Selective Surfaces (FSS) and its applications in quasi-optical (QO) systems. Design challenges that involve higher order filter and practical implementation of multilayer FSS at higher frequencies are reviewed. Multilayer FSS structures are commonly realized by cascading two or more FSS panel to achieve higher order responses, which usually rely on dielectric substrates to support the FSS arrays. It is noted that existing design approaches involved elaborate manufacturing processes as well as the requirement of custom dielectric thickness for the implementation of multilayer FSS. These design issues poses practical problems in the realization of multilayer FSS of higher order and its demonstration at higher frequencies. Furthermore, realization of higher order multilayer FSS with custom dielectric thicknesses are not feasible with low cost Printed Circuit Board (PCB) technology. As a result of this investigation, a novel design and synthesis technique is developed to address the aforementioned design issues. Equivalent circuit modelling and full wave electromagnetic simulation are employed for this purpose. The developed design technique enable practical realization of QO filter to have all transmission lines of predefined fix length. As a result, the proposed technique is able to resolve the limited availability of custom dielectric thicknesses, thus enable demonstration of multilayer FSS of higher order at higher frequencies. Particularly, the proposed design methodology allow rectification by design to adapt to any small variations in the dielectric thicknesses. Subsequently, based on this technique, a novel QO reflector design is developed to demonstrate proof of concept for time delay multiplexing that are employed in a radar system. The implementation of time delay between two polarization multiplexed beams initially requires true time delay structures that are difficult to integrate due to their electrically large structure. In order to address this problem, the designed QO reflector is able to perform same functionalities, i.e. a significant group delay difference for the two orthogonal linear polarization. Specifically, the designed QO reflector has the capability to de-multiplex an incoming wave into two linear polarized waves, whereby one of the reflected wave is time delayed while the other wave is unaffected. A synthesis method for QO reflector design with time delay multiplexing has been presented. Based on the design procedures reported in this thesis, prototypes for both QO filter and QO reflector of fourth order has been developed to operate at 15 GHz with 5% and 3.5% bandwidth respectively. The performances of the developed prototypes are verified with free-space measurement setup. The measured insertion loss of the QO filter is observed to be in the range of 0.5 dB – 2.83 dB, while the measured return loss of the QO reflector is the range of 1.5 dB – 2.3 dB. In order to demonstrate the effect of the group delay from the QO reflector, frequency domain analysis is performed by post-processing the measured data to obtain the required time domain signals. Overall the experimental measurement results corroborate well with both full-wave and circuit simulation

Design and Optimization of Physical Waveform-Diverse and Spatially-Diverse Radar Emissions

With the advancement of arbitrary waveform generation techniques, new radar transmission modes can be designed via precise control of the waveform's time-domain signal structure. The finer degree of emission control for a waveform (or multiple waveforms via a digital array) presents an opportunity to reduce ambiguities in the estimation of parameters within the radar backscatter. While this freedom opens the door to new emission capabilities, one must still consider the practical attributes for radar waveform design. Constraints such as constant amplitude (to maintain sufficient power efficiency) and continuous phase (for spectral containment) are still considered prerequisites for high-powered radar waveforms. These criteria are also applicable to the design of multiple waveforms emitted from an antenna array in a multiple-input multiple-output (MIMO) mode. In this work, three spatially-diverse radar emission design methods are introduced that provide constant amplitude, spectrally-contained waveforms implemented via a digital array radar (DAR). The first design method, denoted as spatial modulation, designs the radar waveforms via a polyphase-coded frequency-modulated (PCFM) framework to steer the coherent mainbeam of the emission within a pulse. The second design method is an iterative scheme to generate waveforms that achieve a desired wideband and/or widebeam radar emission. However, a wideband and widebeam emission can place a portion of the emitted energy into what is known as the `invisible' space of the array, which is related to the storage of reactive power that can damage a radar transmitter. The proposed design method purposefully avoids this space and a quantity denoted as the Fractional Reactive Power (FRP) is defined to assess the quality of the result. The third design method produces simultaneous radar and communications beams in separate spatial directions while maintaining constant modulus by leveraging the orthogonal complement of the emitted directions. This orthogonal energy defines a trade-space between power efficiency gained from constraining waveforms to be constant amplitude and power efficiency lost by emitting energy in undesired directions. The design of FM waveforms via traditional gradient-based optimization methods is also considered. A waveform model is proposed that is a generalization of the PCFM implementation, denoted as coded-FM (CFM), which defines the phase of the waveform via a summation of weighted, predefined basis functions. Therefore, gradient-based methods can be used to minimize a given cost function with respect to a finite set of optimizable parameters. A generalized integrated sidelobe level (GISL) metric is used as the optimization cost function to minimize the correlation range sidelobes of the radar waveform. System specific waveform optimization is explored by incorporating the linear models of three different loopback configurations into the GISL metric to match the optimized waveforms to the particular systems

10kHz Pulse Repetition Frequency CO2 Laser for Processing High Damage Threshold Materials

Power intensities generated at the workpiece by continuous wave carbon dioxide lasers at 10.6 mum are insufficient to induce the non-conduction limited processes necessary for machining many of the refractory metals and ceramics employed in the manufacture of engineering components. Operated in a pulsed mode, analogous to solid state laser operation, the CO2:N2 laser can be designed to overcome these power intensity limitations. Nitrogen Carbon-dioxide mixtures can be pulse excited to give high output pulse intensities combined with a relatively low mean output power, thus, minimising thermal degradation of the optical system. Flat topped pulses with plateau powers controlled and matched to the processing requirements of metals and ceramics can be generated by proper choice of the input electrical pumping pulse, gas composition and design parameters of the optical resonator. Continuous machining is possible provided pulse repetition frequencies of up to 10 kHz can be achieved, since, at this frequency, a constantly evaporating liquid phase can be sustained

A pulse compression radar system for high-resolution ionospheric sounding

A low frequency pulse compression radar system, capable of 0.75 km spatial resolution, has been developed. This system utilizes a linear frequency-modulated signal, and yields an effective peak power enhancement of 14.5 dB, over a conventional radar of equivalent resolution. The required instrumentation, as well as the development of the necessary signal processing software, are described in detail. It is shown that the resolution and peak power enhancement achieved by the system are consistent with those predicted by theory. The effectiveness of the pulse compression radar as a tool for ionospheric observation is demonstrated by comparing its performance to that of a conventional radar operating simultaneously

Wave Propagation

A wave is one of the basic physics phenomena observed by mankind since ancient time. The wave is also one of the most-studied physics phenomena that can be well described by mathematics. The study may be the best illustration of what is “science”, which approximates the laws of nature by using human defined symbols, operators, and languages. Having a good understanding of waves and wave propagation can help us to improve the quality of life and provide a pathway for future explorations of the nature and universe. This book introduces some exciting applications and theories to those who have general interests in waves and wave propagations, and provides insights and references to those who are specialized in the areas presented in the book

Radar Technology

In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design

Strategies for Time Domain Characterization of UWB Components and Systems

In this work new methods and criteria for the analysis of Ultra Wideband (UWB) components and systems are introduced. This permit to have a deeper insight into the component characteristics like signal distortion, ringing and dispersion, introduced by the non-ideal behavior of the UWB components over the wide frequency band. The developed analyses are the basis for correction and optimization strategies for the features of the UWB components and systems, compensating for their non-idealities

Impedance Transformers

Non

Chipless RFID sensor tag system with microstrip transmissionline based ID generation schemes

This dissertation presents a chipless radio frequency identification (RFID) sensor tag system consisting of passive chipless RFID sensor tags and specialized reader. The chipless sensor tags are fabricated on a flexible substrate and contain an ID generation circuit, a sensor, and a microstrip antenna. The ID generation circuit consists of meandered microstrip transmission lines and uses a novel reflection and delay based ID generation scheme. The scheme, using an input RF pulse, constructs an on-off keying (OOK) or pulse position modulated (PPM) signal pattern representing a unique ID code. Two transmission lines and OOK representation are used and the generation of ten different ID codes are demonstrated. The integrated ID generation circuit, sensor, and antenna use a single transmission line and PPM representation, and demonstrate the generation of eight different ID codes. However, the presented schemes allow the generation of higher combinations of bits. A practical method to measure radar cross section (RCS) parameters of antennas that provides complete and more accurate information on scattering properties of antennas, essential for chipless sensor tag design, is presented. The new method uses minimum mean square error estimation solution of a derived received backscattered signal power equation and provides load independent structural-mode RCS, antenna-mode RCS, and relative phase factor of the measured antenna. Two configurations of the chipless sensor tags configuration-I (conf-I) and configuration-II (conf-II) are presented. In conf-I tags, sensors are connected as a load to the antenna and the sensor information is amplitude modulated in the backscattered signal. The testing with conf-I temperature sensor tag resulted in a 28% amplitude change when the temperature at the tag changes from 27°C to 140°C. In conf-II tags, sensors are connected as load to the ID generation circuit and the sensor information is phase modulated in the antenna-mode scattered signal. With the conf-II ethylene sensor tag, a phase change of 33° is observed when the ethylene concentration at the tag changes from 0 to 100 ppm. The specialized reader system is comprised of an analog reader that wirelessly communicates with the sensor tags and a single board computer that computes the sensor information from the received signal. The reader system constructs a 96 bit serialized global trade item number (SGTIN-96) electronic product code (EPC) format unique RFID tag data frame, including 16 bit sensor information, and makes the information available on a secure web interface accessible from cyberspace. The presented sensor tag system has the advantages of passive and chipless sensor tag operation, while offering a wide range of sensors types for integration. Moreover, it offers a viable alternative solution to existing active as well as passive RFID sensor tag systems (eg. SAW based RFID sensor tag systems)