A Rectangular Planar Spiral Antenna for GIS Partial Discharge Detection

A rectangular planar spiral antenna sensor was designed for detecting the partial discharge in gas insulation substations (GIS). It can expediently receive electromagnetic waves leaked from basin-type insulators and can effectively suppress low frequency electromagnetic interference from the surrounding environment. Certain effective techniques such as rectangular spiral structure, bow-tie loading, and back cavity structure optimization during the antenna design process can miniaturize antenna size and optimize voltage standing wave ratio (VSWR) characteristics. Model calculation and experimental data measured in the laboratory show that the antenna possesses a good radiating performance and a multiband property when working in the ultrahigh frequency (UHF) band. A comparative study between characteristics of the designed antenna and the existing quasi-TEM horn antenna was made. Based on the GIS defect simulation equipment in the laboratory, partial discharge signals were detected by the designed antenna, the available quasi-TEM horn antenna, and the microstrip patch antenna, and the measurement results were compared

Joint Time/Frequency Analysis and Design of Spiral Antennas and Arrays for Ultra-Wideband Applications

Ultra-wideband (UWB) systems transmit and receive extremely short pulses, permitting the corresponding antennas to distort their shape. Thus the design of an antenna for a UWB system plays an important role for the reliability and quality of communication. A UWB antenna design coalesces both the determination of conventional frequency domain parameters and the analysis of time domain response into a single overarching system requirement. While the former is needed to ensure system’s sensitivity, the later is critical to minimize pulse distortion. Well-designed spiral antennas are known for their almost frequency independent characteristics; thus they are viable candidates for UWB systems from the frequency-domain side. However, due to their fundamental principles of operation, they are dispersive and arguments were made they should not be used for pulsed UWB applications (time-domain side). The presented research unequivocally proves that spiral antennas and various derivatives thereof, including arrays, can be excellent candidates for multifunctional time/frequency domain systems. A complete framework for joint frequency and time domain characterization of planar spiral antennas in UWB communication systems is developed first. By utilizing theory, simulations, and experiments, all essential to the analysis frameworks, the various hypotheses are comprehensively treated and relevant conclusions are established. The dispersion and pulse distortion of the conventional spiral antennas are characterized in the radiation and system modes and conclusions regarding the effects of geometrical parameters such as number of arms, mode of operations, etc., on time- and frequency-domain performance are derived for the first time. A method based on controlling the spiral’s growth rate and input pulse shape is demonstrated as an effective approach to reduce the pulse distortion. Theoretical pre-distortion compensation method based on a frequency-dependent delay removal technique is employed and performance enhancement of spiral antennas as pulse radiators is successfully demonstrated. A novel spiral antenna topology, named combined power spiral, is derived from first principles to have simultaneously excellent time- and frequency-domain performances without any auxiliary hardware and/or pre-distortion compensation. The role of the reflective cavity backing on the performance of spiral antennas in time and frequency domains is investigated in order to achieve an efficient unidirectional UWB radiation. Resistively-loaded cavity-backed spirals are designed as a compromise for achieving simultaneously good time and frequency domain performances while maintaining high efficiency over the most of operating bandwidth. The lens loading approach is used as a way to further improve the spiral’s gain and reduce the amplitude distortion associated with a typical communication channel. UWB spiral arrays based on the derived good time/frequency two- and four-arm spiral antennas are developed and analyzed in time and frequency domains. Multi-mode capabilities of four-arm spirals are used to engineer a dual-circularly polarized array embodiment. To make these arrays practically more desirable, novel feeding scheme which significantly reduces the beamformer complexity is proposed. Time and frequency scanning capabilities and the advantages of the proposed arrays for UWB communications are also discussed. The results of this thesis can pave the way for the use of spiral antennas in many non-traditional, for spiral antennas, applications across commercial and military sectors

Ultra-Wideband Antenna

No abstract available

Antenna design for ultra wideband radio

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, June 2004."May 2004."Includes bibliographical references (p. 108-109).The recent allocation of the 3.1-10.6 GHz spectrum by the Federal Communications Commission (FCC) for Ultra Wideband (UWB) radio applications has presented a myriad of exciting opportunities and challenges for design in the communications arena, including antenna design. Ultra Wideband Radio requires operating bandwidths up to greater than 100% of the center frequency. Successful transmission and reception of an Ultra Wideband pulse that occupies the entire 3.1-10.6 GHz spectrum require an antenna that has linear phase, low dispersion and VSWR [< or =] 2 throughout the entire band. Linear phase and low dispersion ensure low values of group delay, which is imperative for transmitting and receiving a pulse with minimal distortion. VSWR [< or =] 2 is required for proper impedance matching throughout the band, ensuring at least 90% total power radiation. Compatibility with an integrated circuit also requires an unobtrusive, electrically small design. The focus of this thesis is to develop an antenna for the UWB 3.1-10.6 GHz band that achieves a physically compact, planar profile, sufficient impedance bandwidth, high radiation pattern and near omnidirectional radiation pattern.by Johnna Powell.S.M

Broadband nested antenna

This thesis investigates a novel dual frequency range low profile antenna system containing two nested spiral antennas operating over 2 – 18 GHz and 30 – 40 GHz respectively. The exploration and development of a broadband microstrip spiral without cavity backing has been implemented in the range of 2 - 18 GHz. The relationship between the structural parameters of equiangular spirals and their performance is investigated by simulating a variety of spiral structures. The input impedance, gain, axial ratio and radiation patterns of spiral antennas on a grounded dielectric substrate are compared with that of a spiral in free space to demonstrate the shortcomings of such a structure (i.e. narrow impedance bandwidth and poor gain). An effective way to achieve a broad bandwidth is proposed by introducing an impedance profile to remove the residual current along the spiral arms. Initially a Thin Film Resistive Layer (TFRL) was incorporated into a microstrip equiangular spiral antenna to absorb the residual current along the arms. Four spiral antennas with TFRLs of different thickness were developed to explore the TFRL application technique. Measured results and the difficulties in both simulation and fabrication experienced are demonstrated, analysed and addressed. An alternative to the use of a TFRL as an impedance profile on microstrip spirals, an exploration of spirals with embedded chip resistors had been conducted. The radiation physics of microstrip equiangular spirals are examined in the time domain using the XFDTD simulation package. XFDTD is used to analyse the current density distribution on the spiral arms under the excitation of pulse and harmonic waves. An analysis of the current density distribution at steady state provides guidelines for arranging the chip resistors efficiently. Chip resistor loading rules have been developed from these outcomes. A two dual arm equiangular spiral antennas with embedded chip resistors has been simulated, fabricated and measured. The antenna has a compact tapered balun which is horizontally placed inside the spiral antenna substrate to reduce the volume of the completed spiral/feed structure. The spiral with embedded chip resistors and a compact balun is selected as the low frequency element (2 – 18 GHz) for a nested antenna system. A dual arm Archimedean spiral antenna with cavity backing (operating over 30 – 40 GHz) is developed to be nested within the aperture of the low frequency spiral. The high frequency antenna was integrated into the substrate of the low frequency element, in the opening between the spiral arms. An Electronic Band Gap (EBG) architecture was applied to the rim of the nested antenna substrate to mitigate the consequences of surface waves. The entire nested antenna system was fabricated and measured, and the results are presented and discussed

DEVELOPMENT OF AN UWB RADAR SYSTEM

An ultra-wideband radar system is built at the University of Tennessee with the goal to develop a ground penetrating radar (GPR). The radar is required to transmit and receive a very narrow pulse signal in the time domain. The bistatic radar transmits a pulse through an ultrawide spiral antenna and receives the pulse by a similar antenna. Direct sampling is used to improve the performance of the impulse radar allowing up to 1.5 GHz of bandwidth to be used for signal processing and target detection with high resolution. Using direct sampling offers a less complex system design than traditional lower sample rate, super-heterodyne systems using continuous wave or step frequency methods while offering faster results than conventional equivalent time sampling techniques that require multiple data sets and significant post-processing. These two points are particularly important for a system that may be used in the field in potentially dangerous environments. Direct sampling radar systems, while still frequency limited, are continually improving their upper frequencies boundaries due to more power efficient, higher sampling rate analog to digital converters (ADCs) which relates directly to better subsurface resolution for potential target detection

A Compact Parallel-plane Perpendicular-current Feed for a Modified Equiangular Spiral Antenna and Related Circuits

This work describes the design and measurement of a compact bidirectional ultrawideband (UWB) modified equiangular spiral antenna with an integrated feed internally matched to a 50-Ohm microstrip transmission line. A UWB transition from microstrip to double-sided parallel-strip line (DSPSL) soldered to a short (1.14 mm) twin-line transmission line feeds the spiral. The currents on the feed travel in a direction approximately perpendicular to the direction of the currents on the spiral at the points where the feed passes the spiral in close proximity (0.57 mm). Holes were etched from the metal arms of the spiral to reduce the impedance mismatch caused by coupling between the transmission line feed and the spiral. This work also describes a low-loss back-to-back transition from coaxial line to DSPSL, an in-phase connectorized 3 dB DSPSL power divider made using three of those transitions, a 2:1 in-phase DSPSL power divider, a 3:1 in-phase DSPSL power divider, a radial dipole fed by DSPSL, an array of those dipoles utilizing the various power dividers, and a UWB circular monopole antenna fed by DSPSL. Measured and simulated results show good agreement for the designed antennas and circuits