Dielectric Tubular Endfire Antennas for Industrial Radar Level Measurements: Analysis and Design
Seiten
2011
|
1., Aufl.
Shaker (Verlag)
978-3-8440-0414-4 (ISBN)
Shaker (Verlag)
978-3-8440-0414-4 (ISBN)
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This thesis concerns dielectric antenna design for monostatic radar operation as well as guided still pipe measurement techniques in electrically large tank-mounted metal tubes. The application is for the use in the field of industrial level gauging for process automation industry within the frequency range of 8.5 to 10.5 GHz. At first, Maxwell's theory for cylindrical hollow metallic waveguides as well as for dielectric rods with solid and tubular geometries is revisited in order to derive a combined analytical field approach. This approach aims to be valid for each type of waveguide being considered within this work by solely adapting the boundary conditions.
The antenna optimization starts with an intensive evaluation of the modal radiation properties of cylindrical dielectric waveguides for the purpose to design optimized traveling wave endfire antennas made of polytetrafluoroethylene (PTFE) and polypropylene (PP). Therefore, the theoretical directivity limits, particularly that of the hybrid non-cylindrical symmetric HE/EH eigenmodes in mono- and multimode configurations, are estimated analytically. Based on the eigenmode approach, the applicability of a commercially available state-of-the art 3D field simulator, that numerically solves Maxwell's equations based on the finite integration technique (FIT), is evaluated with regard to the accurate computation of infinitely extended dielectric mode distributions at finite solver domains.
By this means, dielectric and metallo-dielectric waveguide transitions can be separately analyzed from any parasitic influence of field disturbances, that are conventionally caused by feeding structures. This is important, because transitions of this kind are an integral part of optimized dielectric endfire antennas. In order to exploit the promising theoretical directivity limits of single-moded, thin-walled tubes of more than 20 dBi, two classes of mode-preserving waveguide transitions are optimized in particular: Metallo-dielectric waveguide transitions between circular metallic feeding waveguides and dielectric solid rods as well as purely dielectric waveguide transitions connecting these solid rods to thin dielectric endfire radiating tubes. Cascading these two types of transitions yields compact dielectric antennas, that exhibit a significant directivity improvement in comparison to a circular horn aperture having the same diameter as the outer dimensions of the radiating tube. In addition, a length reduction compared to traditional dielectric rod antennas is achieved.
Moreover, the impact of the antenna radiation properties on the monostatic radar system performance is fundamentally studied. Therefore, the theory of frequency modulated continuous wave (FMCW) radar systems for level gauging and their emulation through software and hardware are reviewed. An analytical model of traveling wave antennas is introduced, that is capable of independently varying single antenna parameters and thus allowing to study the individual parameter influence on the distance measurement accuracy. By this, antenna design criteria are systematically derived with respect to a submillimeter overall gauging accuracy and incorporated in the entire antenna optimization procedure consequently.
Finally, manufactured prototype antenna designs are presented and verified by measuring their transient pulse-based behavior and their radiation characteristics. By additionally using a compact radar test range, the accuracy increase, that ensures high-precision radar level measurements by applying these novel prototype antennas, is quantified.
In parallel, two contrary approaches for guided radar measurement techniques within large overmoded still pipes are investigated in this work in order to achieve a submillimeter gauging accuracy even in these applications. Within these applications, the measurement results are commonly degraded by multimode propagation and dispersion effects. After investigating the modal dispersion effects of circular metallic waveguides, the application of a novel mode-preserving waveguide transition as a still pipe excitation structure is firstly considered to ensure a defined modal field distribution inside the tube. This ideally consists of the propagation of the fundamental waveguide mode. In this case, unmodified "free-space" optimized pulse-barycentric signal processing algorithms can be applied.
Secondly, a paradigm shift leads to advanced correlation-based algorithms, which are capable of exploiting the intermodal dispersion, instead of considering it as a parasitic effect. The underlying idea is to evaluate the shape of multimode-distorted impulse responses in the time domain. Their energy spreads out in a unique way and so the shape of the pulse is unambiguously associated with every distinct reflector distance. In summary, both approaches presented in this thesis are revealed to be valid and are verified by measurements.
The antenna optimization starts with an intensive evaluation of the modal radiation properties of cylindrical dielectric waveguides for the purpose to design optimized traveling wave endfire antennas made of polytetrafluoroethylene (PTFE) and polypropylene (PP). Therefore, the theoretical directivity limits, particularly that of the hybrid non-cylindrical symmetric HE/EH eigenmodes in mono- and multimode configurations, are estimated analytically. Based on the eigenmode approach, the applicability of a commercially available state-of-the art 3D field simulator, that numerically solves Maxwell's equations based on the finite integration technique (FIT), is evaluated with regard to the accurate computation of infinitely extended dielectric mode distributions at finite solver domains.
By this means, dielectric and metallo-dielectric waveguide transitions can be separately analyzed from any parasitic influence of field disturbances, that are conventionally caused by feeding structures. This is important, because transitions of this kind are an integral part of optimized dielectric endfire antennas. In order to exploit the promising theoretical directivity limits of single-moded, thin-walled tubes of more than 20 dBi, two classes of mode-preserving waveguide transitions are optimized in particular: Metallo-dielectric waveguide transitions between circular metallic feeding waveguides and dielectric solid rods as well as purely dielectric waveguide transitions connecting these solid rods to thin dielectric endfire radiating tubes. Cascading these two types of transitions yields compact dielectric antennas, that exhibit a significant directivity improvement in comparison to a circular horn aperture having the same diameter as the outer dimensions of the radiating tube. In addition, a length reduction compared to traditional dielectric rod antennas is achieved.
Moreover, the impact of the antenna radiation properties on the monostatic radar system performance is fundamentally studied. Therefore, the theory of frequency modulated continuous wave (FMCW) radar systems for level gauging and their emulation through software and hardware are reviewed. An analytical model of traveling wave antennas is introduced, that is capable of independently varying single antenna parameters and thus allowing to study the individual parameter influence on the distance measurement accuracy. By this, antenna design criteria are systematically derived with respect to a submillimeter overall gauging accuracy and incorporated in the entire antenna optimization procedure consequently.
Finally, manufactured prototype antenna designs are presented and verified by measuring their transient pulse-based behavior and their radiation characteristics. By additionally using a compact radar test range, the accuracy increase, that ensures high-precision radar level measurements by applying these novel prototype antennas, is quantified.
In parallel, two contrary approaches for guided radar measurement techniques within large overmoded still pipes are investigated in this work in order to achieve a submillimeter gauging accuracy even in these applications. Within these applications, the measurement results are commonly degraded by multimode propagation and dispersion effects. After investigating the modal dispersion effects of circular metallic waveguides, the application of a novel mode-preserving waveguide transition as a still pipe excitation structure is firstly considered to ensure a defined modal field distribution inside the tube. This ideally consists of the propagation of the fundamental waveguide mode. In this case, unmodified "free-space" optimized pulse-barycentric signal processing algorithms can be applied.
Secondly, a paradigm shift leads to advanced correlation-based algorithms, which are capable of exploiting the intermodal dispersion, instead of considering it as a parasitic effect. The underlying idea is to evaluate the shape of multimode-distorted impulse responses in the time domain. Their energy spreads out in a unique way and so the shape of the pulse is unambiguously associated with every distinct reflector distance. In summary, both approaches presented in this thesis are revealed to be valid and are verified by measurements.
| Reihe/Serie | Berichte aus der Hochfrequenztechnik |
|---|---|
| Sprache | englisch |
| Maße | 148 x 210 mm |
| Gewicht | 362 g |
| Einbandart | Paperback |
| Themenwelt | Technik ► Elektrotechnik / Energietechnik |
| Schlagworte | dielectric antennas • Industrial radar level gauging • radar distance measurement • radar signal processing • radar system simulation |
| ISBN-10 | 3-8440-0414-9 / 3844004149 |
| ISBN-13 | 978-3-8440-0414-4 / 9783844004144 |
| Zustand | Neuware |
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