Electromagnetic waves in loaded cylindrical structures : a radial transmission line approach

The motivation for developing the computational electromagnetic methods presented in this thesis is to model the radiation of leaky slotted coaxial cables (LCXs), which are used as distributed antennas in environments that are not readily accessible via conventional antenna substations, and to model ring cavities that act as circular waveguide ??lters. We employ circuit-based electromagnetic wave theory in the solution of guided-wave scattering problems. Here the term ¿guided wave¿ is actually to be interpreted loosely, since even free space can be viewed as a waveguide. Propagation in usual rectilinear waveguides is often phrased in literature in the language of transmission line theory. The theory of equivalent transmission lines has been contrived as a way to give physical insight into the mathematical method of separation of variables. This opens the way to the use of unconventional equivalent transmission lines, such as radial or angular ones. In this thesis we have focused on the concept of radial waveguide, a structure that has the radial direction as the direction of propagation, and that is possibly bounded by metal plates parallel to the coordinate surfaces. Unlike the traditional vector mode functions encountered in conventional waveguides, the radial transmission line concept is introduced in a component basis. Radial lines are peculiar, because they have an absolute origin and hence is not shift invariant. Nevertheless, using a suitable vector formalism, the usual circuit theory concepts can be still applied, including the de??nition of voltages and currents, impedances, propagators, scattering matrices, etc. The LCXs are standard coaxial cables from which, on the outer conductor, slots are cut in order to induce energy exchange between the interior of the cable and the surrounding external domain. These kinds of antennas are usually employed for indoor communications in places where the traditional antenna systems fail or their application and installation are problematic, such as in subways and tunnels. They are also used for security reasons, e.g., in outstations and airports, in order to con??ne the communications inside speci??c places. In particular, nowadays, there is an increasing interest in the application of this technology in the GSM and UMTS frequency bands. LCXs have been studied by several researchers in the past. The analysis techniques employed in these studies produce solutions, to a varying degree of accuracy, for the particular problem of the in??nite periodically slotted cable. The problem of junctions between closed and slotted cables has so far not been addressed. The periodically slotted LCXs considered in the literature suffers from poor ef??ciency in terms of percentage of incident power used for the radiation. Indeed, since the decay of the power inside the cable is exponential and the radiated ??eld decays along the cable length with the same law, the standard periodically slotted LCX requires a compromise between an almost constant level of power along the slotted cable length and minimum power at the end of the cable that is not employed for radiation. In the present thesis we have developed accurate and ef??cient modeling techniques, enabling us to analyze both periodic and aperiodic LCXs, as well as transitions between open and closed cables. The second type of devices of interest is a particular category of stop-band ??lters commonly used in antenna systems to isolate receivers from the signals produced by transmitters, internal or external to the system, and operating in adjacent frequency bands. The structure that we have analyzed presents advantages in terms of the radial and longitudinal dimensions, which allows for the high level of integration that is often essential for space applications. Due to the resonance behavior of the device, the commercial numerical codes require long computational times before suf??ciently accurate ??eld solutions are obtained. Our dedicated modeling method is much more ef??cient in attaining the required results, which has made it possible to produce several design examples. Our modeling techniques are based on the magnetic ??eld integral equation. The associated kernel is the Green's function of the structure, which is been computed in the spectral domain, using radial transmission line theory. The solution of the corresponding integral equation is obtained, for both problems, by the method of moments in the Galerkin form, using a suitable set of basis functions. The computation of the moments requires particular care. We have developed dedicated numerical techniques by which the numerical convergence is improved and the computation of the integrals is accelerated considerably. For LCXs, we have developed a design procedure based on tapering the geometrical dimensions of the slots in order to obtain an uniform radiation and to maximize the radiated power. Since a typical LCX consists of thousands of slots, one approaches practical limitations of integral equation techniques, as the dimension of the linear system resulting from the discretization of the integral equation increases with the number of slots. For this reason, we have augmented our approach to analyze LCXs in two alternative directions. One is based on the application of the Bloch wave approach, the other comprises an extension, for the electromagnetic problem under consideration, of the so-called eigencurrent approach, that was originally developed for linear arrays of patches. First, the Bloch wave approach is not standard in this case since the structure consists of two different regions, one is closed (the interior of the coaxial cable) the other is open (the unbounded exterior domain). We have employed a particular mathematical formalism to overcome this problem, viz., we have solved the junction problem between an closed cable and a slotted one using the mode matching technique. In the Bloch wave approach a LCX with any number of slots, all equal and equally spaced, can ef??ciently be analyzed. Second, the eigencurrent approach is a versatile two-step technique for modelling large compound structures. The ??rst step is to evaluate the eigenvalues and current eigenfunctions of the integral operator associated with a single slot. Subsequently, the pertaining eigencurrents act as global-domain basis functions for the slotted array. In the resulting equivalent linear system, the interaction between the slots is adequately described in terms of very few of these eigencurrents. We have applied this method for LCXs with slots of different geometric dimensions, and have observed a substantial reduction of computation times. For a LCX with a large but ??nite number of identical slots, it turns out that the dominant Bloch wave is the same as the one excited in the semi-in??nite case. When this so-called Forward wave reaches the junction between the slotted and unslotted cable, it gives rise to several re??ected Bloch waves that, upon scattering at the ??rst junction, couple only with the Forward wave. Further, we have observed that all the regressive Bloch waves have globally a negligible effect on the magnetic currents on the slots. Hence the ??eld propagating in the slotted region of the ??nite slotted cable is essentially a progressive wave. As regards the radiation properties of an in??nite LCX, a paradox arises. In practical LCX applications the receiver is always in the near-??eld region of the array, but in the far-??eld region of the majority of the slots. This is related to the in??nite length of a LCX. Application of the Poisson sum formula to the expression for the radiated ??eld emanating from a LCX converts that expression into a linear superposition of spatial harmonics, in line with the Bloch-wave de scription. As a consequence, cables with different slot spacings are perfectly explained in terms of the various modes of operation resulting from the Bloch-wave description, i.e., surface-wave, mono-radiation and multi-radiation operation

Accuracy of complex internal channels produced by laser powder bed fusion process

Additive manufacturing (AM) technology has great potential in manufacturing complex internal channels for several applications such as satellite-communication microwave systems. These systems can have complex shapes and make traditional finishing processes a challenge for additive parts. Therefore, it is desirable that the internal surfaces are as close as possible to the tolerance of the field of application. In this study, a complex component, a unique waveguide device with bending, twisting and filtering functionalities, has been designed and manufactured in AlSi10Mg alloy through laser powder bed fusion (L-PBF) process. Three different prototypes with three different curvature (R of 50 mm, 40 mm and 30 mm), operating in Ku/K band, have been manufactured and tested showing a very good agreement with the desired performances. Using 3D scan data, the internal deviations from the CAD model have been evaluated showing an average deviation of the internal areas of about 0.08 mm, 0.046 mm and 0.023 mm from the CAD model for the R of 50 mm, 40 mm and 30 mm respectively The surface roughness measured in the internal channel is about Ra (arithmetic average roughness) of 8 μm ± 1.3 μm and Rz (average maximum height of the roughness profile) of 62.3 μm ± 0.34 μm

Experimental research activity on additive manufacturing of microwave passive waveguide components

All metal passive waveguide components are key building-blocks of several RF systems used for telecommunications, navigation, imaging, radio-astronomy, and cosmology. The accurate manufacture of these devices in Additive Manufacturing (AM) technologies can open the way to a high integration level of microwave functionalities with a significant cost and mass reduction. In the paper, after an introduction on the most common AM technologies with particular detail on selective laser melting (SLM) and stereo-lithography apparatus (SLA) processes, the results on the on-going research activity are discussed. Measured performances are reported for AM prototypes of Ku/K/Ka-band rectangular and circular waveguide lines, microwave filters and a smooth wall horn

Additive Manufacturing Technology for High Performances Feed Horn

In this work the design and manufacturing through selective laser melting technology of single-band dual circular feed-system operating in Ka-band is reported. In the feed design an AM oriented architecture has been employed. The measured performances confirms the good manufacturing of the system that satisfies very stringent requirements in terms of polarization purity

The Role of Water in the Photocatalytic Degradation of Acetonitrile and Toluene in Gas-Solid and Liquid-Solid Regimes

Photocatalytic degradation of acetonitrile and toluene was carried out both in gas-solid and in liquid-solid regimes by using commercial TiO2 samples ( Merck and Degussa P25). The investigation was mainly aimed to study the influence of water present in the reaction environment on the mechanism and degradation rate of two probe molecules. In gas-solid regime, the reacting mixture consisted of toluene or acetonitrile, oxygen, nitrogen, and water vapour. The main degradation product of toluene was CO2 with small amounts of benzaldehyde. In the presence of water vapour, the activity of TiO2 Merck remained stable but greatly decreased if water was absent. TiO2 Degussa P25 continuously deactivated, even in the presence of water vapour. With both catalysts, the photodegradation products of acetonitrile were CO2 and HCN; the activity was stable and was independent of the presence of water vapour in the reacting mixture. The production of HCN represents a drawback of acetonitrile photocatalytic degradation but the elimination of HCN is not actually a problem. In liquid-solid regime, the main intermediates of toluene photodegradation were p-cresol and benzaldehyde; traces of pyrogallol and benzyl alcohol were also found. Benzoic acid, hydroquinone, and trans, trans muconic acid were detected only when TiO2 Merck was used. The photodegradation products of acetonitrile were cyanide, cyanate, formate, nitrate, and carbonate ions

Mitomycin-ifosfamide-cisplatinum (MIP) vs MIP-interferon vs cisplatinum-carboplatin in metastatic non-small-cell lung cancer: a FONICAP randomised phase II study. Italian Lung Cancer Task Force.

The FONICAP group is screening, with randomised phase II studies, the activity of new chemotherapy programmes for advanced non-small-cell lung cancer (NSCLC) looking for regimens with > 30% activity. In the present study, three regimens were tested: MIP (mitomycin 6 mg m-2, ifosfamide 3 g m-2, cisplatinum 80 mg m-2 on day 1 every 28 days); MIP-IFN (MIP and interferon alpha-2b 3 MU s.c. three times a week); and PC (cisplatinum 60 mg m-2 and carboplatin 400 mg m-2 on day 1 every 28 days). Overall 93 chemotherapy-naive patients were enrolled: 23 received MIP, 27 received MIP-IFN and 43 received PC. Eighty per cent of the patients had stage IV and 20% stage IIIb disease (positive pleural effusion or supraclavicular nodes). Response rates were as follows: MIP = 9% (95% CI 1-28%), MIP-IFN = 7% (95% CI 1-24%) and PC = 14% (95% CI 5-28%). The overall median survival was 183 days. Grade III-IV leucopenia was observed in 36% of patients treated with MIP-IFN vs 10% in the other two arms, and thrombocytopenia grade III-IV was reported in nearly 10% of patients overall. In conclusion, (1) all three regimens investigated have poor activity (< 30%); (2) when tested in multicentre randomised phase II trials, MIP displays lower activity than in phase II trials; (3) PC has similar activity to other platinum-containing regimens; (4) randomised phase II studies are a reliable and quick method of determining the anti-tumour activity of novel chemotherapeutic regimens in NSCLC

Characteristic Mode Analysis of Multi-Octave Asymmetric Dipoles

This paper discusses the impedance and front-to-back ratio performance of asymmetric dipoles. These parameters are very important when the antennas are placed over a conductive ground plane and should operate over multi-octave frequency bands. The operation of these antennas is usually described relying on analogies with more classical structures such as symmetric dipoles and tapered slot antennas. To provide a solid theoretical background to this intuition, this work presents the application of characteristic mode analysis to multi-octave dipole antennas. Firstly, a brief review of the main characteristic mode content is presented. Then, characteristic mode analysis is applied to three antenna concepts to emphasize how their geometry impacts on the relevant figures of merit. This allows to draw some conclusions on the achievable performance by different designs

Electromagnetic Design of Broadband Antenna Feed Systems for the Northern Cross Radio Telescope

This contribution deals with the design and implementation of broadband antenna feed systems for the cylindrical offset parabolic reflector of the Northern Cross radio telescope, in the framework of the Square Kilometer Array Design Study (SKADS-FP6) project. Such feed systems have to maintain a proper radiation pattern as well as a good matching condition in the operative frequency band (120-430 MHz) in order to efficiently feed the main reflector. This task is not trivial since more than octave bandwidths are required. Several feed system designs have been carried out on the basis of different architectures such as log periodic antenna arrays, linear arrays of fat dipoles and branched Vivaldi (tapered slot) radiators inside a wired subreflector. Each configuration provides a different trade-off between electrical performance and manufacturing complexity. The most significant computed and experimental results are discussed. Some of the proposed configurations have already been mounted on the Northern Cross Radio Telescope. The adopted mechanical and electronic solutions such as wiring, canalization, amplifier housing and protection are reported. A preliminary study on the application of Focal Plane Arrays on the E/W Arm is also discussed

A coherent polarimeter array for the Large Scale Polarization Explorer balloon experiment

We discuss the design and expected performance of STRIP (STRatospheric Italian Polarimeter), an array of coherent receivers designed to fly on board the LSPE (Large Scale Polarization Explorer) balloon experiment. The STRIP focal plane array comprises 49 elements in Q band and 7 elements in W-band using cryogenic HEMT low noise amplifiers and high performance waveguide components. In operation, the array will be cooled to 20 K and placed in the focal plane of a $\sim 0.6$ meter telescope providing an angular resolution of $\sim1.5$ degrees. The LSPE experiment aims at large scale, high sensitivity measurements of CMB polarization, with multi-frequency deep measurements to optimize component separation. The STRIP Q-band channel is crucial to accurately measure and remove the synchrotron polarized component, while the W-band channel, together with a bolometric channel at the same frequency, provides a crucial cross-check for systematic effects.Comment: In press on the Proceedings of the SPIE Conference Astronomical Telescopes + instrumentation 2012, Amsterdam, paper 8446-27