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

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

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

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

B-Pol: Detecting Primordial Gravitational Waves Generated During Inflation

B-Pol is a medium-class space mission aimed at detecting the primordial gravitational waves generated during inflation through high accuracy measurements of the Cosmic Microwave Background (CMB) polarization. We discuss the scientific background, feasibility of the experiment, and implementation developed in response to the ESA Cosmic Vision 2015-2025 Call for Proposals.Comment: Experimental Astronomy - The original publication is available at http://www.springerlink.co

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

The Large-Scale Polarization Explorer (LSPE)

The LSPE is a balloon-borne mission aimed at measuring the polarization of the Cosmic Microwave Background (CMB) at large angular scales, and in particular to constrain the curl component of CMB polarization (B-modes) produced by tensor perturbations generated during cosmic inflation, in the very early universe. Its primary target is to improve the limit on the ratio of tensor to scalar perturbations amplitudes down to r = 0.03, at 99.7% confidence. A second target is to produce wide maps of foreground polarization generated in our Galaxy by synchrotron emission and interstellar dust emission. These will be important to map Galactic magnetic fields and to study the properties of ionized gas and of diffuse interstellar dust in our Galaxy. The mission is optimized for large angular scales, with coarse angular resolution (around 1.5 degrees FWHM), and wide sky coverage (25% of the sky). The payload will fly in a circumpolar long duration balloon mission during the polar night. Using the Earth as a giant solar shield, the instrument will spin in azimuth, observing a large fraction of the northern sky. The payload will host two instruments. An array of coherent polarimeters using cryogenic HEMT amplifiers will survey the sky at 43 and 90 GHz. An array of bolometric polarimeters, using large throughput multi-mode bolometers and rotating Half Wave Plates (HWP), will survey the same sky region in three bands at 95, 145 and 245 GHz. The wide frequency coverage will allow optimal control of the polarized foregrounds, with comparable angular resolution at all frequencies.Comment: In press. Copyright 2012 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibite

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

The UAV-based test source as an end-to-end verification tool for aperture arrays

A UAV-mounted radio-frequency transmitter is proposed as a known reference field source to perform a set of functional tests on aperture arrays. The experimental results obtained on complete prototypes (end-to-end) and sub-assemblies provide good confidence on both amplitude and timing verification