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This letter presents the design strategy and the experimental results on the Ku/Ka dual-band feed-horn developed within the Phase A/B1 study of the Copernicus imaging microwave radiometer, which is one of the new six expansion missions of the European Copernicus flagship program on Earth observation operating in five frequency channels. The radiometer requirements translate into a dense focal plane composed by compact and lightweight dual-band feed horns. The optimum illumination was derived in terms of Bloch waves and the applicability of piecewise-linear profile feed-horns for its synthesis in the case of two highly separated Ku--/Ka--frequency bands (1:1.95) was investigated. The presented feed-horn design was validated up to a technological readiness level of 6. The reported performances at antenna level for the complete Ku-/Ka-band feed cluster demonstrate the feasibility of dual-band smooth-wall feed-horns focal-planes meeting all the Earth observation requirements in terms of footprints, beam- and wide-beam efficiencies, and cross-polarization. [ABSTRACT FROM AUTHOR]

Additive manufacturing technologies have been increasingly applied to the development of radio frequency components in the past few years. Indeed, the free-form capability of these processes allows for the design of novel components, whose actual implementation through conventional machining is rather complex or even not possible. This paper describes a monolithic WR51 component integrating three radio frequency functionalities, namely, bending, twisting, and filtering. Three aluminum prototypes with different bending/twisting radii have been manufactured through the selective laser melting process. They exhibit a measured rejection higher than 60 dB in 17.5 and 21.2 GHz, and a measured return loss better than 20 dB in 12.5 and 15 GHz. Significant mass and envelope reductions (higher than 60% depending on the bending/twisting radius) with respect to the reference subsystem with distinct waveguide components are achieved. These results assess the effectiveness of 3-D metal printing in the miniaturization and integration of waveguide systems. [ABSTRACT FROM PUBLISHER]

In this paper we present the electromagnetic modeling and beam pattern measurements of a 16-elements ultra wideband sparse random test array for the low frequency instrument of the Square Kilometer Array telescope. We discuss the importance of a small array test platform for the development of technologies and techniques towards the final telescope, highlighting the most relevant aspects of its design. We also describe the electromagnetic simulations and modeling work as well as the embedded-element and array pattern measurements using an Unmanned Aerial Vehicle system. The latter are helpful both for the validation of the models and the design as well as for the future instrumental calibration of the telescope thanks to the stable, accurate and strong radio frequency signal transmitted by the UAV. At this stage of the design, these measurements have shown a general agreement between experimental results and numerical data and have revealed the localized effect of un-calibrated cable lengths in the inner side-lobes of the array pattern. [ABSTRACT FROM AUTHOR]

One of the most challenging aspects of the new-generation Low-Frequency Aperture Array (LFAA) radio telescopes is instrument calibration. The operational LOw-Frequency ARray (LOFAR) instrument and the future LFAA element of the Square Kilometre Array (SKA) require advanced calibration techniques to reach the expected outstanding performance. In this framework, a small array, called Medicina Array Demonstrator (MAD), has been designed and installed in Italy to provide a test bench for antenna characterization and calibration techniques based on a flying artificial test source. A radio-frequency tone is transmitted through a dipole antenna mounted on a micro Unmanned Aerial Vehicle (UAV) (hexacopter) and received by each element of the array. A modern digital FPGA-based back-end is responsible for both data-acquisition and data-reduction. A simple amplitude and phase equalization algorithm is exploited for array calibration owing to the high stability and accuracy of the developed artificial test source. Both the measured embedded element patterns and calibrated array patterns are found to be in good agreement with the simulated data. The successful measurement campaign has demonstrated that a UAV-mounted test source provides a means to accurately validate and calibrate the full-polarized response of an antenna/array in operating conditions, including consequently effects like mutual coupling between the array elements and contribution of the environment to the antenna patterns. A similar system can therefore find a future application in the SKA-LFAA context. [ABSTRACT FROM AUTHOR]

Radial transmission-line formalism is a generalization of Marcuvitz–Schwinger theory that permits to solve complex scattering problems in circular geometry. The formalism is exploited in this work for the analysis and design of ring loaded slots in circular waveguide whose applications span from microwave filters to mode converters. The scattering problem is formulated in terms of coupled magnetic field integral equations and solved using novel numerical schemes. The method is applied to study a choke flange and a stub filter in circular waveguide. A comparison with commercial software is reported to confirm the effectiveness of the approach. [ABSTRACT FROM AUTHOR]

A cavity-backed Vivaldi antenna is suggested as dual-polarization array element for the low-frequency instrument of the Square Kilometer Array (SKA) project. A design strategy aimed at maximizing the sensitivity for such an array element is described. As an example, an antenna was obtained, with a sensitivity higher than 10cm²/K in the operative bandwidth and in the 45° sky coverage angle, for each polarization. [ABSTRACT FROM AUTHOR]

A cavity-backed Vivaldi antenna is suggested as dual-polarization array element for the low-frequency instrument of the Square Kilometer Array (SKA) project. A design strategy aimed at maximizing the sensitivity for such an array element is described. As an example, an antenna was obtained, with a sensitivity higher than 10 cm²/K in the operative bandwidth and in the 45° sky coverage angle, for each polarization. [ABSTRACT FROM AUTHOR]

This study presents the design and experimental results of a wide-band passive antenna-feed system developed for the C-band dual-circular-polarisation receiver of the Sardinia radio telescope (SRT). The latter is a 64 m diameter shaped radio-telescope under construction designed to operate with high efficiency from 300 MHz to over 100 GHz. The developed C-band antenna-feed system exhibits very high performances in a 30% band centred at 6.7 GHz, for example the return loss at all electrical ports is higher than 30 dB and the cross-coupling between the two polarisations is lower than -34 dB. The design solutions of all the feed-system components such as marker injector, polariser, transitions and the ortho-mode transducer (OMT) are reported in the study. In particular, the novel architecture of the OMT that provides an isolation between the two rectangular ports better than 70 dB is described in close detail. Computed and experimental results regarding both the complete system and its sub-assemblies are reported and discussed. [ABSTRACT FROM AUTHOR]

The design of a broadband antenna feed system for the cylindrical offset parabolic reflector of the Italian Northern Cross radio telescope is described. Its operative frequency band spans from the Low Frequency Array (LOFAR) upper band, i.e. 120-240 MHz, to the present telescope operative band centered at 408 MHz. The proposed configuration consists of a linear array of gridded Vivaldi (tapered slot) radiators inside a wired subreflector. Numerical simulations have been carried out using both commercial software and a specialized Method-of-Moments approach. They show that the designed feed system provides both a good impedance matching and an efficient illumination of the main reflector in the overall frequency band. [ABSTRACT FROM AUTHOR]

Describes a reduced-order model for the optimized mode-matching computer-aided design of microwave waveguide components. Application of the Krylov subspace concept; Application of the singular-value-decomposition algorithm to the coupled integral equations solved by the mode-matching technique; Accuracy and numerical efficiency of the proposed model.

A W-band orthomode transducer has been designed for polarimeter clusters in dense focal planes. Its compact geometry, with aligned output ports, allows for a closely-spaced triangular-lattice arrangement. At these high frequencies, the platelet manufacturing strategy has been applied and verified experimentally on seven prototypes, showing reflection coefficients lower than -20 dB, insertion loss of about 0.25 dB and cross-coupling and isolation levels of -42 dB and 45 dB, respectively, in a 30% bandwidth. [ABSTRACT FROM PUBLISHER]

A waveguide polarizer exploiting two different phase shift phenomena is presented in this letter. Iris-type discontinuities are in fact introduced in a waveguide structure having different propagation constants for the two principal polarizations. In this way, the required 90 differential phase shift is obtained combining the iris phase shift with the waveguide one. Several operative conditions arise from the combination of the two contributions. This approach has been used to design a broadband waveguide polarizer for the C-band antenna feed system of the Sardinia radio telescope with -40 dB reflection coefficients and a -35 dB cross polarization level in a 30% bandwidth. [ABSTRACT FROM PUBLISHER]

Novel profiled irises for the design of waveguide polarizers are presented. The two degrees of freedom of their piecewise-circular profile allow one to better control the frequency behavior of the differential phase shift. Thanks to this feature, an optimum iris set can be found by selecting the discontinuities for which the differential-phase-shift deviation from the average value is minimum in the operative bandwidth. This optimum iris set can be identified for several values of the ratio r/lambda0, where r is the waveguide radius and lambda0 is the free-space wavelength at the central frequency. Hence, even if both the waveguide size and central frequency are assigned in the specifications, polarizers with a very low deviation from 90deg of the total differential phase shift can be designed. In this way, the number of waveguide transitions in the antenna feed system can be reduced and the effect of spurious higher-order-mode coupling can be minimized. A Ka-band polarizer in circular waveguide with piecewise-circular-profile irises is described, showing a return loss better than 55 dB and a phase error of about 0.9deg in a 10% bandwidth [ABSTRACT FROM PUBLISHER]

A new configuration of improved rectangular-waveguide bend for advanced millimeter-wave applications is presented. It consists of few lengths of constant-curvature bends, properly designed in order to obtain enhanced matching conditions, without matching elements. Comparisons between the proposed bends and the uniform ones are reported, showing that the formers exhibit a better return loss. Measurements on a Ka-band prototype, in its operative condition, and a worst-case analysis on a W-band design, confirm the high electrical performances also in presence of significant manufacturing uncertainties. [ABSTRACT FROM PUBLISHER]

Rectangular waveguide twists are components that provide an on-axis rotation of the transverse waveguide section. In this letter, a step twist configuration, obtained by the direct connection of rotated rectangular waveguide lengths, is considered. The advantages of this configuration are the easy manufacturing with tight control on the relative rotation angles and the reduction of the overall dimensions. By means of a full-wave synthesis approach various wide-band devices were designed and reported in the letter. In particular, a couple of 45° twists was manufactured and integrated in the Ka-band OMT realized for the SPOrt project. The experimental results match the excellent predicted data. [ABSTRACT FROM PUBLISHER]