Advanced Techniques for VNA Characterization of Millimetre-Wave Orthomode Transducers (OMTs)

We report on advanced techniques for the characterization of millimeter-wave orthomode transducers (OMTs). These techniques include standard mm-wave frequency-domain VNA (Vector Network Analyser) measurement and time-domain methods, which can be applied to remove the effects of the waveguide transitions necessary to access the OMT ports and excite the desired modes. First, we present the main parameters of the OMT by defining its general S-matrix and discuss the different methods that allow characterizing the insertion loss, the reflection, the cross-polarization and the isolation of the device. Advantages and disadvantages of each method are presented and compared between them. We provide a list of waveguide components necessary in the various OMT test setups (adapters, loads, quarter-wave and longer waveguide sections, feed-horn, etc.). Different OMT configurations, with distinct orientation of the waveguide input and outputs are discussed. Alternative characterization methods of the OMT parameters are presented and the associated setups discussed. Although the presented techniques refer to the characterization of a specific configuration of a W-band (3 mm wavelength) OMT, the described method can be applied to other OMT configurations and frequency ranges (from microwave to THz frequencies), therefore having a general validity

A waveguide cavity 180° hybrid coupler with coaxial ports

We describe the design, construction, and performance of a 180° hybrid coupler for the frequency band 1.3-1.8 GHz (L-band). The hybrid utilizes a WR650 rectangular waveguide cavity and has three 50 Ω, coaxial ports. The signals are coupled in and out of the cavity through broadband coaxial probes attached to 7/16-type connectors. The measured performances are in excellent agreement with the electromagnetic simulations. © 2009 Wiley Periodicals, Inc

Preface to the special section on “Radio astronomy: A continuous demand for breakthrough technology”

Radio astronomy is a relatively young science: about an average human lifetime has passed since Karl Jansky’s measurement campaign took place at Holmdel, New Jersey, in the early 1930s, now celebrated as the birth date of radio astronomy. Most people working in the field today can claim to have personally known the pioneers in their countries. In the case of Italy, one such pioneer was Gianni Tofani, who passed away in February 2015. He fully devoted his professional life to scientific and technological research in astrophysics, mainly from the wonderful Arcetri hill of his beloved city, Florence. Furthermore, his management style was highly respected, bringing him to hold leadership positions such as the Director of the Institute of Radio Astronomy

Ricevitore multifeed banda 33-50GHz: stima delle prestazioni stand alone e con il collegamento fibra ottica

Nel presente rapporto vengono descritte le prestazioni simulate del ricevitore multifeed 19 beam operante nella banda 33-50 GHz (Q-band) da installare su SRT

Optimisation of the LFI Edge Taper values. I. FH #3 and #9 Main Beam and Full Pattern Simulations w/o Shields

This technical note describes preliminary electromagnetic simulations performed on the LFI feed horns (FH) #3 and #9 coupled to the Planck telescope, with the aim of optimising the LFI Edge Taper (ET). The ET optimisation is mandatory to reach the LFI angular resolution requirement, and possibly the goal, preserving at the same time the needed straylight rejection. The analysis is carried out at 100 GHz, where the scientific benefit of gaining angular resolution is most important. Five different FH designs have been considered: the FH #3 and #9 Qualification Model (QM) designs, and FH designs denoted with #3A, #9A, and #9B, which have been specifically designed with an edge taper that leads to an angular resolution of 12’, 10’, and 9.5’, respectively, when Gaussian feed models are considered. For FH horn design the main beam and the full pattern have been computed. The effect of shields has not been considered here, and will be the subject of a forthcoming note

INAF/JPL LNAs: VNA WARM TEST. As Run Procedure and Results.

INAF/JPL LNAs will be implemented as a part of the B2+3 WTB (Warm Test Baseplate)to amplify the signal coming from the OMT: the signal is expected to be amplified by roughly 40 dB before being delivered to a downconverter. This is obtained using two cascaded LNAs. LNAs have been designed to be used in the nominal W band [75 GHz: 110 GHz],originally furnished with a filter peaked around 94 GHz and a square law detector. Nevertheless, we want to test the LNAs in the extended B2+3 band between 67 GHz and 116 GHz

Estimates of system noise temperature in W-band at SRT and effects of beam truncation due to the Gregorian radome

We report on system noise temperature estimates from the SRT site in W-band (70-116 GHz) based on recorded atmospheric data at four specific days, three-months apart, in the period 15 Oct. 2019-15 July 2020. The estimates are based on the atmospheric model described in [1] and on the feed-horn beams model and receiver noise specification of the W-band multibeam receiver being built for the Gregorian focus of the SRT. We used different values for the antenna forward efficiency ηf to estimate the impact of such parameter on overall system noise Tsys. The beam truncation due to the 1 m diameter SRT Gregorian focus radome, which protects the receiver cabin from the atmospheric agents, is evaluated assuming that the cabin surrounding the radome contributes with a 293 K thermal noise (greater than the sky noise). The beams from the W-band receiver will be slightly truncated by the radome, especially at the lowest frequencies, where the beams are larger. We conclude that the effects of truncation on Tsys are negligible even in the scenario of lowest thermal emission from the sky, expected during winter season. The estimated seasonal variations of the atmospheric conditions at the SRT show that, for the four specific days for which the system noise temperature was calculated, the Tsys have broad minima near the 3 mm band atmospheric window, around 85-105 GHz and achieves values of order 100 K or lower during winter. The system noise increases towards the W-band receiver band edges at 70 GHz and 116 GHz; the highest Tsys is obtained at the highest frequency of the band, 116 GHz, and reaches values beyond 200 K the 15th of October, 2019 and the 15th of July, 2020

Development Plan Study for Optimization and Production Engineering of Band 2+3 Prototype Components for ALMA Receivers INAF Mid Term Report

Scope of this document is to report the activity @ INAF in relation to the work of the collaboration agreement No.74288/16/8223/OSZ entitled ‘Band 2+3 Prototype Passive Components for ALMA Receiver’ for the Development Advanced Study for upgrades of the Atacama Large Millimeter / Submillimeter Array(ALMA). Specifically, this release covers the activities performed in agreement with the Statement of Work [AD2] from Kick-off to up to now and serve as activity report for the Mid Term Revie

Super-resolution with Toraldo pupils: analysis with electromagnetic numerical simulations

The concept of super-resolution refers to various methods for improving the angular resolution of an optical imaging system beyond the classical diffraction limit. In optical microscopy, several techniques have been developed with the aim of narrowing the central lobe of the illumination Point Spread Function (PSF). In Astronomy a few methods have been proposed to achieve reflector telescopes and antennas with resolution significantly better than the diffraction limit but, to our best knowledge, no working system is in operation. A possible practical approach consists of using the so-called "Toraldo Pupils" (TPs) or variable transmittance filters. These pupils were introduced by G. Toraldo di Francia in 1952,1 and consist of a series of discrete, concentric circular coronae providing specific optical transparency and dephasing in order to engineer the required PSF. The first successful laboratory test of TPs in the microwaves was achieved in 2003,2 and in the present work we build upon these initial measurements to perform electromagnetic (EM) numerical simulations of TPs, using a commercial full-wave software tool. These simulations were used to study various EM effects that can mask and/or affect the performance of the pupils and to analyze the near-field as well as the far-field response. Our EM analysis confirms that at 20 GHz the width of the central lobe in the far-field generated by a TP significantly decreases compared to a clear circular aperture with the same diameter