Dielectrically Loaded Quad-Ridge Flared Horn for Beamwidth Control Over Decade Bandwidth-Optimization, Manufacture, and Measurement

We present the design, manufacture, and measured performance of a dielectrically loaded quad-ridge flared horn (QRFH) feed for decade bandwidth radio astronomy application. The introduction of the dielectric load improves the QRFH beamwidth control in H-plane at the mid and upper frequency range. Consequently on the reflector, illumination efficiency, phase efficiency, and the intrinsic cross-polarization ratio (IXR) have been improved. The dielectric load is made from homogeneous low-loss polytetrafluoroethylene and has a low profile with a cylinder shape for simple installation at the center of the QRFH. The dielectrically loaded QRFH presented here covers 1.5-15.5 GHz with a calculated average aperture efficiency above 50% on a f/D = 0.3 prime-focus reflector. We present a calculation of system noise temperature and sensitivity for the QRFH on a 100 m prime-focus reflector. Measured beam patterns of the QRFH are in good agreement with the simulations over the full frequency band. The input reflection coefficient was predicted to be below -10 dB across the bandwidth. We present a tolerance analysis that explains why the measured one deviates

Circular Eleven Feed with Significantly Improved BOR1 and Aperture Efficiency Over 1.3-14 GHz

A new decade bandwidth circular Eleven feed for future radio telescope projects has been developed, with a significantly improved BOR 1 efficiency (therefore aperture efficiency). This Eleven feed is constructed of "circularly" curved folded dipoles on a flat printed circuit board (PCB), with the aim to make this antenna structure more rotationally symmetrical at a very low manufacture cost. The simulated results show that the BOR 1 efficiency of the circular Eleven feed achieves better than 1 dB over a decade bandwidth of 1.3-14 GHz, which is considered as a significant improvement for decade-bandwidth feed technology

Compact dual-polarized 1.2 - 10 GHz eleven feed by folding outer elements for large decade-bandwidth radio telescopes

The Eleven antenna is a log-periodic folded-dipole-pair array which has two unique radiation characteristics: constant beamwidth and fixed phase center location over decade bandwidth. Therefore, the Eleven antenna is very suitable as a feed for reflector antennas. This paper presents a new compact design of 1.2 - 10 GHz Eleven antenna by folding down the outermost elements of the array. By doing so, it is possible to put the Eleven feed inside a compact cryostat, which is critical for applications in radio telescopes. The new compacted Eleven antenna has only 40% volume of the original standard Eleven antenna with similar performance. Simulations and measurements have verified the design and are presented in the paper

The Circular Eleven Antenna: A New Decade-Bandwidth Feed for Reflector Antennas With High Aperture Efficiency

Future ultra-wideband (UWB) radio telescopes require UWB feeds for reflector antennas, and many new UWB feed technologies have gained substantial progress to satisfy the tough specifications for future radio telescope projects, such as the square kilometer array (SKA). It has been noticed that, different from traditional narrow-band horn feeds, all UWB feeds are non-BOR (Body of Revolution) antennas. Therefore BOR1, efficiency becomes an important characterization for the modern UWB feed technologies. We present a novel circular Eleven feed, constructed of "circularly" curved folded dipoles printed on flat circuit boards, in order to have high BOR1 efficiency at a low manufacture cost. The Genetic Algorithm (GA) optimization scheme has been applied to the design for achieving a low reflection coefficient. Simulated and measured results show that the circular Eleven feed has a reflection coefficient below -6 dB over 1.6-14 GHz and below -10 dB over 78% of the band, and an aperture efficiency higher than 60% over 1-10 GHz and 50% up to 14 GHz

Development of a Compact Eleven Feed Cryostat for the Patriot 12-m Antenna System

The Eleven antenna has constant beam width, constant phase center location, and low spillover over a decade bandwidth. Therefore, it can feed a reflector for high aperture efficiency (also called feed efficiency). It is equally important that the feed efficiency and its subefficiencies not be degraded significantly by installing the feed in a cryostat. The MIT Haystack Observatory, with guidance from Onsala Space Observatory and Chalmers University, has been working to integrate the Eleven antenna into a compact cryostat suitable for the Patriot 12-m antenna. Since the analysis of the feed efficiencies in this presentation is purely computational, we first demonstrate the validity of the computed results by comparing them to measurements. Subsequently, we analyze the dependence of the cryostat size on the feed efficiencies, and, lastly, the Patriot 12-m subreflector is incorporated into the computational model to assess the overall broadband efficiency of the antenna system

Development of a detailed system model of the Eleven feed receiver using the CAESAR software

A mathematically general method is presented for exporting the far-field patterns, radiation efficiency and impedance data, for multi-port antennas, from EM solvers to the microwave circuit simulator of the CAESAR software in order to perform the analysis of a multi-port antenna-receiver system. This hybrid modelling approach offers a few important advantages over the early developed modelling methods and standard simulation tools; including the capability to predict the correlated noise contributions due to both internal and external noise sources, while exploiting the translation/rotation symmetry of the antenna structure to reduce computation time. This approach is validated using folded dipole antennas and applied to model a more complex antenna-receiver system the Eleven antenna feed operating from 2 to 12 GHz which consists of four log-periodic dipole arrays co-integrated with LNAs, a balun and hybrid combining network. The Eleven feed receiver model is verified by comparing the simulation results with the measurements performed with a practical system

Design trade-offs in feed systems for ultra-wideband VLBI observations

Due to the advanced capability of today’s ultra-wideband feed systems and low-noise amplifiers, interesting upgrades for future VLBI receiver and tele- scope design should be considered. Multiple input pa- rameters need to be taken into account for optimal sensitivity and applications of the future astronomical and geodetic observational systems. In this paper we present an overview of some trade-offs for wideband systems between SEFD, bandwidth and telescope re- flector optics. We evaluate receiver bandwidths from 3.5:1 to 10.3:1 bandwidth within the frequency range 1.5-24 GHz in different configurations. Due to poten- tial RFI-pollution of the lower frequencies we present potential feed upgrades for the most common reflector geometries ofVGOS and EVN telescopes that mitigate this problem. The results of this work is relevant for fu- ture VLBI stations and telescope design in general. Keyword

Integrated calibration noise coupler for room temperature SKA band 1 feed system

This paper presents design of a novel coupler for the injection of calibration signal into the RF path of the SKA Band 1 quad-ridged flared horn, covering frequencies from 350–1050 MHz. The coupler is integrated in the feed horn and provides a coupling factor of −35 dB. The calibration signal is injected before the first amplification stage, without any degradation in the noise performance of the room temperature system

A Compact Dual-Polarized 4-Port Eleven Feed with High Sensitivity for Reflectors over 0.35-1.05 GHz

We present significant improvements to the circular Eleven feed technology for a dual-reflector system operating over 0.35-1.05 GHz as a backup for the square kilometer array (SKA) project Band 1. In this work, the number of the feed ports is reduced to 4 from the previous 8 for dual polarization using a novel geometry at the center. The design is carried out by optimizing with a social civilization algorithm. The resulting improvements include a reflection coefficient below -12dB, an aperture efficiency above 70% at the upper end of the band, a maximum cross-polar level under -15dB, and an ohmic loss about 0.05 dB. A prototype based on this design has been manufactured and the design simulations have been verified against measurements. A simulated sensitivity of the dual-reflector receiver system for the SKA project based on the measured data is also presented in this communication

Optimization and Realization of Quadruple-ridge Flared Horn with New Spline-defined Profiles as a High-efficiency Feed over 4.6–24 GHz

In this paper, we present a new optimization and realization of a quadruple-ridge flared horn (QRFH) as a feed for reflector antennas of the Square Kilometre Array (SKA) project. The QRFH has been numerically optimized by spline-defined profiles for both the ridges and the horn sidewall, with a conical cavity in the back-short for maximum aperture efficiency. The final aperture efficiency better than (for horizontal polarization) or around (for vertical polarization) 78% over 4.6–8 GHz, 70% over 8–15 GHz, 65% over 15–20 GHz and 60% over 20–24 GHz in the SKA offset-Gregorian dual-reflector antenna has been achieved. The realization of the horn has been carried out carefully by applying several new mechanical design solutions in order to guarantee the accurate positioning of the ridges, the feeding pins and a good electrical contact. The measured S11 is mostly better than -10 dB and the predicted aperture efficiency based on the measured far field patterns agrees well with the simulated result. System performance, such as the sensitivity and system noise temperature, are also estimated and presented