The feasibility of using a generic Phased Array Feed (PAF) for the radio telescopes within the European VLBI Network (EVN) is explored. Taking into consideration the variations in size (14 m - 100 m) and primary focal distance to diameter ratios f/D(0.3-0.5) of the EVN reflectors, the achievable aperture efficiency of a generic array feed is investigated. For the scan range of 0 degrees -5 degrees, a parametric study based on encircled power is performed to find the optimum location, shape and size of the array. It is concluded that for a generic PAF design, the smallest f/D ratio decides the required array size for a certain aperture efficiency and scan angle. A spherical array with specific radius of curvature and displacement from the focus is found to achieve 80% aperture efficiency with smaller size, both in terms of radius projected onto the focal plane and surface area, than a planar array placed in the focal plane.

This paper concerns the parameters, simulations and techniques involved in designing an active antenna system for detection of global 21cm-signals originating from the Dark Ages at the Lunar far side. A 10.5 m diameter equiangular spiral plate antenna is fashioned to operate from 10 to 70 MHz whilst maintaining a virtually frequency-independent impedance characteristic and radiation pattern. Combined with the stable and low noise performance of the measured PHA-13LN+ amplifier evaluation board, the simulations show that the full active antenna system is well suited to the science objective of this paper.

Low noise receivers play an essential role in wireless systems in radio astronomy and 5G/6G applications. Especially in radioastronomy, the received signal strength is very weak. Therefore, maintaining a good Signal-to-Noise Ratio (SNR) is quite important. A known concept to reduce the system noise temperature is to use noise matching for the Low-Noise Amplifier (LNA) and the antenna to get the optimal SNR. Due to the integrated nature of these systems, it is challenging to measure the noise performance of the total system accurately. For example, existing methods such as the Radiometric or the G/T method can be sensitive to inaccuracies due to the dependency on the sky noise temperature, the radiation pattern of the antenna, or the size of the antenna [1, 2]. Therefore we developed a new method, which can estimate the Noise Figure (NF) of a wireless system over-the-air (OTA), independent of these factors. The new method uses the Reverberation Chamber (RC) to create a consistent and repeatable environment. The uniform behavior of the RC makes the method independent of the radiation pattern of the antenna. This method measures the integrated antenna as one system, so the efficiency of the antenna, the NF of the LNA, and the noise matching between the Antenna and LNA are all taken into account.

Until now the LOFAR (LOw Frequency ARray) radio telescope in the Netherlands used a simple beam model with identical element patterns to calibrate the array (assuming no mutual coupling). To improve the accuracy of the calibration, work has been set in motion to improve the beam model by full-wave electromagnetic simulations. This paper reports the initial commissioning results.

This paper describes the use of spherical wave expansion (SWE) to model the embedded element patterns of the LOFAR low-band array. The goal is to reduce the amount of data needed to store the embedded element patterns. The coefficients are calculated using the Moore–Penrose pseudoinverse. The Fast Fourier Transform (FFT) is used to interpolate the coefficients in the frequency domain. It turned out that the embedded element patterns can be described by only 41.8% of the data needed to describe them directly if sampled at the Nyquist rate. The presented results show that a frequency resolution of 1 MHz is needed for proper interpolation of the spherical wave coefficients over the 80 MHz operating frequency band of the LOFAR low-band array. It is also shown that the error due to interpolation using the FFT is less than the error due to linear interpolation or cubic spline interpolation.

For square kilometer array (SKA) mid-frequency aperture arrays, dense connected aperture arrays such as Vivaldi antenna arrays are being considered, but to achieve the required system sensitivity for radio astronomical observations, this would mean a large number of antenna elements particularly in the order of millions. Two concepts of regular-on-grid and irregular-on-grid sparse array configuration are introduced for these connected arrays to reduce the number of antenna elements and the sensitivity performance of the two concept arrays is compared. Comparing the effective area of these two configurations, it is shown that a regular-on-grid sparse configuration achieves slightly larger effective area than an equivalent irregular-on-grid sparse configuration. Using the regular-on-grid sparse configuration as a case study, the effect that terminating impedance of the inactive antennas has on the receiver noise temperature of a connected array of Vivaldi antennas is investigated.

The Netherlands China Low-frequency Explorer (NCLE) is a scientific payload hosted on the Chang'e 4 relay satellite, part of the Chinese Lunar Exploration Program. It is a pathfinder for a low frequency Moon-based interferometer for frequencies between 80 kHz and 80 MHz. The antenna of NCLE consists of three monopoles with a length of 5 meter. Each pair of monopoles can be configured as a dipole. This will be done in the digital domain. In this paper the design considerations taken into account during the development of the NCLE antenna system will be presented. Furthermore the sensitivity and polarimetric performance achieved over the operating frequency band of the NCLE antenna system are shown and design considerations for future space-based low-frequency radio telescopes will be discussed.

We describe the simulation of a dense, connected array of Vivaldi antennas serving a demonstrator for the Mid-Frequency Aperture Array. Four connected antenna elements are designed and simulated to form the main Unit Cell of the array. Different sizes of arrays are studied, up to 12×12 elements corresponding to a tile of the demonstrator. The technique used is the Array Scanning Method with additional Macro Basis Functions. Ultimately this simulation strategy will enable the simulation of disconnected tiles of dense, connected Vivaldi antenna arrays.

The methodology followed to model the signals coupled into the analog signal path of the Netherlands-China Low-frequency Explorer due to electromagnetic interference produced by the Chang'e-4 satellite is presented. Results indicate interfering signals at frequencies below 1 MHz pose the highest risk to drive the first stage amplifiers into their non-linear region. This paper subsequently describes mitigation measures to meet this challenge.

A simple, inexpensive, fully integrated low-noise amplifier and antenna for the Square Kilometer Array (SKA) Mid-Frequency Aperture Array (MFAA) is presented which achieves a receiver noise figure of about 0.4 dB over more than an octave bandwidth. A novel design technique was used which makes it easy to match the antenna directly to the first amplification transistors, without using an impedance matching circuit, thereby achieving a noise figure close to the minimum noise figure of the transistors used. The receiver also demonstrates how a single-ended amplifier with a floating ground can be used for a differential, planar antenna, by using a balun on the output of the amplifier. These receivers can be used stand-alone in a sparce, irregular array or closely packed in a dense, regular array or in a mixed system, making it possible to investigate various array configurations for the SKA MFAA.

A numerical study on beam-steering arrays of multi-mode antenna (MMA) elements is presented. Each MMA is capable of supporting multiple orthogonal modes (e.g. differential and common modes) to increase the beam coverage or angular diversity of the array antenna. The goal is to investigate how the performance of such MMAs in terms of maximum scan range and bandwidth is modified by the array mutual coupling environment, in particular for dense regular arrays of connected MMA elements with an element spacing smaller than half wavelength. The final results for sparse irregular arrays are presented and considered to be the favorable array environment.

This paper accentuates the similarity in the requirements of the radiation characteristics of antenna elements used in directive beam-steering arrays for radio astronomy and wireless communication systems, i.e. aperture phased array radio telescopes and base transceiver stations. Using two reference antenna elements the equivalence between two beamforming strategies commonly implemented in wireless communication and radio astronomy systems is illustrated. For the case of maximum power receivers it is demonstrated that the methodology followed to assess and characterize the performance of an antenna element in wireless communication systems can readily be implemented to compare the field-of-view (FoV) coverage of antenna elements in radio astronomy applications. Finally, using an ideal reference element, it is shown that a single figure-of-merit - field-of-view coverage gain - can be used to compare the performance of antenna elements over an entire field-of-view coverage.

A conical quad-mode antenna excited through four orthogonal transverse electromagnetic modes is presented. The radiation characteristics of each mode are validated through measurements, illustrating the complimentary nature of the four far-field radiation patterns through which near-hemispherical field-of-view coverage can be achieved.

This paper presents a conical quad-mode antenna for irregular sparse antenna arrays. The antenna integrates tapered slot antennas with two orthogonal dipole antennas and a conical monopole element to achieve good polarimetric performance over an ultra-wide field-of-view coverage. It is shown that the presented antenna element is able to detect two orthogonal field components up to scan angles of 80° from zenith over a 50% relative bandwidth.

The response of a 96 element quad-mode antenna (QMA) array configured in the layout of a Low Frequency Array (LOFAR) Low Band Antenna (LBA) station is assessed. Mutual coupling between the four fundamental excitation modes of each QMA is investigated and the maximum gain achieved by the QMA array is compared with the maximum gain of the LBA array. It is shown that the QMA array results in a 5 dB increase in gain toward the horizon with a variation in gain less than 5 dB over a hemispherical Field-of-View (FoV) coverage.

The polarimetric performance of a quad-mode antenna element, consisting of a pair of crossed dipoles and an integrated monopole fed by a quadraxial transmission line, is analysed. Results are compared to a conventional dual-polarised antenna consisting of two orthogonal dipoles. The presented study shows that the quad-mode antenna effectively doubles the polarimetric capabilities of a dual-polarised antenna over the hemispherical field of view.