Radio Astronomy started with a search for the causes of interference to Trans-Atlantic radio communications. When it was discovered that radio waves did indeed come from beyond the Earth a new Science was born. ( Karl Jansky )
We associate the Dish Antenna with radio astronomy as most research has been done at very high frequencies. To do research at lower frequencies larger antenna are needed due to the longer wavelengths. For this reason phased arrays are popular and many innovative designs have been implemented.
The European LOFAR LOw Frequency ARray was the first of a new design to use many small antenna working together in 'Tiles' to increase sensitivity. The development started in the Netherlands and has also been implemented in many other European countries.
The Netherlands Institute for Radio Astronomy website contains a wealth of information and a fascinating history of interferometers around the World.
In the USA the Long Wavelength Array is a compact array radio telescope operating in the 10-88 MHz band, colocated with the Very Large Array in central New Mexico. LWA1 currently consists of 257 dual-polarization active dipole antennas in a 100 m x 110 m elliptical footprint with an outlier dipole antenna located approximately 300-m east of the main array. Each dipole is individually digitized and then formed into 4 beams using a delay-and-sum technique. The beams can be pointed independently; thus LWA1 can be used similarly to 4 separate radio telescopes. The individual dipole signals can also be recorded. A subset of LWA1 science targets includes pulsars, astrophysical transients, the Sun, Jupiter, and the ionosphere, but innovative, technically feasible investigations of all kinds are welcomed.
As part of the Square Kilometer Array, the Murchison Widefield Array in Western Australia deploys Low Frequency Arrays designed to operate on VHF frequencies around 150MHz. Crossed Dipole antenna are grouped in a 4 x 4 grid and the resulting 32 individual signals are delayed in a beam-former to point the array in a certain direction.
Our plan is to develop our own Low Frequency Array at the Leon Mow Radio Observatory using readily available hardware and build a software platform to manage and control the Array plus a backend correlation, data reduction and storage system. The initial design starts with two antenna in an 'Interferometer' test bed. By comparing the signals received by the antenna as radio objects move across the sky a map can be built up of the radio sky. Known as 'Aperture Synthesis', a large collecting area for radio waves is created by adding together many smaller antenna.
Software written to manage the test bed will give us a great starting point and allow adding on more antenna in a logical expansion. As the size of the array increases so will the sensitivity.
The initial site has been chosen and work has started clearing the area for the development test bed. The cleared area is around 10 meters across and allows for later expansion of the larger array size.LFA Status Test