21cmGFS is an easy-to-use GUI software developed in MATLAB for simulating the end-to-end response of single antenna instruments designed to measure the global 21cm signal. It not only incorporates high resolution foreground maps into the analysis but also various instrumental effects which have a large impact on such experiments. The main output from the tool is antenna temperature and chromaticity function. The user will set the scanning parameters in LST and frequency with the desired resolution, the location of the instrument and load a set of antenna beams and sky maps (LFSM and Haslam provided) to carry out the simulation. A basic model of the 21cm signal is available to use through the 21cm and systematic toolbox as well as a reasonable instrumental model which includes noise and uncalibrated cable reflections, although users can import their own data.

One of the main features of the tool is the ability to store “rotated” maps onto disk for faster future calculations. The simulator does not rely on using a fixed sky map with a spectral index but can use maps like the Low Frequency Sky Model (LFSM) developed by Dowell et al. The typical speed for computing antenna temperature is 3 seconds per point when maps are not stored and 0.03 seconds when using stored maps on a standard laptop. This is considerably faster when using a fixed map with a spectral index such as Haslam. It also means that for a set of simulation parameters (scan settings and location), the simulator can be repeatedly used to calculate parameters like chromaticity function in very high resolution in just a matter of minutes, allowing the designer to for example rapidly evaluate multiple antenna options.

Along with the 21cm and systematic toolbox which allows the user to import or define a certain instrument models, the antenna beam tools is a very powerful feature of 21cmGFS which can be used to import far-field patterns directly from a FEKO .ffe file or a set of CST .txt files. The toolbox can be used to interpolate and plot the data as a .avi file as well as plotting directivity. Furthermore, at all stages, the user can input and output data in .mat (MATLAB) or .npy (NumPy array) formats as well as in HDF5. Figures can also be saved in six graphic formats including the original MATLAB .fig format.

The software can be dowloaded here and a full manual is available here. This work was partially enabled by the Cambridge-Africa Alborada Research Fund.