GRASP 10.2 released

The new release of GRASP introduces a number of new features. Here are some of the more interesting:

• Introduction of variables and expressions
• Choice between specifying absolute or relative dimensions in the reflector design wizard
• Fast BoR MoM solver (optional, only for customers with the MoM add-on)
• Dynamic change of parameters during job execution from the GUI (access to the “Set”-command)
• Selection of number of CPUs for job executions
• Easy setting up a job priority

The release also contains some bug corrections. Information about this is sent directly to the customers.

GRASP users who would like express their views on new developments and possibly share their experience with some of the new features are invited to join the LinkedIn group “TICRA Software Users Network”.

Variables and expressions

With the introduction of variables, GRASP has turned yet another ground-breaking corner. It is now possible to express any parameter by means of a variable, or by arithmetic and/or trigonometric expressions involving variables. This feature makes it easy to perform e.g. parametric studies to see how the antenna performance changes with the variation of certain data.

Variables and expressions are illustrated by the design above, where a feed array is illuminating a standard offset reflector antenna. The feeds are located on the so-called Petzval’s surface, a concept known from optics and sometimes used in antenna designs when studying scanning performance.

The variables are defined in the Variables Editor shown in the upper right, and they are used to specify the coordinates of the individual feed positions. These data are used in the definition of an array, as shown in the left part of the plot where the individual element positions are given.

If a larger feed element is needed (to reduce spill-over, for example), it is easy to move the feeds accordingly by just changing one parameter, feed_spacing. If a different paraboloid is introduced it is also easy to change Petzval’s surface, as it incorporates the paraboloid’s focal length by means of a variable, focal.

Absolute dimensions in Wizard

In earlier versions the size of the reflector aperture diameter was given by the user when designing a system in the Wizard. All other geometrical parameters (e.g. focal length, inter-focal distance of sub-reflector, and others) could be specified relative to the diameter, as this is a common way to specify antenna systems. Many users have missed the alternative to specify these numbers as absolute rather than relative values, since they often are given for example the focal length in this way. Their need is now served.

Fast BoR MoM solver

The 3D MoM solver (optional MoM add-on) is supplemented by a BoR MoM solver that can utilize a scatterer’s rotational symmetry and speed up the Method-of-Moments computations dramatically. The solver uses the same concepts as known from the 3D solver in terms of polynomial current expansion functions and curved surface patches, an essential pre-requisite for efficient computation on curved bodies.

As example, consider the reflector system above. It is a so-called ring focus antenna which is rotationally symmetric. These types of systems are advantageous in that they reduce the unwanted effect of sub-reflector blockage; however, in the example shown the feed is moved away from the focus and there will therefore be a higher degree of multiple scattering between the sub- and the main-reflector.

The antenna can be analyzed with the standard Physical Optics tools in GRASP, but the analysis will require that the PO is set up to calculate a number of successive bounces of the field between the two reflectors. The Method of Moments, on the other hand, alleviates this uncertainty, and even though the feed is offset it is still possible to exploit the speed of the BoR. The patterns below compare the on-axis and scan performances.

The above results were obtained in less than a minute on a standard notebook PC, even though the main reflector is 80 λ in diameter.

Use of “Set” command from within the GUI

“Hard-core” GRASP users are accustomed to a very efficient feature when running jobs in batch mode, namely access to the “Set” command, which enables the user to change attributes of any object in-between calculations. Particularly when time-consuming tasks are considered, it can be advantageous to set up a long list of commands, many of which could be identical, but interspersed with a “Set” command that changes one or more parameters. It becomes particularly powerful when combined with the new variables feature.

The Set command is now available from the GUI when defining commands, and is accompanied by the “Create” and “Delete” commands.

Job priority and CPU selection

GRASP uses the OpenMP standard for multi-threaded execution on computers with more than one CPU core. The standard is to use as many cores as available, but it is now easy to control this from the GUI prior to launching a job as shown in the figure.

It is also seen how the priority of the job can be specified. This can be a very useful feature when running demanding jobs on a Windows computer and you wish to do other things (like surfing) on the PC in the meantime.