Customised CAD helps electronics component firm

Success in the design of electronic components and instruments is being achieved at Thomas Keating Ltd because of calculation enhancements with a low-cost parametric CAD system, CADlogic's paraCAD+

Success in the design of electronic components and instruments at the very leading edge of electronic technology is being achieved at Thomas Keating Ltd, a long-established Billingshurst, West Sussex, engineering company, purely because of calculation enhancements that customise a low-cost parametric CAD system, CADlogic Ltd's paraCAD+.

CADlogic's 2D paraCAD+ system is simple to use, yet offers major assets of tailorability, high-level programming language and functionality found only in CAD software costing far more than its price of ?1500 for a single user licence.

When you specify the style and enter the dimensions you want, parametrics draws up any item instantly.

The customisation of paraCAD+ at Thomas Keating facilitates the design, development and manufacture of components and instruments for millimetre wavelength electronics, employing quasi-optical methodology.

Products cover frequencies of oscillation from 30 to 3,000 GHz, which have until recently lain between the capabilities of both conventional microwave electronics and infra-red optical techniques.

The latest work being designed using CADlogic's paraCAD+ includes the three pathfinding projects outlined below, which demonstrate the scope and versatility of this Windows-based, parametric 2D CAD software.

Firstly, there is the optics for SMILES, a Japanese satellite radiometer instrument designed to measure ozone depletion chemistry: trace elements including ozone, ClO, HCl, BrO, and NO will be measured at an altitude range of 10 to 60 km from space from the Japanese experimental module on a space station.

Thomas Keating is the design authority for much of the signal processing optics within the instrument.

A second project designed using paraCAD+ consists of Terahertz (THz) Electron Spin Resonance (ESR) Spectrometers for the US National High Magnetic Field Laboratory, based in Tallahassee, Florida.

They will cost about US$ 1m each and be used in the pharmaceutical research field.

ESR instruments use very high and uniform magnetic fields (up to a magnetic flux density of 16 tesla) to probe the activity of unpaired electrons in biological macromolecules, allowing biochemists to understand the dynamics of complex enzymes and proteins, such as the pigments haemoglobin and chlorophyll.

Thomas Keating has supplied quasi-optical systems to improve significantly the sensitivity of the American group's instruments.

A third example of paraCAD+ in action is profiled corrugated horns to define the beams in the high-frequency instrument on Planck, ESA's satellite-based cosmic background anisotropy experiment.

This instrument will probe small scale variations in the intensity of the 3K cosmic background radiation, giving cosmologists clues to the state of the universe very close to the initial singularity.

Other applications in Thomas Keating's wide portfolio include: the modelling of radar patterns of ships, aircraft, people, etc at microwave frequencies; missile seeker heads; shortrange battlefield radar to pick up fine detail; astronomy; remote sensing from space of water-vapour lines to indicate temperature and pressure of atmosphere; and the diagnostics of fusion reactors - such as for the Joint European Torus (JET) Project at AEA Fusion, Culham.

Researching a new energy source, JET uses a tokamak machine, consisting of a chamber surrounded by electromagnets which exert massive magnetic fields to confine plasma.

Dr Richard Wylde, Managing Director of Thomas Keating at Billingshurst, is a Visiting Fellow in the Physics Department at Queen Mary Westfield College, Mile End Road, London E1.

There he spends one day per week, working in the Experimental Physics Group, developing millimetric wave instrumentation and computer programs to analyse the propagation behaviour of the transmissions within them.

Originally written in BASIC, the algorithms were then re-written in MLL (a more advanced form of the same language) and added to what was then CADlogic's MultiCad 2D CAD system.

Now they are in the high-level CPL programming language of CADlogic's new Windows-based paraCAD+ 2D CAD software, which, like MultiCad and its predecessor MLD, also features interactive parametrics, of which the CADlogic Group of Lichfield, Staffordshire, was a pioneer from the mid-1970's.

Yet paraCAD+ is far more tailorable and looks better on screen than did MultiCad.

Running on any standard PC and using a single screen, paraCAD+ is less costly, more flexible and more user-friendly than was MultiCad, with its twin screens requiring special graphics cards.

Being Windows-based, paraCAD+ outputs into a much wider range of plotting and printing devices.

In customising CADlogic's software, Dr Wylde has set up his own toolbox of icons for millimetric wave applications and now actively markets this paraCAD+ design package to users worldwide at educational, scientific, meteorological and defence establishments, space and aeronautics agencies.

The marriage between conventional mechanical CAD and highly sophisticated mathematical analysis is crucial to the success of Thomas Keating's work in electronics.

For millimetric radio waves propagate along direct paths in a similar manner to ordinary light, but are still of long enough wavelength to suffer diffraction and interact with macroscopic objects.

Establishing beam paths through a series of mirrors and lenses, the CAD system enables entire instrument layouts to be designed, right-first-time, with focusing precisely at the correct places and everything optimised for maximum efficiency.

Thomas Keating products in this sector include corrugated feed horns for fundamental Gaussian beam mode propagation, millimetre wavelength guides and interferometric spectrometers.

Dr Wylde's quasi-optical approach to the design of the corrugated horns uses an expansion of Gaussian beam modes, alleviating any problems of distortion at the edges of the beam.

With CADlogic's CAD package predicting the field distribution outside its aperture, the horn is treated as a generator of a series of Gaussian beams, in a similar fashion to a laser, and the net effect of the modes yields either the far field or near field patterns of the horn.

Typically 10 beam modes would be used for the analysis, but in practice 3 or 4 modes will define signals down to minus 40dB below the on-axis peak, with about 98 per cent of the field found to be contained within the modes.

Typical corrugated horns for the National Physical Laboratory at Teddington, Middlesex, produce low sidelobe axially symmetrical beams and are suited to feed Cassegrain antenna systems covering the microwave and millimetre wave bands.

Keating manufactures horns by electroforming - the electronic deposition of copper onto a precision machined aluminium mandrel, which is then removed before the interior surfaces of the horn are gold plated to reduce ohmic losses.

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