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The adoption of antennas within almost every branch of modern technology is driven by the requirements of faster communications and greater data transfer rates. Classical antenna technology has been developed using analytic and empirical means since the early days of Marconi and Hertz. While this approach has been extremely fruitful, modern design requirements together with the diversity of potential designs means that a more tractable and efficient design methodology is required.
pulse optimised
TEM hornComputational methods have seen serious and widespread use as design tools since the introduction of programs such as the numerical electromagnetics code (NEC) in the early 1980's. This code and its derivatives still provide the backbone of design methods for antennas, although antennas must generally be constructed from thin wire elements and the analysis is narrowband in nature. This does not lend itself to efficient solution of broadband interactions or complex structures and materials.
monofilar
helical antennaThe FDTD method has been used extensively for more complex structures and materials than can be accommodated using integral equation approaches. It also provides the advantage of being a time domain technique, thereby allowing broadband analysis in a single calculation. This is important for impulse or broadband applications where the use of a frequency domain method would require many calculations to cover the necessary bandwidth.
Sierpinski
fractal monopoleCelia provides a number of feed types that may be used to provide a wide range of antenna excitations. These are extensively validated on a wide range of structures to ensure accurate and dependable results.
Subsurface or ground penetrating radar refers to the wide range of
techniques designed for locating objects or interfaces beneath the surface
of the earth. These techniques are also relevant to the more
general application of remotely investigating any solid or liquid dielectric
region and the space obscured by such a region.
The overall design philosophy of the methodology applied, and also the specific detail of the technique depend on the type of target sought and the nature of the obscuring medium. The types of system employed can be either local to the surface to be probed, or can be remote, for example airborne or satellite systems. The successful deployment of a system depends on a number of factors that must be incorporated into the design including electromagnetic considerations, soil science, geophysics and signal processing.
twin bow-tie GPR system Because of the complexity of the design process for the electromagnetic system, the design of GPR has progressed empirically through experimentation. The usual domain decomposition methods applied in EM design activities cannot be applied in the case of GPR because of the proximity of antenna, ground and target. This means that the response of any component in the system depends on all other components. History shows that empirical approaches to problem solving provide solutions, but they may not be optimal. Furthermore, this work is complex, time consuming and expensive.
An alternative that has recently become available is numerical modelling.
In this approach the initial design and optimisation of the electromagnetic
system are carried out using computer simulation.
Accurate models of the antenna, ground and scatterer are constructed
and the system response evaluated. This
alternative is fast, cheap and allows a greater breadth of consideration in
the scoping and optimisation of systems.
The key to this work is the lossy/dispersive PML boundary conditions
within Celia. To our knowledge no
other commercially available FDTD software currently has this capability.
resistive
vee dipole mine detection system The work carried out within our company is at the forefront of numerical modelling techniques for the computational investigation of GPR system performance. Based on the finite difference time domain method (FDTD), the software and expertise that we have can provide solutions for a wide range of soil media, frequencies and bandwidths, and antenna types from simple CW systems to pulsed wide band horns and loaded dipoles.
Microwave and millimetre wave integrated circuits and components are currently being used in a wide and ever expanding variety of electrical equipment. Design of high frequency circuit components (up into the terahertz range) is a challenging activity that relies on computational models to reduce costly manufacture and test development cycles.
At high frequencies planar transmission line structures are required for passive component design and microstrip components are frequently used in MMIC applications.
probe fed
stacked patchThe majority of microstrip CAD is based on methods such as quasi-static approaches, equivalent wave-guide models or semi-empirical methods. These methods are computationally efficient but unfortunately they cannot account for coupling between components, radiation and surface wave effects. Understanding of these effects is essential for effective circuit design.
Open microstrip elements are frequently used and are free to radiate into space and into surface wave modes. Furthermore, impedance discontinuities, which constitute the circuit elements of the device, represent significant sources of radiation. Moreover, circuit elements may be designed to radiate, for example patch antenna structures. In these cases the full understanding of the network impedance and loss characteristics can only be achieved using a full wave solution technique.
Over the past decade a wide range of full-wave methods have been developed. These methods are broadly categorised into variational methods such as finite elements, integral equation approaches such as method of moments, or difference methods such as FDTD.
microwave
low-pass filterThe advantages of the FDTD method for this application are many. It is a time domain method and so can model non-linear device characteristics, also it can provide extremely wide bandwidth information from a single calculation. The method itself is simple and robust yet can provide a great deal of information about the circuit under study.
Genetic algorithms are non-linear, stochastic algorithms based loosely on the Darwinian theory of decent with modification by natural selection. They have found great utility in electromagnetic optimisation tasks due to their many advantages over traditional gradient based optimisation strategies. VSL are experienced in the development and utilisation of GA methods in a range of design optimisation tasks, illustrations of which can be found below.
See GAO Discussion for more details on genetic algorithm optimisation
Two simple design activities are discussed in the following links to illustrate the use of GAO methods. These examples have been chosen as they have analytic optima with which to compare the GAO result, thereby illustrating the benefit of the method in cases where no analytic result can be obtained.
Design of radar absorbent materials has been an important activity for the reduction of extraneous electromagnetic field levels and reflections since the early days of EM engineering. The first designs were developed during the 1930's from which point increasingly sophisticated absorbers were produced to improve performance and reduce bulk. Traditional design of absorbers relies on approximate closed form expressions, intuitive engineering 'feel', extensive experimentation or relatively simple optimisation methods.
Recently the use of genetic algorithm optimisation has been demonstrated as an effective design methodology that offers many advantages over the traditional approach.
This design approach has been explored at VSL in the pursuit of broadband radar cross section reduction measures. More details of this activity are reported in the following link
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under construction