AN-SOF Overview

Features and Capabilities

AN-SOF is a comprehensive software tool for the modeling and simulation of antenna systems and radiating structures in general.

AN-SOF is intended for solving problems in the following areas:

• Modeling and design of wire antennas.
• Antennas above a lossy ground plane.
• Broadcast antennas over radial wire ground screens.
• Single layer microstrip patch antennas.
• Radiated emissions from printed circuit boards (PCBs).
• Electromagnetic Compatibility (EMC) applications.
• Passive circuits, transmission lines, and non-radiating networks.

AN-SOF is based on an improved version of the so-called Method of Moments (MoM) for wire structures. Metallic objects like antennas can be modeled by a set of conductive wires and wire grids, as it is illustrated in Fig. 1. In the MoM formulation, the wires composing the structure are divided into segments that must be short compared to the wavelength. If a source is placed at a given location on the structure, an electric current will be forced to flow on the segments. The induced current on each individual segment is the first quantity calculated by AN-SOF.

Once the current distribution has been obtained, the radiated electromagnetic field can be computed in the far- and near-field zones. Input parameters at the position of the source or generator can also be obtained, such as the input impedance, input power, standing wave ratio (SWR), reflection coefficient, transmission loss, etc.

The modeling of the structure can be performed by means of the AN-SOF specific 3D CAD interface. Electromagnetic fields, currents, voltages, input impedances, consumed and radiated powers, directivity, gain and many more parameters can be computed in a frequency sweep and plotted in 2D and 3D graphical representations.

In the case of curved antennas like loops, helices and spirals, the MoM has been improved to account for the exact curvature of wires. In traditional calculations, curved antennas are modeled using straight-line segments with a lot of discontinuous wire junctions. This linear approximation to the geometry can be very inefficient in terms of computer memory and the number of calculations to be performed, since several straight segments must be used to reproduce the curvature of smooth curved wires. To overcome this inaccuracy, curved segments that exactly follow the contour of curved antennas are used in AN-SOF. This innovative technique has been coined as the Conformal Method of Moments (CMoM) >.

As an example, Fig. 2 shows the different approaches to a circular disc obtained by means of the MoM and CMoM methods. Both methods are available in AN-SOF since the MoM is a special case of the more general CMoM.

In addition to the CMoM capabilities, advanced mathematical techniques have been implemented in the calculation engine making possible simulations from extremely low frequencies (e.g., electric circuits at 50-60 Hz) to very high ones (e.g., microwave antennas above 1 GHz).

In what follows, a summary of the modeling options and the simulation results that can be obtained from AN-SOF is presented.

Modeling of Metallic Structures

Metallic structures can be modeled by combining different types of wires and wire grids:

Wires

• Straight wire
• Circular arc
• Circular loop
• Helix
• Quadratic wire
• Archimedean spiral
• Logarithmic spiral

Wire grids

• Patch
• Plate
• Disc
• Flat ring
• Cone
• Truncated cone
• Cylinder
• Sphere
• Paraboloid

1. All types of curved wires can be modeled by means of arced or quadratic segments.
2. Wire grids can be defined using either curved or straight wire segments. Curved segments follow the exact curvature of discs, rings, cones, cylinders, spheres, and parabolic surfaces. Wire grids can be used to model grids and approximate conductive surfaces.
3. Tapered wires with stepped radii can be defined.
4. All wires can be loaded or excited at any position.
5. The structure can also have finite non-zero resistivities (skin effect).
6. Electrical connections of different wires and connections of several wires at one point are possible.
7. Metallic wires in either dielectric or magnetic media can be analyzed.
8. Wires with insulation can be modeled. Dielectric and magnetic coatings are available.
9. The structures can be placed in free space, over a perfectly conducting ground plane or over an imperfect ground plane.
10. Flat strip lines can be defined on a dielectric substrate for modeling planar antennas and printed circuit boards (PCB).
11. Vias in microstrip antennas and printed circuit boards can also be modeled.
12. The wire cross-section can either be Circular, Square, Flat, Elliptical, Rectangular or Triangular.
13. The geometry modeling can be performed in suitable unit systems (um, cm, mm, m, in, ft). Different unit systems can also be chosen for inductance (pH, nH, uH, mH, H) and capacitance (pF, nF, uF, mF, F).

Excitation Methods

1. Voltage sources can be placed on the wires, as many as there are segments, with equal or different amplitudes (RMS values) and phases.
2. Current sources (e.g., representing impressed currents) can also be arranged at any segments.
3. The voltage and current sources can have internal impedances.
4. An incident plane wave of arbitrary polarization (linear, circular, or elliptical) and direction of incidence can also be used as the excitation.
5. Hertzian electric and magnetic dipoles can also be modeled and used as the excitation.
6. The antenna input power can be set to obtain the results (current distribution, near and far fields) scaled accordingly.

Frequency options

1. The simulation can either be performed for a single frequency, for frequencies taken from a list or for a frequency sweep.
2. The list of frequencies can either be created inside the program or loaded from a text file. It can also be saved to a txt file.
3. Linear and logarithmic frequency sweeps are possible.
4. A suitable unit system can be selected (Hz, KHz, MHz, GHz).

Data Input

1. 3D CAD tools are implemented for drawing the structure geometry. Wires, wire grids, discrete generators and lumped loads can easily be added, modified, or deleted.
2. The segmentation of the wire geometry is done automatically but can also be set manually.
3. Any wire can be selected and highlighted by left clicking on it.
4. Right clicking on a wire shows a pop-up menu with several options.
5. Wire connections can easily be performed by means of a copy/paste function for the end points of the wires.
6. The source, load element and ground point positions are shown with special 3D-symbols.
7. All dialog boxes check for valid inputs.
8. Rotation, move and zoom functions with mouse support are implemented.
9. Text files containing geometrical data can be imported into the program. Three different file formats for importing wires are supported, including the still-in-use NEC (Numerical Electromagnetics Code) cards. With this feature, old antenna projects can be leveraged and updated. Importation of DXF files having 3D LINE entities is also supported.
10. Powerful numerical methods are integrated into the AN-SOF architecture for getting the fastest calculation speed and, at the same time, the most accurate results.

Data Output

1. All computed data is written to storage files for a subsequent graphical evaluation.
2. Input impedances, currents, voltages, VSWR, return and transmission losses, radiated and consumed powers, efficiency, directivity, gain and other system responses are shown as lists in text format and can be plotted vs. frequency. A Smith chart is available for representing impedances and admittances as well as for showing the reflection coefficient and VSWR at the mouse selected point in the graph.
3. The current distribution on a selected wire can be plotted in amplitude, phase, real and imaginary parts vs. position in a 2D representation. The currents flowing on a structure can also be plotted as a color map on the wires.
4. Radiation and scattering fields are obtained, such as power density, directivity and gain patterns, total electric field, linearly and circularly polarized components, and Radar Cross Section (RCS). The surface-wave field can be obtained as a function of distance in the case of a real ground with finite conductivity.
5. The near-field components can be calculated in Cartesian, cylindrical and spherical coordinates. The field intensities can be plotted in 2D and 3D graphical representations and visualized as color maps in the proximity of a structure.
6. A 2D representation of radiated fields is available in Cartesian and polar coordinates. The ARRL-style log scale is available in polar diagrams.
7. 3D radiation patterns can be viewed with arbitrary viewing angles, zoom functions and colored mesh and surface, including a color bar-scale. 3D patterns can be plotted with specially designed lighting and illumination for an enhanced visualization of the simulation results.
8. Far-field patterns can be resolved into theta (vertical) and phi (horizontal) linearly polarized components, or right and left circularly polarized components.
9. The frequency spectrum of near- and far-fields can be seen in a 2D representation for all the field components versus frequency.
10. An average radiated power test, also known as AGT (Average Gain Test), is performed for checking the accuracy of the simulation.
11. The computed data can be exported to .csv, .dat or .txt files to load the results in other software programs.
12. An embedded transmission line calculator is included to facilitate the feed line design of transmitting antennas. Actual cable part numbers can be chosen from a lot of manufacturers since the data from the cable datasheets has been extracted and added to the calculator.
13. A Bulk Simulation feature allows us to run the calculation of multiple files, each with a different geometry description, automatically. This is used to obtain results based on a variable geometric parameter. The results are automatically exported to .csv files for further processing.
14. Suitable unit systems can be chosen for the plotted results (current scaling in KA, A, mA, uA; voltage scaling in KV, V, mV, uV; electric field scaling in KV/m, V/m, mV/m, uV/m; magnetic field scaling in KA/m, A/m, mA/m, uA/m; decibel scales, etc.).

Integrated graphical tools

AN-SOF has a suite of integrated graphical tools for the convenient visualization of the simulation results. The following applications are installed automatically and used by the main program, AN-SOF:

A friendly 2D chart for plotting two related quantities, Y versus X. Use AN-XY Chart to plot parameters that depend on frequency, such as currents, voltages, impedances, reflection coefficient, VSWR, radiated power, consumed power, directivity, gain, radiation efficiency, radar cross section, and many more. Also plot the current distribution along wires as a function of position, 2D slices of radiation lobes and near fields as a function of distance from an antenna. Choose different units to display results and use the mouse to easily zoom and scroll graphs.

Plot impedance or admittance curves on the Smith chart with this tool. Just click on the graph to get the frequency, impedance, reflection coefficient, and VSWR that correspond to each point on the curve. Plots can be stored in independent files and opened later for a graphical analysis with AN-Smith.

Plot on a polar diagram the radiation pattern versus the azimuth (horizontal) or zenith (vertical) angles. The maximum, -3dB and minimum radiation levels are shown within the chart as well as the beam width and front-to-rear/back ratio. Click on the graph to quickly obtain the values of the radiated field. The represented quantities include power density, directivity, gain, normalized radiation pattern, total electric field, linearly and circularly polarized components, and radar cross section (RCS).

Get a complete view of the radiation properties of a structure by plotting a 3D radiation pattern. AN-3D Pattern implements colored mesh and surface for the clear visualization of radiation lobes, including a color bar-scale indicating the field intensities over the lobes. Quickly rotate, move, and zoom the graph using the mouse. The 3D radiation pattern can be superimposed to the structure geometry to gain more insight into the directional properties of antennas.

The represented quantities include the power density, normalized radiation pattern, directivity, gain, total field, linearly and circularly polarized components, and radar cross section (RCS). Choose between linear or decibel scales. Display near fields as color maps in the proximity of antennas in three different representations: Cartesian, cylindrical and spherical plots. Also plot the current distribution on the structure as a colored intensity map.