April 2005 Newsletter

SuperNEC Newsletter – April 2005

· Simulation of a 20 - 3000 MHz Direction Finding Array

· SuperNEC Application areas

· Winning Assembly - Feb 2005

Simulation of a 20 - 3000 MHz Direction Finding Array

Poynting simulated and evaluated a 20 - 3000 MHz Array using SuperNEC. Low and high frequency numerical models of the Direction Finding (DF) antenna array were created. Simulations over the entire frequency band (20 - 3000 MHz) were performed and compared to available measured results. For the purposes of this article we will only discuss the high frequency results.

Side view of 1500 MHz gridded model of the DF Array (Click the image for more detail)

The numerical high frequency model of the DF array (see photo below) was created for suitable free space simulations between 700 and 3000 Mhz Simulations were performed on two numerical models gridded for frequencies of 1500 MHz and 3000 MHz. The figure above shows a side view of the 1500 MHz gridded model that was built using SuperNEC.

Photo of the DF Array antenna
(Click the image for more detail)

The model clearly shows the low and high frequency dipoles, equivalent dipole impedances as well as equivalent balun ferrite impedances. Plane wave excitation was applied to the DF array over the entire operating frequency range (20 to 3000 MHz). Different azimuth and elevation directions of the incident plane wave were considered. Relative amplitudes and phases of the currents, for the above angles, were recorded and compared with the available field measured data supplied. The figures below show the amplitude and the phase of dipole 2 with reference to dipole 1. The figures on the left show the simulated data and the figures on the right show the field measured data. The SuperNEC simulations are clearly an excellent way of predicting the received phases for the DF Elements in the array. The SuperNEC model is currently used to investigate the change in impedance.

Phase of dipole 2 with reference to dipole 1. Figures on the left show simulated data and figures on the right shows field measured data. (Click the image for more detail)

SuperNEC Applications

Many of the questions that we get for SuperNEC support relate to the suitability of SuperNEC for various applications. For this edition of the newsletter we have decided to highlight what SuperNEC is, and more importantly, what it is not suitable for.

SuperNEC is primarily used for:

- Antenna Design and Analysis

- Antenna Placement studies

The interface makes it easy to simulate and manipulate antennas quickly. As with all packages, SuperNEC has its strong points and weak points.

SuperNEC is extremely good at simulating and optimising wire structure antennas like:

- yagi’s

- lpda’s

- helix

- arrays

- reflectors

- loops

- bow ties

- dielectric coated wires etc.

There are a group of antennas that SuperNEC is capable of simulating, but might not be the most efficient method. These include:

- horn antennas

- patches

- certain fractal antennas

- electrically very large structures etc

The structures that SuperNEC can not simulate are:

- patch antennas on a dielectric substrate (This might be done in the future)

- microstrips

- electrically small antennas

- Multilayer dielectric substrates (This will be implemented in a future release)

- Dielectric solids etc

SuperNEC is well suited for antenna placement studies. Work has been done on aircraft such as:

- Hawk

- Puma

- Rooivalk

- Boeing

- Pilatus etc

For more information on what SuperNEC is capable of simulating go to www.supernec.com or email supernec@supernec.com

Competition – Send in your SuperNEC assemblies

A unique feature of SuperNEC is the use of assemblies to simplify the modeling process for the user. Assemblies are pre-defined (or user defined) antennas or structures that can be re-used when modeling communication systems. In your current version of SuperNEC you will find a wide variety of assemblies including yagi’s, helices, spheres, dipoles, LPDA’s and many others.

In 2005 we would like to encourage our users to create their own assemblies using SuperNEC. The best ones will be added to the next version of SuperNEC where all users can benefit.

If you have never written an assembly in SuperNEC please keep in mind that you need MATLAB to write an assembly. Please have a look at the Input URM (User Reference Manual) under section 1.12 “Writing your own assemblies” for assistance in doing this. (The manuals can be found in the Help Menu of SuperNEC).

Please e-mail the assembly (*.m file) to support@poynting.co.za with the subject Assembly Competition. We will publish the best assembly that we received, in our next newsletter and send the winner an AMAZON gift voucher of USD 50.00.

At the end of the year we will select the best assembly of 2005. This person will receive a full SuperNEC license for one year worth USD 5340.

Winning Assembly - Feb 2005

We would like to congratulate Mr Purushottan from Government of India who was the winner of our February 2005 assembly writing competition. He will be receiving his AMAZON gift voucher soon. Mr Purushottan wrote an assembly for a Zig-zag Monopole which is described here:

The dialogue representation for the zigzag assembly is shown below.

Dialogue window

A short description on how to use the assbly follows with some results:

Wire radius is the radius of the wire to be used,

Angle with horizontal is the angle that the imaginary line joining the top of each zigzag section makes with the ground,

Angle between two sloping sections is the angle between two adjacent zigzag sections,

also is the angle between wires in a single zigzag section,

Height of last section is the maximum height of the antenna (Actually the height is raised a little(30 cm) above the maximum height in the assembly).

Number of sections denotes the number of zigzag sections,

Load Resistance is the resistance that is placed at the end of the structure for making it a traveling wave antenna, default value is 600 Ohms.

The default antenna is in HF band. So the simulation frequency can be taken as 30 MHz. The structure without the ground plane can be seen in the figure below:

Zig-zag structure without groundplane

.A perfect ground plane can be selected.

The antenna has a VSWR as shown in the figure below after changing the Characteristic Impedance to 600 Ohms ( In practical world a 1:12 Impedance transformer has to be used).

The antenna has radiation patterns shown in the figure below.

Radiation Pattern

It can be seen that the antenna has a low take off angle and can be used for long distance communication as reported in the literature ( U.S Patent No. 4,733,243).

8-Way Splitter for Cellular Bands

Due to the high number of cellular engine based applications developed over the last couple of years, a need has arisen for RF splitters that can accommodate more than 2 or 4 antennas. Therefore Poynting Antennas has developed a 8 way splitter for GSM bands.

Most cellular engine based applications combine a number of such units. Most notably where Least Cost Routers (LCR) are installed for companies with high traffic patterns. These routers are then stacked and often located in the basement of the building. This causes bad performance as reception and propagation in the PABX location is often bad and the individual antennas interfere and couple with each other.

The 8 way splitter can combine 8 GSM modules and furthermore can then be used with a single antenna which can be mounted outdoors. The Poynting 800 - 2000 MHz 7 dBi Log Periodic is ideal for this purpose. Where more than 8 Low Cost Routers are co-located, the installer can furthermore point the outdoor directional antennas to different base stations to spread the GSM traffic and reduce the possibility of overloading a single base station.

Please contact sales@poynting.co.za for a quotation on this product.