Newsletter 4.3

Antenna Magus version 4.3 released!

We are pleased to announce the new release of Antenna Magus Version 4.3. This release sees the addition of 5 new antennas:

  • End-tapered wire helix with parasitic element
  • Antipodal Vivaldi antenna
  • Horn reflector (Hogg horn or Cornucopia)
  • 4 x 1 Pin-fed patch array with underside feed network
  • Pattern-fed Offset Gregorian reflector

Antenna Magus has an updated website with a new "resources" section where users can find application notes, videos and articles focussing on specific antennas and product features.

Users with Floating licenses will be pleased to know that the Floating licence manager has been upgraded, making it possible to automatically retrieve licenses from the Magus licensing server.

New antennas

End-tapered wire helix with parasitic element

Image of the End-tapered wire helix with parasitic element.

The End-tapered wire helix with parasitic element is a modification of the Axial-mode helical antenna with linear end-taper - a moderately wide-band, circularly polarised antenna, which is popular in UHF and microwave frequency applications due to its small cross section. The addition of a parasitic helix - as illustrated in the above image - increases the gain of the driven helix without an increase in axial length or diameter.

Comparison between the End-tapered helix with and without the parasitic element. [Both antennas designed for 16 dBi gain at 1 GHz centre frequency]

To illustrate the effect of the parasitic element, the dimensions and radiation performance of the two helices (both designed for 16 dBi gain at 1 GHz for a wire diameter of 2 mm) is shown in the previous image. The design which includes the parasitic element requires up to 20% less helical turns and is up to 20% shorter when compared to the standard single wire End-tapered helix. The radiation performance of both helices is very similar.

Comparative radiation pattern cuts for an End-tapered helix with and without the parasitic element. [Both antennas designed for 16 dBi gain at 1 GHz center frequency].
Radiation pattern of an End-tapered helix with parasitic element, designed in Antenna Magus for 16 dBi gain at 1 GHz center frequency.

Antipodal Vivaldi antenna

Image of the Antipodal Vivaldi antenna.

The Antipodal Vivaldi antenna, also known as the dual exponentially tapered slot antenna (DETSA) forms part of the end-fire tapered slot family of antennas. It has several advantages compared to the single exponentially tapered Vivaldi. Probably the most important being its compact size, simple feed and pattern stability.

The Microstrip-fed Vivaldi (already included in Antenna Magus) includes a small matching section, whereas the Antipodal Vivaldi is fed using a simple parallel plate transmission line. Antenna Magus designs the transmission line feed with a characteristic impedance of 100 Ω. The parallel plate feed may be converted into a microstrip feed by simply adjusting the ground plane width to be greater than three times the feed line width. The following image illustrates the difference in feed complexity between the Microstrip-fed Vivaldi and Antipodal Vivaldi designs in Antenna Magus (it should be mentioned - as this is not apparent from the design sketches - that the physical size of the Antipodal Vivaldi is almost half the size of the standard MS-fed Vivaldi when designed to meet the same performance objectives).

Design sketch comparing the antenna and feed structures of the Antipodal vs MS-fed Vivaldi antennas.
Typical total gain patterns at fmin, 2.5fmin and 4fmin.

Horn reflector

Image of the Horn reflector.

The Horn-reflector antenna was originally conceptualized at Bell Telephone Labs in the early 1940's and developed further by D.C. Hogg at Bell Labs in 1961. It is an adaptation of an offset-fed parabolic reflector or a combination of a square electromagnetic horn and a parabolic reflector - hence Horn reflector. The Horn-reflector is also known as a Hogg horn, Cornucopia or Sugar scoop, due to its characteristic shape.

Due to the shielding effect of the horn, the far side and back lobes are very low. These features, along with high aperture efficiency, make it very suitable for use in satellite communication systems.

Since the 1970's this design has been largely superseded by shrouded parabolic dish antennas (which can achieve similar sidelobe performance with a lighter more compact construction) in commercial communication systems. In many situations - such as at mm-wave frequencies or where mechanical rotation is required - the Hornreflector can provide some distinct advantages over other antenna options.

Typical gain pattern of the Horn reflector.
Typical longitudinal and transverse gain pattern cuts of the antenna.

4 x 1 Pin-fed patch array with underside feed

Image of the 4 x 1 Pin-fed patch array with underside feed.

This 4-by-1 patch array design in Antenna Magus combines the design of the individual patch elements in the array with the design of a corporate feed network realized in microstrip. The feed network is located on a second substrate on the underside of the ground plane, with the patch elements connected to the feed network with pins (vias) that pass through small holes in the ground plane. This reduces unwanted coupling between the radiating elements and the microstrip feed network - which may be a consideration when using other feed methods. The 4-by-1 patch array can be used to realize an antenna with a fan-shaped beam and a gain of around 13 dBi for applications such as point-to-point communication links. The array is also well suited for use as a sub-array or building-block for larger planar or wrap-around arrays.

Example of the feed network designed by Antenna Magus.

Specific substrate properties, as well as the input resistance desired at the corporate feed point (between 50 Ω and 100 Ω) can be designed for in Antenna Magus. The dimensions of a single resonant patch are constrained by the substrate parameters, while the limits on the characteristic impedance of the feed lines are dictated by practical manufacturability considerations. For example, if the feed network design requires microstrip lines with characteristic impedances significantly higher than say 100 Ω, the line widths may become too narrow for etching, depending on the substrate height and relative permittivity. Conversely, if the port input resistance is chosen too low, the line widths might be unacceptably wide.

The following figure shows a design for 5.2 GHz with 50 Ω input resistance on a 787 Μm, RT/duroid substrate with Εr = 2.2.

50 Ω design example at 5.2 GHz on a 787 Μm, RT/duroid substrate with Εr = 2.2.

Pattern-fed Offset Gregorian reflector

Summary of the dual reflector antennas in Antenna Magus.

The Pattern-fed Offset Gregorian reflector is the 7th dual-reflector included in Antenna Magus and the 4th Gregorian-type reflector antenna template.

Dual-reflector antennas are based on principles that have been used in optical telescopes for centuries, with Cassegrain and Gregorian telescopes dating back to the late sixteen hundreds. Though these antennas share many of the underlying principles of operation with typical single-reflector structures, they offer more design flexibility and are more compact. These advantages, however, come at the cost of an increase in design and manufacturing complexity. The dual-reflector topology allows sub reflector shaping to be used to increase the focus-depth or to optimise illumination for an existing feed antenna and main reflector. By using a dual reflector with an offset feed, aperture blockage can be decreased and mounting on a flat or rotating platform is simplified. There are however some factors like spill-over, radiation pattern asymmetry, feed/sub and main-reflector alignment and other manufacturing complexities that have to be considered when choosing an offset-fed dual reflector topology.

Image of the Pattern-fed Offset Gregorian reflector.

When compared with the Horn-fed Offset Gregorian template, the pattern-fed option reduces simulation time and complexity and makes provision for design based on feed properties such as feed-beamwidth, edge-taper and feed distribution efficiency as illustrated below. Properties of any existing feed antenna can be approximated using the pattern-feed approach, or the desired radiation pattern properties of an ideal feed antenna can be derived from the reflector design. Though a physical feed antenna is not included in the pattern-fed design, assumed antenna dimensions are used to ensure that minimal blockage occurs.

Feed antenna pattern properties accounted for by Antenna Magus when designing the Pattern-fed Offset Gregorian reflector.
3D radiation pattern of the Pattern-fed Offset Gregorian.
Normalised radiation pattern of the Pattern-fed Offset Gregorian dual reflector.
Zoomed view of the normalised radiation pattern.

The Antenna Magus Floating Licence system

Antenna Magus provides a flexible and easy-to-use licencing system. The floating licence provides a great option where a number of users would like to have access to Antenna Magus from any PC on the LAN without having to purchase and maintain node-locked licences for all PC's.

An Antenna Magus floating licence setup (illustrated in the diagram below) consists of 3 parts:

  1. Install Antenna Magus on a number of client machines which are connected to the same LAN.
  2. Install the Antenna Magus floating license manager (FLM) on a local licence server machine (connected to the LAN) which provides licencing information to the client machines as needed.
  3. The FLM requires a valid floating license which can be retrieved directly from the Antenna Magus licensing server via the internet or per email request through an Antenna Magus reseller.

Antenna Magus Floating license setup illustration.