Newsletter 2016.1

Antenna Magus Version 2016.1 released!

Version 2016.1 sees a number of extensions to Antenna Magus features as well as the addition of new antennas. Though there are too many new additions to discuss in this newsletter, we will briefly highlight some of the feature extensions and new designs that have been made available. More information on these can be found in the full release notes.

Expanded Libraries

Two variants of the SMP connector have been added to the connector library, and multiple LTE standard specifications have been added (under Smart Devices and Mobile Comms > Cellular Bands) in the Specification Chooser.

New SMP connector models
Specification Chooser with added LTE bands

New Antennas

The new antennas are:

  • Printed meandered inverted-F antenna (Meandered IFA)
  • Compact printed inverted-F antenna (Compact IFA)
  • Printed meandering monopole
  • Substrate mounted normal mode helix (NMHA)
  • Printed Microstrip-fed Yagi-Uda Dipole Array
  • Square truncated capacitively pin-fed circularly polarised patch antenna
  • Backfire Quadrifilar Helix (QHA)

RF Reference Design Antennas

Antennas, such as the two IFA’s, the meandering monopole, the helix and the Yagi-Uda, are similar to reference antennas provided by RF component manufacturers (e.g. the Antenna Development Kit (ADK) antennas from Texas Instruments - www.ti.com). These antennas are typically suited for integration into a PCB layout (using the same substrate as the electronics) and are therefore extremely useful to circuit designers requiring a ‘plug-and-play’ antenna for testing during product development. By avoiding the intricacies of antenna design in the early stages of product development, numerous delays and frustrations can be avoided.

While the reference designs provided by RF component manufacturers are useful when they can be used without modification, adjusting these designs for different frequencies or substrate parameters is not always a simple task. With these antennas in Antenna Magus, however, this becomes trivial! In addition to the design flexibility, Antenna Magus provides parametric export models including a physical microstrip feed line, lumped element matching network and coaxial ports (where applicable).

Planar Printed Meandering Monopole
Image of the Planar Printed Meandering Monopole.

This antenna is similar to the antenna used the Texas Instruments design note DN024. It is typically used for wireless communication in the 868 MHz to 2.4 GHz ISM (Industrial, Scientific and Medical) and SRD (Short Range Device) bands. The meander element is electrically small and can be integrated onto to the same printed circuit board as other electronics.

The input impedance of the antenna is quite low at ≈ 20 Ω due to its small size, but this can be overcome through the use of common matching techniques. The S11 plot shows a comparison between the two available export topologies (with or without matching).

Typical reflection coefficient versus frequency (50 Ω system) with and without matching and typical radiation pattern at the centre frequency
Planar Printed inverted F Compact
Image of the Planar Printed inverted F Compact.

The compact IFA is related to the printed inverted-F antenna (printed IFA) already available in Antenna Magus, but it is smaller in size and provides a broader operational bandwidth - 16.8% vs 13.4% - when designed on the same substrate.

S11 Comparison between the compact and printed IFA and 3D radiation pattern of the compact IFA
Planar Printed Meandered Inverted-F
Image of the Planar Printed Meandered Inverted-F.

The Meandered IFA is similar to the printed IFA except that a meandered element is used to reduce its size. A substantial size reduction compared to the printed IFA can be seen for a design at the same frequency and with the same substrate parameters.

Reflection coefficient and 3D radiation pattern of the printed meandered inverted-F antenna.
Array Printed Yagi microstrip fed
Image of the Array Printed Yagi microstrip fed.

The printed Yagi is commonly used in reference designs where a directional antenna is required. The printed microstrip-fed Yagi consists of a double-sided driven dipole element with a reflector and a number of director elements all printed/etched on a substrate. The Antenna Magus design and export models include an integrated microstrip feed line which relies on the Yagi reflector as its ground plane.

In order to realise a balanced feed, the unbalanced microstrip feed line transitions to a balanced parallel strips line to feed the driven element.

Reasonably high gain can be obtained but the impedance and bandwidth are relatively poor and optimisation of the antenna may be required to achieve optimal performance in a specific layout.

14 dBi Yagi design
Planar Helix normal mode
Image of the Planar Helix normal mode.

This antenna is similar to the antenna used on board #11 in design note DN031 from Texas Intruments. The antenna is typically used for wireless communication in the 915 MHz ISM band. It is advantageous because of its low profile compact size, mechanical strength, and the fact that it can be integrated onto to the same printed circuit board as other electronics.

Compared to its wire counterpart in Antenna Magus, this robust substrate mounted helix has a similar diameter, but reduced physical height.

The radiation pattern resembles a doughnut with a 3 dB beamwidth of approximately 90 degrees in the phi = 90° plane, and maximum radiation in the broadside direction (the plane normal to the helix axis, or phi = 0° plane).

Typical reflection coefficient versus frequency (50 Ω system) with and without matching and typical radiation pattern at the centre frequency
Wire Quadrifilar Helix self phased backfire
Image of the Wire Quadrifilar Helix self phased backfire.

The self-phased backfire QHA has typical application in areas such as satellite communications, as it radiates a cardioid-shaped beam – something very desirable for ground-based GPS receivers. The antenna is similar in structure to the standard self-phased QHA already available in Antenna Magus, but is designed to achieve a backire radiation pattern.

This backfire QHA is often mounted on top of a supporting post - which may be formed by the outside of a rigid coaxial feed cable. The feed point is at the top of the structure, with all arms spiralling downward and shorted to the supporting post. Backfire radiation is achieved by the correct phasing between arms.

By careful choice of the length of the spiral arms, a double resonance resulting in a wide impedance bandwidth is possible.

Typical circular gain pattern at the centre frequency and detail of the feed connecion.
Patch Square Truncated Capacitively pin fed
Image of the Patch Square Truncated Capacitively pin fed.

Due to the typically low bandwidth of patch antennas, circularly polarised patches (such as the truncated rectangular patch) may not achieve good axial ratio at the same frequency that a good impedance match is achieved. By increasing the thickness of the substrate, the impedance bandwidth of the patch may be increased, thereby improving the impedance match at the point of optimal axial ratio. With a pin-feed, however, the increase in pin-inductance with a thicker substrate limits this impact. One approach to negating the impact of this pin-inductance is by introducing a series capacitance - realized as an annular slot on the patch - centred on the connection point of the feed-pin.

By using this configuration, a practical antenna on a thick substrate with wide impedance bandwidth and nearly-perfect circular polarisation at broadside can be achieved.

Typical circular gain pattern at the centre frequency; typical axial ratio at broadside and typical S11 versus normalised frequency