Newsletter 2018.2

Antenna Magus Version 2018.2 released!

Version 2018.2 includes 3 new devices as well as various new features and improvements. This newsletter will discuss the new devices as well as a selection of the features and extensions that have been made available. For more comprehensive information please visit the full release notes.

New Antennas

The new antennas (which brings the total number of devices in Antenna Magus to 333) are:

  • Microstrip Rotman Lens
  • Dualband Coaxial Horn Antenna
  • Printed Folded Quadrifilar Helix Antenna (PFQHA)

Microstrip Rotman Lens
Image of the Microstrip Rotman Lens.

The Rotman lens (developed by W. Rotman and R.F. Turner in the 1960s) is a type of beam-forming network used in wide-angle scanners to feed antenna arrays. It is popular in RADAR applications such as collision avoidance systems in the automotive industry. As a true time delay device, the Rotman lens has wideband scanning capabilities, however it is mostly used in narrowband applications. The main advantages of the Rotman lens are its simplicity, robustness and cost-effectiveness when compared to other beam forming networks.

As a beam forming network, the Rotman lens creates a specific phase taper that can be used to feed an antenna array. The elements of the array are connected to the output ports of the lens with transmission lines of specific length. For this reason, the output ports of the lens, which lie along the ‘array contour’, are often called the array ports. The input points of the lens are known as the beam ports and they are located on the ‘beam contour’. The array and beam contours are designed so that a signal illuminating the antenna array from a specific direction will be focussed on a particular point along the beam contour. The Rotman lens is designed for 3 focal points and beam ports that do not lie exactly on one of these focal points will cause phase errors across the array aperture. The beam contour on which the beam ports lie is therefore designed to minimise the phase error caused by these inter-focal ports.

The Rotman lens is most commonly realised in either waveguide or microstrip. While the waveguide implementation provides higher power-handling capabilities, the microstrip version (implemented in Antenna Magus) has wider bandwidth, is generally lighter and less expensive and also easier to reliably manufacture.

Typical array factor at 0.9f0, f0 and 1.1f0 with beam port 1 excited
Typical array factor at 0.9f0, f0 and 1.1f0 with beam port 2 excited
Dualband Coaxial Horn Antenna
Image of the Dualband Coaxial Horn Antenna.

An ideal feed for a dualband reflector would provide a rotationally symmetric radiation pattern with low side- and back-lobe levels, as well as good isolation between receiving ports for the 2 bands. The port isolation for low- and high-frequency operation bands is critical to allow the feed for each band to be optimised independently and to reduce complexity of the feed electronics.

The dualband coaxial horn antenna - consisting of two circular coaxial guides – can be designed to provide excellent port isolation and good radiation properties as a reflector feed. The outer guide of the construction is longer than the inner guide, and has a quarterwave choke and an iris at its aperture. The inner guide is filled with a dielectric material that extends beyond the aperture.

Dualband coaxial horn: Geometry

The design of the antenna is geometrically constrained to ensure TE11 propagation. The choke, iris and dielectric inner material enable independent optimisation of the lower- and upper-band cut-off frequencies.

At the lower operating frequency (4 GHz for the example shown below) the outer guide is above cut-off and has a narrow passband. The inner guide is below cut-off. At the upper operating frequency (6 GHz for the example shown below) the inner guide is above cut-off and the coupling between the ports is low. The radiation pattern at the lower operating frequency is highly symmetric. The radiation pattern at the upper operating frequency is slightly asymmetric but still provides acceptable illumination for most cases.

Typical reflection coefficient versus frequency
Total typical gain 3D radiation pattern at frequency centre 1 and frequency centre 2
Printed Folded Quadrifilar Helix Antenna (PFQHA)
Image of the Printed Folded Quadrifilar Helix Antenna (PFQHA).

In order to increase the bandwidth of a typical printed quadrifilar helix antenna (PQHA) from 5 % to approximately 30 %, a shorted parasitic strip may be added to each arm. The parasitic strip is folded down from the main radiating strip and shorted to the groundplane at the base of the helix, resulting in a printed folded QHA (PFQHA). This increase in bandwidth might allow the structure to be used in satellite, ground station or GPS applications, where the narrow bandwidth of the standard QHA may have been a limiting factor.

The PFQHA radiates a circularly polarised, cardioid shaped radiation pattern. By proper choice of the helical parameters, half-power beamwidths of up to 180°, high front-to-back ratios and good circular polarisation are simultaneously obtainable.

Typical gain at 0.85fc, fc and 1.15fc
Typical reflection coefficient versus frequency

New Features and Extensions

Inline Editing of Distribution Matrix

Array Distribution Matrices (DMs) in the Array Tool may now be edited inline. Previously this could only be achieved by exporting the DM (to a text file), editing it in an external editor, and then re-importing it. While this approach is extremely versatile for large-scale batch editing, it is quite elaborate for simple (single element) changes.

Array Tool: Duplicate as Editable

Once an array layout has been created in Antenna Magus, it may be edited after duplicating the layout as a Custom Editable array using the Duplicate as Custom Editable in the Array Tool ribbon menu.

Extensions to CST STUDIO SUITE Export models

Anchor Points

CST STUDIO SUITE export models have been expanded to include sensible anchor points. Where Antenna Magus models are used in assembly projects, these anchor points can be used to aid in quick, accurate and consistent model placement in the assembly. All models include six boundary anchor points - placed on the centres of a box bounding the geometry of the device. Additional device-specific anchor points have also been added to typical assembly points, such as feed locations.

CST STUDIO SUITE Export Model: Anchor Points on the boundaries, as well as at the feed location

Dielectric Coaxial Inserts

Dielectric material inserts have been added to all coaxial connectors in CST STUDIO SUITE export models. These added materials simplify changing the coaxial dielectric material, once a model has been exported, but also assist in avoiding potential unexpected behaviour due to geometry overlaps between platform and source models in SAM Hybrid Solver workflows.

CST Export Model: Dielectric Coaxial Inserts

New Automotive Specification Group

An automotive specification group has been added to the Specification Chooser. While Specifications which are already available in Antenna Magus are relevant in the automotive industry (for example GPS, WLAN and Cellular Bands) the Automotive group contains Specifications for applications such as Remote Keyless Entry and Ignition (RKE and RKI), Electronic Toll Collection (ETC), Tyre Pressure Monitoring Systems (TPMS), Vehicle-to-vehicle (V2V) and Short-, Medium- and Long-range radar (SRR, MRR, LRR).

Specification Chooser: Automotive