Newsletter 2016.0

Antenna Magus Version 2016.0 released!

We are pleased to announce the release of Antenna Magus 2016! This is a major product update that includes new features as well as new workflow options and improvements. There are also several new antennas and design revisions. In this newsletter we will briefly look at some of the new features and antennas - for a more comprehensive overview please read the full release notes.

New features and feature extensions

The release of Antenna Magus 2016 improves on many of the existing capabilities.

  • Over 300 antenna and transition types.
  • A new Specification-drive workflow has been introduced.
  • Users may request new antenna snd features directly from the Antenna Magus interface.
  • A new Connectors Library has been added, as well as Export models for existing Libraries.
  • The export models for all antennas and transitions have been updated to better support recent versions of CST STUDIO SUITE® and FEKO®.
  • The design ranges and capabilities of many previously released antennas have been expanded to cover more applications and for increased design flexibility.

And much more.

The most visible changes, however, relate to the Specification-driven workflow and the addition of new tools and capabilities to make design, and subsequent evaluation thereof, faster and more repeatable than ever before.

Workflow improvements

Antenna Magus 2016.0 introduces a Specification-based workflow built on the Smart Design and Specifications introduced in Version 5.0. This workflow guides the user to define a Specification, based on templates for various common industries, or from an Empty Specification. Depending on the values entered in the Specification, Antenna Magus will suggest Keywords that can be used in Find Mode to reorder the antenna templates. Antennas that are added to the Collection are automatically designed according to the underlying Specification, which, if edited, will automatically trigger an update of the relevant designs.

Following the Specification workflow makes finding and designing different antennas very efficient and repeatable.

The Specification Chooser allows the design process to start by selecting an application area.

Design Mode update

Many changes have been made to Design Mode, both in terms of how information is shown but also in order to better support a Specification-based workflow.

The layout of information in Design Mode has been changed to give a better overview of the antenna at first glance and to allow simple navigation to the different perspectives for more detailed information. The different selectable perspectives (above the Design Mode workspace) are: Overview, Sketches, Model Preview, Information, Value Comparison or Estimated Performance.

In Antenna Magus 2016, each Antenna and Transition Prototype in the Collection is linked directly to a Specification in the Specification Library. This underlying Specification enables any antenna or device added in the Collection to be automatically designed, and its performance estimated. An option is available in the Settings menu to disable the automatic performance estimation.

Where the Specification has incomplete information, Smart Design will suggest suitable values to use. In cases where the Specification contains no values, a ‘default’ or typical design – relevant to each specific antenna/transition – is used. This automatically generated design is known as the Reference Design and can only be changed by editing the Specification in the Specification Editor.

If the Prototype/Collection item is linked to a new Specification, a new Reference Design will be added for the new Specification while the previous reference design/s will be kept in the Designs and Tweaks list. If a Specification is edited, the original Reference Design will be saved as a Snapshot. All designs of a particular protoype - including the Reference Design, Snapshots, Designs and Tweaks - are easily compared to one another. The different design types are illustrated in the image below.

The improved Design Model layout with easy access to information and design comparison views.
Advanced and flexible value extraction added to all 2D charts enables effective comparison of designs and tweaks in the Estimated Performance perspective within Design Mode.

Find Mode

Find Mode has been modified to make finding antenna options quicker and more repeatable.

A Template Group may be chosen to show only a certain antenna family or kind of template (e.g. Horn antennas, Arrays, Custom Templates etc.) in the workspace. Some antennas may be found under more than one grouping, e.g. the N-by-1 patch array may be visible under Planar Antennas and Arrays. Templates can also be marked as a Favourite by clicking on the star on the bottom right of a Find Mode card. Favourites are grouped in a special Template Group making them easy to find.

A Find Mode view of the Quick Summary table can be activated by clicking the icon in the bottom right corner of the Find Mode workspace. Only the table of the selected antenna is shown, allowing quick exploration of different possibilities without having to switch to the Info Browser. More detailed information is still available in the Info Browser.

Find Mode may be linked to a Specification. Keywords that have been added to the Specification are loaded into the Keyword list and will reorder the Antenna Templates. The keyword list may be refined by adding or removing keywords or by activating suggested Keywords from the active Specification. Changes made to the Keywords list can easily be saved to the active Specification, to ensure that the same set of keywords can be used at a later stage.

Options to select new or edit current Specifications are available from within Find Mode. Antennas that are added to the Collection are automatically linked to the active Specification and will be designed accordingly.

The Find Mode interface, showing newly added features such as the Specification selection palette, Favourites, Family Groupings and Quick Summary view.

New Antennas

In addition to the following new antennas, a diverse set of new transitions have also been added. The new designs are:

Antennas

  • Folded Spherical Helix Monopole
  • Folded Spherical Helix Dipole
  • CPW-fed annular monopole antenna
  • Planar elliptical dipole for UWB
  • Crossed exponentially tapered slot antenna
  • Dual-ridged horn antenna with printed side posts
  • Dual-ridged horn antenna with side posts
  • Dual Pin-fed conical horn antenna with chokes
  • Pin-fed single choke horn antenna
  • Dielectric lens antenna with enhanced aperture efficiency
  • 2-by-2 array of rectangular inset-fed patch antennas

Transitions

  • Dual coax to circular waveguide transition
  • Coax to Dual-Ridged Rectangular Waveguide Transition

Folded Spherical Helix Monopole
Image of the Folded Spherical Helix Monopole.

The Folded Spherical Helix Monopole (FSHM) is an electrically small self-resonant antenna, which exhibits a good impedance match with a low Q at a value ka ~ 0.38, where k = 2*(pi/wavelength) and 'a' is the radius of a sphere that can completely encapsulate the antenna. An antenna is considered electrically small if ka < 0.5. For antennas on large ground planes the ground plane is excluded when determining 'a'.

For a 4-arm FSHD the input impedance is typically ~ 50 Ohm, but this can be adjusted by varying the number of helical arms and the number of turns. Furthermore the FSHM can be configured to either have linear or elliptical polarisation by changing the size of the ground plane. With a small ground plane elliptical polarisation is achieved and the rotational direction of the helical arms determine the handedness of the polarisation.

Typical radiation pattern at the centre frequency for a Linear polarised design
Typical radiation pattern at the centre frequency for an RHC polarised design
Typical reflection coefficient versus frequency of a 4-arm FSHM for a linearly and elliptically polarised design.
Folded Spherical Helix Dipole
Image of the Folded Spherical Helix Dipole.

The Folded Spherical Helix Dipole (FSHD) is an electrically small self-resonant antenna, which exhibits a good impedance match with a low Q at a value ka ~ 0.27, where k = 2*(pi/wavelength) and a is the radius of a sphere that can completely encapsulate the antenna. An antenna is considered electrically small if ka < 0.5.

For a 4-arm FSHD the input impedance is typically ~ 50 Ohms, but this can be adjusted by varying the number of helical arms and the number of turns. Furthermore the FSHD can be configured to either have linear or elliptical polarization by changing the direction of rotation of the helical arms between the two hemispheres.

Typical radiation pattern at the centre frequency for a Linear (top) and RHC (bottom) polarised design
Typical reflection coefficient versus frequency for a 4-arm FSHD
Dual coax to circular waveguide transition
Image of the Dual coax to circular waveguide transition .

The dual coax to circular waveguide transition consists of two orthogonal coaxial connectors mounted on a circular waveguide. A shorting post, parallel to the front coaxial feed pin, is situated between the two coaxial feeds. The two orthogonal coaxial feeds have the advantage of being able to extract the vertical and horizontal components of the input signal.

Both coaxial inputs convert the coaxial TEM mode to the fundamental TE11 circular waveguide mode which travels along the guide to the open end. The distance between the back coaxial cable and the waveguide backshort is used to control the real impedance of this cable. The impedance of the front coaxial cable is controlled in a similar fashion to the back, just with the waveguide backshort replaced with a shorting post. The cutoff frequency ratio between the TE11 and the TM01 is approximately 1.3:1, limiting the bandwidth of this transition to an absolute maximum of 26%.

Antenna Magus allows the design of a standard (Stnd) or a frequency scaled (Scaled) circular waveguide. The graphs below shows the difference in performance when the centre frequency is 10.75 GHz, input impedances are 50 Ohm, and the two waveguide design options are selected. The TE11 and TM01 cutoff frequencies are indicated by the blue (Scaled) and green (Stnd) dashed lines. Port 1 is the coax closest to the back wall, Port 2 is the coax closest to the waveguide opening and parallel to the shorting post, and Port 3 is the port at the open end of the waveguide.

Typical reflection and isolation coefficients versus frequency for a frequency scaled (Scaled) and a standard (Stnd) circular waveguide design
Typical transmission coefficients versus frequency for a frequency scaled (Scaled) and a standard (Stnd) circular waveguide design
Coax to Dual-Ridged Rectangular Waveguide Transition
Image of the Coax to Dual-Ridged Rectangular Waveguide Transition.

Normal rectangular waveguides' bandwidth is limited at the low end by the fundamental TE10 cuttof frequency and at the upper end by cuttof frequencies of the next higher order modes e.g. TE01 and TE20. By adding a central ridge to either the top, the bottom or both of a rectangular waveguide, the cutoff frequency can be lowered due to the capacitive effect it introduces.

One of the most common ways to launch a wave in a ridged waveguide is through the use of a coaxial to waveguide adapter/transition. The coaxial line's impedance is then matched to the dual-ridged waveguide mpedance through a number of steps in the ridge spacing using a Chebychev impedance matching method. The typical impedance bandwidth is about 2.3:1 but can vary from 1.8:1 to 3.6:1 depending on the feed, cavity and ridge dimensions.

Typical reflection coefficient versus frequency
Typical transmission coefficient versus frequency
CPW-fed annular monopole antenna
Image of the CPW-fed annular monopole antenna.

Integrated, lightweight, wideband antennas have received much attention following the development of wireless communications. The CPW-fed annular annular monopole antenna is a printed version of the Discone (also available in Antenna Magus) and achieves an ultra-wideband (UWB) impedance bandwidth of 8:1, while the radiation pattern transforms from omni-directional at the lower band to multipath at the upper band.

Typical total gain patterns at (a) fmin, (b) 2fmin, (c) 4fmin and (d) 8fmin
Typical S11 versus normalised frequency
Planar elliptical dipole for UWB
Image of the Planar elliptical dipole for UWB.

The standard elliptical dipole antenna may find application for use in the FCC (and ETSI) defined ultra-wideband (UWB) radio band of 3.1 - 10.6 GHz. However, while the basic structure is able to cover the required frequency range, it may not be the most optimal structure to serve as a Gaussian impulse shaping filter required for UWB radio. To address this shortcoming, elliptical slots are used on the dipole arms, resulting in low-level ringing and pulse distortion.

This planar antenna consists of a basic outer elliptical dipole element with inner elliptical slots (cutouts), which may be practically fed in a number of ways. Generally, the planar element is fabricated by etching a metallised dielectric substrate.

The antenna achieves a good (S11 < -10 dB) match over most of the 10:1 bandwidth for a 50 Ohm input impedance, while at one portion in the band it is slightly worse, at around -7.5 dB, depending on substrate.

Typical reflection coefficient
Radiation patterns at (a) 1, (b) 2, (c) 4, (d) 6, (e) 8 and (f) 10 times the minimum operating frequency
Crossed exponentially tapered slot antenna
Image of the Crossed exponentially tapered slot antenna.

The crossed exponentially tapered slot antenna may find application in the FCC (and ETSI) defined ultra-wideband (UWB) radio band of 3.1 - 10.6 GHz. The antenna combines two crossed exponentially tapered slots with a star-shaped slot to produce a stable radiation pattern. Measured UWB figures of merit, like the fidelity factor and the pulse stretch ratio, indicate that the structure is able to serve as a Gaussian impulse shaping filter required for UWB radio. Essentially, the antennas used in UWB radio should only minimally distort the shape of the output pulse - both in the frequency, as well as the spatial domain. [Costa et al.]

The measured transfer function, indicating voltage at the receiving antenna vs. applied voltage at the transmitting antenna exhibits a relatively constant magnitude and almost linear phase. Furthermore, the measured group delay is also quite constant and close to zero.

The antenna achieves a good (S11 < -8 dB) match over a > 3.42:1 (110%) bandwidth for a 50 Ohm input impedance. This covers the official UWB frequency band of 3.1 - 10.6 GHz. The antenna radiates a bidirectional radiation pattern with the required polarisation purity, at an antenna efficiency of between 90 and 97%.

Typical total gain patterns at (a) fmin, (b) fcentre and (c) fmax
Reflection coefficient performance

Jorge R. Costa, Carla R. Medeiros and Carlos A. Fernandes, "Performance of a Crossed Exponentially Tapered Slot Antenna for UWB Systems," IEEE Transactions on Antennas and Propagation, vol. 57, no. 5, pp. 1345-1352, May 2009.

Dual-ridged horn antenna with printed side posts
Image of the Dual-ridged horn antenna with printed side posts.

Electromagnetic compatibility (EMC) measurements for the 1-18 GHz band are extensively performed using the Double-ridged guide horn antenna (DRGH). Several attempts documented in literature have aimed to achieve this bandwidth, while considering input match and radiation pattern behaviour which define UWB operation.

Historically however, designs usually suffered from pattern degradation above 12 GHz, where the pattern splits up into four lobes, instead of maintaining a single main lobe [Bruns et al.], and the boresight gain reduces by approximately 6 dB. [Jacobs et al.]To ensure optimal performance, the H-plane sides are replaced by either a parallel grid of conducting posts or a parallel grid of printed strips on a dielectric substrate. The latter is considered here and also serves as a weatherproofing mechanism.

This antenna covers the full 18:1 bandwidth needed for EMC measurements, both in terms of input match and radiation pattern [Jacobs et al.].

Typical total gain patterns at (a) fmin, (b) 8fmin and (c) 18fmin
Typical total gain patterns at (a) fmin, (b) 8fmin and (c) 18fmin
Typical gain versus normalised frequency

B. Jacobs, J. W. Odendaal, and J. Joubert, 'An Improved Design for a 1-18 GHz Double-Ridged Guide Horn Antenna', IEEE Transactions on Antennas and Propagation, vol. 60, no. 9, pp. 4110-4118, Sep. 2012.

C. Bruns, P. Leuchtmann, and R. Vahldieck, 'Analysis and Simulation of a 1-18GHz Broadband Double-Ridged Horn Antenna', IEEE Transactions on Electromagnetic Compatibility, vol. 45, no. 1, February 2003, pp 55-60.

Dual-ridged horn antenna with side posts
Image of the Dual-ridged horn antenna with side posts.

Electromagnetic compatibility (EMC) measurements for the 1 - 18 GHz band are extensively performed using the Double-ridged guide horn antenna (DRGH).

Several attempts documented in literature have aimed to achieve this bandwidth, while considering input match and radiation pattern behaviour which define UWB operation. Historically however, designs usually suffered from pattern degradation above 12 GHz, where the pattern splits up into four lobes, instead of maintaining a single main lobe [Bruns et al.], and the boresight gain reduces by approximately 6 dB. [Jacobs et al.]

This antenna covers the full 18:1 bandwidth needed for EMC measurements, both in terms of input match and radiation pattern [Jacobs et al.].

Typical total gain patterns at (a) fmin, (b) 8fmin and (c) 18fmin
Typical gain versus normalised frequency
Typical S11 versus normalised frequency

B. Jacobs, J. W. Odendaal, and J. Joubert, 'An Improved Design for a 1-18 GHz Double-Ridged Guide Horn Antenna', IEEE Transactions on Antennas and Propagation, vol. 60, no. 9, pp. 4110-4118, Sep. 2012.

C. Bruns, P. Leuchtmann, and R. Vahldieck, 'Analysis and Simulation of a 1-18GHz Broadband Double-Ridged Horn Antenna,' IEEE Transactions on Electromagnetic Compatibility, vol. 45, no. 1, February 2003, pp 55-60.

Dual Pin-fed conical horn antenna with chokes
Image of the Dual Pin-fed conical horn antenna with chokes .

The dual pin-fed conical horn antenna with chokes is often used as a reflector feed for satellite television. For this application, a dual-linear polarised feed with a bandwidth of more than 17% and a symmetrical radiation pattern is required.

The two orthogonal coaxial feed pins allow for dual-linear operation and is typically used as part of a LNB (Low Noise Block-downconverter) in satellite television where the incoming signal contains information in both horizontal and in vertical directions. For this application, the antenna typically works in two frequency bands ("low" and "high") within the operating bandwidth. At each of these frequency bands, information from the two orthogonal planes ("vertical" and "horizontal") is extracted. The chokes are used to reduce front/back ratio, sidelobes and improves the axial symmetry of the radiation pattern. These properties are all advantageous for a reflector feed.

The design below is for 75 Ohm. Port 1 refers to the coax closest to the back wall of the waveguide. Port 2 refers to the coax closest to the waveguide opening, which is parallel to the shorting post and orthogonal to the coax of Port 1. According to datasheets, a VSWR < 2.5 for more than 17% is acceptable.

The radiation pattern is in the form of an almost axially symmetric broad end-fire lobe with the E-field is polarised in the same direction as the excited feed-pin. For comparison, the E-plane of Port 1 is in the plane where phi = 0°, whilst the E-plane of Port 2 is in the plane where phi = 90°. The E-planes and H-planes are almost identical for the two active feeds making this a suitable antenna for a reflector feed.

Typical VSWR versus frequency
Radiation pattern comparison where Port 1 and Port 2 are active at the centre frequency
Radiation pattern cuts at the centre frequency
Pin-fed single choke horn antenna
Image of the Pin-fed single choke horn antenna.

The pin-fed single choke horn antenna is a slight variation on the pin-fed circular waveguide antenna (Cantenna) already released in Antenna Magus 2.1. A single quarter-wavelength choke is introduced at the open end of the waveguide which will not only increase the gain, but will also decrease the side- and backlobes. A backlobe level reduction of more than 15 dB has been seen through the addition of a single choke.

The circular waveguide is designed to operate between the fundamental TE11 and next TM01 propagating circular waveguide mode. The feed-pin excites the TE11 mode, forming a coaxial-to-circular-waveguide transition. The distance from the waveguide back wall is used to control the input impedance.

The addition of a single quarter-wavelength choke at the open end of the waveguide supresses the current distribution on the outside of the circular waveguide walls which reduces the front/back ratio, sidelobes and improves the axial symmetry of the radiation pattern.

The design below is for 50 Ohm. A comparison between this device and the Cantenna shows the significant reducing in front/back ratio by the addition of this basic choke.

Typical reflection coefficient versus frequency
Typical total gain radiation pattern at the centre frequency
Gain pattern comparison between the antenna designed here and the Cantenna
Dielectric lens antenna with enhanced aperture efficiency
Image of the Dielectric lens antenna with enhanced aperture efficiency.

Dielectric lens antennas have grown in popularity for use in millimeter and sub-millimeter applications. They provide good efficiency, especially in the case of the elliptical dielectric lens, which has high focusing properties. By properly relating the eccentricity of the lens to the dielectric constant, and feeding the lens at one of its focal points, the majority of the rays are refracted in the "forward" direction, thereby constructing a plane phase front.

In the case of the elliptical lens, the high aperture efficiency (~105%) ensures an antenna with a reduced diameter when compared to a standard equal-gain conical horn antenna.

The antenna may be designed for a centre frequency, lens relative permittivity and a gain between 15 and 30 dBi.

Typical radiation pattern at the centre frequency of the operating band
Reflection coefficient of the antenna
2-by-2 array of rectangular inset-fed patch antennas
Image of the 2-by-2 array of rectangular inset-fed patch antennas.

Microstrip antennas are not only used as single elements but are very popular in arrays. Arrays can be used to synthesize a required pattern that cannot be achieved with a single element. The two dimensional nature of planar arrays results in versatile structures, which are able to provide specified radiation patterns with low side lobes.

Applications include, among others, tracking and search radars, altimeters, remote sensing, terrestrial and aerospace communication systems.

Typical radiation pattern at the centre frequency of the operating band

Due to their low weight and profile, microstrip patch arrays, are suitable for numerous microwave and millimeter wave applications, or when flush mounted, conformal arrays are needed. Using inset-fed patches allows far greater control over the various feed network line impedances, keeping them all within a smaller range for overall improved matching and simpler manufacturing.

The 2-by-2 patch array has a gain of around 13 dBi and a relatively narrow 3% bandwidth, on average. The performance bandwidth is primarily limited by impedance.