Antenna Array Synthesis in Antenna Magus
The Array Synthesis Tool in Antenna Magus may be used to design and synthesize a specified physical arrangement of multiple element patterns. This application note presents a typical design workflow to illustrate the synthesis capabilities and features.
Some small differences may be observed between your version of Antenna Magus and ours – this is usually due to the fact that improvements and updates are introduced with newer software versions.
Exploring the Arrays
To start the array design, a new array prototype must be added to the Collection. This is done by selecting Array Synthesis on the Home ribbon or Start Page, which launches the Array Synthesis Tool. The workspace shows an extensive collection of Base Layout configurations, illustrated on thumbnails with orange arrows indicating some of the design parameters supported for each layout. A new configuration setup may be launched from the Workspace or using the drop-down menus in the Palette
Though the Base Layouts cater for many common array shapes, it is also possible to Import a custom layout (defining positions, rotations and excitations of the array elements) in a simple tab-separated file format should more advanced/complex layouts be required. We will not consider imported arrays in this application note, but more information on the import format can be found in the Antenna Magus Help FAQ article.
Planar Array Design
The first array to be considered is a planar array with broadside directivity. In the Base Layout Definition expander, select Planar from the Layout type drop-down and the + Excitation taper entry of the Broadside directivity or beamwidth option. After selecting the Set Up button, additional layout-specific design options may be specified.
Set the center - and display frequency to 30 GHz. The center frequency defines the frequency at which the array layout will be designed, while the display frequency specifies the frequency at which the radiation pattern of the array will be synthesized. Typically, these frequencies should be set the same, but the display frequency may be adjusted to consider synthesized out-of-band performance. Choose Specify beamwidth in the Main-beam drop-down and set the value to 15 degrees in both the x- and y-direction. In the Taper dropdown, select All side lobes equal (Dolph-Chebychev) and set the side-lobe level to 30dBi. Click on Apply after entering all the parameters.
Antenna Magus will switch to the Array Layout perspective; here the Base Layout of the array as well as the Array Factor (each element has an isotropic array pattern – spherical radiator with 0 dBi gain in all directions) may be inspected. Various Base Layout Derived Parameters are shown at the bottom of the Palette. Here we note that the number of elements required for the design is 64.
Array Operators may be used to further refine the Distribution Matrix of the Base Layout, which has been set up. These include basic operators, conformal mapping operators, discretizing operators and special operators. While this example does not contain any specific Array Operators, feel free to investigate further inside Antenna Magus.
To synthesize the array for a specific antenna element, multiple Element Pattern/s may be specified and applied to the various elements of the array. These are available under Choose Element Pattern on the Palette and include analytical (or ideal) models of typical radiation pattern shapes as well as more realistic patterns. Radiation patterns included in the Estimated Performance results of existing antenna designs in the Antenna Magus Collection may also be selected directly as element patterns.
Once added, an element pattern may be assigned to All Elements or Selected Elements in the element table in the Workspace. A 3D preview of the currently selected element pattern is shown in the Element Pattern section of the Workspace. Patterns may also be assigned to individual elements in the table directly by using the drop-down selection available under the Pattern column in the table. For this example, select the Left-hand circular QHA from the drop-down. Select Z as the desired direction of the peak gain of the pattern from the D_max drop-down and add the pattern. This first pattern added to the Element Pattern list is automatically assigned to all elements. Additional element patterns may be added, but will need to be manually assigned to all or selected elements as required. It is important to note that as long as a pattern element has been assigned (linked) to an element(s) in the table; it cannot be deleted from the Element Patterns list.
Concentric Circular Array Design
Synthesizing the Concentric Circular Array is a similar process as that described above. Start a new array design by clicking New Array in the Arrays expander or in the Home ribbon. This time, select Concentric circular from the Layout type drop-down and the Beamwidth with a specific taper and steering angle entry from the layout options.
Additional input parameters are specified in the Base Layout Definition. Design for the same beamwidth and side-lobe level as the previous design. Results of both designs are now displayed in the Workspace. In the Derived Parameters, we note that the number of elements required (77) for this array is higher than for the planar array with similar design objectives. The physical size of the array is also slightly larger than for the planar array.
After selecting, adding and assigning the same element pattern as was used for the Planar array example (Left-hand circular QHA) to all array elements, the Synthesize button calculates the synthesized radiation pattern, which may be viewed in the Synthesized Array perspective. In the workspace, we can compare the results of the two array configurations. Shown below is the XZ-plane cut of the radiation pattern of the two arrays. Note the similarity of the two plots.
We can also compare the 3D synthesized array pattern by switching between the two designs in the Arrays expander located in the Palette. Here the difference between the radiation patterns of the two designs are more noticeable. The concentric circular array configuration results in a pattern, which is rotationally symmetrical around the vertical axis.
We looked at the design and synthesis of two basic antenna array configurations to achieve similar main-beam performance. The configurations were compared by designing them both for similar objectives and then inspecting the synthesized results and noting the differences in physical attributes. We noted that the main beams of the two arrays were almost identical where the concentric circular array has a symmetrical pattern around the vertical axis while the square planar array has highly variable sidelobes in different elevation cuts.