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General Lens

rld_general_lense_clip_image021.jpg As an example demonstrating the use of RLD™, general lens parameters are used to create a lens.

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    Figure 1
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    Figure 2
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    Figure 3
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    Figure 4
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    Figure 5
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    Figure 6
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    Figure 7
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    Figure 8
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    Figure 10
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    Figure 11
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    Figure 12
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    Figure 13
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    Figure 14

As an example demonstrating the use of RLD, general lens parameters are used to create a lens. RLD is used to tune the lens for desired performance by observing the output phase error and array factor while adjusting the focal ratio of the lens. As part of a validation exercise, the RLD-designed lens is exported to XFdtd® format and a full-wave simulation is performed to compare the geometrical optics results from RLD to the full-wave results from XFdtd.

The initial parameters for lens design are listed below


  • Microstrip Lens, 50 ohm system impedance
  • Dielectric substrate of 0.508mm thickness (20mil) and 2.33 permittivity
  • 7 beams, 16 array elements, 0.5 wavelength spacing
  • 20 degree scan angle
  • Center frequency of 16 GHz

After entering these parameters, the following design was produced. To obtain a good design, further parameters must be specified.

A lens width of 0.15 meters is chosen to set the overall size of the lens. An excitation is applied to the center beam port and resulting array factor is plotted. The focal ratio will be adjusted using a slider bar until a well defined beam is formed with low sidelobes. A value of 1.0385 for focal ratio gives decent beam as shown in Figure 1.

The phase error for this design may also be plotted and it is shown to be less than 0.5 degrees for all array ports.

The final design, after the addition of transmission lines, is shown in Figure 4. This design is ready for export.

After loading the lens design into the XFdtd software and simulating with the center and lower beam ports active, the following results for the return loss and transfer S-parameter are found over the active frequency band of 14-18 GHz. As can be seen in Figure 5 and Figure 6, the output from RLD is a theoretical value based on the geometrical optics simulation of the lens while the XFdtd results include more complex interactions such as sidewall reflections.

The magnitude and phase of the S-parameters across the output ports may also be plotted and the results from RLD are a good match to those from XFdtd.

To further expand this example, a slot fed patch array is attached to the output ports of the microstrip Rotman lens and further simulation is performed in XFdtd to generate beam patterns for the lens. The following figure displays XFdtd-generated currents at 16GHz on several elements of the patch array and on the entire lens.

The following figure shows the full three-dimensional gain pattern for the lens/patch array combination with one of the ports active.

 
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