Background
In prior research, Southwest Research Institute (SwRI) made significant progress in developing a two-dimensional retroreflector based on the Van Atta (VA) principle (IR&D Project 14-R8648). This design offers a more compact, easier-to-install, and maintainable alternative to the traditionally bulky trihedral corner reflectors. A critical element of the Van Atta retroreflector is the transmission line design interconnecting the array elements. In this research the focus shifted towards designing a Van Atta configured Substrate Integrated Waveguide (SIW) transmission line design for a 16-element Van Atta array.
Approach
Figure 1: 4X4 SIW Transmission line model (with substrates and ground planes removed).
To achieve optimal line isolation and minimal insertion loss, SwRI is utilizing Substrate Integrated Waveguides (SIW) to interconnect the array elements. Figure 1 shows the mechanical structure of the SIW lines, with dielectric substrates and ground planes removed for clarity. The FEKO Finite Element Method (FEM) solver was employed to model and simulate the transmission properties of the SIW lines. A required key parameter derived from the simulation results is the electrical length of each SIW line, as precise matching is essential for ensuring proper Van Atta (VA) operation.
Accomplishments
Individual FEKO models of the SIW lines shown in Figure 1 have been created and simulated (SIW_8_9 shown in figures 2,3). To optimize transmission performance, SMA tapered feeds and internal corner vias were integrated. Additionally, internal phase shifters were designed and incorporated into the SIW lines to achieve the necessary electrical length matching, which is still a work in progress. A key challenge that remains is the precise simulation of the SIW's electrical length. Currently, the simulation results do not match the analytical estimations. The discrepancy is suspected to be due to line dispersion, and techniques to mitigate this issue are under investigation.
Figure 2: SIW_8_9 FEKO model.
Figure 3: SIW_8_9 Electric Field at 9.7 GHz.