Topology Optimisation of Wideband Coaxial-to-Waveguide Transitions

Abstract

To maximize the matching between a coaxial cable and rectangular waveguides, we present a computational topology optimisation approach that decides for each point in a given domain whether to hold a good conductor or a good dielectric. The conductivity is determined by a gradient-based optimisation method that relies on finite-difference time-domain solutions to the 3D Maxwell’s equations. Unlike previously reported results in the literature for this kind of problems, our design algorithm can efficiently handle tens of thousands of design variables that can allow novel conceptual waveguide designs. We demonstrate the effectiveness of the approach by presenting optimised transitions with reflection coefficients lower than −15 dB over more than a 60% bandwidth, both for right-angle and end-launcher configurations. The performance of the proposed transitions is cross-verified with a commercial software, and one design case is validated experimentally.

Reliability of the fat tissue channel for intra-body microwave communication

“…The skin and muscle tissue are made from agar-based phantom material, and the fat tissue is a rubber block with dielectric properties equivalent to the tissue. The probes used in this work are topology optimized planar antenna (TOPA) based waveguide transition [11]. TOPA waveguide transitions are optimized for the R-band frequency range to launch the electromagnetic waves into the fat channel.…”

Data Packet Transmission Through Fat Tissue for Wireless IntraBody Networks

“…4 shows the fabricated probe. The two copper parts comprising the antenna are a radiating lump, connected to the SMA connector, and a back reflector connected to the rear end of the waveguide section to provide proper matching [34]. The prototype antenna is developed using photolithography on a 0.762 mm thick Rogers-3203 dielectric substrate with relative permittivity (e') of 3.02, loss tangent (tan d) of 0.016, and a total dimension of 25 mm ´ 50.52 mm (width ´ length).…”

“…Each probe consists of a 50 mm ´ 70 mm ´ 25 mm rectangular waveguide section, matched to a 50-Ohm coaxial-cable through a topology optimized planar antenna (TOPA) that vertically resides at the center of the waveguide section. The copper distribution over the antenna part is determined by using a recently proposed gradient-based topology optimization method that can efficiently handle tens of thousands of designs variables [34]. Fig .…”

Topology optimization of compact wideband coaxial-to-waveguide transitions with minimum-size control

“…This configuration is much more challenging to design, since the device is almost short circuited due to its closeness to the metallic back wall. When we attempted to design such a configuration using the continuation strategy that was successful in the in-line configuration (Hassan et al 2017), the algorithm's lack of control over feature sizes, both for the metallic and nonmetallic (etched) parts, became apparent; the final design contained pronounced areas of scattered material and holes. Such features can increase the ohmic losses in microwave circuits, especially when appearing at the boundaries of the device (Pozar 2012, §2.7), and they can also complicate the manufacturing.…”

“…Note that in this strategy, there is no inherent size control of metal or etched areas, since the filter radius successively vanishes. Nevertheless, in a recent work, we successfully used this strategy to design the layout of metal on a printed circuit board serving as the radiating element in a coaxial-to-waveguide transition (Hassan et al 2017). In that study, the circuit board was positioned centered and in-line with the extension of the waveguide.…”