Design of Broadband Low-Profile Transmitarrays at Ka-Band With High-Permittivity 3-D-Printed Materials

Transmitarrays (TAs) are a cost-effective solution for millimeter-wave antenna applications. The widespread use of fully dielectric TAs (DTAs) emerges from the manufacturing simplicity brought by 3-D printing. Previously reported DTAs employ readily available low-permittivity materials ( $\varepsilon _{r} \lt 3$ ). However, this implementation implies thicker lenses (exceeding one free space wavelength, $\gt \lambda _{0}$ ), affecting the DTA performance compared with thinner TA based on printed-circuit-board (PCB) technology. This work shows that, when properly crafted, 3-D-printed high-permittivity dielectric (HPD) materials can solve this problem. The design challenge is to circumvent the free-space mismatch and narrowband responses usually associated with HPD materials. A commercially available HPD material compatible with 3-D printing is used as an example to demonstrate the feasibility of this type of DTA. This study includes the in-house material characterization for the designed frequency ( $\varepsilon _{r} =13.1$ at 30 GHz). A HPD TA is benchmarked against a conventional PCB-based TA for evaluating the impact of HPD materials for the design of this type of TA. A HPD TA with a diameter of $14~\lambda _{0}$ ( $\lambda _{0}$ is the wavelength at 30 GHz in free space) and a height of $0.4~\lambda _{0}$ (excluding the feed horn) is fabricated with the low-cost 3-D printing method of fuse deposition modeling (FDM). When illuminated by a standard horn, the HPD TA antenna provides a 27.4 dBi gain, elevation scanning up to 45° (through the horizontal displacement of the feed horn) with a scan loss of 2 dB and a 1-dB gain bandwidth of 16.3%.