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DECEMBER 2021 I DESIGN007 MAGAZINE 65 property is not low, the RF benefits of con- trolled Dk and Df can be negated. If the mois- ture absorption for a circuit material is high, that will allow the circuit to absorb moisture from the atmosphere as related to humidity. When there are significant humidity changes in the atmosphere, that can also cause changes in the amount of absorbed moisture in the circuit. e absorbed moisture, water vapor, has become embedded in the circuit material and will increase the Dk and the Df of the mate- rial. e new 3D printable dielectric material has an extremely low moisture absorption rate at 0.08% by volume. Generally, good moisture absorption for a high-frequency circuit mate- rial is 0.3% by volume or less and moisture absorption below 0.1% considered excellent. Having a 3D-printable material with good high frequency or HSD properties will allow the engineer to make and evaluate proto- type structures much faster and cheaper than before. is could certainly open tremendous possibilities to evaluate structures that are 3D and were previously very difficult to make with PCB technology. Additionally, 3D printed technology with good RF properties can be used to make planar circuits which are similar to PCBs but also combine 2D circuit features with 3D areas, such as cavities, as an example. We have investigated many different RF structures that can be achieved with using the RF printable 3D technology and one very interesting example is a Luneburg lens. e Luneburg lens is oen used as an antenna lens and it uses different layers of slightly different Dk. is can be done easily with the 3D-print- able RF material technology, where specific layers are printed to have a specific density lat- tice structure, while other layers have a higher or lower density than the previous layer. e difference in density will cause a difference in the effective Dk for that layer. An example of this technology is shown in Figure 1. Historically, prototype circuitry that are built to prove-out concepts can be expensive for time and resources. Having the ability to 3D print an RF structure, or multiples of the same RF structure with slight differences, has the potential to significantly speed the devel- opment of RF and HSD projects. DESIGN007 John Coonrod is technical marketing manager at Rogers Corporation. To read past columns or contact Coonrod, click here. Figure 1: A Luneburg lens that was generated with the new 3D-printable RF material. The basic concept is shown in the upper right where the lens has higher density in the middle and the layers progressing out from the middle have decreasing density. The spatially variant Dk necessary for the Luneburg lens can be applied to other applications.

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