Article: Higher Dielectric Constant Material Enables New RF Capabilities
Published May 2023 | Click here to read the article on MicrowaveJournal.com
Garlock has released WavePro® 150 (WP150), a ceramic-filled polytetrafluoroethylene (PTFE) dielectric material with a dielectric constant (relative permittivity) of 15.0 and a loss tangent of 0.003 at 6 GHz. PTFE is a versatile and durable dielectric that is used in antennas, cables, radomes, RF circuit boards, and many other microwave and mmWave applications due to its low loss and high performance. WP150 extends the range of PTFE dielectrics to higher Dk values that were previously unavailable, unlocking applications where stability and higher dielectric constants are advantageous. It is available in standard flat panels up to 10 mm thick, as well as made-to-order 3D shapes and conformal surfaces.
For unclad WavePro dielectrics, a variety of methods for metallization are available. These methods include metallic ink printing/writing, plating, vapor deposition, and fusion bonding. Proper surface preparation or the use of additives ensures proper adhesion of the metal to PTFE.
An example of a device that was silver printed on a WavePro substrate:
PTFE
PTFE is a thermoplastic polymer with many dielectric and mechanical properties that make it attractive for RF applications:
- Low loss tangent (Df)
- Dielectric constant (Dk) and other material properties can be engineered with the addition of ceramic and other fillers
- Low moisture absorption (hydrophobic)
- Chemically stable and inert
- High operating temperature
Pure ceramics tend to be brittle, which can be challenging when fabricating small, complex shapes. Weight may also be a concern, especially at lower frequencies where the wavelength is longer. At these longer wavelengths, the shapes are larger and that requires more material.
As a ceramic-filled PTFE composite material, WavePro combines attributes of PTFE and ceramics. Pure PTFE acts as the host substrate, to which micro-particles of ceramic are added. Depending on the ceramic(s) used, the dielectric constant, loss tangent, thermal coefficient of expansion, and other properties can be substantially altered and engineered for a desired outcome. Achieving a target value for a specific property requires both the correct recipe of filler materials, as well as precise processing and manufacturing steps.
Figure 2 shows examples of mmWave components fabricated from WavePro WP150 substrates:
EXTENDING THE DIELECTRIC CONSTANT RANGE OF PTFE
As material science and polymer experts, Garlock’s vision for WavePro dielectrics is to push the limits of what can be achieved with PTFE and expand the range of RF designs and applications for which PTFE is well suited. While several material properties can be engineered for specific requirements, we are focusing on the dielectric constant as the key determinant for suitability in a range of applications.
Garlock’s WP150, the highest permittivity commercially available PTFE-based dielectric on the market with a Dk of 15, is the first step in extending the upper limit. Higher Dk are on the product roadmap for 2023, with a Dk of 28 already achieved in prototypes. On the low end, research and defense efforts targeting Dk in the range of 1.6 to 2.0 are also in progress.
The WavePro Dk roadmap, compared to other materials is shown in Figure 3:
SIZE AND WEIGHT REDUCTION
Materials with high dielectric constants and low loss tangents are interesting to RF designers because of their potential to reduce size and weight. The wavelength of a 10 GHz signal is 30 mm in air, compared to 7.75 mm in WP150 (Dk = 15). Microstrip transmission lines become narrower and the size of resonators is greatly reduced. For example, a simple geometry dielectric resonator antenna (DRA) fabricated with Dk = 15 instead of Dk = 10.2 will have each axial dimension reduced by the square root of 10 divided by 15, or the overall DRA volume reduced by 44 percent. From loaded cavity filters to patch antennas to beam steering elements, the use of high Dk dielectrics can play a vital role in many size reduction strategies.
Examples of the size and weight reduction possibilities with WavePro’s WP150 are shown in Figure 4:
Garlock has more than 50 years of experience developing, manufacturing and forming filled PTFE for different applications in multiple industries. Our techniques and know-how result in highly consistent and uniform isotropic materials with superior quality and performance.
Published 5/2023