LAMINATES: DK, DF AND TRACE WIDTH
What are the Dk and Df of Rogers TMM 3?
Rogers TMM 3 has a dielectric constant (Dk) of 3.27 and a loss factor (Df) of 0.002 at 10 GHz, as published by its maker. A 50 ohm surface microstrip over a 0.2 mm dielectric comes out about 0.441 mm wide on it, against 0.353 mm on standard FR-4.
- Dielectric loss on that microstrip is about 0.064 dB per inch at 10 GHz, and the signal travels at about 134 ps per inch.
- Buried as a stripline between planes 0.4 mm apart, 50 ohms needs a trace about 0.175 mm wide.
50 ohm surface microstrip, 1 oz copper
| Dielectric height | Trace width on TMM 3 | On standard FR-4 |
|---|---|---|
| 0.1 mm | 0.210 mm | 0.166 mm |
| 0.2 mm | 0.441 mm | 0.353 mm |
| 0.5 mm | 1.14 mm | 0.920 mm |
| 1.6 mm | 3.74 mm | 3.02 mm |
As published
| Property | Value |
|---|---|
| Series | TMM |
| Dk @ 10GHz | 3.27 |
| Df @ 10GHz | 0.0020 |
| TCDk (ppm/°C) | +37 |
| Key Application | GPS antennas, power amps |
How this was counted
Dk and Df are the maker's published values at 10 GHz, from the MPBxChange material catalogue, which keeps each source's test frequency and method. Where a maker publishes a range, the midpoint is used. Widths are solved with the Hammerstad and Jensen microstrip equations and Wadell's stripline form, for 1 oz copper, and are a starting point: Dk moves with frequency, resin content and glass style, and a fabricator's field solver is the authority. Standard FR-4 here is the median of 22 FR-4 grades in the catalogue (Dk 4.4).