Section 7.8 · Home exercises · 2 of 4
Home exercise 7.8.2: A PTFE-filled cavity
A PTFE-filled cavity
#The copper cavity of Problems 7.8.1 and 7.8.2 () is completely filled with PTFE, , .
- Find the new TE resonant frequency.
- Find of the walls (how does it scale with ?).
- Find and the total .
- Find the bandwidth. Which loss dominates?
Strategy
All resonant frequencies scale as . In , Eq. (7.8.24), only and change, so . The dielectric adds its own channel, , Eq. (7.8.26).
a)
.
b)
.
c)
, and
d)
. The dielectric takes of the loss.
Answer
Check
Direct evaluation at : , and Eq. (7.8.24) with gives .
Remark
Filling makes the cavity smaller for a given frequency (by in each dimension), but even a very good dielectric such as PTFE limits to . High- cavities are therefore air-filled, or use ceramics with (dielectric resonators).