Эпсилон Роджерса 4003, 3.38 или 3.55? Где правда? Опции

[Radiolab]

Коллеги подскажите, какой эпсилон у 4003 роджерса брать для модели? В даташите на эту серию приводят два параметра:

Dielectric Constant (Process specification): 3.38
Dielectric Constant (Recomended for use in circuit design): 3.55

Все бы хорошо и следовал бы указаниям "for circuit design", но смущает что в библиотеке материалов в CST у RO4003 фигурирует именно 3.38.

Сообщение отредактировал Radiolab - Apr 28 2009, 06:06

[Yuri Potapoff]

В 2006 году, когда в доках впервые появились два значения,
у меня была следующая переписка с инженером из Роджерса:

Вопрос:

I have found two different values of dielectric constant in the
attached file. If I understand correctly I should use 3.55 during
project simulation. Is it correct?

Can you explain the reason of this difference?

Ответ:

Regarding RO4000, the most important thing is that nothing has changed in
the material itself. We continue to make and test the material in the same
way, and according to the industry standard tests (IPC), the dielectric
constant is 3.38 for RO4003 and 3.48 for RO4350. These IPC tests are used
for maintaining quality control and ensuring repeatability and consitency
in the material from year to year.

However, the IPC test has a problem. It uses a clamped stripline resonator.
This means that with a rigid material like RO4000, some air is trapped
inside which reduces the measured value. Therefore the reported values for
dielectric constant are lower than the "real" ones. This is not a problem
for PTFE materials which are soft enough to fill the air gap.

Therefore, when designing their circuits, customers should start with the
new/real figures - 3.55 for RO4003 and 3.66 for RO4350.

However, we will continue to test using the IPC method for reasons of long
term consistency.