21. The actual time-reference of an atomic clock consists of an electronic oscillator operating at microwave frequency . 22. The first experimental confirmation of negative index of refraction occurred soon after, also at microwave frequencies . 23. Three additional ISM bands exist in the microwave frequencies , but are not used for microwave cooking. 24. It is therefore applicable at microwave frequencies just as much as it is at lower frequencies. 25. Vacuum-tube detectors do not work at microwave frequencies . 26. Dual TL structures have been used to experimentally demonstrate backward-wave radiation and focusing at microwave frequencies . 27. This instrument makes use of the reflection phenomenon to make many different measurements at microwave frequencies . 28. Traveling wave tube amplifiers ( TWTAs ) are used for high power amplification at low microwave frequencies . 29. Packages for microwave frequency devices are arranged to have minimal parasitic inductance and capacitance in their leads. 30. Thus at microwave frequencies , most of the current flows in an extremely thin region near the surface.
