TABLE OF CONTENTS Those readers who are not familiar with microwave circuit analysis may not be aware of the physics that lies beneath the simple equation of Ohm's Law ( R = V/ I). Ohm's Law is derived from, or more accurately, is a simplification of, Maxwell's equations. Without getting into a detailed analysis, Ohm's Law is derived from Maxwell's equations based on some assumptions. Namely, those assumptions are the mathematical boundary conditions that state that frequency is assumed to be very low (relative to the entire frequency spectrum).
Measurement of a voltage at dc or low frequency (less than approximately 30 MHz) is a straightforward task using a handheld multimeter or oscilloscope. Measuring voltage levels at frequencies higher than that becomes a more arduous task. Measurement of voltage, or power, at high frequencies involves analyzing where the energy is as a function of position. Therefore, the measurement involves the measuring of waveforms. This provides the user with information on phase, in addition to the other parameters.
Spatial information is not used in low-frequency measurements because the wavelength of the electrical signal is much larger than the device that is being measured. For example, the wavelength of a signal at 100 Hz is 3,000m long. This is obviously much longer than the capacitor or inductor (which is, say, 10 mm in length) that the signal will pass through. From the time the signal has entered the device to the time it leaves the...
