TABLE OF CONTENTS As mentioned in Chapter 3, for ease of measurement, it is most advantageous to use wideband meters. However, because of both the accuracy of the monochromatic field measurement and the measurement of the field whose spectrum is unknown, it is important to know, if possible, the precise frequency response of the probe.
The typical wideband probe used for electric field measurement consists of a symmetrical dipole antenna loaded by a detection network. For instance, a diode, a thermocouple or an optical modulator, whose output voltage leads to an indicating device. As has been shown [1], with no regard to the type of detector applied, the probe may have certain maxima in its frequency response, especially at the highest frequencies. They result from the increase of the effective length of the antenna, resonance of the probe's parasitic reactance, alternations of the detector efficiency with frequency and others. Meanwhile, the frequency response of the probe should be maximally flat within the entire measuring band (medium frequency range) and it is assumed that outside the band the sensitivity of the probe should not exceed that within the band. The latter suggests the use of RC low-pass filters that would artificially cut off the response at the highest frequencies on one side and permit its shaping, if desired, on the other. Figure 4.3 is shows a simplified schematic diagram of the probe described. The probe is additionally equipped with the low-pass filter mentioned, which...
