Microwave Band
Electric Field
Probes
Electric Field
Probes
The 872xD series probes operate from 300 MHz to >50 GHz. They contain resistive thermocouples distributed along the length of the dipole. The spacing prevents resonance over the operating frequency range of the probes. The dipole may be viewed as a group of series connected small resistive dipoles or as a very low Q resonant circuit. Element sensitivity decreases with frequency. At frequencies above12 GHz the dipole begins to align along the Poynting Vector with the cold junctions oriented tangential to the electric field. This is the traveling wave mode of operation.
Each of the three mutually orthogonal elements contains four resistive dipoles with the cold junctions oriented at right angles. This provides for the independence of probe orientation relative to the polarization of the field.
These probes operate from 300 kHz to 50 GHz. Two distinct sets of isotropic sensors are used to cover this very broad bandwidth. The output from each set of detectors is processed separately by separate amplifier circuits in the probe handle. The two signals are summed within the 8718B meter. Models include the Model 8741D that has a flat frequency response and the x8722D series that have shaped frequency response characteristics.
In the lower frequency region below 1500 MHz, a dipole with diode detector and both distributed and discrete components are used. Three orthogonally mounted conductive dipoles, each terminated in diode detector, form the low frequency detection circuit. These diode detectors are operated in their square law region. This region is defined as that in which the DC diode current is proportional to the square of electric field tangential to the dipole. The elements that are used in the higher frequency region are
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