An electric field measurement of a scanning radar antenna

For a long time, measurement of high frequency pulsed electromagnetic fields, such as signals generated by scanning radar antennas, has been accomplished only using measurements taken by a spectrum analyzer and wide frequency band antenna. The main disadvantage of this solution is its inconvenience when applied to electromagnetic field dosimetry. For a small, inexpensive electric field meter, the pulsed environment of a scanning radar antenna has been an unsolved measurement problem. This type of measurement is of special interest when considering the problem of a possible health risk from high peak microwave power pulses of radar transmitters despite the fact that microwave hearing has not been shown to be adverse.[1] Also, new guidelines, such as IRPA/INIRC[2] and the European prestandard ENV,50166-2,[3] require a solution to the problem.

The term electric field meter encompasses an electrically small and thin dipole antenna, a detector mounted across the gap of the dipole, electric field nonperturbing high resistive lines, transmitting the detected signal to the instrument for further processing and the instrument itself. An isotropic response is achieved by three dipoles in proper space orientations. Currently, existing electromagnetic field measurement equipment uses mostly thermocoupler- and diode-based detectors. Both detector types have advantages and disadvantages.[4]

Thus far, measurements have been performed on a radar antenna standing still (static case) using the power integration in time advantage of thermocoupler detectors, producing a true RMS value. Unfortunately, this measurement is not always possible because radar operation often cannot be blocked (for example, in air traffic control). When the radar antenna is scanning, the detectors containing thermocouplers have several main disadvantages: sensitivity to a short-term or minor overload, application that is too slow in such measurements (a typical response time of 1.5 s,[5] while radar pulses could be much faster) and sensitivity that is too low (typically 10 V/m) for measuring pulses at distant locations.[6]

Diode detectors have not been used in electric field meters for measuring high peak short pulses because the behavior of the diode changes in the presence of input electric field strength. However, a diode as a detector also has several advantages over a thermocoupler: It is much faster, has a much higher dynamic range, is necessary for handling peak electric fields (66 dB) and can be protected from the overload. In this article, it is proven that knowledge of the reaction of components of the measuring device and diode detector to a pulsed electromagnetic field can be used in making the correction curves necessary for compensation of the instrument's nonideal physical response. The advantages of diode detectors can be combined now with the knowledge of the sensor response to complex signals. This capability opens the doors to many new applications, including performing measurements on rotating radar systems.

AN IDEAL INSTRUMENT FOR MEASURING SHORT HIGH PEAK MICROWAVE PULSES

The first step in solving this problem is to describe microwave pulses, which will enable the definition of ideal electric field measuring equipment. The most important parameter of microwave pulses generated by a radar transmitter is...