The Measurement of Antenna Impedence Using a Receiving Antenna

Energy from a remote transmitter excites a receiving antenna that is erected vertically over a large conducting plane and base-loaded by a vertical slotted coaxial cavity of variable length. From measurements of the location and half-power width of resonance curves, the combined phase and damping factors for the two ends of the cavity are determined. By measuring these factors for the lower end of the cavity separately, those of the upper end are determined and used to calculate the impedance of the antenna. In effect, the receiving antenna is the generator driving the coaxial line, and it is the impedance of this generator that is measured. Curves of the measured impedance as a function of the electrical length of the antenna are given. Excellent agreement is obtained between impedances measured in this manner for the receiving antenna and corresponding impedances of the same antenna when base-driven through the slotted section. Both sets of measurements are in good agreement with the King-Middleton second-order theory.