Vector impedance meter

The easiest way to find out the characteristics of a passive L-C-R network in the rf range is to use a vector impedance meter which can tell you the magnitude and the phase of the impedance simultaneously. Just adjust the components to null the imaginary component and to set the real component to the desired value. The only disadvantage of this device is that it is expensive. It turns out that magic-tees can be used to accomplish some of the same goals and they are orders of magnitude cheaper. 

To go first class in building probes, you should have a vector impedance meter. As pointed out in Section V.C.ll., the magic-tee may be substituted at two orders of magnitude reduction in cost but with signficantly more fiddling. 

Vector Impedance Meters (Vector Volt Meters, Network Analyzers)... 

Membrane impedance measurements can be achieved by using various methods. One possible approach consists to apply a sinusoidal current or voltage signal of a given frequency and to determine the corresponding voltage or current response by means of a lock-in amplifier or a vector impedance meter. This procedure must be repeated for every frequency of interest, which makes the measurements quite time consuming. Two... 

Schmitt (1957) called the lead vector H transfer impedance. This may he misleading hoth because impedance is a spatial scalar, whereas H is a spatial vector and with dimension [Q/meter]. 

From the transmission line approximation for the current distribution, the far electric fields can be computed. From this the Poynting vector, (watts per square meter), can be integrated over a large spherical surface to find the total radiated power. The radiation resistance at the feed point is then found from this radiated power and the known current at the feed point. The near fields dictate the imaginary part of the impedance. Some typical values of radiation resistance for various elements, which have small diameter, are given in Table 13.1. The section on dipole characteristics gives the input impedance of dipoles of various lengths computed from the latest moment method formulation described in Sec. 13.1.4. 

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