Foster s reactance theorem

Furthermore, the lowest resonance is always lower than the null at Xa = Xm that is, the null will always be located between the two resonances, in agreement with Foster s reactance theorem [101],... 

Figure 1.16 shows the relationship between Z 1) and 0 = jLCi lossless line. As for a short-circuited line, the relationship coincides with Foster s reactance theorem. The line is in a resonant condition for 0 = (2n - l)7t/2 n positive integers, as in Equation 1.103. 

This situation in no way violates Foster s reaction theorem [101], which applies only to lossless reactances while antenna impedances of radiating antennas are (or should be) lossy to represent radiated power. 

---