This improvement may be attributed due to the cancellation of feed strip capacitance by inductive reactance
of tapered feed strip [14,17].
The Zst is a complex quantity that combines the material's DC surface resistance (Rs) and its surface inductive reactance
Conversely, at the higher band edge, the input impedance has an inductive reactance. By adding a parallel resonant circuit that has its resonant frequency occurring at the center of the operating frequency range in parallel with this circuit, the reactive part of the input impedance at both of the band edges can be canceled without having an effect on the impedance at the center frequency.
The choices between a capacitive and an inductive reactance at the lower and higher band edge impedances, for the input impedance and an inductive and a capacitive reactance at the lower and higher hand edge impedances, respectively, for the input impedance after the first step in the design process are determined mainly by the location of the original dispersive impedance on the Smith chart coupled with the desire to use a transmission line length that is as short as possible in step 1.
Thus, it follows from Equation 6 that the oscillations in the optimal microwave oscillator arise as a result of the capacitive reactance in the emitter circuit [Mathematical Expression Omitted], inductive reactance
in the base circuit [Mathematical Expression Omitted], and inductive ([X.sub.L] [greater than] 0) or capacitive ([X.sub.L] [less than] 0) reactance in the collector circuit depending on the value of [Mathematical Expression Omitted].
It is interesting to observe that at upper frequencies, the active circuit shows very low inductive reactance
, urging oscillation to occur at almost the resonance frequency of the resonator and thus leaving the frequency control function solely to the varactor.
Consequently, two frequency ranges exist where this resonator will have inductive reactance
. The frequency of oscillation will be at a frequency where the summation of the resonator and the active circuit reactances is zero, that is, canceled.
The term quality factor was first used to describe the quality of a coil by relating its inductive reactance
to its resistance.
In the case of the active loop antenna, the technique is only useful at frequencies below 30 MHz, where the loop's inductive reactance
is not so large that it severely limits the short circuit current.
Although the junction capacitance was scaled by judicious diode selection, the inherent parasitic inductive reactance
of the diode in series with its resistance in the ON state could not be compensated for with one diode.