The equivalent circuit aided in the calculation of the voltages and the
currents developed over each electronic component.
Modelisation of the antenna type B
The tuning capacitor
is positioned in the primary of the autotransformer (FIG 8).
Its equivalent electrical
scheme is given on FIG 9.
The Type B antenna is modeled in the same way as the Type A antenna, and using the same physical parameters. An additional
capacitor may be added in the feed rod to optimize the radioset
II.5. Compared performances type A and type B antennas
compared simulations gave a clear advantage to the Type A
antenna type. As an example, FIG 10
shows a +12 dB gain advantage for the Type A antenna at 12 MHz
simulated results were confirmed by the comparative measured bandwidths
Using 2 antennas having the same radiating surface, the compared
measured bandwidths were 5 to 10 times
higher for the Type B than for the Type A antenna. In a tuned
circuit, bandwidths (B) are inversely proportional to the quality
factor (Q), and Q is proportional to the efficiency (h ); when
Q >> 1, h x B = Rr/2p La = constant If ha and hb are the
Type A and Type B antenna efficiencies , and Ba et Bb their bandwidths
respectively, the applying formulas are ha Ba = hb Bb, and ha
/ hb = Bb / Ba When the measured bandwidth ratios is Bb / Ba =
10 , the efficiency ratio becomes ha/hb is 10.
Observing that Type B antenna optimizes the tuning in the primary circuit,
and that the Q-factors of primary and secondary are quite different,
the energy transfer in the secondary is not maximized. On the
contrary, in the Type A antenna the tuning
brings a maximum Q-factor and the current is the highest in the
The Type A antenna design brings the best antenna efficiency.
of the design
on vehicles were made under strong rain. Modifications of the
tune positions were observed at the highest frequencies (FIG
Such modifications can give an operational problem with no possible reset
in transmission (in FH mode principally).
This shifting problem was resolved by widening the bandwidth by using
two radiating elements in parallel and electrically linked. The
simulation of this structure