RF MODULE

Because the impedance is inversely proportional to the degree of freedom Hϕ , it is
better to use the admittance in the optimization:
The objective function for the optimization is then the squared absolute value of the
difference multiplied with Z 0 ,
(3-1)
where k and l are the design parameters controlling the dipole’s diameter and length,
where λ is the wavelength.
The antenna is a long half-wavelength dipole, so the parameters have to fulfill certain
constraints
Results and Discussion
Y 0
The optimization should give a value of the impedance as close as possible to the real
value 74 Ω. The initial guess gives a value of 94 + i51 Ω, which is quite far from the
goal. After roughly 120 iterations, the optimization process returns an impedance
close to
Z = 74 − i5.9·10 −6 Ω
which is very close to the desired value. The optimization parameters for this
impedance (there may be small deviations between platforms) are
which corresponds to the antenna dimensions
I
= -------- ∼ H
1 V ϕ
fobj( kl , ) = IZ0 – 1 V
L = lλ
Φ = kλ
0.4 < l < 0.6
0.001 < k < 0.1
l
k < -----
10
2
k = kopt = 0.0322
l = lopt =
0.446
OPTIMIZING THE SHAPE OF A DIPOLE ANTENNA | 87