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z
θ
ε
2
ε
3
ε
4
r
2
+ z
2
R =
√
2b
2a 2c
y
2h
r
V
0
e
x
(a)
FIGURE P1.15
a
Insulated dipole in lossy medium.
ε
c
r
ε
4
h
z
Region 2,
ε
2
=
ε
c
Region 3,
ε
3
(b)
FIGURE P1.15
b
Catheter in lossy medium that is similar to insulated monopole cor-
responding to dipole of Figure 1.15
a
.
(c)
Plot the current distribution
I
(
z
) as a function of axial
distance
z
.
(d)
A monopole antenna is built that corresponds to half of the above
dipole (Fig. P1.15
b
). This monopole is fed by a 2.2-mm Teflon-filled
coaxial probe (
a
= 0.255 mm,
b
= 0.84 mm, e
c
= 2.1). Find the input
impedance of the monopole. Assume that the absence of the flange
(ground plane) has a negligible effect on the monopole input
admittance.
1.16.
Repeat problem 1.15 for
h
=
31 mm,
a
=
0.47 mm,
b
=
0.584 mm,
c
=
-
j
17.3, and
f
= 915 MHz.
2
0.8 mm, e
2
= 1, e
3
= 1.78, e
4
= 42.5
1.17.
According to the Wien displacement law, the wavelength-temperature
product is a constant [Eqn. (1.44)]. In Section 1.4.3 a value of 0.0048 mK
2
R. W. King, B. S. Trembly, J. W. Strohbehn, “The electromagnetic field of an insulated antenna in
a conducting or dielectric medium,”
IEEE Trans. Microwave Theory Tech
., Vol. MTT-31, No. 7, pp.
574-583, July 1983.
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