Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Reexamination Certificate
2000-03-23
2001-11-27
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
C343S752000
Reexamination Certificate
active
06323821
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to an improved tapered, inverted-L bow-tie antenna assembly.
BACKGROUND OF THE INVENTION
A hybrid log antenna system is an antenna system which includes a low frequency element described combined with a log periodic dipole array. In a conventional arrangement, the low frequency element is a bow-tie or Brown-Woodward Dipole antenna
10
, shown schematically in FIG.
1
.
A well known variant on the bow-tie antenna of
FIG. 1
is the tapered, inverted-L geometry. An inverted-L geometry is obtained by taking a conventional wire dipole and bending the two straight elements to provide two L-shaped elements. This greatly reduces the overall width of the dipole while only slightly degrading the electrical performance (resonance frequency and bandwidth). Thus it provides a better performance-to-size ratio. A tapered, inverted-L geometry is obtained by taking a tapered dipole, bow-tie, or Brown-Woodward dipole and bending it into two L-shaped pieces in a similar fashion. A perspective schematic view of such a tapered, inverted-L antenna
20
is shown in
FIG. 2
a
. A top view of the antenna of
FIG. 2
a
is shown in
FIG. 2
b.
A problem with this antenna design, however, is the relatively large capacitive reactance, especially when compared to the resistive component of the input impedance which is exhibited by the electrically-short dipole. Another drawback to the tapered, inverted-L antenna is that matching the impedance of the antenna to the signal generator is difficult. A conventional 1.5 meter tapered, inverted L-Antenna configured to operate at a frequency of about 25 MHZ has an input impedance of around 5 ohms, making it difficult to match the antenna to components having a conventional 50 ohm input impedance. A mismatched impedance limits the efficiency and power transfer of the antenna/matching network and thus the overall efficiency of the system.
Accordingly, it would be advantageous to provide an improved tapered, inverted-L bow-tie antenna assembly which has lower capacitive reactance than conventional designs and also provides for better impedance matching.
SUMMARY OF THE INVENTION
These and other objects are achieved by a tapered, inverted-L bow-tie antenna which is modified to introduce a series inductance partway between the feed and the antenna tips, preferably at the point where the L bend occurs. In one embodiment, discrete inductors are placed at the bend between the bow-tie and the tapered portion. To avoid the structural and performance problems associated with a conventional wire coil inductor, in a more preferred embodiment, the inductive loading is introduced by a buttonhook or hairpin curve between the bow-tie portion and the tapered portion.
The buttonhook reduces the capacitive reactance and also introduces a series inductance. The low impedance partway on stem increases current flow, and thus the antenna's performance. The increase in resistance makes it easier to match the antenna to a conventional 50 ohm transmitter/receiver system. Compared to a conventional 1.5 meter antenna configured to operate at about 25 MHZ, the capacitive reactance is increased from about−200 ohms to about−100 ohms, while the input resistance is increased from about 5 ohms to about 15 ohms. In addition, the buttonhook bend does not have the structural or performance limitations associated with the use of conventional inductors.
REFERENCES:
patent: 5696372 (1997-12-01), Grober et al.
patent: 5774094 (1998-06-01), Yonezaki
patent: 5926150 (1999-07-01), McLean et al.
patent: 5977919 (1999-11-01), Kudo et al.
patent: 5986609 (1999-11-01), Spall
patent: 6057805 (2000-05-01), Harrington
patent: 6154182 (2000-11-01), McLean
Darby & Darby
Nguyen Hoang
TDK RF Solutions Inc.
Wong Don
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