Progress In Electromagnetics Research Symposium Proceedings, Taipei, March 25–28, 2013
223
Compact Size Antenna for Car FM Radio
Dau-Chyrh Chang1 , Fong-Yi Lin1 , Bing-Hao Zeng2 , and Jay Chen2
1
Oriental Institute of Technology, Taiwan
2
Lorom Industrial Co. Ltd, Taiwan
Abstract— Car antenna can be divided into different types, various forms of car antenna is
like below types: internal antenna, external antenna, hidden antenna and we have seen in the
car is almost the mast antenna, but the mast antenna is easy to collide when we driving in
the restricted space of occasions. Therefore the structure of shark fin antenna doesn’t easily to
influence at narrow space and that have appearance and function of advantages but the drawback
is the poor reception. This paper describes combination of the antenna board and the car FM
amplifier, and to set the shape of the car antenna board to the shark fin antenna that in order to
achieve compact size, ease assembly and lower manufacturing costs, and kept to good reception
on the FM radio.
1. INTRODUCTION
FM radio is almost required for any kinds of car. From the FCC regulation, the frequency band
for FM radio is from 88 MHz to 108 MHz that means the wavelength the FM car radio is around 3
meters. Due to the car environment, the size of antenna should be as small as possible to reduce
the wind resistance when the car is moving. For the size of quarter wavelength monopole antenna
for this band is about 75 cm. It is large in length for the car. In order to reduce the size of the
wire antenna, broadside mode helix antenna with height about 6 cm is used for the traditional FM
car radio. This paper describes a wire antenna, which is printed on FR4 with thickness 0.8 mm, is
used for car FM radio.
2. WIRE ANTENNA
The car FM radio, which is composed of a wire antenna and a printed circuit board FM amplifier,
and they was etched on an FR4/Epoxy substrate with a thickness of 0.8 mm. This wire antenna
is a metal strip, and the metal strip is bent around the printed circuit board FM amplifier. The
ground plane area is 50 × 30 cm, and it is below the wire antenna and is simulated as roof of the
car. The shape of the car antenna board is for a shark fin antenna, which size is 10 × 6 cm. The
wire width is 1 mm, the wire between each other is 1 mm meter. The wavelength of FM is 3 meters,
and this band of the quarter-wave length is 75 cm, but now this wire antenna isn’t enough for the
quarter-wave length. The wire antenna simulations the FM band impedance of the imaginary parts
is capacitive. so we used the parallel LC, by using the equating of the imaginary parts to solve the
jXc . We were used lumped elements such as SMD capacitors/inductors, and let the wire antenna
to achieve compact size. Figure 2 shown the Equivalent circuit model of the wire antenna, and jB
is Equivalent circuit as parallel LC.
Figure 1: The Equivalent circuit model of the wire
antenna.
Figure 2: Efficiency of wire antenna.
PIERS Proceedings, Taipei, March 25–28, 2013
224
Figure 3: The car FM wire antenna.
Figure 4: The environment of performance test for
S21 .
Figure 5: Test S21 of car FM wire antenna.
Figure 6: The environment of performance test for
car FM radio.
3. MEASUREMENT RESULTS
When measured, we have to simulate the car of the roof, so the wire antenna was placed in the
metal plane, and connected a 12 V battery to make it work. We compared the wire antenna and
other commercially available shark fin antenna, the wire antenna of the S21 is better than the
other. Figure 3 the car FM wire antenna. Figure 4 is the environment of performance test for S21 .
Figure 5 shows that test S21 of the car antenna.
4. CONCLUSIONS
The car FM wire antenna full use of shark fin antenna some of the space, and does not interfere
with the reception of the signal, such a combination of methods, making the car antenna can be
compact size, low-cost, and also to simplify the complicated assembly, and the test result shows that
there are 38 radio base station are received with good audio quality. Figure 6 is the environment
of performance test for the car FM wire antenna with amplifier and radio receiver mounted on the
1 meter by 1.5 meter ground. This paper had patent applications by Lorom Industrial Co. Ltd,
Taiwan.
REFERENCES
1. Ali, M. and S. S. Stuchly, “A meander-line bow tie antenna,” IEEE Antenna and Propagation
Society International Symposium, Vol. 3, 1566–1569, 1996.
2. Best, S. R. and J. D. Morrow, “Limitations of inductive circuit model representations of
meander line antenna,” IEEE Antenna and Propagation Society International Symposium,
Vol. 1, 852–855, 2003.