PIERS ONLINE, VOL. 3, NO. 7, 2007
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A Frequency Notched Inverted-trapezoid UWB Antenna
Min Ding, Ronghong Jin, and Junping Geng
Department of Electronic Engineering, Shanghai Jiao Tong University, 200240, China
Abstract— A new ultra wideband monopole antenna is presented in this paper. An invertedtrapezoid structure is constructed to obtain ultra wideband (UWB) performance. The parameters
and characteristics of the antenna and the simulation results show that the ultra wideband
performance is achieved with the inverted-trapezoid structure. An inverted-trapezoid slot is used
to be exempt from interference with existing wireless systems.
DOI: 10.2529/PIERS061006002923
1. INTRODUCTION
The UWB antenna has become an intensive topic of current antenna research due to some of its
unique features such as transmitting and/or receiving very short time durations of electromagnetic
energy and avoiding frequency dispersion and space dispersion. Recently, many methods are developed to realize conventional UWB antennas [1–3] in the commercial domain, the frequency range
of which is between 3.1 GHz and 10.6 GHz meeting with FCC standard. However, they cause interference for existing wireless communications, for example, wireless LAN with IEEE 802.11a, and so
on. Consequently, a good antenna for UWB applications should provide low voltage standing wave
ratio (VSWR) and be exempt from interference with existing wireless systems. Recently, UWB
antennas with band-notched characteristic were presented in [4, 5].
In this paper, an inverted-trapezoid structure is used to construct a UWB antenna, on which
an inverted-trapezoid slot is embedded to reject the existing wireless local area network (WLAN)
band, such as the 5.25-GHz band (5.15–5.35 GHz) and 5.8-GHz band (5.725–5.875 GHz). This kind
of band-notched UWB antenna requires no external filters and thus greatly simplifies the circuit
design of the communication system.
Figure 1: The structure of the inverted-trapezoid antenna without slots.
Figure 2: S11 of the inverted-trapezoid antenna without slots.
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(a)
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(b)
Figure 3: The input impedance of the inverted-trapezoid antenna without slots. (a) the real part, (b) the
imaginary part.
Figure 4: The structure of the antenna with the trapezoid-shape slot.
Figure 5: S11 of the antenna with the trapezoid-shape slot.
(a)
(b)
Figure 6: The input impedance of the antenna with the trapezoid-shape slot. (a) the real part, (b) the
imaginary part.
2. ANTENNA CONFIGURATIONS AND SIMULATION RESULTS
The inverted-trapezoid antenna structure without slots is shown in Figure 1. In particular, the
inverted-trapezoid antenna element is made by a 0.18-mm copper sheet, which is located vertically
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(a1)
(b1)
(c1)
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(a2)
(b2)
(c2)
Figure 7: Radiation patterns of the second order iteration structure. (a1) E-plane in 4 GHz, (a2) H-plane in
4 GHz, (b1) E-plane in 7 GHz, (b2) H-plane in 7 GHz, (c1) E-plane in 10 GHz, and (c2) H-plane in 10 GHz
above a finite-size ground plane with an SMA connector. The rectangular ground plane has dimensions of 120 × 50 × 1 mm, with a thickness of 1 mm. Return losses are simulated for the prototype
antenna without slots as shown in Figure 2. It is known from Figure 2 that this prototype antenna
covers frequency range from 2.8 GHz to above 12 GHz. The simulated input impedance of the
prototype antenna in Figure 3 is affected by changing parameters of the top side width b1 of the
inverted-trapezoid antennathe bottom side width b2 of the inverted-trapezoid antenna, the height
h of the inverted-trapezoid antenna, and the distance between the bottom side of the invertedtrapezoid antenna and the ground plane. Figure 3 demonstrates that the prototype antenna yields
good UWB impedance performance.
The band-notched antenna is composed of the inverted-trapezoid prototype antenna structure
with the inverted-trapezoid slot is shown in Figure 4. The return losses are simulated for the
band-notched antenna with the inverted-trapezoid slot as shown in Figure 5. It is known from
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Figure 5 that the band-notched antenna with the inverted-trapezoid slot covers frequency range
from 3 GHz to above 12 GHz, except from 4.7–5.9 GHz. As a result, the notched bandwidth of the
antenna with the inverted-trapezoid slot satisfies the requirement for exempt from interference with
existing wireless systems. It is shown in Figure 6 that input impedance of the band notched antenna
is matched for 3 GHz to above 12 GHz, except from 4.7–5.9 GHz, which satisfies the requirement for
exempt from interference with existing wireless systems, too. Figure 7 plots the simulated E-plane
and H-plane radiation patterns at 4 GHz, 7 GHz and 10 GHz.
3. CONCLUSIONS
A new inverted-trapezoid ultra wideband antenna has been presented in this paper, and the interference with existing wireless systems is prevented successfully by the inverted-trapezoid slot. The
simulated return losses and input impedance of the inverted-trapezoid prototype antenna demonstrate that the prototype antenna provides good UWB frequency performance. The simulated
return losses, input impedance and radiation pattern of the band notched antenna demonstrate
that an impedance bandwidth of 3–12 GHz, with VSWR<2, while avoiding interference with the
5.15–5.35-GHz and 5.15–5.825-GHz bands, which are occupied by existing wireless systems.
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