04656862The Design of UWB Bandpass Filter-Combined Ultra-Wide Band Antenna

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The Design of UWB Bandpass Filter-Combined Ultra-Wide Band

Antenna

Jung N. Lee, Jin H. Yoo, Ji H. Kim, Jong K. Park and Jin S. Kim

Department of Radio Wave Engineering, Hanbat National University, Korea

We have proposed a compact filter-combined ultra-wide band antenna for the use of DS-UWB low band or MB-OFDM lower threebands (3.1-5.2 GHz). The designed antenna has a microstrip-fed trapezoidal radiating patch, UWB band pass filter using the

dumbbell-shaped DGS (defected ground structure) and IDC (interdigital capacitor), two steps for impedance matching, and microstrip

feeding. Three kinds of prototypes (trapezoidal UWB antenna, UWB band pass filter, and the compact filter-combined ultra wideband

antenna) are fabricated and measured. The designed antenna has the figure-of-eight radiation pattern, wide bandwidth, and negligible

dispersion over the operating frequency band. Details of the proposed antenna design and the simulated and measured results are

presented and discussed.

Key word — UWB antenna, DS-UWB, MB-OFDM, UWB band pass filter, DGS, IDC, dispersion, group delay, path loss

I. I NTRODUCTION

ltra Wideband (UWB) is short distance radio

communication technology that can do high speed

communication with the speed more than 100 Mbps in 3

– 10 GHz frequency band. UWB enables wireless connectivity

with consistent high data rates across multiple devices and

PCs within the digital home and the office [1]. The UWB

systems can be divided into two categories: direct sequence

UWB (DS-UWB) and multiband orthogonal frequency

division multiplexing (MB-OFDM). The DS-UWB proposal

foresees two different carrier frequencies at 4.104 (low band:

3.1 to 5.15 GHz) and 8.208 GHz (high band: 5.825 to 10.6

GHz). Especially, DS-UWB using low band has been

developed as its first generation devices. By the MB-OFDM

format in 802.15.3a, the interval between 3.1 and 10.6 GHz is

divided into 14 sub-intervals. Each sub-interval corresponds to

one band of the MB-OFDM, with the bandwidth of 528 MHz[2, 3]. The MB-OFDM transceiver uses the low three bands

(centered at 3432, 3960, and 4488 MHz) as a mandatory

mode.

In UWB communications, in addition to achieving a good

return loss and radiation efficiency, the ultra wideband

antenna should be non-dispersive or dispersive in an

acceptable range. UWB antennas are the particularly

challenging aspect of UWB technology. The UWB antenna

requires an omni-directional, ultra-wideband, small size for

mobility, gain flatness and phase linearity for no distortion of

signal, and low-cost for manufacturing. Recently, many

researchers have developed UWB antennas operating in the

full UWB frequency band such as UWB patch antenna, planardiamond antenna, L-shaped metal-plate monopole antenna,

bowtie antenna, fractal dipole, Vivaldi antenna, and monopole

antenna [4-8]. A narrow band pass filter is integrated with the

patch antenna to serve as a transition between the CPW feed

and a microstrip patch antenna and also to cut the higher order

patch resonances [9].

In this paper, we will focus on the design of a compact

filter-combined ultra wideband antenna operating in the

frequency range of 3.1 to 5.2 GHz (DS-UWB low band or

MB-OFDM lower three bands). The designed compact filter-

combined ultra wideband antenna has a microstrip-fed

trapezoidal radiating patch, UWB band pass filter using the

dumbbell-shaped DGS (defected ground structure) and IDC

(interdigital capacitor), two steps for impedance matching, and

microstrip feeding. The design procedure is as follows. First,

we have designed a microstrip-fed trapezoidal UWB antennaoperating in a frequency range of 3.1-10.6 GHz [4, 5]. Second,

we have designed a UWB band pass filter having a pass band

of 3.1 to 5.2 GHz by using the DGS [10-12] and IDC [13]

structures. Finally, we have integrated the microstrip-fed

trapezoidal UWB antenna and the UWB band pass filter on

the single dielectric substrate to be used in the frequency range

of 3.1 to 5.2 GHz. Three kinds of prototypes (the microstrip-

fed trapezoidal UWB antenna, the UWB band pass filter, and

the compact filter-combined ultra wideband antenna) are

fabricated and measured. The dimension of the compact filter-

combined ultra wideband antenna is 30 mm by 41.2 mm. The

designed antenna exhibits a voltage standing wave ratio

(VSWR) of less than 2.0 over 3.1-5.2 GHz, and the figure-of-eight radiation patterns with gain from 2.3 to 3 dBi in a

frequency range of 3.1 to 5.2 GHz. The path loss (|S21|) and

the group delay are simulated and measured. The path loss is

almost constant across the frequency band (3.1 to 5.2 GHz)

and the group delay variation is less than 0.5 ns. Numerical

analysis using Ansoft HFSS [14] and measurement results are

presented.

II. A NTENNA DESIGN AND SIMULATED/MEASURED RESULTS

Figure 1 shows the top and rear side layouts of a microstrip-

fed trapezoidal UWB antenna with partial ground plane. We

have designed the proposed UWB antenna using the partial

ground plane technique and microstrip feeding [4] andtrapezoidal patch [5]. The proposed UWB antenna has

dimensions of 30×30 mm² and FR-4 (thickness: 0.8 mm, εr =

4.4) is used. As shown in the figure, the antenna is fed by a

microstrip line. The optimal UWB antenna parameters can be

chosen as SW1 = 20 mm, SW2 = 14 mm, SL1 = 1 mm, SL2 = 3

mm, L1 = 12 mm, and GA = 11 mm based on the extensive

simulation using Ansoft HFSS [14].

U

978-1-4244-1722-3/08/$25.00 ©2008 IEEE. 1



(a)

(b)

Fig. 1. Top and rear side layouts of a microstrip-fed trapezoidal UWB antenna

with partial ground plane.

Fig. 2. Measured and simulated results of the proposed UWB antenna.

The return loss (S11) of the UWB antenna was measured with

an Agilent Vector Network Analyzer (85107B) in an anechoic

chamber. Figure 2 shows the simulated and measured results

of the proposed UWB antenna. As shown in the figure, the

impedance bandwidth for S11 < -10 dB is 114 % (3.1-7.9

GHz). The simulated results have a reasonable agreement with

measured results.

(a)

(b)

Fig. 3. Top and rear side layouts of the proposed UWB band pass filter.

Top and rear side layouts of the proposed UWB band pass

filter are shown in Figure 3. The UWB band pass filter

consists of the dumbbell-shaped DGS [10-12] and IDC [13].

We have designed the UWB band pass filter by combining

high pass (using IDC) and low pass filters (using DGS) [10-

13]. The optimal parameters for the UWB band pass filter areGW1 = 3 mm, GW2= 0.4 mm, GL1= 3 mm, GL2 = 1.45 mm, g1

=0.1 mm, g2 = 0.1 mm, FL = 3.5 mm, and FW = 0.3 mm.

Fig. 4. Measured and simulated results of the proposed UWB band pass filter.

Figure 4 shows the simulated and measured results of the

proposed UWB band pass filter. Simulated and measured

2



results are found to be in good agreement with each other. As

can be seen in the figure, the low and high cutoff frequencies

of the UWB band pass filter are 3 and 5 GHz, respectively. At

the central frequency of 4 GHz, the measured insertion and

return loss is 1.48 dB and 20 dB, respectively.

(a)

(b)

(c)

Fig. 5. Top and rear side layouts of a compact filter-combined ultra wideband

antenna.

Figure 5 shows the top and rear side layouts of a compact

filter-combined ultra wideband antenna. The proposed antenna

consists of a trapezoidal UWB antenna (Figure 1), UWB band

pass filter (Figure 3), and two steps for impedance matching.

The two steps are used for fine tuning of the filter-combined

ultra wideband antenna over 3.1 - 5.2 GHz. The optimal

parameters for the two steps are L2 = 24.2 mm, MW1 = 0.5

mm, MW2 = 1 mm, MW3 = 1.45 mm, ML1 = 4.5 mm, ML2 = 1

mm, ML3 = 3 mm, and G = 22.7 mm.

Fig. 6. Measured and simulated results of the compact filter-combined ultra

wideband antenna.

Fig. 7. Variation of the return loss versus frequency as a function of the

matching steps (measured result).

Simulated and measured results of the filter-combined ultra

wideband antenna are presented in Figure 6. It can be seen that

the antenna bandwidth (S11 < -10 dB) covers the range of 3.1 –5.2 GHz. Figure 7 shows the variation of the return loss versus

frequency as a function of the matching steps. Without

matching steps, an unnecessary frequency is passed and the

return loss level is increased. With matching steps, more

improved impedance matching is obtained within the

operating frequency band (3.1 – 5.2 GHz). To evaluate the

dispersion performance of the filter-combined ultra wideband

antenna, we have measured the path loss |S21| and group delay

using an HP Vector Network Analyzer in an anechoic

3



chamber. For the measurement, the distance between the two

antennas is 30 cm.

(a)

(b)

Fig. 8. Measured and simulated results of group delay and path loss: (a) groupdelay, (b) path loss.

In Figure 8, we have plotted the simulated and measured

results for two cases: UWB antenna only and filter-combined

ultra wideband antenna. From the figure, it can be seen thatthe measured group delay varies in between 0.1 ns and 0.5 ns

in the pass band (variation is about 0.4 ns) and path loss is

almost constant (-35 dB) across the operating frequency band.

Figure 9 shows the simulated radiation patterns at 3, 4, and 5

GHz for the two cases. The obtained radiation patterns are

very close to those of a conventional dipole antenna and the

shape of the patterns are almost unchanged for two cases.

(a)

(b)

(c)

Fig. 9. Simulated radiation patterns at: (a) 3 GHz, (b) 4 GHz, (c) 5 GHz.

(a)

4



(b)

Fig. 10. Simulated antenna efficiency and gain: (a) antenna efficiency, (b)

antenna gain.

The simulated antenna efficiency and gain are shown inFigure 10. For two cases, the antenna efficiency and gain are

almost similar in the frequency band (3.1 – 5.2 GHz) but

outside the frequency band, large reduction is observed for the

filter-combined ultra wideband antenna.

III. CONCLUSION

A compact filter-combined ultra wideband antenna has been

proposed for UWB applications. We have designed the UWB

band pass filter by combining high pass (using IDC) and low

pass filters (using DGS). The bandwidth of the filter-combined

ultra wideband antenna for VSWR 2:1 covers the frequency

range of 3.1-5.2 GHz. The measured path loss is almost

constant across the frequency band and the group delayvariation is less than 0.5 ns and thus the proposed UWB

antenna has a good linearity (low dispersion). Good radiation

characteristics of figure-of-eight radiation pattern and almost

constant gain were obtained over the operating frequency

band, thus indicating that the designed UWB antenna is a good

candidate for the UWB communication applications.

ACKNOWLEDGMENT

This work was supported by the second stage of BK21.

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Corresponding author: Jong Kweon Park (e-mail: [email protected];

optional phone: +82-42-821-1222; optional fax: +82-42-821-1595).

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04656862The Design of UWB Bandpass Filter-Combined Ultra-Wide Band Antenna