Figure 1(b). Figure 5(a) presents the input reflection coefficient

characteristic of the proposed antenna compared with that of the

STDA antenna. The bandwidths for a VSWR < 2 are about

47.62% (1.68–2.73 GHz) and 50.45% (1.66–2.78 GHz), respec-

tively, for the simulation, and about 48.89% (1.70–2.8 GHz) and

51.02% (1.68–2.76 GHz), respectively, for the measurement.

The bandwidth of the proposed band-notched antenna is

increased by about 2.13% compared to the original STDA

antenna without the U-shaped slots. The simulated notch band

for a VSWR > 2 is 2.38–2.52 GHz, while it is 2.39–2.54 GHz

for the measurement. The simulated and measured data show

good agreement. The simulated and measured realized gain of

the proposed BN_STDA and STDA antennas are compared in

Figure 5(b). It is observed that the notch frequency band in the

gain complies with that of the input reflection coefficient, and

the simulated and measured results agree well with each other.

This confirms that the proposed antenna successfully performed

with rejection in the 2.4–2.484 GHz band.

Figure 6 shows the simulated current distribution of the pro-

posed band-notched antenna at 1.8 and 2.45 GHz. The current is

concentrated on the two dipoles at 1.8 GHz, which is one of

operating frequencies of the antenna, as shown in Figure 6(a),

and the antenna operates normally. On the other hand, it is con-

centrated on the U-shaped slots at the center frequency of 2.45

GHz in the notch band, and the antenna does not work because

the slots resonate and stop the signal.

5. CONCLUSION

We have proposed a band-notched broadband series-fed two

dipole array antenna. A design method to obtain a band rejec-

tion in the 2.4–2.484 GHz WLAN band is investigated for an

STDA antenna consisting of two dipoles and a ground reflector

operating in the frequency range between 1.7 and 2.7 GHz for

mobile communication applications. The notch band is achieved

by inserting U-shaped slots on the coplanar strip line connecting

the two dipole elements. The location and dimension of the slots

are varied to ascertain their effects on the notch band

characteristic.

To validate the proposed design method, a prototype of the

proposed band-notched antenna is fabricated on an FR4 sub-

strate. Experimental results show that the proposed antenna

presents a broad bandwidth of 1.65–2.78 GHz (51.02%) for a

VSWR < 2 and a rejection band of 2.39–2.54 GHz, which cov-

ers the desired notch band.

ACKNOWLEDGMENT

This research was supported by the Daegu University Research

Grant.

REFERENCES

1. R. Waterhouse, Printed antennas for wireless communications,

Wiley, Hoboken, NJ, 2007.

2. R.L. Li, B. Pan, T. Wu, K. Lim, J. Laskar, and M.M. Tentzeris,

Equivalent-circuit analysis and design of a broadband printed

dipole with adjusted integrated balun and a printed array for base

station applications, IEEE Trans Antennas Propag 57 (2009),

2180–2184.

3. F. Tefiku and C.A. Grimes, Design of broad-band and dual-band

antennas comprised of series-fed printed-strip dipole pairs, IEEE

Trans Antennas Propag 48 (2000), 895–900.

4. A.A. Eldek, Design of double dipole antenna with enhanced usable

bandwidth for wideband phased array applications, Prog Electro-

magn Res 59 (2006), 1–15.

5. N. Kaneda, W.R. Deal, Y. Qian, R. Waterhouse, and T. Itoh, A

broad-band quasi-Yagi antenna, IEEE Trans Antennas Propag 50

(2002), 1158–1160.

6. Z. Zhou, S. Yang, and Z. Nie, A novel broadband printed dipole

antenna with low cross-polarization, IEEE Trans Antennas Propag

55 (2007), 3091–3093.

7. Y.-S. Hu, M. Li, G.-P. Gao, J.-S. Zhang, and M.-K. Yang, A dou-

ble-printed trapezoidal patch dipole antenna for UWB applications

with band-notched characteristic, Prog Electromagn Res 103

(2010), 259–269.

8. J. Ding, Z. Lin, and Z. Ying, A compact ultra-wideband slot

antenna with multiple notch frequency bands, Microwave Opt

Technol Lett 49 (2007), 3056–3060.

9. J. Liu, S. Gong, Y. Xu, X. Zhang, C. Feng, and N. Qi, Compact

printed ultra-wideband monopole antenna with dual band-notched

characteristics, Electron Lett 44 (2008), 1106–1107.

10. J. Yeo and J.-I. Lee, Broadband series-fed two dipole array antenna

with an integrated balun for mobile communication applications,

Microwave Opt Technol Lett 54 (2012), 2166–2168.

VC 2012 Wiley Periodicals, Inc.

COMPACT WIDEBAND BANDPASSFILTER USING TWO OPEN LOOPRESONATORS

Xing-Bing Ma and Hong-Xing ZhengInstitute of Antenna and Microwave Techniques, Tianjin Universityof Technology and Education, Tianjin 300222, China;Corresponding author: maxingbing2008@sohu.com

Received 1 August 2012

ABSTRACT: In order to obtain a wideband passband filter, a compact

filter with two open-loop resonators has been designed and fabricated,which has introduced two transmission zeros at the passband’s upper

frequency area. The proposed topology is demonstrated with a designoperating at 5.19 GHz with 19.7% bandwidth. More than 20 dB ofspurious suppression from 0 to 3.69 and from 6.27 to 9.71 GHz is

demonstrated in the experimental results. VC 2012 Wiley Periodicals, Inc.

Microwave Opt Technol Lett 55:915–917, 2013; View this article online

at wileyonlinelibrary.com. DOI: 10.1002/mop.27415

Key words: wideband; bandpass filter; open loop resonator

1. INTRODUCTION

In modern multimode wireless communication systems, the high

performance wideband bandpass filters (BPFs) are widely used.

Thus, they have been extensively investigated, and various

design approaches have been proposed [1–6]. For example, com-

pact wideband bandpass filters based on the folded stepped im-

pedance resonator (SIR) are investigated in Refs. 1 and 2. To

achieve a compact footprint, multilayer technologies have

attracted much interest in recent years for ultra-wideband

(UWB) filter application [1, 3, 4], where some promising results

are reported. In Refs. 5 and 6, filters structures using transversal

signal interaction concepts based on planar Marchand balun

have been proposed, and have some advantages such as high-

selectivity filtering responses and good harmonic suppression,

owing to the input signal being split into differential feed-for-

ward signal paths. And then a super UWB bandpass filter based

on a simplified composite right-/left-handed transmission line

(SCRLHTL) structure is designed in Ref. 7. In this Letter, a

compact filter with two open-loop resonators has been designed

and fabricated, which has a simple structure by using two open-

loop resonators and has two transmission zeros at the passband’s

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 4, April 2013 915

upper frequency area. Full-wave simulation is adopted to inves-

tigate the proposed wideband bandpass filter. Measurement

results are provided and compared with simulated results to

demonstrate the performance of proposed filter.

2. STRUCTURE DESIGN

The proposed filter comprises input and output feeding lines,

two common microstrip half-wavelength resonators as shown in

Figure 1(a), where the resonators have same line width. Since

the filter is symmetrical to T-T0 plane, the odd- and even-mode

methods can be applied to analyze it.

For odd-mode excitation, the equivalent circuits of the two

resonators are shown in Figures 1(b) and 1(c). From the reso-

nance condition of Zin,odd ¼ 8, the first odd-mode resonant fre-

quencies (fodd1, fodd2) can be respectively deduced as

fodd1 ¼ c

4ðL1 þ L2 þ L3Þffiffiffiffiffiffiffieeff

p ; (1)

fodd2 ¼ c

4ðL5 þ L3Þffiffiffiffiffiffiffieeff

p ; (2)

where c is the speed of the light in free space, and eeff denotes

the effective dielectric constant of the substrate. However,

because of the tight coupling between the open-loop resonators

and the input/output feeding lines, wideband characteristics can

be established mainly by the open-loop resonator R1, the open-

loop resonator R2 can adjust and improve wideband characteris-

tics, and the fodd2 is included in the wideband, the fodd1 is

designed in the lower frequency area. For even-mode excitation,

the resonant frequencies are much higher than ones of odd-

mode excitation, which does not make contributions to the wide-

band, and has not been discussed in this Letter.

To verify aforementioned analysis, full-wave simulation

about the return loss (S11) and insertion loss (S21) was carried

out by HFSS software, the proposed wideband bandpass filter is

designed on a TACONIC TLC-32 substrate with dielectric con-

stant 3.2, and thickness 1.14 mm. The proper parameters are

given with f ¼ 7.5, b ¼ 9.28, c ¼ 2.72, d ¼ 2.5, e ¼ 0.5, L1 ¼2.2, L2 ¼ 3, L3 ¼ 5, L4 ¼ 6.5, L5 ¼ 4.63 mm, respectively, the

line width is all 0.5 mm except of the input and output ports,

and the coupling gaps are 0.5 mm. As shown in Figure 2, the

simulated frequency responses of the proposed filter with only

open-loop resonators R1, R2, and both two resonators have been

given, and from it we can know that the wideband characteris-

tics of the proposed filter is decided mainly by the open-loop

resonator R1, and the resonator R2 can effectively improve the

frequency responses of the wideband passband by establishing

two signal paths, especially in lower frequencies. In design, to

achieve good resonance, set that f þ b þ c � d � 2(L3 þ L5).

In addition, the two frequencies at transmission zeros are

approximately decided by the feeding line lengths f-d and b.

3. EXPERIMENTAL RESULTS

To demonstrate the proposed concept, an experimental wideband

bandpass filter was designed and fabricated, the parameters are

the same as given above, the total size is 17 � 12 mm2. Figure 3

shows the simulated and measured results. The measured results

agree quite well with those obtained from simulation. The simu-

lated and measured wideband passbands centred at 5.275 GHz

with 23.7% bandwidth and 5.19 GHz with 19.7% bandwidth,

respectively, and the return loss is under �10 dB over the most

part of the passband. More than 20 dB of spurious suppression

Figure 1 Structure of the proposed filter with two open-loop resona-

tors; odd-mode equivalent circuits. (a) Structure of the proposed filter

with two open-loop resonators. (b) Odd-mode equivalent circuit of the

open-loop resonator R2. (c) Odd-mode equivalent circuit of the open-

loop resonator R1

Figure 2 The simulated frequency responses of the proposed filter

with only open-loop resonators R1, R2, and both two resonators. [Color

figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com]

Figure 3 Simulated and measured S-parameters of proposed filter.

[Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com]

916 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 4, April 2013 DOI 10.1002/mop

from 0 to 3.69 and from 6.27 to 9.71 GHz is demonstrated in

the experimental results. Difference between simulation and

measurement is due to the fabricated error and unperfected

ground. It can be improved by more careful fabrication

technology.

4. CONCLUSION

A novel wideband bandpass filter with two open-loop resonators

is proposed, which has good wideband passband performance at

5.19 GHz with 19.7% bandwidth. The wideband passband char-

acteristics can be generated by properly controlling the lengths

of the open-loop resonators. The simulated results have been

verified by the experiment of the fabricated filter.

ACKNOWLEDGMENT

This work was supported by Tianjin Research Program of Applica-

tion Foundation and Advanced Technology, China, under Grant

No. 12JCYBJC10500.

REFERENCES

1. X.J. Zhang, H.H. Zhang, and X.P. Ma, ‘‘Design of compact wide-

band LTCC filter using pentagonal-shaped SIR,’’ Electron Lett 47

(2011), 327–328.

2. F. Wei, L. Chen, X.W. Shi, and B. Liu, ‘‘Compact UWB bandpass

filter with tunable notch band based on folded SIR,’’ Electron Lett

47 (2011), 1229–1230.

3. C.X. Zhou, Y.X. Guo, S.L. Yan, and Z.L. Wang, ‘‘Dual-band UWB

filter with LTCC technology,’’ Electron Lett 47 (2011), 1230–1231.

4. Z.C. Hao and J.S. Hong, ‘‘High selectivity UWB bandpass filter

using dual-mode resonators,’’ Electron Lett 47 (2011), 1379–1381.

5. W.J. Feng, W.Q. Che, and T.F. Eibert, ‘‘Ultra-wideband bandpass

filter based on transversal signal-interaction concepts,’’ Electron

Lett 47 (2011), 1330–1331.

6. H.T. Zhu, W.J. Feng, W.Q. Che, and Q. Xue, ‘‘Ultra-wideband dif-

ferential bandpass filter based on transversal signal-interference

concept,’’ Electron Lett 47 (2011), 1033–1035.

7. J. Wang, B. Liu, Y. Zhao, C. Yuan, and H. Deng, ‘‘Wide upper-

stopband super-UWB BPF based on SCRLH transmission line

structure,’’ Electron Lett 47 (2011), 1233–1235.

VC 2012 Wiley Periodicals, Inc.

SHARED APERTURE DUAL BAND DUALPOLARIZATION MICROSTRIP PATCHANTENNA

Devendra Kumar Sharma, Sanjeev Kulshrestha,S. B. Chakrabarty, and Rajeev JyotiSpace Applications Centre, ISRO, Ahmedabad, India;Corresponding author: devendrasharma@sac.isro.gov.in

Received 2 August 2012

ABSTRACT: This article presents the design and development of a new

type of wideband shared aperture dual band dual microstrippolarization patch antenna (MPA) operating at L&S band. In this

configuration, square ring shaped radiating element at L band andsquare shaped patch printed on different dielectric substrate layershoused within the square ring at S-band has been used. The probe fed

feeding mechanism is employed to get wide bandwidth performance atboth bands. The measured 10-dB return loss bandwidth is 28.3% at L

band and 29.4% at S-band. The simulated and measured antennaparameters of this antenna are in excellent agreement. VC 2012 Wiley

Periodicals, Inc. Microwave Opt Technol Lett 55:917–922, 2013; View

this article online at wileyonlinelibrary.com. DOI: 10.1002/mop.27414

Key words: dual polarization; dual band, antenna array; probe fedmicrostrip antenna; shared aperture

1. INTRODUCTION

The modern radar systems require compact antennas with multi-

functional capabilities catering dual band or multiband fre-

quency operation. It is desirable to cover the frequency range at

dual band or multiband using single aperture antenna without

band interference. Dual-frequency microstrip polarization patch

antennas (MPAs) should operate on both frequencies with

desired performance. There are numerous solutions to dual-fre-

quency operation suggested by many researchers [1–11]. In the

literature, the dual frequency operation is achieved by (i) Excita-

tion of orthogonal modes [2–5], (ii) stacking of patches [6–12],

and (iii) suitable loading of MPAs [13, 14]. All these configura-

tions result into narrow bandwidth of the order of 1–2% at indi-

vidual frequency bands. Shafai et al. [15] and Pozar et al. [16]

has reported dual band antenna having frequency ratio of 4:1 in

which perforated patch geometry at lower band to accommodate

the higher frequency patch is selected. The reported bandwidth

is 4% at C-band and 8% at L-band. The L-probe patch reported

by Li et al. [17] has bandwidth of the order of 28% at lower

band and 42% at higher band. In this article, the shorting vias

are used to place the patch of higher frequency over the patch

of lower frequency to avoid the hindering of the radiation pat-

tern of the higher band. Also, the use of shoring vias will add

fabrication complexity in the large size planar array antenna

configuration where higher gain is required and result into poor

reliability in space-borne applications.

In this article, a new type of wideband shared aperture dual

band dual polarization (DBDP) microstrip patch element has

been proposed and investigated. In this configuration, square

ring shape has been preferred at lower frequency band to

accommodate the higher frequency patch. The modified L-probe

feed mechanism is used for the easy realization when compared

to the conventional L-shape/hook probe feeding structure [18,

19] for wide bandwidth performance. The proposed element

with modified L-probe fed square ring at lower frequency and

square patch at higher frequency with return loss bandwidth and

stable radiation patterns at both bands is not reported to best of

author’s knowledge. The proposed element with a frequency

separation of more than 1:2 is best suitable for the SAR applica-

tions at L/S//C/X bands. This new dual band patch antenna ge-

ometry can be generalized for dual polarization and circular

polarization operations.

2. DESIGN AND SIMULATIONS

The geometry of proposed DBDP antenna and its side view are

depicted in Figures 1 and 2. The antenna is optimized using the

method of moment (MOM) based full-wave EM solver Ansoft

Designer Ver 4.0.0. This antenna consists of a square ring,

which is electromagnetically coupled to probe fed strip for both

the polarization at L band with center frequency of 1.25 GHz.

For higher band, the patch is coupled to probe fed strip for dual

polarization having center frequency of 2.5 GHz. The perfora-

tion in square ring is optimized at L-band so that it should be

large enough to avoid hindering the radiation from S band ele-

ments. A larger perforation is preferred in terms of good isola-

tion performance between the two bands and more symmetric

pattern at both bands. The square ring with outer dimension of

66 mm and inner dimension of 52 mm is optimized for the

lower band and square patch of 40 mm for higher band. The

strip dimension of 15.5 mm � 28 mm is selected for L-band

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 55, No. 4, April 2013 917