3. FABRICATION AND MEASUREMENT

One prototype BPF, as shown in Figure 4, having the dimensionsw1 � 1.2, l1 � 5.5, g � 0.8, r1 � 4.4, r2 � 4.7, r3 � 5.2, r4 � 5.5,r5 � 6.0, and r6 � 6.3 mm is fabricated on the same Rt/duroid®5880 substrate. The LPF dimensions are w2 � 2.5, w3 � 0.5, l2 �6.3, l3 � 3.7, and l4 � 6.7 mm. Here, the LPF dimensions arechosen to increase the upper stopband rejection level. Figure 5shows the measured and simulated S-parameters of the filter. Fora better comparison, narrowband S-parameters variation is shownin Figure 6. Measured cutoff frequencies are 2.939 and 4.651 GHzwhich results in a FBW of 45.1%. Passband IL is within 2.0 dB.The BPF implementing area is 0.2191 �g � 0.2261 �g without theLPF and 0.3653 �g � 0.2261 �g with the LPF, �g being microstripguided wavelength at f0 � 3.795. There is only one passband fromDC to 15 GHz. Upper stopband of 40 and 18 dB is extended from5.703 to 10.080 and 4.964 to 15.0 GHz, respectively. Figure 7shows the BPF passband group delay variation. The filter has amaximum passband group delay variation of 1.21 nS.

4. CONCLUSION

This article presents a new structure for compact BPF design. Theprocedure to obtain a wide passband with good in band as well asout of band filter characteristics is presented. The filter has theadvantages of low passband group delay variation, compact sizeand wide upper stopband. Present BPF has a wider upper stopbandcompared to those reported in Refs. 2–6 and compact size thanthose reported in Refs. 2, 4–6. As no via holes or lump element isrequired, the filter is easy to fabricate.

REFERENCES

1. G.L. Matthaei, L. Young, and E.M.T. Jones, Microwave filters, imped-ance-matching network, and coupling structures, Artech House, Nor-wood, MA, 1980.

2. J.T. Kuo and E. Shih, Wideband band pass filter design with three-linemicrostrip structures, IEE Proc Microwave Antennas Propag 149(2002), 243–247.

3. L. Zhu, H. Bu, and K. Wu, Broadband and compact multi-pole micro-strip bandpass filters using ground plane aperture technique, IEE ProcMicrowave Antennas Propag 149 (2002), 71–77.

4. C.-Y. Chen, C.-Y. Hsu, and S.-F. Lin, A novel compact miniaturizedwideband microstrip bandpass filters with dual-mode ring resonators,Microwave Opt Technol Lett 45 (2005), 312–315.

5. T. Tumer and A. Gorur, Reduced-size wideband microstrip bandpassfilter with low loss and high selectivity, Microwave Opt Technol Lett 45(2005), 147, 148.

6. J. Bonache, F. Martin, I. Gil, J. Garcia-Garcia, R. Marques, and M.Sorolla, Microstrip bandpass filters with wide bandwidth and compactdimensions, Microwave Opt Technol Lett 46 (2005), 343–346.

© 2006 Wiley Periodicals, Inc.

WIDE STOPBAND EBG STRUCTUREDESIGN BASED ON 2D NONLINEARLYTAPERED SLOT ARRAY

Jack Wu,1 S. N. Qiu,2 C. X. Qiu,2 and I. Shih1

1 Department of Electrical and Computer EngineeringMcGill UniversityMontreal, Quebec H3A 2T5, Canada2 CIS ScientificMontreal, Quebec J4Z 1W6, Canada

Received 30 May 2006

ABSTRACT: Electromagnetic bandgap structures are well known fortheir stopband features and can be applied at microwave frequencies. Inthis work, a wide stopband electromagnetic band-gap (EBG) structuredesign based on 2D tapered slot array is presented. Each tapered slotlength is designed to provide stopband at a specific frequency to maxi-mize the attenuation level. The tapered slot array is positioned in theground plane of a microstrip transmission line structure. Thus, the over-all 9-slot nonlinearly tapered array produces a wide stopband from 9.3to 20 GHz with attenuation better than 25 dB, which is observed in bothsimulation and actual measurements. The nonlinearly tapered EBGstructure can be applied as an efficient lowpass filter. © 2006 WileyPeriodicals, Inc. Microwave Opt Technol Lett 49: 31–34, 2007;Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.22038

Key words: electromagnetic bandgap; lowpass filter; microstrip trans-mission line; tapered slot array

1. INTRODUCTION

Photonic band-gap (PBG) was initially referred to the preventionof light propagation in optical regime due to strong reflection. Such

Figure 6 Narrowband S-parameters of the BPF in Figure 4. Dashed andsolid lines are for simulations and measurements, respectively

Figure 7 Passband group delay variation of the BPF

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 49, No. 1, January 2007 31

reflection is caused by a periodic change of dielectric layers withdifferent index of refractions [1–3].

This remarkable property inspires many researchers to putefforts into the development of PBG structures in microwave andmillimeter-wave components [4], which are also known as elec-tromagnetic band-gap (EBG). Interests have been paid to EBGstructures because of their special features such as prohibitingelectromagnetic waves from traveling at frequencies within theEBG. In addition, the EBG structure is an attractive design becausevarious shapes of periodic lattice can be implemented easily in theground plane of a microstrip transmission line. Because of theinterference created by periodic perforations, the traveling signal at

a certain frequency range is prohibited [5–8]. Furthermore, cas-caded and paralleled periodic perforations were utilized to increasethe robustness of the EBG structures in terms of stopband atten-uation and width [9, 10]. Spiral slots and perforation patternsutilized with open-ended stub were also reported to enhance theEBG filter performance [11, 12]. Ordinary EBG designs exhibitS11 ripples in the passband region and therefore, the transmissionquality near the stopband edge is usually degraded significantly[13–15]. This drawback can be improved by considering a specialtype of periodic perforation called “Tapered Array” (TA) pattern.TA patterns offer superior passband and notably wider stopbandcharacteristics with a compact structural size.

In this article, the design of nonlinearly tapered slot array EBGstructure is first studied. Then, analysis of the simulation resultscomparing both linearly and nonlinearly TA patterns are presented. Inthe end, the comparison between the measurements on a fabricatedsample and simulation results is shown to validate the design.

2. DESIGN PROCEDURE

The most unique characteristic of TA patterned EBG structure isthat it is consisted of a periodic array of slots with different slotlengths. Figure 1 illustrates linearly and nonlinearly TA patterns.

The general performance of TA patterned EBG structure can bedemonstrated through the linear configuration. However, to fullyutilize the TA patterned EBG structure in any specific application,nonlinear configuration can be used to maximize the stopbandeffect at a wide range of frequency. In this section, the design ofa nonlinearly TA pattern with stopband from 9.3 to 20 GHz isstudied and verified. To model the nonlinearly TA pattern, RLCequivalent circuit is used to represent each slot. Simulations wereperformed with Agilent Advanced Design System. Figure 2 showsthe equivalent circuit and the layout of a single slot.

Figure 3 shows the comparison of the S-parameters betweenthe equivalent circuit model and simulation results from the layout.

From Figure 3, it is noticed that the RLC equivalent circuit modelsthe slot perforation fairly well. Therefore, it is possible to find the restof the slot lengths (L1, L2, L3, and L4) using this technique andconstruct a wide stopband lowpass filter. The dimensions of the

Figure 1 (a) Linearly and (b) nonlinearly 9-slot TA patterned EBGstructure implemented in the ground plane of a microstrip transmission line

Figure 2 (a) Equivalent circuit with R � 500 �, L � 1.05 nH, and C �0.185 pF, and (b) layout of the center slot with LC � 7.9 mm and h � 0.5mm (microstrip width � 0.25 mm and, thickness of Alumina � 0.25 mm)

Figure 3 A comparison of S-parameters between the equivalent circuitmodel and the layout design for the center slot, LC � 0.79 mm

TABLE 1 Dimensions of Nonlinearly Tapered Array Pattern

Number of slots (n) 9Center slot length (L) 7.9 mmStructure period (a) 1.5 mmSlot lengths (L1, L2, L3, and L4) 7.4, 5.7, 4.5, AND 3.7 MMSlot width (h) 0.5 mm

32 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 49, No. 1, January 2007 DOI 10.1002/mop

nonlinearly TA patterned EBG structure, which can be utilized as awide stopband lowpass filter, are summarized in Table I.

It is seen from Figure 4 that the overall 9-slot nonlinearly TApatterned structure has a very flat passband up to 9 GHz and astopband with high attenuation up to 20 GHz. Therefore, thesimulation results show promising performance for the nonlinearlyTA patterned EBG structure to be utilized as a lowpass widestopband filter. To illustrate the significance of the nonlinearlytapered structure, Figure 5 shows the simulation results of S21 ofboth linearly and nonlinearly TA patterned structure.

It is observed from Figure 5 that the nonlinear structure has asuperior stopband performance, especially near the stopband edge at9.5 and 10.5 GHz where the attenuation is 20 dB more than the linearstructure. Also, the nonlinear structure has a more defined passbandedge, which allows a better transmission near the cutoff frequency.

In the next section, the performance of the nonlinearly TApatterned EBG structure is verified with experimental results.

3. MEASUREMENTS AND COMPARISONS

A vector network analyzer (VNA) was used to carry out theS-parameters measurements of the nonlinearly TA patterned EBGsample. A universal test fixture fixed the sample in place and thesetup was connected to the VNA via microwave cables. Thus, theEBG structure was being measured as a two-port network whereS21 and S11 were used to characterize its performance.

Figure 6 shows the simulated and measured results on the 9-slotnonlinearly TA patterned EBG structure.

It is observed from Figure 6 that the simulated and measuredresults match very well. Therefore, the concept of constructing anonlinearly TA patterned EBG structure is verified.

4. CONCLUSION

In this work, the possibility of constructing a lowpass wide stop-band filter based on nonlinearly TA patterned EBG structure isexplored. Both simulation and measurement results suggest that itis feasible and the performance of stopband is significantly im-proved. The nonlinearly TA patterned structure is straightforwardto design and simple to implement with microstrip transmissionline configuration. Therefore, the nonlinear structure can easily beutilized and applied in microwave components that require alowpass filter.

REFERENCES

1. E. Yablonovitch, Inhibited spontaneous emission in solid-state physicsand electronics, Phys Rev Lett 58 (1987), 2059–2062.

2. K.M. Ho, C.T. Chan, and C.M. Soukoulis, Existence of a photonic gapin periodic dielectric structures, Phys Rev Lett 65 (1990), 3152–3155.

3. E. Yablonovitch and T.J. Gmitter, Photonic band structures: Theface-centered-cubic case, Phys Rev Lett 63 (1989), 1950–1953.

4. Y. Qian and T. Itoh, Planar periodic structures for microwave andmillimeter wave circuit applications, IEEE MTT-S Int MicrowaveSymp Dig 4 (1999), 13–19.

5. J. Wu, I. Shih, S.N. Qiu, C.X. Qiu, P. Maltais, and D. Gratton,Photonic bandgap microstrips with controlled bandstops, Paper pre-sented at Second CanSmart Workshop on Smart Materials and Struc-tures, Oct. 2002, pp. 171–179.

6. V. Radisic, Y. Qian, R. Coccioli, and T. Itoh, Novel 2-D photonicbandgap structure for microstrip lines, IEEE Microwave Guid WaveLett 8 (1998), 69–71.

7. T. Lopetegi, M.A.G. Laso, M.J. Erro, M. Sorolla, and M. Thumm,Analysis and design of periodic structures for microstrip lines by usingthe coupled mode theory, IEEE Microwave Wireless Comp Lett 12(2002), 441–443.

8. M.A.G. Laso, T. Lopetegi, M.J. Erro, D. Benito, M.J. Garde, and M.Sorolla, Multiple-frequency-tuned photonic bandgap microstrip struc-tures, IEEE Microwave Guid Wave Lett 10 (2000), 220–222.

9. I. Rumsey, M. Piket-May, and P. Keith Kelly, Photonic bandgapstructures used as filters in microstrip circuits, IEEE Microwave GuidWave Lett 8 (1998), 336–338.

10. T. Kim and C. Seo, A novel photonic bandgap structure for low-passfilter of wide stopband, IEEE Microwave Guid Wave Lett 10 (2000),13–15.

11. Shan Fuqi and Gao Baoxin, Novel compact photonic band-gap struc-tures using rectangular increasing-distance spiral slots, Microwave OptTechnol Lett 43 (2004), 144–146.

Figure 4 S21 results for both single slot (L � 7.9, 7.4, 5.7, 4.5, and 3.7mm) and 9-slot nonlinearly TA patterned EBG structure

Figure 5 S21 results for both linearly and nonlinearly TA patterned EBGstructure

Figure 6 S-parameter results of simulated (S) and measured (M) 9-slotTA patterned EBG structure

DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 49, No. 1, January 2007 33

12. Man-Long Her, Yi-Chyun Chiou, Yu-Zhen Wang, and Kun-Ying Lin,Electromagnetic periodic structure bandpass filter (EPS-BPF) with twotransmission zeros, Microwave Opt Technol Lett 42 (2004), 265–267.

13. N.C. Karmakar and M.N. Mollah, Investigations into nonuniformphotonic-bandgap microstripline low-pass filters, IEEE Trans Micro-wave Theory Technol 51 (2003), 564–572.

14. M. Bozzetti, A.D’Orazio, M. De Sario, V. Petruzzelli, F. Prudenzano,and F. Renna, Tapered photonic bandgap microstrip lowpass filters:Design and realization, IEE Proc Microwave Antennas Propag 150(2003), 459–462.

15. T.Y. Yun and K. Chang, Uniplanar one-dimensional photonic-bandgap structures and resonators, IEEE Trans Microwave TheoryTechnol 49 (2001), 549–553.

© 2006 Wiley Periodicals, Inc.

COMPACT DESIGNS OF A SHORTEDTRIANGULAR PATCH ANTENNA WITHA V SLOT

Chow-Yen-Desmond Sim and Tuan-Yung HanDepartment of Computer and Communication EngineeringChienkuo Technology UniversityChang-HuaTaiwan 500, Republic of China

Received 6 May 2006

ABSTRACT: The compact designs of a shorted triangular patch an-tenna embedded with a V slot are proposed and studied. A broadbandV-slotted triangular patch antenna with one shorting wall is initiallyconstructed as a reference. By inserting an additional shorting wall tothis reference antenna, a new broadband operation can be obtained andits operating frequency is decreased by 22%, which corresponds to areduction of 40% in the antenna area. The antenna area can be furtherreduced by symmetrically halving the patch size, and it is found that theimpedance bandwidth of the broadband operation demonstrated no obvi-ous variation and the operating frequency is only increased by around 8%.Details of the antenna designs and obtained results are presented. © 2006Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 34–37, 2007;Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.22061

Key words: shorted patch antenna; compact antenna; broadband antenna

1. INTRODUCTION

Because of the demand for compacting wireless communicationdevices, much attention has been given to the design of small sizeantennas with broadband operation. One popular design of doingso is by embedding a slot into a short-circuited patch antenna,which only needs one radiating patch to achieve broadband oper-ation. The characteristics of the slotted patch antenna with ashorting pin or wall have been studied in Refs. 1–3, and it is foundthat three resonant modes can be excited in the antenna structure.Moreover, by selecting a proper shorting wall width, two resonantmodes can be coupled together to form a broadband operation. Anexample of one such broadband design with impedance bandwidthof more than 30% is described in Ref. 3. In this study, a newbroadband design of a short-circuited triangular patch antennaembedded with a V-slot, which demonstrated a lower operatingfrequency as compared to the design reported in Ref. 3 is pro-posed. Note that the reduction in frequency implies that the patchsize of the proposed design is smaller at a given frequency. Inaddition, since the proposed broadband design possessed symmet-rical current distributions along the centerline of the slotted trian-

gular patch, the technology of halve patch size, which is describedin Ref. 4, can be used to further decrease the required patch area.Details of the proposed design and measured results are presented,and the simulated results by IE3D are also carried out to providevalidation for the experiments.

2. ANTENNA CONFIGURATION

Figure 1 shows the proposed antenna geometry. A small triangularwith a side length of 8.4 mm, is truncated at the tip of anequilateral triangular patch with a side length of 50 mm. This Vslot loaded truncated triangular patch, excited by a coaxial probe ofradius 0.6 mm, is fabricated on a FR4 substrate (thickness 0.6 mmand relative permittivity 4.4) and mounted above the ground planeat a height of 6 mm by two shorting walls, shorting wall A and B,with different widths; w and s respectively. For the case (s � 0mm) of without shorting wall B, the antenna is similar to thedual-frequency PIFA (planar inverted-F antenna) studied in Ref. 3.An example of this PIFA antenna with dimensions; w � 21 mm,d � 22 mm, a � 28 mm, and b � 4 mm is first constructed as areference antenna. The measured return loss is shown in Figure 2.

Figure 1 Geometry of the proposed V-slotted triangular patch antennawith two shorting walls; ground plane size: 100 � 100 mm2. [Color figurecan be viewed in the online issue, which is available at www.interscience.wiley.com]

Figure 2 Measured and simulated Return loss for the Prototype A

34 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 49, No. 1, January 2007 DOI 10.1002/mop