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to (16) above. A corollary is that a significant part of the error is due tothe contaminating fields launched by edge diffraction from the upperedge of the ogive.

The positions of the normals to the wedge faces at the lower edge areindicated in Figs. 6 and 7. These are the boundaries to the definition of�i in (13). It is noted that the error is small and without discontinuities

at and between these boundaries.

VI. CONCLUSION

This paper concludes that the expression of (3), together with theEGO expressions of (11) or (12) and (13), usefully represent the fieldat the edge of a curved face wedge, provided that the radius of cur-vature of the wedge faces is sufficiently large. The expressions for theEGO field are continuous through the shadow boundary and are simpleto evaluate. The expression has been tested against numerical data cal-culated for an ogive cylinder. Close agreement has been found. Fur-thermore, in the limits as radius of curvature becomes infinite, or thewedge angle approaches � radians, the expression reproduces the re-sults of established theories.

REFERENCES

[1] J. B. Keller, “One hundred years of diffraction theory,” IEEE Trans. An-tennas Propagat., vol. 33, Feb. 1985.

[2] P. Pathak, “High frequency techniques for antenna analysis,” Proc.IEEE, vol. 80, Jan. 1992.

[3] R. G. Kouyoumjian and P. H. Pathak, “A uniform geometrical theory ofdiffraction for an edge in a perfectly conducting surface,” IEEE Trans.Antennas Propagat., vol. 62, Nov. 1974.

[4] S. Lee and G. A. Deschamps, “A uniform asymptotic theory of electro-magnetic diffraction by a curved wedge,” IEEE Trans. Antennas Prop-agat., vol. AP-24, pp. 25–34, Jan. 1976.

[5] W. D. Burnside, P. H. Pathak, and R. J. Marhefka, “A uniform GTDanalysis of the diffraction of electromagnetic waves by a smooth convexsurface,” IEEE Trans. Antennas Propagat., vol. 28, Sept. 1980.

[6] C. W. Chuang, M. C. Liang, and P. H. Pathak, “A generalized uniformgeometrical theory of diffraction ray solution for the diffraction by awedge with convex faces,” Radio Sci., vol. 31, no. 4, pp. 679–691,July–Aug. 1996.

[7] A. Michaeli, “Transition functions for high frequency diffraction bya curved perfectly conducting wedge, Part I: Canonical solution for acurved sheet,” IEEE Trans. Antennas Propagat., vol. 37, Sept. 1989.

[8] , “Transition functions for high frequency diffraction by a curvedperfectly conducting wedge, Part II: A partially uniform solution for ageneral wedge angle,” IEEE Trans. Antennas Propagat., vol. 37, Sept.1989.

[9] , “Transition functions for high frequency diffraction by a curvedperfectly conducting wedge, Part III: Extension to overlapping transitionregions,” IEEE Trans. Antennas Propagat., vol. 37, Sept. 1989.

[10] N. C. Albertsen, “Diffraction of Creeping Waves (Rep LD24),” Tech-nical University of Denmark, 1974.

[11] V. A. Borovikov, “Diffraction by a wedge with curved faces,” Akustich-eskii Zhurnal, vol. 25, no. 6, pp. 825–835, 1979.

[12] N. C. Albertsen and P. L. Christiansen, “Hybrid diffraction coefficientsfor first and second order discontinuities of two-dimensional scatterers,”SIAM J. Appl. Math., vol. 34, no. 2, pp. 398–414, Mar. 1978.

[13] P. Pathak, R. Kouyoumjian, and W. Burnside, Theoretical Methods forDetermining the Interaction of Electromagnetic Waves with Structures,Part II. Chapter 5. A Uniform GTD for the Diffraction by Edges, Verticesand Convex Surfaces, The Netherlands: Sijthoff and Noordhoff, 1981.

[14] E. G. Knott and T. B. A. Senior, “Comparisons of three high frequencydiffraction techniques,” Proc. IEEE, vol. 62, no. 11, Nov. 1974.

[15] P. Ufimtsev, “Comments on comparisons of three high frequency diffrac-tion techniques,” Proc. IEEE, vol. 63, no. 12, Dec. 1975.

[16] P. K. Murthy and G. A. Thiele, “Nonuniform currents on a wedge illu-minated by a TE plane wave,” IEEE Trans. Antennas Propagat., vol. 34,Aug. 1986.

[17] K. M. Pasala, “Closed form expressions for nonuniform currents on awedge illuminated by a TM plane wave,” IEEE Trans. Antennas Prop-agat., vol. 36, Dec. 1988.

[18] G. N. Milford, “Calculation of the current on the surface of a curved facewedge under TE plane wave illumination,” Ph.D. dissertation, Schoolof Elect. Eng., Univ. College, Univ. New South Wales, Australia, 2002.Campbell, ACT 2600.

[19] C. Balanis, Advanced Engineering Electromagnetics. New York:Wiley, 1989.

[20] D. A. McNamara, C. W. I. Pistorius, and J. A. G. Malherbe, Introduc-tion to theUniformGeometrical Theory of Diffraction. Norwood,MA:Artech House, 1991.

[21] G. James, Geometric Theory of Diffraction, 3rd ed. New York: PeterPeregrinus, 1986.

[22] M. Abramowitz and I. Stegun, Handbook of Mathematical Func-tions. New York: Dover, 1964.

[23] R. Kouyoumjian, Numerical and Asymptotic Techniques in AppliedPhysics, Chapter 6. The GTD and its Applications. New York:Springer Verlag, 1975.

A New Ultrawideband Printed Monopole Antenna: ThePlanar Inverted Cone Antenna (PICA)

Seong-Youp Suh, Warren L. Stutzman, and William A. Davis

Abstract—Anew antenna, the planar inverted cone antenna (PICA), pro-vides ultrawideband (UWB) performance with a radiation pattern similarto monopole disk antennas [1]–[8], but is smaller in size. Extensive simula-tions and experiments demonstrate that the PICA antenna provides morethan a 10:1 impedance bandwidth (for VSWR 2) and supports amonopole type omnidirectional pattern over 4:1 bandwidth. A second ver-sion of the PICA with two circular holes changes the current flow on themetal disk and extends the high end of the operating frequency range, im-proving the pattern bandwidth to 7:1.

Index Terms—Monopole disk antenna, pattern enhancement, planar an-tenna, ultrawideband (UWB) antenna.

I. INTRODUCTION

The need for ultrawideband (UWB) antennas with omnidirectionalcoverage is increasing for both military and commercial applications.A current example is UWB applications for imaging and communica-tion operating in the 3.1–10.6 GHz band, which is a 3.4:1 bandwidth.Most of these applications require an antenna with a compact, thin an-tenna geometry. The classic solution for achieving an omnidirectionalpattern is to use a thin wire dipole or its counterpart monopole versionwith a ground plane (if a half-space is to be illuminated). However,the wire dipole and monopole suffer from a narrow impedance band-width. The bandwidth can be widened using a flat metal structure ratherthan a thin wire structure [9]. Many flat plate radiator geometries havebeen explored over several decades, as discussed in [1]–[8]. However,

Manuscript received November 14, 2002; revised July 9, 2003.S.-Y. Suh was with the Virginia Tech Antenna Group, Bradley Department of

Electrical and Computer Engineering, Virginia Polytechnic Institute and StateUniversity, Blacksburg, VA 24061 USA. He is nowwith the Radio Communica-tions Laboratory, Intel Corporation, Santa Clara, CA 95052 8119 USA (e-mail:seong-youp.suh@intel.com).

W. L. Stutzman and W. A. Davis are with the Virginia Tech Antenna Group,Bradley Department of Electrical and Computer Engineering, Virginia Poly-technic Institute and State University, Blacksburg, VA 24061 USA.

Digital Object Identifier 10.1109/TAP.2004.827529

0018-926X/04$20.00 © 2004 IEEE

1362 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 52, NO. 5, MAY 2004

Fig. 1. Geometries of PICA. (a) Basic PICA antenna. (b) General PICA antenna.

Fig. 2. Hardware test models of the PICA antenna. The shaded part is the substrate used to support the radiating element, and is not necessary for proper operation.(a) PICA antenna (without holes). (b) Two-circular-hole PICA antenna.

these antennas suffer from pattern degradation at the high end of theirimpedance bandwidth.

This communication presents a new wideband, omnidirectional, flatantenna called the planar inverted cone antenna (PICA)1 [10], [11].The PICA antenna can be thought of as an evolution of the volcanoantenna [12] and the circular disk antenna [2]. The PICA is composedof a single flat element vertically mounted above a ground plane asshown in Fig. 1. The antenna geometry is very simple, yet provides out-standing impedance and radiation pattern performance. The impedancebandwidth is more than 10:1 and the pattern bandwidth is about 4:1.The antenna characteristics of the PICA element are similar to typicalmonopole disk antennas presented in [1]–[8]. Even greater bandwidththan the basic PICA form of Fig. 1(a) is achieved by adding two cir-cular holes in the PICA element as shown in Fig. 2(b). This alterationimproves the radiation pattern performance dramatically without im-pairing the impedance performance of more than 10:1 forVSWR < 2.The radiation patterns of the two-circular-hole PICA antenna providegood omnidirectional performance over a bandwidth up to 7:1 and havevery low cross polarization, 20 dB or less. A circular disk antenna witha single hole centered in the disk was reported in [13], but the hole didnot significantly enhance the radiation pattern bandwidth. The resultsin [13] did demonstrate that annular monopole antennas operate likethe plain monopole antenna even after half of the circular element hasbeen removed [13].

1Patent application filed; see http://www.vtip.org/licensing/disclo-sures/00-130.htm

Fig. 3. Measured VSWR of the PICA hardware model antennas shown inFig. 2.

This communication shows that two circular holes made in the PICAelement dramatically enhance the pattern of the antenna without de-grading the impedance performance. The PICA characteristics wereextensively investigated using simulations and experiments by exam-ining impedance and radiation pattern performance. The two circular

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 52, NO. 5, MAY 2004 1363

Fig. 4. Measured radiation patterns of the PICA antennas shown in Fig. 2(a) and (b). (a) Elevation patterns at 1.0 GHz. (b) Elevation patterns at 3.4 GHz. (c)Elevation patterns at 7.0 GHz.

hole modification for pattern improvement can be also applied to themonopole disk antennas presented in [1]–[8].

II. ANTENNA DESIGN

The basic PICA antenna geometry in Fig. 1(a) is based on the con-ventional, circular-disk antenna [2]. The top part of the circular-disk

antenna is trimmed to the shape of a planar-inverted cone, inspiring thename PICA. The height of the PICA antenna in Fig. 1 is about a quarterwavelength at the low-end operating band; that is, L = �L=4where �Lis the wavelength at the lowest acceptable performance frequency. Thedimensions L1, L2, and L3 in Fig. 1(a) can be varied to obtain optimumperformance.

1364 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 52, NO. 5, MAY 2004

Fig. 5. Computed maximum gain of the two-circular-hole PICA antennashown in Fig. 2(b).

Themore general geometry of the PICA antenna of Fig. 1(b) reducesto the basic PICA geometry when dimension P1 = 0. Varying dimen-sion P1 alters the PICA shape and size, providing a means to customizeperformance for specific applications. The shape of edge P2 influencesthe impedance bandwidth and pattern; circular, elliptical, and exponen-tial shapes offer broad impedance bandwidth and an omnidirectionalantenna pattern. Note that the circularly tapered edge P2, as shown inFig. 1(b), is related to the volcano antenna discussed in [12] but has asimpler geometry. The ground plane of the volcano antenna of [12] isgradually tapered to obtain wide impedance bandwidth, but the PICAhas a circular or elliptical base with a flat ground plane. The circular orelliptical base functions similarly to the gradually tapered ground planeof the volcano antenna. The simple geometry of the PICA antenna iseasier to construct than the volcano antenna while offering a similarbandwidth.

III. MEASURED AND CALCULATED RESULTS

The two hardware test models shown in Fig. 2 were constructed andmeasured. The first hardware model of Fig. 2(a) is a slightly modi-fied version of the basic geometry of the PICA in Fig. 1(a), forming ateardrop shape by tapering the straight line between vertex and curve asshown in Fig. 2(a). The second hardware model of Fig. 2(b) with twocircular holes was developed as a result of extensive investigations ofthe PICA antenna to find geometries with improved radiation patterns.The circular hole of the PICA examined in this communication is onlyrepresentative of various shaped holes that are possible for customizingantenna performance for specific performance criteria.

Both PICA elements in Fig. 2 were constructed with dimensionsof L1 = 47 mm (1.8500), L2 = 29:2 mm (1.1500) and L3 = 76:2mm (3.000). The ratio L1=L2 = 1:609, is close to the golden ratio(or Sacred ratio) of 1.618 [14]. The radiating element was etchedon a substrate with a dielectric constant of 2.33 and a thickness of0.79 mm (31 mils). The feed is 0.64 mm (h = 0:02500) above analuminum ground plane with dimensions of 609.6 mm� 609.6 mm(2400

� 2400), corresponding to about 2:0� square at the low-endoperating frequency. The circular holes of the second hardware modelin Fig. 2(b) were etched with a radius of r = 10:16mm at locations of(y; z) = (�15:24 mm; 15:24 mm).

Fig. 3 shows the measured VSWR curves of the two PICA hardwaremodel antennas referenced to 50-. Both PICA antennas provide abouta 10:1 impedance bandwidth for VSWR < 2, although the VSWR

versus frequency curves are slightly different. This decade impedancebandwidth is extremely large for such a simple structure.Radiation patterns were measured in the Virginia Tech indoor

anechoic chamber using a near-field scanner. Fig. 4 shows themeasured radiation patterns at representative selected frequencies.The radiation patterns gradually degrade with increasing frequencyand the upper-frequency operating limit is determined by pattern re-quirements. For many applications the pattern at 7 GHz is acceptable,leading to the conclusion that the PICA antenna has a monopole-typepattern over a 7:1 bandwidth. Since the pattern bandwidth is less thanthe 10:1 impedance bandwidth, PICA antennas are bandwidth limitedby the pattern. The PICA and two-circular-hole PICA behave similarlyin impedance performance. However, the two-circular-hole PICA hasbetter patterns at the high end of the frequency band; see Fig. 4(c).Extensive calculations were performed using Fidelity, which is a

FDTD code from Zeland [15], to find antenna geometries with goodperformance. The calculated results for pattern and impedance agreevery well with measured results. Gain was also calculated using the Fi-delity. The results for the two-circular-hole PICA of Fig. 2(b) are shownin Fig. 5. Gain gradually increases with frequency. It is about 5 dBi atthe lowest operating frequency of 1 GHz and is about 8 dBi at the highend of both the pattern and impedance operating bands, 7 and 10 GHz.

IV. CONCLUSION

A new and simple antenna with extremely wide bandwidth was in-troduced. Experiments with hardware test models showed that PICAantennas are capable of a 10:1 impedance bandwidth. Measurementsalso showed that the PICA antenna provides monopole type omnidi-rectional patterns over 7:1 bandwidth. The two-circular-hole PICA hasbetter patterns, without degrading the impedance bandwidth of morethan 10:1 for VSWR < 2. The gain gradually increases from 5 to 8dBi over the operating band, based on simulation of the hardware testmodel geometries.The PICA’s wide bandwidth is likely due to the fact that the radiating

element is of the biconical antenna family [1], which has many formswith wide bandwidth. The concept of using holes in the disk can also beapplied to the monopole disk antennas in [1]–[8] to enhance the patternperformance.The PICA antenna is an excellent candidate radiating element for

UWB antenna applications. UWB requires that the antenna efficientlypropagate pulses with minimal distortion over 3.4:1 bandwidth. TheUWB can be covered in a single PICA antenna element. Examples ofthe UWB antennas are the modified tapered-slot antennas with metalshaped as rabbit ears [16] and planar elliptical dipole [17]. When thePICA antenna is modified into a dipole form, the geometry is very sim-ilar to these antennas [16] and planar elliptical dipole [17]. DetailedPICA antenna characterization in the time domain for UWB applica-tions is in progress using a scaled PICA antenna operating from 3.1 to10.6 GHz.

REFERENCES

[1] G. H. Brown andO.M.Woodward Jr., “Experimentally determined radi-ation characteristics of conical and triangular antennas,” RCA Rev., vol.13, pp. 425–452, Dec. 1952.

[2] B. J. Lamberty, “A class of low gain broadband antennas,” in Proc. IREWescon Convention Rec., Aug. 1958, pp. 251–259.

[3] S. Honda, M. Ito, H. Seki, and Y. Jinbo, “A disc monopole antennawith 1:8 impedance bandwidth and omni-directional radiation pattern,”in Proc. ISAP 92, Sapporo, Japan, Sept. 1992, pp. 1145–1148.

[4] P. P. Hammoud and F. Colomel, “Matching the input impedance of abroadband disc monopole,” Electron. Lett., vol. 29, pp. 406–407, Feb.1993.

[5] R. M. Taylor, “A broadband omni-directional antenna,” in Proc. IEEEAntennas Propagat. Soc. Int. Symp. Dig., vol. 2, Seattle, WA, June 1994,pp. 1294–1297.

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 52, NO. 5, MAY 2004 1365

[6] N. P. Agrawall, G. Kumar, and K. P. Ray, “Wide-band planar monopoleantennas,” IEEE Trans. Antennas Propagat., vol. 46, pp. 294–295, Feb.1998.

[7] J. A. Evans and M. J. Ammann, “Planar trapezoidal and pentagonalmonopoles with impedance bandwidth in excess of 10:1,” in Proc. IEEEInt. Symp. Dig., vol. 3, Orlando, FL, 1999, pp. 1558–1559.

[8] E. Lee, P. S. Hall, and P. Gardner, “Novel compact wideband or multi-band planar antenna,” inProc. IEEEAntennas Propagat. Soc. Int. Symp.,Salt Lake City, UT, July 2000, pp. 624–627.

[9] W. L. Stutzman and G. A. Thiele, Antenna Theory and Design, 2nded. New York: Wiley, 1998, p. 172.

[10] A Planar Inverted Cone Antenna, S.-Y. Suh and W. L. Stutzman. (2000,Sept. 8). [Online]. Available: http://www.vtip.org/Licensing/disclo-sures/00-130.htm

[11] S.-Y. Suh, “A comprehensive investigation of new planar wideband an-tennas,” Ph.D. dissertation, Virginia Polytech. Inst. State Univ., Blacks-burg, VA, July 2002.

[12] J. D. Kraus, Antennas. New York: McGraw-Hill, 1950, p. 9.[13] Z. N. Chen, M. J. Ammann, M. Y. W. Chia, and T. S. P. See, “Annular

planar monopole antenna,” Proc. Inst. Elect. Eng. Microw. AntennasPropag., vol. 149, pp. 200–203, Aug. 2002.

[14] Phi: The Golden Number, G. Meisner. [Online]. Available:http://goldennumber.net/

[15] Fidelity User’s Manual (2000). [Online]. Available: www.zeland.com[16] J. C. Adams, W. Gregorwich, L. Capots, and D. Liccardo, “Ultra-wide-

band for navigation and communications,” in Proc. IEEE AerospaceConf., vol. 2, 2001, pp. 2/785–2/785.

[17] H. G. Schantz, “Planar elliptical element ultra-wideband dipole an-tennas,” in Proc. IEEE Antennas Propagat. Soc. Int. Symp. Dig., vol. 3,San Antonio, TX, June 2002, pp. 44–47.

A Circularly Polarized Stacked ElectromagneticallyCoupled Patch Antenna

Kwok L. Chung and Ananda S. Mohan

Abstract—In this communication, we present a high-performance cir-cularly polarized (CP) stacked electromagnetically coupled patch antennaand its subarray at X band. In addition to low boresight axial-ratios, thesubarray has measured 10-dB impedance and 3-dB axial-ratio bandwidthsof 25.6% and 23.5% respectively as compared to the measured 20.2% and8.0% for a single element. The mutual coupling for this element is shown tobe lower than other reported stacked patch antennas and obtained a gain( 10 dbic) bandwidth of 23.5%. The calculated antenna efficiency is 89%around center frequency for the single element whereas the subarray hasan overall efficiency of 71% ( 1 5 dB) over 21% bandwidth.

Index Terms—Antenna efficiency, axial-ratio bandwidth (A BW),EMCP antennas, singly fed circularly polarized (SFCP) patch antennas,stacked patch antennas.

I. INTRODUCTION

Traditional single layer, singly fed circularly polarized (SFCP) mi-crostrip patch antennas have inherent limitations in gain, impedanceand axial-ratio bandwidths. This is mainly owing to the resonant natureof the patch antennas—a high unloaded Q-factor and the frequency-de-

Manuscript received March 18, 2003; revised June 14, 2003. This work wassupported by the Commonwealth of Australia through the Cooperative ResearchCentres Program.

The authors are with the Microwave andWireless Technology Research Lab-oratory, ICT Group, Faculty of Engineering, University of Technology, Sydney,NSW 2007, Australia.

Digital Object Identifier 10.1109/TAP.2004.827490

Fig. 1. X-band RHCP-EMCP element: geometry and dimensions of thestacked patches.

Fig. 2. Silhouette of 90 sequentially rotated subarray composed of rotatedelements with offset patches.

pendent excitation of the two degenerative modes (TM01 and TM10)when using a single feed. One way to increase the impedance band-width is by minimizing the unloaded Q-factor with the use of an elec-trically thick substrate for the patch. However, the feed reactance andsurface-wave power due to the thick substrate can become additionalproblems. As an alternative to increase the gain and bandwidth, thestacked patches and electromagnetically coupled patch (EMCP) con-figurations for linear polarization (LP) were proposed [1], [2]. The sur-face-wave problems can be overcome either by the use of Lo-Hi (sub-strate-superstrate) dielectric layer combination [3] or having an electri-cally large printed patch particularly for complex structures [4]. How-ever, these methods can result in complicated antenna structures withlimited bandwidth improvement. Owing to the larger patch, to buildan array composed of such elements having a center spacing of lessthan 0:7�o can be difficult. Waterhouse proposed a technique that usesstacked patches printed on Hi-Lo dielectric layers (two-layers) to ob-tain not only high surface-wave efficiency but also broad impedancebandwidth (ZBW) and axial-ratio bandwidth (AxBW) for the CP patchantennas [5]. The fundamental basis for the technique in [5] is thatthe patch antennas require loosely bound field for radiation into space,while circuitry and feed network require tightly bound fields to sup-press undesired radiation and coupling. Therefore, the use of high di-electric constant for substrate and low dielectric constant for super-strate becomes a straightforward choice. Based on this and those avail-able in [5], the authors have developed a design method to optimize

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