8. H.J. Chaloupka, X. Wang, and J.C. Coetzee, Superdirective 3-elementarray for adaptive beamforming, Microwave Opt Technol Lett 36 (2003).

9. H.J. Chaloupka, X. Wang, and J.C. Coetzee, Performance enhance-ment of smart antennas with reduced element spacing, IEEE ConfWireless Commun Networking, 2003, pp. 425–430.

10. J.B. Anderson and H.H. Rasmussen, Decoupling and descatteringnetworks for antennas, IEEE Trans Antennas Propagat 24 (1976),841–846.

11. Mathematica, ver. 4.0, Wolfram Research, Inc.12. D.M. Pozar, Microwave engineering, 2nd ed., Wiley, New York, 1998.13. D.H. Schrader, Microstrip circuit analysis, Prentice Hall, New York,

1995.14. J.A.G. Malherbe, Microwave transmission line filters, Artech House,

London, 1979.15. P.L.D. Abrie, The design of impedance-matching networks for radio-

frequency, Artech House, London, 1985.16. High-Frequency Structure Simulator, Ver. 9.2.1, Ansoft, Pittsburgh,

PA, 2004.17. H.J. Chaloupka, HTS antennas, H. Weinstock and N. Nisenoff (Eds.),

Microwave superconductivity, Kluwer, Dordrecht, 2001.

© 2005 Wiley Periodicals, Inc.

AN INTERNAL PLANAR MOBILE-PHONEANTENNA WITH A VERTICAL GROUNDPLANE

Kin-Lu Wong,1 Shao-Lun Chien,1 Chih-Ming Su,1 andFa-Shian Chang2

1 Department of Electrical EngineeringNational Sun Yat-Sen UniversityKaohsiung 804, Taiwan2 Department of Electrical EngineeringROC Military AcademyFeng-Shan 830, Taiwan

Received 11 March 2005

ABSTRACT: An internal planar mobile phone antenna with a smallvertical ground plane electrically connected to the system ground planeof the mobile phone is presented. The vertical ground plane can func-tion as an effective shielding wall between the antenna and the nearbyRF-shielding metal case or other associated elements in a mobile phone.In this case, the internal antenna can be compactly integrated within themobile phone without degradation of the antenna performances. Thisvertical-ground design concept applied to an internal PIFA with a hol-low shorting cylinder for a UMTS mobile phone is studied. © 2005Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 597–599, 2005;Published online in Wiley InterScience (www.interscience.wiley.com).

DOI 10.1002/mop.21061

Key words: antennas; planar inverted-F antennas (PIFAs); internalmobile-phone antennas; UMTS antennas

1. INTRODUCTION

Conventionally, the ground plane of an internal mobile phoneantenna such as the planar inverted-F antennas (PIFA) is parallel tothe antenna’s top patch [1]. With this configuration, there is anopening between the antenna’s top patch and ground plane facingtoward the interiors of the mobile phone. In this case, when theantenna is in operation, fringing fields are expected to be presentoutside the opening; thus, coupling between the antenna and thenearby associated elements such as the RF shielding metal case orthe battery will occur. This possible coupling will then causedegradation effects on the antenna performances. Thus, for prac-tical applications, an isolation distance (usually about or larger

than 7 mm) between the antenna and the nearby associated ele-ments is usually required such that the antenna performances willnot be degraded due to the possible coupling effects.

To overcome this problem, we apply a vertical-ground designconcept to an internal UMTS (Universal Mobile Telecommunica-tion System, 1920–2170 MHz) planar antenna with its shortingportion connected to the system ground plane of the mobile phone,while the antenna’s feeding portion is oriented perpendicular to anadded vertical ground plane. The results obtained in this paperindicate that the proposed internal antenna shows very good iso-lation to the nearby elements inside the mobile phone. Details ofthe proposed antenna are described, and the experimental andsimulated results are presented.

2. ANTENNA DESIGN

Figure 1(a) shows the geometry of the proposed antenna mountedat the top portion of the system ground plane of a mobile phone ora PDA phone for UMTS operation. Note that the antenna uses ahollow shorting cylinder [2] in place of a conventional shortingpin. This hollow shorting cylinder (8 mm in diameter here) can beused to accommodate the charge-coupled device (CCD) of anembedded digital camera in a mobile phone, thus leading to acompact integration of the antenna and the CCD. This integrationarrangement also results in almost no effects on the impedancematching of the antenna. (More detailed results will be analyzedwith the aid of Fig. 4 in the next section.)

The studied antenna occupies an area of 16 � 60 mm2 and hasa thickness of 7 mm from the antenna’s top patch to the systemground plane. The occupied volume of the antenna is about thesame as that in [2], although an additional vertical ground plane isadded as an integral part of the antenna. Also note that the verticalground has the same height (7 mm) as the antenna thickness. Withthe presence of the vertical ground plane, a parallel feeding ar-rangement for the antenna is used, which includes a small trian-

Figure 1 (a) Geometry of the proposed internal UMTS planar mobile-phone antenna with a vertical ground plane and a hollow shorting cylinder;(b) dimensions of the top patch including the small triangular feeding patch

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 46, No. 6, September 20 2005 597

gular feeding patch extended from the antenna’s top patch [dimen-sions shown in Fig. 1(b)] and a feed gap of 1 mm between thetriangular feeding patch and the vertical ground plane. Across thefeed gap, the feeding point (point A) is at the tip of the triangularfeeding patch and the grounding point (point B) is at the center ofthe top edge of the vertical ground plane. For testing the antennain this study, a 50� mini coaxial line with its central conductorconnected to point A and its outer grounding sheath connected topoint B is used to feed the antenna.

Note that the small triangular feeding patch has a flare angle �and a length of 1.5 mm extending from the antenna’s top patch.Good impedance matching over a wide frequency range in order tocover the UMTS band can be achieved by adjusting the flare angleonly. In this study, the optimal flare angle is about 73°.

3. EXPERIMENTAL RESULTS AND DISCUSSION

Figure 2 shows the measured and simulated return losses of theconstructed prototype of the studied antenna. The simulated resultsare obtained using Ansoft simulation software HFSS (High-Fre-quency Structure Simulator) [3]. Good agreement between themeasurement and simulation is seen. The measured impedancebandwidth, defined by 2:1 VSWR, reaches 333 MHz (1903–2236MHz) and covers the UMTS band. Figure 3 shows the simulatedreturn loss for the studied antenna with a nearby RF shieldingmetal case of size 40 � 60 � 3 mm3. The parameter d in the insetof the figure denotes the distance between the vertical groundplane and the RF-shielding metal case. Very small variations in thesimulated results of the return loss for the cases with and withoutthe RF-shielding metal case are seen. This behavior indicates that

there are very small coupling effects between the antenna and theRF-shielding metal case, thus causing almost no degrading effectson the antenna performances.

An antenna directly attached to a RF-shielding metal case (d �0) and loaded with a shielding metal case for the CCD in thehollow shorting cylinder is also studied. Figure 4 shows the sim-ulated results of the return loss. Again, small variations in thereturn loss are seen for different sizes of the CCD shielding caseloaded in the shorting cylinder. Figure 5 shows the measuredradiation patterns of the antenna at 2045 MHz, the center fre-quency of the UMTS band. Stable radiation patterns are alsoobtained for frequencies over the UMTS band, and the radiationcharacteristics are about the same as observed in [2]. Figure 6shows the measured antenna gain versus frequency. Over theUMTS band, the antenna gain is in the range of about 3.7–4.2 dBi.

4. CONCLUSION

The vertical-ground design technique for improving the antennaisolation has been successfully applied to an internal PIFA with ahollow shorting cylinder for a UMTS mobile phone. The addedvertical ground plane has been arranged as an integral part of theantenna, and good isolation behavior between the antenna and a

Figure 2 Measured and simulated return losses vs. frequency

Figure 3 Simulated return loss for the studied antenna with a nearbyRF-shielding metal case of size 40 � 60 � 3 mm3

Figure 4 Simulated return loss for the studied antenna directly attachedto a RF-shielding metal case and loaded with a shielding metal case for theCCD in the hollow shorting cylinder

Figure 5 Measured radiation patterns at 2045 MHz

598 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 46, No. 6, September 20 2005

nearby element such as the RF-shielding metal case inside themobile phone has been achieved. The obtained results also suggestthat compact integration between the studied internal antenna andthe associated elements inside a mobile phone can be obtained.

REFERENCES

1. K.L. Wong, Planar antennas for wireless communications, Wiley, NewYork, 2003.

2. S.L. Chien, F.R. Hsiao, Y.C. Lin, and K.L. Wong, Planar inverted-Fantenna with a hollow shorting cylinder for mobile phone with anembedded camera, Microwave Opt Technol Lett 41 (2004), 418–419.

3. Ansoft Corporation, HFSS, http://www.ansoft.com/products/hf/hfss/.

© 2005 Wiley Periodicals, Inc.

TWO-DIMENSIONAL MICROWAVETOMOGRAPHIC IMAGING OF LOW-WATER-CONTENT TISSUES

G. Bindu, Vinu Thomas, Anil Lonappan, A. V. Praveen Kumar,V. Hamsakkutty, C. K. Aanandan, and K. T. MathewDepartment of ElectronicsMicrowave Tomography and Materials Research LaboratoryCochin University of Science and TechnologyKochi–682 022, India

Received 8 March 2005

ABSTRACT: Microwave tomographic imaging is explored in order toanalyze the contrast in dielectric properties of low-water-content tissuessuch as bone and bone marrow. Two-dimensional tomographic imagesand dielectric-permittivity profiles of a calf femur are reconstructedfrom experimentally collected scattered fields, using the distorted Borniterative method (DBIM). The effects of bound water content on the di-electric permittivities of bone and bone marrow are studied. This ap-proach has an application in the medical field for painless, cost-effec-tive, and early diagnosis of leukemia in humans. © 2005 WileyPeriodicals, Inc. Microwave Opt Technol Lett 46: 599–601, 2005;Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.21062

Key words: microwave tomography; dielectric properties; low-water-content tissues

INTRODUCTION

Microwave medical tomography is emerging as a novel, nonhaz-ardous method of imaging for the early detection of tumors.

Tomographically reconstructed microwave images can potentiallyprovide information about the physiological state of the tissue aswell as the anatomical structure of an organ. In the microwaveregion, a tissue is differentiated based on its complex permittivity,which in turn depends on the concentration of bound water. Re-cently, there has been extensive research to develop a viablesystem for microwave medical tomography [1]. A clinical proto-type of active microwave imaging of the breast has been reported[2].

A successful prototype of 2D microwave tomographic imagingis presented here. The experimental studies are performed usingthe femur of a calf at a frequency of 3000 MHz and 2D tomo-graphic images are reconstructed using the distorted Born iterativemethod (DBIM).

EXPERIMENTAL SETUP

The designed 2D microwave tomographic imaging prototype isshown in Figure 1. The bone sample is mounted on a circularplatform capable of circular motion in the horizontal plane. Theplatform, along with the sample, is kept inside a tomographicchamber of radius 12 cm and height 30 cm, which is coated insidewith suitable absorbing material. Suspended coplanar strip-line-fedbowtie antennas [3] generated in the TM01 mode are designed forboth transmission and reception of microwave signals. All themeasurements are done using an HP 8714ET network analyzer;interfaced with a Compaq SP 750 workstation using a GPIB bus.

METHODOLOGY

SamplesThree samples of the calf femur are considered for the analysis: (i)a freshly excised bone (used within 1 h of extraction), the samebone after (ii) seven days of natural drying and (iii) after fourteendays.

Data AcquisitionFor data acquisition, the bone sample is illuminated by bow-tieantenna [3] at a frequency of 3000 MHz. As shown in Figure 1, thetransmitting antenna is placed at a fixed position on the circularrail, while the receiving antenna is rotated with an arm around the

Figure 1 2D prototype of the microwave tomographic-imaging setup

Figure 6 Measured antenna gain vs. frequency

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 46, No. 6, September 20 2005 599