1204 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013

Design of Antenna on Glass Integrated PassiveDevice for WLAN Applications

Tzu-Chun Tang, Student Member, IEEE, and Ken-Huang Lin, Member, IEEE

Abstract—An antenna miniaturization technique that cansubstantially miniaturize an antenna to allow its incorporationinto a compact package for WLAN (2.4–2.484 GHz) applicationsis proposed. For this purpose, the semiconductor-based glassintegrated passive device (GIPD) manufacturing technology isadopted. However, the inherently lower dielectric constant andmore limited number of layers that can be used in a GIPD thanlow temperature co-fired ceramic (LTCC) pose a serious chal-lenge in miniaturization. To facilitate the design, an equivalentcircuit approach is applied to the loop-based antenna in whichthe structure is conveniently integrated with the ground trace inthe semiconductor fabrication process to improve both miniatur-ization and radiation efficiency. The loop antenna incorporates astrip that is capacitively fed by the coplanar waveguide (CPW)feedline, and the combined equivalent circuit shows that withoutdetuning the structure of the antenna, resonance can be obtainedsimply by adjusting the equivalent capacitance between the feed-line and structure. Furthermore, the ground of the CPW is partof the antenna, so its length affects the resonant frequency of theantenna. Under these conditions, the resonant length of the loopantenna is not necessarily one wavelength, so the antenna can bemade electrically small. Therefore, the antenna proposed hereinhas dimensions 2.4 1.1 mm , occupyingonly 2.4% of the package area mm , allowing theflexibility of the integration of other components in the package.The package is mounted on the printed circuit board (PCB) witha ground plane of size mm . The effect of the size of theground plane is discussed. The radiation efficiency is 58% in theWLAN band (2.4–2.484 GHz). Therefore, the proposed method isvery useful for designing a package antenna.

Index Terms—Antenna integrated package, glass integratedpassive device (GIPD) manufacturing technology.

I. INTRODUCTION

T HE REQUIREMENTS of small and easily portable de-vices have created the demand for more compact modules

that include passive and active components and antennas. Glassintegrated passive device (GIPD) manufacturing technologywas recently developed for realizing high-density componentsin a package due to its thin-film processing technique. Fur-thermore, a GIPD can be employed as an interposer in chipsstacking technology. GIPD substrates are made of lower-lossdielectric material than silicon substrate, so they are suitable for

Manuscript received May 22, 2013; revised August 11, 2013; acceptedSeptember 03, 2013. Date of publication September 27, 2013; date of currentversion October 01, 2013. This work was supported in part by the NationalScience Council under Grant NSC100-2622-E-110-001-CC1.The authors are with the Department of Electrical Engineering, National Sun

Yat-sen University, Kaohsiung 80424, Taiwan (e-mail: a565656kimo@pcs.ee.nsysu.edu.tw; khlin@mail.nsysu.edu.tw).Color versions of one or more of the figures in this letter are available online

at http://ieeexplore.ieee.org.Digital Object Identifier 10.1109/LAWP.2013.2282391

microwave applications [1]–[5]. They can be used to promoteantenna integration and improve antenna radiation efficiency.Related papers have discussed antenna design for 60-GHzapplications using GIPD technology [1]–[4]. A GIPD antennafor biomedical applications has been realized in [5]. However,it suffers from a low radiation efficiency probably because themeander line technique was used or no additional ground planewas utilized. Unlike low temperature co-fired ceramic (LTCC)manufacturing technology, in which a material with a highdielectric constant is used as the substrate to reduce the sizeof the antenna, antenna design in GIPD manufacturing uses asubstrate with a low dielectric constant, making size reductionmore difficult. The inclusion of an antenna at 2.45 GHz is stillchallenging owing to issues of size and radiating efficiency.Therefore, a capacitively fed loop antenna has been proposedfor antenna miniaturization; similar methods have been dis-cussed [6], [7]. However, the equivalent circuit approach hasnot been extensively studied. It provides clear physical insightinto the operation of the antenna. Moreover, design considera-tions for an antenna in a package differ from those for antennason mobile handsets. Therefore, the purpose of this letter is torealize an antenna into a package for WLAN (2.4–2.484 GHz)applications.

II. DESIGN OF ANTENNA IN GIPD (AIPD)

A. Configuration

In this letter, the proposed WLAN antenna was designed in acompact package module with dimensions mm ;it is comparable to most commercially available WLAN mod-ules. The difference between them is that themodule includes anantenna, while commercially available modules do not. There-fore, the antenna should be as small as possible to ensure thatit does not occupy an excessively large area in a high-densityICs package. Fig. 1 shows the configuration of the AIPD. TheAIPD is located on the printed circuit board (PCB) of the FR4substrate with a dielectric constant of 4.4 and a loss tangent of0.02, and the size of the PCB is chosen to ensure that it fits in typ-ical portable devices. The performance of the discrete antennamay be affected by its placement as well as the material and sizeof the PCB. Therefore, the co-design of the AIPD and the PCBprovides a good solution for practical applications. As shown inFig. 2, the antenna in the GIPD is designed. The metal ground(with a thickness of 3 m) is etched between the glass wafer(with a thickness of 200 m and dielectric constant of 5.2) andthe first polymer layer (with a thickness of 5.5 m and a dielec-tric constant of 2.7), which is shorted to the system ground by

1536-1225 © 2013 IEEE

TANG AND LIN: DESIGN OF ANTENNA ON GLASS INTEGRATED PASSIVE DEVICE FOR WLAN APPLICATIONS 1205

Fig. 1. Geometry of the proposed antenna. (a) Oblique view. (b) Extendedoblique view.

Fig. 2. Cross-sectional view.

TABLE IDIMENSION PARAMETERS OF THE PROPOSED AIPD

vias and bond wires. The feedlines and antenna elements (thick-ness of 3 m) are etched on the first layer of the GIPD substrate,and the metal pads (with a thickness of 1 m) are formed on thesurface of the second polymer layer (with a thickness of 5.5 mand a dielectric constant of 2.7).Table I presents the design parameters. The loop-based an-

tenna is preferred because the structure is conveniently inte-grated with the ground trace in the semiconductor fabricationprocess to improve miniaturization and radiation efficiency. InFig. 3, the loop antenna consists of the coupling strip and theradiating element. The feeding strip is the extended feedline ofthe coplanar waveguide (CPW), which is used as the feedingnetwork to excite the antenna, and it can be used to control theimpedance matching of the antenna. The radiating element iscapacitively fed by the strip and shorted to the CPW ground (G)at the end of the structure. The advantage of co-design is thatthe parasitic effects that are caused by the integration of the an-tenna and PCB can be included during simulation, increasingthe accuracy of the results. The AIPD is located on the PCB,and the wire bonds are applied to electrically connect the signaland ground pad to the trace on the AIPD and PCB, respectively.Under these conditions, the antenna -parameters can be mea-sured from the feeding point, and its radiation pattern can beconveniently measured in an anechoic chamber.

Fig. 3. Antenna extended view.

Fig. 4. Equivalent circuit of the proposed antenna.

B. Design Technique

Loop antennas are resonant when they are around one wave-length using direct-fed method. However, a one-wavelengthresonant antenna is too large for use in package devices, es-pecially in WLAN applications. Alternatively, the capacitivefeeding method was developed to solve the problem. Thedesign technique is as follows. Since , where

, and resonance occurs at ,we have

or

In Fig. 4, the loop antenna can be seen as the short-circuitedtransmission line with characteristic impedance when it iselectrically small. The required capacitance can be obtainedby tuning the strip and the spacing between the feeding strip andantenna element. The required capacitance of the correspondingstructure can be realized by taking advantage of the resolution inGIPD manufacturing technology. The reactance of the inputimpedance is nearly zero when the required capacitance isachieved. Using this method, the resonant length of the loopantenna is not necessarily one wavelength. Therefore, the sizeof the loop antenna can be minimized. In this work, the cor-responding inductance and capacitance are approximately 0.64nH and 6.49 pF, respectively. A larger capacitance correspondsto a smaller antenna. However, the size of the antenna typicallydetermines its radiation efficiency. Therefore, a tradeoff mustbe made between the antenna size and the radiation efficiency.Based on the above considerations, an antenna with a size of

mm is realized.

C. Influences of CPW, Ground Plane, and Metallic StripsNear the Antenna

To further investigate the design method that is discussedabove, its parameters are studied as follows. The antenna end

1206 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 12, 2013

Fig. 5. Variation of with the different lengths of the CPW ground.

Fig. 6. Current distribution. (a) Extended view (b) Top view.

is shorted to the CPW ground (G) to form a loop structure, sothe ground strip of the CPW serves as part of the radiator. Fig. 5presents the impact of the ground strip on antenna performance.Since the length of the ground strip gives the equivalent induc-tance of the antenna, as the length of ground strip increases, itscorresponding inductance increases as well. The operating bandof the antenna therefore shifts to a lower frequency. Therefore,the required capacitance that is created by the coupling shouldalso be adjusted to achieve the desired resonant frequency.Fig. 6 plots the current distribution on the antenna and the

system ground plane. The current is excited on part of theground plane, indicating that the ground plane is also utilizedas a radiator which contributes to the radiation efficiency. Fur-thermore, most of the current is concentrated around the AIPD,revealing that a small ground plane can be adopted withoutworsening the antenna performance. Fig. 7 shows the results offurther investigation. It reveals that as the length of the groundplane (L) is changed, the corresponding is slightly varied.Nevertheless, in the typical cases that were investigated here,the antenna performance was acceptable.The performance of AIPD is affected if the metallic strip is

placed close to the antenna. This impact should be studied toprovide guidelines for GIPD antenna design. Fig. 8 shows theplacement of the antenna and metallic strip. The metallic strip isgrounded and separated from the antenna by a spacing (S). Fig. 9plots the variation of performance with S. The metallic strip

Fig. 7. Variation of the with different lengths of the ground plane.

Fig. 8. Configuration of the metallic strip and the antenna.

Fig. 9. performance of the antenna nearby the metallic strip.

slightly affects because part of the ground serves as a ra-diator. Since the metallic strip protrudes from the ground, itperturbs the current distribution. Thus, the impedance of the an-tenna can also be affected. To avoid this problem, the antennaand the integrated circuit should have separated grounds.

III. FABRICATION AND MEASUREMENT

The implementation was carried out to examine the effec-tiveness of the approach to integration of the antenna usingGIPD manufacturing. Fig. 10 shows the fabricated prototype.The AIPD is mounted on a PCB, and wire bonds are applied toelectrically connect the signal and ground pad to the trace onthe AIPD and PCB, respectively. Then, the SMA connector isconnected to the input port when the return loss is measured.Fig. 11 compares the measured and simulated results. The

TANG AND LIN: DESIGN OF ANTENNA ON GLASS INTEGRATED PASSIVE DEVICE FOR WLAN APPLICATIONS 1207

Fig. 10. Fabrication andmeasurement of the AIPD. (a) Prototype. (b) Extendedview of the measurement setup.

Fig. 11. Comparison of the simulation and measurement results.

Fig. 12. Comparison of the simulation and measurement gain and radiationefficiency.

measured impedance bandwidth dB covers2.4–2.49 GHz. The slight difference between the simulatedand measured results probably arises from the SMA connector,which is not included in the simulation. Nevertheless, the mea-surements confirm that the fabricated antenna met the designrequirement for the operating band. The measurements agreeclosely with the simulation.Fig. 12 plots the gain and radiation efficiency of the antenna.

The parameters are measured over the operating band in an ane-choic chamber. The measured peak gain and radiation efficiencyare 0.8 dBi and 58%, respectively. The discrepancy between themeasured and simulated results is attributed to the induced cur-rent on the SMA connector, which is not included in the sim-ulation. Nevertheless, the trend of the measurements is highlyconsistent with that in the simulation. Fig. 13 shows the simu-lated and measured normalized radiation patterns at 2.45 GHz.

Fig. 13. Simulation and measurement of the radiation pattern in (a) -planeand (b) -plane.

The radiation pattern of the antenna is nearly omnidirectional inthe -plane. The radiation pattern can change with position onthe ground plane.

IV. CONCLUSION

An AIPD for a WLAN (2.4–2.484 GHz) application was pre-sented. An antenna element with a size of mm , a gainof 0.8 dBi, and a radiation efficiency of 58% was realized in asmall package. The influence of the size of the ground plane onthe antenna performance was studied; it slightly affected ,but the antenna performance remained acceptable. The antennaoccupied only 2.4% of the area of the package device, leavingthe remaining area of the package to be used by other compo-nents. The experimental results agreed well with the simulationresults, demonstrating the feasibility of the proposed method.

ACKNOWLEDGMENT

The authors would like to thank the National Chip Implemen-tation Center (CIC), Taiwan, for the GIPD antenna fabrication.The authors are also grateful for many helpful discussions withProf. L.-T. Hwang.

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