IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009 693

Meshed Patch Antennas Integrated on Solar CellsTimothy W. Turpin and Reyhan Baktur

AbstractThis letter presents the study of integrating meshedpatch antennas directly onto the solar cells of a small satellite tosave valuable surface real estate. The cover glass of the solar cellis used as the substrate for the antennas. The integrated patch an-tennas are designed to have sufficient optical transparency to en-sure the proper functionality of the solar cells. A prototype meshedpatch antenna is designed and integrated on after-market solarcells. The antenna has an optical transparency of 93%, and themeasurements agree well with the design.

Index TermsAntenna radiation patterns, microstrip antennas,solar cells, satellite communication.

I. INTRODUCTION

A S SMALL satellites are getting smaller to reduce the pay-loads in missions, there rises the challenge of how tomanage limited satellite surface area to fit solar cells, antennas,and space instruments. A traditional satellite system has sepa-rate solar cells and antennas. An effective integration of them,however, would save valuable real estate. The main challenge ofoverlapping the antennas and solar cells is to ensure the compat-ibility. The antennas should not block the solar cells to functionproperly, and the effectiveness of antennas should not be sig-nificantly reduced by the presence of solar cells. It should benoted that most small satellites have surface mount solar cellsand the solar arrays do not need to be always tracking the sun[Fig. 1(a)]). Therefore, the rise of the temperature of the solarcells and antenna is not the major concern in this letter. Thetemperature of the sky is used to compute the link budge whenthe antenna noise temperature is concerned. Also, the commu-nication link between the satellite and the earth is relativelysimple compared to the larger satellite system, so a simple phaseshifting as needed to the patch antenna is enough to ensure thecommunication.

Although it is feasible to construct transparent antennas frompolyester films with conductive coatings [1], the transparentconductor technology is relatively expensive. Other reportedmethods of integrating antennas with solar cells include placinga patch antenna under the solar cells [2] and creating radiatingslots on the ground plane under the solar cells [3]. In both cases,the solar cells need to be custom-made to ensure the function-ality of the antennas. The objective of this work is to presentan antenna topology that can be integrated on after-market solar

Manuscript received March 31, 2009; revised May 18, 2009. First publishedJune 16, 2009; current version published July 21, 2009. This work was supportedin part by National Science Foundation Award 0801426.

The authors are with the Department of Electrical and Computer Engineering,Utah State University, Logan, UT 84322 USA (e-mail: timoturpin@gmail.com;breyhan@engineering.usu.edu).

Color versions of one or more of the figures in this letter are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/LAWP.2009.2025522

Fig. 1. Meshed patch antennas. (a) Isometric view of meshed patch antennasintegrated on solar panels of a small satellite. (b) Geometry of the meshed patchantenna.

cells. We have found that the meshed patch antennas are cost-friendly and effective candidates. The meshed patch antennashave been studied by several researchers [4][8], and Turpin etal. showed that both the transparency and antenna propertiescan be optimized by refining the mesh width and predicted thefeasibility of integrating meshed antennas with solar cells forsatellite applications [9].

Following previous work of optimizing the meshed antennas[9], this letter presents the design and measurement results ofintegrating meshed patch antenna with high optical transparencyon top of off the shelf solar cells.

II. DESIGN

The geometry of the proposed antenna is shown in Fig. 1. Theoptical transparency of the antenna is defined by the percentageof the see-through area of the patch antenna [9]. It has beenshown that to optimize the design for optical transparency andradiation characteristics simultaneously, the line width of thegrid needs to be thin, and the number of grid lines parallelto the length of the antenna can be reduced since they donot affect the antenna significantly [9]. Following the previousstudy [9], we prototyped two types of antennas as presented inthis letter. The simulations of the antennas are performed withAnsofts HFSS.

A. Effect of the Substrate on the Antenna DesignThe antenna in this work uses the cover glass of the solar cells

as its substrate. In general, a thinner substrate results in a lessefficient radiator [10]. In order to determine a reasonable sub-strate thickness, we examined three types of plastic substrateswith different thickness and dielectric properties (relative per-mittivity of 2.4 at 1 MHz) similar to those of common com-mercial cover glass. Meshed patch antennas were designed by

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694 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009

Fig. 2. Effect of the substrate thickness on the peak gain of the meshed patchantenna with varied the line width .

Fig. 3. Effect of the substrate thickness on the impedance bandwidth of themeshed patch antenna with varied line width .

using these substrates without integrating on solar cells. The an-tenna gain and the impedance bandwidth areplotted as functions of substrate thickness and the line widthof the mesh in Figs. 2 and 3. The antennas were excited with50-Ohm microstrip lines for the purpose of simplicity. In bothstudies, the optical transparency of the antennas was held con-stant at 75%, and the length and width of each antenna were37 and 45 mm, respectively. It is seen from Fig. 2 that whenthe thickness of the substrate is less than 1 mm, the antennahas a low gain in spite of being optimized through line width( in Fig. 1) and number of lines. This suggests that in case ofoff-the-shelf solar cells having a thin cover glass, the meshedpatch antennas should be printed on an additional substrate be-fore integrating with the solar cells. When there are various solarcell assemblies to choose, then one needs to choose those withthicker cover glass if additional treatment to increase patch an-tenna efficiency in the presence of substrates is not performed.

B. Effect of Solar Cells on the Antenna DesignWhen integrating the meshed patch antenna with solar cells,

the effect of solar cells on antenna design needs to be consid-ered. The configuration of the integrated solar cell antenna is asfollows. The meshed patch antenna is printed (or attached) ontop of the solar cell cover glass. Beneath the cover glass, there

Fig. 4. Effect of the conductivity of the peak gain of a meshed patch antenna.Conductivity is varied from 0 to 1 S/m.

Fig. 5. Effect of the conductivity of the peak gain of a meshed patch antenna.Conductivity is varied from 10 to 100 S/m.

is a layer of photovoltaic cells. The solar cells in our applicationare gold-plated on the back side, and the gold layer serves as theground for the integrated antenna.

The conductivity of photovoltaic cells may vary from one fab-rication process or vendor to another. To study the effect of theconductivity on the performance of antennas, we modeled solarcell layer as silicon and continuously increased itsconductivity to examine the performance of the antenna inte-grated on a substrate on top of the silicon layer and backed witha perfect electric conductor. The conductivity is varied from 0to 100 S/m. The thickness of the solar cell is taken as 0.16 mm(measured from a commercial solar cell). The examination re-sults are shown in Figs. 47. As seen in Figs. 5 and 7, whenthe conductivity is above 10 S/m, there is no significant changein the peak gain and impedance bandwidth of the antenna. Thesignificant change on antenna properties only occurs when theconductivity of the silicon layer is varied from 0 to 1 S/m. Theresults in Figs. 4 and 6 suggest that raising the conductivity from0 to 1 S/m is equivalent to reducing the total thickness of sub-strates (silicon layer and cover glass) or raising the ground planeof the meshed path antenna.

III. MEASUREMENTSTo verify the feasibly of integrating the meshed patch an-

tenna with the solar cells, two types of antennas have been fab-

TURPIN AND BAKTUR: MESHED PATCH ANTENNAS INTEGRATED ON SOLAR CELLS 695

Fig. 6. Effect of the conductivity of the impedance bandwidth of a meshedpatch antenna. Conductivity is varied from 0 to 1 S/m.

Fig. 7. Effect of the conductivity of the impedance bandwidth of a meshedpatch antenna. Conductivity is varied from 10 to 100 S/m.

ricated and integrated with solar cells. The first one is an an-tenna screen printed with conductive ink (Creative Materialsproduct number 12446) on a polyethylene terepthalate glycol(PETG) thermoplastic sheet. The plastic substrate has a thick-ness of 0.762 mm and relative permittivity of 2.4 at 1 MHz and isused to act as the cover glass for the solar cell. The solar cells areassembled on an aluminum plate with a silver-based conductiveepoxy (Resin Technology Group, Silver Conductive 402). Theplastic and aluminum plate are then fastened together with nylonscrews. The second type of antenna is fabricated from off-the-shelf electroformed meshed conductor (Unique Wire WeavingCo., BM0020-03-N). The antenna is attached to the plastic sub-strate and integrated with solar cells as described above for theprinted meshed antenna.

A. Measured Results

The screen printed antenna has a length and width of 35.0and 40.8 mm, respectively, and a line width of 0.5 mm. Thetransparency of the antenna is 61%. It can be challenging toscreen print a highly transparent (such as 90%) antenna withprecision, but the design method of a 90% transparent antennais the same as those of 61% transparent antenna. With a more

Fig. 8. The radiation pattern in the H-plane for a meshed patch antenna withan optical transparency of 61%.

advanced printing (or surface writing) facility, one can easilyprint antennas with conductive ink to desired transparency.

The resonant frequency of the antenna is measured (using anHP 8510 network analyzer) to be 2.61 GHz. The simulation re-sult is 2.52 GHz, and the discrepancy is mainly due to nonexactvalue of the dielectric constant of the plastic substrate. It shouldbe noted that the value we have used from the data sheet isfor the frequency of 1 MHz, and Carver noted that the dielectricconstant is one of the most sensitive parameters in the antennadesign [11]. The selected radiation patterns for the simulationand the measured values are presented in Fig. 8. The maximumdirectivity for the simulation is 7.6 dB, and 8.4 dB for the mea-sured antenna.

B. Meshed Patch versus Solid Patch

To verify the effect of meshing on the antenna performanceand to normalize the meshed patch antenna to a reference, a solidpatch antenna is fabricated from the same conductive ink andtuned to resonate at the same frequency as the meshed patch an-tenna. The solid patch antenna also has a width of 40.8 mm, butthe length of the solid patch is 38.9 mm, so the two types ofantenna are resonant at the same frequency. The measured radi-ation patterns are shown in Fig. 9. As can be seen, the meshingof the patch does not change the shape of the radiation pattern,and the result agrees with Clasens study [6]. Additionally, thereis only minimal change in the directivity. The solid patch has adirectivity of 8.6 dB, and the meshed patch antenna has a direc-tivity of 8.4 dB.

C. Antenna Made From Electroformed Meshed ConductorAs an alternative to printing antennas on the substrate, an

off-the-shelf meshed conductor is used to design the antenna.The meshed conductor is electroformed and has an optical trans-parency of 93%. The radiation pattern of this antenna comparedwith the antenna fabricated from the conductive ink is shownin Fig. 10. The antenna has a maximum directivity of 8.2 dB incomparison to 8.4. The decrease in the directivity is expected

696 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009

Fig. 9. The radiation pattern in the H-plane for a meshed patch antenna withan optical transparency of 61% and a solid patch antenna.

Fig. 10. The radiation pattern in the H-plane for two meshed patch antenna withan optical transparency of 61% and 93%. The solid line for the 93% opticallytransparent antenna constructed from a wire mesh. The dashed line is for the61% optically transparency antenna constructed from conductive ink.

because the electroformed mesh has a higher transparency thanthe printed antenna.

D. Cross Polarization

The cross-polarization level is measured for all three antennas(solid patch from conductive ink, screen printed mashed patch

from conductive ink, and the antenna fabricated from the elec-troformed mesh). It is found that, over all, meshing lowers thecross-polarization level, but no significant decrease is noted forthe antenna with 61% transparency comparing with the solidpatch antenna. The average cross-polarization level for both thesolid antenna and the 61% antenna are lower than dB,while the antenna fabricated from the electroformed mesh has across-polarization level of lower than dB.

IV. CONCLUSION

The letter presents the feasibility study of integrating opti-cally transparent meshed patch antenna on top of off-the-shelfsolar cells. To enable the proper functioning of the solar cells,the transparency of the antenna is required to be higher than90%, and we found that it is feasible to design such an antennafrom two methods (screen print with conductive ink and designfrom electroformed meshed conductors). The meshing of thepatch antenna does not hinder the radiation pattern, and with thecorrect geometry of the mesh, the performance of the antenna iscomparable to that of a solid patch antenna. It is also shown thatthe addition of the solar cell layer has minimal effect on the per-formance of the antenna. In order to have an effective antenna,there is a minimum requirement on the thickness of the solar cellcover glass. Either a cover glass with sufficient thickness has tobe chosen, or the antenna needs to be printed on an additionallayer, then integrated on the solar cell.

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