mesh antenna

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1412 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 52, NO. 6, JUNE 2004

Meshed Patch AntennasGisela Clasen and Richard Langley, Member, IEEE

AbstractConventional microstrip patch antennas are printedwith continuous solid copper shapes and ground planes. The gen-eral properties of meshed patches are presented in this paper whereboth the patch itself and the ground plane are meshed. The gain,cross-polarization,bandwidth and radiation patterns are discussedfor different combinations of patch and ground plane. The radia-tion patterns are not significantly affected by meshing the patchalone, but meshing the ground plane increases the back radiation.The gaincan sufferby upto 3 dBor morewhen comparedto a stan-dard patch. Cross-polarization is improved providing that the cor-rect mesh line geometry is chosen for the excitation mode. Meshinglowered the resonant frequency in some cases by up to 30% andalso improvesthe bandwidth by a factor of up to 2.5 insomemodes.Overall, the meshed patch offers a complex tradeoff between pa-rameters but gives opportunities for improving the bandwidth andreducing the cross polarization and the antenna dimensions at theexpense of the gain.

Index TermsCommunication antennas, mesh antennas, meshpatch antennas, metal mesh antennas, microstrip patch antennas.

I. INTRODUCTION

VEHICLES are becoming mobile electronic communi-

cation systems, part of a wider telematics network with

applications at microwave and millimeter wave frequencies.

Many low frequency antennas below 1 GHz are printed on

glass screens in the motor industry to reduce costs, hide the

antennas and protect them from vandalism. Microstrip patches

are widely used as cheap, conformal antennas for a wide variety

of higher frequency applications and so there is currently much

interest in printing such antennas on, or within, the glass areas

of vehicles for intelligent transport and telematics systems.

References [1], [2] reported on the performance of patch

antennas fixed directly to glass which formed a superstrate.

Mounting antennas within the glass offers the prospect of re-

ducing costs but presents production problems such as thermal

distortion of the glass during processing and feeding the signal

to the embedded antenna. In addition it is not possible to printa solid conductor area on glass if it exceeds a few millimeters

across as the metal area reflects heat and distorts the glass

during the shaping/lamination process. In that case the metal

must be meshed. Rectangular printed patch antennas made

from a conducting mesh have been reported previously [3],where the antennas were stated to have improved bandwidth

but lower gain. In [4], we reported the performance of circular

meshed patches printed on glass while [5] presented the results

Manuscript received June 1, 2001; revised May 16, 2003. This work was sup-ported by Harada Industries Europe, Ltd., Birmingham, U.K.

G. Clasen was with the Electronics Department, University of Kent, Canter-bury, Kent CT2 7NT, U.K. She is now with C. Plath GmbH, 20097 Hamburg,Germany.

R. Langley is with the Electronics Department, University of Kent, Canter-bury, Kent CT2 7NT, U.K. (e-mail: [email protected]).

Digital Object Identifier 10.1109/TAP.2004.830251

Fig. 1. Circular and square mesh patches with their solid equivalents above.

for a patch antenna printed into a glass laminate and fed by a

surface mount connector on the inner side of the glass. It isnot the intention for this paper to look solely at glass based

applications but to present some interesting general properties

of meshed antennas that are not reported in the literature. Thepaper discusses both square and circular antennas where the

patch and ground plane were meshed in various combinations.

The effects of the varying line widths and line density on

gain, cross-polarization, resonant frequency and bandwidth

are discussed. Meshes for higher order modes on circular

patches concentrate on the mode. The study was largely

experimental but simulations made using Hewlett Packards

Momentum Software are included to help with a physical

interpretation of the results. The antennas were fed using

coaxial probes but coplanar feeds were presented in [5], and

similar antenna properties are measured for microstrip line

feeds whether directly or electromagnetically coupled.

Gain and radiation pattern measurements were carried out ina conventional far field anechoic chamber.

Fig. 1 shows the geometries of two types of meshed patches.

In the first part of the paper we concentrate on the square patch

but similar observations were made for circular mesh patches.Square mesh patches have an overall dimension of with square

holes of side spaced apart.

If is the number of holes in one direction then the amount

of metal in themeshed patch compared to thesolidpatchis given

by and the number of lines per wavelength

by . The geometry of circular patch shown relates

0018-926X/04$20.00 2004 IEEE


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CLASEN AND LANGLEY: MESHED PATCH ANTENNAS 1413

Fig. 2. Effect of line width and line spacing on measured normalized gain andcross-polarization. (a) Line spacing (b) line width. gain change - - - - -- - xpolar level.

to the mode where the mesh lines follow the current di-

rections on the patch. The exact mesh is mode dependent [4]

and it is important to follow the current patterns to avoid in-

creased cross-polarization as discussed later. A different mesh

shape for the higher order mode is also described. A ref-

erence patch, a conventional solid metal patch and ground plane

printed on RT Duroid substrate with , was used in

all cases for comparing the measured parameters to provide a

consistent benchmark. The mesh must be two dimensional, i.e.

there must be two sets of crossing orthogonal lines for the patch

to radiate. If only a single set of lines are printed current flow is

restricted and the antenna does not function as a patch.

II. MESHED PATCH OVER SOLID GROUND PLANE

A series of meshed patches were manufactured with different

line widths and line densities to establish the basic properties

of gain, cross-polarization and resonant frequency. The input

impedance is higherfor the meshed patch andso thefeed point is

closer to the center. The meshed patches were placed over solid

ground planes at this stage. The first measurements examined

the effects of changing the line width and the line spacing on

gain and cross-polarization.

Fig. 3. Measured resonant frequency of mesh square patch as a percentage ofmetal content compared to a solid metal patch.

Fig. 4. Current distribution on meshed patch over solid ground plane. (a)Magnitude and (b) direction.

The measured results for five samples are plotted in Fig. 2,

where it can be seen that the gain improves as the line widthincreases and the spacing decreases, i.e. as the area of metal

increases over the patch. On the other hand thin, widely

spaced lines have better cross-polarization. There is, therefore,

a tradeoff between gain and cross-polarization for a given

geometry. More work is needed to understand the effect of the

meshing parameters on the bandwidth. In general the band-

width remained at about 1% for this patch study but variations

up to 0.3% were noted.

The resonant frequency reduces as the percentage of metal

decreases as shown in Fig. 3, e.g. a meshed patch with side

65 mm, 2.5 mm, and 0.7 mm resonates at 1.37 GHz

(52% metal) while the same standard patch antenna unmeshed

has a resonance at 1.48 GHz. Hence for a given patch size theresonant frequency goes down as the number of mesh lines is

reduced resulting in a smaller antenna at a given frequency. The

relationship was not linear as the frequency of resonance re-

duces more quickly when the metal percentage falls below 60%

as seen in Fig. 3.

The effects noted in Figs. 2 and 3 were investigated further

using the simulation package Momentum. Fig. 4 shows the cur-

rent distribution computed over the meshed patch in two forms,

Fig. 4(a) shows the magnitude while Fig. 4(b) shows the vector.

The feed point is clearly visible. Fig. 4(a) shows that current is

distributed on each of the vertical lines of the mesh uniformly

whereas for a conventional patch the current density is high only


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Fig. 5. Meshed ground planes of two densities for T M mode on circularpatch.

at the edges of the patch. Note also the high current magnitudes

at the edges of each mesh line in Fig. 4(a). These excited mesh

lines are closely coupled and the resulting radiation pattern is

similar to that measured for a standard patch. The loss in gain

noted in Fig. 2 is mainly accounted for by the conductor losses

due to the high currents at the edge of each mesh line.

The current vector diagram in Fig. 4(b) shows that the cur-rents flowing from the top to the bottom of the patch flow into

the horizontal conductor lines as well at the junctions with the

vertical lines. The consequence of this is that the current paths

are longer and hence the meshed patch radiates at a lower fre-

quency than a standard patch. Therefore thicker mesh lines give

rise to a lower resonant frequency than thin ones.

The cross-polarization was difficult to model accurately using

the software. However from Fig. 4(b) we noted that for thick

lines the current flows across the conductors and, just as for a

thick dipole compared to a thin one, this increases the cross-

polarization. This bears out our experiments where thin lines

improved the cross-polarization and thick ones increased the

levels.

III. MESHED GROUND PLANES

The ground planes used in this study were about 2.5 times

the size of the patch, resulting in some radiation diffracted to

the rear. An experimental study investigated meshing the ground

plane in a similar way to that of the patches, thus creating a more

optically transparent antenna. A theoretical study was more dif-

ficult due to excessive computation times and storage require-

ments needed for Momentum. The ground plane geometry op-

timized for a mode circular patch is shown in Fig. 5. A

square mesh structure was used for the rectangular patches op-

erating in the fundamental mode. It should be noted that usinga standard patch over a meshed ground offered no significant

benefits.

A number of effects were observed when the ground plane

was meshed and combined with a meshed patch. Meshing the

ground plane improved the bandwidth which increased typically

from 0.6% to 1.6% for 25% metalization while the resonant fre-

quency reduced further to 1.21 GHz. Hence the resonant fre-

quency of the standard patch at 1.48 GHz was reduced to 1.21

GHz for the fully meshed patch, a reduction of 32%. The radia-

tion patterns were most affectedas shown in Fig. 6. Themost no-

table change was in the back radiation which increases inversely

with the density of the mesh. This is because the ground plane

Fig. 6. Measured radiation patterns in H plane for rectangular meshed patch

with solid and meshed ground planes. Solid ground plane;Meshed ground plane.

Fig. 7. T M mode meshed patch.

effectively leaks radiation through the mesh, the more holes in

the mesh the greater the leakage. The meshing also improves the

cross polarization levels in the forward direction by about 5 dB.

Before completing this section it is worth noting that these

meshed patches can excite circular polarization in a similar

manner to conventional patches [6].

IV. HIGHER ORDER MODES ON CIRCULAR PATCHES

There have been many paperspublished on higherorder mode

circular patch antennas where either a lower elevation coverage

is required as for satellite communications applications [7], [8]

or for omni-directional azimuth patterns [9] .I n [10] we reported

how the patch could be meshed for the mode. Here we

discuss the performance of a mode mesh as shown in

Fig. 7 where the mesh line geometry is immediately recognis-

able from the current pattern. Computed current distributions on

the meshed patch, Fig. 8, show that this pattern is the optimized

one for peak performance at the mode.

Table I summarizes the measured changes in the properties of

the patch at this higher order mode. Meshing the patch reduces


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CLASEN AND LANGLEY: MESHED PATCH ANTENNAS 1415

Fig. 8. Currents over patch of Fig. 7.

TABLE IMEASURED RESULTS FOR THE T M MODE PATCH MESHED AS IN FIG. 7

Fig. 9. Measured radiation patterns for TM21 mode in three planes for ameshed patch over a meshed ground plane. 0 plane; 45plane; 90 plane.

the bandwidth to 1.2% compared to 1.6% measured for the stan-

dard patch. This is restored on meshing the ground in addition

to the patch. On meshing the ground plane the front to back ratio

suffers as noted above but this produces the best cross-polariza-

tion. The resonant frequency can be reduced from 2.91 GHz for

the standard patch to 2.58 GHz for the fully meshed structure.

Radiation patterns for the mode fully meshed patch

structure are plotted in Fig. 9 for the three principle planes,

0 , 45 , and 90 . As was found for the fundamental mode an-

tennas described in the earlier section, meshing only the patch

did not affect the radiation patterns. Fig. 9 shows that the pat-

tern broadens when the ground is meshed in the 45 plane while

it narrows slightly in the other planes. The main lobes are little

affected in the forward region but significant rearward radiation

is noticeable.

The effect of exciting a given mode on the wrong mesh ge-

ometry, i.e. a line geometry that does not follow the intrinsic

surface current directions for that mode, has been studied. As

expected the cross-polarization increased by 58 dB while the

gain was reduced slightly by 1 dB.

V. DISCUSSION

The study has discussed theeffects of meshing patch antennas

and their ground planes. The radiation patterns are not signif-

icantly affected by meshing the patch alone, keeping a solid

ground plane, but the gain suffers by up to 3 dB when compared

to a standard patch. In general the denser the mesh the higher

the gain. Cross-polarization can be improved using a mesh pro-

viding the correct mesh line geometry is chosen for the excita-

tion mode. Thin, widely spaced lines improved levels to 20dB

or better in this study. Meshing the patch lowered the resonant

frequency by up to 20% and hence provides a method for re-ducingpatch sizes fora given frequency. On meshing the ground

plane as well as the patch radiation leaks through the mesh in-

creasing the radiated fields in the reverse direction dependent

on the mesh density. The resonant frequency drops further and

a reduction of 32% was measured for one example. Meshing

the complete antenna improved the bandwidth by a factor of up

to 2.5 for the fundamental modes but higher order mode band-

widths were not changed. Several aspects of performance are

not fully understood and need further investigation, the most no-

table being thebandwidth andloss mechanisms. Improved mod-

eling will be investigated to understand these structures better.

Overall the meshed patch offers a complex tradeoff between

parameters but gives opportunities for improving the bandwidthand reducing the cross polarization and the antenna dimensions

at the expense of the gain.

ACKNOWLEDGMENT

The authors wish to thank Harada Industries Europe, Ltd.,

Birmingham, U.K., for sponsoring this work.

REFERENCES

[1] L. Economou and R. J. Langley, Circular microstrip patch antennason glass for vehicle applications, in Proc. Inst. Elect. Eng. Microwave,

Antennas and Propagation, vol. 145, 1998, pp. 416420.[2] P. Lowes, S. R. Day, E. Korolkiewicz, and A. Sambel, Performance of

microstrip patch antenna with electrically thick laminated superstrate,Electron. Lett., vol. 30, pp. 19031905, 1994.

[3] M.-S. Wu and K. Ito, Meshed microstrip antennas constructed on atransparent substrate, IEICE Trans., vol. E74, pp. 12771281, 1991.

[4] G. Clasen and R. J. Langley, Gridded circular patch antennas, Mi-crowave Opt. Technol. Lett., vol. 21, pp. 311313, 1999.

[5] , Meshed patch antenna integrated into car windscreen, Electron.Lett., vol. 36, no. 9, pp. 781782, 2000.

[6] Handbookof Microstrip Antennas, J.R. James and P. S.Hall,Eds.,PeterPeregrinus, Stevenage, U.K., 1989.

[7] A. Das, S. K. Das, and S. P. Mathur, Radiation characteristics of higherorder modes in microstrip ring antenna, in Proc. Inst. Elect. Eng. Mi-crowave, Antennas and Propagation, vol. 131, 1984, pp. 102106.

[8] J. C. Batchelor and R. J. Langley, Dual, switched mode stacked ringarray, Electron. Lett., vol. 29, no. 15, pp. 13191320, 1993.

[9] L. Economou and R. J. Langley, Patch antenna equivalent to simplemonopole, Electron. Lett., vol. 33, no. 9, pp. 727728, 1997.


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[10] G. Clasenand R. J. Langley, Patch antennas constructed from meshes,in Proc. Antennas Propagation, Orlando, FL, 1999, pp. 26382641.

Gisela Clasen was born in Germany in 1970. Shereceived the Dipl.Ing. degree from the University ofSiegen, Germany, and the Ph.D. degree in electronicengineering fromthe Universityof Kent at Caterbury,U.K., in 1996 and 2000, respectively.

Since 2000, she has been an Antenna Engineer atC. Plath GmbH, Hamburg, Germany, specializing indirection finding antennas.

Richard Langley (M85) was born in 1949. He re-ceived the B.Sc. and Ph.D. degrees from the Univer-sity of Kent, Kent, U.K., in 1971 and 1979, respec-tively.

In 1997, he founded the European TechnologyCentre for Harada Industries Japan, the worldsleading automotive antennas manufacturer, and wasDirector of the Centre until 2003 when he returned toacademic life. While at Harada Industries of Japan,

he developed automotive antenna technologies thatresulted in many patents and direct industry linkedresearch. He is currently a Professor of antenna systems at the University ofKent. He has published over 200 papers in leading journals and internationalconferences. For many years his main research was in the field of frequencyselective surfaces applying them in the satellite and defence fields. This ledto his current interest in the development of novel electromagnetic band gapmaterials. In recent years, his interests have also included patch antennas basedon glass and ferrite substrates, and particularly hidden vehicle antennas rangingfrom low frequency radio to multiband telematics antennas.

Prof. Langley is an Honorary Editor of the Institution of Electrical EngineersProceedings on Microwaves, Antennas and Propagation.

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