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current was computed from the line integral of themagnetic fields around the base of the probe according toAmpere's Law. The input impedance of the antenna isdetermined from the ratio of the Fourier transform of theincident voltage wave and the Fourier transform of theinput current wave.

shorting planeI

Iee dpoint b

a12

I IU

shorting plane

l- a - Ia b

Fig. 1 Geometry ofshortedpatch(a) Top view(b )Top view

Table 1: Resonant frequencies and bandwidths of theshorted square patch of Fig. 1 with a = b = 3.06cm and E, =1.08

h(mm) dlb

2 0.723 0.75

4 0.65

5 0.56

6 0.16

7 0.16

Experiment

fo (GHz) BW(%)

2.19 3.59

2.06 4.73

2.11 6.40

2.17 9.70

2.57 14.0

2.46 17.7

Calculation

fo (GHz) BW(%)

2.19 1.8

2.13 4.2

2.13 6.3

2.17 8.6

2.54 12.7

2.49 16.4

Table 2 Resonant frequencies and bandwidths of the regu-lar rectangular patch of Fig. 1 with a = 3.06 cm, b 6.12 cmand E , = 1.08

Experiment Calculation

h ( m m ) d/ b fo(GHz) B W ( % ) fo(GHz) BW(%)

2 0.75 2.20 3.2 2.23 1.57

3 0.75 2.16 3.7 2.18 2.30

4 0.75 2.14 3.75 2.12 2.60

5 0.65 2.15 5.3 2.12 3.55

6 0.59 2.16 6.3 2.13 4.66

7 0.49 2.20 7.3 2.16 5.55

2.7 Resonant frequency and bandwidth

2.1.1 Foam substrate ( E ~ 1.08): Fig. 1 shows thegeometry of a shorted square patch (with a = b = 3.06cm)on a foam substrate with relative permittivity of about 1 08.The measured and calculated results for resonant frequen-cies and impedance bandwidths (SWR = 2) for severalthickness are given in Table 1. The corresponding calcu-lated results for the regular halfwave patch (with a = b =6.12cm) are shown in Table 2. The feed location dlb in eachcase is chosen for optimum bandwidth. It is observed fromTables 1 and 2 that

The measured and calculated results for resonant frequen-cies are in excellent agreement. The calculated bandwidthsare smaller than the measured bandwidths but the agree-ment is still reasonable. The discrepancy is mainly due tothe use of fuced space steps in the modelling, which areunable to match all the antenna dimensions.

Both measurement and calculation show that the band-width of the classic shorted patch on foam substrate is

52 2

significantly larger than the corresponding bandwidth ofthe regular patch. This is consistent with the claim in thefootnote of [2]. The reason is that the shorted patch has asmaller volume and therefore less stored energy. This leadsto a smaller Q and larger bandwidth.

2.1.2 Microwave substrates: Calculated results forresonant frequencies and bandwidths for a shorted rectan-gular patch with a = 1.56 (Fig. 2) on microwave substrateswith E, = 2.33 and 4.0 and several thickness are shown inTable 3. The corresponding results for the regular halfwavepatch (a = 75mm, b = 50mm) are also shown. As before,the feed position d b is chosen for optimum bandwidth.

2oo [

-1 000.95 1 oo 1.05

a m p a r k o n o calculated results und measured results reported m Fiflfo

Fi .23 . 8 of [7 ] fo r shorted atch with a = I .52cm, b = 3.04m, S = b/a = 2, 6= 0.7, h = 0 . 1 6 0 ~ ?& = 2.55

~ computed- 0 . - measured [I

Table 3: Calculated resonant frequencies and bandwidths ofthe shorted rectangular patch of Fig. 1 and the regular patchwith twice the dimensions

Shorted patch Regular patch

h ( m m ) dlb fo(GHz) BW(%) d b fo(GHz) BW(%)

(a ) E, = 2.32, a = 2.4, b = 1.6cm

0.8 0.81 2.98 1.4 0.28 2.98 1.5

1.6 0.81 2.95 1.8 0.28 2.96 2.4

3.2 0.78 2.89 3.4 0.20 2.97 4.6

(b) E, = 4.0, a = 1.9, b = 1.25cm

0.8 0.84 2.95 1.2 0.30 2.93 1.5

1.6 0.84 2.95 1.4 0.32 2.92 1.8

3.2 0.84 2.91 2.2 0.28 2.93 3.3

Contrary to the foam substrate case, the bandwidths forregular patches in microwave substrates are larger than thatof the shorted patch, ranging from 7.1% larger for the caseE, = 2.32, h = 0.8" to 50% larger for the case = 4.0, h= 32" This is qualitatively consistent with the state-ments in [12]. The reason is likely the excitation of surface

wave in microwave substrates. Since the regular patch islarger, the loss due to surface wave is higher, leading to alower Q and larger BW compared to the quarterwaveshorted patch. This is more pronounced for thicker sub-strates and/or larger values of E,, which is consistent withthe data in Table 3.

Although no measured data was available to comparewith the calculated results of Table 3, we did apply ourFDTD code to obtain calculated results for the shortedand regular patches of Fig. 3.17 and 3.5 in [7], with E, =2.55, and compared with the measured data reported

IE E Proc-Microw . Antennas Propug.. Vol. 147, No. 6, December 2000



therein. The case for the shorted patch is shown in Fig. 2.Similarly close agreement was obtained for the regularpatch previously cited.

2.2 Pattern and gain for foam substrateThe measured E and H-plane patterns for the classicshorted patch of Fig. 1 on foam substrate have been givenin [4] and are not repeated here. These patterns show largecross polarisations in the E-plane. It also shows that,depending on the thickness, the maximum radiation can

occur off broadside. Since [4] does not contain any infor-mation on gain, we present here the measured gain of thispatch as a function of frequency in the broadside directionas well as in the m a x i " direction. These are shown inFigs. 3a-c for h = 3, 5 and 7 The gain values at theresonant frequencies are summarised in Table 4. It is seenthat typical values of the maximum gain are in the range of2-3.5dBi. This is about half of the regular halfwave patch.

3

1.90 1.95 2.00 2.05 2.10 2.15 2.20 2.25 2.30

frequency, GHz4 a

-2

1.90 1.95 2.00 2.05 2.10 2.15 2.20 2.25 2.30

frequency, GHzb

g 2 /

1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8

frequency, GHzC

Fig. 3F&. I

(a ) h = 3mm, maximum direction is in broadside(b)h = S m m , maximum direction is at 30"(c )h = 7mm, maximum direction is at 45"_ _ maximum direction~ - ~ ~ roadside

IE E Proc.-Microw. Antennas Propug.. Vol. 147. No . 6 , December 2000

M e m e d gains ai muxi" divectwn ru?d at broadride or potch o

Table 4: Measured gain of the shorted square patch of Fig. 1

Gain (dBi)

broadside maximu m direction 0 *h(mm) fo(GHz)

3 2.06 2.5 2.5 at 0"

5 2.17 2.5 3.5 at 30"

7 2.46 0.2 2.2 at 45"

0 * s measured from the perpendicular direction in the €-plane(1,erpendicular o the shorting plane).

3 Partially shorted patch

Fig. 4 shows the geometry in which the shorting wall,instead of extending fully across the width of the patch a,has a width s, where s s a. It was shown in [7] that the useof a partially shorting wall had the effect of reducing theresonant frequency of the antenna. However, in [7] there isno information on the effect of a partial short on the band-width of the antenna.

shorting plane

I- C

a

Fig. 4 Geometry ofpartiallyshortedpatch:::I3.0

29 -(3 2.5 -

2.0

1.5 -

1 o0 0.2 0.4 0.6 0.8 1.0 1.2

slaa

*r

0 0.2 0.4 0.6 0.8 1.0 1.2

bsl a

Fig.5 Calculated re so m t p r y nd budwidth o partully shorted witha = 3.8em, b = 2Scm onfomn(a ) Resonant frequency(b )Bandwidth

strate (E,. = I ) ofthielmss h = 3.2mm

Fig. 5 shows the calculated results of the effects of apartial short on the resonant frequency and bandwidth.

523



The parameters used in the calculation are U = 38mm, b =25mm, h = 3.2mm, and = 1.0. It is seen that, as sfadecreases from 1 O to 0.1, the resonant frequency decreasesfrom 2.69 to 1.61GHz, representing a 60% reduction infrequency or size. However, this is accomplished at theexpense of bandwidth, which is reduced from 7.4% for sfu= 1.0 to 3.7% for s h = 0.1.

4 Wideband shorted patc h antenna

Recently, it has been shown that, using an L-probe proxim-ity feed, over 30?4 impedance bandwidth can be obtainedfor rectangular patch antennas on foam substrates of aboutO. l& thick [lO].We present experimental results whichdemonstrate that the shorting-wall technique can beapplied to reduce the size of this wideband antenna.

The geometry of the short-circuited patch antenna withan L-probe feed is shown in Fig. 6. The patch is excited inthe TMol mode. For an antenna with the parameters

D = 2mm, R = 0.5" and h = 7.5mm, the measured SW Rand gain of the antenna are shown in Fig. 7. The frequen-cies for which the SW R is 5 2 range from 3.33 to 4.95GHz.The impedance bandwidth is thus 39%, centred at4.14GHz. In terms of the free-space wavelength at thiscentre frequency & the antenna thckness h is about O.l&.

Compared with a halfwave regular patch resonating at thesame frequency of the TMnl mode, the antenna has a four-fold reduction in area.

Lp = 12m111, Wp = 30m111 L h = 11.5", L, = 45"

I

\ground

plane

a bFig. 6(U) Top view(b )Side view

Geometryo wideband shortedpatch with Lp rob e proximity ee d

frequency, GHz

Fi .7

0 . 5 m and h = 7.5&(i) E-plane(ii) H-plane

Meamred SWR andgam o wdban dshortedp atch antennaof Fig. 6 wi 8 L, = 12" W = 30 m, Lh = 11.5", L, = 4.5", D = 2 ~ m , =

The radiation patterns at 4.14GHz are shown in Fig. 8. They are stable withm the band. Note that there is a beam

524

squint of 15 and 60" in the H and E-planes, respectively.This is due to the asymmetric current distribution of thepatch arising from the shorting wall and the L-probe. Notethat in Fig. 2 a gain of > 6dBi was measured across theband in the main beam direction of the E-plane. This rela-tively large gain is attributed to the thickness of thesubstrate and the L-probe. In the mainbeam direction ofthe H-plane, however, the gain was only about 2.4dBi in anarrow band of frequencies. T h ~ ss because the H-planecrosspolarisation evel is high while the E-plane crosspolari-sation level is relatively low.

0"

270

2 1 0 L I - 4 5 0

180

Fig. 8~ E-copol.

_ _ _ _ Hcopol..

Radiation patternr o wiukband shorted patch o fig. 6 IOdB/div

E-crosspol.

Hcrosspol.

5 Concluding remarks

We have presented experimental and calculated results

which contribute to the understanding of the classic shortedpatch. We have further showed that the shorting planemethod can be successfully applied to achieve a compactwideband L-probe proximity fed patch antenna.

6 Acknowledgment

The research of K.F. Lee was supported by the Universityof Missouri Research Board. This work is also supportedby the Competitive Earmarked Research Grant (CERG),Hong Kong (project 9040449).

7 References

1 MUNSON, R.E.: 'Microstrip antenna' in JOHNSON, R.C., andJASIK, H. (Eds.): 'Antenna engineering handbook' (McGraw-Hill,

2 PINHAS, S., and SHTRIKMAN,S.: 'Comparison between com-puted and measured bandwidthof quarterwave m icrostrip radiators',ZEEE Trans., 1988, AP-36, (ll), pp. 1615-1616

3 WA TER HOU SE, R.B.: 'Small microstrip patch antenna',Electron.Lett., 1995,31, (3 , pp . 6 M 0 5

4 CHAIR , R., LEE, K.F., and LUK, K.M.: 'Bandwidth and cross-polarization characteristicsof quarterwave shorted patch antennas',Microw. Opt. Technol. Lett., 1999,22, (2), pp. 101-103

5 CHAIR, R., LUK, K.M., and LEE, K.F.: 'Small dual patchantenna', Electron. Lett., 1999, 35, lo), pp. 762-763

6 ZAID, L., KOSSIAVAS, G., D AUVIG NAC,J.Y., CAZAJOUS, J.,and PAPIER NIK, A.: 'Dual-frequency and broad-band antennaswith stacked quarter wave elements', ZEEE Trans., 1999, AP-47, (4),pp. 654660

New York, 1984), Chap. 7

IEE Proc.-Microw. Antennas Propug., Vol. 147, No . 6, December 2000



I HIRASAWA, K., and HANEISHI, M. (Eds.): ‘Analysis, design, andmeasurementof small and low-profile antennas’ (Artech House, 1992),pp. 13-14 1442-1 443YEE, K.S.: ‘Numerical solution of initial boundary value problemsinvolving Maxwell’s equa tions in isotrop ic media’,ZEEE Trans., 1966,AP-14, pp. 302-307

9 BERENGER, J.P.: ‘A perfectly matched layer for the absorption ofelectromagnetic waves’,J. Compuf.Phys., 1994, 114, (2) ,pp. 185-200

10 LUK , K.M., MAK , C.L., CHOW, Y.L., and L EE, K.F.: ‘Broad-band microstrip patch antenna’,Electron Lett., 1998, 34, (15), pp.

11 JENS EN, M.A., and RA HMA T-SA MII, Y.: ‘Performance analysisof antennas for hand-held receivers using FD T D,ZEEE Trans., 1994,AP42, pp. 110&-1113

12 JAMES , J.R., HALL, P., and WOOD,C. : ‘Microstrip an tenna theoryand design’ (Peter P eregrinus, 1981), p. 106

8

IE E Proc.-Microw. Antennas Propug.. Vol. 147, No . 6, December 2000 52 5

feding on patch

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