117
`
`A VERY SMALL DOUBLE CPATCH ANTENNA
`CONTAINED IN A PCMCIA STANDARD PC CARD
`
`Mohamed Sanad
`
`Nokla Mobile Phones R I D Center
`San Mego, Califomla, USA
`
`INTRODUCTION
`
`PC cards are small formfactor adapters for
`personal computers, personal communicators or
`other electronic devices. They are about the size
`and shape of a credit card and they can be used
`with any personal portable computer system
`equipped with a PCMCIA (Personal Computer
`Memory Card lntemational Association) slot (1).
`These PC cards provide the flexibility of adding
`any necessary features after the base computer
`system has been purchased. It is possible to add
`and remove PCMCIA PC cards without powering
`off the system or opening the covers of the
`personal computer system unit, as shown in Fig.
`1.
`
`4-
`
`a
`
`L2
`
`Fig. 1 A portable computer with a PCMCIA slot
`and a PCMCIA wireless communication
`card.
`
`The PC card has standard PCMCIA dimensions
`of 8.56 x 5.4 cm. The actual size of the card is
`shown in Fig. 2. The thickness of the PCMCIA
`card varies dependent upon its type. A type II
`PCMCIA PC card, issued in September 1991, (1)
`has a thickness of 0.5 cm. It is typically used for
`memory enhancements and/or I/O features such
`as wireless modems, pagers, LANs, and host
`
`Antennas and Propagation, 4-7 April 1995
`Conference Publication No. 407,O IEE 1995
`
`communications. The card can provide wireless
`communication capability to laptops, notebooks.
`palmtops, and any other portable computer
`system having a PCMCIA slot. The PCMCIA
`card may also work as a standalone wireless
`communication card when it is not connected to
`a computer. For such applications. it is always
`required to design a very small built-in antenna
`having an isotropic radiation pattem. Since these
`PCMCIA wireless communication cards may also
`be han&held or may be used in an operator's
`pocket, their antennas must have a negligible
`these
`human body's effect. Furthermore,
`portable PCMCIA communication cards are
`usually randomly orientated and hence, they
`suffer from multipath reflections and rotation of
`polarization. Therefore, their antennas must be
`sensitive to both vertically and horizontally
`polarized waves. Moreover, these antennas must
`have
`the same
`resonant
`frequency,
`input
`impedance and radiation pattems in free space
`and inside any PCMCIA type II slot in any
`portable computer.
`
`Fig. 2 The actual size of the PCMCIA card.
`
`GOOG 1054
`IPR of U.S. Patent No. 8,572,279
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`

`

`ANTENNA GEOMETRY
`
`To fulfill the above requirements a very small
`size, partially shorted, double Cpatch antenna,
`on a very small ground plane has been
`developed (2)-(3). The geometry of a double C
`patch antenna having a rectangular aperture
`shape is shown in Fig. 3(a). The antenna is
`coaxially fed between the two apertures and it
`has a smaller size than the conventional half-
`wavelength rectangular microstrip antenna. To
`reduce the size of the double C-patch antenna to
`about half of its size, the zero potential plane of
`the antenna, excited with the dominant mode, is
`short-circuited. To further reduce the size of the
`shorted double Cpatch antenna, only a small
`portion of the entire length of the shorted edge is
`short-circuited. The geometry of the partially
`shorted double Cpatch antenna is shown in Fig.
`3(b). The entire length of the partially shorted
`edge is defined to be the width of the antenna
`while the length of the antenna is the distance
`between the partially shorted edge and the main
`radiating edge which is parallel to the partially
`shorted edge. The side of
`the rectangular
`aperture which is parallel to the partially shorted
`edge is defined to be the width of the aperture
`while the other side of the aperture is defined to
`be its length. The length of the partially shorted
`double Cpatch antenna is less than half of the
`length of the conventional quarter-wavelength
`shorted
`rectangular microstrip
`antenna
`resonating at the same frequency and having the
`same width and thickness.
`
`The effect of the human body on the antenna is
`negligible because such a double C-patch
`antenna configuration is excited mainly by a
`magnetic current rather than an electric current
`the
`(4). Furthermore, the ground plane of
`antenna acts as a type of shield against adjacent
`materials such as circuit components in the
`PCMCIA communication card and any other
`metallic materials in the PCMCIA slot. The
`ground plane of the antenna is truncated such
`that the dimensions of the ground plane are
`almost the same as those of the radiation patch.
`Because of this and the geometry of the Cpatch
`antenna, the generated radiation pattems are
`isotropic (5). Furthermore, the antenna
`is
`sensitive to both vertically and horizontally
`polarized waves. Moreover, the total size of the
`antenna is much smaller than the conventional
`quarter-wavelength
`rectangular microstrip
`antenna which assumes infinitely large ground
`plane dimensions. However, it should be noted
`that truncating the ground plane of the partially
`
`118
`
`shorted double Cpatch antenna does not have
`any effect on the efficiency of the antenna. This
`is different from the conventional rectangular
`microstrip antenna, where truncating the ground
`plane beside the radiating edge(s) reduces the
`gain considerably (6).
`
`For example, a partially shorted double w a t c h
`antenna is designed to resonate around 900
`MHz, which is close to the ISM, cellular and
`paging frequency bands in USA. The total size of
`the antenna is 2.7 x 2.7 cm, using Duroid 6002
`having a dielectric constant of 2.94 and a loss
`tangent of 0.0012. The thickness of the dielectric
`material is 0.1016 cm and the density of the
`electrodeposited copper clad is 0.5 oz per
`square foot. The length of the aperture is 0.7 cm,
`the width is 2 cm and it is located at 0.6 cm from
`the partially shorted edge. The input impedance
`of the antenna is 50 ohms and it is coaxially fed.
`To make the partially shorted C-patch antenna
`relatively easy to manufacture, the electric short
`circuit of the shorted section is simulated and
`replaced by a small number of very thin shorting
`posts (7). The partially shorted double C-patch
`antenna does not have a regular shape and it is
`almost impossible to study the effect of the
`circuit components in the PCMCIA card and the
`metallic materials in the PCMCIA slot on the
`antenna
`theoretically.
`Therefore,
`the
`performance of the partially shorted double C-
`patch antenna inside and outside the PCMCIA
`type II slot has been investigated experimentally
`and experimental results will be presented. In
`
`( 4 Open
`
`(b) Partially shorted
`
`Fig. 3 Geometry of the double Cpatch antenna.
`
`GOOG 1054
`IPR of U.S. Patent No. 8,572,279
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`

`

`119
`
`these measurements, the antenna was located
`very close to the outer edge of the PCMCIA card
`and the main radiating edge of the antenna was
`facing outward. In such a case, when the
`PCMCIA card is completely inserted inside the
`PCMCIA slot, the entire radiating edge of the
`antenna will still be close to the outer door of the
`slot as shown in Fig. 4.
`
`were obtained in the other principal planes but
`they are not presented here. However, the
`horizontal plane is the most important one,
`especially if the PCMCIA card is operating inside
`the PCMCIA slot in any personal computer,
`because personal computers are usually used in
`a horizontal position.
`
`Fig. 4 The antenna inside a PCMCIA card.
`
`RESULTS
`
`Fig. 5 shows the return loss and the input
`impedance of the double C-patch antenna in free
`space and while it is contained in a PCMCIA slot
`of a palmtop computer. It is clear that inserting
`the antenna inside the PCMCIA slot has a
`negligible effect on the resonant frequency and
`the return loss of the antenna. The corresponding
`radiation pattems were measured in the principal
`planes. In these measurements, the antenna was
`immersed in both vertically and horizontally
`polarized waves to determine the dependence of
`its performance on the polarization of
`the
`incident waves. For example, the measured
`pattems in the horizontal plane while the antenna
`was outside and inside the PCMCIA slot are
`shown in Figs. 6 and 7, respectively. It is clear
`that the radiation pattems are almost isometric
`and polarization independent. Furthermore, the
`performance of the antenna inside the PCMCIA
`slot is excellent and it is almost the same as its
`performance outside the slot. Similar results
`
`Fig. 5 Return loss of the double C-patch
`antenna inside and outside the PCMCIA
`slot.
`
`Fig. 6 Vertically and horizontally polarized
`radiation pattems in the horizontal plane
`while the antenna is outside the PCMCIA
`slot.
`
`GOOG 1054
`IPR of U.S. Patent No. 8,572,279
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`

`120
`
`The above measurements were repeated inside
`several PCMCIA slots in different portable
`computers and similar results were obtained.
`Furthermore,
`these measurements were
`repeated while a palmtop computer, containing
`the antenna inside its PCMCIA slot, was hand
`held and also inside the operator‘s pocket. It was
`found that the human body has a negligible
`effect on the performance of the antenna as
`shown in Fig. 8.
`
`CONCLUSIONS
`
`A very small size partially shorted double C-
`patch antenna on a truncated ground plane has
`been successfully integrated to a PCMCIA card.
`The antenna has the same performance and
`characteristics in free space and inside the
`PCMCIA slot in any personal computer. The card
`has a good reception sensitivity from any
`direction and regardless of its orientation. That is
`because the used partially shorted double C-
`patch antenna has isotropic radiation pattems
`and it
`is sensitive
`to both vertically and
`horizontally polarized radio waves. Furthermore,
`double Cpatch antennas have an excellent
`performance beside the human body. Hence, the
`PCMCIA card has also a high
`reception
`sensitivity when it is hand-held and inside the
`operator’s pocket.
`
`Fig. 7 Vertically and horizontally radiation
`patterns in the horizontal plane after
`inserting the PCMCIA card inside
`the PCMCIA slot.
`
`l U C I
`
`
`
`..U. M
`a..
`
`8 0 0 . 0 0 0 0 0 0
`
`0 0 0 **z
`
`Fig. 8 Return loss in free space and while the
`PC card, contained in a palmtop computer,
`is hand-held inside the operator’s pocket.
`
`REFERENCES
`
`1. Greenup, J., 1992, “PCMCIA 2.0 Contains
`Support For 110 Cards, Peripheral Expansion”,
`Comouter Technoloav Review. USA, 43-48.
`
`2. Sanad, M., 1995, “Double C-Patch Antennas
`Having Different Aperture Shapes”, IEEE AP-S
`Svmmsium. Newmrt Beach, California, USA.
`
`3. Sanad, M., 1995, “A Small Size Microstrip
`Antenna Having A Partial Short Circuit“ ,
`Ninth International Conference on Antennas and
`ProDaaation.
`Eindhoven
`Universitv
`of
`Technoloav. The Netherlands.
`
`4. Sanad, M., 1994, ‘Effect Of The Human Body
`On Microstrip Antennas”,
`IEEE AP-S
`Svmmsium. Seattle. USA, 298-301.
`
`5. Sanad, M., 1994, ‘Microstrip Antennas On
`Very Small Ground Planes For Portable
`Communication
`Systems”,
`IEEE
`AP-S
`Svmmsium. Seattle. USA. 81 0-81 3.
`
`6. James, J.R., and Hall, P.S.. 1989, “Hand Book
`Of Microstrip Antennas”, Peter Perearinus Ltd..
`London. U K. Vol. 2, Ch. 19, 1094-1099.
`7. Sanad, M., 1994, “Effect Of The Shorting
`Posts On Short Circuit MicrostriD Antennas”.
`IEEE AP-S Svmmsium. Seattle,’ Washinaton,
`794-797.
`
`GOOG 1054
`IPR of U.S. Patent No. 8,572,279
`
`