wlan.rar_STRAIGHT

PRINTED STRAIGHT F ANTENNAS FOR WLAN AND

BLUETOOTH

H.Y. David Yang

Dept. of Electrical and Computer Engineering, Univ. of Illinois at Chicago

Chicago, IL 60607, Emails: [email protected]

Abstract Miniaturized printed-circuit-board antennas are proposed in

PCMCIA cards for WALN and Bluetooth applications. The proposed antenna

is a straight F in shape printed on a FR4 substrate together with the rest of the

communication systems for local access networks (WLAN) including

bluetooth, IEEE 802.11a, and 802.11b. This demand has stirred significant

renewed interest in antenna design particularly at the ISM bands. Many novel

antenna structures for single, dual, or multiple bands have been proposed [1-

2]. Among them, printed circuit antennas are desirable for their low cost, low

profile, and conformality. Furthermore, the material substrate provides

substantial antenna size reduction. A drawback is the narrow bandwidth,

when a conductor backing is presented. Parasitic elements may be used to

provide multiple resonances to enhance the bandwidth. Recently, inverted

inductive and capacitive arms of a printed inverted F antenna add up to the

total antenna length much larger than what is desired for. In this paper, a

modified inverted F antenna named as a straight F antenna is proposed. The

design and test results show that this antenna is much smaller that the usual F

antenna with sufficient bandwidth for ISM band.

Design Considerations

An example of a usual printed inverted F antenna is shown in Figure 1. A

truncated ground plane is on the surface of the bottom substrate. The

protrusion of the F over the ground plane edge determines the antenna

inverted F antenna. A modified F antenna structure that provides significant

area reduction is shown in Figure 2. It utilizes both antenna corners and

moves the inductive arm into and around the edge of the ground plane covered

area. Meandering further reduces the capacitive arm. The resulting overall

antenna area is down to below 9mm by 8 mm for a 4-layer stack-up FR-4

substrate of 18 mil overall thickness for 2.4 GHz band operation.

A Design Example

Figure 2 is shown in Figure 3. For IEEE 802.11b WLAN, the required

120 MHz, sufficient for the required applications. Additional loss will be at

Figure 1. A printed inverted F