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Industry News / Antennas

A Small, Low Cost Antenna for WLAN and Bluetooth Applications

February 1, 2003
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Wireless device manufacturers today must fit a growing amount of functionality into continuously decreasing circuit board space. In particular, finding space for the antenna without compromising its performance characteristics has become a major challenge.


The AccuWave™ 5800 antenna is an ultra-small tri-band device designed to provide full coverage of the 2.4 GHz Bluetooth™ and 802.11b frequency band, as well as the 5.2 through 5.8 GHz bands for 802.11a and HYPERLAN 2. Its 10 mm x 14 mm x 3 mm form factor is designed to permit the antenna to be mounted directly onto the printed circuit board using standard surface-mount techniques with no cables or connectors.

The unique design makes the AccuWave 5800 antenna less than half the size of typical antennas offered for these applications and it weighs just 0.25 g. In addition, the new tri-band antenna has the same board dimensions as the AccuWave™ 2400 single-band antenna, making it an easy upgrade to tri-band capability for wireless manufacturers. Both antenna types are manufactured with standard low cost plastic and metal, using reproducible and reliable high volume production techniques.

Location and Performance

The AccuWave 5800 tri-band antenna's unique table-top design, using a low cost insert-molding manufacturing technique, enables the antenna to straddle other components on the circuit board to support high density electronic boards. This saved space translates into increased profits for manufacturers by enabling them to add more functionality to a device or reduce overall costs by incorporating alternative lower cost, larger components into the circuit board design.

The AccuWave 5800 antenna product utilizes Etenna's DC-Inductive (DCL) Frequency Selective Surface (FSS) antenna technology (patent pending). Its energy mechanism and radiation characteristics create an antenna resistant to frequency de-tuning.

A major challenge facing the industry today is that most antennas are adversely affected by the proximity of other components within the circuit board or by their orientation to the antenna's ground plane. The tri-band antenna, however, is insensitive to its local environment. Its frequency of operation varies little with close proximity to nearby components such as ICs, passive chips or the plastic housing, and is designed to be mounted directly to the ground plane. Varying the ground plane size from 30 x 20 mm to 250 x 250 mm causes a frequency shift of only 7 MHz.

Figures 1 , 2 and 3 show the antenna's typical radiation patterns at 2440, 5250 and 5775 MHz. All of the electrical tests have been performed on a 45 x 45 mm test board, with the antenna mounted on the corner of the board (the preferred location). Table 1 lists the AccuWave 5800 antenna's electrical and mechanical specifications.

Table 1
AccuWave 5800 Specifications

Frequency range (GHz)

2.4 to 2.48
and 5.15 to 5.85

Efficiency (%)

50 min., 70 typ. (2.4 to 2.48);
50 min., 65 typ. (5.15 to 5.85)

Peak gain (dBi)

+1.0 nominal (2.4 to 2.48);
+3.5 (5.15 to 5.85)

3 dB bandwidth

200 MHz min. (2.4 to 2.48);
1.2 GHz min. (5.15 to 5.85)

Voltage standing wave ratio

<2.0 nominal

Polarization

linear

Power handling

2 W CW

Feed point impedance

50 unbalanced

Temperature (°C)

-35 to +85

Size

10 x 14 x 3 mm

Weight

0.18 g max.

Mounting area
required on printed circuit board (PCB)

140 mm2

Total contact area on PCB

2.0 mm2

Maximum height
of components under antenna

1.5 mm

Conclusion

An ultra-small tri-band antenna has been introduced for 2.4 GHz Bluetooth and 802.11b use, as well as 802.11a and HYPERLAN 2 applications at 5.2 to 5.8 GHz. The small form factor and unique design allows it to be mounted directly over PCB components, saving board space without compromising performance. Its surface-mount design mounts directly to the ground plane without the need for external matching components or cables and connectors. The AccuWave 5800 antenna is designed for high volume production using lightweight molded plastics and offers high performance at a very competitive cost.

Etenna Corp., Laurel, MD (240) 456-4100, www.etenna.com. Circle No. 303

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