Wireless Reviews

Introduction

Aerialix Mini Dipole Antenna
Summary	Miniature antenna for wireless notebook adapters with external antenna connectors
Update	10/8/2003 - Corrected available connector type info.
Pros	• Gets your laptop into same polarization as your AP • Can make a difference in weak signal areas
Cons	• Somewhat pricey

Aerialix is a small WLAN equipment supplier located up in the Boston MA area. Among their small line of APs, antennas, cables and cards is a handy little item called the ARLX-OM-MINI2400.

The Mini is a hand-crafted omnidirectional simple 1/2 wave collinear dipole with a gain of approximately 2.15dBi. It's specifically designed for the few WLAN PC cards that support external antennas via either MC or MMCX miniature connectors (see Table 1).

MC	MMCX
Buffalo Technology Cabletron Enterasys Lucent ORiNOCO Proxim Wavelan	Aerialix Engenius Ext2 Cisco 34x/35x series Senao
Table 1: PC Cards with antenna connectors

NOTE! Although MC and MMCX connector options are standard, Aerialix can make the Mini with any Cable "Group B" connector, i.e. Types MC, MMCX, SMA, TNC and N on a special order basis.

Although the Mini doesn't provide much more gain than the integrated printed-circuit antenna built into your laptop's wireless card, it has two advantages over it:

1) It's much less directional - Anyone who's used a wireless laptop that doesn't have a built-in radio knows the contortions they often have to resort to in order to get a decent connection. The reason for this is shown in Figure 1.

Figure 1: PC card antenna gain plot
(click on image for a larger view)
From Antennas Enhance WLAN Security by Trevor Marshall
Used by permission

It shows the gain plot of a typical wireless PC card. If a PC card's antenna were properly omni-directional, the red and blue dotted lines would look more like circles. Instead, the lopsided patterns you see are the reason why you have to aim your laptop in a certain direction in order to connect to your access point.

The MINI is a classic dipole and has the same gain in all directions.

2) Its polarization matches your AP's - Most access points and wireless routers have external antennas that generally point straight up or at a slight angle. This yields a vertically polarized signal. Of course, WLAN PC card antennas provide a horizontally polarized signal because of the way they sit in your laptop's PC card slot. The result is yet another obstacle in the way of optimum performance.

Since you can move the MINI around, you can orient it vertically - same as your AP / wireless router.