Table of Contents
Antenna Selection Guide
A guide to antenna options with our products
Many wireless products feature the ability to attach an external antenna to improve wireless performance. Most customers choose to use an antenna for:
- Improving range
- Improving antenna positioning
The purpose of this guide is make customers aware of their antenna options, advise them of some trade-offs when using an antenna and to relate this information to the LM product line-up.
Improved wireless range/performance is often desirable and, antennas are a quick and cost-effective means to accomplish this. Every 6dBi of antenna gain will approximately double the effective transmission distance, however, it’s important to realise that antennas are not power amplifiers, they do not make a signal stronger, they instead improve range by focusing a wireless signal over a smaller effective area, as pictured below:
The antennas pictured above are omni-directional, that is that they transmit evenly in all directions horizontally, however, as you increase their size and gain, vertical coverage is reduced in-order to achieve gain through a more focused signal. From a three-dimensional point-of-view, the transmission pattern looks very-much like that of a doughnut in shape, that becomes squashed as gain and size increases.
It’s important to realise from this that as you increase gain, positioning and angling of antennas becomes increasingly important, especially over short distances, a slight misalignment will make a significant difference to the achievable signal strength.
LM offers a full-range of omni-directional antennas with Reverse Polarity SMA connectors.
|Product Code||Antenna Gain (dBi)||Directionality||Connector Type||Frequency (GHz)|
|LM251||2||H: 365° V: ~365°||Male Reverse-Polarity SMA||2.4|
|LM252||5||H: 365° V: 40°||Male Reverse-Polarity SMA||2.4|
|LM253||7||H: 365° V: 30°||Male Reverse-Polarity SMA||2.4|
|LM254||9||H: 365° V: 25°||Male Reverse-Polarity SMA||2.4|
Improving Antenna Positioning
Wireless signals are easily influenced by metal, walls and various other obstacles and enclosures. It often becomes necessary to reposition an antenna to establish a superior line-of-sight that features fewer obstacles or less obstacles that include materials that are unfriendly to wireless transmissions.
It’s possible to use antenna extension products to relocate an antenna, much in the same way cars often feature roof antennas, in fact, even modern smartphones internally route and extend the antenna to a more suitable location on the device.
Antenna extension products are great, but it’s important to be aware that loss of signal-strength will occur and that the level of loss varies from product-to-product and from length-to-length. LM measures this loss in VSWR (Voltage Standing Wave Ratio), this figure represents the amount of signal that is reflected back from the antenna, instead of being transmitted by it. The table below represents the level of signal loss to expect for a certain VSWR rating, it’s typically recommended to select a product with a VSWR rating of less than 3.0:
|VSRW||Reflected Power %||Reflected Power dB|
Available Antenna Extensions
LM offers a limited-range of stock antenna extensions, however is able to source alternative products upon customer request.
|Product Code||Form Factor||Cable Length m||Connector Type||Frequency GHz||VSWR|
|LM242||Square-Base Platform||1.5||Female-Reverse Polarity SMA||2.4||1.6:1|
LM Products Featuring External Antenna’s
|Product Code||Product Type||Connector Type||Technology|
|LM058||RS232 to Bluetooth Serial Adapter||Female Reverse-Polarity SMA||Bluetooth 2.0/2.1+EDR 2.4GHz|
|LM540||Long-Range USB to Bluetooth Serial Adapter||Female Reverse-Polarity SMA||Bluetooth 2.1+EDR 2.4GHz|
|LM300||Bluetooth Ethernet Serial Switch / Server||Female Reverse-Polarity SMA||Bluetooth 2.1+EDR 2.4GHz|
|LM410||Class 1 Bluetooth SPP Serial Module||Female Reverse-Polarity SMA||Bluetooth 2.1+EDR 2.4GHz|