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Helical Style

Whip Style

Loop Style

1/4-wave wire lengths

for RMfrequencies:

418MHz = 6.7"

433MHz = 6.5"

Where:

L=length in feet of quarter-wave length

F=operating frequency in megahertz

COMMON ANTENNA STYLES

There are literally hundreds of antennas styles that can be successfully employed with the

RM Series. Following is a brief discussion of the three styles most commonly utilized in

compact RF designs. Additional antenna information can be found in Linx application notes

#00500, #00100, #00126 and #00140.

A

whip-style

monopole

antenna

provides

outstanding

overall

performance and stability. A low-cost whip can be easily fabricated from

wire or rod, but most product designers opt for the improved

performance and cosmetic appeal of a professionally made model. To

meet this need, Linx offers a wide variety of straight and reduced-height

whip-style antennas in permanent and connectorized mounting styles.

The w avelength of the operational frequency determines an antenna's

overall length. Since a full wavelength is often quite long, a partial 1/4-

wave antenna is normally employed. Its size and natural radiation

resistance make it well matched to Linx modules. The proper length for

a 1/4-w ave antenna can be easily found using the formula belo w. It is

also possible to reduce the overall height of the antenna by using a

helical winding. This decreases the antenna's bandwidth but is an

excellent way to minimize the antenna's physical size for compact

applications.

A helical antenna is precisely formed from wire or rod.A helical antenna

is a good choice for low-cost products requiring average range

performance and internal concealment. A helical can detune badly in

proximity to other objects and its bandwidth is quite narrow so care must

be exercised in layout and placement.

A loop- or trace-style antenna is normally printed directly on a product's

PCB. This makes it the most cost-effective of antenna styles. There are

a variety of shapes and layout styles which can be utilized.The element

can be made self-resonant or externally resonated with discrete

components. Despite its cost advantages, PCB antenna styles are

generally inefficient and useful only for short-range applications. Loop-

style antennas are also very sensitive to changes in layout or substrate

dielectric which can introduce consistency issues into the production

process. In addition, printed styles initially are difficult to engineer,

requiring the use of expensive equipment including a network analyzer.

An improperly designed loop will have a high SWR at the desired

frequency which can introduce substantial instability in the RF stages.

Linx offers a low-cost planar antenna called the “SPLATCH”which is an

excellent alternative to the sometimes problematic PCB trace style. This

tiny antenna mounts directly to a product's PCB and requires no testing

or tuning. Its design is stable even in compact applications and it

provides excellent performance in light of its compact size.