Three types of integral antenna are recommended:
A) Helical
Wire coil, connected directly to pin 2, open circuit at other end. This
antenna
is
very
efficient given it's small size (20mm x 4mm dia.). The helical is a high Q antenna, trim the wire
length or expand the coil for optimum results. The helical de-tunes badly with proximity to other
conductive objects.
B) Loop
C) Whip
A loop of PCB track tuned by a fixed or variable capacitor to ground at the 'hot' end and fed
from pin 2 at a point 20% from the ground end. Loops have high immunity to proximity de-
tuning.
This is a wire, rod, PCB track or combination connected directly to pin 2 of the module.
Optimum total length is 15.5cm (1/4 wave @ 433MHz). Keep the open circuit (hot) end well
away from metal components to prevent serious de-tuning. Whips are ground plane sensitive
and will benefit from internal 1/4 wave earthed radial(s) if the product is small and plastic cased
0.5 mm enameled copper wire
close wound on 3.2 mm diameter former
RF
433 MHz = 24 turns
A. Helical antenna
Feed point 15% to 25% of total loop length
track width = 1mm
RF-GND
4 to 10 cm2 inside area
C2
C1
RF
C3
C4
B. Loop antenna
16.4cm
wire, rod, PCB-track or a combination
of these three
RF
433 MHz = 16.4 cm total from RF pin.
C. Whip antenna
Fig.4: Antenna configuration (BiM2G @ 433.92MHz)
helical
**
loop
*
whip
***
Ultimate performance
Easy of design set-up
Size
Immunity proximity effects
Range open ground to similar antenna
(for BiM2G-433-15)
**
***
**
*
**
***
100m
***
*
*
200m
300m
Antenna selection chart
Radiometrix Ltd, BIM2/3G Data Sheet
page 8
RADIOMETRIX [ RADIOMETRIX LTD ]
