Rainbow Electronics RC1090 - Manual (Page 11)

RC1040/1080/1090
 2005 Radiocrafts AS RC1040/RC1080/RC1090 Data Sheet (rev. 1.3) Page 11 of 17
Antenna Connection
The antenna should be connected to the RF pin. The RF pin is matched to 50 Ohm. If the
antenna connector is placed away from the module at the motherboard, the track between the
RF pin and the connector should be a 50 Ohm transmission line.
On a two layer board made of FR4 the width of a microstrip transmission line should be 1.8
times the thickness of the board, assuming a dielectric constant of 4.8. The line should be run
at the top of the board, and the bottom side should be a ground plane.
Example: For a 1.6 mm thick FR4 board, the width of the trace on the top side should be 1.8 x
1.6 mm = 2.88 mm.
The simplest antenna to use is the quarter wave whip antenna. A quarter wave whip antenna
above a ground plane yields 37 Ohm impedance and a matching circuit for 50 Ohm are
usually not required.
A PCB antenna can be made as a copper track where the ground plane is removed on the
back side. The rest of the PCB board should have a ground plane as large as possible,
preferably as large as the antenna itself, to make it act as a counterweight to the antenna. If
the track is shorter than a quarter of a wavelength, the antenna should be matched to 50
ohms.
The lengths of a quarter wave antenna for different operational frequencies are given in the
table below.
Frequency
[MHz]
Length
[cm]
433 16.4
868 8.2
915 7.8