文档介绍：PCB Trace Antenna Design Considerations and
Implementation Guidelines for the AT86RF401 RF
Wireless MicroTransmitter
This document details the process of obtaining the output load impedance for
AT86RF401[1] and matching a balanced printed circuit board loop antenna to that
impedance to achieve optimum radiated output power. A detailed description of the
FCC regulations and the results of the FCC testing of the prototype evaluation board AT86RF401
are also included. RF Wireless
Analysis and Design MicroTransmitter
Output Impedance and Matching
Theoretically, to realize maximum power transfer from the output of an RF transmitter Application
to its antenna, the impedance of the antenna load must be plex conjugate of
the transmitter’s output impedance. However, for transmitters at this power level, the Note
optimum load impedance is different than plex conjugate of the output imped-
ance. Because it is not of interest to directly measure the output impedance of the
device, an alternate method to obtain the optimum load impedance must be utilized.
To determine the optimum load impedance, one can present different load imped-
ances to the device and note the impedance that produces maximum power output. In
this way, the optimum load impedance can be found empirically by identifying the load
impedance that yields maximum output power. This technique requires a tuner, power
meter or spectrum analyzer, and work analyzer.
To apply this approach to the AT86RF401, refer to Figure 1. First, the output pins need
to be biased to the supply voltage. This is done by placing a 220 nH wire wound induc-
tor (Coilcraft 0603CS) in series with the supply voltage, a DC blocking capacitor (100
pF) at the output of the device, and a bypass capacitor (100 pF) between supply volt-
age and ground. Note that the bypass capacitor should be connected as close to the
inductor as possible. Next, the tuner is connected to the output of the work.
The output of the tuner is