Adjacent Channel Rejection:
This test uses one or
more signal generators to produce the desired signal
and one or more interfering signals. It measures the
ability of the receiver to reject the interfering signal in
an adjacent channel.
Test Instruments of Choice
Many specialized RF test instruments are available.
But the key devices, and the ones most commonly used,
include the arbitrary waveform generator (AWG), the signal
generator, the vector signal generator, the spectrum
analyzer, the vector signal analyzer (VSA), and the power
meter (Figure 4 and Figure 5). These instruments are vital for
making fast and accurate measurements.
The vector generator and analyzer are based on an SDR
architecture that makes them an ideal fit for today's wireless
standards, as well as for speeding up measurements.
That's because the SDR architecture makes these instruments
flexible - they can be quickly changed, updated, and
improved with a software or firmware addition.
A programmable DSP and/or an FPGA or ASIC generate
the modulation in the generator and perform the
demodulation, downconversion, and decoding in the analyzer.
A high-performance PC often is used for the DSP
and is built into the instrument. Specialized software or
firmware may be added to the generator or analyzer to set
it up for measurements on a specific radio technology or
wireless protocol (Table 2).
Though they aren't commonly used in RF testing, oscilloscopes
do play a role in some applications. For example, Tektronix's
DPO/DSA70000 oscilloscopes are an ideal platform
for very wide-bandwidth RF signals like UWB. Tektronix's UWB
software makes it possible to fully test popular WiMedia UWB
radios and other broadband wireless devices (Fig. 6).
Most test setups will need the proper probes and
cables. Always use the manufacturer's matching probes,
and have the necessary coax cables with the right connectors.
Other common accessories for most tests
include signal combiners or splitters, fixed and/or
adjustable attenuators, and isolators.
Acknowledgments
I want to personally thank Jeff
Owen, Ken Voelker, and Ben Zarlingo
of Agilent Technologies, Mark
Elo of Keithley, David Hall and Hon
Yee at National Instruments, and
Darren McCarthy of Tektronix for
providing valuable information and
insight for this article.
For More Information
RF and wireless measurement is
a vast and considerably deep subject.
For further detail, see the Web
sites of the equipment manufacturers.
They all have extensive lists of
data sheets, application notes, articles,
white papers, and the like.
Even the equipment brochures are
highly informative.
For a good reference book, see Production
Testing of RF and System-ona-
Chip Devices for Wireless Communications
by Keith Schaub and Joe
Kelly (2004), published by Artech
House (www.artechhouse.com).