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A G R E AT E R M E A S U R E O F C O N F I D E N C E the spectrum analyzer ideal for development
work and few instruments can approach it in
its areas of strength.
An RF power analyzer (Figure 1) is a
much more specialized instrument. It mea-
sures RF power and frequency over defined
bandwidths and frequency ranges. It doesn't
cover the hertz-to-gigahertz frequency range
of a spectrum analyzer, and it doesn't do
the complex modulation analysis of a vec-
The RF Power
tor signal analyzer. Instead of a sweeping
oscillator, it uses multiple oscillators for
the multiple narrow bands it measures. This
Analyzer:
increases measurement speed, because fre-
quency changes are very quick. Intended for
production line use, it has no built-in graphi-
cal display, but reports its results directly to
A lower-cost alternative to the spectrum a computer. It is, first and last, a production
analyzer for cell phone and RFIC power amplifier test instrument. It also costs considerably
less than a spectrum analyzer, and is much
production test faster to set up for a particular test.
Ease of Setup
Robert Green A spectrum analyzer, being a very versa-
Telecommunications Market Development Manager tile instrument, is correspondingly laborious
Keithley Instruments to set up. An RF power analyzer, because it
is intended for certain specific tests, has the
parameters for those tests pre-programmed.
It can be set up from the front panel using
Today's RF power analyzers can automate Descriptions of the Two Classes of a menu, or by computer via an IEEE-488
many of the steps in testing cell phones and Instruments link. It can take just five GPIB commands
similar RF devices, saving users time and A spectrum analyzer does swept-frequen- to measure and transfer five readings--car-
money. cy measurements on RF signals and displays rier channel power, upper adjacent channel
T
results on a screen. In many cases, it can also power, lower adjacent channel power, upper
HE choice between laboratory and store screen images in .gif or similar formats alternate channel power, and lower alternate
production test equipment is the and sometimes provide output in spreadsheet channel power--to the external PC control-
choice between general-purpose form. It has a very broad frequency range. ler. A spectrum analyzer may take from two
instruments and dedicated instru- For example, one spectrum analyzer suitable to eight times as many commands to do the
ments. A spectrum analyzer is for cell phone test applications covers 3Hz to same job.
a very flexible piece of equipment that can 6.7GHz. This and many other things make
be used for many things, but that flexibility
comes at the price of low speed, complicated
setups, and high equipment costs. An RF
power analyzer is dedicated to production
testing of cell phones, RFIC power ampli-
fiers, and similar devices. It can perform an
array of tests that previously required sev-
eral instruments, and do them faster and at
lower cost--but it's not designed for general
laboratory use. This article will explore the
differences between RF power analyzers and
spectrum analyzers and make the point that,
for the jobs for which it is suited, an RF pow-
er analyzer is a more attractive choice than a Figure 1. The Keithley Model 2800 RF Power Analyzer is intended for production testing of cell
spectrum analyzer. phones and RFIC power amplifiers.
The RF Power Analyzer May 2004 1
Speed Carrier Channel
Power
An RF power analyzer is from four to ten
1.23MHz
times faster for cell phone production tests
than a spectrum analyzer. For example, it Lower Adjacent Upper Adjacent
Channel Power Channel Power
can make a 1.23MHz bandwidth cdmaOne
Lower Alternate Upper Alternate
primary power measurement and transfer Channel Power Channel Power
the measurement to a computer in 6ms. It 885kHz 885kHz
can make a 3.84MHz bandwidth primary 30kHz 30kHz