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James Tabuchi, Brian Hughes and Julio Perdomo

Hewlett-Packard Company
Network Measurements Division
Microwave Technology Division
Santa Rosa, CA 95403

ABSTRACT frequency and reduce the extrapolation span.
It is evident that as technology pushes devices
A broadband, millimeter-wave on-wafer and circuits to higher frequencies, the
network analyzer system is necessary for the network analyzer systems must also evolve.
characterization and design of millimeter-
wave devices and circuits. The HP 85109B
45 MHz to 62.5 GHz network analyzer was' CRITICAL REQUIREMENTS OF A
used to determine the fT and f max of a BROADBAND ON- WAFER NETWORK
0.25}Lm MODFET. The S-Parameters were ANALYZER SYSTEM
also used to model an equivalent circuit of the
MODFET. A broadband 0.5 to 50 GHz The most important criteria of a
travelling wave amplifier [I] was measured to broadband on-wafer network analyzer system
determine the cutoff frequency and the is measurement bandwidth. For device
potential for out-of-band oscillations. measurements, it is desirable to have the
Finally, a criteria was established for the widest bandwidth possible. For circuit
selection of a broadband millimeter-wave measurements the bandwidth should not only
network analyzer. be adequate to measure the device under test
in its operating bandwidth, but should also
extend higher in frequency for guardband
INTRODUCTION measurements. Broadband on-wafer network
analyzers are currently limited to 62.5 GHz
In recent years improvements in semi- and broadband wafer probes are limited to 65
conductor processes have resulted in the GHz. V-Band network analyzer systems and
ability to produce FETs with gate lengths as wafer probes are available for measurements
small as O.I}Lm[2]. This, together with from 50 to 75 GHz [6], but are narrow
improved material systems, such as banded.
AlGaAsjInGaAs and AlInAsjInGaAs[3][4], In addition to measurement bandwidth,
has provided the capability to produce another very important characteristic to
MODFETs with fTS as high as 250 GHz[5]. consider in selecting an on-wafer network
analyzer system is accuracy. Since modelling
Until recently the only broadband network accuracy is derived from measurement data, it
analyzer systems available to measure these is necessary to use measurement data of the
devices and circuits were 26.5 or 40 GHz highest accuracy. The accuracy of the
systems. Measurements were made on these measurement system will be determined by
systems and the data was extrapolated to the raw performance of the system and the
predict performance at higher frequencies. accuracy of the calibration. It is important to
Since' these extrapolations were made over note that there is a trade-off between
large frequency spans, large uncertainties measurement bandwidth and accuracy. The
resulted. In order to reduce these uncer- best trade-off should be sought in the
tainties, it is necessary to measure as high in

log ~G
selecti on of a broadb and networ k anal 'zer
REF -0.5 dB
e.2 dB/
system . -- ,
For versati lity, the networ k analyz er p
should suppor t at least the three most commo n C

on-wa fer calibra tion techniq ues: Open- Short-
Load- Thru (OSLT ), Thru-R eflect- Line (TRL) ~
SOU: i
and Line-R eflect- Match (LRM) . The ' -~ ~ \
selecti on of the approp riate techniq ue will ....... I
depend upon the availab ility of standa rds, the
wafer probe config uration (fixed vs. movea ble
probes ), and the measu remen t freque ncy
I V~ N\ A

LRM Vl ~ ~{jJ
range (see Figure I). V ~

CAl FlHlLEN:;Y , ry: I ;
'T'IPE rw..a: ST