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THE HP 85108
ASA
HIGH PERFORMANCE ANTENNA
AND
RADAR CROSS-SECTION ANALYZER
John W. Boyles
Network Measurements Division
1400 Fountaingrove Parkway
Santa Rosa, California 95403
RF & Microwave
Measurement
Symposium
and
Exhibition
Flin- HEWLETT
~~ PACKARD
www.HPARCHIVE.com
ANTENNA AND RCS TESTING WITH THE' HP 8510B NETWORK ANALYZER
John W. Boyles
Network Measurements Division
1400 Fountaingrove Parkway
Santa Rosa, CA 95401
ABSTRACT:
The HP 8510B Network Analyzer contains enhancements and new features that expand its scope beyond
network analysis to include new capability for high performance Antenna and Radar Cross-Section (RCS)
Testing.
This paper describes different measurement techniques used for Antenna and RCS testing including the
use of Far-Field, Near-Field, and Compact Antenna and RCS test ranges. The unique requirements that
these measurement techniques place on the instrumentation and how they are satisfied by the appropriate
HP 8510B configuration are discussed. Other topics include descriptions of the harmonic sampler (HP
8511A) and external mixer based front ends for the HP 8510B and the use of software (time domain) and
hardware gating techniques to remove RCS range clutter.
Author:
John W. Boyles is a development engineer at the Network Measurements Division of Hewlett-Packard
located in Santa Rosa, CA. He has a BS degree received from North Carolina State University in 1978
and a MSEE degree received from the Georgia Institute of Technology in 1979, both in electrical
engineering. With HP since 1979, he has performed both microwave oscillator and analog circuit design
and has developed training materials on time domain network analysis. Since 1984, he has been involved
in application and system development for Antenna and Radar-Cross Section Measurements with High
Performance Vector Analyzers.
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Antenna and Radar Cross Section (RCS)
measurements are performed in a variety of
ways, each of which presents unique challenges
to the test instrumentation and measurement
system. While there are several different kinds
of antenna and RCS test ranges, the required
test equipment does not change significantly
between them. This paper describes how to
configure the HP 8510B Network Analyzer to
make high performance Antenna and RCS
measurements.
6751
The HP 8510 Network Analyzer is a high
performance stimulus/ response measurement
system that consists of a microwave source,
receiver front end, and the HP 8510B as IF
receiver and system controller. Its modularity
and general flexibility have made the HP 8510
useful for a variety of antenna and RCS
applications (Reference 1). Recent HP 8510B
enhancements have greatly expanded the
analyzer's antenna and RCS capability. [This
paper lists many features found only in the HP
8510B. To upgrade an HP 8510A to an HP
8510B, order the HP 85103A Performance
Upgrade Package (Reference 2).]
The HP 851 OB can be configured as a
multi-input, phaselocked antenna test receiver
HP Sl510B AINITIEINIINIA TIEST that offers very broad frequency coverage, wide
CAPAB ~ UT~ IES dynamic range and high measurement
sensitivity. Its hardware triggering and fast
l1li 4-lnput Phaselocked Receiver internal processing combine to give precise CW
IIIi Magnitude and Phase Measurement Pattern measurements at a data rate fast enough
l1li Broad Frequency Coverage even for near-field antenna testing. The
I!IlI High Measurement Sensitivity frequency list mode allows testing at multiple
I!IlI Extremely Fast Measurement Speed frequencies. Both HP-IB and Analog outputs
l1li Precise Triggering are provided for automated measurements or
IIIi Frequency List Mode direct interface with antenna pattern recorders.
IIIi HP-IB & Analog Outputs These capabilities, coupled with its proven
l1li Proven Reliability (>3000 hr MTBF) reliability (>3000 hours mean time between
failures (MTBF)), make the HP 8510B a very
attractive choice for antenna test.
6753
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For RCS test, the HP 8510B provides an
extremely fast RAMP sweep mode for
broadband measurements at up to 801
frequencies. The built-in calibration models
can be used to automatically correct the RCS
data for systematic measurement errors. Time
IIa High Speed Measurements
domain processing then provides RCS
IlII Broad Frequency Coverage
down-range imaging and software gating
iIII RCS Error Correction
capability. For more advanced RCS systems,
IIlI Time Domain Imaging
IIa Software Gating
the analyzer can also be operated under
IIa Pulsed-RF Operation
pulsed-RF test conditions.
l1li Antenna, RCS, and Network Analysis
In addition to its antenna and RCS test
capabilities, the HP 8510B also makes high
performance network measurements.
6754
We will begin with a description of the HP
8510B configurations that are most appropriate
OILJJTUINlIE for Antenna and RCS testing, focusing on both
HP 8511 A and external mixer front-ends.
Next, several antenna and RCS test categories
I. HP 8510B FRONT ENDS will be described to show how the HP 8510B
can be configured and applied to meet the
II. ANTENNA TESTING unique requirements of each application.
Far-field, compact range, and near-field
III. RCS TESTING antenna measurements and far-field, compact
range, and pulsed-RF RCS measurements will
IV. SUMMARYI RECOMMENDATIONS be covered. This will be followed by a short
summary.
6756
We will begin with a description of the HP
8510B antenna and RCS test configurations,
their features, and the performance that can be
achieved. The two basic receiver configurations
use either the HP 8511A or external mixer front
ends. This will be followed by a performance
comparison of each configuration.
A. HP 8511A CONFIGURATION
B. EXTERNAL MIXER CONFIGURATION
C. COMPARISON OF FRONT ENDS
6757
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HP 8511A CONFIGURATION
REFERENCE
TEST
HP 9000)~
Series 200
,I ~ I JH~P~IB~H;;;;;;P;S8:;;;51;;0~B
/1-
HP 8340/41
or 300
Synthesizer
Controller
HP 37204A
~~<=>[ ]~
I
HP-IB BHC or HP 8510
Extenders Fiber System Bus HP 8511A
6758
HP 8511A CONFIGURATION
The HP 8510B Analyzer consists of a microwave source (HP 8340B/ 8341B), a receiver front end for RF
to IF conversion, and the HP 8510B as the IF receiver and system controller. This configuration shows
the HP 851lA Frequency Converter as the receiver front end.
The HP 8511A uses a Harmonic Sampling technique to convert the RF at each of its four inputs to 20
MHz IF signals that are processed by the HP 8510B. The RF source is provided by the HP 8340B/ 8341B
Synthesized Sweeper (the HP 8350B Sweep Oscillator family is also compatible). The source and test set
are controlled by the HP 8510B over a private (HP-IE) system bus, with an additional IF interconnect
cable to the test set. Because the Voltage Controlled Oscillator (YCO) inside the HP 8511 A phaselocks to
the incoming RF signal (instead phaselocking the RF to a synthesized LO), the RF source can be
separated a great distance from the receiver and operated under remote control using HP- IE extenders.
To measure amplitude and phase, the HP 8510B must have a Reference signal that remains constant
during the measurement. This signal provides the denominator of the measured parameter (Test/
Reference). Usually, this amplitude and phase signal also serves as the phaselock reference signal as well,
although this is not always the case (for example, for pulsed-CW RCS as described later). The phaselock
reference signal is obtained using a separate reference antenna or else a cable to route to the test set a
signal coupled off from the RF source.
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The HP 8511 A provides a compact, low cost
microwave front end with an extremely broad
bandwidth (45 MHz to 26.5 GHz) and wide
dynamic range (75-105 dB, depending on
II Compact, Low Cost Front End
averaging). Operating in the RAMP Sweep
II Broad Bandwidth (45 MHz-26.5 GHz)
mode, the HP 8511 A provides extremely fast
iii Wide Dynamic Range (75-105 dB)
broadband ReS measurements.
III Extremely Fast RAMP Sweep
The HP 8511 A tradeoffs come from its use of a
TRADEOFFS
harmonic sampler, a technology with a
relatively high noise figure that limits its input
III Limited Sensitivity sensitivity. Although not affected by RF
l1li Susceptible to RFI harmonics or subharmonics, the HP 8511 A is
III RF Cable Losses susceptible to RF Interference (RFI) at other
frequencies (more on this topic later). And
because the RF signals are routed from the
antenna to the test set, RF cable losses are
6759 encountered.
This slide lists the dynamic range, maximum
input, and sensitivity (for signal to noise ratio
of 13 dB) of the HP 8510B/ HP 8511A
configuration for the cases of 0 and 1024
Frequency Range averages (the noise reduction effects of
0.045 - 20 GHz 20 - 26.5 GHz
averaging will be covered in more detail later).
These numbers will be helpful in determining
Dynamic Range 75 dB 68 dB the best configuration for a particular antenna/
o Averages (-10 to -85 dBm) '*
(-15 to -83 dBm) ReS range.
Dynamic Range 105 dB 98 dB
1024 Averages (-10 to -115 dBm) (-15 to -113 dBm)
* Signal to Noise Ratio of 13 dB.
6760
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EXTERNAL MIXER CONFIGURATION
REFERENCE
~
HP 9000)~
Series 200
,III\ IH:!!P=_~IB~H;;:;;:;;P;S8;;;51;;0~B
/L
HP 8340/41
or 300 It---+--'
Synthesizer
Controller
HP 37204A
~~~~ I
HP-IB HP 8510
Extenders System Bus
6761
EXTERNAL MIXER CONFIGURAnON
In applications where the highest receiver performance is required, the HP 85l0B External Mixer
configuration should be selected. In this configuration, the HP 85llA Frequency Converter in the
previous block diagram is replaced with external mixers, the HP 8350B sweeper as the phaselocked LO, a
power splitter, and various IF and LO amplifiers (as required). This test configuration makes possible a
wide variety of measurement configurations and performance.
The mixers are shown located near the test and reference antennas. The output of the HP 8350B LO
source is split and applied to the two mixers through the LO isolation amplifiers, and the mixer IF
outputs at 20 MHz are amplified and applied to the HP 85l0B. The LO source is phaselocked to the
incoming Reference signal. The HP 85l0B controls both RF and LO sources over the HP 8510 system
bus.
This configuration can be extended to millimeter wave frequencies by using the appropriate HP 83500
Series Source Modules (multipliers) and test set kits that include millimeter wave mixers.
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It is also possible to use an HP 8340B/ 8341B
Synthesized Sweeper as the LO source for a
non-phaselocked (fully synthesized) test
configuration. With the synthesized LO, there
are no restrictions on the remotability of the
reference mixer (unlike the phaselocked LO,
described later). In addition, it also allows
(magnitude-only) pattern testing with no
reference signal.
HP 9000
Series 200 I[D~\-'H'..':.P-::.'.'I~~~
,-
HP 8340/41
or 300
Synthesizer
Controller
6762
A receiver front end with external mixers
allows RF to IF (20 MHz) conversion to take
ADVAINlIAGIES Of' place very close to the antenna under test.
Advantages of the HP 8510B external mixer
IEX1IERINlAl M ~XIERS configuration include improved measurement
sensitivity, minimized RF cable (and rotary
l!Il Improved Sensitivity joint) losses between the antenna and receiver,
and reduced susceptibility to spurious RFI
III Minimum RF Cable Losses signals. The external mixer configuration is
also capable of full millimeter wave coverage to
iii Reduced RFI Susceptibility 100 GHz (no holes).
III Extension to Millimeter
6763
The external mixer configuration can be
operated with either Fundamental or Harmonic
f'IUINlIDAMlElNllAl VSo Mixing. With fundamental mixing, the IF
frequency equals the LO frequency minus the
~ARMOINl~C M~X~INlG RF frequency. The "harmonic" mixer is one
FUNDAMENTAL MIXING: that is designed to use a harmonic of the LO
signal in the conversion process. The harmonic
IF = LO - RF mixer output is IF = (N * LO) - RF, where N
is the LO harmonic number. Each mixing
technique offers certain advantages and
HARMONIC MIXING
tradeoffs.
IIF = N '* LO - RF I
N = MIXER LO HARMONIC NUMBER
6764
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The use of harmonic mixing lowers the required
La source frequency by the mixer harmonic
number, N. For example, a x4 harmonic mixer
AID>VA~lAGIES Of operating at an RF frequency of 16 GHz
requires a La frequency of only 4 GHz. This
HA!RMO~~C M~X~~G
reduces the cost of the La source, isolation
amplifiers, cabling, and antenna rotary joints.
m Lower Frequency LO Source Harmonic mixers also usually have much better
RF to La isolation than fundamental mixers,
III Lower Cost of LO Source, Amplifiers which reduces the need for La isolation
Cabling, and Rotary Joints amplifiers. For low mixer harmonic numbers,
these improvements are achieved with little
m Better Mixer RF/ LO Isolation sacrifice in measurement performance.
6765
The major tradeoff with harmonic mixing is the
increased mixer conversion loss (of roughly
20*10g(N) dB), which reduces measurement
sensitivity. And because a harmonic mixer
m Higher Conversion Loss Reduces front end can also downconvert signals at each
Sensitivity (by> 20*LOG
10
[N]) La harmonic, it is susceptible to interference
from spurious RF signals, particularly at lower
Susceptible to RFI at Each LO Harmonic
III
La harmonics where the mixer has less
conversion loss. For example, ifax5 harmonic
RFI EXAMPLE:
mixer is used to measure a 15 GHz RF signal,
RF= 14 GHz. LO= RF/ 7 = 2 GHz it will also convert any signals at 3, 6, 9, and 12
The Mixer Will Also Convert Signals at GHz with lower conversion loss, and at 18,21,
2, 4, 6, 8, 10, and 12 GHz With Lower Loss,
24, ... GHz with higher conversion loss. See
and at 16, 18, 20, ... GHz With Higher Loss.
Reference 3 for more information.
6766
The fundamental mixer front end provides the
highest measurement sensitivity of the HP
85l0B antenna test configurations because of
the low mixer conversion loss (typically 6-8
dB). Because only one La signal is present in
ADVANTAGES the mixer, it also provides the highest immunity
all Highest Sensitivity Because of to RFI signals. The tradeoff with using
Low Mixer Conversion Loss fundamental mixing is the increased cost of the
III Highest RFI Immunity Because La source, isolation amplifiers, cables, and
of Fundamental LO Frequency rotary joints, which must operate at a higher
frequency than with harmonic mixing.
TRADEOFF
III Increased Cost of LO Source, Cables,
Amplifiers. and Rotary Joint
6767
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This slide gives a graphical comparison of the
difference in sensitivity that can be achieved
with different mixing approaches. Fundamental
mixing offers the highest sensitivity that stays
essentially constant over the full mixer
Sensitivity frequency range. The use of a low numbered
-85 (dBm) harmonic mixer with a 2-8.4 GHz La has only
-90 slightly worse sensitivity, which makes it
-95 attractive for many applications. The high
-100 x4 x4 2-8.4 GHz LO
d ,------ numbered harmonic mixer with a 1-2 GHz La
-105 x2 J
---------- 1-20 GHz LO starts out with high sensitivity, but it degrades
-110
'- Fundamental Mixing in a stairstep fashion as the frequency in
increased (by greater than 30 dB at the high
1 2 4 6 8 10 12 14 16 18 2022 f (GHz) end).
6768
This slide illustrates the RFI susceptibility of
the fundamental mixing, harmonic mixing, and
HP 8511 A harmonic sampler configurations.
With fundamental mixing, only RFI signals that
Fundamental are very close to the test (RF) frequency will
Mixing cause interference. For harmonic mixing,
several La harmonics are present, which
Harmonic
1
RF increases the likelihood that RFI will be
Mixing
LOI detected. This is compounded by the mixer
conversion loss being better at lower La
u
harmonics, and is why the lowest practical
Harmonic RF
LO harmonic mixing number should be used. With
Sampling the harmonic sampler, there are very many La
t t + t! t
!
u u u u u u u u u u u u
ti
u u
t harmonics present, but with approximately
equal conversion loss, making it much more
susceptible to RFI.
6769
When using the phaselocked HP 8350B as La in
the external mixer configuration, the total
electrical delay of the phaselocked loop is
lEXlrlElRlNIAl IM~XlElR restricted to 300 feet (requires option H 15).
This limits the separation between the HP
COINIS~ ID>lE IRA1~OU\ijS
8510B and the reference mixer (but not the test
mixer) to a maximum of 150 feet (45.5 m).
II Reference Mixer Phaselocked Loop can The external mixer configuration supports all
Have up to 300 Ft. Total Delay instrument features and data modes except for
(Unlimited with Synthesized LO) Ramp sweep operation.
ill Supports Single Point, Fast CW, and
Step Sweep Modes
6770
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The following example shows how to calculate
the performance of the HP 8510B external
mixer configuration. The receiver average
NOISE FLOOR CALCULATIONS noise floor is described by the equation
Pn=k*T*F*B/ A, where k= Boltzman's constant
I Pn = kTFB/A (1.379 E-20 mW/Kelvin-Hz), T= the receiver
front end temperature (Kelvin), F= the receiver
K = Boltzman's Constant front end noise figure, B= the noise bandwidth
T = Front End Temperature (approximately 10 kHz for the HP 8510B), and
F = Front End Noise Figure A= the averaging factor. Expressed in decibels
B = Receiver Noise Bandwidth (assuming T=290K and B=10 kHz), Pn(dBm) =
A = Averaging Factor -134 dBm + F(dB) - 10*log lO (A).
Pn(dBm) = -134 dBm + F(dB) -10 10910(A)
6771
The HP 8510B IF detector (20 MHz inputs) has
a average noise floor of -110 dBm, measured in
a 10 kHz IF bandwidth, for a noise figure
HP 8510B (F DET ) of 24 dB. Adding an IF preamp with a
2.7 dB noise figure and 25 dB gain (A vantek
~e3 ACT5-200) will reduce the IF noise figure
(F IF ) to 4.2 dB, according to the equation F IF =
F amp + (FDET-1)/G amp ' The RF noise figure
F = 2.7dB F = 24dB
AMP OET (F RF ) is approximately equal to F IF plus the
mixer conversion loss. Using a fundamental
mixer with 6.8 dB loss gives an RF noise figure
of 11 dB. RF cable losses add directly to F RF .
Further improvement is possible with a low
F (dB)
RF
= L MXR (dB) + FIF(dB) = 11 dB noise RF preamp.
6772
The HP 8510B noise floor can now be
calculated: Pn = -123 dBm (-134 dBm + 11 dB
F RF )