A STANDALONE RF SYSTEM FOR SOLID-STATE PHASED ARRAY
ANTENNA MEASUREMENTS
David S. Fooshe
Nearfield Systems Inc., 19730 Magellan Drive
Torrance, CA 90502 USA
Chris Smith
Lockheed Martin Corp.
Moorestown, NJ 08057 USA
ABSTRACT
Lockheed Martin MS2 has a long history of utilizing
antenna ranges for calibration, test and characterization of
the phased array antennas. Each range contains an
integrated RF receiver subsystem for performing antenna
measurements, typically on the full array. For solid-state
phased array testing, what is often needed, however, is a
test station capable of performing complex S-parameter
measurements on a subarray or subset of the full antenna
system without incurring the expense of a test chamber.
To address this requirement, Lockheed Martin, working
with Nearfield Systems, has developed a portable
standalone RF measurement system.
The standalone system consists of an Agilent PNA,
automated transmit/receive unit (TRU) and a waveform
generation (WFG) subsystem for interfacing to the
phased array beam-steering computer.
This paper will discuss the capabilities of the Standalone
RF System including the TRU and WFG subsystems. The
TRU is used to tailor the RF signal by automated
switching of amplifiers and programmable step
attenuators for various test scenarios. The WFG is an
automated pattern generator used to present many digital
waveforms in arbitrary sequences to the phased array
beam steering computer. The design features of the
standalone RF system will be presented along with the
COTS hardware utilized in assembling the station.
Keywords:
phased array antenna, RF subsystem,
automated test, waveform generator, beam-steering
computer.
1.0 Introduction
Lockheed Martin MS2 has a long history of utilizing
antenna ranges for calibration, test and characterization of
the phased array antennas. As the performance features of
phased array antennas advance, so too must the antenna
ranges utilized to test them. One key component of
antenna measurement ranges is an integrated RF stimulus
& receiving subsystem for performing RF measurements,
typically on the full array. For solid-state phased array
testing, what is often needed, however, is a method to
perform the above plus a capability to measure complex
S-parameter measurements on a subarray or subset of the
full antenna system without incurring the expense of a
test chamber. To address this requirement, Lockheed
Martin, working with Nearfield Systems, has developed a
portable standalone RF measurement system.
2.0 Solid-State Antenna Measurement
Application
The developments of solid-state phased array antennas
have increased the performance requirements on antennas
as sensors. Such applications may range from typical
radar
functionality
to
communications,
target
illumination, and countermeasures all packaged into one
sensor. Coupled with the integration of typical offantenna components into the modern solid-state antennas,
the integrated package contains a wide range of stimulus
and processing hardware.
Measurement requirements of these integrated phased
array antennas places needs upon measurement systems
once relegated to many test systems. Furthermore, the
ability to provide stimulus and response to an antenna in a
manufacturing test environment is advantageous. Thus
with such a test system, an antenna test range with
anechoic material is not required. Non-pattern antenna
integration and testing could occur on the factory floor.
Active components within an antenna environment are
susceptible to changing conditions such as temperature
induced thermal drift, start-up transients and thus may
create non-linear performance behaviors. To account for
these factors, antenna designs include electrical
calibration and alignment schemes to allow both factory
and in field adjustments [1]. Secondary benefits of such
designs allow the antenna to self-diagnose problems
associated with malfunctioning hardware before the
antenna is tested an antenna range.
From a manufacturing implementation viewpoint, test
systems utilized for factory testing of solid-state antennas
must be portable, flexible, and cost effective while
providing commonality of test platforms. The antenna test
system solution presented here meets such requirements.
3.0 Test System Solution
Lockheed Martin, working with Nearfield Systems, has
developed a portable standalone RF measurement system
(Figure 1). The test system is considered stand-alone in
that it is capable of providing the required stimulus,
antenna control, and response measurement capability is
void of scanning mechanisms. It is portable in the fact
that all components are contained in a single rolling
equipment rack.
Finally, the system has a built-in self test capability to
verify signal levels and operational readiness.
3.1 NSI 2000 Software
Control of the standalone system is performed by the NSI
2000 software. Using the NSI 2000 scripting capability,
automated test scenarios may be developed to coordinate
the control of the phase array for pulsed or CW
measurements. The waveform generator (WFG)
subsystem is controlled directly by the NSI 2000 software
and allows the test operator to select and generate timing
waveforms to control the phased array. The TRU
subsystem may also be controlled directly by NSI 2000
scripts to configure the standalone system into the
appropriate test mode. The test data may also be plotted
or integrated with other applications to generate
automated test reports.
3.2 Receiver
ECN
Windows rackmount computer configuration:
- 19" LCD monitor
- Removable hard disk (2)
- GPIB interface card
- Qty 2, LAN interfaces
- Windows XP Professional
- NSI 2000 Software
NSI2000 Workstation
LAN2
KVM
Switch
REV
Description
- Preliminary - unreleased
DW N CHK APPR
DF
BS
BW
Date
3/26/2008
LMMSS Stand-Alone RF Cable Diagram, 1 to 18 GHz
KVM
AUT
(CSP)
COM
GPIB
Serial
LAN
NSI Controller
LAN
DSP INTERFACE UNIT
10 MHz
A4
T3, T4
GPIB
WFG IF UNIT
NSI
Pulse
RecTrig Stop
Sweep
33220A
A22, 60'
Switch Control
(3-bits)
LAN
AUT TRU
Pulse Gen
A5
W7
15'
A21
PNA-X (CSP)
Trig
A IF In
B IF In
Pulse
Agilent PNA-X
Microwave
Network
Analyzer
AUT TRU mounted near AUT
Rdy
LAN
S3
S4
3
2
PORT 1
AUT Cables
W7a-W7h
(CSP)
Rx/Cal
2
B IN
LO Out
PORT 2
1
PSA1
AD01
R 1 IN
Options 200, 080, 020
RF
Test/Cal
Mixer
RF Emerg.
ON/OFF
W3
4
1
S4
3
2
A1, 6'
2
AT2
T1
REF
Mixer
AD12
SW1 1
1
PSA1
4
SW1
C
1
3
FSSW
2
Mixer
C
4
W4
L1
LO/IF
AD11
W24, 3'
1
Loop
W23, 3'
AT3
AT1
P1
C2
3
W2, 3'
AD19
W21
W22
LO In
IF1
IF2
AD20
Test
LO/IF
NSI DFC
LO/IF Unit
AUT Rx
8:1
Switch
L1
3
S3
NSI-RF-5939
LO Amplifier
W8
3'
C
Mixer
LO/IF
W1, 3'
P2
+24V Power Supply
2
C
2
W5
3'
Tx
P1
S1
Coupler
1
S2
DFC LO/IF
WBS
CONTRACT NO.
APPROVALS
NSI
NEARFIELD SYSTEMS INCORPORATED
19730 MAGELLAN DRIVE
TORRANCE, CA 90502
TEL: 310-525-7000
FAX: 310-525-7100
Remarks:
NSI PROPRIETARY
W6, UFB 293C, 15'
+20 dBm
Amp
C
RF IN
Ref
DATE
DRAWN
This document contains proprietary information and except with D. Fooshe 3-26-08
CHECKED
written permission of Nearfield Systems, Inc. such information shall B. Schluper 3-31-08
not be published or disclosed to others, or to be used for any
APPROVED
purpose, and the document shall not be copied in whole or in part. B. Williams 3-31-08
TITLE
SIZE
LM Standalone RF Cable Diagram
B
DRAWING NUMBER
PROJECT NAME
CAGE CODE:
LM 23x18
0KDP3
REV
747851
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C:\Documents and Settings\Dave\My
Documents\NSI\_NSI Projects\_B1713 LM
Standalone RF\RF Design\747851.vsd
FILENAME
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As mentioned above, the base receiver chosen for this
application is the Agilent PNA-X. However, for dynamic
range improvements in antenna ranges with potentially
long cable lengths, an external mixer system, the NSI
DFC LO/IF system, was integrated with the PNA. This
implementation allows the PNA to be used as either
antenna measurement receiver or as a standard network
analyzer with little reconfiguration. The inherent benefit
of this design is a measurement system with a high
dynamic range, fast data acquisition, and broad frequency
range. In this case, the base system is capable of but not
limited to measurements from 1.0 GHz to 18.0 GHz.
Figure 1 Standalone System Diagram
The brain of the standalone measurement system is the
NSI2000 antenna measurement system for data
acquisition. The NSI2000 software allows the efficient
development of data acquisition scenarios in a scripting
language which are transferable across other
measurement systems.
The heart of the standalone measurement system is the
receiver or network analyzer, in this case the Agilent
PNA-X. The network analyzer serves as both an “Sparameter” meter and a pulsed measurement receiver.
Application is not limited to just those two uses as
capability now exists to perform spectrum analysis type
measurements with a PNA.
The arms and legs of this system are the waveform
generator (WFG).subsystem for stimulus and the RF
switching subsystem (TRU) for signal conditioning and
routing..
3.3 Stimulus
The stand-alone test system is capable of providing all RF
& control stimulus to the antenna under test (AUT).
Specifically, the PNA provides the RF source for either a
CW or Pulsed RF waveform to the AUT. However, a key
requirement for solid-state antenna testing is that the RF
stimulus must be coordinated with the AUT timing and
control commands. These signals may be T/R gates, beam
steers, operating modes, gain/attenuation states, and or
measurement dwells.
A programmable multi-channel waveform generator
(WFG) was developed and integrated with the NSI2000
software (Figure 2).
The WFG and PNA are
synchronized via a common 10 MHz clock source
allowing precise control of timing signals. The WFG
design allows the user to program specific scenarios and
events via a convenient user interface. Furthermore, test
scenarios can be saved and recalled for a variety of test
applications.
All measurements are thus managed
through the NSI2000 software for integrated data
acquisition.
Panther 9000 Receiver
& Beam Controller
Agilent 32220A
Pulse Gen
Trigger, T3
Panther 9100
Receiver
33220A
LAN
BSC Interface Unit
16 Channel Waveform Generator PCI Card
(Installed in computer)
NSI
BSC Signal Interfaces
- 16 Unique waveform outputs x 2, differential RS422
- 10 MHz Clk Out, differential RS422
- 2.5 MHz Clk Out, differential RS422
Rackmount computer
Figure 2 Waveform Generator Subsystem
The TRU is a subset of the NSI Range Transition
Manager (RTM) for automating antenna ranges [2]. The
RTM provides a wide range of capability for automating
large antenna ranges, but is oversized for smaller ranges.
To address this problem, the TRU integrates the basic
capabilities of the RTM into two module types while
maintaining the LAN control scheme [3].
The TRU may be configured using two different module
types; the base module and the mixer module. The base
module contains elements from three of the RTM
modules; the control module, Tx module and Cplr
module. The mixer module contains elements from the
mixer, PSA and Rx RTM modules. See Table 1.
Table 1 – TRU Modules
3.4 Signal Conditioning and Routing
Pulling the standalone measurement system design
together between the stimulus and receiving components
is a Transmit/Receive switching and signal conditioning
subsystem (TRU). See Figure 3. The combination of RF
switches, amplifiers, and programmable attenuators allow
the optimum signal distribution to the antenna under test.
This design allows programmable & automatic signal
switching between Transmit and Receive test
configurations. Significant forethought was applied to
component selection to optimize measurement system
performance over various operating modes and from 1 to
18 GHz frequency band.
Module Type
Description and Key Specs
BASE
Provides interface between host computer
and mixer modules. Includes coupler, RF
switching and amplifier, 33 dB, P1dB = +??
dBm.
MIXER
0.5 to 18 GHz mixer, LO/IF is multiplexed.
Includes programmable step attenuator, 0 to
70 dB in steps of 1 dB, RF switching and
LNA, 33 dB, P1dB = +15 dBm.
In a typical near-field range, as shown in Figure 4, two
TRUs are used: one near the NF probe, possibly mounted
on the probe carriage, and the other near the AUT.
The TRU was developed specifically for the antenna
range and includes the building blocks that are often used
in the RF design of large ranges. The TRU is packaged in
a 3U rack mount chassis for the standalone system, but is
modular in construction allowing modules to be mounted
directly on a scanner or positioner, if needed.
RF Out
S3
W19
RF In
PSA1
S4
2
3
1
4
Ref In
C
Mixer
1
L1
3
Figure 4 TRUs Employed in Near-Field System
RF Out
S3
W18 RF In
PSA1
REF
Mixer
Test In
2
S4
2
3
1
4
Test In
T3
2
Ref In
C
Mixer
1
3
L1
W17
LO/IF
W16
For the standalone system, a single TRU is employed
with a single base module and two mixer modules, as
shown in Figure 5.
REF
TR
RF IN
T4
1
AT1
P1
C2
2
3
Tx
C
2
Coupler
S1
Loop
C
1
S2
Figure 3 Transmit Receive Unit (TRU)
Figure 5 TRU Package for Standalone System
A graphical user interface, Figure 6, allows the settings of
the switches and attenuators to be programmed and
integrated into test scenarios.
5.0 Summary
A novel test system design and implementation has been
presented for use in the measurement of solid-state
antennas. This effort resulted in a turnkey measurement
system with versatility needed for current and future test
needs. The test system capability is expandable in either
frequency range or measurement channels, and is
comprised of COTS components. Furthermore, with
additional investment, the system could be married with
almost any type of antenna measurement scanner.
6.0 References
[1] W.T. Patton and L.H. Yorinks, "Near-Field
Alignment of Phased-Array Antennas", IEEE
Transactions on Antennas & Propagation Vol 47, No.3,
March 1999.
[2] D.S. Fooshe, “Improving Automation for Antenna
Ranges”, AMTA Proceedings 2006, p. 339, Austin, TX,
Oct 2006.
Figure 6 TRU Graphical User Interface
[3] D. Lee, S. Mishra, “Automated Antenna
Measurements in a Networked Environment”, AMTA
Proceedings 1995, p. 64, Williamsburg, VA, Nov 1995.
3.4 Built-In Test
One key feature of the standalone measurement system is
a “loop-back” measurement path. The loop-back path is
used to test the test system. With any measurement
system, one of the first tasks encountered is the
certification that the measurement system is ready to go
and operating as needed. The loop-back RF path allows a
signal to be routed from the source to the receiver
bypassing the AUT. With RF switches, amplifiers, and
attenuators in the loop-back path, each component can be
exercised via software scenarios providing a health check
or calibration of the measurement system. This feature
provides the confidence, stability, and repeatability of the
measurement system.
4.0 Test Results and Status
The standalone system has been built and tested with a
phased array antenna to verify the interfaces and
capabilites. Test results will be available at the AMTA
conference.
[4] D. Slater, Near-field Antenna Measurements, p. 63,
Artech House, Norwood, MA, 1991