Continued on page 2 

Volume 3, Number 3

July 2002

Contents

Weapon System

Effectiveness 1

Anti-Jam GPS Pt III 4

Director’s Corner 9

New Sensors & Seekers

Course 8

Calendar of Events 12

WSTIAC is a DoD Information

Analysis Center Sponsored by the

Defense Technical Information

Center and Operated by IIT

Research Institute

WST

WEAPON SYSTEMS TECHNOLOGY INFORMATION ANALYSIS CENTER

IAC

Weapon System Effectiveness

against the 

Time Critical Mobile Target

by Mitchell Douglas

Teledyne Solutions, Inc.

Introduction

Ever since the 1991 Gulf War, DoD has become more and more concerned about the threat

of time critical or mobile targets (TCMT) and has recognized the need for ability to place

TCMT at risk from surface, subsurface, and/or airborne platforms. It seems that every indirect

fire weapon system in development in the early 90's had implemented a product improvement

program with a requirement to defeat the TCMT threat. For the most part, DoD has the capability to satisfy such a requirement in situations such as Standoff Outside Point Defense (SOPD)

where shooters stand off about 10 to 15 nautical miles (18 to 27 km) and Standoff Outside

Area Defense (SOAD) where the shooters launch weapons from about 35 to 150 nautical

miles (63 to 270 km). However, in many cases DoD forces may be restricted to Standoff

Outside Theater Defense (SOTD) at ranges in excess of 150 nautical miles such as in the Gulf

war. 

Although we did not face a viable TCMT threat during the fighting that took place in

Afghanistan in Operation Enduring Freedom, we will most certainly face a TCMT threat if

allied forces return to Iraq as part of a future phase of our war on terrorism. The key to successfully defeating the TCMT threat is to minimize the moving target uncertainty (MTU). In

other words, deliver the weapon system to the target position as fast as possible. This means

increasing weapon flight speed and/or decreasing Command, Control, Communications,

Computers, and Intelligence (C4I) time.

In early 1998, the Navy started a Hypersonic Weapons Technology (HWT) program, which

was coordinated with hypersonic programs in the Air Force, DARPA and NASA. The HWT program was sponsored by the Office of Naval Research and aimed at maturing technologies,

not procuring a weapon. The HWT technology development program was based on a

Mission Needs Statement (MNS), produced by the Navy, for a joint tactical strike capability

against TCMT. Basically, the MNS outlines the need for a hypersonic weapon capability to

engage time critical targets as well as the high value hard target assets such as bunkers buried

underground and reinforced by concrete. Not only does a hypersonic capability provide the

speed and range to engage the time critical assets, but it also provides the kinetic energy to

penetrate the buried assets as well. 

Today's military technology to deliver ordnance quickly enough to take advantage of the

increasing capability in C4I has not followed suit. The C4I efforts involve technologies such

as, Centric Warfare and Smart Sensor Webs, designed to significantly reduce the decision

making process and command & control timelines. It seems our present force structure lacks

a good capability to attack the detected targets of opportunity considered time critical, such

as mobile ballistic missile launchers (TELs) or military leadership (or terrorists) whose whereabouts are considered time critical. However, the near term solution may be what we have

seen in Afghanistan - the armed UAV.
2

Continued from page 1 

Continued on page 3

Weapon System Effectiveness

In the following analysis we will present the results of a limited set of

parametric simulation runs in order to establish the trends in operational effectiveness of three different types of weapon systems against

the "shoot and scoot" TCMT scenario. The GENEric Smart Indirect fire

Simulation (GENESIS) was used to simulate the various scenarios.

GENESIS is a generic many-on-many (M-on-N), indirect fire submunition (IFSM) weapon system endgame effectiveness simulation. It is a

Monte Carlo simulation and allows evaluation of multiple systems,

concepts, and technologies in the context of a single, generic simulation. 

GENESIS provides system effectiveness results. Here, system effectiveness (1) describes the ability of the IFSM weapon system to perform its

mission in terms of the number of kills achieved by a given volley and

(2) measures the number of encounters, detections, engagements, and

hits as well as kills. The determination of system effectiveness is based

on the performance of all elements making up the weapon system

including C4I, launchers, carriers, smart munitions, and their interaction with the targets and the battlefield.

Time Critical Target Scenario

The time critical scenarios consist of a single transporter erector

launcher (TEL) target that has the capability to shoot and move in less

than 10 minutes. Upon firing a theater ballistic missile (TBM), detection occurs and the fire mission is sent to the weapon system launching platform and fired toward the targeting position. During weapon

system flight, the TEL prepares the launching platform for movement.

This is considered the dwell time of the launcher. After the dwell time,

the launcher is traveling at some average velocity. Therefore as a

function of time, the distance traveled from the original aimpoint is

defined as the moving target uncertainty (MTU) radius. The figure

below illustrates the scenario.

MTU is a component of the total Target Location Error (TLET). TLETis

equal to the root sum squared (RSS) value of the targeting TLE 

(TLETGT from a JSTARS, FireFinder, etc.,) and MTU.

Average velocity of TEL v

Time for TEL to start travel (dwell time) t

Time for targeting (C4I) t

Time of missile flight t

MTU v t t t

TEL

TEL

c4I

f

TEL f C I TEL

=

=

=

=

= ⋅ ( + − )

4

2

2

TLET = TLETGT + MTU

For this analysis we assume perfect TLETGT. Therefore, the TLETis

equal to the MTU. Also, for this analysis we are interested in relating

the TLET or MTU as a function of the targeting time or command time

(tC4I ). So, if we assume typical target and indirect fire weapon system

delivery characteristics such as:

·Moving target average velocity = 13.3 m/s

·Weapon system flight time = 151 seconds (Mach 2 @ 

100 km range)

·Target dwell time = 5 minutes (300 seconds)

Then the resulting MTU as a function of tC4I can be plotted (Figure 2).

From the plot we see that for a tC4I delay of 5 minutes, the target will

have moved approximately 2 km from its original launch position. The

direction of movement is unknown therefore modeled randomly. 

MTU vs C4 Time

Vtel=13.3 m/s, Tf=151 s, Ttel=300 s 

0

2000

4000

6000

8000

0 1 2 3 4 5 6 7 8 9 10

Tc4I (min)

MTU (m)

MTU vs C4 Time

Vtel=13.3 m/s, Tf=151 s, Ttel=300 s 

0

2000

4000

6000

8000

0 1 2 3 4 5 6 7 8 9 10

Tc4I (min)

MTU (m)

Weapon System Descriptions

The three weapon systems used in this analysis are generic representations of indirect fire systems currently being fielded or procured to be

fielded in the near future: (1) a GPS guided missile carrying 600 cluster munitions (bomblets), (2) a GPS guided missile carrying six

autonomous broomsweep glide submunitions, and (3) 2 loitering

autonomous broomsweep submunitions.

A submunition implementing an autonomous search capability such as

a gimbaled seeker typically scans the ground in a side-to-side pattern.

This resembles the way one would use a broom to sweep the floor.

Therefore this pattern is referred to as a broomsweep pattern.

The cluster munitions concept has an effective footprint radius based

on 100 meters 1 sigma normal distribution. The conditional probability of kill (given an encounter) is 80%. 

The autonomous broomsweep glide submunitions dispense from the

tactical missile in an area offset from the initial position of the target.

The dispense distribution is assumed to be an elliptical pattern, 500

meters by 2500 meters. This was used for the purpose of spreading

the submunitions out to maximize the area covered during search. The

submunition initial altitude is set at 300 meters with a horizontal velocity of 250 m/s and vertical velocity of 22 m/s resulting in a 10:1 glide

ratio. The seeker cumulative footprint coverage results in an initial

width of 437 meters, final width 0, total length 2889 meters, and total

search time approximately 14 seconds. The conditional performance

is based on a 90% probability of target detection given an encounter,

Figure 1. Shoot and Scoot Scenario.

Figure 2. MTU as a Function of C4I Time

The equation representing the MTU is presented below:

MTU vs C4 Time

VTEL = 13.3m/s, Tf = 151 s, TTEL = 300 s

TC4I (min)
3

Continued from page 2 WSTIAC Newsletter 3rd Quarter 2002

Continued on page 4

90% probability of hit given a detection, and 90% probability of kill

given a hit.

The loitering munition concept is a generic representation of a powered submunition capable of flying a predefined waypoint guidance

flight path at a constant altitude of 500 meters and velocity of 100

m/s. For each submunition played, the total flight time is approximately 1 hour and flight distance is approximately 225 miles. 

The resulting weapon system lethal footprint coverages are illustrated

below in figure 3.

Cluster Munitions

Glide Submunitions

Loitering Submunitions

Surface Map

Contour Map

Results

For this analysis, two cases were used to model the weapon system

effectiveness against the time critical target - without terrain and with

terrain. For the terrain case, a mountainous region in Korea was used.

Figure 4 shows both the surface map and contour map. The target initial position is indicated by the arrow located at 276, -136 meters from

the origin (4 o'clock position from the center). For each weapon system and terrain combination, the target position was varied parametrically (0 to 6000 meters in increments of 1000) to simulate the MTU.

For each parametric run, the MTU varies from replication to replication (300 Monte Carlo replications) within the boundaries of the parametric region of uncertainty (i.e. 0 - 1000 meters, 1000 - 2000

meters, etc., out to 6000 meters). 

The results of the operational effectiveness as a function of MTU

against the single time critical target are presented in Figure 5. Each

graph shows 2 curves - probability of target encounter and probability of target kill. The base line performance can be interpreted as the

encounters, which would be equivalent to kills when all reliabilities and

performance data are perfect. The probability of target kill curve represents some realistic system performance data (i.e. Pdet|enc=0.9,

Phit|det=0.9, Pkill|hit=0.9, reliability=1.0). Please note these results

are from generic representations of weapon system concepts.

However, the trends are realistic. 

These results show that the loitering concept provides excellent operational effectiveness against the TCMT out to an MTU of 4000

meters,which correlates to approximately 7.5 minutes C4I time delay

(refer to figure 2). Beyond 4000 meters the effectiveness is acceptable. The glide submunition performance in terrain is very poor. This

is a result of the low altitude (300 meters initial) characteristic of these

submunitions in the high mountainous terrain characteristic of Korea.

In many cases, the submunitions fly into the side of a mountain. The

cluster munitions are also very effective, as long as the target is inside

of 500 meters placing the C4I time requirement less than 3 minutes.

Figure 3 Weapon System Concepts

Figure 4. Korean Terrain Map.
4

The results presented from this analysis are

not surprising. The GENESIS model is a

powerful tool for conducting quick reaction,

"what if" scenarios often required in developing and understanding performance trends

with various indirect fire weapon system concepts. For more information about GENESIS

or related services, contact WSTIAC: Ms.

Vakare Valaitis at (703)933-3362.♦

About the Author

Mr. Douglas is an electrical engineering

graduate from the University of Alabama in

Huntsville. He worked at IITRI for 14 years,

where he supported Army and Air Force indirect fire systems and related smart munitions

programs. 

Anti-Jam GPS. Part III.

Protecting Weapon Receivers from Jamming.

By Mark Scott

IIT Research Institute

Background

In last September's issue of the WSTIAC newsletter, Part I of this series

described the proliferating employment of Global Positioning System

(GPS) navigation receivers in precision guided munitions (PGMs). Also

described were the fundamentals of GPS navigation from the perspective of a weapon guidance function. This discussion explained how a

GPS receiver's acquisition and tracking of signals transmitted from the

GPS satellites, enables computation of accurate position fixes for

application to weapon precision guidance functions.

If simple jamming techniques are effective in blocking reception of

GPS signals, then the precision guidance that we are beginning to

depend on GPS providing, could be denied to current/future generations of weapons. Accordingly, in the March issue of the newsletter,

Part II in this series described the characteristics of GPS navigation signals and receivers that relate to the potential for a weapon-grade

receiver to be jammed by tactically feasible electronic countermeasure

(ECM) devices.

Sample calculations performed in the Part II article demonstrated that

relatively small, low power, unsophisticated noise jammers hold the

potential to significantly disrupt/deny GPS navigation for C/A-code

receivers (similar results hold for the encrypted precision P(Y)-coded

GPS signals). Furthermore, since these jammers are based on relatively simple technology, they may represent an electronic countermeasure (ECM) that is tactically feasible to field in large numbers. A 

large matrix of such jammers could create a GPS denial zone with

dimensions of hundreds of kms (areas of tens of thousands of square

kms).

The tactical feasibility of fielding significant numbers of effective GPS

jammers has led to the development of anti-jam (AJ) electronic counter-countermeasures (ECCM) for GPS receivers. In this newsletter, the

third and final installment in this series of articles presents the fundamental AJ techniques available to GPS receivers in weapon applications. These ECCM techniques are designed to mitigate the effects of

the tactically feasible noise jammers described in the previous article,

as well as some other basic classes of jammers. For a more comprehensive description of ECM/ECCM aspects of GPS in weapon applications (including P(Y)-code receiver performance in jamming environments), WSTIAC will be publishing a state-of-the-art-review (SOAR)

on this subject this coming summer (4th quarter FY02). The reference

number for this SOAR is WSTIAC-SOAR-02-02.

Principal Jamming Techniques

A brief summary of the main categories of jamming applicable to GPS

receivers will be given prior to describing the AJ techniques that are

designed to counter these jammers.

There seems to be a broad consensus among the experts, that wideband noise jamming represents the most affordable, tactically feasible,

effective jamming technique that is likely to be encountered by GPS

receivers in the near term. With numerous sources of information

available (many on the internet), a competent electronics technician

should be easily able to build a noise jammer with an effective range

of tens of kilometers for $1K to $10K. Wideband jamming was the

electronic countermeasure (ECM) used in the example calculations of

the Part II article in this series (see WSTIAC Newsletter, Vol. 3 No. 2,

March 2002).

continued from page 3

Continued on page 5

EFFECTIVENESS

600 Bomlet Munitions in Flat Terrain

0

0.2

0.4

0.6

0.8

1

0 1000 2000 3000 4000 5000 6000

MTU (m)

Probability

Encounters

Kills

EFFECTIVENESS

600 Bomblets in Mountainous Terrain

0

0.2

0.4

0.6

0.8

1

0 1000 2000 3000 4000 5000 6000

MTU (m)

Probability

Encounters

Kills

EFFECTIVENESS

6 Glide Submunitions in Flat Terrain

0

0.2

0.4

0.6

0.8

1

0 1000 2000 3000 4000 5000 6000

MTU (m)

Probability

Encounters

Kills

EFFECTIVENESS

6 Glide Submunitions in Mountainous Terrain

0

0.2

0.4

0.6

0.8

1

0 1000 2000 3000 4000 5000 6000

MTU (m)

Probability

Encounters

Kills

EFFECTIVENESS

2 Loitering Submunitions/Flat Terrain

0

0.2

0.4

0.6

0.8

1

0 1000 2000 3000 4000 5000 6000

MTU (m)

Probability

Encounters

Kills

EFFECTIVENESS

2 Loitering Submunitions/Mountainous Terrain

0

0.2

0.4

0.6

0.8

1

0 1000 2000 3000 4000 5000 6000

MTU (m)

Probability

Encounter

Kills

Figure 5. Effectiveness Results

EFFECTIVENESS

600 Bomblet Munitions in Flat Terrain

EFFECTIVENESS

600 Bomblet Munitions in Mountainous Terrain

EFFECTIVENESS

6 Glide Submunitions in Mountainous Terrain

EFFECTIVENESS

2 Loitering Submunitions in Mountainous Terrain

EFFECTIVENESS

2 Loitering Submunitions in Flat Terrain

EFFECTIVENESS

6 Glide Submunitions in Flat Terrain
5

The power in wideband jamming is diluted over a broad frequency

interval (usually matched to the spread spectrum bandwidth of the targeted signal/receiver). However, even though wideband jamming is

characterized by low power spectral density, it is virtually impossible to

filter out with embedded receiver signal processing techniques. The

fraction of the jamming signal that makes it through a GPS receiver

(and into baseband processing functions) becomes additive to the

noise floor, degrading the output signal-to-interference power ratio

(SIR) and corresponding receiver operation.

Narrowband (or spot) noise and continuous wave (CW) tone jammers

can cause degradation to receiver SIR and degradation/denial of GPS

navigation similar to wideband noise. In fact, the effectiveness of these

jamming techniques is potentially greater than wideband noise since

they result in higher power spectral densities at receiver outputs, being

more concentrated signals in the frequency domain. However, unlike

wideband noise, spot noise and CW tone jamming signals can be

located in frequency and filtered out of the GPS signals with practical

(and low cost) embedded signal processing techniques that result in

only minor degradation in receiver signal-to-noise power ratio (SNR)

and navigation function.

Wideband pulse jammers deliver high peak power interference signals

at low duty cycles to damage or saturate receiver front ends. Since

GPS receivers typically employ PIN (microwave) diode-based limiters in

the RF front end, pulse jamming represents a minimal threat. The limiter passes normal signal levels without distortion but clips the amplitude of high peak power jamming signals or interference (e.g., a radar

transmitter). Even with the limiter in place, the receiver is still inhibited

while the pulse jamming signal is high; however, this represents a small

percentage of time in accordance with the low duty cycles typical of

pulse jammers. Meanwhile, the limiter protects the RF front end from

damage and prevents amplifiers from being driven into saturation such

that the receiver can recover and function between pulses. 

Continued from page 4

Continued on page 6

WSTIAC Newsletter 3rd Quarter 2002

Accordingly, pulse jamming effectively represents a degradation in

receiver SNR that is directly proportional to the complement of jammer

duty cycle (e.g., 10% duty cycle results in an effective SNR degradation

by a factor of 0.9 or 0.5 dB).

Finally, spoofing is a deception jamming technique wherein a hostile

entity transmits a replica of an actual GPS satellite signal, complete

with a valid pseudo-random noise (PRN) binary code sequence modulated onto the L1 and/or L2 GPS carrier frequencies. The goal of the

spoofer is to cause a receiver channel to lock onto the deception signal instead of the actual satellite signal. This denies the receiver

access to valid range measurements from that satellite and substitutes

false or meaningless range measurements in their place. The false

range measurements will, in turn, degrade, disrupt, or deny the GPS

receiver's navigation function.

The use of actual GPS signals makes spoofing a potentially devastating deception jamming technique; accordingly, an inherent anti-spoofing (AS) feature was designed into GPS at its inception. This feature is

the encryption of the P-code, which converts it to the P(Y)-code.

Without the keys to properly seed the P-code generator, an adversary

cannot transmit a valid encrypted P(Y)-code.

Fundamental AJ ECCM Techniques - Receiver-Based

The fundamental receiver-based ECCM techniques applicable to GPS

are described in this section along with the corresponding jamming

techniques that they are designed to counter. Of primary interest in

military applications of GPS receivers (such as the PGM application

that is our focus here), these techniques are of growing interest in critical civilian applications, such as aviation, where the potential for terrorist jamming is an increasing concern. Figure 1 illustrates the location, within a generic GPS receiver architecture, of the AJ ECCM features discussed below.

RF Filter *

Limiter *

RF Amp

Frequency

Down-converter

IF Filter

Parallel Digital Receiver

Channels

ü Code Correlators

ü Signal Detection *

ü Signal Tracking *

ü Range Measurements

ü Data Demod

Antenna *

A/D Adaptive *

Notch Filter

AGC

Jam *

Detector

Navigation

Processor

Weapon Position,

Velocity, Time * ECCM Related Functions

IF Amp

Figure 1. Generic GPS receiver architecture highlighting AJ ECCM
6

Basic to any AJ receiver design are the abilities to detect the presence

of jamming and characterize jamming features. Detection of jamming

can be accomplished by comparing signal levels to the noise floor in

the receiver, prior to the code correlators. At this stage in the receiver, the GPS signal amplitude is well below the noise floor. Detection

of significant signal amplitude at this stage is indicative of the presence

of jamming or other interference. Automatic gain control (AGC)

measurements can characterize the amplitude of the jamming signal.

A discrete Fourier transform (DFT) provides an effective spectral characterization.

Once the presence of jamming is established, a GPS receiver with AJ

features can begin to adapt to the jamming environment within which

it finds itself. The first tier of responses may be employment of simple

tactics such as elimination of satellites at low elevations where antenna gain is lower and propagation losses are higher. This will focus the

receiver's efforts on track maintenance, acquisition, and reacquisition

of satellites with maximum signal levels.

The GPS receiver's next layers of defense, that are aimed at actually

reducing the level of jamming contaminating signal processing functions, are embodied in various levels and types of filtering. At the first

level, GPS receivers require fixed bandwidth front-end RF filters that

pass the L-band frequencies of the spread spectrum satellite signals

while simultaneously rejecting out-of-band jamming/interference.

Out-of-band jamming would probably not be intended to inhibit GPS

users but could incidently disable receivers if not eliminated early in the

receive chain.

At the next level, military receivers should have intermediate frequency

(IF) adaptive notch filters to counter narrowband noise and CW tone

jammers. As described in the previous section, these jamming signals

can be located in the frequency domain via DFT measurements performed by the jammer detection process. Once detected and isolated

in frequency, various spectral and temporal signal processing techniques can be employed to implement a band rejection (or notch) filter that is adaptively tuned to the narrow frequency interval occupied

by the jammer. Such notch filtering techniques can provide 15-30 dB

of jamming suppression with only minor distortion/attenuation of the

GPS signal, since only a small fraction of the signal's spread bandwidth

is affected by the filter.

Adaptive notch filtering will not work on wideband noise jamming,

however. To reduce the effects of wideband noise contaminating

receiver functions, process base bandwidths should be minimized in

receiver designs or be allowed to adaptively reduce in response to

detected jamming. Such adaptive bandwidth filtering in the predetection bandwidth and carrier/code tracking loops will minimize the jamming power that is able to influence these receiver processes. The

minimum predetection bandwidth is 50 Hz to accommodate the satellite ephemeris data carried on the GPS signal. The tracking loops can

be reduced in bandwidth to 10 Hz or less to maintain carrier/code lock

and maximize the accuracy of satellite range measurements via optimum SIR in the presence of wideband jamming. Adaptive bandwidth

filtering is effective particularly for the signal tracking loops where it

can provide on the order of 10 dB of jamming resistance.

The down side of narrow tracking loop bandwidths, however, is that

they do not accommodate platform dynamics very well, and most

PGMs are fairly dynamic platforms. Accordingly, the narrow bandwidths of AJ GPS receivers require inertial measurement units (IMUs)

to rate aid the tracking loops. In this process, velocity measurements

from the IMU are provided to the tracking loops, enabling them to follow rapidly time varying Doppler shifts (that are the result of platform

dynamics) with their narrow tracking filters. Without velocity aiding

from the IMU, these Doppler effects would shift the GPS signal out of

the narrow pass band of the tracking loops, resulting in loss of carrier/code lock.

Over and above velocity aiding to the tracking loops, maximum AJ 

Continued from page 5

benefits are realized from an on board IMU by configuring it as a fullup navigator, coupled to the GPS receiver via a Kalman filter. The

Kalman filter provides an optimum navigation solution based on the

measurements of both navigation systems. The integrated GPS/IMU

navigator is a truly synergistic combination - the long term stability of

the GPS solution compensating for the drift in the inertial sensors, and

the short term accuracy of the IMU aiding jam-resistant signal tracking

in the receiver. Furthermore, since the IMU is a self-contained unit, it

is immune from RF jamming and can hence maintain the navigation

solution through intermittent GPS outages and on terminal approach

to a jammer-protected target site. In terms of practicality for weapon

applications, it is fortunate that advances in both electronics and

MEMS (micro-machined electro-mechanical system) technologies continue to push reductions in size, weight and cost in integrated

GPS/IMU packages.

The 10 dB (~ or so) of resistance afforded by aided adaptive bandwidth filtering (as described in the preceding paragraphs) does not

provide GPS an adequate AJ capability against feasible wideband

jamming threats. The calculations in the Part II article of this series

assumed narrowband tracking filters (the source of the 1.5 dB tracking

threshold), and yet a tiny 10 W wideband jammer was able to deny

C/A-code navigation out to about a 20 km range. Adaptive bandwidth filtering is hence a necessary but not sufficient component of an

AJ GPS solution. A comprehensive AJ solution must include ECCM

techniques implemented at the receiver's antenna.

Fundamental AJ ECCM Techniques - Antenna-Based

Antenna-based ECCM techniques fall into the basic categories of

antenna switching, polarization nulling, and adaptive array processing.

Adaptive array processing includes the techniques of beam steering

toward satellites, null steering (AKA spatial filtering) toward jammers,

and combinations thereof aimed at optimizing the overall signal-tojammer power ratio (SJR).

Antenna switching is simple in concept but somewhat cumbersome in

terms of practical implementation. This technique employs multiple

antennas with narrower main beams than the hemispheric coverage

typical of most GPS antennas. In a jamming environment, antennas

are selected that have the best combination of gain in the satellite's

direction and low sidelobes in the jammer's direction - SJR is then maximized for the available set of antennas. However, jammer suppression is relatively marginal for this technique (~ 10 dB) and installation

of multiple directional antenna apertures is impractical for some host

platforms (especially PGMs).

Adaptive array processing techniques attempt to remedy the drawbacks of the antenna switching concept by utilizing arrays of small

antenna elements rather than full directional apertures. This makes

installation on even small weapon platforms practical. Furthermore,

implementation of phased-array processing is the key to significant

multiple jammer suppression that can substantially restore GPS receiver operation in extensive jamming environments.

Adaptive arrays provide phase control to each element of their multiple element antennas. In the absence of jamming, the individual phases are adjusted and combined to create hemispheric satellite coverage

by the resulting antenna reception pattern. In the presence of jamming, the phases are adjusted to steer high gain beams in the direction of satellites and/or low gain nulls in the direction of jammers. If

null steering is implemented exclusively, the adaptive array is referred

to as a controlled reception pattern antenna (or CRPA). The number

of nulls a CRPA can generate and steer is dictated by the number of

antenna elements in the array - the number of nulls being one less than

the number of elements.

Adaptive array processing (AAP) is expensive due to the RF/IF electronics and signal processing required - a CRPA typically rivals or
Continued on page 9 7

WSTIAC Newsletter 3rd Quarter 2002

exceeds the cost of the GPS receiver it protects (thousands of dollars,

order of magnitude). However, the digital beam forming and/or null

steering supported by AAP provide the maximum dBs of wideband

jamming suppression per dollar invested of any AJ ECCM technique -

35 dB or more immunity versus multiple wideband noise sources (and

even more against narrowband jammers). Accordingly, AAP is an area

that has received much attention and investment for R&D. There are

AAP designs for AJ GPS receivers in PGM applications - both fielded

and in development.

Polarization nulling is one last antenna-based AJ technique that has

demonstrated significant suppression of wideband jamming (25 dB or

more). This technique employs a simple, low-cost, single aperture

antenna that adapts well to PGM applications, and provides AJ GPS

protection against narrowband as well as wideband jammers. The

principle of operation is to sense and adaptively develop a mismatch

between the polarization (electric field orientation in space) of the jamming signal and the polarization of the receive antenna. This selective

polarization of the receive antenna may have a slight attenuative effect

on the right-hand circularly polarized (RHCP) GPS satellite signals - but

the polarization nulling has a large impact on the targeted jamming

signal such that the receiver's SJR is greatly enhanced. Furthermore if

multiple jamming sites are radiating with similar polarizations, this

technique can be effective against multiple jammers. Accordingly,

polarization nulling holds the potential for significant jamming suppression at more affordable cost levels - a significant consideration in

throw-away weapon applications.

Translating Jamming Suppression into Range Effects

As a point of reference for intuition, let's translate a 25 dB wideband

jamming suppression capability of an antenna-based ECCM feature

into range effects for the jamming example from the Part II article.

Recall that the jammer in this example was a small, simple wideband

noise jammer with an effective radiated power (ERP) of 10 W. Figure

2 illustrates the performance of a receiver protected only by adaptive

bandwidth filtering (repeated from the Part II article). The jammer

causes the receiver to lose signal lock out to a 20 km range and

inhibits signal acquisition out to a 70 km range in this example calculation.

Figure 3 shows the improvement in GPS receiver performance via the

degradation in jammer range effects due to 25 dB suppression of an

antenna-based ECCM feature (AAP or polarization nulling). The jammer's influence is reduced from 20 km to about 1 km in causing loss

of GPS signal lock, and from 70 km to about 4 km in inhibiting signal

acquisition. Thus, as long as the weapon's GPS receiver were locked

up and tracking outside of a 4 km radius from the jammer, the weapon

would have GPS navigation available down to about a 1 km range to

the jammer. At this point, the weapon's freshly initialized IMU could

take over the guidance function for the short remainder of the trajectory into the target.

Conclusion

Jamming represents a serious threat to unprotected GPS receivers in

precision guided munition (PGM) applications for the current configuration of GPS. Low power satellite transmitters and lofty orbits put the

GPS signal power density at a big disadvantage compared to even

small earth-bound jammers, despite spread spectrum signal processing gains inherent in the GPS signal structure. From all the potential

techniques of deception, narrowband and wideband jamming, wideband noise represents the most serious near-term threat that is feasible for adversaries to field in significant numbers - and this fact has

been widely advertised on the internet and elsewhere. GPS jammer

assembly instructions and off-the-shelf units are available for modest

investments from foreign sources. These jammers could easily 

15

10

5

0

-5

-10

-15

-20

-25

0 10 20 30 40 50 60 70 80 90

Range to Jammer (km)

SIR (dB)

Jammer

Location

For Rj < 20 km GPS

receiver loses lock,

cannot track signals,

is completely

inoperative.

Weapon

approaching

jammer

For 20 < R j < 70 km

GPS receiver can:

track signals,

measure ranges.

For Rj > 70 km GPS

receiver can:

acquire signals,

track signals,

measure ranges,

demodulate data.

~ 12 dB

~ 1.5 dB

Acquisition

Threshold

Threshold

Tracking

Figure 2. Degraded SIR of GPS receiver due to wideband jamming - 

minimal AJ protection.

15

10

5

0

-5

-10

-15

-20

SIR (dB)

~ 12 dB

~ 1.5 dB

Acquisition

Threshold

Threshold

Tracking

Range to Jammer (km)

Weapon

approaching

jammer

0 1 2 3 4 5

Jammer

Location

For R j < 1 km, GPS

receiver loses lock,

cannot track signals,

is completely

inoperative.

For 1 < R j < 4 km

GPS receiver can:

track signals,

measure ranges.

For Rj > 4 km GPS

receiver can:

acquire signals,

track signals,

measure ranges,

demodulate data.

Figure 3. Enhancement in GPS receiver SIR due to antenna-based 

ECCM - reduction in wideband jammer's range of influence.

degrade precision munition accuracies from the 10 m or better accuracy associated with GPS guidance, out to the tens to hundreds of

meters associated with uncorrected inertial guidance (depending on

weapon flight duration). 

ECCM techniques exist that are capable of largely mitigating the nearterm GPS jamming threat. Receiver based filtering techniques can be 
8

is pleased to announce the availability of its

Introduction to Sensors and Seekers for

Smart Munitions and Weapons Course

Primary instructor: Mr Paul Kisatsky, IIT Research Institute

Course Description: 

The Weapon Systems Technology Information Analysis Center

(WSTIAC) developed this 2-1⁄2 day Introduction to Sensors and

Seekers for Smart Munitions and Weapons Course to provide

an introduction to the most commonly used sensors and seekers employed in smart weapons (projectiles, missiles, and wide

area mines). It is oriented to managers, engineers, and scientists who are engaged in smart weapon program development

and who desire to obtain a deeper understanding of the sensors they must deal with, but who do not need to personally

design or analyze them in depth. The course stresses the basic

principles and underlying physics of how sensors work, what

they can do, and how they are limited. Both airborne (projectiles and missiles) as well as ground based (smart mines and

wide area denial) weapon platforms are covered. The course

provides both managers and non-sensor-specific engineers

with the framework they need to manage the development of

sensor based smart munitions and weapons. An undergraduate

technical degree is recommended. Mathematics is kept to a

minimum, but important formulas are introduced. This course

also serves as an excellent foundation for those scientists and

engineers who desire to pursue this discipline to intermediate

and advanced levels. 

Course Outline:

The course covers:

♦ Classification of Seekers and Sensors; 

♦ Fundamentals of Waves and Propagation; 

♦ Fundamentals of Noise and Clutter; 

♦ Fundamentals of Search Footprints; 

♦ Introduction to Infrared; 

♦ Introduction to Radar; 

♦ Introduction to LADAR; 

♦ Introduction to Visionics; 

♦ Introduction to Acoustics; 

♦ Future Projections and Interactive Brainstorming.

Training at Your Location:

WSTIAC can conduct this Sensors and Seekers for Smart Munitions

andWeapons Course at your location to reduce your travel time and

cost. This is a very cost effective way to provide training on sensors and

seekers to up to 25 people on-site.

Fee: The registration fee for this 2-1⁄2 day course is $950 for US government personnel and $1150 for government contractors. Contractor

teams of 3 or more, registered at the same time, are charged $950

per person.

For additional information, contact: 

Ms. Kelly Hopkins, 

Seminar Administrator, 

at (256) 382-4747, fax: (256) 382-4702 

or by e-mail: khopkins@iitri.org

Location: Huntsville, Alabama

15-17 October 2002

The WSTIAC Newsletter is the current awareness publication of the Weapon Systems Technology Information Analysis Center (WSTIAC).

WSTIAC, a Department of Defense (DoD) Information Analysis Center (IAC), is administratively managed by the Defense Information Systems

Agency (DISA), Defense Technical Information Center (DTIC) under the DoD IAC Program. The Contracting Officer's Technical Representative

(COTR) for WSTIAC is Mr. H. Jack Taylor, ODUSD (S&T), Defense Pentagon, Washington, D.C. 20301-3080, (703) 588-7405. IIT Research

Institute operates WSTIAC, which services Government, industry, and academia as a Center of Excellence in Weapon Systems Technology.

WSTIAC Director: Dr. Wes Kitchens Database Inquiries: Vakare Valaitis

703.933.3317, Email: wkitchens@iitri.org 703.933.3362 Email: vvalaitis@iitri.org

Internet: http://iac.dtic.mil/wstiac/

All data and information herein reported are believed to be reliable; however, no warrant, expressed or implied, is to be construed as to the

accuracy or the completeness of the information presented. The views, opinions, and findings contained in this publication are those of the

author(s) and should not be construed as an official Agency position, policy, or decision, unless so designated by other official documentation.

Notice: WSTIAC reserves the right to substitute speakers and cancel and/or change the course schedule for any reason. In the event of a schedule change or cancellation, registered 

participants will be individually informed. 
9

T

he recent DoD decision to cancel the Crusader Artillery System is unexpected in some quarters, but really not all that surprising. Crusader

has been under attack almost since its inception. Crusader was envisioned to be a fully automated 155mm artillery system that could fire

10-12 rounds/minute and deliver existing ammunition out to 40 km. The range could be extended to 50 km when firing the XM982

Excaliber precision guided artillery projectile (currently in development). In the mid-1990's Clinton administration officials proposed purchasing

the Panzerhaubitze PzH 2000 155mm Self-Propelled Howitzer under development by Germany in lieu of developing and fielding Crusader. In

the end, even though the PzH 2000 represented an improvement over the U.S. Army's Paladin 155mm Self-Propelled Howitzer, it couldn't meet

all of the Army's requirements for Crusader. Crusader was put on notice, but allowed to proceed. The need for Crusader was again questioned

when the plans for the Army's Future Combat Systems were announced. Crusader was viewed as too heavy and it was put it on a "diet" to try to

get it down to about 40 tons. It remained on notice, but was again permitted to proceed. Now (June 2002), it again appears that Crusader

will be terminated. This is surprising to many because Army support seemed very solid, as indicated by the statement on 6 March 2002 by the

Honorable Thomas White, Secretary of the Army, before the Senate Appropriations Subcommittee on Defense ... "I view Crusader to be absolutely vital to the Army going forward." People need to remember that in Washington, DC, nothing can be taken for granted. Crusader appears to

be a victim of the DoD transformation effort and our recent experience in Afghanistan where we routinely employed aircraft-delivered precision

guided munitions, like the Joint Direct Attack Munition (JDAM), instead of artillery. It now appears that Crusader will be cancelled and the funds

freed up in the out years will be made available to accelerate the development of smart/precision weapons such as Net Fires, Guided Multiple

Launch Rocket System and the XM982 Excaliber, among others. Only time will tell if the weapons systems selected for development in lieu of

Crusader will be able to make a significant difference on the battlefields of the 21st century.

This issue of the WSTIAC Newsletter features an article by Mr. Mitch Douglas on weapon system effectiveness against time-critical ground mobile

targets. The simulations discussed in this article were conducted using the IIT Research Institute-developed GENEric Smart Indirect fire Simulation

(GENESIS) model, recently upgraded to treat loitering munition concepts. This Newsletter also includes the last of a three-part series on antijam Global Positioning System (GPS) technology by Mr. Mark Scott. The implementation of robust anti-jam GPS technology is critical to the success of precision weapons that rely on GPS as their primary or secondary guidance system. 

We welcome your feedback about the WSTIAC Newsletter and solicit your suggestions for future topics you would like to see included. You can

reach me by Email at wkitchens@iitri.org or by phone at (703) 933-3317. ♦

Director/Chief Scientist’s Corner

A view from Washington

by Dr. Wes Kitchens

Anti Jam GPS Part III (continued from page 7.)

very effective against narrowband jamming and should be implemented in weapon receivers. However, the large quantum leaps in AJ GPS

receiver performance are realized via antenna-based measures.

Polarization nulling and especially spatial filtering based on adaptive

phased array processing can provide significant suppression of fairly

extensive wideband jamming environments.

This AJ protection for GPS guidance receivers comes at an increased

cost per weapon that varies from a fraction to a multiple of the cost of

the receiver being protected (depending on the level of immunity

afforded). Planned improvements in the GPS space segment in the

coming years include a new military code and increased satellite effective radiated power that will greatly enhance the jamming immunity of

the overall navigation system. Until these upgrades reach IOC, maintaining the effectiveness of GPS guidance functions in precision munition applications will depend on effective ECCM implemented in the

weapon receiver and especially in the receiver's antenna.

References

Open literature references employed in writing Parts I, II and III of this

series, that you may find useful for background and depth on GPS topics, include:

♦ Casabona and Rosen, "Discussion of GPS Antijam Technology,"

www.ericorp.com

♦ Herring, "The Global Positioning System," Scientific American, Vol

274, No 2, February 1996.

♦ Herskovitz, "GPS Insurance Antijamming the System," Journal of

Electronic Defense, December 2000.

♦ Hurn, GPS - A Guide to the Next Utility, Trimble Navigation,

1989.

♦ Kaplan, Understanding GPS - Principles and Applications, Artech

House, 1996.

♦ Logsdon, The Navstar Global Positioning System, Van Nostrand

Reinhold, 1992.

♦ Parkinson & Spilker, Global Positioning System:Theory and

Applications, Volume I, AIAA, 1996.

♦ Tsui, Fundamental of GPS Receivers, John Wiley & Sons, Inc.,

2000.

♦ Warner, "GPS: America's 'Maginot Line" in Impending Conflict?,"

Global Position & Navigation News, www.satellitetoday.com, 3

October 2001. ♦

WSTIAC Newsletter 3rd Quarter 2002
10

Smart/Precision Weapons Training Seminar

LOCATION: Huntsville, Alabama

20-22 August, 22-24 October, 3-5 December 2002

(Seminar starts at 8:00 AM Tuesday and ends at 12:00 PM Thursday)

Seminar Scope:

The Weapon Systems Technology Information

Analysis Center (WSTIAC) developed this 2-1⁄2 day

Smart Weapons Training Seminar to provide a comprehensive understanding of smart weapons and

related technologies. This seminar is aimed at providing general knowledge about smart weapons

technology and a source of current information on

selected U.S. and foreign smart weapons, to include

system description, concept of employment, performance characteristics, effectiveness and program

status. 

Seminar Objectives:

The seminar's objective is to inform materiel and

combat developers, systems analysts, scientists,

engineers, managers and business developers about

smart weapons to include: State of the art of representative U.S. and foreign smart weapon systems;

Employment concepts; Smart weapons related systems, subsystems, and technologies; and

Technology trends.

Seminar Sponsors:

hDUSD(S&T) Weapons

hDefense Technical Information Center(DTIC)

hJoint Technical Coordinating Group Munitions

Effectiveness(Smart Munitions Working Group) 

About the Seminar:

This seminar was originally developed for the U.S.

Army Command and General Staff College in Fort

Leavenworth, Kansas. It has proven to be enormously popular with attendees from both government and industry. The seminar is updated annually to include current information about the latest

technology and capability upgrades being made to

representative US and foreign smart weapon systems. Instructors include: Dr. Wes Kitchens, WSTIAC Director and former DDR&E Director for

Weapons Technologies; Mr. Mark Scott and Mr.

Hunter Chockley, IITRI Science Advisors; and Mr.

Mike Holthus, foreign weapons expert at the

National Ground Intelligence Center. 

Security Classification:

The security classification of this seminar is SECRET

(U.S. Citizens Only).

Fee:

The registration fee for this 2-1⁄2 day seminar is

$950 for US government personnel and $1150 for

government contractors. Contractor teams of 3 or

more, registered at the same time, are charged

$950 per person.

Registration:

Attendance is limited to 35 people and the seminars

generally fill up fast. All registrations will be

acknowledged, and each attendee will be sent an

agenda, maps, and directions to the seminar site.

Please call Ms. Kelly Hopkins 

at (256) 382-4747 or 

email khopkins@iitri.org 

for more information and a brochure with seminar details.

Smart Weapons Training Seminar Offered at Your Location

WSTIAC can conduct its 2-1⁄2 day Smart Weapons Training Seminar at your location during 2002 to reduce your travel time and cost. This seminar has been presented to hundreds of students over the past decade. This is a very cost effective way to provide smart

weapons training to up to 35 people at your site. 
11

Upcoming Conferences and Courses

7-11 July 2002

International Symposium on Optical Science and

Technology

SPIE's 47th Annual Meeting 

Seattle WA

For additional information:

http://spie.org/Conferences/Calls/02/am/ 

9-11 July 2002

AUVSI Unmanned Systems Symposium

Lake Buena Vista FL

For additional information:

http://auvsi.org/symposium/ 

21-25 July 2002

Joint Advanced Weapon Systems Sensors, Simulation and

Support Symposium (JAWS S3)

Air Force Academy

Colorado Springs, CO

For additional information:

Email: CGriffith@anteon.com 

29 July-2 August 2002

11th Annual AIAA/MDA Technology Conference

(SECRET/U.S. Only)

Monterey, CA

For additional information:

http://www.aiaa.org/calendar/ 

5-8 August 2002

AIAA Guidance, Navigation, and Control Conference

Monterey, CA

For additional information:

http://www.aiaa.org/calendar/ 

19-21 August 2002

AFCEA International 24th Annual Symposium and

Exposition

Fort Bragg NC

For additional information:

http://www.afcea.org 

20-22 August 2002

Smart/Precision Weapons Training Seminar

Huntsville, AL

For additional information:

Call: Kelly Hopkins at 256.382.4747

Email: khopkins@iitri.org

9-12 September 2002

NanoTech 2002

"At the Edge of Revolution"

Houston, TX

For additional information:

http://www.aiaa.org/calendar/ 

10-12 September 2002

Homeland Security Conference

Secret/US-Only

Atlantic City, NJ

For additional information 888-OLD-CROW

E-mail bnelms@crows.org

http://www.crows.org/events.htm 

16-19 September 2002

2002 Joint Undersea Warfare Conference

Groton, CT at SUBASE

For additional information:

Email: kwilliams@ndia.org

http://register.ndia.org/interview/register.ndia?PID=Brochure&SID

=_0MF0QZX7J&MID=2240

23-27 September 2002

20th International Symposium On Ballistics

The Rosen Center Hotel

Orlando, FL

For additional information:

http://register.ndia.org/interview/register.ndia?~Brochure~2210 

24-27 September 2002

ION GPS 2002

Oregon Convention Center

Portland, Oregon

For additional information:

http://www.ion.org/meetings/meetings.cfm#am 

15-17 October 2002

Introduction to Sensors and Seekers for 

Smart Munitions and Weapons Course

Huntsville, AL

For additional information:

Call: Kelly Hopkins at 256.382.4747

Email: khopkins@iitri.org

22-24 October 2002

Smart/Precision Weapons Training Seminar

Huntsville, AL

For additional information:

Call: Kelly Hopkins at 256.382.4747

Email: khopkins@iitri.org

WSTIAC Newsletter 3rd Quarter 2002
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12

Inside this issue

Weapon System Effectiveness

Anti-Jam GPS Pt III 

Director’s Corner

New Sensors & Seekers Course

Calendar of Events

1901 N Beauregard Street,Suite 400

Alexandria VA 22311-1705