Phased Array Radars - Past, Present, And Future

8/9/2019 Phased Array Radars - Past, Present, And Future

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PHASED

ARRAY RADARS -PAST, PRESENT AND

FUTURE

E.

BROOKNER

Raythe on Compan y, U.S.A.,

ABSTRACT

This i s a s w e y paper summariz ing the recent

. developments and h tu re trends in passive, active

bipolar and Monolithic Microwave Integrated Circuitry

(MMIC) phased array radars for ground, ship, air, and

space applications. Covered is the DD(X ) ship radar

suite; THAAD (formerly GBR); European COBRA;

Israel BMD radar antennas; Dutch shipboard M A R ;

airborne US F-22, JSF and F-18 radars, European

AMSAR, Swedish AESA, Japan

FSX

and Israel

Phalcon; Iridium (66 satellites in orbit for total of 198

antennas) and Globalstar MM IC spac ebom e active array

systems (these last two are communications hut the

technolog y is the same as used by radar systems, in fact

the IRIDIUM T/R module technology derives from

.technology developed for a space based radar); Thales

(formerly Thomson-CSF) 4 inch MMIC wafer 94 GHz

seeker antenna; digital beamforming; ferroelectric row-

column scanning; optical electronic scanning for

communications and radar; the MMIC C-band to Ku-

band Advadced Shared Aperture Program (ASAP) and

AMRFS antenna systems

for

shared 'use for

.

comm unications,~ radar, electronics counterm easures

(ECM) and ESM; and continuous transverse stub (CTS)

voltage-variable dielectric (WD) antenna.

1.0

h

DECADES

Phased arrays have com e a long way in the last three

decades. This is illustrated by the many tube passive

arrays and solid-state active arrays, which u se dlscrete

and MM IC technology, that have been deployed or are

under development [l-24,

821;

see Figures

1

through 4

and Table 1. Figures 1 and 2 are for passive phased

arrays-the fust generation of phased arrays;Fig. 3

is

for active solid state arrays using discrete compo nents;

Fig. 4is for phased arrays using microwave analog

integrated circuits, the thud generation. The numb ers in

parentheses in the figures represent the numbers

manufactured. Note that in some cases very large

numbers have been produced, even for MM IC active

phased arrays. Also one sees that phased arrays are

being developed around the world. The People's

Republic of China has come a long way in a very short

time in the development of phase arrays passive,

active, over-the-horizon, du al band, wide-ha nd, nltra-

low-sidelobe, synthetic aperture, adaptive, digital-beam-

forming, super-resolution and pha se only null steering

[76].

The question addressed now is what doe s the

future hold

ACCOMPLISHMENTS OVER THE LAST

2

Figure I -Ex am ple U.S.A. Passive Phased Arrays Having

arge

Production

" P h a s e d A r ra y s F o r T h e New Millenium" by Eli Brookner which App ear ed in 2000

IEEE International

C o n f e r e n c e

on

P h a s e d A r r ay S y s t e m s & T e c h n o l o g y P ro c e d d i n g s , M a y 21-25,2000.0 2000

IEEE


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105

Figure 2 -Exam ple Passive Phased Arrays From Around the World

Figure

3

-Exam ple Discrete Active Arrays


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Figure 4 -Exam ple MMICActive Arrays Deployed and Under Development

TABLE

I

-EXAMPLE RADAR PHASED ARRAYS HAVING LARGE PRODUCTIONS

Raytheon

NITPN-25

X

824

14 850

ANIGPN-22

X 60 443

~

COBRA DANE


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2.0 DEVELOPMENT O F MMIC ACTIVE

PHASED

ARRAYS

With the recent prdduction awards for three THAAD

EDM (Engineering Development Model) radars,

COBRA radars, SAM PSON radars, F-22 and JSF

airborne radars, the planned development contracts for

t he new U S A . D D ( X ) shi p radar suite, and the on going

development of the Dutch X-band 4-faced APAR radar

the future looks very good for MMIC phased-array

radars; seeFigure 4[79,80].

3.1 Clutter Rejection for

an

Airborne System

(STAP and DPCA)

To cope with ground clutter and sidelobe jamming for

an airborne radar, extensive work is ongo ing toward the

develop men t of airborne phased array using Space-

Time Adap tive Processing (STAP) 125,261. STAP is a

general form of Displaced Phase Center Antenna

(DPCA) processing. STAP had been demonstrated

several years ago on a modified E2-C system by

NRL

[27,

281. More recently a flight demonstration STAP

provided

52

to

69 dB

of sidelobe clutter cancellation

relative to the mainbeam clutter

[29].

This system used

an

array m ounted

on

the side of an a,ucrafi. The antenna

had

11

degrees

of

freedom in azimuth and 2 in elevation

for a total of 22. Before STAP, the antenna r s

sidelobe level was -30 dBi, with STAP it was -45 dBi.

3.2 C- to Ku-band Multi-User Advanced Shared

Aperture Program (ASAP) MMIC array and

Dual-Band AMR FS and RECA P Arrays

The COBR A DA NE radar system of Figure 1 and Table

1

has a 16% bandwidth and Rotmari lens mult i-beam

array systems have a 2.5 to frequen cy bandwidth.

Technology bad been carried out to develop an active

MM IC phase-phase steered array that has over a 2 to 1

frequency bandwidth and at the same time is shared by

multiple users. Specifically the Nava l Air Weapo ns

Center (NAWC ) and Texas Instruments (TI, now part of

Raytheon) were developing a broadban d array having

continuous

coverage from C-band through K u-band that

would share the functions of radar, passive ESM

(Electronic

Support

Measures), active ECM (Electronic

Counter

Measures)

and communications [3 0 ] . To

achieve this wide bandwidth, a flared notch-radiating

elemen t was used. Cross notches were used so that

horizontal, vertical or circular polarization can be

obtained. They had built a solid state TIR module that

provides coverage

over

this wide band from C-band to

Ku-band continuously. The module bad a power output

of

2

to 4 W per element over the ban d;.a noise figure

betwee n .6.5 and 9 dB over the band and power

efficiency between 5.5 and 10%over the band. A

IO

x

IO-element array having eight active TIR modules was

built for test purposes. A typical full up array would be

approximately

29"

wide by 13 high. With this type of

array it. would ultimately be possible to use

simultaneous part of the array as radar, part of

he

array

for ESM, part of the array for ECM and part of the array

for communications. The parts used for each function

would change dynamically depending on the need.

Also, these parts c ould .be non-o verlappin g or

overlapping, depending

on

the needs. Although

the

ASAP funding has ended, the shared aperture

technology is' being pushed-forward now by the USA

Office of Naval Research

(ONR)

Advanced

Multifunction Radar Frequency System (AMRFS)

program [71, 781 and the DARF'A Reco nfigura ble

Aperture

Program

[RECAP] program.

DERA o f the UK had been developing a dual frequency

array which would enable a single radar to use L-band

for search at and X-band fo rtra ck

so

as to avoid the use

of a single comp romise frequ ency for search and track

[ 52 ] . Consideration

is

being given to the use of

waveguide L-band radiating elements and dipole X

band elements.

3.3

Table

2

lists where digital beam forming (DBF) has bee n

operationally used, some developmental systems that

have been built, and its significant advantages. The first

operational radars to use digital beamforming are the

over-the-horizon (OTH) radars. Specifically the GE

OTH-B and Raytheon ROTHR (Relocatable OTH

Radar). The ROTHR receive antenna is ahout

8,500

feet

long.

More ,recently Signaal used. digital

beamforming for their deployed 3-D stacked heam

SMA RT-L and SMA RT-S shipboard radars. The digital

beamforming is done only on receive. FoFthe SMART-

L system the antenna consists of 24 rows. The signal

from each row is down converted and pulse compressed

with SAW lines and then AiD'd with 12-bit 20 MH z

Analog Devices AID S. The signal is then modulated

onto an optical signal and passed down through a fiber

optic rotary joint to a digital beamformer where 14

beams are formed [3I].

Digital Beamforming and

Its

Potential

Table

2 Digital eamforming

(DBF)

.

OTHRMYTHEON); I -D

. MART-LAND SMART-S (SIGNAAL);

I-D STACKED BEAM SYSTEMS

D W B L O P M N T A L S Y ST E MS

ROME LAB: 32 COLUMNS,

32

INDEPENDENT BEAMS

MICOM: ARRAY FEED OF6

ELEMENTS

BRITISH MESAR: SUBARRAY DBF

BRLTISX: DBF ON TRANS. AND RTC..

.

I ? Er

ADVANTAGES:

FLEXLBILTTY:

-ANTENNA WEIGHTING

-GROWTH W T H

TECHNOLOGY .

.

ADAPTNE PROCESSEO

IMPROVED PERFORMANCE

ULTRA-LOW SIDELOBES

-DYNAMIC W G E

J A M M E R A N D C L U I T E R

SUPPRESSION

-REDUCED EM1

MULTIBEAMS

.__

LINCOLN LAB. ALLDIGITALUNF

RECEIV

R:8BIT3GSPSAC

. MSAR:

S m A R R A Y

DBF

A

number of experimental DBF systems have been

developed; see Table

2.

One is the Rome Laboratory

(Hanscom AFB, MA) 32 column linear array at C-band

that can form

32

independent beams and which uses

a

novel self-calibration system

[32].

Rome Lab. also bas

developed a fast digital heamformer that utilizes a


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systolic processor architecture [77] based on the

Quadratic Residue Number System (QRNS) [32].

MICOM (U.

S.

Army) built a 64 element feed that used

DB F for a space fed lens [33].

The experimental Brit ish MESAR S-band system does

digital beam formin g at the subarray level [34]. This

experimental system h as 16 subarrays and a total

of

918

waveguide-radiat ing elements and 156 T R solid state

modules. Roke Manor Research Ltd. of Britain has

built an experimental 13 element array using digital

beamforming on transmit

as

well as on receive [35].

This experimental system uses the Plessey SP2002 chip

running at a 400 MHz rate as a digital waveform

generator at every element. Doing digital beamforming

on m nsm i t a l lows one to put nulls in the direction of an

ARM

hreat

or

where there is high clutter.

National Defense Research Establishment of Sweden

bas buil t an experimental S-band antenna operating

between 2.8 and 3.3 GHz which does digital

beamforming using a sampling rate

of

25.8

MHz

on a

19.35 MHz IF signal [23]. The advantage of using IF

frequency sampling rather than baseband sampling is

that one doesn't have to wony about the imbalance

between the two channels, that is, the I and Q channels,

or

the DC offset. They demonstrated that , by using

digital beamforming, they could compensate for

amplitude and phase variat ions that occur from element-

to-element across angle and across the frequency band.

Via a calibration, they were able to reduce an element-

to-element gain variat ion over angle due to mutual

coupling from

I dB

to about

O.l

dB. Using

equalization, they were also able to reduce a i0.5 dB

variation in the gain over the 5 MHz bandwidth to a less

than *0.05 d variation. With this calibration and

'equalization, they were able to demonstrate peak

sidelobes 47 dB down ov er a

5 MHz

bandwidth.

A

50

dB Chebyshev weighting was used. The

RMS

of the

error sidelobes was down

65dB

from the peak near

boresight [63]. They de mon strated that the calibration

was maintained fairly well over a period of two weeks.

This work demonstrates the potential advantage offered

by digital beamforming with respect to obtaining ultra-

low antenna sidelobes. These results were not achieved

in real time in the field. The goal for the future is to

obtain these results in real time in th e field.

MIT Lincoln Laboratory developed the technology

for

an all-digital radar receiver for an airborne surveillance

array radar like that of the UHF E-2C [43]. They are

AID

sampling directly at

UHF

( -430 MHz) us ing a

Rockwell 8 bit 3 Gigabit per sec

AID

running at room

temperature. Three stages of down conversion are done

digitally and because the

AID

quantization noise is

filtered the effective number of bits of the

AID

is

increased. For example if the signal bandwidth was

only, 5

MHz

the increase in signal-to-noise ratio is 3

.GHz/2 (5 MHz) = 25 dB

so

the increase in the number

of effective bits is 25 dB divided by 6 @/bit

or

4.2 bits

to yield 12 bits total. The w hole digital receiver is on an

8 inch x 8 inch card that uses three 0.6 )m hips. In the

future these three chips could be replaced by a single

0.35 Fm CMOS chip.

The Naval Research Laboratory

(NU),

MIT Lincoln

Laboratory and NSWC are jointly developing an L-band

active array which has an ID converter at every

element [64.

65 , 811.

Using digital beamforming

NRL

demonstrated the ability to obtain a constrained

beamwidth with frequency while at the same t ime

achieving low sidelobes over specified angles and

frequen cy band s [66].

MIT Lincoln Laboratory had been developing a high-

performance, low-pow er signal processor to do digital

beamforming and signal processing for a notional X-

band Discoverer I1 space-based radar [67,6:3]. This

notional version of the system did ground moving target

indication (GMTI) and synthetic aperture radar (SAR)

mapping. I ts antenna consisted of 12 subarrays and 4

SLCs. The signal bandwidth was assumed to he 180

M H z For this system it is necessary to do the signal

processing on-board

in

real time because telemetering

the

signal down would require too

high

a data rate -35

Gbps if a 12 bit A D is assumed, well beyond the

present state-of-the-&.The on-board signal processor

must do digital beamforming, pulse compression,

doppler processing, STAF' and SLC. To do this on-

board in real time requires a signal processor capable

of

1100 G O P S (1.1 TERAOP). Lincoln Laboratory has

shown that it is feasible to do the processing on board

using a systolic array type architecture having volume

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