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.IMILLIMETER-WAVE MULTIPLIERS RELY ONDIODE INTEGRATED CIRCUITS IN FINLINESTRUCTURES FOR HIGH OUTPUT POWER

ARLEN DETHLEFSEN, ROLF DALICHOW,DALE ALBIN, DAVID WILSON

NETWORK MEASUREMENTS DIVISION1400 FOUNTAIN GROVE PARKWAYSANTA ROSA, CALIFORNIA 95401

RJ &. MicrowaveMeasurementSymposiumandExhibition

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MILLIMETER-WAVE MULTIPLIERS RELY ONDIODE INTEGRATED CIRCUITS

IN FINLINE STRUCTURES FOR HIGH OUTPUT POWER

This paper presents several design aspects of HP's new frequency-multiplyingmillimeter-wave source modules. The tradeoffs between using fundamentaloscillators vs. frequency multiplying techniques are examined, followed by adiscussion of various ways of realizing both frequency doublers and triplers atmillimeter-wave frequencies. A diode integrated circuit, which forms the heartof both the doubler and tripler circuits by achieving very good conversionefficiency, is also described. The block diagram of the source modules andtheir typical performance are presented.

Authors: Arlen Dethlefsen, Engineering Section Manager for scalar networkmeasurements, HP Network Measurements Division, Santa Rosa, CA. BSEE and BS(Mathematics), California State Polytech Univ., 1961; MSEE, Northeastern Univ.,1963. Seven years with Bell Telephone Labs. With HP since 1968 designingmicrowave microcircuits for HP sweepers, then managing sweeper developmentprojects. Now responsible for swept sources and scalar network analyzerdeve1opment.

Rolf Dalichow, Engineering Section Manager for precision sources, HP NetworkMeasurements Division, Santa Rosa, CA. Ing. grad. degree, StaatilicheIngineurschule Giessen, W. Germany (1961). Joined HP in 1973 with 12 yearsexperience designing hybrid RF circuits and communications transmitters inGermany and U.S. Was design project leader for portion of HP 8505A RF networkanalyzer, then project manager for HP 8350 sweep oscillator and its RFplug-ins, also for HP 8349A microwave amplifier and millimeter-wave sourcemodules. Now managing R&D section developing synthesized sweepers, millimetersources and microwave amplifiers.

Dale Albin, Design Project Leader for 83554A, 83555A, 83556A millimetersources. BSEE, University of Texas at Arlington, 1977. Joined HP in 1977 as amanufacturing engineer involved with processing and testing of GaAs and siliontransistors. Designed finline couplers, detectors, and triplers for themillimeter sources, as well as 11-20 GHz power amp.

David Wilson, Development Engineer for millimeter sources, HP NetworkMeasurements Division, Santa Rosa, CA. BSEE (1981) and M. Eng. (1983),California Polytechnic State University, San Luis Obispo. With HP since 1981developing finline components and microcircuits for millimeter sources.

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3606

MILLIMETER-WAVEMULTIPLIERS RELY ON

DIODE INTEGRATEDCIRCUITS IN FINLINE

STRUCTURES FOR HIGHOUTPUT POWER

This paper will give an overview ofvarious methods of achieving millimeterwave swept sources. The concepts ofdoubling and tripling will be reviewedand the design of millimeter wavedoublers and triplers using diodeintegrated circuits in a finlinestructure will be described.

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MILLIMETER-WAVEPROGRAMS

• Direct Broadcast (20 & 30 GHz)

• Milstar (44 & 60 GHz)

• Guided Munitions (75-110 GHz)

• Helicopter and Tank Radar(85-95 GHz)

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The past ten years have seen increasedapplications for millimeter waves bothin commercial and defense activities.The primary categories have been in thefields of communication and radar.

Some of the major programs implementedduring this period and others still inthe development phase are shown here.Because of these programs, the- demandfor millimeter wave test instrumentationis expected to grow significantly. Oneof the major instruments needed in theseprograms are swept solid-statemillimeter wave sources.

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Before starting the design of millimeterwave sources the design objectives werereviewed and were broken down into thetwo categories shown here.

Under electrical performance. one of themajor design objectives for the sourceswas a concept capable of working to 100GHz. as based on the market needs shownearlier. Output power at thesefrequencies is very important so anattempt was made to achieve relativelyhigh power while maintaining broadfrequency coverage. Noise, spurioussignals and harmonics were also animportant consideration.

To be convenient for the user a sweptsource used for test instrumentionshould have leveled and calibratedoutput power and should be easilyfrequency-stabilized. Pulse and FMmodulation capability are importantconsiderations. Portability and ease ofuse are also to be considered as well asproviding good performance at reasonablecost.

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MM SOURCEDESIGN OBJECTIVE

CATEGORIES• Electrical Performance

• User Convenience

ELECTRICAL PERFORMANCE• Frequency Coverage

• Tuning Range to Cover StandardWaveguide Bands

• Output Power + 10 dBm to 40 GHz+ 5 dBm to 60 GHz

odBm to 100 GHz

• Harmonics < - 20 dBc

USER CONVENIENCE• Leveled and Calibrated

Output Power

• Easily Stabilized

• Pulse and FM Modulation

• Portability & Flexibility

• Reasonable Cost

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TECHNIQUES FORGENERATING MM

FREQUENCIES• YIG Tuned Gunn Diode

Oscillators

• YIG Tuned GaAs FET Oscillators

• Impatt Oscillators

• Frequency Multipliers

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Currently there are several techniquesavailable that will generate millimeterwave frequencies with solid-stateinstrumentation. Their main differenceis that the first three generators usefundamental oscillators while the lastemploys a frequency multiplicationtechnique.

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FET orGunn Diode

Waveguideshort

YIG TUNED OSCILLATORS

Magnetic Field

,-A--.

YIG Sphere

= Key Performance Data:Frequency Coverage: ,.; 40 GHzTuning Range: 26·40 GHz

Output Power: "-'10 mW

Single Side Band Noise: - 80 dBc(100 kHz Offset, 1 Hz BWl

IMPATT DIODE OSCILLATOR

Bias

III" Po

Key Performance Data:

Frequency Coverage: ,.; 160 GHzTuning Range: 6-10 GHzOutput Power (eW): 1-3 mWSingle Side Band Noise: - 40 dBc(100 kHz Offset, 1 Hz BW)

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YIG-Tuned oscillators employ Gallium­Arsenide FETs, or Gunn diodes as activedevices. These oscillators can tuneover a whole waveguide band. Atpresent, the technology on hand cannotmanufacture an oscillator that will gobeyond 40 GHz. However, they providegood output power and good phase-noiseperformance.

Impatt Diode oscillators have been usedfor many years, and their outstandingfeature is that they can operate up tovery high frequencies. Theirdisadvantages are a narrow tuning rangeand limited output power. Theirphase-noise performance is relativelypoor.

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FREQUENCY MULTIPLIER

BP Filler

~--I At-----Dn xfo

NonlinearDevice

fo

Frequency multipliers use a non-lineardevice to create harmonics from a lowerfrequency. Bandpass filters have to beused to reject unwanted harmonics orsubharmonics.

pt

t/ "

I t\ /t"\I \I \ I \

\ I \I \ , \

"fo 2fo 3fo

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90 100+

I [GHz]

W I110

[Leveled]

FREQUENCY RANGE, TUNING RANGE,LEVELED OUTPUT POWER

025 40 50 60 75

I A I u I E26.5

I Q I IV33 50 75

5

10

Po[dBm)

A comparison between the differentmillimeter wave generators in terms offrequency coverage, tuning range andleveled output power shows theiradvantages and limitations.

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Examining the phase-noise performance ofthe generators shows a range from theImpatt diodes having the poorestperformance to the excellent resultsachieved by multipliers driven bymicrowave synthesizers.

SSB NoisedBclHz

-40

-60

-80

-100

SINGLE SIDEBAND NOISE

.001 .01 .1 10

Offset from Carrier [MHz]

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HARMONICS/SUBHARMONICS

• Fundamental Oscillators: < - 20 dBc(Harmonics Only)

• Frequency Multipliers: < - 20 dBc(Harmonics & Subharmonics)

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FUNDAMENTAL OSCILLATOR BLOCK DIAGRAM

MM WaveFrequencies

..

MOD f--------t~

3619

Fundamental oscillators have harmonicsbetter than 20 dB below the carrier.Because the waveguide bands cover lessthan one octave frequency range, theproblem of harmonic signals does notoccur if proper low-pass filters areused. The performance of frequencymultipliers allows harmonically relatedspurs to be on the order of 20 dB belowthe carrier, but these spurs can be inband. This of course can degrade themeasurement accuracy and the dynamicrange of receivers in certain testsetups.

Another aspect to consider is the systemperformance of fundamental oscillatorsversus frequency multipliers. If afundamental oscillator is being used amodulator has to be implemented withinthe signal pass to provide a levelledoutput. This modulator reducesavailable output power by its insertionloss. If a frequency stabilizationcircuit has to be used the insertionloss of the necessary coupler alsoreduces the output power.

FREQUENCY MULTIPLIER BLOCK DIAGRAM

3620

Microwave Frequencies

,.-- --'A~ ~

MM Wave Frequencies

r--_~A~__~,

Multiplier I---X~"

7

In the case of frequency multiplication,amplitude modulation and frequencystabilization are being performed at themore convenient microwave frequencies,thus reducing the power losses andsimplifying the necessary circuitry forphase-lock and leveling. AM and FMmodulation techniques are alsosimplified.

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In summary, the advantages of themultiplying concept are in the area ofhigher broadband output power, fullwaveguide coverage up to higherfrequencies, better phase noise, andimproved system performance with respectto phase lock and levelling. The onlydisadvantage of the multiplying approachis the harmonic/subharmonic performance.Taking all these facts intoconsideration, the multiplying techniqueto generate swept millimeter wavefrequencies was chosen.

ADVANTAGES OFMULTIPLYING TECHNIQUE

• High Output Power

• Full WG Bandwidth Coverage

• Phase Noise

• System Performance

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We will now look at the methods ofdoubling and tripling to achievefrequency multiplication at mmwave frequencies. FREQUENCY

MULTIPLICATIONMETHODS

• Doubling

• Tripling

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4fo2fo

DOUBLING CONCEPT

~. T;~D.~;" NV\

I Full Ifo --_~ Wave ---..~ nxfoRectifier

pL ~;;':~~;.:'fo

Doubling can be achieved by using diodesas full-wave rectifiers. The full-waverectifier approach generates secondharmonics of the input signal which aretheoretically 7.4 dB below the inputsignal level. The fourth harmonic is21.4 dB below the input signal level.If the circuit is perfectly balancedthere will be no odd-order products.

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DOUBLER SCHEMATIC

A schematic for doubling is shownhere. The input signal is rectified bythe diodes and the second harmonic iscoupled to the load by the transformer.

3624

AsLPF

3625

DIODE V-I CHARACTERISTICS

OutputSignal

V -+_=...::....=..:::...=..:.:..-.::L:...:IL.:::I..- _

J

"

InputSignal

In the doubler design. the diodes arenot completely turned on at low inputpower levels so the conversion loss ishigh. As input power increases theconversion loss improves until thediodes begin to experience currentsaturation.

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ConversionLoss

DOUBLER CONVERSION LOSS

+25 dBm

Input Power

withoutCurrent

Saturation

9

This results in a conversion loss thatvaries as a function of input power asshown in this slide. If currentsaturation does not occur the conversionloss remains constant once the diodesare fully turned on.

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Tripling at millimeter frequencies canbe achieved by symmetrically clippingthe input signal with a limiter. Thistechnique generates odd order productsand if the wave is completely symetricalthere will be no even-order products.

TRIPLING CONCEPTTime Domain

fo ----I LIMITER I----...~ nfo

fo

In the tripler schematic shown the inputsignal, fo, is limited by anti-paralleldiodes. The diodes conduct when theinput voltage exceeds the barrier heightof the diode, thereby clipping the inputwave.

ptU Frequency Domain tI t + ,

----_~ f LLLLfo 3fo 5fo

TRIPLER SCHEMATIC

Rs

3627

3fo

3628

DIODE CLIPPING ACTIONSince there will be little clipping atsmall input levels there will only be asmall third order component generated.Therefore the conversion loss at thetripled frequency will be high. As theinput power increased the clipping isgreater resulting in less conversionloss. As the signal continues toincrease the output waveform does notchange significantly. This causes theconversion loss of the tripler to onceagain begin to increase.

IDiodeBarrierVoltage

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InputWaveformsOutputWaveforms

3629

ConversionLoss

TRIPLER CONVERSION LOSS

+15 dBm

Input Power

Since the barrier height of the diode issmall, the minimum conversion loss ofthe trip1er occurs at a relatively lowinput power of +15 dBm as shown here.This presents a problem if the trip1eris expected to deliver high outputpower.

3630

SELF-BIASING TRIPLER SCHEMATIC

3631

In order to maintain low conversion lossat high input power levels aself-biasing technique was used in whichthe diode bias is increased withincreasing input power, this wasaccomplished by the addition ofresistive/capacitive elements attachedto the diodes.

Input Waveform

- Output Waveform

CLIPPINGLEVELS

SELF-BIASED DIODECLIPPING ACTION

HighPower

MedPower

Low --­Power

The output waveshapes of the self-biasedtrip1er shown here indicate how thetrip1er automatically adjusts to theinput signa1 power level. As the inputpower increases the self bias increasecausing the diode clipping to occur athigher voltage levels.

It can be shown by Fourier analysis of aclipped sinusoid that for minimumconversion loss the input signal shouldbe clipped approximately at 0.6 of itspeak value.

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The resulting tripler conversion loss asa function of power for the self-biasedtripler is shown here.

SELF-BIASED TRIPLERCONVERSION LOSS

16dB ----------------- l~ ------_r_IIIIIII

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ntoOutput

nloOutput

+25 dBm+20 dBm

Input Power

PRE-AMPLIFIER

POST-AMPLIFIER

MULTIPLIERBLOCK DIAGRAMS

toInput

10Input

ConversionLoss

Now that it has been shown how to doubleand triple signals using diodes as thenonlinear device, it is necessary tofocus in on the type of diode neededto provide the performance objectives atmillimeter frequencies. In order todetermine the diode parameters we had todetermine block diagram possibilitiesfirst. Two presented themselves. Theamplifier, to compensate for theoccuring conversion losses, could havebeen placed before or after the actualmultiplier circuit. If it had beenplaced after the multiplier, itsfrequency range would need to be thesame as the output frequency. At thepresent time, however. there are nobroadband solid state amplifiersavailable which work above 40 GHz.Placing the amplifier in front of themultiplier requires that the multiplierdiodes be able to handle high rf powerlevels. We chose to opt for thisapproach because we wanted to coverfrequencies in excess of 40 GHz.

3634

Once the decision was made to usehigh-power input signals to themultiplying diodes it proved necessaryto design a millimeter diode capable ofhandling input powers on the order of+27 dBm. This required breakdownvoltages of greater than 16 volts andcurrent densities of less than 1E6 ampsper square centimeter to assure thereliability of the device. In addition,diode symmetry was necessary to assure alow level of unwanted harmonic products.Low diode resistance and capacitancehave to be present in the diode if theyare to work up to 100 GHz.

DIODE ELECTRICALREQUIREMENTS

• + 27 dBm of Input Power

• > 16 V Breakdown Voltage

• Current Density up to< 1 X 106 AMPS/CM2

• Capacitance < SOfF to 100 fF

• Better Than 50/0 Symmetry

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MM DIODE INTEGRATED CIRCUITS

These diode parameters were achieved bydesigning the diodes on millimeterintegrated circuits mounted ina beamlead package. This allowed multiplediode configurations which would achievethe breakdown voltage and currentdensity requirements. It also minimizedthe diode stray capacitance andinductance.

Doubler Diodes Tripier Diodes

3636

FINLINE STRUCTURE

Photographs of the integrated circuitdiodes are shown here. The multiplefingers can be seen which allow thediodes to handle high input power whilekeeping the current densities low.The doubler circuit requires morefingers because the diodes conduct morecurrent than the tripler diodes. Thedoubler integrated circuit can handle+30 dBm of input power withoutexperiencing current limiting.

Since it was a design goal to have thesources go to 100 GHz it was necessaryto provide a means to take an inputsignal of 10 to 20 GHz in a coaxialconfiguration, multiply it and thencouple it into a waveguide environment.The method that was used involved thefinline structure. The structure isshown in this slide. The finlinestructure is a modified form ofdouble-ridged waveguide whose ridges arevery thin metallizations supported by adielectric substrate. This structuremakes a convenient method of transitionbetween a coax input and waveguideoutput. It also allows for easyintegration of multiple functions suchas filters, couplers, and detectors.All of the critical dimensions areconfined to the thin film circuits.Since these circuits are produced usingstandard thin film technology, themanufacturing process maintainsdimensional integrity without addingundue cost.

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TRIPLERIC

Finline

DOUBLERIC

Waveguide

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These multiplying concepts have firstbeen implemented in the three sourcesshown here.

The overall block diagram of the 26.5 ­40 GHz doubler source is shown here. Ithas an input power amplifier, low passfilter and doubler. The directionalcoupler and detector are used forleveling and power sensing.

MM SOURCES

• 26.5-40 GHz Doubler

• 33-50 GHz Tripier

• 40-60 GHz Tripier

26.5-40 GHz SOURCE BLOCK DIAGRAM

3639

The input power amplifier shown here hasa frequency range of 11 to 20 GHz, gainof 9 dB and a saturated output power of+25 dBm. The output stage consists oftwo GASFET transistors combined with aWilkinson combiner. This amplifier wasdesigned to be the driver for all themultipl iers.

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13.25·20 GHzInput

• •

26·40 GHzOutput

3640

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210

(Finline) III.

DOUBLER CIRCUIT REALIZATION

% @ 210

Backshortlor

UnbalancedMode

3641

3642

26.5-40 GHz DOUBLER OUTPUT POWER

A number of different techniques couldbe used to realize the full-waverectifier doubler. The technique thatwas used is shown here. The inputsignal is applied to the diodes by athin film coplaner waveguidetransmission line. The rectifying diodesare placed at the coplaner wave-slotline junction. The second harmonic isback shorted by bondwires across theslot line. This back short also reducesthe fourth harmonic, since it is a halfwavelength long at the fourth harmonicfrequency.

This slide shows the coplanar inputcircuit, the directionalcoupler/detector mounted in the fin1inestructure. The cover contains the slotsnecessary to complete the other half ofthe waveguide structure. It alsocontains millimeter wave absorbtivematerial to eliminate unwantedresonances.

The typical output power of the 26.5 ­40 GHz source is shown here.

+12 dBm

+10 dBm

+8dBm

I T i

,./

""'" '-N',,~

It +- --j

~ I

-,~.-JI I

! T1HI ,

UNLEVELED

LEVElED

The leveled output power is at +8 dBmand is flat to within +ldB. Theunleveled output power-of the unit istypically greater than +lldBm.The unwanted harmonically relatedsignals are greater than 30 dB below thedesired signal.

3644

26.5 GHz 40.0 GHz

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The overall block diagram of the tripleris shown here. It uses the same inputamplifier as the doubler.

11-16.6 GHz

13.3·20 GHz

TRIPLER SOURCE BLOCK DIAGRAM

"..

~33-50 GHz

.0-60 GHz

3649

The self biased tripler circuit wasrealized by designing the input low passfilter on a thin film co-planer wavestructure. The anti-parallel diodes areplaced across the wave-guide in afinline structure. The backshort is setto be a quarter wave at the thirdharmonic of the input signal. The highpass filtering is accomplished by usingreduced width wave guide. The lowerorder signals are filtered by thecut-off frequency of the finlinestructure.

TRIPLER CIRCUIT REALIZATION

'o(CPW)

ToReduced

WidthWaveguide

-""="""","""",""",,,~WlI

Backshort

3646

The 40 - 60 GHz tripler source is shownhere. The input circuit with thelow-pass filter can be seen. Filteringof unwanted harmonics are provided bythe highpass filter structure machinedinto the waveguide.

3647

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40-60 GHz TRIPLER OUTPUT POWER

3648

+9 dBm

+1 dBm

+5dBm

40 GHz

i-"t

UN LEVELED

LEVELED

--j

---j~60 GHz

The typical output power of the 40 - 60GHz source is shown here. The leveledoutput is shown at +5 dBm. It can beseen that the typical output power isgreater than +7 dBm for this unit. Theunwanted harmonic products occuring at2/3 and 4/3 the output frequency aremore than 20 dB below the desiredsignal.

In summary, we have shown that abroadband millimeter source capable ofrelatively high output power and goodharmonics can be achieved usingmillimeter diode integrated circuits asa multiplying device. The objectives ofuser convenience and circuit integrationwere achieved using the finlinestructure in a small, portable unitwhich can easily be driven by either amicrowave sweep oscillator orsynthesizer as shown in these slides.These concepts can be readily extendedto provide millimeter sources up tofrequencies of 100 GHz.

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