DDiscussing general trends in the RF/microwave designindustry is tricky business for a couple of reasons. Forone, the number of unique technologies that fall underthe umbrella of “RF/microwave” is vast, incorporatingeverything from tiny discrete components to large inte-grated systems. In addition, the scope of applicationareas for RF/microwave products is nearly as broad asthe number of technologies themselves, with a reachthat grows wider with each passing year. As a result,meaningful trend identification becomes almost impos-sible because an important factor in one sector may becompletely irrelevant to another.So rather than make a few sweeping claims, this arti-

cle explores a variety of niche RF/microwave designtrends, each applicable to a specific technology orapplication area. And instead of making grand pro-nouncements from an ivory tower, it borrows the voic-es of those directly involved in the creation of the next-generation of technologies. What follows are theirwords, commentaries on their individual technology orapplication area of expertise. When viewed as a whole,however, these varied perspectives create a fascinatingcollage, one that accurately depicts the future outlookfor the RF/microwave industry.

SiC, GaN Replace MOSFETs In Amplifier ModulesBy AR Modular RFEveryone wants something for nothing. In the world

of RF amplifiers, that means wanting more RF output forless DC input, which presents a serious dilemma fordesigners of custom RF amplifier modules and systems.The good news is that new amplifier technologies areemerging, and these technologies are pushing ustoward the goal of delivering higher output with betterefficiency.For years, MOSFETs (metal-oxide-semiconductor

field-effect transistors) have been the technology of

choice for RF amplifier modules. These devices haveperformed very well in this role, at least compared totheir predecessors (high-power bipolar devices).Unfortunately, as the demand for higher output powerand higher efficiency increases, the MOSFET is nolonger sufficient.In addition, growing demand for reduced unit size

means that new amplifier technologies must be able tosurvive higher temperatures, because small packagesproduce much higher thermal densities. While somerecent heat-sinking techniques have become very effec-tive, new power devices are operating in more hostileenvironments than they did 10 years ago. As a result, RFmodule designers must build new packages that allowconsistent amplifier function, even as it becomes hotenough to fry an egg (temperatures that would dramat-ically reduce the life expectancy of MOSFETs, if notcause them to fail outright).Responding to these requirements, the latest genera-

tion of silicon carbide (SiC) and gallium nitride (GaN)devices offer improvements in both efficiency and heatload tolerance. These new designs offer the ability tobuild wide bandwidths and achieve improved flatnessover the band, in part due to smaller junction capaci-tance, as shown in the 20 to 3000 MHz design pictured.Some newer devices claim to be capable of sustainingperformance over significantly higher temperatures;however, field experience is still limited with thesedevices.Improved efficiency does not come without a cost, lit-

erally. For example, the price of a SiC or GaN devicemay be 300% higher than for an equivalent MOSFET.This is not necessarily a concern if you are building anexpensive and complex system, where the device costis only a small percentage of the total cost. But if youbuild smaller, higher-volume RF modules, where activedevice costs are a significant part of the total cost, end-

Future Outlook For The RF And Microwave Industry

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40 The RF & Microwave Solutions Update www.rfglobalnet.com

Experts from leading RF and microwave organizations discuss what is next for this ever-changingindustry and what they are doing to keep up.

By Chris Heavens, AR Modular RF,Sandeep Natekar, Berkeley Varitronics Systems, Inc.,

Kalyan Thumaty, Cadence Design Systems, Inc.,Wally Arceneaux, Tektronix, Inc.,

Darren R. Magas, W. L. Gore & Associates, Inc.David Menzer, Auriga Measurement Systems,

Russ Hornung, Arlon Inc., Materials for Electronics, AndDonn Mulder, Anritsu Company

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41www.rfglobalnet.com The RF & Microwave Solutions Update

user price must be increased — or you may be forcedto take a lower margin on an already competitivelypriced product.Since many of these new devices also need higher DC

voltages, replacement designs for legacy productsrequire new power supply solutions in the system,which means significant reworking of the designs. Inaddition, these devices require more critically designedbias circuits than those of simple MOSFETs. Expectamplifier designers to address these concerns in next-generation SiC and GaN designs.

Predicting RF Coverage For WiMAX DeploymentsBy Berkeley Varitronics Systems, Inc.WiMAX promises to deliver last-mile high-speed

mobile wireless Internet connectivity, enabling Wi-Fihotspots to connect to one another and to the Internetwithout reliance on broadband cable or DSL (digitalsubscriber line) services. Under ideal circumstances,WiMAX is projected to deliver impressive performanceof 100 Mbps speed over a radius of 70 miles. Moreover,installing a WiMAX hub in conjunction with a cell tower,or even installing a WiMAX tower alone, is much lessexpensive than establishing wired infrastructure.This potential has inspired some very large companies

to invest billions of dollars in the installation of WiMAXequipment. As such, it has become critically importantto obtain accurate coverage data — by means of drivetesting — to predict RF coverage and aid in the opti-mization of infrastructure. When making these coveragemeasurements, there are two types of fading that affectsignal quality: 1) terrain-based, or “slow,” fading, whichis caused by propagation losses, and 2) Rayleigh, or“fast,” fading, caused by subtractive mixing of multiplereflected versions of a signal.Rayleigh fading manifests itself, for example, in the

form of the static noise heard on your car’s FM radiowhen waiting at a traffic light. Upon moving a short dis-tance, outside the extremely small region of a deep sig-nal fade, the reception becomes clear again. This fastfading is purely spatial in nature. Hence, the goal of anycoverage measurement exercise must be to obtain datathat is free from the influence of Rayleigh fading andpurely indicates terrain-based signal characteristics.Many commercially available hardware-software pack-

ages filter out Rayleigh fading by employing mathemat-ical and statistical models. One such mechanism is 40-lambda averaging, developed by Dr. William Lee. In thisprocess, raw samples obtained from a drive study arefirst filtered in order to remove Rayleigh fading. Thesampled data is then averaged for a time period equalto the time it takes to traverse 40 wavelengths (lambda)in the measurement vehicle. Since the goal is to averageuncorrelated samples to produce an unbiased (byRayleigh fading) average, each sample, within the tra-versed 40 lambda distance, should be at least the uncor-related distance apart.

For example, sup-pose the minimumuncorrelated distanceis 0.38 times the wave-length. This means upto ~105 (40/0.38)equally spaced anduncorrelated samplescan be obtained fromthe sampling and thefiltering process, per 40lambda distance tra-versed. Averagingthese 105 uncorrelatedsamples provides anunbiased meanreceived signalstrength indication (RSSI) value free from influencesfrom Rayleigh fading. It should be noted that if the spac-ing between the filtered samples is too large, the drivingspeed is too fast, or the sampling rate of the receiver istoo low, then there will be insufficient samples for theaveraging process to be successful.

New Approaches To RFIC DesignBy Cadence Design Systems, Inc.RF integrated circuit (RFIC) design has undergone a

dramatic revolution in recent years. Foundry-basedcomplementary metal-oxide-semiconductor (CMOS)technologies have gradually replaced specialty semi-conductor technologies as the process technology ofchoice for RF circuits. More and more designs now inte-grate ever-larger quantities of digital logic gates on-chip,offering designers new opportunities to integrate cali-bration schemes or data processing functions into theirIC. At the same time, today’s rapidly evolving RF mar-ket increasingly demands RF transceivers be capable ofsupporting multi-mode and multi-band capabilities, andcapable of complementing a wide range of basebandprocessors as well. Each of these developments has had a major impact

on the RFIC design flow. Together, they have forcedengineers to develop increasingly dense and complexsolutions, which require challenging and time-consum-ing integration, verification, and test strategies. As RFICdesigns run into the millions of transistors with increas-ing amounts of mixed-signal content, designers mustquickly and efficiently verify their solution across multi-ple domains. Moreover, time-consuming modeling,extraction, and re-simulation of parasitics now pose areal threat to first-time silicon success and the designteam’s ability to meet time-to-market goals. Clearly, tra-ditional microwave or RF component design flows areno longer sufficient to address these many new chal-lenges.What RFIC designers need is a new methodology to

address this increasingly complex environment — a

Drive testing can be conducted using BerkeleyVaritronics Systems’ Coyote dual modularreceiver (left) and Gator stimulus transmitter(right).

new approach to RFIC design that, by looking at theproblem from a systems-level view and progressing tothe transistor level, will increase silicon predictability,shorten simulation time, enable greater RF design pro-ductivity, and in the process shrink the design cycle.This new methodology must link systems-level designwith IC implementation, address the key challenges ofRFIC design, and allow the designers to accurately, butrapidly, verify their complete design across digital, ana-log and RF domains. In order to support efficient appli-cation of the required EDA technologies, this solutionmust include a pre-packaged set of flows that have beenproven on a representative design, which can then bequickly adapted to the designer’s environment.

Supporting Next-Generation Digital RF TechnologiesBy Tektronix, Inc.The power of digital computing technologies has fully

arrived in the radio world, a development that has hada profound impact on traditional RF applications. Forexample, digital computing has greatly increased thepace of innovation. It has also led to the growing avail-ability of more powerful, specialized, and inexpensiveintegrated mixed-signal circuits to perform analog radiofunctions. And these advanced “digital RF” technologiesare shaping the future of wireless communications.For example, the advent of digital RF is making possi-

ble intelligent power amplification, which has advan-tages in 2G, 3G, and 4G transmissions. Digital RF alsosupports rapid innovation in software-defined radio(SDR) and cognitive radio (CR), technologies that willfundamentally change spectrum allocation methodolo-gies and resource effectiveness. Digital RF also enables

time-varying techniques for more efficient use of avail-able spectrum, interference avoidance, and more seam-less operation.Digital RF techniques all exhibit frequency and modu-

lation changes that occur over time. This results in RFsignals that are increasingly complex and transient innature, and in problems that are harder than ever tofind, identify, and troubleshoot. As a result, digital RFhas created a need for test tools that can capture, recre-ate, mirror, and analyze the time-varying nature oftoday’s signals.Engineers need test equipment that allows them to dis-

cover the unexpected problems that are commonplacein digital RF by selectively triggering on time and fre-quency domain anomalies and acquiring a seamlesstime record of a span of RF frequencies into memory.Their test instruments must be able to solve many tran-sient problems ranging from modulation switching onSDR systems to identification of rogue pulses in radartransmission to dynamic modulation changes during awireless LAN (WLAN) transmission.Signal generators will also play an important role in

digital RF testing by providing engineers with the abilityto exercise designs under real-world conditions. To testdigital RF devices during development, designers willneed to generate complex, fast-changing signals thatowe as much to the digital world as to the RF world.Digital RF devices often use a low intermediate fre-quency (IF) or zero-IF (direct conversion) approach toproducing the modulatedRF signal, which means thatthe traditional use of analogfilters is no longer easy oreven feasible. The emphasisis now moving toward cor-rection in the baseband, uti-lizing active nulling of gainand DC offset mismatchesas well as IQ (in-phase/quadrature) imbal-ances. This requires digitallyarchitected signal sources.

Achieving Maximum RF Signal DensitiesBy W. L. Gore & Associates, Inc.Electronics processors, modules, and subsystems con-

tinue to evolve into smaller and lighter packages. Thereasons behind this trend vary from industry to industry.On commercial aircraft and business jets, reduction ofsize and weight can be translated into increased payloadcapacity, increased range, or the ability to install addi-tional features. Subsystems and processors for militaryaircraft are reducing their weight and footprint to allowgreater mission capability. On spacecraft, the ability toreduce footprint and associated weight significantlyimpacts the overall satellite size and the resulting costto launch.

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The DPX spectrum display onTektronix RSA6100A Series Real-Time Spectrum Analyzers offers alive color view of signal tran-sients changing over time in thefrequency domain.

Mission-critical processors and modules require thehighest level of signal integrity for RF signals passedbetween components. The parameters defining signalintegrity vary based on the functionality of the subsys-tem or processor. Despite the differences in signalprocessors, there are common goals for system electri-cal performance including: cross-talk, maximizingshielding effectiveness, minimizing skew, minimizingjitter, minimizing phase change (as a function of tem-perature), and minimizing residual (additive) phasenoise.The electrical performance goals may seem to be dia-

metrically opposed to the mechanical goals of systemdesigners: reduce size and weight while providing arobust mechanical solution. In the past, these twogoals were mutually exclusive. This is no longer thecase. By selecting high-performance RF blindmate con-nectors and cable, designers can achieve superior sys-tem performance while meeting their mechanicalgoals.For example, new super high-density RF blindmate

connectors can provide .085” center-to-center spacingand .110” overall stack height for orthogonally stackedcomponents, while accommodating 0.00 to -0.10” axialmisalignment and up to +/-.012” radial misalignment,opening the allowable mechanical tolerances for sys-tem designers. The larger tolerance band combinedwith a reduction in the number of ceramic layersrequired for the package creates a huge cost savingsfor the overall system. In addition, these connectorsfeature typical VSWR of less than 1.15:1 through 50GHz, and provide excellent shielding effectiveness.Although original applications focused strictly on

board-to-board installations, the industry is adoptingthese connectors to solve additional problems. Newapplications require signals to be transmitted overlonger distances in multiple axes, and connect usingmulti-port headers. In order to accommodate theseneeds, new cable-mount designs have been intro-duced including bulkhead mount shrouds, right-angleprofiles, and custom headers.By combining these new cable-mount connectors

with high-performance microwave cables, intercon-nect solutions are achievedthat can meet tight center-to-center spacing while pro-viding a low-loss, flexibleinterconnect operating upto 65 GHz. Low-mass cablescan be employed in varyingdiameters depending uponthe system’s loss budget andlength of the overall cablerun. As an example, appli-cations inside moduleswhere lengths are typicallyshort, flexible assembliesprovide the ability to easily

route and bundle cables in three dimensions. In orderto run these signals over distances measured in feetinstead of inches, connectors can be used in customassemblies with cables as large as .085” diameter.

Using Synthetic Instrumentation To Speed Commercial Product DesignBy Auriga Measurement SystemsToday’s consumers — particularly today’s young con-

sumers — are adopting and demanding mobile videoand other new cell phone features at a furious pace.To keep up with these changes, design engineers arebeing asked to send more bits over less bandwidth,use less battery power, and createproducts that aresmaller, cheaper, and more flexible. In this fast-pacedenvironment, the need to achieve first-pass success oncomplex, challenging designs has become paramount.Fortunately, engineers can now deliver accurate

models more quickly and efficiently than ever beforeby integrating new synthetic instrument-based pulsedI-V/RF measurements and modeling methodologiesinto their design process. This measurement and mod-eling approach enables designers to respond veryrapidly to design parameter and condition changes,such as the modification of a bias voltage or the needto scale a device to enhance available power or effi-ciency.Adding synthetic instruments to a characterization

system allows for faster test results, cost savings (dueto reduced footprint), and more flexibility to keep upwith advancing technology. For example, by using apulsed I-V/RF system based on synthetic instrumenta-tion for your device characterization and modeling,you can now replace your traditional two-bay, 2-metertest system with a 1-microsecond RF pulse with a one-bay, 1.3-meter test system that is capable of 100-microsecond RF pulses, all at a significantly reducedcost.Synthetic instruments are proving a critical element in

the effort to improve device models and the measure-ment techniques they are based upon. In addition, syn-thetic instrumentation gives you the ability to rapidlyupgrade measurement systems as technology evolves,removing budgetary constraints commonly associatedwith implementing new techniques. This allows mod-eling and device engineers to rapidly answer the callfor better models to support improvements in mobiledevices.Our youth-based culture’s hunger for new features

like mobile video is changing the technology drivers inthe microwave industry from the government elec-tronics sector to the consumer marketplace. While theU.S. government is, in fact, leading the charge in thedevelopment of standards and interfaces to supportand encourage the growing synthetic instrumentindustry, the payoff will be in further reduction in testcosts and associated improvements in quality andaccuracy for the commercial market.

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GORE 100 Series Connectors are newhigh-density RF blindmate connectorsthat offer low profile and mass.

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New Thermal Management Considerations For Circuit BoardsBy Arlon Inc., Materials for ElectronicsThe electronics industry continues to drive the devel-

opment of new circuit board materials to satisfy higherpower and higher thermal stability requirements.Designers point to the Arrhenius equation, in which a10 C increase in temperature typically doubles compo-nent failure rate. In other words, get the heat away from

the components, reduce oreliminate hot spots, reduceoverall device operating tem-perature, and increase productlifespan.In RF and microwave appli-

cations, power amplifiers andhigh-power transmitter net-works are major applicationsthat demand high reliabilitywhile also pushing powerdensity and operating temper-ature limits. As such, thesetechnologies place highdemand on heat rejection to

ensure material life and/or component reliability. This isparticularly true where passive cooling is desired from areliability, maintenance, and size perspective.Engineering focus for these higher-power designs —where temperature extremes are normal and heat rejec-tion is a primary consideration — require advancementsand innovation in materials. New materials must exhib-it: low coefficient of thermal expansion (lower CTEoffers more reliable component attachment), low loss(loss creates additional heat), and high thermal conduc-tivity to improve heat dissipation. As RF materials aretypically fairly strong thermal insulators, finding theoptimal balance of material properties is critical fordevice reliability, cost, and performance.In the lower-frequency electronic substrate market,

thermal management requirements have stimulated aquantum leap in the demand for thermally conductiveprinted circuit boards (PCBs) that provide a much high-er degree of thermal conductivity and lower thermalresistance, when compared to conventional FlameResistant 4 (FR-4) based PCBs. Markets requiring thislevel of thermal management include: automotiveengine control modules, power conversion modules,and the exploding light-emitting diode (LED) lightingmodule market.To complicate things, new lead-free soldering process-

es are also exposing materials and components to high-er temperatures during manufacturing. Thus, thesematerials need to have a high glass transition tempera-ture (Tg) and a high decomposition temperature toensure survivability during lead-free processing.In addition to increases required in thermal conduc-

tivity, other material requirements include mechanicalstability and thinner PCB styles. The PCB is a thermal

barrier compared to higher conducting metaland heat sinks. So the ability to manufacturestable thinner laminates serves to lower thethermal resistance barrier, just as increasingthe thermal conductivity decreases the barri-er. Knowing the relationship between thick-ness and thermal conductivity, and its effecton thermal resistance, is critical to materialchoices relative to other design constraints.

RF And Microwave Test Equipment Gets More FlexibleBy Anritsu CompanyIn the test and measurement sector, one

trend that continues to gain momentum is theneed for instruments with the flexibility tomeasure the wide variety of digitally modu-lated signals that are on the market.Engineers and technicians require test equip-ment that can measure many different sig-nals, whether W-CDMA/HSDPA, CDMA/EV-DO, WiMAX, GSM/EDGE, or a proprietarymodulation. And they must be able to mea-sure all these complex signals with extreme accuracy.For test manufacturers, it also means they must devel-

op instruments that do more than just measure signals.The new communications and modulation formatsrequire powerful analysis capabilities. Engineers canoptimize designs more efficiently when simulation andanalysis tools can be used seamlessly with their testequipment. That requires an open platform that allowsanalysis tools such as The MathWorks’ MATLAB andSimulink to be integrated directly into the instrument.The open platform must also allow for engineers towrite their own tests into an instrument in order to mea-sure proprietary signals.Software will continue to be a strong emphasis, as

well. The development of application-specific softwaretailored to specific standards and modulation schemesallows engineers to get a maximum return on the capi-tal expenditure of a test instrument. It also allows engi-neers to use existing hardware for emerging technolo-gies, which is a necessity in today’sdesign and manufacturing environ-ments. As data-intensive technologies such as

HSDPA and WiMAX continue to bedeployed, test manufacturers will haveto develop field instruments that canaccurately measure these complex sig-nals yet still maintain a lightweight,handheld form factor that is easy touse. Similar to bench instruments,field solutions must be able to con-duct a variety of different key mea-surements on numerous technologies. Their perfor-mance will also have to be similar to bench instruments,given the continued crowding of the RF spectrum. l

Equipment based on syntheticinstrumentation, like theAU4550 Pulsed IV System pic-ture here, is helping engineerskeep pace in the demanding worldof mobile phone design.

Advancements inRF/microwave materialsare enabling designersto simultaneously pushpower density and oper-ating temperature limitsin their circuit boarddesigns.

Anritsu's BTS Master MT8222Ais an example of a lightweight,handheld field instrument thataccurately measures complexsignals.