BALTIMORE HAS BEEN HOST to several successful IEEE International Microwave Symposium (IMS) events over the years. It is an ideal venue, with restaurants and hotels in close proximity to the Baltimore Convention Center. During its history, the symposium and exhibition have visited a large number of American cities, once even leaving the mainland (Honolulu for the 2008 IMS), with perhaps the six events hosted by Boston marking the most of any one city. Looking back over the 50 years of Microwaves & RF and its coverage of the IEEE IMS, it is clear that this annual event has served as a key launching pad for many companies' announcements of new products and technologies.

Before there was an IMS, the industry would gather at various electronic trade shows, including as part of Electro on the East Coast and Wescon on the West Coast. An event simply known as the IEEE was held for several years in New York City, at the New York Coliseum. Those early events focused on microwave components and systems for satellite communications or military applications. At the IEEE 1965 event, for example, engineers from TRW Space Technology Laboratories detailed a communications satellite transponder based on a traveling-wave tube (TWT) operating in re-entrant mode. It achieved 110-dB gain and 7-dB noise figure across 500-MHz bandwidths in the 4- and 6-GHz carrier bands. Another report, by a presenter from Cornell University (Ithaca, NY), explained that it would be some time before solid-state devices could replace tubes in high-power, high-frequency, wide-bandwidth applications.

At IEEE 1967, Hugh Hair, head of Syracuse University Research Corp.'s Special-Projects Lab (Syracuse, NY), who would later go on to become a founder of Anaren Microwave, described an innovative method for forming ferrite circuits, critical for such microwave functions as multiport circulators and phase shifters. His group would form boules, or "logs," of ferrite substrate material in a deposition chamber, and then cut thin slices from the boule for use as a circuit substrate. The slices would be coated on both sides with evaporated copper. Then circuits would be etched from the copper, with the ferrite wafer serving as the dielectric material. These ferrite wafers had been used at the time to fabricate compact hybrid circulator, isolator, and phase-shifter circuits for use as part of microwave integrated circuits (MICs).

It would not be until exhibitors began gathering at an IEEE symposium in Washington, DC in 1971 that the combination of sales, marketing, and technology now known as "Microwave Week" would be born. And it wasn't until 1974, when the Atlanta chapters of the IEEE's Microwave Theory & Techniques Society (MTT-S) and the Antennas & Propagation Society (APS) teamed on a technical program that would attract a dozen exhibitors (and was called the International Microwave Symposium), that the possibility of a microwave product and services exhibition running concurrent with an IEEE technical program would start to crystallize. Since the IEEE has many deserving chapters throughout the US and abroad, this US-based conference and exhibition moves from year to year to different sites. It frequently returns, as is has done this year, to sites that have worked well in the pastand Baltimore has established itself as a premiere site for this and other conferences and exhibitions, having set attendance records in prior Baltimore IMS events.

In reviewing old IMS programs and notes from products at the exhibition, it is easy to see how drastically this industry has changed over the past 30 years. For example, in 1981, a technology that is now considered mature (if not outdated), the gallium arsenide (GaAs) field-effect transistor (FET) would emerge during that Los Angeles IMS as a serious device-level contender for solid-state microwave amplification. Several technical presentations touted GaAs FET-based amplifier designs at frequencies through 39.5 GHz.

One series of multistage GaAs FET amplifiers from Texas Instruments delivered as much as 26-dB gain from 12 to 18 GHz. One unit promised 4.5 W output power at 13.3 GHz with efficiency of 15.8% and was promoted as a replacement for a traveling-wave-tube amplifier (TWTA). An amplifier from M/A-COM addressed one of the most significant microwave applications of that daytelevision-receive-only (TVRO) receivers working from 3.7 to 4.2 GHz. The GaAs low-noise amplifier (LNA) was available with noise figure options from 85 K (1.12 dB) to 120 K (1.5 dB).

In a separate session on the bioeffects of microwave radiation, Cletus Hoer, then of the US Department of Commerce in Boulder, CO, presented a report on that group's automatic network analyzer (ANA) based on dual six-port networks. The analyzer was designed for S-parameter measurements in the 10-to-100-MHz range. In a session on computer-aided design (CAD), representatives from Compact Engineering offered details on the MICRO-COMPACT program designed to run on the HP9845 desktop computer from Hewlett-Packard Co. The program could aid in the design of antennas, amplifiers, filters, multipliers, and oscillators.

On the exhibit floor that year, Weinschel Engineering of Gaithersburg, MD demonstrated the operation of their VM- 4A measurement system, one of the premiere microwave test solutions of that time. With a 100-dB measurement range and frequency range of 0.01 to 18.00 GHz, the computer-controlled test system was capable of phase resolution to 0.1 deg. and amplitude resolution to 0.001 dB. Across the hall, EIP Microwave showed their model 548A microwave frequency counter (Fig. 1), with its new series of remote sensors for automatic frequency measurements to 110 GHz. EIP incorporated a unique source-locking technology, stabilizing a source under test to a reference oscillator within the frequency counter for more accurate measurements.

The following year, the IMS would move to Dallas. Several important trends in the industry would become apparent at that show: namely, that computers and digital electronics (and modulation formats) would become larger parts of microwave designs. In this magazine's preview of that 1982 IMS, Les Besser, then-President of Compact Engineering in Palo Alto, CA, spoke about the coming of computer-aided design tools and how one day, every engineer would have a computer terminal at their workstation (replete with powerful minicomputer and full graphics capabilities. An IMS session on computer-aided-engineering (CAD) techniques featured presentations on the design of microwave and millimetre-wave filters, amplifiers, MICs, and resonators.

A separate session on digital techniques included presentations on a digital frequency discriminator from Anaren Microwave providing 8-b resolution from 1 to 18 GHz and able to handle RF pulses as short as 100 ns. The session also had a presentation on the demodulation of a 14-GHz phase-shift-keying (PSK) signal for satellite communications systems and another presentation on experiments to generate a 4-Mb/s baseband-to-microwave generation of minimum-shift-keying (MSK) signals. A great deal of the talk on the exhibition floor during that IMS was tied to the potential opportunities for the microwave industry related to the proposed Space Operations Center or Space Station to be built for NASA by Boeing. Projected to provide a permanent manned American presence in space, the total cost for the Space Station estimated at that time was $8 billion.

On the 1982 IMS exhibit floor, Integra Microwave's model FPM-2000 test instrument would embody a trend that would continue to the present: integrated multiple measurement functions into a single housing. The model FPM-2000 (Fig. 2) combined the functions of separate power meter and frequency counter, simultaneously reading power and frequency for signals from 2.0 to 18.5 GHz. Texscan Corp. showed its model XR-1500A sweep generator for testing from10 kHz to 1500 MHz, with as much as +7 dBm output power and 0.5 output flatness. And Wavetek San Diego offered its model 910 signal generator, with frequency range from 10.0 to 15.5 GHz and output power range from -90 to +10 dBm.

Two years later, in 1984, the IMS was held in San Francisco, with another record crowd attending. The trend of GaAs amplifier designers continuing to push TWTs was in evidence at the Litton Industries exhibition booth, as the company showed GaAs FET amplifiers from 2.0 to 18.6 GHz, including a model 5007 with more than +19 dBm output power and 11 dB gain from 8.0 to 12.4 GHz. Microphase showed their DLH series of log-video amplifiers for applications from 0.5 to 18 GHz with standard log slopes of 100 mV/dB, input ranges of 0 to -40 dBm, and log linearity of +/-0.5 dB (Fig. 3). The rise time is 35 ns or better. RHG Electronics Laboratory showed their ICLLW series flatpack logarithmic amplifiers available at IF center frequencies from 300 to 1000 MHz, with 70-dB dynamic range and +/-1 dB linearity, and 20 ns typical rise time.

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A new market was the talk of that 1984 exhibition floor: cellular radio. California Eastern Laboratories introduced several transistors for cellular handsets, including their +12-VDC NEM0800 (6, 12, 24, and 40 W output power) and +24-VDC NEM0900 (20, 40, and 60 W) NPN epitaxial UHF power transistors. This was a time when cellular technology was in its infancy. Motorola had just introduced its first hand-held cellular telephone, and many competitors were working on their own cellular radio designs.

In addition, the digital radio market was emerging as a strong area for RF and microwave components. Companies such as Avantek, which operated at both the component and system levels, were seemingly well poised to offer digital radio systems capable of serving local telephone distribution applications. (Fig. 4). Because of the growing need to send higher data rates, one of the technology needs at that time was to develop more sophisticated digital modulation formats. The state of the art in digital modulation at that time was 64-state quadrature amplitude modulation (64QAM).

Solid-state technology continued to gain quickly, as evidenced by that 1984 IMS. Harris Microwave Semiconductor displayed power GaAs FETs for amplifier applications through 18 GHz, including model HMA-2215 with 35-dB small-signal gain and +23 dBm output power from 2 to 6 GHz. Acrian showed its model PB- 5003 Class AB preamplifier based on ISOFET transistor technology (Fig. 5). Operating from 30 to 400 MHz with at least 27 dB gain that is linear within +/-2 dB, the preamplifier offered an automatic-level-control (ALC) range of 80 dB at control voltages from -3 to +7.5 VDC. Avantek arrived with amplifier modules based on its silicon MMIC technology. Model UTM-1053 was a three-stage cascaded amplifier in a hermetic TO-8 package, with +9 dBm output power and 30 dB typical gain from 5 to 1000 MHz. Amperex, of Hicksville, NY, unveiled their model RZ2833B45 pulsed S-band power transistor rated for 45 W output power from 2800 to 3300 MHz (Fig. 6). It was designed to operate with 100-s pulses at 10% duty cycles. Input and output impedance matching networks were included within the flange-mount power package.

In June 1997, the IMS moved to the Colorado Convention Center in downtown Denver. The picturesque site attracted a full and active exhibition floor. Boonton Electronics Corp. demonstrated their model 4500A digital sampling power analyzer with 60-dB peak power dynamic range at microwave frequencies, depending on which power sensor was connected. In 2005, at the Long Beach, CA IMS, Boonton would return with an improved version of the instrument, the model 4500B, capable of making measurements from 30 MHz to 40 GHz at pulsed and modulated power levels from -40 to +2 dBm and on CW power levels from -50 to +20 dBm.

Among the many products at its booth during that 1997 Denver IMS, Mini-Circuits offered details on its TO, ZEL, and ZHL low-noise amplifiers for applications from 800 to 2400 MHz requiring low noise figure of 1.5 dB. Available in tiny TO-8 housings as well as in compact EMI-shielded enclosures, the amplifiers provided minimum gain of 20 dB from 800 to 1200 MHz and 30 dB from 1200 to 2400 MHz. Mini-Circuits would also invite all who wished to attend to breakfast at their expense, at the Denver Marriot City Center, with a chance to pick up the company's new 760-page 1997 Designer's Handbook.

Microsource of Santa Rosa, CA displayed a series of YIG-based frequency synthesizers from 23 to 41 GHz. With 1-MHz step size and 15 ms tuning speed, they delivered +10 dBm output power with second harmonics of -30 dBc and spurious content of -75 dBc. Times Microwave Systems displayed their LMRDB series of flexible coaxial cables with diameters from 0.405 to 1.67 in. and bend radii from 1.0 to 13.5 in. At 2 GHz, the attenuation ranged from 1.5 to 6.0 dB/ft.

Cascade Microtech showed its aircoplanar on-wafer precision probes for measuring the performance of semiconductor devices and integrated circuits (ICs) through 110 GHz. The probes achieved low loss, with only 0.35 dB insertion loss at 40 GHz and features a probe life of more than 500,000 contacts. Voltronics of Denville, NJ introduced a line of surface-mount trimmer capacitors, the JS Series, measuring only 2.8 x 2.2 x 1.0 mm. They provided wide tuneable capacitance ranges of 3 to 10 pF and 4.5 to 20 pF with self-resonant frequencies to 1.5 GHz at their highest capacitance values. Synergy Microwave of Paterson, NJ introduced their JPLL Series of phase locked loops (PLLs) in surface-mount packages measuring as small as 0.800 x 0.583 x 0.187 in. and available in fractional bandwidths from 100 to 2500 MHz.

The IMS would return to San Francisco in 2006, along with the Radio Frequency IC (RFIC) Conference and the 67th Automatic RF Techniques Group (ARFTG) meeting. Drawing more than 10,000 attendees to the famed Moscone Center, the 2006 IMS's technical sessions were greatly influenced by this time by the evolution of the cellular telephone into a multimode, multifunction electronic product. That evolution guided RF/microwave designers to higher levels of integration in ICs, in system-on-chip (SoC) devices, and in system-in-package (SiP) designs. Multiple-input, multiple-output (MIMO) radio configurations were becoming more widespread, influencing the way that test equipment manufacturers were responding to the needs for wireless measurements.

On the exhibit floor that year, Rogers Corp. introduced their RO4450B-dx version of the firm's popular RO4450B laminate material. The high fill/flow version of the laminate was developed for high-density, high-frequency circuits. Anritsu was on hand with the latest version of their MS2781A "Signature" signal analyzer (Fig. 7), with an option for making WCDMA/HSDPA cellular-signal measurements. Long-time IMS exhibitor M/A-COM was on hand to serve a new market, WiMAX, with high-power GaAs pHEMT devices capable of output power levels of 5 and 10 W at frequencies through 3.8 GHz. And LadyBug Technologies excited curiosity on the show floor for embracing a growing trend of using a computer's USB port to assist microwave measurements. Their LB479A (Fig. 8) is one of a line of USB power sensors capable of making measurements from -65 to +20 dBm on pulsed and CW signals from 10 MHz to 10 GHz.

The 2011 Baltimore IMS will no doubt contribute to this rich history with many technology and product announcements and surprises. For a preview of some of the news, don't miss the Special Report beginning on p. 38.