Passive Components Shrink With Time

March 14, 2011
Although surface-mount passive components are a more recent phenomenon, high-frequency circuit designers have been creating miniature components for many decades.

PASSIVE COMPONENTS, like many other building blocks in the high-frequency industry, have improved in terms of electrical performance per unit size over the last five decades. When looking back over the years at earlier passive components and assemblies, it is not so much the pure electrical performance that is striking as much as the advances in packaging that have taken place over that time.

In 1980, for example, one of the leading suppliers of microwave mixers, Watkins-Johnson of Palo Alto, CA, made news with their M4 series of flatpack mixers. The products included the model WJ-M4A with local-oscillator (LO) and RF range of 10 to 1500 MHz and intermediate-frequency (IF) range of DC to 1000 MHz.

During the same time period, a company still going strong, Mini-Circuits, was selling coaxial power dividers for only $39.95 each. The firm's ZAPD line of power dividers included models from 0.5 to 1.0 GHz, 1.0 to 2.0 GHz, and 2.0 to 4.2 GHz (Fig. 1). The insertion loss was 0.2 dB for all models, still considered good today.

Another company still going strong, ARRA, Inc., of Westbury (now Bay Shore), NY, offered a line of miniature continuously variable attenuators in 1968. Available for applications from 2.0 to 12.4 GHz, the attenuators handled 5 W average power and 3 kW peak power with maximum insertion loss of 0.5 dB.

An article in March 1968 by members of the technical staff of the Microwave Department of Sylvania Electric Products, Inc. of Woburn, MA detailed how a new type of diode, the beamlead Schottky barrier diode (Fig. 2), appeared to be a more electrically efficient device than point-contact diodes for frequency-conversion applications. The article compared the performance characteristics of both semiconductor devices, and showed how a microwave mixer could be formed using a beam-lead Schottky diode pair (Fig. 3).

Around the same time, Bill Marshall, Switch Marketing Manager for Transco, demonstrated his firm's modular approach to waveguide switch assemblies (Fig. 4). Using a variable waveguide switch design, the assemblies performed transmitter switching to 18 GHz under full-power operation. They provided switching speed of better than 50 ns.

The Micro State Electronics Operation of Raytheon in Murray Hill, NJ was working with advanced stripline, leading to the group's development of a switch/driver assembly for applications from 1020 to 1100 MHz (Fig. 5). It achieved hot switching of 10 kW peak power in only 150 ns.

For those who doubted digital technology existed five decades ago, Daico Industries offered a pair of digital variable attenuators with integral TTL (model DA0295) and CMOS (model DA0285) drivers. Switching under 7-b control, the digital attenuators (Fig. 6) provided 63.5-dB attenuation control ranges from 30 to 500 MHz with least significant bit (LSB) of 0.5 dB. They could handle input power levels to +13 dBm with nominal switching speed of 5 s.

Last but not least, Systron Donner was among a group of companies promoting their capabilities in "supercomponents." These were essentially compact assemblies that combined the functions of multiple components. One of the company's supercomponents was an assembly designed for X-band radar (Fig. 7), with a low-noise mixer and Gunn diode LO. The LO provided a 40-MHz tuning range around 9.375 GHz.

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