Power transistors are the building blocks of the high-power amplifiers (HPAs) at the heart of second- and third-generation cellular base stations. Characterizing these devices is often considered a fine art, although the HTF Series of high-power transistor test fixtures from Intercontinental Microwave (Santa Clara, CA) helps restore science to the measurement process. These precision fixtures offer good

RF performance with high measurement repeatability. Their interchangeable components can accommodate nearly any device package and connector combination. The fixtures can be fabricated with several substrate options and connector types for power-handling capability exceeding 200 W CW for both packaged and chip (with adapters)transistors.

The HTF Series fixtures (see figure) include both 50W models with broad bandwidths and prematched fixtures (such as 11W) for narrowband (several hundred megahertz) testing. Users can tailor a test fixture to a device under test (DUT) by selecting different fixture component parts. Building a fixture involves selecting a midsection that is the correct width and mounting height for the DUT. Then, the launch assembly is chosen (either 50W or a specific matched circuit). Pusher assemblies are also selected for the fixture input and output sides to match the width of the transistor tab. A transition is then chosen with the connector type and RF pin to match the size of the microstrip launch. A base plate, heat sink, and through-reflect-line (TRL) calibration standards round out the configuration.

Fixtures can be fabricated with different substrates, including soft boards, 25- and 50-mil alumina, and customer-defined substrates. The frequency coverage can be as wide as DC to 18 GHz. A series of TRL calibration standards is available based on both FR-4 and alumina for applications from DC to 4 GHz and DC to 26.5 GHz, respectively. The FR-4-based calibration standards are available matched to 50W while the alumina standards can be specified to 11 or 50W.

The HTF Series midsection can handle flanged or flangeless transistor package types. A special clamping mechanism ensures proper heat transfer. A heat sink created for the HTF Series can also be used, which allows fan cooling.

The HTF Series fixtures are available with a variety of different connector types, including APC-7, APC-3.5, SSMA, Type N, and 7/16 EIA connectors. Intercontinental Microwave, 1515 Wyatt Dr., Santa Clara, CA 95054-1586, (408) 727-1596, FAX: (408) 727-0105, e-mail: sales@icmicrowave.com, Internet: www.icmicrowave.com.