Spatial Combining Leads To More Millimeter-Wave Power

Solid-state millimeter-wave power has long been an elusive goal of high-frequency engineers. While high power levels at millimeter-wave frequencies (above 30 GHz) are readily available from vacuum electronics, most solid-state millimeter-wave devices are limited to output levels in the milliwatt range. But at least one fledgling company thinks they may have a solution to the problem of generating reasonable solid-state power levels at millimeter-wave frequencies. Wavestream Corp. ( has developed its revolutionary Grid Amplifier technology to replace the traditional passive power combiners used to combine the output powers of multiple solid-state devices. The power lost in conventional binary power combiners increases rapidly with the number of elements combined and with the operating frequency. Wavestream Corp. ==>

In Wavestream's spatial combining approach, individual elements contribute power to a millimeter-wave beam in free space, eliminating the losses incurred by passive combiners. Phased-array radar systems, of course, rely on spatial combining to produce high power levels from electrically steerable antennas, but such systems are expensive. The Wavestream approach is a practical method of combining the outputs of large numbers of transistors on a single integrated circuit.

A grid array amplifier contains an integrated circuit with an array of identical amplifying elements or unit cells. Each unit cell has an input antenna to receive the horizontally polarized input wave incident on the back of the integrated circuit. The on-chip transistors amplify this signal and radiate it from the face of the chip through an output antenna. Passive elements on the chip provide tuning and isolation between the input and output sections. An inexpensive waveguide adapter is used to distribute an input signal uniformly over the face of the grid array; similarly, output signals are collected into a waveguide port. A low-voltage, pHEMT single-chip prototype amplifier using the technology achieved 4 W output power at 1-dB compression at 38 GHz.

Wavestream, which was founded in 2001 by five doctorates from the California Institute of Technology, is well funded by Anthem Venture Partners, ITU Ventures, Holden Capital, and the Falcon Fund, among others. (For a full review of the company's amplifiers, don't miss the June 2003 issue of Microwaves & RF magazine).

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