Monolithic microwave integrated-circuit (MMIC) frequency converters have been developed for use in satellite- and ground-based communications (see figure) at frequencies from about 18 to about 30 GHz. These and similar converters can be expected to exert significant effects on the sizes, costs, and performances of terminals for the next generation of K- and Ka-band communication systems. The rapid increase in the number of such systems is expected to give rise to a demand for tens of millions of frequency converters during the next few years.

The emphasis in this development program was on low cost, and the technical approach involved reliance on well-established design practices and mature, commercially available processes for fabrication of MMIC chips. The practices and processes selected were those of GaAs metal/semiconductor field-effect transistors (MESFETs) with 1/2-µm design rules.

The Transmitter and Receiver at a ground station of a typical ground/satellite communication system would be contained in an outdoor unit mounted adjacent to the antenna. The receiver and transmitter would contain converters of the type developed in this program.

The converters are capable of operation as both up- and down-converters, and are passive in the sense that external local oscillators (LOs) must be provided. Some of the converters are designed for use with subharmonic LOs, taking advantage of the decrease in cost and increase in availability of oscillators with decreasing frequency.

Some of the converters contain integrated buffer amplifiers for the LO and intermediate-frequency (IF) signals of several gigahertz, as in the example of Figure 1. However, a fundamental limitation on the range of operating frequencies of 1/2-µm MESFET amplifiers precluded the integration, into the converters, of radio-frequency (RF) amplifiers operating at frequencies from 20 to 30 GHz. As a first step in an effort to overcome this limitation, the developers fabricated a set of advanced MMICs for converters and amplifiers, using an acceptor-doped high-electron-mobility transistor (p-HEMT) design and process. It is anticipated that as the p-HEMT art matures, p-HEMT devices will offer a potential to manufacture inexpensive, highly integrated chips.

The performance of an MMIC chip can be altered by its surroundings. Factors that can affect performance include box resonances, coupling to walls, and transmission-line effects on bonding wires. Therefore, considerable attention was given to packaging. Two alternatives to conventional MMIC packaging were considered: One involved the use of a low-temperature cofired ceramic. The other involved a ball-grid-array package, which is a leadless ceramic package in surface-mount configuration with noncollapsing balls made of a copper/silver eutectic alloy.

Results of tests have shown that the up- and down-converters and p-HEMT devices perform well enough to be useful in ground terminals of ground/satellite communication systems. Of the two low-cost packaging concepts considered, the ball-grid-array concept was found to be worthy of further development and to offer the potential for cost-effective packaging of converter MMICs.

This work was done by Paul Blount of Hittite Microwave Corp. for Glenn Research Center.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center
Commercial Technology Office
Attn: Steve Fedor
Mail Stop 4 - 8
21000 Brookpark Road
Cleveland
Ohio 44135

Refer to LEW-16752