The current technology drive in space communications is toward higher frequencies (12, 20, 30, and 60 GHz) and toward using solid-state technology at higher power levels. GaAs material is well suited to serve as the base for the construction of both devices and MMICs. European and Japanese manufacturers presented some of their current products and developments.
Thomson Composants Microondes (TCM) has GaAs products on the market with gate lengths of 0.7, 0.5, and 0.2 micron. A 0.2 micron, discrete, ultra-low noise MESFET operating up to 40 GHz is available (3 dB NF, 6 dB gain, at 40 GHz). MMICs of 0.5 micron are available as LNAs and as low and medium power amplifiers up to 20 GHz. TCM has under development 0.2 micron GaAs HEMT MMIC amplifiers at 40 GHz. A 60 GHz, 0.02 śm amplifier under development is shown in Figure 2.30. TCM has scheduled for 1994 production GaAs MESFET, high density, digital integrated circuits with up to 350,000 gates.
Figure 2.30. VLN02 Process - 60 GHz LNA
In the area of power generation diodes, TCM has products of GaAs Gunn diodes (8- 94 GHz, 400 mW, CW), InP Gunn diodes (80 to 94 GHz, 60 mW), and silicon IMPATT diodes (94 GHz, 400 mW, CW). MMICs under development by TCM include a GaAs depletion MESFET power amplifier with 0.5 micron gate length (1 W average power, 30% efficiency).
Alcatel developments in MMIC technology cover a range of functions and frequencies, as shown in Table 2.7.
At 30 GHz Alcatel is developing a LNA (HEMT, 3 dB NF, 27 dB gain). A Ka-band power amplifier under development has 1 W output power, 40 dB gain, and 20% power-added efficiency. An Alcatel MMIC phase shifter under development is shown in Figure 2.31.
Alenia has developed a Ku-band MMIC for TVRO applications and is also using it in VSAT terminals. Alenia MMICs use MOSFETs. A development goal is output powers of 1 to 5 W, beyond their present levels of 0.1 to 1 W.
In Japan, ATR has developed a MMIC approach known as "LUFET" -- line unified field effect transistors (FET) -- which integrates microwave coplanar waveguide (CPW) transmission lines directly into the FET structure. This technique eliminates the need for impedance matching and large transmission lines on some circuits, thereby reducing circuit size by a factor of as much as ten.
MMIC Technology Development by Alcatel
Figure 2.31. Development MMIC Phase Shifter
The MMIC program at NTT is aimed at reducing equipment size and mass. Their program is evolving through three stages: MMIC, uniplanar MMIC, and multi-layer MMIC. Their target is to achieve multilayer MMIC by 1999. Conventional MMICs for RF/IF conversion produced about 75% mass reduction. Uniplanar MMICs will be much thinner and lighter.