ABSTRACT
Compact wearable communication systems may be designed only by employing modern microwave technologies such as monolithic microwave integrated circuit (MMIC), micro-electro-mechanical systems (MEMS) and low-temperature co-fired ceramic (LTCC) technologies. The popular microwave technologies for wearable communication systems are:
microwave integrated circuit (MIC)
MMIC
MEMS
LTCC.
MIC technology was the first step in the process of miniaturization of microwave modules. The invention of the microstrip transmission line, in 1950, led to the development of MIC technology. Active and passive elements can be assembled on the same substrate in MICs. The next step in the development of microwave technology was the invention of MMICS technology. MMICS are usually fabricated on gallium arsenide (GaAs) substrate. Microwave MMIC devices are compact. For example, the dimensions of a 30 GHz 1 W power amplifier are around 4 × 3 × 0.1 mm. Modern power amplifier MMICs are fabricated on gallium nitride (GaN). GaN transistors can operate at much higher temperatures and work at much higher voltages than GaAs transistors. Indium phosphide offers better electrical performance than GaAs MMICs in terms of gain, higher cutoff frequency and low noise. However, they also are more expensive due to smaller wafer size. Radio frequency (RF) modules such as front end, filters, power amplifiers, printed antennas, passive components and limiters are important modules in wearable communication devices. Minimization of the size and weight of the RF modules is achieved by employing MIC, MMIC, MEMS and LTCC technology.
