2.2.1 RF Applications: Broadband Communication

In the last two decades wireless mobile technologies have matured from enthusiast and business niche-market to a dynamical mass-market industry. Starting with the first analog networks in the 80s the first fourth generation networks are already available in 2010. Transmission speeds are rising accordingly (Fig. 2.1). The limiting factor for all systems is the microwave power amplifier (PA) performance. Both on subscriber and base station side it has an impact on power consumption, volume, and weight. While weight is not substantial in the base station design, low efficiency dramatically increases power consumption and thereby the complexity of the required cooling equipment. Thus development is focused on high efficiency. GaN power amplifiers with characteristics surpassing those of GaAs have been demonstrated [20] and prove that the material system and the device structure are an excellent choice for RF PAs (Table 2.1). The frequency range of the reported amplifiers extends from the S-band [21,22,23] and C-band [24,25] up to the Ka-band. Devices for the X-band [26] - Ka-band [27,28] range have been demonstrated.

Figure 2.1: Down link rate for mobile communication systems.

Table 2.1: Device/material features and merits of GaN HEMTs.

device/material features	merits for RF PA	merits for automotive applications
high breakdown	high efficiency, high-voltage operation	high efficiency, high-voltage operation
wide band gap	high temperature operation	high temperature operation
high current density	high power density	high power density
high electron velocity	high frequency
HEMT topology	high linearity