Passive Microwave Feed Chains for High Capacity Satellite Communications Systems

The successful implementation of satellite communication systems requires robust wireless channels providing the up-links and down-links for the communication signals. The frequency operative bands employed depend on the particular application. Navigation and mobile satellite systems are typically operated in the L (1-2 GHz) and S (2-4 GHz) bands, whereas remote-sensing applications are mostly offered in C (4-8 GHz) band. In the commercial communication area, due to the increasing demand of high quality services, the operating frequency bands has evolved towards the Ku (12-18 GHz), K (19-21 GHz) and Ka (27-32 GHz) bands. Although communication systems operating in high frequency bands provide more channel capacity, the effect of free-space attenuation and atmospheric absorption can limit the performances of these systems (e.g. signal-to-noise ratio). In this contest, the employment of efficient transmission algorithms and protocols provide meaningful advantages, but the bottle-neck is however represented by the antenna system that has to satisfy very strict requirements. For these reasons each device composing the antenna-feed chain has to be designed in order to guarantee significant electromagnetic performances and, at the same time, high integration levels (Cecchini et al., 2009). Moreover, when high power levels are employed (also of the order of tens of KW), further problems are related to spurious interferences generated by non-linear devices, as microwave amplifiers, and by metallic contacts that behave as a diode junction due to the oxidation of the metals. Additionally, high-power and low-pressure conditions can cause multipaction discharges in the devices (Addamo et al., 2010). This phenomenon is an exponential growth of electrons emitted by the metallic surfaces due to the synchronism between the applied electromagnetic field and the free electrons inside the components. The final effect consists in the damage and even in the destruction of the RF device.