Transmission Media -Cont

™   Extremely High Frequency (EHF) (Figure) o    Use space propagation o    Used for Radar , Satellite and Experimental Communication Terrestrial Microwave o    Microwaves do not follow the curvature of earth and therefore require line-of-sight TX and RX equipment o    Distance covered by line-of-sight signal depends to a large extent on the height of the antennas o    Height allows the signal to travel farther by crossing a lot of obstacles like low hills and buildings o    Microwave signals propagate in one direction at a time, which means that two frequencies are necessary for 2-way communication such as telephone conversation o    One frequency is reserved for MICROWAVE communication in one direction and the other for TX in the other direction o    Each frequency requires its own transmitter & receiver combined in a Transceiver nowadays

Repeaters o    To increase distance for terrestrial microwave, a system of repeaters can be installed with each antenna o    A signal received by one antenna can be converted back to the transmittable form and relayed to the next antenna o    The distance required b/w repeaters varies with frequencies of the signal and the environment in which the antennas are found o    A repeater may broadcast the regenerated signal either at original frequency or a new frequency depending on system o    Used in Telephone systems worldwide

Antennas Two types of Antennas are used for Microwave communication: -Parabolic Dish ƒ     Parabolic Dish o    Based on the geometry of a Parabola o    Every line parallel to the line of symmetry (line of sight) reflects off the curve at an angle such that they intersect in a common point called FOCUS o    Parabolic dish works like a funnel catching a wide range of waves and directing them to a common point o    In his way most of the signal is recovered  than would be possible with a single-point receiver ƒ     HORN o    Outgoing transmissions are broadcast through a horn aimed at the dish. The microwaves hit the dish and and are deflected outward in a reversal of the receipt path o    A horn antenna looks like a gigantic scoop o    Outward TXs are directed upward a stem and are deflected outward in a series of narrow parallel beams