The ground equipment of the ILS consists of two directional transmitters that send out radio beams, sometimes of microwave frequencies (i.e., frequencies of more than 1,000 MHz), from either side of the runway's centreline.
Such a link topology permits the use of highly directional transmitters with low beam divergence and narrow field-of-view (FOV) receivers.
The network uses readily available components such as opto-electronic directional couplers, fixed wavelength transmitters, and diffraction-based parallel receivers while avoiding the use of relatively slow and expensive tunable components.
Only locations in the main lobe direction of the directional antenna have high probabilities to detect the transmitter, the detection probabilities at other directions are very low. Figure 5 An omnidirectional antenna's detection probability map. Figure 6 A directional antenna's detection probability map.
Regarding the existing IMT-Advanced UMi channel model, due to the impact of the directional antenna pattern of eNB transmitter and the phenomenon as described above, the intra-site interference from the neighboring sectors of the same micro eNB may be underestimated and thus, leads to overestimation of the single point MIMO system performance.
Although it has the advantage of high-speed modulation, maintenance of line-of-sight between two FSO transceivers during a transmission is a challenge since FSO transmitters are highly directional.
Initially, in the 1950s, animals carried simple radio-transmitters so that researchers with directional antennae could use them to derive the direction from which the signal came – with two people doing that at the same time in different places, the tag, and therefore the animal, could be triangulated and its position determined, even when it was hiding in thick forest.
For each directional link l i, we denote its transmitter and receiver nodes as t i and r i, respectively.
The transmitter array was formed by directional sectorial antennas with a gain of 15 dBi separated 10 and pointing towards the measurement scenario.
