## 1 Introduction  
Tropospheric communication systems use the inhomogeneous nature of the troposphere for the propagation of radio frequencies beyond the horizon over distances as large as a few hundred kilometers. The volume of the tropospheric region enclosed by the intersection of transmit and receive antenna beams is known as the common volume. Tropospheric inhomogeneities present in the common volume, with a higher refractive index than the surrounding regions, scatter the incident RF signal in all directions. A part of the RF energy is scattered toward the receiver, making communication possible. The development of high-power microwave tubes during World War II resulted in the transmission of broadcast signals over very large distances. This long-distance propagation phenomenon could not be explained by the theories that were prevalent in those times. Dedicated efforts were made by many individuals and organizations [1, 2] to understand this mysterious phenomenon. Two important studies conducted in the Caribbean Sea [3] and Arizona desert [4] during the 1940s proved that tropospheric scatter was responsible for the long-distance propagation of transmitted signals. The rate of signal attenuation over long distances in these experiments was observed to be much less than that expected from theory. [PERSON] [5] has explained that scattering from atmospheric turbulence, which is more pronounced at higher frequencies, results in lower attenuation and, hence, long-distance propagation. The discovery of the troposcatter propagation phenomenon led to the development of the first beyond-the-horizon troposcatter communication system, known as Polevault, in 1952 [6]. The success of the Polevault system inspired extensive research and development in the field of troposcatter communication, and it has been used extensively since then for civil as well as military applications. However, 21 st-century warfare is heading toward network centricity with real-time communication between various fighting elements, requiring high-performing communication links with high availability and large data-carrying capacity. The performance of tropospheric communication links, owing to their long path distance, is significantly affected by atmospheric conditions. Signals received over a tropospheric channel experience attenuation due to both fast and slow fading. Fast fading of a received signal occurs due to rapid fluctuations in the tropospheric refractive index that are particularly close to the Earth's surface. It is minimized to a large extent using various diversity techniques like angle, space, and frequency diversity [7]. Slow fading, on the other hand, occurs due to the diurnal and seasonal movement of scatterers (inhomogeneities) to higher or lower heights in the troposphere, reducing their density in a common volume region. Signal attenuation due to slow fading can vary up to 10 dB or higher in a day, with maximum attenuation in the afternoon. The annual variation can exceed 20 dB for tropo links situated in desert areas and experiencing dry and hot climates, with maximum attenuation in summers [8]. Techniques for reducing transmit power loss due to slow fading in tropospheric communication systems are not available in the existing literature. Beam steering can mitigate the effect of slow fading by pointing the transmit and receive antenna beams to the portion of that troposphere that has the highest density of scatterers at any given time, ensuring the maximum received power, improving the link availability, and enabling higher data rates. However, no work related to beam steering on tropospheric links is available in the present literature concerning tropospheric links. The main reason for this is the belief that any increase in the elevation of transmit and receive antenna beams increases the path loss and, hence, the lowest beams (just clearing their respective horizons) always deliver the highest possible received power.