At low frequencies (such as AM broadcast), arrays of vertical towers are used to achieve directionality  and they will occupy large areas of land. For reception, a long Beverage antenna can have significant directivity. For non directional portable use, a short vertical antenna or small loop antenna works well, with the main design challenge being that of impedance matching. With a vertical antenna a loading coil at the base of the antenna may be employed to cancel the reactive component of impedance; small loop antennas are tuned with parallel capacitors for this purpose.
Why is this specific antenna type used?
achieve directionality

In 1993, the city passed a massive redevelopment package known as the Metropolitan Area Projects (MAPS), intended to rebuild the city's core with civic projects to establish more activities and life to downtown. The city added a new baseball park; central library; renovations to the civic center, convention center and fairgrounds; and a water canal in the Bricktown entertainment district. Water taxis transport passengers within the district, adding color and activity along the canal. MAPS has become one of the most successful public-private partnerships undertaken in the U.S., exceeding $3 billion in private investment as of 2010. As a result of MAPS, the population living in downtown housing has exponentially increased, together with demand for additional residential and retail amenities, such as grocery, services, and shops.
How much money was invested in MAPS by 2010?
$3 billion

Symbiotic relationships include those associations in which one organism lives on another (ectosymbiosis, such as mistletoe), or where one partner lives inside the other (endosymbiosis, such as lactobacilli and other bacteria in humans or Symbiodinium in corals). Symbiosis is also classified by physical attachment of the organisms; symbiosis in which the organisms have bodily union is called conjunctive symbiosis, and symbiosis in which they are not in union is called disjunctive symbiosis.
What is it called when the organisms are not physically joined?
disjunctive symbiosis