# Effect of Buildings on the Radiation Characteristics of MF Broadcast Antennas
## 1 Introduction  
Although the problem of the propagation of MF (medium-frequency) and HF (high-frequency) waves in built-up areas has long been considered [1], there is a very limited number of available studies focusing on the effects one should expect on the radiation characteristics of MF and HF broadcast antennas due to blockage [2]. Most papers that deal with antenna blockage focus on frequencies higher than 1 GHz [3; 4; 5; 6]. Studies that deal with the propagation of MF and HF waves in the presence of obstacles, such as buildings, concentrate mostly on the prediction and measurements of the propagation losses [1; 7; 8; 9; 10; 11]. The propagation along a rounded hill assumed to have a knife-edge obstruction was analyzed by [PERSON] [7]. MF and HF ground-wave propagation in urban areas were examined by introducing a new method for the modeling of buildings [8]. Propagation in HF, VHF, and UHF bands, in a wide range of environments, was the subject of [9], including the study of the effect that building blockage has on degrading the propagation distance at each frequency band. The signal attenuation caused by the terrain obstruction of path profiles in the MF band was investigated in [10] by modeling the terrain irregularities as triangular-wedge-shaped obstacles. The impact of buildings on the far field of a broadcasting antenna was examined in [11] by using a finite-difference method. Furthermore, the effect of buildings on the radiation characteristics of an antenna or an antenna array was studied in [12; 13]. The impact of local terrain topology on the radiated electric near field of HF broadcast antennas was examined by [14], in an attempt to assess human exposure to electromagnetic radiation in close proximity to high-power HF transmitters. The changes in the antenna response associated with the geometry of the buildings and the effect of the latter on theHF direction was analyzed by using the method of moments (MoM) and the physical optics (PO) technique [15]. Recently, blockage effects on HF antennas were studied; their influence on the radiation characteristics was analyzed and a relationship between the antenna and the size of the blockage was determined [2]. Furthermore, the modeling and simulation of the influence of buildings on the signals of navigation devices for aviation were presented in [16; 17; 18]. Recently, the wireless performance of buildings has been extensively studied [19; 20; 21; 22; 23]; interference-signal blockage is examined in [19], the interference gain and the power gain are adopted to assess the impact of buildings on the power of signals in [20; 21], the building wireless performance (BWP) when the building materials are integrated with antenna arrays is evaluated in [22], while an overview of the BWP is offered in [23]. Moreover, the performance of concrete-embedded antennas is investigated in [24] by using artificial neural networks. In this study, we present an investigation of the antenna blockage by buildings in MF broadcasting; our literature survey revealed that similar studies are particularly lacking and there is a lack of models that address pertinent problems. The aim of this study is to estimate the distance from a broadcast antenna at which buildings have negligible effects on its radiation characteristics by taking into account the size/height of these buildings. Since broadcast antennas may be found near residential areas, it is essential to determine how far from the antenna we may construct buildings and the maximum number of stories that permit the unimpeded operation of the antenna. The main contribution of our work is a solution to the aforementioned \"real-life\" problem by combining existing methods and techniques. The buildings are modeled as wire-grid bodies, considering their steel frame construction; the presence of these bodies in the vicinity of a radiating antenna is taken into account in order to determine the change in the antenna's free-space radiation pattern.