Leaky Coax Distributed Antenna

An antenna system that uses a leaky coaxial cable to radiate signal all along the length of the cable is modeled as a distributed antenna. This type of antenna can be used only in Area Studies where the Direct-to-Grid calculation option is chosen. It is also limited to a propagation model available only when the Advanced Propagation or DAS module is installed. The path that the antenna cable takes through the study area is defined in a polyline file using the ASCII Format Line file as described in Appendix G, section G.4.1. Note that two files need to be created. One file contains the coordinates of the horizontal path taken by the cable and the other file (ending with the .ELEV file name extension) contains the elevation of each point above mean sea level. The horizontal path file can easily be created by displaying the study area on the EDX program map and then using the Draw -> Polyline to create the path and save it as a .BNA file. Then make a copy of this file and add the .ELEV suffix to the file name. For example, if the original polyline file is named "subway.bna", then name the copy of this file "subway.bna.elev". Open the .ELEV file in a text editor in order to add the height values for each point along the path. When the "Leaky Coax" type of antenna is chosen in the Transmitter Parameters dialog there are several parameters that can be entered to specify the radiation characteristics: Leaky coax cable loss in dB/100m, Coupling loss specified in dB and specification distance is in meters. These parameters are specified by the manufacturer of the cable. A typical set of values for 12.7 mm (1/2 inch) cable might be: 11db/100m loss at 1GHz 67dB coupling loss at 2m Coupling loss is significantly affected by the way the cable is installed and how it interacts with the environment. Because of this the manufacturers specification is considered to be the mean value (50% of the locations). Manufacturers can supply statistical values for coupling loss for other than the median value. For example, if the total loss (due to length) in a section of cable was 10dB, an additional 16dB coupling loss might need to be applied to achieve confidence for 90% of the locations. The EDX program calculates the received power level at a particular location by first determining the point along the cable that is closest to the receiver location. The ERP from the cable at this point is the transmitter power minus the cable loss which is a function of the total cable length between the transmitter and this point and the coaxial cable loss specified above. The free-space coupling loss between the cable and the receive antenna is: db_loss = c_loss + 10*log ( dist / c_loss_spec_dist ) Where c_loss is Coupling Loss and c_loss_spec_dist is the Coupling loss specification distance from the Leaky Coax Details dialog. "dist" is the distance between the receiver antenna and the cable. When the EDX Simplified Indoor model is used, the total path loss between cable and receiver is the sum of the db_loss above plus the total wall attenuation loss.