Refraction interference elimination employing smart arrays at VHF

Radio interference from the Middle East is one of the most significant problems plaguing the local radio services in Cyprus today. The issue is particularly noticeable on the highway, where it affects in-car tuners in all coastal areas of the island when the weather is hot and humid. In this work, the problem of interference from the Middle East was explored in the context of field strength variations versus the type of propagation mechanism favouring the radio waves in Band II, allowing them to travel from the Middle East to beyond the horizon in Cyprus. This problem was significant, since no line of sight exists between the two regions. After in-depth analysis adhering to the ITU (International Telecommunications Union) Recommendations, it was demonstrated that interference is caused by “Tropospheric Ducting”, i.e., trapping of the overseas transmitted signals between two layers of the troposphere at different heights. The upper air data were obtained using the Weather Research Forecasting (WRF-ARW version 3.4) model. The results yielded by the present study confirm that this model provides accurate prediction of interference for up to five days in advance. The interference problem is widely recognized, and therefore many attempts have been made to explicate its causes and provide solutions. The aim of the present study was to present a robust solution based on an innovative receiving antenna design. The antenna is a receiver’s component that collects electromagnetic waves from various directions. The rationale behind focusing on a circular array topology is that its tuning ensures that the receiver processes the desired signal only, while rejecting the unwanted interference. This can presently only be achieved by a large directional external antenna that must be steered mechanically in the desired direction. As this arrangement is not practical, an innovative smart antenna was proposed as an alternative. A circular phased array is a very compact antenna that produces a predicted radiation pattern, whereby it receives maximum energy from the desired direction without the need for mechanical control. Circular arrays exhibit high gain as well as immunity to interference, making them ideal for use in high interference environments. This combination allows the antenna to be incorporated into a commercial deck receiver or installed on vehicles.