THE ANTENNA SYSTEM FOR FM BROADCASTING WITH CIRCULAR POLARIZATION AND THE POSSIBILITY OF SIMULTANEOUS WORK BY TWO GROUPS OF TRANSMITTERS

Abstract

In large radio centers with a large number of broadcasting transmitters of the VHF band operating in the range of 87.5-108 MHz the most common type of antennas are panel antennas. The advantage of these antennas is a large capacity – up to hundreds of kilowatts, the ability to form radiation patterns of various shapes based on the characteristics of the service area, the distribution of population density in this zone and sanitary requirements for residential areas. To meet these requirements, in some cases, the use of antennas that occupy a significant place on masts is required. The implementation of these requirements often interferes with the absence of sufficient free space on masts. In addition, at large radio centers there is a serious problem of placing a large number of powerful FM broadcasting transmitters on one antenna. One of the reasons for the limitation of the number of transmitters is large losses in inseries included combiners. One of the ways to increase the number of transmitters working on one antenna is the use of panel antennas with a doubled number of dipole in each panel having different polarization – vertical and horizontal. Such antennas allow you to work simultaneously with two groups of transmitters with different polarizations on two feeders. The disadvantage of such a solution is that different radio stations operating on the same antenna with different linear polarizations in different conditions of propagation of radio waves at the same power can create different field levels at reception points, which puts them in unequal conditions. Such an antenna can also work with circular polarization but has the only input for only one group of transmitters. An antenna supply scheme is proposed which allows two independent groups of transmitters to work simultaneously on one antenna with circular polarization and use all the advantages of the propagation of circular polarization radio waves in urban conditions and with mobile reception.