ANALYSIS OF COURSE ERRORS ON CVOR ANTENNAS (INCLUDING EFFECTS OF MUTUAL COUPLING BETWEEN ELEMENTS)

A VHF omnidirectional radio range (VOR) is a navigation aid radio beac on facility, which provides aircraft with azimuth information relative to the VOR station in question as the origin, In Japan, two types of VOR-the conventional type (referred to as a CVOR) and the Doppler type (referred to as a DVOR)-are currently in use. An element known as the Alford loop antenna (ALA), which changes the loading reactance, is us ed for the VOR because the horizontally polarized wave and nondirectiv ity in the horizontal plane are preferred. A VOR antenna consists of a carrier antenna and a sideband antenna-an aircraft receives separate signals from these two antennas and compares them to obtain azimuth in formation. The mutual coupling between the elements forming the carrie r and the sideband antenna affects the directivity of single elements, resulting in errors in azimuth information. With the mutual coupling between the antenna elements being taken into consideration, quantitat ive calculation was made by using the moment method-the results of the calculation made it clear that a loading reactance value of -320 Omeg a is better to make not mutually coupled elements nondirectional while a loading reactance value of -600 Omega is optimum to minimize the az imuth error of a CVOR.