Patent ID: 8154465

Claim:
A portal antenna comprising: a portal structure defining an area through which an animal can pass; at least one coil of antenna conductor wound around the portal structure to extend around the area through which an animal can pass, where the antenna coil has a read field including a null zone; and a plurality of elongate radiator elements of magnetically conductive material, where the radiator elements are configured to extend the read field of the antenna coil; wherein the antenna coil and at least one of the elongate radiator elements are aligned at an angle so that an animal moving through the portal structure does not follow the null zone; wherein the elongate radiator elements include a plurality of pipes which are spaced apart and parallel and extend between vertical end pipes to form a side frame, the side frame forming a separate structure or part of a wall structure of a stock race, a pair of side frames being coupled together by cross members.