Abstract An FM antenna for a vehicle with a ground plane comprising a horizontal roof having supporting pillars at the front and rear corners comprises a side fed, looped, annular slot antenna in the roof of loop length substantially one wavelength in the commercial FM broadcasting band, the slot antenna being displaced from the center of the roof toward one of the front and rear of the roof. An opening is formed in the ground plane adjacent the slot antenna effective to force ground currents around it toward the pillars at the corners in the other of the front and rear of the roof; and an aperture wire discontinuity in the opening of the ground plane, in the form of a finger of the ground plane projecting from the edge of the opening adjacent the slot antenna toward the other of the front and rear of the roof, provides a passive, lumped ground impedance element which modifies the phase relationships of the ground currents in the pillars at the front and rear corners of the roof to reduce directionality in the vertically polarized FM radiation/reception pattern of the slot antenna.
An FM antenna for a vehicle having a body and a substantially rectangular, horizontal roof supported above the body by substantially vertical pillars at the front and rear corners thereof, the roof and pillars comprising a ground plane of conducting material with ground currents therein, the antenna comprising, in combination: a side fed, looped, annular slot antenna in the roof, the slot antenna having a loop length of substantially a wavelength in the commercial FM broadcasting band and being displaced from the center of the roof toward one of the front and rear of the roof; an opening in the ground plane adjacent the slot antenna and somewhat smaller in size but displaced therefrom toward the other of the front and rear of the roof; a narrow finger of the ground plane projecting into the opening from the center of the edge adjacent the slot antenna toward the other of the front and rear of the roof, the antenna with the opening and narrow finger having reduced directionality in its vertically polarized FM radiation/reception pattern.
Claim 2
Dependent Claim
175 words
An FM antenna for a vehicle having a body and a substantially rectangular, horizontal roof supported above the body by substantially vertical pillars at the front and rear corners thereof, the roof and pillars comprising a ground plane of conducting material with ground currents therein, the antenna comprising, in combination: a side fed, looped, annular slot antenna in the roof, the slot antenna having a loop length of substantially a wavelength in the commercial FM broadcasting band and being displaced from the center of the roof toward one of the front and rear of the roof; an opening in the ground plane adjacent the slot antenna and somewhat smaller in size but displaced therefrom toward the other of the front and rear of the roof; a narrow finger of the ground plane projecting into the opening from the center of the edge adjacent the slot antenna toward the other of the front and rear of the roof, the antenna with the opening and narrow finger having reduced directionality in its vertically polarized FM radiation/reception pattern.