Planar antenna
A planar antenna includes: first and second conductors each of which forms a microstrip line in combination with a ground electrode, and which are arranged in parallel with each other on a substrate; a plurality of first resonators disposed between the first conductor and the second conductor which electromagnetically couple the first conductor at one longitudinal end of each of the first resonators to generate electric fields which are in phase with each other; and at least one second resonator disposed between the first conductor and the second conductor which electromagnetically couples the second conductor at one longitudinal end of the at least one second resonator to generate an electric field which is in phase with the electric fields generated by the plurality of first resonators, wherein the at least one second resonator is arranged alternately with the plurality of first resonators.
1. A planar antenna comprising:
a substrate which is formed from a dielectric material;
a ground electrode which is provided on one surface of the substrate;
a first conductor which is provided on the other surface of the substrate, and which forms a microstrip line in combination with the ground electrode;
a second conductor which is provided on the other surface of the substrate so as to extend in parallel to the first conductor, and which forms a microstrip line in combination with the ground electrode;
a plurality of first resonators disposed between the first conductor and the second conductor which electromagnetically couple the first conductor at one longitudinal end of each of the first resonators to generate, with a current having a predetermined wavelength and flowing through the first conductor, electric fields which are in phase with each other; and
at least one second resonator disposed between the first conductor and the second conductor which electromagnetically couples the second conductor at one longitudinal end of the at least one second resonator to generate, with a current having the predetermined wavelength and flowing through the second conductor, an electric field which is in phase with the electric fields generated by the plurality of first resonators, wherein the at least one second resonator is arranged alternately with the plurality of first resonators.
2. The planar antenna according to claim 1 , wherein the plurality of first resonators is arranged so as to be spaced the predetermined wavelength apart along the first conductor, and the at least one second resonator is disposed at a position displaced away from the nearest one of the plurality of first resonators by one half of the predetermined wavelength along the second conductor.
3. The planar antenna according to claim 2 , further comprising a third conductor for connecting one end of the first conductor to an end of the second conductor that is nearer to the one end, and wherein
the first and the second conductors are fed at the other end of the first conductor, the other end of the second conductor is formed as an open end, and the distance from each of the plurality of first resonators to the at least one second resonator, measured along the first, second, and third conductors, is equal to the sum of an integral multiple of the predetermined wavelength and one half of the predetermined wavelength.
4. The planar antenna according to claim 2 , wherein the first conductor and the second conductor have the same length, and the first conductor and the second conductor are each fed at one end on the same side so as to be in phase with the current having the predetermined wavelength.
5. The planar antenna according to claim 4 , wherein the other ends of the first and second conductors are open ends, and wherein
the plurality of first resonators is each located at a position spaced away along the first conductor from the other end of the first conductor by a distance equal to an integral multiple of the predetermined wavelength, and the at least one second resonator is located at a position spaced away along the second conductor from the other end of the second conductor by a distance equal to the sum of an integral multiple of the predetermined wavelength and one half of the predetermined wavelength.
6. The planar antenna according to claim 4 , wherein the other ends of the first and second conductors are short-circuited to the ground electrode, and wherein
the plurality of first resonators is each located at a position spaced away along the first conductor from the other end of the first conductor by a distance equal to the sum of an integral multiple of the predetermined wavelength and one quarter of the predetermined wavelength, and the at least one second resonator is located at a position spaced away along the second conductor from the other end of the second conductor by a distance equal to the sum of an integral multiple of the predetermined wavelength and three quarters of the predetermined wavelength.
7. The planar antenna according to claim 2 , wherein the first conductor is longer than the second conductor by a value equal to the sum of an integral multiple of the predetermined wavelength and one half of the predetermined wavelength, the first conductor and the second conductor are each fed at one end on the same side so as to be 180 degrees out of phase with the current having the predetermined wavelength, and the other ends of the first and second conductors are located at the same position when viewed in a direction along the first conductor.
8. The planar antenna according to claim 1 , wherein the plurality of first resonators is each disposed with a longitudinal direction thereof perpendicular to the first conductor, and the at least one second resonator is disposed with a longitudinal direction thereof perpendicular to the second conductor, and wherein the planar antenna further comprises:
a plurality of third resonators disposed in parallel to the first conductor which electromagnetically couple the first conductor to generate, with the current having the predetermined wavelength and flowing through the first conductor, electric fields which form circular polarization when combined with the electric fields generated by the plurality of first resonators; and
at least one fourth resonator disposed in parallel to the second conductor which electromagnetically couples the second conductor to generate, with the current having the predetermined wavelength and flowing through the second conductor, an electric field which forms circular polarization when combined with the electric field generated by the at least one second resonator.
9. The planar antenna according to claim 1 , wherein the plurality of first resonators and the at least one second resonator are each formed in the shape of a loop whose overall length is equal to the predetermined wavelength.
10. The planar antenna according to claim 1 , wherein the plurality of first resonators and the at least one second resonator are each a dipole antenna whose overall length is equal to the predetermined wavelength or one half of the predetermined wavelength.