Antenna device

1. An antenna device comprising:

a first antenna element formed on a surface of a substrate, said first antenna element transmitting waves of a frequency;

a second antenna element formed on the surface of said substrate, said second antenna element receiving waves of the frequency;

an input signal line connected to the first antenna element;

an output signal line connected to the second antenna element;

a ground conductor formed on a rear surface of said substrate; and

a photonic crystal structure formed between said first antenna element and said second antenna element,

wherein said photonic crystal structure is made of a plurality of throughholes arranged in said substrate, a substance of said substrate, and a substance different from the substance of said substrate,

the substance different from the substance of said substrate is formed in said plurality of throughholes,

said photonic crystal structure has a photonic band gap corresponding to the frequency, and

said photonic crystal structure blocks the waves of the frequency transmitted by said first antenna element and the waves of the frequency received by said second antenna element.

2. The antenna device according to claim 1 , further comprising

a top surface conductor formed on a surface of said substrate between said first antenna element and said second antenna element,

wherein said top surface conductor is electrically connected to ground, and

said plurality of throughholes penetrate said top surface conductor.

3. The antenna device according to claim 1 ,

wherein the substance different from the substance of said substrate is a wave absorber made of a magnetic substance.

4. The antenna device according to claim 1 ,

wherein a dielectric loss tangent of the substance different from the substance of said substrate is greater than a dielectric loss tangent of the substance of said substrate.

5. The antenna device according to claim 1 ,

wherein a gap is formed in said ground conductor between said first antenna element and said second antenna element, and

said ground conductor includes:

a first ground conductor formed on a first region of the rear surface of said substrate, said first antenna element being formed over the first region; and

a second ground conductor formed on a second region of the rear surface of said substrate, said second antenna element being formed over the second region, and the second ground conductor being independent from the first ground conductor,

wherein the gap is formed between said first ground conductor and said second ground conductor.

6. The antenna device according to claim 5 ,

wherein said ground conductor includes:

a connection line electrically connecting said first ground conductor to said second ground conductor,

wherein said connection line is a serpentine line formed on the rear surface of said substrate.

7. The antenna device according to claim 1 ,

wherein the substance different from the substance of said substrate is filled in said plurality of throughholes and protrudes from the surface of said substrate on which the first and second antenna elements are formed.