Null-fill antenna, omni antenna, and radio communication equipment
A wide-angle null-fill antenna with no null in the depression angle range, an omni antenna using the same, and radio communication equipment. A null-fill antenna comprises a first antenna array including antenna elements arranged with a prescribed point as the center, and a second antenna array having amplitude characteristics substantially equal to those of the antenna elements forming the first antenna array. The first antenna array is excited so that the excitation amplitude distribution is to have symmetry with respect to the prescribed point, while the excitation phase distribution is to have point symmetry with respect to the prescribed point. The phase center of the first antenna array is substantially coincident with that of the second antenna array.
1. A null-fill antenna comprising:
a first antenna array including antenna elements arranged with a prescribed point as the center; and
a parasitic element which is spaced apart from the phase center of the first antenna array substantially not more than one wavelength forwardly in the vertical direction with respect to the first antenna array, said parasitic element being indirectly excited by radiation waves from the first array; wherein:
the first antenna array is excited so that the excitation amplitude distribution is to have symmetry with respect to the prescribed point, while the excitation phase distribution is to have substantially point symmetry with respect to the prescribed point; and
the phase center of the first antenna array is substantially coincident with that of the parasitic element.
2. The null-fill antenna claimed in claim 1 , wherein the excitation amplitude of the parasitic element is less than that of the antenna elements adjacent to the phase center of the first antenna array among those forming the first antenna array.
3. The null-fill antenna claimed in claim 1 , wherein, when one of the antenna elements forming the first antenna array is placed at the phase center of the first antenna array, the phase difference between electromagnetic waves radiated from the antenna clement and the parasitic element is within ±60 degrees.
4. The null-fill antenna claimed in claim 1 , wherein the parasitic element has directivity along the direction of arrangement of the antenna elements forming the first antenna array.
5. The null-fill antenna claimed in claim 1 , wherein each of the antenna elements forming the first antenna array is provided with a parasitic element.