Cross-dipole antenna configurations
An apparatus has an improved antenna pattern for a cross dipole antenna. Such antennas desirably have an omnidirectional antenna pattern. Conventional cross dipole antennas exhibit nulls in their antenna patterns, which can cause antennas to deviate from a standard or specification. Applicant recognized and confirmed that the connection of a coaxial cable to the antenna arms is a cause of the nulls in the antenna pattern, and has devised techniques disclosed herein to compensate or cancel the effects of the connection. In one embodiment, the arms of the cross dipole antenna that are coupled to a center conductor of the coaxial cable remain of conventional length, but the arms of the cross dipole antenna that are coupled to a shield of the coaxial cable are lengthened by a fraction of the radius of the outer diameter of the coaxial cable.
1. A method for designing a cross-dipole antenna intended to be used for a signal having a wavelength λ, wherein the cross-dipole antenna comprises a first arm, a second arm, a third arm, and a fourth arm, the method comprising:
generating a simulation model of the cross-dipole antenna, wherein the simulation model includes the first arm, the second arm, the third arm, the fourth arm and a coaxial structure to which the first arm, the second arm, the third arm, and the fourth arm are connected;
simulating the cross-dipole antenna via computer execution of the simulation model; and
adjusting arm lengths of one or more of the first arm, the second arm, the third arm, and the fourth arm in response to simulation results.
2. The method of claim 1 , further comprising:
starting with a length aλ for the first arm and the third arm, wherein a value for a is about 0.5, wherein the first arm is connected to a center conductor of the coaxial structure and the third arm is connected to a shield of the coaxial structure;
starting with a length bλ for the second arm and the fourth arm, wherein a value for b is about 0.5, wherein the second arm is connected to a center conductor of the coaxial structure and the fourth arm is connected to a shield of the coaxial structure;
adjusting the value for a of the shorter arms and adjusting the value for b of the longer arms until a quadrature phase relationship is established among the arms, wherein a final value for a of the shorter arms is less than a final value for b of the longer arms, wherein the quadrature phase relationship is determined via computer execution of the simulation model;
increasing a length of the third arm relative to the first arm by a fraction x of a radius R of the coaxial structure; and
increasing a length of the fourth arm relative to the second arm by the fraction x of the radius R of the coaxial structure.
3. The method of claim 2 , wherein a value for x is between about 0.3 to about 1.2.
4. The method of claim 2 , wherein a value for x is between about 0.42 to about 0.78.
5. The method of claim 2 , wherein a value for x is between about 0.48 to about 0.72.
6. The method of claim 2 , wherein a value for x is between about 0.54 to about 0.66.