Balanced dipole antenna
View Patent ↗A balanced dipole antenna has a coaxial cable connected between a load or source and the left and right dipole arms to substantially eliminate common mode current and radiative coupling between the coaxial cable and the left and right dipole arms. The connection between the source/load coaxial cable and the left and right dipole arms is a symmetric balun having a center branch that is an extension of the source/load coaxial cable, and left and right stubs. When the stubs are segments of coaxial cable, the outer conductors of the left and right stubs of the symmetric balun are respectively coupled to the left and right dipole arms, and one of the inner conductors of the left and right stubs is connected to the inner conductor of the center branch, while the other of the inner conductor of the left and right stubs is connected to the outer conductor of the center branch. When the stubs are metallic, the inner conductor of the center branch is electrically connected to one of the left and right dipole arms, while the outer conductor of the center branch is electrically connected to the other of the left and right dipole arms. A sliding bar at the base of the stubs electrically connects the outer conductors of the left and right stubs and the center branch.
1. A balanced dipole antenna, comprising:
a left dipole arm having a center end,
a right dipole arm having a center end,
a coaxial cable having an outer conductor and a single inner conductor and a top end electrically located between the center ends of the left and right dipole arms,
a left stub coupling the left dipole arm and the coaxial cable, and
a right stub coupling the right dipole arm and the coaxial cable,
wherein one of the left and right stubs has an inner conductor that electrically connects to the inner conductor of the coaxial cable, and the other of the left and right stubs has an inner conductor that electrically connects to the outer conductor of the coaxial cable.
2. The balanced dipole antenna of claim 1 , wherein the left and right stubs are formed of respective lengths of coaxial cable.
3. The balanced dipole antenna of claim 1 , wherein the inner conductor of the coaxial cable is connected to one of the left and right dipole arms, and the outer conductor of the coaxial cable is connected to the other of the left and right dipole arms.
4. The balanced dipole antenna of claim 1 , further comprising a bar that electrically connects the left stub, the right stub and the coaxial cable.
5. The balanced dipole antenna of claim 4 , wherein the bar is slidable along the coaxial cable.
6. The balanced dipole antenna of claim 1 , wherein the length of the left and right dipole arms is adjustable.
7. The balanced dipole antenna of claim 1 , wherein the length of the left and right dipole arms is slightly less than λ/4, where λ is the free space wavelength of a center frequency of a signal being received or transmitted.
8. The balanced dipole antenna of claim 1 , wherein the height of the left and right stubs is about λ/4, where λ is the free space wavelength of a center frequency in a bandwidth of signals being received or transmitted.
9. The balanced dipole antenna of claim 1 , wherein the left and right stubs substantially eliminate radiative coupling between the coaxial cable and the left and right dipole arms.
10. The balanced dipole antenna of claim 1 , wherein the left and right stubs substantially eliminate common mode current between the coaxial cable and the left and right dipole arms.
11. A symmetric balun, comprising:
a left stub for coupling to a left arm of a dipole antenna,
a right stub for coupling to a right arm of the dipole antenna, and
a center branch for connecting to a coaxial cable, the center branch having an inner conductor and an outer conductor,
wherein the left and right stubs each have inner conductors, and one of the inner conductors of the left and right stubs is connected to the inner conductor of the center branch, while the other of the inner conductor of the left and right stubs is connected to the outer conductor of the center branch.
12. The symmetric balun of claim 11 , wherein the left and right stubs are formed of respective lengths of coaxial cable.
13. The symmetric balun of claim 11 , wherein the left and right stubs each have outer conductors respectively connected to the left and right dipole arms.
14. The symmetric balun of claim 11 , wherein the inner conductor of the coaxial cable is connected to one of the left and right dipole arms, and the outer conductor of the coaxial cable is connected to the other of the left and right dipole arms.
15. The symmetric balun of claim 11 , further comprising a bar at the base of the left and right stubs and the center branch for electrically connecting the left and right stubs and the center branch.
16. The symmetric balun of claim 15 , wherein the bar is slidable along the length of the left and right stubs.
17. The symmetric balun of claim 15 , wherein each of the left and right stubs and the center branch has an outer conductor, and the bar electrically connects the outer conductors of the left and right stubs and the center branch.
18. The symmetric balun of claim 11 , further comprising a connector for connecting the center branch to a coaxial cable.
19. The symmetric balun of claim 11 , wherein the height of the left and right stubs is about λ/4, where λ is the free space wavelength of a center frequency in a bandwidth of signals being received or transmitted.
20. The symmetric balun of claim 11 , wherein the left and right stubs substantially eliminate radiative coupling between the coaxial cable and the left and right dipole arms.
21. The symmetric balun of claim 11 , wherein the left and right stubs substantially eliminate common mode current between the coaxial cable and the left and right dipole arms.