Dual band antenna having separate matched inputs for each band

In a portable two-way wireless radio including a receiver which receives signals in a first frequency range, a transmitter which transmits signals in a second frequency range, an antenna having first and second inputs corresponding to the first and second frequency ranges, and a housing in which the antenna is enclosed, the improvement in the antenna comprising:

• first and second spaced apart radiating elements each having a base end and a distal end;
• first transmission line means for connecting the base end of said first radiating element to a first filter having a predetermined impedance in the first frequency range and a substantial reactance in the second frequency range, the end of the first transmission line means which is connected to the first filter comprising said first input;
• second transmission line means for connecting the base end of said second radiating element to a second filter having a predetermined impedance in the second frequency range and a substantial reactance in the first frequency range, the end of the second transmission line means which is connected to the second filter comprising said second input;
• third transmission line means for connecting the distal ends of said first and second radiating elements, said third transmission line means having an electrical length intermediate the first and second frequency ranges of approximately N/2 wavelengths where N is an integer greater than zero;
• said first and second transmission line means having characteristic impedances equal to said predetermined impedances of the first and second filters, respectively;
• said first transmission line means having a length such that the impedance at the base end of said second radiating element in said second frequency range is substantially equal to the characteristic impedance of said second transmission line means;
• and
• said second transmission line means having a length such that the impedance at the base end of said first radiating element in said first frequency range is substantially equal to the characteristic impedance of said first transmission line means, whereby the first and second inputs provide impedance matches at the first and second frequency ranges, respectively.

An antenna having first and second inputs which correspond to first and second frequency ranges of operation of the antenna, the antenna comprising:

• first and second spaced apart radiating element each having a base end and a distal end;
• first transmission line means for connecting the base end of said first radiating element to a first circuit having a predetermined impedance in the first frequency range and a substantial reactance in the second frequency range, the end of the first transmission line means which is connected to the first circuit comprising said first input;
• second transmission line means for connecting the base end of said second radiating element to a second circuit having a predetermined impedance in the second frequency range and a substantial reactance in the first frequency range, the end of the second transmission line means which is connected to the second circuit comprising said second input;
• third transmission line means for connecting the distal ends of said first and second radiating elements, said third transmission line means having an electrical length intermediate the first and second frequency ranges of approximately N/2 wavelengths where N is an integer greater than zero;
• said first and second transmission line means having characteristic impedances equal to said predetermined impedances of the first and second circuits, respectively;
• said first transmission line means having a length such that the impedance at the base end of said second radiating element in said second frequency range is substantially equal to the characteristic impedance of said second transmission line means;
• and
• said second transmission line means having a length such that the impedance at the base end of said first radiating element in said first frequency range is substantially equal to the characteristic impedance of said first transmission line means, whereby the first and second inputs provide impedance matches at the first and second frequency ranges, respectively.