Low common mode resonance multiband radiating array
A higher band radiating element for use in a multiband antenna includes first and second dipole arms supported by a feedboard. The feedboard includes first and second matching circuits, each comprising a capacitor-inductor-capacitor (CLC) matching circuit. The matching circuit further includes a CM tuning circuit connecting a portion of the matching circuit to ground via a microstrip trace selected to pass lower band currents while blocking higher band currents. The CM tuning circuit moves the common mode resonance of the higher band support PCB down below the operating frequency of additional, lower band radiating elements present in the multiband antenna, which is preferable to moving the common mode resonance above the lower band frequencies.
1. A higher band radiating element for a multiband antenna having at least higher band elements and lower band elements, comprising:
a. first and second dipole arms, each dipole arm having a capacitive coupling area; and
b. a feedboard having a balun and first and second matching circuits coupled to the balun, the first matching circuit being coupled to the first dipole arm and the second matching circuit being coupled to the second dipole arm, the first and second matching circuits each comprising in series:
1. a stalk, coupled to the balun,
2. a first capacitive element;
3. an inductor; and
4. a second capacitive element, the second capacitive element being coupled to a dipole arm;
each matching circuit further comprising a common mode tuning circuit connecting the first capacitive element and the inductor to the stalk to move the common mode resonance of the matching circuits to a frequency below the lower band frequency.
2. The higher band radiating element of claim 1 , wherein the common mode tuning circuit further comprises a microstrip line providing a DC connection to the stalk and having a length selected such that it appears as a high impedance at an operating frequency of the higher band radiating element.
3. The higher band radiating element of claim 2 , wherein the common mode tuning circuit has a length selected such that it appears as a relatively low impedance at the operating frequency of the lower band radiating element.
4. The higher band radiating element of claim 1 , wherein the first capacitive element and an area of the stalk comprise parallel plates of a capacitor and the feedboard substrate comprises a dielectric of a capacitor.
5. The higher band radiating element of claim 1 , wherein the second capacitive element and dipole arm capacitive coupling area combine to form a capacitor that blocks out of band currents.
6. The higher band radiating element of claim 1 , wherein the radiating element further comprises a cross dipole radiating element.
7. The higher band radiating element of claim 1 , wherein the higher band radiating element further comprises a high band radiating element of a dual-band array.
8. The higher band radiating element of claim 1 , wherein the higher band radiating element has a first operational frequency band within a range of about 1710 MHz-2700 MHz, and each lower band radiating element has a second operational frequency band within a range of about 698 MHz-960 MHz.
9. The radiating element of claim 8 , wherein the common mode tuning circuit has a length selected to pass low band current and block high band current.
10. The higher band radiating element of claim 1 , wherein the common mode tuning circuit has a length such that it does not de-tune the higher band radiating element.
11. The multiband antenna of claim 10 , wherein the first operational frequency band comprises a mobile communications low band and the second operational frequency band comprises a mobile communications high band.
12. The multiband antenna of claim 10 , wherein the first operational frequency band is located within an approximate range of 698 MHz to 960 MHz, and the second operational frequency band is located within an approximate range of 1710 MHz to 2170 MHz.
13. A multiband antenna, comprising:
a. a first array of first radiating elements having a first operational frequency band; and
b. a second array of second radiating elements having a second operational frequency band, the second operational frequency band being higher than the first operational frequency band, the second radiating elements further comprising: a. first and second dipole arms, each dipole arm having a capacitive coupling area; and b. a feedboard having a balun and first and second matching circuits coupled to the balun, the first matching circuit being coupled to the first dipole arm and the second matching circuit being coupled to the second dipole arm, the first and second matching circuits each comprising in series:
1. a stalk, coupled to the balun,
2. a first capacitive element;
3. an inductor; and
4. a second capacitive element, the second capacitive element being associated with one of the first and second dipole arms,
each matching circuit further comprising a common mode tuning circuit connecting the first capacitive element and the inductor to the stalk, the common mode tuning circuit comprising a microstrip line dimensioned to short any induced low band currents to the stalk without substantially affecting high band currents, thereby moving common mode resonance down below the second operational frequency band.
14. A higher band radiating element for a multiband antenna having at least higher band elements and lower band elements, comprising:
a first dipole arm;
a second dipole arm;
a feedboard having a balun and first and second matching circuits coupled to the balun, the first matching circuit being coupled to the first dipole arm and the second matching circuit being coupled to the second dipole arm, the first matching circuit comprising a first stalk that is coupled to the balun and a first capacitor coupled between the first stalk and the first dipole arm, and the second matching circuit comprising a second stalk that is coupled to the balun and a second capacitor coupled between the second stalk and the second dipole arm,
wherein the first matching circuit further comprises a common mode tuning circuit that provides a direct current path from a first node that is between the first capacitor and the first dipole arm to ground.
15. The higher band radiating element of claim 14 , wherein the first matching circuit further includes a third capacitor coupled in series between the first capacitor and the first dipole arm, wherein the first node is located between the first and third capacitors.
16. The higher band radiating element of claim 14 , wherein the common mode tuning circuit comprises a transmission line connecting the first node to the stalk, and wherein a length of the transmission line is selected such that it appears as a high impedance at an operating frequency of the higher band radiating element.
17. The higher band radiating element of claim 16 , wherein the length of the transmission line is further selected such that it appears as a relatively low impedance at the operating frequency of the lower band radiating element.
18. The higher band radiating element of claim 14 , wherein the first matching circuit is further configured to move the common mode resonance of the matching circuits to a frequency below the operating frequency of the lower band radiating element.
19. The higher band radiating element of claim 15 , wherein the first matching circuit further includes a first inductor in series between the first capacitor and the third capacitor and a second inductor in series between the second capacitor and the fourth capacitor.