Combiner for an RF power amplifier
Embodiments of the invention include a combiner for an RF amplifier comprising wiring and a transmission line transformer. The transmission line transformer may include a ferrite core having a hole defined therein; a coaxial cable having a first dielectric constant and routed through the hole of the ferrite core; and a stripline having a second dielectric constant and routed around the ferrite core. In some embodiments, an electrical length of the stripline is matched to an electrical length of the coaxial cable. The electrical length of the coaxial cable may be defined by the first dielectric constant and the electrical length of the stripline may be defined by the second dielectric constant.
1. A combiner for an RF amplifier comprising:
(a) a ferrite core for low frequency operation, the ferrite core having a hole defined therein;
(b) a coaxial cable dimensioned to the highest operating frequency of the RF amplifier, the coaxial cable having a first dielectric constant, wherein the coaxial cable connects an RF output of at least two final stages in parallel to the output of the RF amplifier, and wherein the coaxial cable is routed through the hole of the ferrite core;
(c) a stripline having a second dielectric constant, wherein the stripline connects the RF output of the at least two final stages in parallel to the output of the RF amplifier, wherein the stripline is routed around the ferrite core; and
(d) wherein an electrical length of the stripline is matched to an electrical length of the coaxial cable, wherein the electrical length of the coaxial cable is defined by the first dielectric constant and wherein the electrical length of the stripline is defined by the second dielectric constant, wherein a physical length of the stripline is longer than a physical length of the coaxial cable, and wherein a relationship between the physical lengths of the stripline and coaxial cable is defined by the first dielectric constant and the second dielectric constant.
2. The combiner of claim 1 , wherein the physical length of the stripline is longer than the physical length of the coaxial cable by a factor given by the square root of the first dielectric constant divided by the square root of the second dielectric constant.
3. The combiner of claim 1 , wherein the combiner is operable from 20 MHz to 1 GHz.
4. The combiner of claim 1 , further comprising:
a wiring layer connecting a terminus of the coaxial cable and a terminus of the stripline to the at least two final stages; and
a heat sink defining a base of the combiner, the heat sink including a groove, wherein the wiring layer fits within the groove, and wherein the heat sink serves as an EMI shield for RF and spurious emissions.
5. The combiner of claim 4 , further comprising:
an EMF cover shield for RF and spurious emissions disposed over the wiring layer, ferrite core, coaxial cable and stripline.
6. A combiner for an RF amplifier comprising:
(a) a ferrite core having a hole defined therein;
(b) a coaxial cable dimensioned to a highest operating frequency of the RF amplifier, the coaxial cable having a first dielectric constant, wherein the coaxial cable connects an RF output of at least four final stages in parallel to the output of the RF amplifier, and wherein the coaxial cable is routed through the hole of the ferrite core; and
(c) a stripline having a second dielectric constant, wherein the stripline connects the RF output of the at least four final stages in parallel to the output of the RF amplifier, wherein the stripline is routed around the ferrite core, wherein a physical length of the stripline is longer than a physical length of the coaxial cable, and wherein a relationship between the physical lengths of the stripline and coaxial cable is defined by the first dielectric constant and the second dielectric constant.
7. The combiner of claim 6 , wherein the physical length of the stripline is longer than the physical length of the coaxial cable by a factor given by the square root of the first dielectric constant divided by the square root of the second dielectric constant.
8. The combiner of claim 6 , wherein the combiner is operable from 20 MHz to 1 GHz.
9. The combiner of claim 6 , further comprising:
a wiring layer connecting a terminus of the coaxial cable and a terminus of the stripline to the at least four final stages; and
a heat sink defining a base of the combiner, the heat sink including a groove, wherein the wiring layer fits within the groove, and wherein the heat sink serves as an EMI shield for RF and spurious emissions.
10. The combiner of claim 9 , further comprising:
an EMF cover shield for RF and spurious emissions disposed over the wiring layer, ferrite core, coaxial cable and stripline.
11. The combiner of claim 9 , wherein an electrical length of the stripline is matched to an electrical length of the coaxial cable, wherein the electrical length of the coaxial cable is defined by the first dielectric constant and wherein the electrical length of the stripline is defined by the second dielectric constant.
12. A method for assembling a combiner for an RF amplifier comprising the steps of:
disposing a heat sink defining a base of the combiner in an RF amplifier casing, the heat sink including a first groove;
disposing a wiring layer within the first groove of the heat sink, the wiring layer having wiring thereon to connect the wiring layer with at least two final stages;
disposing a ferrite core for low frequency operation within a hole in the wiring layer, the ferrite core having a longitudinal hole defined therein;
positioning a coaxial cable through the longitudinal hole of the ferrite core, the coaxial cable dimensioned to the highest operating frequency of the RF amplifier, the coaxial cable having a first dielectric constant, wherein a first end of the coaxial cable connects to the wiring of the wiring layer and a second end the coaxial cable connects to an output of the combiner; and
disposing a stripline having a second dielectric constant around the ferrite core so that a first end of the stripline connects to the wiring of the wiring layer and a second end of the stripline connects to ground;
wherein an electrical length of the stripline is matched to an electrical length of the coaxial cable, wherein the electrical length of the coaxial cable is defined by the first dielectric constant and wherein the electrical length of the stripline is defined by the second dielectric constant.
13. The method for assembling a combiner according to claim 12 , further comprising the step of:
positioning a second heat sink on the wiring layer, the second heat sink having a second groove formed therein, wherein the stripline is positioned in the second groove of the second heat sink.
14. The method for assembling a combiner according to claim 13 , further comprising the steps of:
disposing a first EMF cover shield over the second heat sink and stripline; and
disposing a second EMF cover shield over the wiring layer and the first EMF cover shield.
15. The method for assembling a combiner according to claim 14 , wherein the ferrite core is at least partially disposed in the first groove in the heat sink.
16. The method for assembling a combiner according to claim 14 , wherein the wiring connecting the at least two final stages extends through the wiring layer into the first groove to connect to the first end of the coaxial cable and the first end of the stripline.