Compact and broadband Doherty power amplifier

1 . A Doherty power amplifier comprising:

a) an input;

b) an output;

c) a main power amplification device connected between the input and the output; and

d) an auxiliary power amplification device connected between the input and the output, and arranged in parallel with the main power amplification device;

wherein the Doherty power amplifier further comprises a first dual-mode impedance transformer (IT) connected between the main power amplification device and the output; and a second dual-mode IT between the auxiliary power amplification device and the output; the first and second dual-mode ITs each adapted to convert an input impedance of a corresponding one of the main and auxiliary power amplification devices to a load impedance at the output, at two frequencies simultaneously;

wherein each of the first and second dual-mode ITs comprise a first inductor, a third inductor, and a shunt short-ended stub; the first inductor having a first end connected to an output of a corresponding one of the main and auxiliary power amplification devices; a second end of the first inductor connected to a first end of the shunt short-ended stub and to a first end of the third inductor;

a second end of the shunt short-ended stub being grounded; a second end of the third inductor connected to the output of the Doherty power amplifier.

2 . The Doherty power amplifier of claim 1 , wherein each of the first and second dual-mode ITs comprises a drain bias that is connected to an output of a corresponding one of the main and auxiliary power amplification devices.

3 . The Doherty power amplifier of claim 2 , wherein the drain biases each is smaller than λ/4 at ƒ 0 .

4 . The Doherty power amplifier of claim 1 , wherein the input impedances of the first and second dual-mode ITs is designed to be close to the load-pull impedances of the main power amplification device and the auxiliary power amplification device.

5 . The Doherty power amplifier of claim 1 , wherein the shunt short-ended stubs of the first and second dual-mode ITs form a couple-line bandpass filter.

6 . The Doherty power amplifier of claim 5 , wherein the couple-line bandpass filter and the first inductors of the main and auxiliary power amplification devices, define an out-of-phase second harmonic injection path.

7 . The Doherty power amplifier of claim 1 , further comprises a wideband coupler; the wideband coupler connected between the input of the Doherty power amplifier, and the main and auxiliary power amplification devices.

8 . The Doherty power amplifier of claim 7 , further comprises first stepped-impedance lines connected between the wideband coupler and the main power amplification device; and second stepped-impedance lines connected between the wideband coupler and the auxiliary power amplification device.

9 . The Doherty power amplifier of claim 1 , wherein the input impedances of the main and auxiliary power amplification devices are complex impedances, and the load impedance is a real impedance.

10 . The Doherty power amplifier of claim 1 , further comprises a third dual-mode IT connected between the first dual-mode impedance transformer and the output of the Doherty power amplifier; and a fourth dual-mode IT connected between the second dual-mode impedance transformer and the output of the Doherty power amplifier; the first and third dual-mode ITs forming a two-order cascaded structure; the second and fourth dual-mode ITs forming a two-order cascaded structure.

11 . The Doherty power amplifier of claim 10 , wherein each of the third and fourth dual-mode ITs comprises a shunt short-ended stub.

12 . The Doherty power amplifier of claim 11 , wherein the shunt short-ended stubs of the third and fourth dual-mode ITs form a couple-line bandpass filter.

13 . The Doherty power amplifier of claim 1 , wherein the Doherty power amplifier is free of a post-matching network.