Dual-frequency large-backoff doherty power amplifier and design method thereof

Abstract

The application discloses a dual-frequency large-backoff Doherty power amplifier and a design method thereof, comprising an asymmetric power divider, a carrier power amplification module, a peak power amplification module and a combining impedance matching network, and a dual-frequency phase shifter is constructed by using a left-hand and right-hand composite line theory. The dual-frequency phase shifter realizes arbitrary phase shifts of any two frequency bands, so that the S parameter of the output matching network of the peak power amplification module can be as close as possible to the vicinity of an open-circuit point in a small-signal input state, and the backoff interval of the asymmetric Doherty power amplifier can be further improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of microwave radio frequency communication, and particularly relates to a radio frequency power amplifier, in particular to a dual-frequency large backoff Doherty power amplifier based on a left-right hand composite transmission line structure. BACKGROUND

[0002] The radio frequency power amplifier is a key component of a radio frequency communication front end, 5G communication has the characteristics of complex modulation, large bandwidth and high signal peak-to-average ratio, and higher requirements are put forward for the backoff interval and efficiency of the power amplifier. The Doherty power amplifier adopting the load modulation technology has excellent characteristics of high backoff efficiency and good linearity. By studying the dual-frequency phase shifter, the S parameter output of the peak power amplifier is matched to the open circuit point, thereby the backoff interval is improved, so as to adapt to the characteristics of the high peak-to-average ratio of the 5G communication signal. Due to the advantages of small occupied space and low power consumption, the multi-band radio frequency power amplifier has been widely concerned in recent years. The earliest multi-band amplifier mainly realizes the function by installing multiple amplifiers of different frequency bands and using a single-pole multi-throw switch or using a specially designed wideband load network to cover the entire frequency band. With the miniaturization and cost reduction of devices, the high cost, large size and low working efficiency of the former are more and more difficult to meet the requirements of the related industry; and it is quite difficult to obtain high efficiency in a wide band range by using the latter.

[0003] In view of the difficulties existing in the prior art, it is necessary to study a simple dual-frequency structure to realize the phase shift required for matching the output port of the peak power amplifier to the open circuit point, and on this basis, a dual-frequency Doherty power amplifier capable of working in the 5G frequency band is proposed under the condition of ensuring the large backoff interval efficiency. SUMMARY

[0004] In order to overcome the technical defects existing in the prior art, the application proposes a dual-frequency large backoff Doherty power amplifier based on a left-right hand composite transmission line structure and a design method thereof, adopts an asymmetric power divider, a dual-frequency input-output matching network composed of a T-shaped microstrip structure and a series microstrip line, a multi-stage stepped microstrip line series dual-frequency impedance inverter and a multi-stage stepped microstrip line series combining output matching network to expand the bandwidth, and a dual-frequency phase shifter composed of a composite left-right hand transmission line structure to improve the backoff interval under the premise of ensuring the backoff efficiency and sufficient saturation efficiency in the 5G working frequency band.

[0005] In order to solve the technical problems existing in the prior art, the technical scheme of the application is as follows:

[0006] A dual-frequency large backoff Doherty power amplifier, comprising an asymmetric power divider, a carrier power amplification module, a peak power amplification module, a dual-frequency impedance inverter, a dual-frequency phase shifter and a combining output matching network.

[0007] The asymmetric power divider is connected with the radio frequency signal output end at the input end and connected with the carrier power amplifier module and the peak power amplifier module at the output end.

[0008] The carrier power amplifier module comprises a carrier power amplifier phase compensation line, a carrier input matching / bias network, a carrier power amplifier, a carrier output matching / bias network and a dual-frequency impedance inverter.

[0009] The peak power amplifier module comprises a peak input matching / bias network, a peak power amplifier, a peak output matching / bias network and a dual-frequency phase shifter.

[0010] The combiner output matching network comprises three sections of stepped impedance matching microstrip lines.

[0011] As a preferred technical solution, the asymmetric Wilkinson power divider is composed of microstrip lines TL1-TL9, arc-shaped microstrip lines Curve1-Curve4 and a resistor R1. One end of the microstrip line TL1 serves as a port 1, and the other end is connected with one end of the microstrip lines TL2 and TL3. One end of the microstrip lines TL8 and TL9 serves as a port 2 and a port 3, and the other end is connected with one end of the microstrip lines TL6 and TL7, respectively. The microstrip line TL2, the arc-shaped microstrip line Curve1, the microstrip line TL4, the arc-shaped microstrip line Curve3 and the microstrip line TL6 are connected in series to form one path of the power divider, and the microstrip line TL3, the arc-shaped microstrip line Curve2, the microstrip line TL5, the arc-shaped microstrip line Curve4 and the microstrip line TL7 are connected in series to form the other path of the power divider. The resistor R1 is connected in series between the microstrip line TL6 and the microstrip line TL7 to balance the current and increase the isolation, thereby forming the asymmetric Wilkinson power divider. The working frequency band is 0.7-2.8 GHz, and the ratio of the length to the width is 1:2.

[0012] As a preferred technical solution, the input and output matching networks adopt a T-shaped structure and a stepped microstrip line series structure for dual-frequency impedance matching, and to some extent, the bandwidth of the two working frequency bands is expanded.

[0013] As a preferred technical solution, the carrier output is matched to 3R opt , and the peak output is matched to R opt .

[0014] wherein R opt is the optimal load resistance value of the carrier amplifier and the peak amplifier under the class-B biasing condition.

[0015] As a preferred technical scheme, the double-frequency phase shifter adopts a left-right hand composite line structure. The left-right hand composite line structure is composed of a microstrip line TL10, capacitors C1, C2, C3, and a microstrip line TL13 connected in series, and at the connection between the capacitor C1 and the capacitor C2 and the connection between the capacitor C2 and the capacitor C3, short-circuit stub microstrip lines TL11 and TL12 are connected in parallel, respectively.

[0016] The propagation constant and characteristic impedance of the left-right hand composite line are respectively:

[0017]

[0018]

[0019] wherein β R and β L are the propagation constants of the single right hand line and the single left hand line, respectively; L' R , C' R , L' L , C' L are the distributed inductance and capacitance per unit length, respectively; ω is the working frequency point; if the composite left-right hand transmission line is used to construct the phase shifter, the following conditions need to be met:

[0020]

[0021] β CRLH (ω = ω1) = β1 (4)

[0022] wherein Z t is the optimal impedance value R opt of the peak output matching; ω1 is the first working frequency point; β1 is the phase shift corresponding to the first working frequency point;

[0023] The formula meeting the conditions and the optimal impedance value constitute three independent equations containing four variables, thus having one degree of freedom, which makes it possible to meet the phase shift requirement of the second working frequency point, and the parameters of the left-right hand composite transmission line are:

[0024]

[0025] wherein ω1 and ω2 are the two working frequency points, and β1 and β2 are the phase shifts required by the two working frequency points, respectively; the above parameters are ideal uniform composite left-right hand transmission lines, but in actual applications, the LC ladder network is usually used to construct the composite left-right hand transmission line, and thus the parameters of the actual left-right hand transmission line are:

[0026]

[0027] wherein N is the number of LC ladder structure units, and φ1 and φ2 are the total phase shifts of the N structure units.

[0028] As a preferred technical solution, the combining output matching network is formed by multiple sections of series stepped microstrip lines, which expands the output bandwidth of the combining output matching network to a certain extent.

[0029] The application further discloses a design method of a dual-frequency large-backoff Doherty power amplifier based on a left-hand and right-hand composite line structure.

[0030] Step S1: performing Load pull on the used power amplifier according to a required frequency to obtain an impedance of a required optimal power and optimal efficiency point;

[0031] Step S2: performing corresponding dual-frequency output matching circuit design on the optimal impedance value;

[0032] Step S3: designing a dual-frequency impedance inverter,

[0033] Step S4: designing an input matching circuit;

[0034] Step S5: designing a bias circuit;

[0035] Step S6: designing an asymmetric power divider;

[0036] Step S7: designing a dual-frequency phase shifter, and the specific steps are as follows:

[0037] obtaining two center frequency points ω1 and ω2 according to required dual-frequency bands; and testing the two center frequency points ω1 and ω2 before

[0038] In the Doherty circuit constructed in the step, the S parameters of two frequency points in the peak power amplifier branch are obtained, and the required phase shifts φ1 and φ2 of the S parameters of the peak power amplifier in the two working frequency bands to the open circuit point are calculated; the required number N of LC structure units is obtained according to circuit parameter requirement analysis, and the impedance Z is confirmed t = R opt = 50Ω; the parameters obtained through the above analysis are converted into actual inductance and capacitance element parameters of the left-hand and right-hand transmission lines by using the following formula; the equivalent left-hand and right-hand line parameters of the microstrip line are considered, and the obtained structure is used to construct a dual-frequency phase shifter;

[0039]

[0040] Step S8: designing a phase compensation line circuit;

[0041] Step S9: designing a post-matching circuit;

[0042] Step S10: building an overall circuit and optimizing the overall circuit.

[0043] Compared with the prior art, the present application has the following technical effects:

[0044] 1、 The present application adopts a left-hand and right-hand composite transmission line to construct a dual-frequency phase shifter, realizes that the S parameters of the output matching network of the peak power amplifier are as close as possible to the open-circuit point in the working frequency band of 0.7-0.8 GHz and 2.6-2.8 GHz, so that the peak power amplifier can be completely in an open-circuit state in a small-signal input state, the influence of the peak output matching network on the carrier loop is reduced, and the backoff range is further improved.

[0045] 2、 The present application can be applied to a power amplifier module of a 5G base station, realizes concurrent functions of two 5G frequency bands, reduces the overall cost, and can be well applied to a fifth-generation mobile communication system. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a traditional Doherty power amplifier module block diagram.

[0047] Figure 2 is a principle block diagram of a dual-frequency large backoff Doherty power amplifier based on a left-hand and right-hand composite line structure of the present application.

[0048] Figure 3 is a structure schematic diagram of an asymmetric power divider of the present application.

[0049] Figure 4 is a small-signal simulation result of an asymmetric power divider of the present application.

[0050] Figure 5 is a simplified equivalent circuit model of a left-hand and right-hand transmission line under an ideal balanced condition of the present application.

[0051] Figure 6 is a structure schematic diagram of a dual-frequency phase shifter of the present application.

[0052] Figure 7 is a peak power amplifier loop S parameter simulation result graph of the present application applying a dual-frequency phase shifter.

[0053] Figure 8 is a large-signal characteristic simulation result schematic diagram of a dual-frequency large backoff Doherty power amplifier based on a left-hand and right-hand composite line structure provided by the present application. DETAILED DESCRIPTION

[0054] The following is a specific embodiment of the present application and further describes the technical solutions of the present application in combination with the drawings, but the present application is not limited to these embodiments.

[0055] Reference Figure 2, which is a principle block diagram of a dual-frequency large back-off Doherty power amplifier based on a left-right hand composite line structure according to an embodiment of the present application, and comprises an asymmetric power divider based on a left-right hand transmission line, a carrier power amplifier module, a peak power amplifier module, a dual-frequency phase shifter, and a combined output matching network. Figure 1 Compared with the conventional Doherty structure shown in the figure, the present application uses a dual-frequency phase shifter based on a left-right hand composite line structure to adjust the S parameter state of the peak power amplifier loop. The carrier power amplifier module comprises a carrier power amplifier phase compensation line, a carrier input matching / bias network, a carrier power amplifier, a carrier output matching / bias network, and a dual-frequency impedance inverter; the peak power amplifier module comprises a peak input matching / bias network, a peak power amplifier, a peak output matching / bias network, and a dual-frequency phase shifter; and the combined output matching network comprises three sections of stepped impedance matching microstrip lines. The asymmetric power divider realizes a power 1:2 distribution in a certain frequency range; the phase shifter based on the left-right hand transmission line theory can make the S parameter of the output matching network of the peak power amplifier as close as possible to the open circuit point in the designed working frequency band, so as to make the peak power amplifier completely in an open circuit state at a small signal input state, reduce the influence of the peak output matching network on the carrier loop, and further improve the back-off interval.

[0056] In the present embodiment, the input and output matching networks use a structure of T-shaped structure and stepped microstrip line in series for dual-frequency impedance matching, and expand the bandwidth of the two working frequency bands to a certain extent. The bias circuit is realized by using the conventional technical method in the field; the carrier output is matched to 3R opt , and the peak output is matched to R opt . The peak power amplifier phase shifter and the carrier power amplifier phase compensation line are both dual-frequency phase shifters (at the center frequency) based on the left-right hand transmission line with a characteristic impedance of 50Ω.

[0057] wherein R opt is the optimal load resistance value of the carrier amplifier and the peak amplifier working in a class B mode.

[0058] Referring to Figure 3 and Figure 4The diagram below shows the principle block diagram and simulation results of the asymmetric power divider in this embodiment. The asymmetric power divider consists of microstrip lines TL1 to TL9, curved microstrip lines Curve1 to Curve4, and a resistor R1. One end of microstrip line TL1 serves as port 1, and the other end is connected to one end of TL2 and TL3. One end of microstrip lines TL8 and TL9 serves as port 2 and port 3, respectively, and the other ends are connected to one end of microstrip lines TL6 and TL7. Microstrip line TL2, curved microstrip line Curve1, microstrip line TL4, curved microstrip line Curve3, and microstrip line TL6 are connected in series to form one path of the power divider. Microstrip line TL3, curved microstrip line Curve2, microstrip line TL5, curved microstrip line Curve4, and microstrip line TL7 are connected in series to form the other path of the power divider. A resistor R1 is connected in series between microstrip lines TL6 and TL7 to balance the current and increase the isolation, forming an asymmetric Wilkinson power divider with an operating frequency band of 0.7–2.8 GHz and a power divider ratio of 1:2.

[0059] See Figure 6 The dual-frequency phase shifter in this embodiment employs a left-handed composite line structure. This structure consists of a microstrip line TL10, capacitors C1, C2, and C3, and microstrip line TL13 connected in series. At the connection points of capacitors C1 and C2, and C2 and C3, short-circuit stub microstrip lines TL11 and TL12 are connected in parallel, respectively. The propagation constants and characteristic impedances of the left-handed composite lines are as follows:

[0060]

[0061]

[0062] Where, β R and β L The propagation constants for a single right-handed line and a single left-handed line, respectively; L' R C' R L' L C' L Here, ω represents the distributed inductance and capacitance per unit length, respectively; ω is the operating frequency. If a phase shifter is to be constructed using a composite left-handed / right-handed transmission line, the following conditions must be met:

[0063]

[0064] β CRLH (ω=ω1)=β1 (4)

[0065] Among them, Z t The optimal impedance value R for matching the peak output opt ω1 is the first operating frequency; β1 is the phase shift corresponding to the first operating frequency;

[0066] The formula meeting the condition and the optimal impedance value constitute three independent equations containing four variables, thus having one degree of freedom, which makes it possible to meet the phase shift requirement of the second operating frequency point, and the parameters of the left-hand and right-hand transmission lines are:

[0067]

[0068] where ω1 and ω2 are the two operating frequency points, β1 and β2 are the phase shifts required by the two operating frequency points, respectively; the above parameters are for an ideal uniform composite left-hand and right-hand transmission line, but in actual applications, an LC ladder network is usually used to construct a composite left-hand and right-hand transmission line, thus the parameters of the actual left-hand and right-hand transmission line are:

[0069]

[0070] where N is the number of LC ladder structure units, and φ1 and φ2 are the total phase shifts of the N structure units.

[0071] In this embodiment, L R , C R , and L L are converted into microstrip lines, and the original value of C L is retained. The left-hand and right-hand composite lines in the dual-frequency phase shifter are selected as C L = 2.6 pF, the short-circuit stub line is selected as Z0

[0072] = 120 Ω and θ = 51°, and the right-hand line at both ends is selected as Z0 = 50 Ω and θ = 138°

[0073] Referring to Figure 7 the simulation result diagram of the S parameter output matching of the peak power amplifier circuit after the dual-frequency phase shifter is applied in this embodiment, the S parameters of the two center frequencies can be very close to the open-circuit point of the Smith chart in the frequency bands of 0.7-0.8 GHz and 2.6-2.8 GHz, and the S parameters of the two frequency bands are close to the edge of the Smith chart.

[0074] Referring to Figure 8This diagram illustrates the simulation results of the large-signal characteristics of the dual-frequency Doherty power amplifier with a large backoff based on a left- and right-handed composite line structure in this embodiment. By adding a dual-frequency phase shifter based on the left- and right-handed composite line structure at the output of the peak power amplifier, the Doherty amplifier can improve the backoff range while maintaining backoff and saturation efficiency in two frequency bands. In the operating frequency band of 2.6–2.8 GHz, the saturated output power is approximately 45 dBm, the saturated drain efficiency is 70%–60%, the 6 dB backoff efficiency is 50%–48%, and the 11 dB backoff efficiency is 47%–44%. In the 0.7–0.8 GHz band, the saturated output power is approximately 44.5 dBm, the saturated drain efficiency is 66%–61%, the 6 dB backoff efficiency is 45%–42%, and the 11 dB backoff efficiency is 50%–48%.

[0075] This invention also discloses a design method for a dual-frequency Doherty power amplifier based on a left- and right-handed composite line structure, which specifically includes the following steps: Step S1: Load pull the power amplifier used according to the required frequency to obtain the impedance of the required optimal power and optimal efficiency point;

[0076] Step S2: Design the corresponding dual-frequency output matching circuit for the optimal impedance value;

[0077] Step S3: Design a dual-frequency impedance inverter.

[0078] Step S4: Design the input matching circuit;

[0079] Step S5: Design the bias circuit;

[0080] Step S6: Design an asymmetric power divider;

[0081] Step S7: Design a dual-frequency phase shifter. The specific steps are as follows:

[0082] Two center frequencies, ω1 and ω2, were obtained according to the required dual-band frequency distribution; and before testing...

[0083] In the Doherty circuit constructed in the steps, the S-parameters at two frequencies in the peak power amplifier branch are calculated, and the phase shifts φ1 and φ2 required to match the S-parameters of the peak power amplifier to the open-circuit point in the two operating frequency bands are calculated. Based on the circuit parameter requirements, the required number of LC structural units N is determined, and the impedance Z is confirmed. t =R opt =50Ω; The parameters obtained from the above analysis are converted into the inductance and capacitance parameters of the actual left and right hand transmission lines using the following formula; Considering the actual circuit, the equivalent left and right hand line parameters of the microstrip line are used, and the resulting structure is used to construct a dual-frequency phase shifter;

[0084]

[0085] Step S8: design phase compensation line circuit;

[0086] Step S9: design post matching circuit;

[0087] Step S10: build the overall circuit, and optimize the overall circuit.

[0088] As a further improved scheme, in the step S7 6, the parameters obtained by the above analysis are converted into the inductance and capacitance element parameters of the actual left and right hand transmission lines by using the following formula:

[0089] The propagation constant and characteristic impedance of the left and right hand composite line are respectively:

[0090]

[0091]

[0092] Where, β R and β L are the propagation constants of the single right hand line and the single left hand line respectively; L' R , C' R , L' L , C' L are the distributed inductance and capacitance per unit length respectively; ω is the working frequency point; if the composite left and right hand transmission line is used to construct a phase shifter, the following conditions need to be met:

[0093]

[0094] β CRLH (ω = ω1) = β1 (4)

[0095] Where, Z t is the optimal impedance value R opt of the peak output matching; ω1 is the first working frequency point; β1 is the phase shift corresponding to the first working frequency point;

[0096] The formula that meets the conditions and the optimal impedance value constitute three independent equations containing four variables, so there is one degree of freedom, which makes it possible to meet the phase shift requirements of the second working frequency point, and the parameters of the left and right hand composite transmission line are:

[0097]

[0098] Where, ω1 and ω2 are the two working frequency points, and β1 and β2 are the phase shifts required by the two working frequency points respectively; the above parameters are ideal uniform composite left and right hand transmission lines, but in actual application, LC ladder networks are usually used to construct composite left and right hand transmission lines, so the parameters of the actual left and right hand transmission lines are:

[0099]

[0100] wherein N is the number of LC ladder structure units, and φ1, φ2 are the total phase shifts of the N structure units.

[0101] In this embodiment, L R , C R , L L are converted into microstrip lines, and the original value of C L is retained.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A dual-frequency, high-back-off Doherty power amplifier, characterized in that, It includes an asymmetric power divider, a carrier power amplifier module, a peak power amplifier module, a dual-frequency impedance inverter, a dual-frequency phase shifter, and a combiner output matching network; The input terminal of the asymmetric power divider is connected to the RF signal output terminal, and it is divided into two outputs that are respectively connected to the carrier circuit and the peak circuit. The carrier circuit includes at least a carrier power amplifier module and a dual-frequency impedance inverter. The carrier power amplifier module includes a carrier power amplifier phase compensation line, a carrier input matching / bias network, a carrier power amplifier, and a carrier output matching / bias network. The peak circuit includes at least a peak power amplifier module and a dual-frequency phase shifter. The peak power amplifier module includes a peak input matching / bias network, a peak power amplifier, and a peak output matching / bias network. The carrier circuit and the peak circuit are combined and output, and then connected to the load via a combined output matching network. The combined output matching network adopts a three-section stepped impedance matching microstrip line. The dual-frequency phase shifter adopts a composite left- and right-handed transmission line structure.

2. The dual-frequency large backoff Doherty power amplifier according to claim 1, characterized in that, The power divider is an asymmetric Wilkinson power divider, consisting of microstrip lines TL1-TL9, curved microstrip lines Curve1-Curve4, and resistor R1. One end of microstrip line TL1 serves as the input port, and the other end is connected to one end of microstrip lines TL2 and TL3. Microstrip lines TL2, Curve1, TL4, Curve3, and TL6 are connected in series to form one channel of the power divider. Microstrip lines TL3 and Curve4... Curve2, microstrip line TL5, curved microstrip line Curve4, and microstrip line TL7 are connected in series to form another path of the splitter; a resistor R1 is connected in series between microstrip line TL6 and microstrip line TL7 to balance the current and increase the isolation. One end of microstrip line TL6 is connected to one end of microstrip line TL8 and one end of resistor R1, and one end of microstrip line TL7 is connected to one end of microstrip line TL9 and the other end of resistor R1. The other ends of microstrip lines TL8 and TL9 are used as output ports respectively.

3. The dual-frequency large backoff Doherty power amplifier according to claim 1, characterized in that, The asymmetric power divider operates in the frequency band of 0.6–2.8 GHz; the ratio is 1:

2.

4. The dual-frequency large backoff Doherty power amplifier according to claim 1, characterized in that, The carrier input / output matching network and peak input / output adopt a T-type structure and a stepped microstrip line series structure for dual-frequency impedance matching, and extend the bandwidth of the two operating frequency bands.

5. The dual-frequency large backoff Doherty power amplifier according to claim 1, characterized in that, Carrier power amplifier module output matched to 3R opt The peak power amplifier module output is matched to R opt Among them, R opt This is the optimal load resistance value for the carrier amplifier and peak amplifier to operate under Class B bias conditions.

6. The dual-frequency large backoff Doherty power amplifier according to claim 1, characterized in that, The dual-frequency impedance inverter is constructed using multiple series-connected step microstrip lines to utilize the frequency repeatability of the microstrip lines. The two operating frequency bands are 0.7–0.8 GHz and 2.6–2.8 GHz, with an octave of 3.

6.

7. The dual-frequency large backoff Doherty power amplifier according to claim 1, characterized in that, The dual-frequency phase shifter adopts a left-handed composite line structure; the left-handed composite line structure is composed of microstrip line TL10, capacitors C1, C2, C3 and microstrip line TL13 connected in series. At the connection of capacitors C1 and C2, and at the connection of capacitors C2 and C3, short-circuit stub microstrip lines TL11 and TL12 are connected in parallel respectively. Based on the simplified equivalent circuit model of the left-handed and right-handed transmission lines under ideal equilibrium conditions, the propagation constant and characteristic impedance of the left-handed composite line are respectively: Where, β R and β L The propagation constants for a single right-handed line and a single left-handed line, respectively; L' R C' R L' L C' L Here, ω represents the distributed inductance and capacitance per unit length, respectively; ω is the operating frequency. If a phase shifter is to be constructed using a composite left-handed / right-handed transmission line, the following conditions must be met: b CRLH (ω=ω1)=β1 (4) Among them, Z t The optimal impedance value R for matching the peak output opt ω1 is the first operating frequency; β1 is the phase shift corresponding to the first operating frequency; The formula that satisfies the conditions, together with the optimal impedance value, forms three independent equations, each containing four variables. This gives it one degree of freedom, making it possible to satisfy the phase shift requirement for the second operating frequency. Therefore, both the left and right hands conform to the transmission line parameters: Where ω1 and ω2 are the two operating frequencies, and β1 and β2 are the phase shifts required for the two operating frequencies; a composite left-handed and right-handed transmission line is constructed using an LC ladder network, and the parameters of the actual left-handed and right-handed transmission line are as follows: Where N is the number of LC trapezoidal structural units, and φ1 and φ2 are the total phase shifts of the N structural units.

8. The dual-frequency large backoff Doherty power amplifier based on a left- and right-handed composite transmission line structure according to claim 1, characterized in that, The output matching network is constructed using multiple series-connected step microstrip lines.

9. A design method for a dual-frequency, large backoff Doherty power amplifier based on a left- and right-handed composite transmission line structure, characterized in that... Specifically, the following steps are included: Step S1: Load pull the power amplifier used according to the required frequency to obtain the impedance of the optimal power and optimal efficiency point; Step S2: Design the corresponding dual-frequency output matching circuit for the optimal impedance value; Step S3: Design a dual-frequency impedance inverter. Step S4: Design the input matching circuit; Step S5: Design the bias circuit; Step S6: Design an asymmetric power divider; Step S7: Design a dual-frequency phase shifter. The specific steps are as follows: Based on the required dual-band frequency, two center frequencies ω1 and ω2 are obtained; the S-parameters of the peak power amplifier branch in the Doherty circuit constructed in the previous steps are tested at the two frequencies, and the phase shifts φ1 and φ2 required to match the S-parameters of the peak power amplifier to the open-circuit point in both operating frequency bands are calculated; the required number of LC structure units N is obtained based on the circuit parameter requirements, and the impedance Z is confirmed. t =R opt =50Ω; The parameters obtained from the above analysis are converted into the inductance and capacitance parameters of the actual left and right hand transmission lines using the following formula; Considering practical circuits, we utilize the equivalent left and right hand line parameters of microstrip lines and use the resulting structure to construct a dual-frequency phase shifter. Step S8: Design the phase compensation line circuit; Step S9: Design the post-matching circuit; Step S10: Build the overall circuit and optimize it.

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