Radio Frequency (RF) Power Amplifier Design Providing High Power Efficiency in a Wide Dynamic Range
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe design is complete following a routinized process. The results, at the present version, can be regatded as competitive. But the novelty is not clearly stated.
I have the following suggestions:
1. A general impression of the layout of the paper is that there are quite much redundacies. Some redundant text should be removed or significantly simplified.
2. The paragraphing in the introduction can be integrated and reorganized for clearer presentation, with each paragraph fosusing on one issue.
3. Sec. 2.2. Control path amplifier. This section can be more briefly revised for better focusing on the LMBA.
4. Sec. 2.4. Can be simplified by saving the three figures.
5. Since "Load modulated balanced amplifier (LMBA)" is stated in the beginning, the abbreviated form LMBA should be preferred in the following description.
6. Figs. 22 to 24 can be combined into one figure with different marks on the curves to help better comparing. So for Figs. 25 to 27.
7. Table 2. Please check the data in the last column.
8. Table 3. The LMBA is now becoming hot again since the pursuit of efficiency is urgent. But the compared references are not up-to-date sufficiently. Please add comparisons with some latest works.
9. Fig. 11. Even in the enlarged mode, it is hard to identify the details.
10. In Sec.5, Too long a conclusion. Some descriptions should have appeared in the introduction. Thus it is recommended to delete the text of line 774 to 792, and line 797 to 799.
11. References. There are few latest works. Please try to update.
Comments on the Quality of English LanguageThe language style is just plain description and readers will feel it somehow dull to read.
Also the redundancy is an issue, as has been pointed out in my review.
Author Response
Please check in the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors- The abstract is somewhat lengthy and lacks emphasis on the core innovations. It is recommended to concisely summarize the research content and highlight the unique contributions of the LMBA technology. For example: What are the limitations of existing PA technologies? How does LMBA address these issues? What are the main contributions of this study?
- In Section 2.1, the phrase "microwave circuit simulator was used for simulations" is mentioned. Please specify the exact name of the microwave simulation software used.
- The standardization of images can be improved. For instance, Figures 4 and 10 require enhanced clarity, and Figure 11 appears distorted.
- In power amplifier design, noise performance is typically a crucial consideration. Although LMBA technology focuses on enhancing amplifier efficiency across various output power levels, attention to its noise characteristics is essential in practical design and application to ensure overall system performance optimization. Please include noise performance test results and discussions in the article.
Author Response
Reviewer#1, Concern # 1: The abstract is somewhat lengthy and lacks emphasis on the core innovations. It is recommended to concisely summarize the research content and highlight the unique contributions of the LMBA technology. For example: What are the limitations of existing PA technologies? How does LMBA address these issues? What are the main contributions of this study?
Author response: We agree with the reviewer’ concern .
Author action: We updated the manuscript accordingly by emphasizing why LMBA technology is used and what is the contribution of our study. We added the sentence below to the abstract and we deleted some sentences to shorten the abstract.
Recent advances in wireless communications have favored increasing data rates. For this purpose, complex modulation techniques with high peak-to-average power ratios (PAR) have been introduced. Conventional RF power amplifiers (PA) provide high efficiency only at saturated power levels. At lower power levels, the efficiency decreases significantly. In modulation techniques with high PAR, it is necessary to increase the efficiency at the back-off power levels. Various techniques have been developed for this purpose. Among these techniques, the Load Modulated Balanced Amplifier (LMBA), a promising technique, has come to the fore in recent years.
Reviewer#1, Concern # 2: In Section 2.1, the phrase "microwave circuit simulator was used for simulations" is mentioned. Please specify the exact name of the microwave simulation software used.
Author response: We agree with the reviewer concern.
Author action: We updated the manuscript by specifying the simulation software packages as below.
“ AWR software package were used for LMBA design and Solidworks software package was used for mechanical design. ”
Reviewer#1, Concern # 3: The standardization of images can be improved. For instance, Figures 4 and 10 require enhanced clarity, and Figure 11 appears distorted.
.Author response: We agree with the reviewer concern. Figure 4 and Figure 11 show the full details of the electronic circuit designed and manufactured. However, the resulting drawing is very difficult to simplify in such a way that it can be included in an article. We also felt that including this level of detail in the scope of the article did not contribute much. Therefore, it really seems to have lowered the quality of the drawing of our paper. On the other hand, since there is not enough explanation in the text about the Smith Chart visuals in Figure 3 and Figure 10, we tried to make the figures speak and added explanatory sentences.
Author action: We have therefore removed the schematics in Fig.4 and Fig.11. Furthermore, we updated the manuscript by inserting the paragraph below to further elaborate Fig.3 and Fig. 10.
“As seen in the Smith Chart, pink contours represent PAE and blue contours represent Output Power. The blue contours represent impedance values where the output power increases with decreasing impedance values and the pink contours represent impedance values where the PAE increases with decreasing impedance values. The normalized impedance value was chosen to maximize the output power and the matching network was constructed accordingly. “
Reviewer#1, Concern # 4: In power amplifier design, noise performance is typically a crucial consideration. Although LMBA technology focuses on enhancing amplifier efficiency across various output power levels, attention to its noise characteristics is essential in practical design and application to ensure overall system performance optimization. Please include noise performance test results and discussions in the article.
.Author response: We agree with the reviewer concern. Noise performance is an important factor for an amplifier. In our LMBA study, our main focus was to increase the efficiency both at maximum power and at low output power. We wanted to show that we could do this without reducing the system gain. We recognize the importance of noise performance measurement, but due to our current workload, it is not possible to do this in a short period of time. Therefore, we emphasize the importance of this issue in the conclusion of our paper and recommend that it be considered in future work.
Author action: We updated the manuscript by adding the paragraph below in the conclusion section.
Noise performance is an important factor for an amplifier. In our LMBA study, our main focus was to increase the efficiency both at maximum power and at low output power. We wanted to show that we could do this without reducing the system gain. We consider the importance of noise performance measurement as an important issue. Therefore, we strongly recommend that it be considered in detail as a further study.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe discussion regarding the state-of-the-art in the Introduction (lines 84–128) seems somewhat out of context concerning the authors' proposed work, given that those MMIC implementations operate at different carrier frequencies compared to the 1.7–1.8 GHz range of the proposed prototype. I suggest focusing instead on LMBA solutions within this frequency range and removing some of the discussion and references from [11] to [19].
The Introduction could provide more information on the novelty of this work. Otherwise, it might come across as merely a well-documented design exercise. Also, the comparison to the state-of-the-art in the final section should be better focused on other similar amplifiers in the same frequency range as well as similar technology.
The quality of the figures and descriptions in the captions should be fundamentally improved. Readers should be able to understand the plots even without reading the full paper. In particular, the block diagram and circuit illustrations are of low quality.
In Section 2.2, it is mentioned that the control path should feature lower power than the main path. Why is that? I would have expected the control path to require equal or even higher power to perform load-pull effectively. This is similar to benchtop active load-pull systems, where the pulling amplifier (driver) is typically larger than the DUT. For example, see: A. M. Angelotti et al., "Wideband Active Load–Pull by Device Output Match Compensation Using a Vector Network Analyzer," IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 1, pp. 874–886, Jan. 2021.
It is somewhat confusing that the authors claim to design a single-RF input system while presenting a classical two-input LMBA stage. Please clarify which results correspond to standalone LMBA operation (thus leveraging the full flexibility of the two inputs) and which are constrained to the single-RF input case. Additionally, it would be helpful to better describe how the control signal is chosen and managed in this scenario.
Comments on the Quality of English LanguageThe manuscript is understandable but would benefit from a grammar revision.
Author Response
Reviewer#2, Concern # 1: The discussion regarding the state-of-the-art in the Introduction (lines 84–128) seems somewhat out of context concerning the authors' proposed work, given that those MMIC implementations operate at different carrier frequencies compared to the 1.7–1.8 GHz range of the proposed prototype. I suggest focusing instead on LMBA solutions within this frequency range and removing some of the discussion and references from [11] to [19].
Author response: We agree with the reviewer’ concern . Reviewer is right. In order to make a fair comparison, we excluded 4 reference studies that were outside the frequency band of our study. We left the studies that were in and near the frequency band of our study.
Author action: We updated the manuscript by deleting references [11], [13 ], [17 ], [18 ].
Reviewer#2, Concern # 2: The Introduction could provide more information on the novelty of this work. Otherwise, it might come across as merely a well-documented design exercise. Also, the comparison to the state-of-the-art in the final section should be better focused on other similar amplifiers in the same frequency range as well as similar technology.
Author response: We agree with the reviewer’ concern. We tried to provide more information about the novelty of our work in the Introduction section. Furthermore, in order to make a fair comparison under the same conditions, we added the study of Y.E. Aras[19], who worked at the same frequencies, to the comparison table. We removed the study of Z.Yin [17], who worked at a different frequency range, from the comparison table. Thus, as the reviewer tried to state, we made a comparison with the studies done at a similar frequency (1.7 GHz). Furthermore, we also included more related literature and compare additional 2 state-of-the art and recent publications listed below.
[ 19 ] J. Xie, K. -K. M. Cheng, X. Fang and P. Yu, "Extension of Output Backoff Range in Three-Stage Load Modulated Balanced Amplifier Using Asymmetric Coupling and Non-Zâ‚€ Load," in IEEE Transactions on Microwave Theory and Techniques, vol. 73, no. 1, pp. 553-567, Jan. 2025, doi: 10.1109/TMTT.2024.3425168.
Jieen Xie et al. obtained 42-44.4 dBm output power at 1.8-2.05 GHz. At these power levels, they achieved drain efficiencies of 48.2%-63.2% and 50.8%-59.5% in the 7.5 dB Output back-off region (OBO).
[20 ] L. Ding and J. Xia, "Design of Load-modulated Balanced Amplifier Based on Broadband Output Matching Network," 2024 IEEE 12th Asia-Pacific Conference on Antennas and Propagation (APCAP), Nanjing, China, 2024, pp. 1-2, doi: 10.1109/APCAP62011.2024.10881063.
The study by Long Ding and Jing Xia was conducted at frequencies of 1.4-2.8 GHz and the saturation output power was 43.7-44.3 dBm. At these power levels, 64.6-70.5% efficiency and 44.9-50.4% at 10dB OBO were achieved.
Author action: We have added the results obtained in Table 3 and interpreted them. We revised the relevant paragraphs as below. We updated the manuscript accordingly.
Reviewer#2, Concern # 3: The quality of the figures and descriptions in the captions should be fundamentally improved. Readers should be able to understand the plots even without reading the full paper. In particular, the block diagram and circuit illustrations are of low quality.
Author response: We agree with the reviewer concern. Figure 4 and Figure 11 show the full details of the electronic circuit designed and manufactured. However, the resulting drawing is very difficult to simplify in such a way that it can be included in an article. We also felt that including this level of detail in the scope of the article did not contribute much. Therefore, it really seems to have lowered the quality of the drawing of our paper. On the other hand, since there is not enough explanation in the text about the Smith Chart visuals in Figure 3 and Figure 10, we tried to make the figures speak and added explanatory sentences.
Author action: We have therefore removed the schematics in Fig.4 and Fig.11. Furthermore, we updated the manuscript by inserting the paragraph below to further elaborate Fig.3 and Fig. 10.
“As seen in the Smith Chart, pink contours represent PAE and blue contours represent Output Power. The blue contours represent impedance values where the output power increases with decreasing impedance values and the pink contours represent impedance values where the PAE increases with decreasing impedance values. The normalized impedance value was chosen to maximize the output power and the matching network was constructed accordingly. “
Reviewer#2, Concern # 4: In Section 2.2, it is mentioned that the control path should feature lower power than the main path. Why is that? I would have expected the control path to require equal or even higher power to perform load-pull effectively. This is similar to benchtop active load-pull systems, where the pulling amplifier (driver) is typically larger than the DUT. For example, see: A. M. Angelotti et al., "Wideband Active Load–Pull by Device Output Match Compensation Using a Vector Network Analyzer," IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 1, pp. 874–886, Jan. 2021.
Author response: The purpose of the control arm is to increase the load impedance of the main arm when the output power is low so that it can operate with higher efficiency. If the control arm is too powerful, the load impedance of the main arm may change too much and the efficiency gain may decrease. For this reason, the control arm is usually chosen to be less powerful than the main arm. If the control arm is too strong, it may create an aggressive effect during load modulation, which may adversely affect the linearity performance of the system.
As a result, selecting the control arm power lower than the main arm increases efficiency, makes load modulation more stable and improves linearity performance. The same considerations can be found in Pednekar etal. studies listed below ;
[12] P. H. Pednekar, E. Berry, and T. W. Barton, “RF-Input Load Modulated Balanced Amplifier With Octave Bandwidth,” IEEE Trans Microw Theory Tech, vol. 65, no. 12, pp. 5181–5191, 2017, doi: 10.1109/TMTT.2017.2748123.
[16] P. H. Pednekar, “Advanced Load Modulated Power Amplifier Architectures,” Doctoral Thesis, Faculty of the Graduate School, University of Colorado at Boulder, Colorado, United States, 2019.
Author action: We updated the manuscript by adding some explanatory sentences about how to arrange the control arm and the main arm as below .
The purpose of the control path is to increase the load impedance of the main arm when the output power is low so that it can operate with higher efficiency. If the control path is too powerful, the load impedance of the main path may change too much and the efficiency gain may decrease. For this reason, the control path is usually chosen to be less powerful than the main path. If the control path is too strong, it may create an aggressive effect during load modulation, which may adversely affect the linearity performance of the system.
As a result, selecting the control path power lower than the main path increases efficiency, makes load modulation more stable and improves linearity performance. The same consideration can be found in [12] and [16].
[12] P. H. Pednekar, E. Berry, and T. W. Barton, “RF-Input Load Modulated Balanced Amplifier With Octave Bandwidth,” IEEE Trans Microw Theory Tech, vol. 65, no. 12, pp. 5181–5191, 2017, doi: 10.1109/TMTT.2017.2748123.
[16] P. H. Pednekar, “Advanced Load Modulated Power Amplifier Architectures,” Doctoral Thesis, Faculty of the Graduate School, University of Colorado at Boulder, Colorado, United States, 2019.
Reviewer#2, Concern # 5: It is somewhat confusing that the authors claim to design a single-RF input system while presenting a classical two-input LMBA stage. Please clarify which results correspond to standalone LMBA operation (thus leveraging the full flexibility of the two inputs) and which are constrained to the single-RF input case. Additionally, it would be helpful to better describe how the control signal is chosen and managed in this scenario.
Author response: In our study, the measurement results of the balanced amplifier topology and the Single RF-Input LMBA architecture were obtained by adding a control signal to the balanced topology (this control signal was obtained by generating the control signal from the input signal, not from outside). The measurement results of these two architectures were compared.
No work has been done on the classical two-input LMBA architecture. Therefore, there are no measurement results for this architecture.
Author action: We further clarified the topology in our research as below by adding two paragraphs in “Discussion” section ,
Concerning the management of the control signal, the input signal power of the system is adjusted for maximum output power, 3db low output power, 6db low output power for each frequency, the phase of the control arm is changed by changing the control voltage (The load impedance of the transistors in the main arm is changed). Frequency / Input power / Output power / Control Voltage Value information is stored in a Look-Up-Table for Adaptive Load Modulation.
In our study, the measurement results of the balanced amplifier topology and the Single RF-Input LMBA architecture were obtained by adding a control signal to the balanced topology (this control signal was obtained by generating the control signal from the input signal, not from outside). The measurement results of these two architectures were compared.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe revised version has added some new references to justify the comparing results. Although revised, some redundancies can still be found. It is strongly suggested that the authors should take more effort to compress possible redundancies.
Detailed comments are as follows.
1. p3. The listed references should be integrated into less paragraphs and re-organized in group rather than individually, with each paragraph focusing on one similar issue.
2. In describing the control path, powerful or strong are not technical terms. If you mean high power, directly use high power.
3. Still too long a conclusion. At the most, it should not exceed two paragaphs.
4. In the text, please use dB rather than db.
Author Response
Reviewer # 1
Comments to Author :
The revised version has added some new references to justify the comparing results. Although revised, some redundancies can still be found. It is strongly suggested that the authors should take more effort to compress possible redundancies.
Detailed comments are as follows.
Author response: We checked the manuscript once more again and we realized that there are some sentences in the abstract and in the Introduction section which are very similar to each other. In this respect , we reduced the redundancies as much as possible .
Author action: We updated the manuscript accordingly . For example ; the sentence below is the first two sentences both in the Abstract and in the Introduction.” . Therefore, we removed the sentence from the Introduction.
“Recent advances in wireless communications have supported increased data rates. For this purpose, complex modulation techniques with high peak-to-average power ratios (PAR) have been introduced. “
Reviewer#1, Concern # 1:
p3. The listed references should be integrated into less paragraphs and re-organized in group rather than individually, with each paragraph focusing on one similar issue.
Author response: We agree with the reviewer’ concern.
Author action: We updated the manuscript accordingly as below.
“Several studies have focused on the performance of LMBA in different frequency bands. Quaglia and Cripps [13] achieved a maximum output power between 63W and 78W in the 1.7 GHz – 2.5 GHz range.
Another important research direction has been the introduction of RF-Input LMBA architectures, which eliminate the need for an additional control signal. Pednekar and Barton [14] proposed an RF-Input LMBA configuration where the control signal is synthesized from the input signal, achieving 63.2% PAE at 41.7 dBm output power and 47.1% PAE at 6 dB output back-off in the 700-850 MHz range. In their subsequent work, Pednekar et al. [15] extended this approach to a broader frequency range (1.8-3.8 GHz), reporting efficiencies of 37%-59% at 44 dBm output power and 29%-45% at 6 dB output back-off. Their theoretical analysis of RF-Input LMBA was later refined and validated with prototype fabrication [16], demonstrating 60% PAE at 45.6 dBm output power at 2.4 GHz and 50% PAE at 6 dB output back-off.
Further improvements to LMBA architectures have been explored through circuit enhancements. Cao et al. [17] integrated a reconfigurable phase-shifting circuit in the control path, achieving 69% efficiency at 43 dBm output power at 2.4 GHz, with efficiency remaining above 50% up to 12 dB output back-off. Aras [18] presented an analytical model predicting LMBA efficiency and linearity, and his fabricated design achieved 53% efficiency at 37.5 dBm output power at 1.7 GHz, with 47% efficiency at 6 dB output back-off.
Jieen Xie et al. [19] proposed a novel three-stage LMBA using asymmetric coupling and a non-Zâ‚€ matched load to expand the OBO range. In this study, an output power of 42-44.4 dBm was achieved in the frequency range of 1.8-2.05 GHz. At these power levels, drain efficiencies of 48.2%-63.2% were obtained, while efficiencies of 50.8%-59.5% were achieved in the 7.5 dB output back-off (OBO) region.
In another study by Long Ding and Jing Xia [20], optimizes the output matching network (OMN) of the amplifier to enable wideband operation, and applies it to a symmetrical load-modulated balanced amplifier (SLMBA). Saturation output power was measured as 43.7-44.3 dBm at frequencies of 1.4-2.8 GHz. This power 64.6-70.5% efficiency was obtained at 64.6-70.5% levels and 44.9-50.4% at 10dB OBO.”
Reviewer#1, Concern # 2: In describing the control path, powerful or strong are not technical terms. If you mean high power, directly use high power.
Author response: We agree with the reviewer’ concern.
Author action: We updated the manuscript accordingly as below.
“The purpose of the control path is to increase the load impedance of the main path when the output power is low so that it can operate with higher efficiency. If the control path is of high saturation power , the load impedance of the main path may change too much and the efficiency gain may decrease. For this reason, the control path is usually chosen to have less saturation power than the main path. If the control path is of high power, it may create an aggressive effect during load modulation, which may adversely affect the linearity performance of the system.
Reviewer#1, Concern # 3 : Still too long a conclusion. At the most, it should not exceed two paragaphs.
Author response: We agree with the reviewer.
Author action: We updated the “Conclusion section” as below and reduced 5 paragraphs into two paragraphs.
“In this paper, a Single RF-Input Load Modulated Balanced Amplifier has been designed and fabricated. The amplifier was tested and measured by using calibrated RF measurement devices at RFTR Elektronik A.Åž. facilities. The measurements showed that 47 dBm (50W) output power, 60.1%-63.3% drain efficiency at maximum output power and 40.5%-46.8% drain efficiency at 6 dB output back-off were achieved in the frequency range of 1.7 GHz – 1.9 GHz. The LMBA measurement results were compared with conventionally designed balanced amplifiers without load modulation. With the LMBA configuration, it was measured that the efficiency was increased by 12.4% - 20% at maximum output power and by 16.7% - 23.4% at 6dB output back-off in the same frequency range.
Noise performance is an important factor for an amplifier. In our LMBA study, our main focus was to increase the efficiency both at maximum power and at low output power. We wanted to show that we could do this without reducing the system gain. We consider the importance of noise performance measurement as an important issue. Therefore, we strongly recommend that it be taken into account in detail as a further study. Furthermore, as a follow-up study, it is proposed to design and compare LMBAs with a similar output power level and octave bandwidth.”
”Reviewer#1, Concern # 4 :
In the text, please use dB rather than db
Author response: We agree with the reviewer’ concern.
Author action: We corrected the mistake accordingly.
Dear Reviewer , Thank you very much for your time and effort to provide excellent feedback for our manuscript. Thanks to your feedback, We think that our article is now in a very good condition compared to the previous version.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have addressed my concerns, and I have no further questions.
Author Response
Dear Reviewer , Thank you very much for your time and effort to provide excellent feedback for our manuscript. Thanks to your feedback, We think that our article is now in a very good condition compared to the previous version.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have replied to the comments.
Author Response
Dear Reviewer , Thank you very much for your time and effort to provide excellent feedback for our manuscript. Thanks to your feedback, We think that our article is now in a very good condition compared to the previous version.
