A 5-Bit X-Band GaN HEMT-Based Phase Shifter
Round 1
Reviewer 1 Report
The paper does not contains novel aspects since the design is rather conventional.
In any of the sections describing the different phase shifting, explicit citations to literature are needed, to help readers to find the theoretical handle and to better understand the implemented idea.
The effect of the switches parasitics in term of losses and phase shift is completely ignored. The choice of the dimension of the switches should be addressed since the power is flowing through them, and their impact on distortion and power handling capabilities is important.
The only mention to shift is in this sentence''Two
single-pole/double-throw switches, which are located external to the filters, are used to select the high- or low-pass paths". The sentence is above all misleading since the meaning of "external to the filters" is not clear: switches are hopefully on board of the MMIC.
The results on Fig 8 does not seems good for the high phase curves. For example in the 360 deg a phase error of more than 30 deg is shown. The only reported RMS error is flattening/averaging this figure of merit, some absolute and punctual errors should be reported and not only the RMS.
Some comparison with similar works, for example in terms of bandwidth, should be exhibited to locate the present work in the overall paramount.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript demonstrated a 5-bit X-band GaN HEMT-based phased shifter monolithic microwave integrated circuit. The reviewer believes that this manuscript has many weaknesses such as lacks novelty, short of discussion/explanation, and relatively poor results compared to the device performances in the reference [13] (Sun, P.; Liu, H.; Zhang, Z.; Geng, M.; Zhang, R.; Luo, W. X-band 5-bit MMIC phase shifter with GaN HEMT technology. Solid-State Electronics 2017, 136, 18-23.). For example, the fabricated phase shifter showed a phase error of 6.23º, which is one of very important performances of phase shifter, compared to that of the reference device (5.5º). Therefore, the reviewer believed that this manuscript cannot be accepted in Electronics. The authors should clearly state the novelty/difference of their device in terms of device characteristics.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
-5V, 8GHZ, 0V
-5 V, 8 GHZ, 0 V
Which one is correct? Unify and write correctly.
We have improved results for your design and recommend publishing after some modifications.
page 5: line 149 : inappropriate representation 45°-22.5°-90°-11.25°-180°
Modification is required.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
The article describes the design and physical realization of a 5-bit beamformer in 0.25 um AlGaN/GaN-on-SiC. The work is very timely and of wide interest given the need for high-power phased-array solutions for radar/communications. Please address the following comments:
- The authors should necessarily add a comparison table with other state-of-the-art beamformers, possibly in (but not limited to) similar GaN technologies.
- In the Introduction, the phrase 'The use of GaAs-based and silicon-based phase shifters is limited because of their poor linearity because of their small breakdown voltage although they have high integration [7-10].' is somehow misleading. Indeed, the reduced breakdown voltage is the main issue, but GaAs and silicon do not typically feature worse linearity than GaN in their operating range. Actually, GaN involves soft-compression and complex nonlinear behavior.
- In Fig. 4, the authors use the wording 'traveling wave' but isn't it the implementation of a transmission line? As from my understanding, 'traveling wave' is the description of a quantity, not to indicate a structure.
- The authors exploit integrated switches in their design. However, it has been shown (e.g., C. Florian et al. "Characterization and modeling of RF GaN switches accounting for trap-induced degradation under operating regimes." IEEE TMTT vol. 66 no. 12, 2018) that for this type of technology switches might show nonlinearity and, more importantly, long recovery time due to trapping effects. Could the authors comment on this aspect in the article? During the design, did the authors monitor the blocking voltages that switches have to withstand during the operation, as this impact the turn-on time and insertion loss?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I confirm that the novelty introduced by the paper is all considering limited.
However it is true that this shifter is on GaN, as it is also true that the authors answered properly to all my objections modifying the paper accordingly. Browsing also through the responses of the other reviewers too, it seems to me that this apply also to the other comments, but of course I will leave the other reviewers exhaustive comments on that.
Please double check for the possible typos still uncorrected
Reviewer 4 Report
I thank the authors for having replied to the comments.
