Millimeter-Wave Choke Ring Antenna with Broad HPBW and Low Cross-Polarization for 28 GHz Dosimetry Studies
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1. In Figure 2, the authors want to identify the spot size by intersecting the power density curve by the -0.5 dB line (blue line). However, the blue line is not located at -0.5 dB (it may be around -1.5 dB), Why?
2. The Caption of Figure 18 is wrong, please correct.
3. Why the authors get multiple resonances in the measured reflection coefficient (S11), while only two resonance s can be figured out in the HFSS simulation curve.
4. Could you emphasize more about the role of EM slots in cross polarization enhancement?
Author Response
Comment 1:
In Figure 2, the authors want to identify the spot size by intersecting the power density curve by the -0.5 dB line (blue line). However, the blue line is not located at -0.5 dB (it may be around -1.5 dB), Why?
Response 1:
Thank you for the comment. You are right in saying the position of the arrow is not indicative of the -0.5dB uniformity mark. This may have occurred due to rescaling of the graph, which is our blunder. The graph has been replaced with a different one showing the right arrow at the -0.5dB uniformity level. This replacement was easier since the picture is an example to illustrate the levels at which the spot size is calculated from a normalized power density profile curve.
Comment 2: The Caption of Figure 18 is wrong, please correct.
Response 2:
Thank you for the comment. The caption on Figure 18 has been corrected to reflect the curve illustrated. Caption reads: “Figure 18. Simulated and measured S11 curves of proposed CRHA”
Comment 3: Why the authors get multiple resonances in the measured reflection coefficient (S11), while only two resonances can be figured out in the HFSS simulation curve.
Response 3:
Thank you for the comments.
The ripples are a normal response of the measurement setup. As shown in Figure 16, the assembly includes a rectangular to circular waveguide attached to a rectangular waveguide to coaxial transition.
The two additional attachments were not included in the simulation setup as this was impractical. The normal impedance response of the transition and converter elements have multiple ripples as they operate in a wide bandwidth.
It was thus sufficient for the authors to have the impedance response of the complete setup operate under -20dB for the targeted bandwidth of 27.75 to 28.25 GHz.
This section of the manuscript has been updated to make this clearer.
The ripples in the measured results are a normal impedance response from the included attachments for measuring setup which were well captured by the large frequency sampling of the network analyzer. The two attachments as shown in Figure 16 are the cylindrical to rectangular waveguide transition and the waveguide/coaxial adapter. Also, the mismatch between the simulation and measurement can be attributed to the loss factor from the aforementioned attachments; both of which were not considered in the simulation setup.
Comment 4: Could you emphasize more about the role of EM slots in cross polarization enhancement?
Response 4:
Thank you. The authors have repositioned the sub-section 3.2 which gives a detailed method by which the slots suppress the cross-polarization in the radiator. This also includes the illustrations in figure 13.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors1. Both authors' affiliation is the same, why are 1 and 2 used for two authors?
2. The full name should be given when a short form appears the first time in the paper.
3. One short form can not be used to represent two items, samples under test (SUT) or surface-under-test (SUT).
4. Why the parameter specifications are set as the values in Table I should be explained.
5. Every variable in Equation 1 should be defined.
6. How is Figure 2 is obtained? What does "X,Y cordinate" mean?
7. In line 151, what is dBW？
8. In lines 182 & 183,there are a small h and a big H. Anything wrong here?
9. In Figure 4, psi is used, which is different from phi in Equation 6.
10. More remodeled parameters corresponding to Table I should be provided in Figure 5.
11. Can the authors explain "the single choke ring naturally achieved high coupling with the center horn ring" in line 247? What is the meaning of "coupling" here?
12. In lines 259 & 262, what are 13F and 12F?
13. In Figure 7, is the E-field in near field? Is there any relationship between the E-fieled and the 3D radiation pattern?
14. What are the sizes of the electromagnetic slots? Can the authors provide better drawing to show the slots?
15. For the current distribution in Fig. 13, the current directions should be shown.
16. The description from line 313 to 321 does not make sense.
17. In line 376, "The ripple in the measured results is mostly due to the large frequency samples used by the Network Analyzer (Figure 17b)." This does not make sense.
18. Is the author's name corrrect in Reference 16?
19. What kind of document is Reference 23? Is the author's name corrrect?
In general, the presentation of this paper is not clear enough for this review to better understand the work.
Fine.
Author Response
Comment 1. Both authors' affiliation is the same, why are 1 and 2 used for two authors?
Response 2
Thank you for the comment. This was a formatting error. Superscript 1 has been used for both authors.
Comment 2. The full name should be given when a short form appears the first time in the paper.
Comment 3. One short form can not be used to represent two items, samples under test (SUT) or surface-under-test (SUT).
Response 2, 3
Thank you. The term samples under test, found in section 1 has been renamed test samples to avoid the confusion created with surface under test (SUT).
The term surface under test first used in section 1 (line 67) has the proper abbreviation SUT.
Comment 4. Why the parameter specifications are set as the values in Table I should be explained.
Response 4.
Thank you. The values used in the specifications for the proposed RF applicator in Table I were partly obtained by imperial deductions from various reference papers; some of which were included in the manuscript. That is Ref. [8]-[10]. The details of such deductions were not in the scope of the present manuscript and was thus not included. Nonetheless and broadly speaking, the authors have included the following statements to provide some context on how the values were obtained.
Other factors that influenced the parameters were also based on economics of scale regarding the cost of building the chamber and some space constraints.
To design a compact in vitro dosimetry chamber measuring 100cm x 100cm and operating at 28GHz will require a specialized RF applicator, which is not available commercially. The compact chamber will require space for high frequency wave suppressants, ventilators, thermal cameras, positioners, etc which then leave a compact space for the RF applicator. Thus a 50 x 50 mm applicator is proposed. From the specified physical dimension of the radiator, more details on the values of Table I are elaborated in section 2.1. A detailed chamber specification has been outlined in [10].
Comment 5. Every variable in Equation 1 should be defined.
Response 5.
Thank you for the comment. Equation 1 has been redefined with all terms explained.
Comment 6. How is Figure 2 is obtained? What does "X, Y cordinate" mean?
Response 6.
The authors have elaborated the use of Figure 2 in the manuscript to illustrate a power density profile.
This statement was included as an explanation to Figure 2; in section 2.2.1
The power density profile example as shown in Figure 2 measures the concentration of the radiated power or the field intensity at a predefined illumination spot (S) on the SUT; which is usually at the center of the antenna.
Also, the graph has been replaced to better illustrate this explanation. However, the X, Y coordinate meant the horizontal positioning of the surface under test. Since the SUT is 3 dimensional, the X-Y will indicate the direction in which the spot size is calculated.
Comment 7. In line 151, what is dBW？
Response 7.
Thank you for the comment.
dBW is another expression for the unit of power (Watts) expressed in decibel and referenced to 1W. The authors did not see the need to explain a known power unit in the manuscript.
Comment 8. In lines 182 & 183, there are a small h and a big H. Anything wrong here?
Response 8.
This was a typo error. The correct letter is h, instead of H.
This has been corrected. Thank you.
Comment 9. In Figure 4, psi is used, which is different from phi in Equation 6.
Response 9.
Thank you for the correction. The symbol phi has been correctly used in equation 6 and its corresponding texts and in Figure 4.
Comment 10. More remodelled parameters corresponding to Table I should be provided in Figure 5.
Response 10.
The remodelled horn antennas shown in Figure 5 were used to illustrate the limitations of existing horn antennas for the purpose of obtaining wider HPBW. The authors had not included more details as they were referenced models from other researchers.
The authors have nonetheless heeded to your advice in adding more parameters to make the figure more holistic.
In addition to the gain and HPBW values, the authors have included the dimensions of the designs as well as the spot sizes in the graphs. The corresponding comments have also been included in section 3.0 (Antenna Design).
Thank you.
Comment 11. Can the authors explain "the single choke ring naturally achieved high coupling with the center horn ring" in line 247? What is the meaning of "coupling" here?
Response 11.
Thank you for the comments.
In this context, the term coupling refers to the interaction of the TEM wave of the horn antenna (center ring) with the second ring (otherwise known as a choke). Other researchers (Reference 12) use multiple of these chokes within the same design to achieve much broader beamwidth at the expense of gain degradation.
With the use of a single choke as in the proposed design, the electromagnetic waves from the center horn couples or interacts with the first choke much stronger than if successive chokes were attached.
The authors had built-up this thought process from the preceding paragraphs.
From line 248...
The depth of every successive choke is also chosen with the 180-degree phase shift. The beam coupling effect of the main beam and the successive chokes give rise to the sectoral beam. As the chokes increase, there is less coupling with the main beam, and thus a reduced gain.
In the design analysis with HFSS software [29], the single choke ring naturally achieved high coupling with the center horn ring.
Comment 12. In lines 259 & 262, what are 13F and 12F?
Response 12.
Thank you for the observation. The authors are equally puzzled by these texts within the manuscript. They seem to be errors from Microsoft word in the dynamic cross-referencing. These have been removed.
Thank you.
Comment 13. In Figure 7, is the E-field in near field? Is there any relationship between the E-fieled and the 3D radiation pattern?
Response 13.
Thank you. You are correct. The E-field shown in figure 7 is in the nearfield region of the antenna at 150mm.
Generally speaking, there is a correlation between the nearfield region of an antenna and the farfield pattern. In that a plane wave propagation is gradually formed from the radiative nearfield region into the farfield region, thus creating the shape of a radiation as shown in Figure 7. The proposed radiator has a constant plane wave property in the radiative NF region, which is illustrated in figure 24 by the impedance curve.
However, the authors were not intending to show this correlation in Figure 7. Rather to illustrate how the E-field data is obtained at a given exposure distance in a simulation model.
Comment 14. What are the sizes of the electromagnetic slots? Can the authors provide better drawing to show the slots?
Response 14.
Thank you.
To keep the appearance of the diagrams clean and not cluttered with dimensions, the authors are confident the slots can be re-created by readers using the dimensions shown. Sufficient detail on the proposed radiator dimensions including the slots in Figure 12 have been presented. The fabricated photos of Figure 16 also gives more physical details about the slot.
Comment 15. For the current distribution in Fig. 13, the current directions should be shown.
Response 15.
Thank you for the comments.
The authors had used the heat map to show the concentration of the fields within the choke structure in the presence and absence of the electromagnetic slots in Figure 13.
Although the use of arrows is equally useful in displaying current direction and concentration, the authors are of the opinion that, a contoured heat map better explains the usefulness of the proposed slots.
Comment 16. The description from line 313 to 321 does not make sense.
Response 16.
Thank you.
The authors have described the design inspiration behind the use of the proposed slot structure in the horn antenna. In that, from observing the current distribution within the antenna’s choke (space between the first and second ring) shown in Figure 13a, the authors had the idea to introduce these slots to alter the current distribution within the choke.
Another explanation
This slot structure was essential in reducing the cross-polarization of the horn by ensuring a more linearized propagation. Without the slots as shown in Figures 13a, the current concentration is angled at 45deg with a reduced linearity of the main beam. Adding the slots ensures a more linearized propagation and current distribution.
The authors will appreciate a specific comment as to what does not make sense in the paragraph.
Comment 17. In line 376, "The ripple in the measured results is mostly due to the large frequency samples used by the Network Analyzer (Figure 17b)." This does not make sense.
Response 17.
Thank you for the comment.
The ripples are a normal response of the measurement setup. As shown in Figure 16, the assembly includes a rectangular to circular waveguide attached to a rectangular waveguide to coaxial transition.
The two additional attachments were not included in the simulation setup as this was impractical. The normal impedance response of the transition and converter elements have multiple ripples as they operate in a wide bandwidth.
It was thus sufficient for the authors to have the impedance response of the complete setup operate under -20dB for the targeted bandwidth of 27.75 to 28.25 GHz.
We have updated this section of the manuscript to make this clearer.
The ripples in the measured results are a normal impedance response from the included attachments for measuring setup which were well captured by the large frequency sampling of the network analyzer. The two attachments as shown in Figure 16 are the cylindrical to rectangular waveguide transition and the waveguide/coaxial adapter. Also, the mismatch between the simulation and measurement can be attributed to the loss factor from the aforementioned attachments; both of which were not considered in the simulation setup.
Comment 18. Is the author's name corrrect in Reference 16?
Response 18.
The author names have been corrected. The reference number is now 17.
- V. Boriskin, M. Zhadobov, D. Diedhiou and R. Sauleau, "Advanced feed for a 60-GHz exposure chamber," in EuCAP, The Hague, 2014.
Comment 19. What kind of document is Reference 23? Is the author's name corrrect?
Response 19.
Reference 23 has been correctly formatted.
W. Rosenthal, L. Birenbaum, I. T. Kaplan, W. Metlay, W. Z. Snyder and M. M. Zaret, "Effects of 35 and 107 GHz CW Microwaves on the Rabbit Eye," in Proc. USNC/URSI Annual Meeting, 1976.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsCongratulations on this research. It is a very interesting paper.
Please find below few comments/ questions:
SAR abbreviation was explained right after (1). No need to re-do it Section 2.2.2
Same remark applies for SUT abbreviation as well.
In (1) H (italic) is used for magnetic peak phasor, while in Figure 4 H represents the distance – maybe another notation would bring more clarity.
In Section 3.1, what ‘distance13F’ means ? - ‘The E-field magnitude at a 150 mm exposure distance13F is also shown in Figure 7.’ Same for condition12F - ‘boundary condition12F in HFSS’
Can you please explain this sentence ‘The stem of the antenna is reduced from 19.3mm (Figure 6) to 10.2mm (Figure 13)’? How was this reduction made and based on what input?
Author Response
Comment 1. SAR abbreviation was explained right after (1). No need to re-do it Section 2.2.2. Same remark applies for SUT abbreviation as well.
Response 1.
Thank you for the comments.
You are right. The authors have removed the abbreviation repeats within the manuscript, including the SUT and SAR.
Comment 2. In (1) H (italic) is used for magnetic peak phasor, while in Figure 4 H represents the distance – maybe another notation would bring more clarity.
Response 2.
Thank you for the observation and comment. The authors have changed the exposure distance to letter h; to distinguish it from the magnetic symbol H. All corresponding texts, equations and figures have been changed accordingly.
Comment 3. In Section 3.1, what ‘distance13F’ means ? - ‘The E-field magnitude at a 150 mm exposure distance13F is also shown in Figure 7.’ Same for condition12F - ‘boundary condition12F in HFSS’
Response 3.
Thank you for the observation. The authors are equally puzzled by these texts within the manuscript. They seem to be errors from Microsoft word in the dynamic cross-referencing. These have been removed.
Thank you.
Comment 4. Can you please explain this sentence ‘The stem of the antenna is reduced from 19.3mm (Figure 6) to 10.2mm (Figure 13)’? How was this reduction made and based on what input?
Response 4.
Thank you for the comment.
The reduction of the antenna’s stem (in simulation model) was made from an approximate wavelength at 28GHz (free space wavelength at 28GHz = 10.71mm). The authors intended to keep the length of the conical horn in multiples of this wavelength. (ie Fig. 12 has total length of 22.3mm (≈ 2λ) including the flange. The previous value in Fig. 6 was 32mm ((≈ 3λ)
The authors have therefore included this statement in the manuscript to make this point clearer.
This length reduction for horn antennas does not reduce the performance; provided the transition distance is in multiples of λ at 28GHz.
Author Response File: Author Response.pdf
