Broadband Dual-Polarized 2 × 2 MIMO Antenna for a 5G Wireless Communication System
Round 1
Reviewer 1 Report
In this paper, the authors propose the use of an antenna for 5G communications in the sub-6GHz band. Although the results of the paper looks correct, the innovation is very limited. The theory of MIMO antennas has been already developed. The two antennas are classical microstrip antennas fed with a coaxial cable. There is nothing new either in the MIMO conception or in the antenna design. Therefore, I do not believe that this paper should be published for the lack of innovation.
Author Response
feedback on our manuscript. We are grateful to the you for your insightful comments on our paper. We have been able to incorporate changes to reflect most of the suggestions provided.
Once again, thank you for your time to review our manuscript and valuable feedback. Your comments were very helpful to our manuscript.
Thank you for your kindness.
Point 1: In this paper, the authors propose the use of an antenna for 5G communications in the sub-6GHz band. Although the results of the paper looks correct, the innovation is very limited. The theory of MIMO antennas has been already developed. The two antennas are classical microstrip antennas fed with a coaxial cable. There is nothing new either in the MIMO conception or in the antenna design. Therefore, I do not believe that this paper should be published for the lack of innovation.
Response 1: Thank you for pointing out that innovation is very limited. We added more detailed of proposed antenna. Also, we improve our manuscript reference. Thank you for your comment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper proposes an antenna design for broadband MIMO applications based on circular monopole antennas and rectangular dipoles.
- The main concern about the paper is the lack of simulated results, these are essential for cross-validation and to reduce the chances of measurement errors. The authors should include the simulated results from a commercial/open-source simulator.
- It is unclear what the benefit of the hybrid monopole/dipole structure is compared to conventional 2x2 MIMO antennas. This has to be justified in the introduction, reflecting on the limitations of recent MIMO antennas
- How is the ground plane connected to the two radiators of the dipole? i.e. is this an electrical ground connected to the feed or an unconnected reflector. Please revise Figuer 8 to show the ground connections (or specify the lack-of)
-Please consider taking a clearer photograph of the antenna which shows all the ground connections as well as the monopole.
-Polarized radiation properties are extremely important in MIMO systems where the co/cross-pol. isolation is essential for a good performance. However, the presented results appear to only show (measured) co-pol. patterns. It is impossible to evaluate a "dual-polarized" antenna, as stated in the title and the main contributions without cross-polarization date. Please present both the measurements and simulations of the cross-polarization.
-In the pattern plots, it will be useful to specify the coordinates of each plane (e.g. XY/XZ planes) instead of solely stating the E/H-plane, due to the multiple ports and polarizations in the antenna.
- As the antenna is quite large, please include the electrical size (normalized to the free space wavelength) in Table 1, including the clearance between the different elements.
- Several recent works have presented 4-port MIMO antennas with polarization diversity, comparable performance, and smaller size, with better designs which include shared radiators while maintaining high isolation. Please consider and comment on the following (among others)
K. R. Jha, Z. A. P. Jibran, C. Singh and S. K. Sharma, "4-port MIMO antenna using common radiator on a flexible substrate for sub-1GHz sub-6GHz 5G NR and Wi-Fi 6 applications", IEEE Open J. Antennas Propag., vol. 2, pp. 689-701, 2021.
M. S. Khan, A. Iftikhar, R. M. Shubair, A. Capobianco, B. D. Braaten and D. E. Anagnostou, "Eight-Element Compact UWB-MIMO/Diversity Antenna With WLAN Band Rejection for 3G/4G/5G Communications," in IEEE Open Journal of Antennas and Propagation, vol. 1, pp. 196-206, 2020, doi: 10.1109/OJAP.2020.2991522.
M. Wagih, G. S. Hilton, A. S. Weddell and S. Beeby, "Dual-Polarized Wearable Antenna/Rectenna for Full-Duplex and MIMO Simultaneous Wireless Information and Power Transfer (SWIPT)," in IEEE Open Journal of Antennas and Propagation, vol. 2, pp. 844-857, 2021, doi: 10.1109/OJAP.2021.3098939.
S. S. Jehangir and M. S. Sharawi, "A Compact Single-Layer Four-Port Orthogonally Polarized Yagi-Like MIMO Antenna System," in IEEE Transactions on Antennas and Propagation, vol. 68, no. 8, pp. 6372-6377, Aug. 2020, doi: 10.1109/TAP.2020.2969810.
- Please revise the writing of the paper to correct grammatical and typographical errors.
Author Response
Response to Reviewer 2 Comments
We appreciate the time and effort that you have dedicated to providing your valuable feedback on our manuscript. We are grateful to the you for your insightful comments on our paper. We have been able to incorporate changes to reflect most of the suggestions provided.
Once again, thank you for your time to review our manuscript and valuable feedback. Your comments were very helpful to our manuscript.
Thank you for your kindness.
Point 1: The main concern about the paper is the lack of simulated results, these are essential for cross-validation and to reduce the chances of measurement errors. The authors should include the simulated results from a commercial/open-source simulator.
Response 1: Thank you for pointing out that our paper is lack of simulated results. We agree with your maim concern. So we use Ansys HFSS 21 R1 to simulate our proposed antenna. Also, we added simulated results such as S11, S21, ECC, radiation pattern in our revised manuscript. Thank you for your comment.
Point 2: It is unclear what the benefit of the hybrid monopole/dipole structure is compared to conventional 2x2 MIMO antennas. This has to be justified in the introduction, reflecting on the limitations of recent MIMO antennas
Response 2: Thank you for pointing out that we should say clear about benefit of the hybrid monopole/dipole structure compared to conventional MIMO antenna. We agree with your comment. Conventional MIMO antenna for 5G wireless communication is cross dipole structure or patch antenna. However, it is difficult to achieve bandwidth over 100% using the conventional crossed-dipole MIMO antenna. The conventional structures for which it is difficult to achieve broad-band characteristics cannot cover all 5G bands in the current situation of expanding 5G band. Also crossed-dipole antennas have little space between the ports. The lack of space between the ports makes difficult to use relatively big N-type connector which widely use wireless industry and wireless module. However, hybrid monopole/dipole structure gives sufficient space between the ports. It makes easier to use relatively big N-type connector and connect antenna with wireless module. We add this explanation in page 1, Introduction. Thank you for your comment.
Point 3: How is the ground plane connected to the two radiators of the dipole? i.e. is this an electrical ground connected to the feed or an unconnected reflector. Please revise Figuer 8 to show the ground connections (or specify the lack-of)
Response 3: Thank you for pointing out about ground plane connected. The ground plane is electrical ground connected to monopole antenna. However, the ground plane is unconnected to modified dipole antenna and it acts as reflector to dipole. To clear this issue, we add explanation at page 7, section 3 2X2 MIMO Antenna. Also we revise figure 8. Thank you for your comment.
Point 4: Please consider taking a clearer photograph of the antenna which shows all the ground connections as well as the monopole.
Response 4: Thank you for pointing out we need clear photograph of the antenna. We agree with your comment. We added side view of photograph of the antenna at figure.9. Thank you for your comment.
Point 5: Polarized radiation properties are extremely important in MIMO systems where the co/cross-pol. isolation is essential for a good performance. However, the presented results appear to only show (measured) co-pol. patterns. It is impossible to evaluate a "dual-polarized" antenna, as stated in the title and the main contributions without cross-polarization date. Please present both the measurements and simulations of the cross-polarization.
Response 5: Thank you for pointing out we need both cross-pol and co-pol simulated and measured radiation pattern. We agree with your comment. We added simulated and measured circular monopole and modified rectangular dipole antenna cross-pol and co-pol radiation pattern at revised manuscript fig. 14, 15, 16 and 17. Thank you for your comment.
Point 6: In the pattern plots, it will be useful to specify the coordinates of each plane (e.g. XY/XZ planes) instead of solely stating the E/H-plane, due to the multiple ports and polarizations in the antenna.
Response 6: Thank you for pointing out we should use specific coordinates of each plane. We agree with your comment. We added specific coordinates of each plane (XY/XZ/YZ planes). You can see it at revised manuscript fig. 14, 15, 16 and 17. Thank you for your comment.
Point 7: As the antenna is quite large, please include the electrical size (normalized to the free space wavelength) in Table 1, including the clearance between the different elements.
Response 7: Thank you for pointing out about antenna’s electrical size. We agree with your comment. We added antenna electrical size at Table 1. And each antenna electrical size is calculated by lowest operating frequency of antenna. Thank you for your comment.
Point 8: Several recent works have presented 4-port MIMO antennas with polarization diversity, comparable performance, and smaller size, with better designs which include shared radiators while maintaining high isolation. Please consider and comment on the following (among others)
Response 8: Thank you for pointing out recent works of MIMO antennas with shared radiators and gave us related research. And we read and study related manuscript. MIMO antennas with shared radiator have small size, high isolation and low ECC. However, they are hard to achieve wide impedance bandwidth more than 100%. So, for wide impedance bandwidth (more than 100%) we choose monopole and dipole hybrid structure. We added this explanation at page 2, Introduction. Thank you for your comment.
Point 9: Please revise the writing of the paper to correct grammatical and typographical errors.
Response 9: Thank you for pointing out that we should correct grammatical and typographical errors. We agree with your comment. We revise the writing of the paper to correct grammatical and typographical errors with Editage. Thank you for your comment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Authors in this research work have designed and investigated a broadband dual-polarized 2×2 MIMO antenna for application in 5G wireless communication systems, comprising two vertically polarized circular monopole antennas, two horizontally polarized modified rectangular dipole antennas, and a ground plane. The idea and concept of the paper are interesting, and its promising results have been experimentally validated. The proposed design validity has been approved by providing a fair comparison with state-of-the-art literature. As resultant, the proposed research art seems to be attractive for scholars in the antenna community. However, before final recommendation for its consideration its organization needs to be improved and the following comments should be carefully addressed to improve the quality of this paper.
1) Please add the average radiation efficiency value besides the radiation gain in the abstract section.
2) The design process of the proposed 2X2 MIMO antenna should be briefly discussed in the abstract section as well.
3) In the introduction section authors are requested to add explanations about various mutual coupling suppression techniques applied in MIMO antennas along with proper references. In below there are appropriate suggestions.
"Low-Interacted Multiple Antenna Systems Based on Metasurface-Inspired Isolation Approach for MIMO Applications", Arab J Sci Eng (2021). https://doi.org/10.1007/s13369-021-05720-6.
“Study on Isolation and Radiation Behaviours of a 34×34 Array-Antennas Based on SIW and Metasurface Properties for Applications in Terahertz Band Over 125-300 GHz”, Optik, International Journal for Light and Electron Optics, Volume 206, March 2020, 163222.
“Wideband linear microstrip array antenna with high efficiency and low side lobe level” Int J RF Microw Comput Aided Eng. 2020;e22412, doi: 10.1002/mmce.22412.
"Isolation Enhancement of Densely Packed Array Antennas with Periodic MTM-Photonic Bandgap for SAR and MIMO Systems", IET Microwaves, Antennas & Propagation, Volume 14, Issue 3, February 2020, pp. 183 - 188.
"Miniaturized microstrip patch antenna with high inter‐port isolation for full duplex communication system", doi: 10.1002/mmce.22760.
Comprehensive Survey on "Various Decoupling Mechanisms with Focus on Metamaterial and Metasurface Principles Applicable to SAR and MIMO Antenna Systems"", IEEE Access, vol. 8, pp. 192965-193004, 2020, doi: 10.1109/ACCESS.2020.3032826.
"Surface Wave Reduction in Antenna Arrays Using Metasurface Inclusion for MIMO and SAR Systems", Radio Science, 54, 1067–1075, 2019.
“High efficiency X-band series-fed microstrip array antenna", Progress In Electromagnetics Research C, Vol. 105, 2020.
"Mutual-Coupling Isolation Using Embedded Metamaterial EM Bandgap Decoupling Slab for Densely Packed Array Antennas", IEEE Access, vol. 7, pp. 5182–51840, April 29, 2019.
"Antenna Fundamentals for Legacy Mobile Applications and Beyond"; Springer: Cham, Switzerland, 2017; pp. 1-659.
"Mutual Coupling Suppression Between Two Closely Placed Microstrip Patches Using EM-Bandgap Metamaterial Fractal Loading", IEEE Access, vol. 7, Page(s): 23606 – 23614, March 5, 2019.
"A Comprehensive Survey of "Metamaterial Transmission-Line Based Antennas: Design, Challenges, and Applications"", IEEE Access, vol. 8, pp. 144778-144808, 2020.
4) Why circular radiator has been used? Why not square or rectangular?
5) The proposed design seems complicated with large size. Please discuss these two issues in deep throughout the manuscript.
6) The quality of the figures can be improved.
7) Table 1 is an interesting table which can be extended by adding the abovementioned works. Besides that, the presented comparison can be more comprehensive by comparing the proposed work with prior arts in terms of: (i) design approach, (ii) design complexity, (iii) average isolation level, (iv) size of each single element antenna, and (v) edge-to-edge distance between the elements.
8) The reference section needs to be improved by a proper extension as per suggested above.
Author Response
Response to Reviewer 3 Comments
We appreciate the time and effort that you have dedicated to providing your valuable feedback on our manuscript. We are grateful to the you for your insightful comments on our paper. We have been able to incorporate changes to reflect most of the suggestions provided.
Once again, thank you for your time to review our manuscript and valuable feedback. Your comments were very helpful to our manuscript.
Thank you for your kindness.
Point 1: Please add the average radiation efficiency value besides the radiation gain in the abstract section.
Response 1: Thank you for pointing out average radiation efficiency values. We agree with your comment. We added average measured radiation efficiency value 87.19% besides the radiation gain at the bottom of abstract section. Thank you for your comment.
Point 2: The design process of the proposed 2X2 MIMO antenna should be briefly discussed in the abstract section as well.
Response 2: Thank you for pointing out we should briefly discuss design process of the proposed 2X2 MIMO antenna in the abstract section. We agree with your comment. We added design process and distance between each radiator in MIMO antenna in abstract section. Thank you for your comment.
Point 3: In the introduction section authors are requested to add explanations about various mutual coupling suppression techniques applied in MIMO antennas along with proper references. In below there are appropriate suggestions.
Response 3: Thank you for pointing out we need to add various mutual coupling suppression techniques. We agree with your comment. We read and study the mutual coupling suppression techniques research. We added various mutual coupling suppression techniques such as neutralization lines, defected ground structure, pin diode, varactor diode, electromagnetic bandgap decoupling structure, etc with references at page 2, section 1 Introduction. Thank you for your comment.
Point 4: Why circular radiator has been used? Why not square or rectangular?
Response 4: Thank you for pointing our why we use circular radiator. We use circular radiator for enhance bandwidth of monopole antenna. The impedance matching is easier with a circular radiator than in a square or rectangular radiator. Thank you for your comment.
Point 5: The proposed design seems complicated with large size. Please discuss these two issues in deep throughout the manuscript.
Response 5: Thank you for pointing out that proposed antenna design seems complicated with large size. We agree with your comment. MIMO antenna which shared radiator can achieve small size, easy design process. However, this design is hard to achieve impedance bandwidth over 100%. So we use monopole/dipole hybrid structure to achieve wide impedance bandwidth over 100%. Also The lack of space between the ports makes difficult to use relatively big N-type connector which widely use wireless industry and wireless module. However, hybrid monopole/dipole antenna structure gives sufficient space between the ports and it makes easier to use relatively big N-type connector and connect with wireless module. We added this explanation at page 1-2, section 1 Introduction with appropriate references and related works. Thank you for your comment.
Point 6: The quality of the figures can be improved.
Response 6: Thank you for pointing out our quality of figures. We agree with your comment. We try to improve our figure. We change radiation pattern figure at revised manuscript figure 14, 15, 16 and 17. Also we added EM simulation results and revised antenna photograph. Thank you for your comment.
Point 7: Table 1 is an interesting table which can be extended by adding the abovementioned works. Besides that, the presented comparison can be more comprehensive by comparing the proposed work with prior arts in terms of: (i) design approach, (ii) design complexity, (iii) average isolation level, (iv) size of each single element antenna, and (v) edge-to-edge distance between the elements.
Response 7: Thank you for pointing out Table 1. We agree with your comment. We added isolation level at table and electrical size of each antenna. We also added two more comparison study of MIMO antenna. You can see it at our revised manuscript Table 1. Thank you for your comment.
Point 8: The reference section needs to be improved by a proper extension as per suggested above.
Response 8: Thank you for pointing out that reference section needs to be improved. We agree with your comment. As using your kind suggestion of related study and the other paper, we improved our manuscript reference. Thank you for your comment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
My opinion about the paper did not change with the new version. The innovation is not clear for this reviewer. Research is not doing something that nobody did before, but to illustrate a general goal. There is no scientific goal in this paper.
In addition, the quality of the graphs is very poor. They do not have sufficient quality for a journal paper.
Author Response
Response to Reviewer 1 Comments
We appreciate the time and effort that you have dedicated to providing your valuable feedback on our manuscript. We are grateful to the you for your insightful comments on our paper. We have been able to incorporate changes to reflect most of the suggestions provided.
Once again, thank you for your time to review our manuscript and valuable feedback. Your comments were very helpful to our manuscript.
Thank you for your kindness.
Point 1: My opinion about the paper did not change with the new version. The innovation is not clear for this reviewer. Research is not doing something that nobody did before, but to illustrate a general goal. There is no scientific goal in this paper.
In addition, the quality of the graphs is very poor. They do not have sufficient quality for a journal paper.
Response 1: We reduce the size of the MIMO antenna by using hybrid structure. When we used four circular monopole antennas in this study to MIMO antenna. The total size of the antenna is 250mm x 250mm x 33.6mm. However, if we use hybrid structure with two circular monopole antennas and two modified dipole antennas, its total size is reduce to 242mm x 200m x 40mm with peak isolation of 15dB and impedance bandwidth of more than 100%. We combine simulated result and measured result into one figure. And we check English grammar with Editage.
Author Response File: Author Response.pdf
Reviewer 2 Report
Thanks to the authors for carefully following my comments. However, some issues relating to the presentation and the clarity of the results still arise. Please address the following comments in your manuscript:
- Please combine the simulated and measured results in a single graph for ease of interpretation and comparison, for example using dashed/solid lines for simulation/measurement, respectively. The manuscript is currently too long and hard to follow due to the repetition of the figures.
- In my previous question about the motivation behind the antenna design having two different elements (helical and dipoe) the authors responded with bandwidth being the main motivation. However, this isn't fully convincing as the four elements can be realized using a simple existing design such as the circular disc monopole, and will still achieve a bandwidth in excess of 50%. Most importantly, please specify why not use four similar elements and the performance gains by the proposed "hybrid" design
- As the antenna is dual-polarized, it is hard for the reader to follow on and fully-appreciate what co/cross-polarization means in each of the plots. I suggest using vertical/horizontal polarization, with respect to a coordinate axis defined alongside the antenna's dimensions, then specifying whether V or H is the co/x-pol. in each setup.
-Similar to the S11/VSWR, please included the simulated and measured co/cross-polarized patterns on the same plot, for ease of comparison and improved presentatio.
-The radiation efficiency has been added to the abstract but I can't find its discussion in the paper. Please clarify if this was simulated/measured, and if it was measured please clarify the efficiency measurement approach (e.g. if the total radiated power was used, or the gain-to-directivity ratio was used from a path-loss model).
- In line 80, only the real relative permittivity of FR4 was discussed, it is however widely known that FR4 is lossy and has a tan-delta>0.01. Was the tan-delta considered in the simulation? Similarly were the conductive losses included in the gain (and efficiency) simulations
- Please mention the simulator used (HFSS) in the manuscript main body, when discussing the simulations, to make the results more reproducible.
Author Response
Response to Reviewer 2 Comments
We appreciate the time and effort that you have dedicated to providing your valuable feedback on our manuscript again. Your comment about the figure and main motivation about the proposed MIMO antenna is grateful to us and it is helpful to improve quality of manuscript. We have been able to incorporate changes to reflect most of the suggestions provided.
Once again, thank you for your time to review our manuscript and valuable feedback. Your comments were very helpful to our manuscript.
Thank you for your kindness.
Point 1: Please combine the simulated and measured results in a single graph for ease of interpretation and comparison, for example using dashed/solid lines for simulation/measurement, respectively. The manuscript is currently too long and hard to follow due to the repetition of the figures.
Response 1: Thank you for pointing out we should combine simulated and measured data into one graph. We agree with your point, and we combine simulated and measured data such as S11, S21, VSWR in to one graph.
Point 2: In my previous question about the motivation behind the antenna design having two different elements (helical and dipoe) the authors responded with bandwidth being the main motivation. However, this isn't fully convincing as the four elements can be realized using a simple existing design such as the circular disc monopole, and will still achieve a bandwidth in excess of 50%. Most importantly, please specify why not use four similar elements and the performance gains by the proposed "hybrid" design
Response 2: Thank you for pointing out we should clear that why we use two circular monopole antennas and two dipole antennas. If we used four circular monopole antennas used in this study, we can achieve bandwidth in excess of 100%, however the size of the MIMO antenna with isolation under 15dB should be 250mm x 250mm x 34.6 mm. This size is relatively big. So to reduce the total size of MIMO antenna we used two circular monopole antennas and two dipole antennas. We added the simulated result of the MIMO antenna with four circular monopole antennas used in this study at the revised manuscript figure 7, 8 and 9. Also we added discussion about it at page 5 and 6.
Point 3: As the antenna is dual-polarized, it is hard for the reader to follow on and fully-appreciate what co/cross-polarization means in each of the plots. I suggest using vertical/horizontal polarization, with respect to a coordinate axis defined alongside the antenna's dimensions, then specifying whether V or H is the co/x-pol. in each setup.
Response 3: Thank you for pointing out that we should use vertical/horizontal polarization. We agree with your comment. We change co/cross-pol to vertical/horizontal-pol, also we specified whether V or H is the co/x-pol in each set up. You can see it at page 10 and 11.
Point 4: Similar to the S11/VSWR, please included the simulated and measured co/cross-polarized patterns on the same plot, for ease of comparison and improved presentatio.
Response 4: Thank you for pointing out we should include the simulated and measured co/cross-pol on the same plot. We agree with your point, and we included the simulated and measured co/cross-pol patterns on the same plot. You can see it at Figure 16 and 17.
Point 5: The radiation efficiency has been added to the abstract but I can't find its discussion in the paper. Please clarify if this was simulated/measured, and if it was measured please clarify the efficiency measurement approach (e.g. if the total radiated power was used, or the gain-to-directivity ratio was used from a path-loss model).
Response 5: Thank you for pointing out we should clarify it was measured or simulated radiation efficiency. It is measured radiation efficiency and it was gain-to-directivity ratio. Also we added it in revised manuscript. You can see it at page 9.
Point 6: In line 80, only the real relative permittivity of FR4 was discussed, it is however widely known that FR4 is lossy and has a tan-delta>0.01. Was the tan-delta considered in the simulation? Similarly were the conductive losses included in the gain (and efficiency) simulations
Response 6: Thank you for your comment. We considered FR4 loss tangent = 0.02 and copper conductivity 58000000 S/m into simulation. Also, the conductive losses is included in the simulated gain. We added fr4 loss tangent value at line 80.
Point 7: Please mention the simulator used (HFSS) in the manuscript main body, when discussing the simulations, to make the results more reproducible.
Response 7: Thank you for pointing out we should mention the simulator. we mentioned that EM simulation tool Ansys HFSS was used to simulate at revised manuscript line 85.
Author Response File: Author Response.pdf
Round 3
Reviewer 1 Report
The answer from the authors does not respond to my original question. I continue with my opinion that this work should not be accepted for publication.
Reviewer 2 Report
Thanks again to the authors for carefully revising their manuscript - I think the paper can be recommended for publication. Please consider revising the writing of the paper to clear all grammatical and spelling issues.
