Methodology for Improving Scanning Performance Loading an Array Element with a 3D All-Metal WAIM

Round 1

Reviewer 1 Report

The authors present the characterization of 3D all-metal unit-cell for oblique incidence, which has its practical application. The main contribution is clearly explained, and the paper is well organized. There are several minor factors the authors need to consider as below:

1.       Line 110, there is non English word.  

2.       Line 114, the extra (2) needed to be removed.

Author Response

Thank you so much for your careful review and your corrections.

1. Line 110, there is non English word. 

Correction done, the reference to the equation has been rewritten.

2. Line 114, the extra (2) needed to be removed.

Correction done, the (2) has been specified to be the reference to the equation (2).

Author Response File: Author Response.pdf

Reviewer 2 Report

The article "Methodology for improving scanning performance loading an array element with a 3D all-metal WAIM" is showing some merit with respect to design aspects and analysis. Need few modifications to process to next level

1) The abstract does not convey the novelty of the work in technical representation. Need numerical result-oriented and outcome-based presentation.

2) The array antenna performance characteristics like radiation and efficiency in three-dimensional representation is missing in the article

3) No comparative analysis with literature is presented before the conclusion section in the form of a table for understanding the novelty and specialty of the proposed model   

The suggested modifications will enhance the quality of the article and increase the readability. 

Author Response

Thank you so much for your careful review and your suggestions.

1) The abstract does not convey the novelty of the work in technical representation. Need numerical result-oriented and outcome-based presentation.

The abstract has been modified to show the novelty of this publication by introducing numerical results.

2) The array antenna performance characteristics like radiation and efficiency in three-dimensional representation is missing in the article

The reviewer is right: performance at the array antenna level is ideal to assess the quality of a real finite array. In this case, theoretical radiation and efficiency have to be compared to measured performance. However, in this paper, we stay at the level of an ideal infinite array. Then, the active reflection coefficient is the classical figure of merit to assess the benefit brought by a WAIM to match the antenna on a wide angular sector. Giving a radiation pattern would be possible assuming truncation of the theoretical infinite aperture but it would not bring any further information (only the magnitude would differ when comparing the radiation of the naked array and that of the array + WAIM, the difference in magnitude being directly correlated with the shown difference in active reflection coefficient).

Indeed, what the reviewer suggests will be the objective of our next study: a real finite array will be designed together with its WAIM and it will be characterized both theoretically and experimentally.

3) No comparative analysis with literature is presented before the conclusion section in the form of a table for understanding the novelty and specialty of the proposed model   

The following comparative table has been introduced in the paper.

	Matching range improvement	Dual scanning plane performance	WAIM type
[25]	- H-plane improved up to Θ=56° - E-plane already matched at  Θ=56° (almost unmodified)	Affects mostly the H-plane.	Single dielectric layer
[27]	- H-plane improved at Θ=70° from  to . - E-plane already matched at Θ=70°.	Affects mostly the H-plane.
[28]	- H-plane scans up to Θ=50°. - E-plane scans up to Θ=60°. No results shown without WAIM.	No information.
[33]	- H-plane is matched up to Θ=55°. - E-plane is not shown.	E-plane is not shown	Single layer metamaterial
[29]	- H-plane improved from Θ=52° to Θ=65°. - D-plane improved from Θ=62° to Θ=81°. - E-plane does not vary.	Affects mostly the H- and D-plane.
[30]	- . - . - . Without WAIM the antenna is unmatched.	Affects the 3 scanning planes.
[35]	Compensates mismatching produced by back reflector. - H-plane up to - E-plane up to	Affects the 2 scanning planes.	Multilayer metamaterial
[36]	- Scanning up to (not specifying the scanning plane). - Improving the gain of the antenna between 3 to 5 dB.	No information.
[37]	- H-plane improved up to - E-plane improved up to	Affects 2 planes for 1 polarization.	3D WAIM (dielectric + metal)
Loaded TEM unit-cell (This work)	- H-plane improved up to - E-plane degraded.	Affects 2 planes for 1 polarization.	3D WAIM (all-metal)

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors utilize a 3D unit-cell topology to achieve wide angle impedance matching with help from an equivalent circuit. The reflection magnitude and phase are represented as functions of operational frequency for various incidence angles. The results from simulation and semi-analytical model are in good agreement each other. Both polarizations are considered.

The article is interesting but several weak points prevent it from being publishable at MDPI Electronics. In particular:

(A) What is the advantage of the presented structure against other competing structures [1,2]?

(B) In-between circuit modeling and full-wave simulations, there are more rigorous techniques like mode matching. The authors should discuss this approach in treating the considered problem [3,4].

(C) More details on the way they optimized the designs are required. How the result modify if both polarizations are taken into account simultaneously. Wide-angle designs should be also polarization-insensitive.

(D) The authors should mention the possibility of incorporating active structures towards achieving their aim [5,6].

 

[1] Papadimopoulos et al., Wide-angle absorption of visible light from simple bilayers, Applied Optics, 2017.

[2] Li et al., Observation of wide-angle impedance matching in terahertz photonic crystals, New Journal of Physics, 2020.

[3] Valagiannopoulos, High selectivity and controllability of a parallel-plate component with a filled rectangular ridge, Progress in Electromagnetics Research, 2011.

[4] Jungfeng Li, Waveguide Simulation Using Mode Matching Method, MSc Thesis, McMaster University, 2014.

[5] Alibakhshikenari et al., Improved adaptive impedance matching for RF front-end systems of wireless transceivers, Scientific Reports, 2020.

[6] Monticone et al., PT-symmetric planar devices for field transformation and imaging, Journal of Optics, 2015.

Author Response

Thank you so much for your careful review and all your proposed references, it has been really interesting to know about them.

(A) What is the advantage of the presented structure against other competing structures [1,2]?

A new comparison table has been included in the publication, comparing the proposed solution with the literature. This comparison has been restricted to WAIM structures in a similar frequency range.

However, after reading both references and interpolating the material used in the unit-cell designs of both papers for WAIM applications, these could be classified as dielectric layers of 1 or more layers, belonging to two of the groups represented in the table. This makes them inherit the disadvantages of using dielectric materials, as mentioned in the paper (lines 40-42).

(B) In-between circuit modeling and full-wave simulations, there are more rigorous techniques like mode matching. The authors should discuss this approach in treating the considered problem [3,4].

Mode-matching method is an analytical procedure that emulates the electromagnetic behavior of a given structure with high accuracy in exchange for greater complexity. However, the technique employed in this publication (circuit-modeling) allows to have a simple model to obtain a quick pre-dimensioning and then to validate it with full-wave simulations.

A mention to this approach has been included in the conclusions as a way of greatly improving  the design methodology.

(C) More details on the way they optimized the designs are required. How the result modify if both polarizations are taken into account simultaneously. Wide-angle designs should be also polarization-insensitive.

The optimization of the 3D model is made by doing a parametric study modifying the radius of the loads (). This value is initially fixed with the data-base together with the inter-columns distance (), in order to obtain an equivalent load impedance () in the equivalent circuit model. It is just necessary some little variations of R to considerably improve the final results.

The design presented in this publication is a single-polarization design with single scanning plane improvements. The idea of this design is to show two main ideas; firstly, the developed circuit models for oblique incidence of the unit-cell topologies used, either unloaded or loaded, can be used to represent the electromagnetic behavior of the unit-cell under oblique incidence. Secondly, the WAIM design methodology which is conceived to work with any possible antenna, and it is tested practically to obtain the final 3D unit-cell design. This design also allows understanding that a layer made out of all-metal unit-cells, which a priori could be thought of as fully reflective, has the ability to match the output impedance of an antenna and allows the transmission of the wave through the metal structure. Efforts are being made in the conception of unit-cells with this topology to work with both scanning-planes and providing polarization-insensitivity. This will be the subject of a future paper.

(D) The authors should mention the possibility of incorporating active structures towards achieving their aim [5,6].

Active structures can be used to improve the matching of an antenna. However, the use of reconfigurable active structures is a different problem than the WAIM proposal, which aims to match a given antenna passively.  Active elements bring much more complexity in the structure with the necessity to handle bias, thermal aspects, etc. The objective of the present paper was definitively to focus on passive matching structures that can be handled easily.

A mention to this matching technique has been introduced in the Introduction section.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have only added a short phrase regarding the rigorous treatment of their model. A longer discussion is required by covering the basic semi-analytical techniques that can solve discontinuities in waveguides or open structures.  

Author Response

Thank you very much for your correction and your advice about talking more about the basic semi-analytical techniques that can model discontinuities in waveguides and open structures, it will surely increase the quality of the paper by including references to other techniques not mentioned during the introduction.

1. The authors have only added a short phrase regarding the rigorous treatment of their model. A longer discussion is required by covering the basic semi-analytical techniques that can solve discontinuities in waveguides or open structures.  

The technique presented in this publication (circuit-modeling) is simple and fast. It allows modeling a complex structure with a very simple model, in addition to understanding the equivalent electromagnetic behavior of each different part of the unit-cell under oblique incidence.

The disadvantages of using a quick and simple methodology is that it provides less accurate estimations, but still allows to obtain a 3D model that is able to match one scanning plane (H-plane) of an example antenna.

 The reviewer is right that there are other semi-analytical techniques that can help model the structure in a much more accurate way in exchange for increased complexity, such as the mode-matching techniques mentioned during the first review. Therefore, in order to consider them in this publication, a paragraph has been written in the introduction mentioning the good performance of these techniques that have not been discussed in the paper, and referring to two of the articles provided by the reviewer that discuss these more accurate techniques.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

The authors have addressed the raised points. The paper is publishable at MDPI Electronics.