On the Reuse of a Matching Network for IoT Devices Operating at 900 MHz Embedding Antenna Boosters

Round 1

Reviewer 1 Report

The paper is original and well written. The proposed work is recommended to accept for publication with following minor revision.

It is advised to add a comparison table of antenna booster technology and the comparison of performance parameters which are published recently (in the available open literature)

Author Response

The paper is original and well written. The proposed work is recommended to accept for publication with following minor revision.

It is advised to add a comparison table of antenna booster technology and the comparison of performance parameters which are published recently (in the available open literature)

Answer: corrected. A table comparing the antenna booster solution with other single-band antennas at 900MHz has been included (Table 1, section 5).

Many thanks for your encouraging words.

Reviewer 2 Report

It presented an method on how to reuse the known  antenna booster  to make a good match for the IOT devices with the assigned frequency bands.  The propsoed method is quite good to solve such a problem.  But the spelling need to be checked again. In total, it is a good paper, suggest to accept it in current form.

Author Response

Answer: corrected. Grammar has been reviewed.

Many thanks for your encouragement.

Reviewer 3 Report

The concept presented in the paper is very interesting and the abstract/title present this highly as a solution for most IoT devices. However, the paper itself falls very short of its objectives, the antenna booster design is not presented, and from the photographs, it appears to the reviewer that this is a commercial component and the authors simply designed a matching network for it using other commercial parts, which brings very limited contributions. 

1. The model of the antenna booster, which appears from Figure 4 to be a commercial component is missing. Its impedance is not detailed and the matching network design is not adequately presented. The work is not reproducible in its current form
2. Sizing the ground plane is an additional design constraint as opposed to a parameter which antenna designers are often allowed to use. The case of sweeping ground dimensions to achieve certain resonances, in Figure 10 is artificial. It is preferable to adjust the frequency of operation using different impedance matching networks. 
3. The authors should discuss the impedance of the booster, over frequency, in more detail along with the matching network design procedure.
4. How was the total efficiency measured and defined? It's unlikely, given the series losses in commercial inductors to be around 90%,
5. The influence of the 50 Ohm transmission line (SMA connector) on the impedance matching is not clearly discussed. It is widely known that the current path along the coaxial cable will influence the current distribution in the ground plane and subsequently the overall impedance and radiation.
6. The work only deals with half of the antenna's radiation problem: efficiency and reflection coefficient. However, the effect on the ground plane size on the radiation patterns and polarization is unknown. Therefore, it is impossible to evaluate the antenna/booster combination without detailed radiation analysis 
7. In Figure 9, the <10% fractional bandwidth cannot be considered broadband, in fact, such reactive matching is expected to be inherently narrow-band. Also, the term broad "banding" is incorrect
8. The writing of the manuscript needs improving. E.g. IoT should be preceded by "The" in the abstract.

Author Response

The concept presented in the paper is very interesting and the abstract/title present this highly as a solution for most IoT devices. However, the paper itself falls very short of its objectives, the antenna booster design is not presented, and from the photographs, it appears to the reviewer that this is a commercial component and the authors simply designed a matching network for it using other commercial parts, which brings very limited contributions. 

1. The model of the antenna booster, which appears from Figure 4 to be a commercial component is missing. Its impedance is not detailed and the matching network design is not adequately presented. The work is not reproducible in its current form

Answer: corrected. A paragraph has been included above figure 4 included the needed data to be reproduced by other researchers.

1. Sizing the ground plane is an additional design constraint as opposed to a parameter which antenna designers are often allowed to use. The case of sweeping ground dimensions to achieve certain resonances, in Figure 10 is artificial. It is preferable to adjust the frequency of operation using different impedance matching networks. 

Answer: corrected. You are right, however in this case the objective is to analyse how the solution can be reused without any hardware adjustment of the matching network. The reason is that many IoT designers are experts on RF and electronics not on antennas. What they typically require is a solution that works for any form factor with any tuning of the matching network. We have included this rationale in the text.

1. The authors should discuss the impedance of the booster, over frequency, in more detail along with the matching network design procedure.

Answer: corrected. A paragraph is included above figure 4 that directs to figure 1 to show what is the impedance of the antenna booster without the matching network. Also, above the figure 2 we have detailed the process.

1. How was the total efficiency measured and defined? It's unlikely, given the series losses in commercial inductors to be around 90%.

Answer: Total efficiency is measured with 3D pattern integration using Star-Lab chamber. Total efficiency takes into account radiation losses and mismatching as total efficiency ht (ht=hr·(1-|S11|2)). This equation is widely adopted and can be found in any antenna book. Ex. Balanis “Antenna Theory and Design”, 2008 Edition, pag.23, eq. 1.23. This equation comes from:

• Pdelivered to antenna= Pin* (1-|S11|²);
• Pradiated=Pdelivered to antenna * hr so at the end
• Pradiated= Pin* (1-|S11|²)* hr which is Prad=Pin*h

In the Star-Lab chamber in our lab (see photo below), we place our device in the middle of the gate. The 3D radiation pattern is measured(both Etheta and Ephi). Then this data obtains Pradiated. Since Pin is known ht can be obtained.

We should take into account that the inductors are high-Q (Q>85) and therefore the matching losses are minimum. Our chamber is calibrated, and results obtained in our Chamber in Barcelona are the same as the ones obtained by Microwave Vision Company in France. Please, let us know .

1. The influence of the 50 Ohm transmission line (SMA connector) on the impedance matching is not clearly discussed. It is widely known that the current path along the coaxial cable will influence the current distribution in the ground plane and subsequently the overall impedance and radiation.

Answer: Corrected. That is the reason why the outer conductor is soldered to the ground planes at three points (at both ends and at the middle). We have just made it clear in the picture. If the transmission line is not properly grounded into at least those 3 points, you are right that transmission line affect the impedance.

1. The work only deals with half of the antenna's radiation problem: efficiency and reflection coefficient. However, the effect on the ground plane size on the radiation patterns and polarization is unknown. Therefore, it is impossible to evaluate the antenna/booster combination without detailed radiation analysis

Answer: Corrected. A new section 5 has been added analysing the impact of radiation properties: current, polarization, directivity.

1. In Figure 9, the <10% fractional bandwidth cannot be considered broadband, in fact, such reactive matching is expected to be inherently narrow-band. Also, the term broad "banding" is incorrect

Answer: corrected. The term “transition zone” has been specified as a zone where a matching network with 3 or more components can enhance the potential bandwidth.

1. The writing of the manuscript needs improving. E.g. IoT should be preceded by "The" in the abstract.

Answer: reviewed.

Many thanks for your detailed review and comments to improve the paper.