WO2021111460A1

WO2021111460A1 - Path loss compensation in mmwave 5g antenna with 3d-printed radome

Info

Publication number: WO2021111460A1
Application number: PCT/IN2020/050151
Authority: WO
Inventors: Shiban Kishen KOUL; Karthikeya Gulur SADANANDA
Original assignee: Indian Institute Of Technology, Delhi
Priority date: 2019-12-06
Filing date: 2020-02-19
Publication date: 2021-06-10

Abstract

An access point, comprising a first shell aligned along a horizontal plane for securing a first antenna and a second shell and a third shell placed at opposite ends of the first shell and oriented at 45 degree to the plane of the first shell for securing a second antenna and a third antenna, such that bottom sides of the second shell and the third shell face each other.

Description

“PATH LOSS COMPENSATION IN mmWave 5G ANTENNA WITH 3D-PRINTED

RADOME”

The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD

[0001] The present disclosure relates to a design of access point antenna. More specifically, the present disclosure relates to the access point antenna operating in millimeter wave region for 5G communication applications.

BACKGROUND

[0002] In the known state of art, antenna designs rely on phased array antennas. The primary issue with phased array is the scanning loss. The gain deteriorates as the beam is scanned away from a boresight of the antenna. Further, as the number of elements in the antenna module increase the complexity of the design also increases which might further generate various performance issues for example poor antenna gain.

[0003] Fig. 1 illustrates a four-port phased array consisting of inset fed patch antennas separated by half-wavelengths. When the beam is steered away from the boresight it results in scanning loss i.e. gain deterioration. The requirement of an access point is to provide uniform illumination on the ground and that needs gain enhancement when the beam is scanned away from boresight. Hence, the existing phased array antenna would fail to achieve the afore-mentioned criterion.

[0004] Another popular approach to achieve more coverage is leaky wave design, where the beam could be scanned by varying the frequency of operation. But this scheme is also not preferred in commercial applications since the operating bandwidth must strictly adhere to the licensed frequency bands which are of range 0.7GHZ-2.7GHZ. [0005] Further, reconfigurable antenna designs for beam scanning can be considered as an option but this fails in the 28 GHz regime, since bias lines feeding PIN diodes also contribute to radiation. The diode post- integration would create additional detuning of the antenna element, hence compromising the pattern integrity.

[0006] Therefore, to overcome all these problems of the stated art, wireless industry has diverted its focus from mid band or high band spectrum to millimeter wave spectrum for mobile communication. However, feasibility of utilizing the millimeter wave spectrum for mobile communication sets several challenges for a radio designer. The major hurdle for implementation of millimeter wave communication links is high path loss. Further, sometimes due to environmental conditions, the signals coming from the antenna modules also degrades. To prevent damage to the antenna from environmental factors, it is desirable to enclose the antenna module in a protective casing. However, in conventional designs, the antennas lack radome enclosure (i.e. protective casing) as that leads to gain deterioration and increase in the cost of overall antenna module.

[0007] Thus, there is a need in the art to provide a unique architecture of antenna module that can overcome the problems of conventional arts such as high path loss and simultaneously provide protection of antenna module from environmental factors without gain deterioration.

[0008] The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY of Invention

[0009] The present disclosure overcomes one or more shortcomings of the prior art and provides additional advantages discussed throughout the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure. [00010] In one non-limiting embodiment of the present disclosure, an access point antenna is disclosed. The access point antenna comprising a first shell aligned along a horizontal plane for securing a first antenna and a second shell and a third shell placed at opposite ends of the first shell and oriented at 45 degree to the plane of the first shell for securing a second antenna and a third antenna, such that bottom sides of the second shell and the third shell face each other,

[00011] In another non-limiting embodiment of the present disclosure, in the access point, the first, second and third antennas are secured in their respective shells via respective front sides.

[00012] In yet another non-limiting embodiment of the present disclosure, in the access point, the first shell has dimensions of 22Lxl0Wxl0.5H mm and the second and third shells have dimensions of 22Lx.9Wx6.5H mm.

[00013] In still another non-limiting embodiment of the present disclosure, in the access point, thickness of first, second and third shells is 2mm.

[00014] In yet another non-limiting embodiment of the present disclosure, in the access point, the second antenna and the third antenna have 3dB higher gain than the first antenna.

[00015] In another non-limiting embodiment of the present disclosure, in the access point, the first antenna, second antenna and third antenna are placed away on the bottom surface away from top surface of the respective shells for maximum gain enhancement.

[00016] In still another non-limiting embodiment of the present disclosure, in the access point, the first antenna is placed 10mm away from top surface of the first shell and the second antenna and the third antenna are placed 6.5mm away from the top surface of the second and third shells.

[00017] In yet another non-limiting embodiment of the present disclosure, in the access point, the first antenna has an impedance bandwidth of 27 to 28.4 GHz and second antenna and third antenna have impedance bandwidth of 27.4 to 28.4 GHz. [00018] In still another non-limiting embodiment of the present disclosure, the access point achieves an angular coverage of 140 degrees at 28 GHz.

[00019] In another non-limiting embodiment of the present disclosure, in the access point, an aperture efficiency corresponding to second and third antennas is 72%.

[00020] In yet another non-limiting embodiment of the present disclosure, access point comprises a radome structure made up of PLA substrate with a dielectric constant in the range of 2.75 with a corresponding dielectric loss tangent of 0.01 such that the radome acts as a superstrate.

[00021] In another non-limiting embodiment of the present disclosure, the radome structure is 3D printed.

[00022] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[00023] The features, nature, and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken conjunction with the drawings in which like reference characters identify correspondingly throughout. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures.

[00024] FIG.1 depicts an arrangement of inset-fed patch antenna according to prior art.

[00025] FIG.2 depicts exemplary inset-fed patch antenna in accordance with an embodiment of the present disclosure. [00026] FIG.3 depicts 3D-printed radome integrated with an inset-fed patch antenna, in accordance with an embodiment of the present disclosure.

[00027] FIG.4a depicts schematic of the 3D-printed radome, in accordance with an embodiment of the present disclosure.

[00028] FIG.4b depicts schematic of 3D-printed Radome with inset-fed patch antenna, in accordance with an embodiment of the present disclosure.

[00029] FIG. 5a depicts gain variation of inset-fed patch antenna with radome for various heights, in accordance with an embodiment of the present disclosure.

[00030] FIG.5b depicts graphical representation of gains of the corresponding ports vs frequency, in accordance with an embodiment of the present disclosure.

[00031] FIG.6 depicts graphical representation of input reflection coefficients of ports 1 and

2, in accordance with an embodiment of the present disclosure.

[00032] FIG.7 depicts graphical representation of aperture efficiency of antennas with 3D- printed radome for ports 2 and 3, in accordance with an embodiment of the present disclosure.

[00033] FIG.8 depicts graphical representation of mutual coupling across the ports, in accordance with an embodiment of the present disclosure.

[00034] FIG.9 depicts graphical representation of the radiation patterns of the antennas, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

[00035] While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.

[00036] The terms “comprises”, “comprising”, “include(s)”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, system or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or system or method. In other words, one or more elements in a system or apparatus proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.

[00037] The access point may also be referred to as a base station, a Node B, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), or some other suitable terminology. The access point plays an important role in providing communication between various UEs. Examples of UEs include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, or any other similar functioning device. The UE may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

[00038] The present disclosure relates to a pattern diversity antenna module termed as an access point with radome structure operating in the 28 GHz band, targeting the millimeter wave 5G base station applications. The pattern diversity antenna module consists of two or more co-located antennas with different radiation patterns. This type of diversity makes use of directional antennas that are usually physically separated by some (often short) distance. Collectively they are capable of discriminating a large portion of angle space and can provide a higher gain versus a single omnidirectional radiator. This disclosure teaches about how an access point achieves maximum gain with radome structure without any path loss compensation. The pattern diversity antenna module of the present disclosure supports communication services for mobile devices by making use of the new spectrum i.e in 28 GHz regime to improve broadband services, increase network capacity and throughput. Further, the pattern diversity antenna module of the present disclosure is also protected from the environmental conditions with minimal cost.

[00039] FIG. 2 depicts an inset fed patch antenna, in accordance with the embodiment of the present disclosure. It is designed on 0.508 mm thick Nelco NY9220 substrate with a dielectric constant in the range 2.2±0.02 with a corresponding dielectric loss tangent of 0.0009. Since, the thickness of the substrate is a fraction of the wavelength of the intended operating frequency of 28 GHz, the cross-polarization radiation is minimal in this embodiment. Also, since the dielectric constant of the substrate is low, surface wave modes are kept minimum. The dielectric loss tangent plays a critical role is deciding gain yield of the antenna. Higher dielectric loss would lead to higher losses in the substrate leading to reduced gain. The patch radiator is a standard strong resonant element. The width of the antenna is chosen to accommodate end-launch connector. The distance between the radiator and the feed-line is kept at least 1λ away from the edge of the feed plane to reduce coupling between the electrically large connector and the antenna. The patch has a broadside gain of approximately 8 dBi and operates at a frequency band of 28 GHz.

[00040] To secure the inset-fed patch antenna, as described in fig.2, a 3D printed radome structure is provided. The same is depicted in fig.3 of the present disclosure. 3D printing is an inexpensive method to realize any arbitrary geometry within the specifications of the available 3D printer. The chosen material for 3D printing is Polylactic acid (PLA) which has a dielectric constant of 2.75 and an associated dielectric loss tangent of 0.01. Although, the dielectric is lossy but arbitrary geometries can be realized in a cost-efficient way hence the chosen dielectric is justified.

[00041] The 3D printed radome made of PLA is placed above the inset-fed patch antenna as evident from Fig. 3. It must be observed that the radome enclosure is only above the radiating element of the antenna as the radiation emitted from the transmission line is negligible. The commercial implementation of access point module also has a few millimeters of transmission lines thus not significantly altering the performance of the radome encased antenna. The thickness of the radome enclosure is around 2 mm, which is necessary to maintain mechanical sturdiness. Due to this thickness and overall 3D structure for securing the antennas, the requirement of additional scaffolding may be avoided.

[00042] Typical all-dielectric superstrates which are available till date have high dielectric constant, thus increasing the cost of manufacturing. It must also be noted that conventional substrates might not be compatible with 3D printing, hence making it harder to realize the desired geometry to fit in the antenna module.

[00043] FIG. 4a depicts a 3D printed radome for pattern diversity module comprises of three shells that are arranged to form a single 3D structure for securing pattern diversity antenna module. Each shell of the 3D printed radome is utilized by securing one access point antenna. In an exemplary embodiment, the 3D printed radome structure comprises of three shells which are named as first shell, second shell and third shell. The first shell is aligned along a horizontal plane. The second shell and third shells are placed on opposite ends of the first shell, therefore, the first shell may be considered as the central shell. The second and third shells are arranged in a way that the orientation of second shell is at +45degree with respect to the plane of first shell and the orientation of third shell is at -45 degree with respect to the plane of the first shell. In another embodiment, the orientation of second shell is at -45degree with respect to the plane of first shell and the orientation of third shell is at 45 degree with respect to the plane of the first shell.

[00044] The second and third shells are identical with respect to each other in all aspects except angular orientation. In particular, if one of the shell is mounted at +45 degree (i.e. +45°) then the other shell will be mounted at -45 degree (i.e. -45°) with respect to the first shell to arrange all the three shells as single structure. The pattern diversity antenna module of the present disclosure is for a typical indoor base station scenario where beams beyond 45° may not be required.

[00045] In one exemplary embodiment, the dimensions of the second and the third shells are 22Lx.9Wx6.5H. All the units are measured in millimeters (mm). In other words, the length of the second or the third shell is 22mm, breadth or depth is 9 mm and the height is 6.5 mm. Both the second and third shells are identical, therefore the gain requirement for both the shells are also same. The dimensions of the first shell are different from the second and the third shells. In particular, the dimensions of the first shell are 22Lx10Wx10§§H mm. The thickness of all the shells are of the order of 2mm. In an exemplary embodiment, the outer dimensions of the 3D structure may be different than the inner dimensions. The outer dimensions of the complete 3D radome structure are arranged in such a way that the length of the outer boundary of second and third shells is 33.5mm whereas the length of outer boundary of first shell is 24mm. The outer width of all the shells is same and may be considered as 10mm. The arrangement of shells is in such a manner that the bottom sides of the second shell face the bottom side of the third shell.

[00046] Fig. 4b depicts the schematic of the pattern diversity module integrated with 3D printed radome. In particular, fig. 4b depicts the arrangement for securing the antennas inside the shells of the 3D printed radome structure. The antennas are secured inside the shells of the structure. Each of the shell of the 3D printed radome structure secures one of the inset-fed patch antenna. For taking connections through these antennas, ports are defined as well. For example, the antenna inserted in first shell is connected through portl. The antenna inserted/secured inside shell 2 is connected through port 2 and antenna secured inside shell 3 is connected through port 3. As the antennas are secured in different shells, therefore the chances of mutual coupling are reduced.

[00047] When the 3D printed radome is immediately above the radiating aperture of each antenna, the radome would act as a parasitic hence detuning the antenna consequently leading to a lower gain of 6 dBi across the band. In an indoor scenario, if an antenna (P_t = OdBm) is mounted on the ceiling then the received power is -63 dBm when the gain of the central element i.e. for antenna at port 1 is 8 dBi. When the beam is illuminated at an angle ±45°, the distance increases to 4.24m consequently increasing the path loss as 3 dB. In order to compensate the additional 3 dB path loss for port 2 and port 3, the gains of the antennas illuminating at ±45° must be 11 dBi, to achieve a uniform illumination on the ground.

[00048] This path loss may be compensated by providing an offset between the antenna and tip surface of the shell. In accordance with an exemplary embodiment, when the top surface of the shell is away from the antennas, gain enhancement is observed due to the phase correction of the radiated waves in the low-dielectric surface which acts as a superstrate. In an exemplary embodiment, the gain enhancement is maximum when the dielectric superstrate is placed at 10mm away from the antenna. Thus, the height of the 3D printed radome could be varied to achieve gain variation, which is necessary to achieve path loss compensation.

[00049] Fig. 5a depicts graphical representation for gain variation of inset-fed patch antenna with radome for various heights. It is clear from the graph that the gain deterioration is maximum when the radome is placed on top of the antenna without any gap. The gain increases upto 11 dBi at 28 GHz when the gap between the radiator and the radome is 10 mm. Thus, the height of the 3D- printed radome could be varied to achieve gain variation, which is necessary to achieve path loss compensation. In particular, the first, second and third antennas are placed away from top surface of their respective shells for achieving maximum gain enhancement. In an exemplary embodiment, the second antenna and the third antenna have 3dB higher gain than the first antenna. In particular, the gain enhancement of 3dB with respect to first antenna may be achieved if the the first antenna is placed 1 Omm away from top surface of the first shell In same embodiment, the second antenna and the third antenna are placed 6.5mm away from the top surface of the second and third shells to compensate for path loss.

[00050] As mentioned above, in order to achieve path loss compensation, the gain at the first antenna where the beam orientation is 0° must be 8 dBi and the gain at the second and third antennas where the beams are oriented at ±45° must be 11 dBi. The same is evident from Fig. 5b. The gain variation is achieved by varying the heights of the superstrate with respect to the antenna.

[00051] The input reflection coefficients of the pattern diversity module enclosed in radome structure is depicted in Fig. 6, in accordance with an embodiment of the present disclosure. The reflection coefficient is a parameter that describes how much of an electromagnetic wave is reflected by an impedance discontinuity in the transmission medium. The radome superstrate has minimal influence on the input impedance of the antenna. The |S₁₁| of the inset fed patch antenna is designed to be operational in the 27-29 GHz band. The 10% narrow bandwidth is due to the impedance match achieved with the standard 50W line and the strongly resonant patch antenna. It must be noted that the input impedance of the antenna integrated with the superstrate is identical to that of the conventional inset-fed patch antenna. The heights of the superstrate do not create a deviation in the input impedance of the antenna. Hence, the antenna module with different heights of the superstrate placement would still be operational in the 28 GHz band, as evident from Fig. 6.

[00052] The aperture efficiency corresponding to antennas of ports 2 and 3 is shown in Fig. 7, the aperture efficiency is around 72% at 28 GHz. The mutual coupling between the ports is less than 35 dB across the band as depicted in Fig. 7 for ports 2 and 3, the corresponding gains of the beam are 11 dBi respectively. Since, the physical size of the 3D printed radome which doubles up as the radiating aperture is 20mmxl0mm, the aperture efficiency is 72% at 28 GHz, indicating a high gain yield for a relatively compact size.

[00053] Fig.8 depicts mutual coupling across the ports and the band is less than 35 dB, due to the orientations of the antennas being 0°, +45° and -45° for ports 1,2 and 3 respectively. Even though, the antennas are placed electrically close to each other, the radiators are oriented in different planes hence reducing the mutual coupling due to change in the polarization of the radiating wave.

[00054] Fig. 9 depicts the radiation pattern of the access point at 28 GHz, when each of the corresponding ports are excited. The 3dB angular coverage is 140°. It is also observed that the 8 dBi element has a wider beam width compared to the 11 dBi counterparts. The 3dB half-power points also coincide indicating a compact module to achieve path loss compensation with wide angular coverage and high aperture efficiency.

[00055] The illustrated structure of radome is set out to explain the exemplary embodiments shown, and it should be anticipated that ongoing technological development will change the manner in which particular limitations are arranged. These examples are presented herein for purposes of illustration, and not limitation. Further, the boundaries of the functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternative boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. Alternatives (including equivalents, extensions, variations, deviations, etc., of those described herein) will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Such alternatives fall within the scope and spirit of the disclosed embodiments. [00056] Advantages of the embodiment of the present disclosure are illustrated herein:

1. An access point with a low cost 3D printed radome structure.

2. Gain enhancement of 3 dB using the superstrate radome design.

3. High aperture efficiency of 72% for a 28 GHz antenna integrated with radome.

4. Realization of path loss compensation.

5. Pattern diversity module for wide angular coverage of 140° at 28 GHz.

6. A mutual coupling of less than 35 dB across the ports in the millimeter wave pattern diversity module.

7. A radome which also doubles up as a superstrate for gain enhancement.

8. An impedance bandwidth of 27 to 28.4 GHz (port 1) and 27.4 to 28.4 GHz (ports 2 and 3).

9. A mechanically sturdy construction of the 3D printed radome, hence no requirement of additional scaffolding.

10. The disclosed 3D printed radome has similar operational characteristics with orthogonal incident polarizations as well.

Claims

The Claims:

1. An access point, comprising: a first shell aligned along a horizontal plane for securing a first antenna; and a second shell and a third shell placed at opposite ends of the first shell and oriented at 45 degree to the plane of the first shell for securing a second antenna and a third antenna, such that bottom sides of the second shell and the third shell face each other.

2. The access point as claimed in claim 1, wherein the first, second and third antennas are secured m their respective shells via respective front sides.

3. The access point as claimed in claim 1, wherein the first shell has dimensions of 22Lxl0Wxl0.5H mm and the second and third shells have dimensions of 22Lx.9Wx6.5H mm.

4. The access point as claimed in claim 1, wherein thickness of first, second and third shells is 2mm.

5. The access point as claimed in claim 1, wherein the second antenna and the third antenna have 3dB higher gam than the first antenna.

6. The access point as claimed in claim 1 , wherein the first antenna, second antenna and third antenna are placed on the bottom surface away from top surface of the respective shells for maximum gam enhancement.

7. The access point as claimed in claim 1, wherein the first, second and third antennas are placed at an offset between the antenna and a tip surface of the respective shells.

8. The access point as claimed m claim 1, wherein the first antenna is placed 10mm away from top surface of the first shell and the second antenna and the third antenna are placed 6.5mm away from the top surface of the second and third shells.

9. The access point as claimed in claim 1, wherein the first antenna has an impedance bandwidth of 27 to 28.4 GHz and second antenna and third antenna have impedance bandwidth of 27.4 to 28.4 GHz.

10. The access point, as claimed in claim 1, wherein the access point achieves an angular coverage of 140 degrees at 28 GHz.

11. The access point as claimed in claim 1, wherein an aperture efficiency corresponding to second and third antennas is 72%,

12. The access point as claimed in claim 1 , further comprising: a radome structure made of PLA substrate with a dielectric constant in the range of 2.75 with a corresponding dielectric loss tangent of 0.01 such that the radome acts as a superstrate.

13. The access point as claimed in claim 12, wherein the radome structure is 3D printed.