EP2615688A1

EP2615688A1 - Microwave antenna and its outer cover

Info

Publication number: EP2615688A1
Application number: EP10856889.0A
Authority: EP
Inventors: Zhihang Wu; Daolin Fu; Rudan Jiang; Suqin Liu; Qingnan Xie; Yong Wang; Yan Wang; Rong TANG; Jun Pan
Original assignee: Comba Telecom Systems China Ltd
Current assignee: Comba Network Systems Co Ltd
Priority date: 2010-09-07
Filing date: 2010-11-11
Publication date: 2013-07-17
Anticipated expiration: 2030-11-11
Also published as: BR112013005521A2; CN101958461A; EP2615688A4; EP2615688B1; WO2012031427A1; CN101958461B

Abstract

A microwave antenna radome used for covering a microwave antenna and of rotatablely symmetrical includes the following components all of which are arranged concentrically; a compensation portion located at a central portion of the radome and used for compensating phase delay of electrical field at the central portion of an antenna aperture plane caused by blocking of a feed; a main reflective portion located on a periphery of the compensation portion and used for reflecting electromagnetic wave originating from the feed of the microwave antenna at a specific direction biased from the feed; and an auxiliary reflective portion located on a periphery of the main reflective portion and used for bunching and reflecting diffraction electromagnetic wave at edge of the microwave antenna. All components of the radome are specifically shaped. The microwave antenna thus formed has good electrical performance, stable structure and low cost.

Description

FIELD OF THE INVENTION

The present invention relates to communication field and more particularly, relates to a microwave antenna and radome thereof.

BACKGROUD OF THE INVENTION

With the increasing requirements for microwave communications, point-to-point or point-to-multipoint microwave telecommunication networks composed of microwave Antennas become denser in their distribution. As such, it is more possible to result in interference among various microwave systems. More restrict standard has been made by corresponding authorities and network operators to limit the radiation patterns envelope (RPE) of the microwave antenna. Antennas meeting different classes of regulatory compliance are selected according to different network requirements. Among various electrical characteristics of the antenna, front-to-back ratio (F/B) is especially important and heavy attention should be paid to design of the antenna.
1) In terms of electrical characteristics, the antenna radome should not deteriorate gain, return loss, RPE and F/B of the antenna. The best design object is to improve electrical performance of the antenna.
2) In terms of mechanical characteristics, the antenna radome should have robust mechanical strength, small size and small wind load.
3) In terms of cost, the cost of the antenna radome itself and cost for installing the radome to the antenna should also be small.
The influences of the antenna radome on electrical performance of the antenna are given as below.
1) Reduction of antenna gain. This is resulted mostly by insert loss of the radome. As such, dielectric material with lower insert loss should be used in design of the antenna radome. Moreover, suitable thickness must be maintained for the radome in order to bring best wave permeability.
2) Increase of return loss of the antenna. In other words, the input voltage standing wave ratio (VSWR) is deteriorated because the electromagnetic wave reflected by the radome returns to the feed.
3) Having influence on RPE performance of the antenna. This is because the phase distribution of electrical field at the aperture plane of the antenna gets uneven due to the radome, thus increasing level of proximal side-lobe or distal side-lobe of the radiation pattern of the antenna.
4) Making F/B performance of the antenna deteriorated. This is because that the radome damages the distribution of diffraction field at edge of the antenna aperture plane. The radome even has backward guiding to the diffraction filed, thus enhancing backward transmission.
A traditional antenna radome used in a microwave antenna normally includes three different types of constructions (See a, b, and c portion of figure 1):
a) Flat radome; b) Protruded radome; and c) Recessed radome.
The antenna radome is generally made from dielectric material with uniform density, stable dielectric constant and low loss. It is clear that above traditional radome solutions fail to completely meet above electrical design objects or mechanical performance. In addition, they have no advantage in cost. The thickness of a flat antenna radome normally is about half wavelength of the dielectric for getting better wave permeability, thereby reducing influence of the radome to gain and VSWR. The flat radome however, has the following drawbacks.
1) The bandwidth of frequency is limited and therefore, this kind of radome is not suitable for wide frequency bandwidth antenna system;
2) It has great influence on RPE especially F/B performance of the antenna as edge portion of the radome is generally not specifically shaped; and
3) It has poor mechanical strength.
Though a recessed antenna may bring wider frequency bandwidth performance by suitably designing cone angle thereof, influence on RPE especially F/B performance is usually not considered. In addition, the recessed antenna radome suffers from poor mechanical strength and wind load.
Good frequency bandwidth and F/B performance may be resulted for a protruded antenna radome by specific shaping. Moreover, good mechanical strength and wind load may also be achieved. However, regarding RPE performance, though this kind of radome will not deteriorate RPE, it brings no improvement on RPE performance. Furthermore, this type of antenna radome often increases overall size and accordingly, increases package and transportation cost.

SUMMARY OF THE INVENTION

The object of the invention is to overcome drawbacks of the above antenna radomes and therefore provide a microwave antenna and radome related thereto. The radome of the microwave antenna has better electrical and mechanical characteristics, and also has low cost.
To realize the above object, the following technical solution is presented.
A microwave antenna radome of the invention is used for covering the microwave antenna and is rotatably symmetrical. The radome includes the following components all of which are arranged concentrically:
a compensation portion located at a central portion of the radome and used for compensating phase delay of electrical field at the central portion of an antenna aperture plane caused by blocking of a feed;
a main reflective portion located on a periphery of the compensation portion and used for reflecting electromagnetic wave originating from a feed of the microwave antenna at a specific direction biased from the feed; and
an auxiliary reflective portion located on a periphery of the main reflective portion and used for bunching and reflecting diffraction electromagnetic wave at edge of the microwave antenna.
The compensating portion has the shape recessed towards the covering side direction of the radome such as gauss shape, conical shape or spherical shape.
The main reflective portion is recessed towards the covering side direction of the radome, and takes on an inclined conical plane shape.
The auxiliary reflective portion is protruded towards the opened side direction of the radome.
The thickness of the compensating portion is smaller than that of the main reflective portion.
A specific direction at which electromagnetic wave is reflected by the main reflective portion is defined to be corresponding to a region outside of the main lobe of an entire antenna radiation pattern. The specific direction corresponds to zero-point angular position or a distal side lobe angular position of the entire antenna radiation pattern.
The diameter of the compensating portion of the radome is equal to that of the sub reflector of the feed.
The microwave antenna of the invention includes a feed, a reflector and a radome as described above. A rim is outwardly defined on an opened surface of the reflector. In addition, a skirt engaged with the rim is disposed on the radome at a location adjacent the auxiliary reflective portion. The rim is secured onto the skirt by means of screws.
The rim and skirt are assembled together by a plurality of locating and holding members provided on a surface of the radome at the covering side.
Absorbing material is provided on the radome at location adjacent the skirt at the opened side. The absorbing material is selected from any one of foam, sponge and rubber.
Compared to prior arts, the invention bears the following good effects.
At first, in terms of electrical performance, the invention is able to evidently improve radiation F/B performance of the microwave antenna, phase characteristics of aperture plane electric field distribution of the antenna, thus improving antenna gain and aperture efficiency. In addition, it is capable of improving RPE performance such as level of side lobe while having little influence on other electric performance for example input voltage standing wave ratio and cross-polarization discrimination.
Secondly, in terms of mechanical performance, the arcuate structure of the radome operates as an enhancement rib and as such, the entire antenna radome has strong strength. Moreover, the antenna radome has small size, weight and wind load. The radome also has attractive appearance.
Thirdly, in terms of cost, the radome of the invention may be formed integrally by plastic molding process thus leading to low cost. In addition, the overall size of the antenna after assembled with the antenna radome increases moderately due to recessed structure of the antenna radome. Furthermore, package and transportation cost is also low.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows some cross-section view of traditional microwave antenna radomes installed onto corresponding reflectors, in which (a) represents a flat antenna radome, (b) represents a protruded antenna radome, and (c) represents a recessed antenna radome;
Figure 2 shows a cross-sectional view of a microwave antenna radome according to the invention applied to a microwave antenna;
Figure 3 illustrates a top plane view of the radome of figure 2;
Figure 4 illustrates a bottom plane view of the radome of figure 2;
Figure 5 illustrates a cross-sectional view of the radome of figure 2;
Figure 6 explains working principle of the microwave antenna of figure 2;
Figure 7 shows typical phase distribution curves of electrical field at an aperture plane of the microwave antenna radome according to the invention, wherein the solid curve represents phase distribution when the radome is installed, while the broken curve represents phase distribution when no radome is installed;
Figure 8 shows typical input voltage standing wave ratio curves of the microwave antenna radome according to the invention, wherein the solid curve represents input voltage standing wave ratio when the radome is installed, while the broken curve represents input voltage standing wave ratio when no radome is installed;
Figure 9 shows some embodiments and working principles of the auxiliary reflective portion of the microwave antenna radome according to the invention;
Figure 10 shows typical radiation pattern curve of the microwave antenna radome of the invention; and
Figure 11 shows assembling state of the microwave antenna radome of the invention with other components.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is further explained in conjunction with the accompanying drawings and embodiments.
Reference is made to figures 2-4, a microwave antenna employing a microwave antenna radome of the invention includes a rotatablely symmetric shaped dielectric antenna radome 1, a plurality of mounting bolts 14, a plurality of locating and holding members 15 and wave absorption material 4. The radome 1 is mounted onto a rim of a microwave antenna main reflector 2 by means of a number of additional screws 5 (See figure 11) and is kept in place by the locating and holding members 15. Some concentric portions are outwardly distributed on the radome 1 from a symmetric axis of the radome 1. These portions includes a compensating portion 11 located at a central region, a main reflective portion 12 extending from the compensating portion 11 and constituting a periphery of the compensating portion 11, and an auxiliary reflective portion 13 extending upon the main reflective portion 12 and defining a periphery of the main reflective portion 12. All these portions have been specifically shaped to improve electrical characteristics. In addition, a skirt 18 perpendicular to all of the above portions is disposed at a periphery of the auxiliary portion 13 of the radome 1 to realize assembling function. The skirt 18 of the radome 1 is intended to be pressed against and assembled by means of screw with a rim 28 of the main reflector 2, thus forming a complete antenna structure and making a feed 3 contained therein. Here, a side on which the main reflector 2 and feed 3 are disposed respect to the radome 1 is defined as a covering side, and another side by which the radome 1 faces free space is defined as an opened side. These definitions help to better description of the invention hereinafter.
The antenna radome 1 should be made from dielectric material with uniform density, stable dielectric constant, and low loss such as ABS, ASA, polystyrene, Polytetrafluoroethene, Polypropylene, alumina, high temperature ceramics, fiber glass reinforced plastics and some compound materials. All these material have unchanged relative dielectric constant εr and dielectric loss tangent tanδ so as to represent electric characteristics of the material.
Referring to figures 5 and 6, the thickness of the compensating portion 11 of the radome 11 is smaller than that of the main reflective portion portion 12. In other words, the compensating portion 11 is thinner slightly than the main reflective portion 12 so as to compensate phase delay of electric field at a central region of the antenna aperture plane caused by blocking of the feed 3, thus making phase distribution of electric field at the antenna aperture plane more uniform, and improving gain and efficiency of the antenna. The compensating portion 11 is of a circular shape due to rotatable symmetry of the radome 1. The diameter of the compensating portion 11 is equal to that of the feed. The profile of the compensating portion 11 may be designed to have the shape recessed towards the covering side direction (feed direction) of the radome 1 such as gauss shape, conical shape or spherical shape, hence as less as possible electromagnetic wave 22 transmitted by the feed 3 will be again reflected by the compensating portion 11 back to the feed. Therefore, influence on input voltage standing wave ration is reduced.
The compensating portion 11 should be specifically shaped because it is the place where electromagnetic wave normally comes to. The electromagnetic wave 21 coming from the feed 3 is reflected by one surface of the compensating portion 11 facing the radomeing side, thus generating electromagnetic wave 22. The electromagnetic wave 22 is further reflected by the main reflector 2 thus generating electromagnetic wave 23, and less or even no wave 23 will be returned to the feed 3 and received again by the feed 3, which otherwise will influence the entire performance of the antenna especially input voltage standing wave ratio on performance.
As a sub-reflector of the feed 3 produces certain blocking effects to radiation characteristics of the microwave antenna itself, phase delay is resulted at a central region of electric field distribution at the antenna aperture plane. Therefore, the thickness of the compensating portion 11 is adjusted to compensate phase of transmitted electromagnetic wave. In other words, the thickness t1 of the portion 11 is designed to be smaller slightly than the thickness t0 of a circular cone 12 such that phase of electric field distribution at the aperture plane is more uniform, thereby improving antenna gain and efficiency. The diameter ϕ of the compensating portion 11 is equal or equivalent to that of the sub-reflector of the feed 3.
Referring to figure 7 which shows aperture electric field phase distribution curves according to one embodiment of the invention, as phase distribution at the aperture plane of the compensating portion 11 is delayed about 60 degree, the thickness t1 is slightly smaller than the thickness t0 of the circular cone portion 12, thus phase of electric field at the aperture plane becomes more uniform.
Reference is further made to figures 5 and 6. The main reflector 12 of the radome 1 is made up of an inclined conical plane with a thickness half a wavelength of dielectric and recessed at the covering side towards toward the feed 3. The cone angle of the conical plane is specially designed so that electromagnetic wave 25 originating from the feed 3 and then reflected by the reflective 12 will not return to the feed 3. The cone angle α of the main reflective 12 is designed such that electromagnetic wave 25 reflected by the main reflector 12 is directed to a specific direction biased from the feed. The above specific direction corresponds to other region than the main lobe region of the entire radiation pattern of the microwave antenna. For example, it may correspond to zero-point angular position or a distal side lobe angular position.
Reflection and refraction occur many times when electromagnetic wave travels across the dielectric material. Reflection energy will certainly influence performance of the microwave itself and therefore, reflection should be reduced. To this end, the main reflector 12 should have suitable thickness t0. When the thickness t0 is half wavelength of dielectric or is integer times of it, phase difference between paths though which electromagnetic wave is reflected and refracted many time is integer times of 2π, thus making reflected waves counterbalanced with each other, while transmitted waves being added with each other. This makes the main reflective portion 12 has a minimal reflective coefficient.
The cone angle α of the main reflector 12 is specially designed such that electromagnetic wave 25, which is part of electromagnetic wave 24 transmitted normally at the aperture plane of the antenna and which is reflected against the conical plane, is constantly reflected at a direction corresponding to an angle of 180-2α. On one end, by twice reflection of the reflector 2, the reflected electromagnetic wave 25 will not return to the feed 3, reducing influence on the overall performance of the antenna, especially on input voltage standing wave ratio at a wider range of frequency bandwidth. On the other hand, the electromagnetic wave 25 is reflected at a specific direction selectively corresponding to a location outside of the main lobe region of the radiation pattern of the antenna (that is, region outside of the main lobe region). Preferably, the above location corresponds to zero-point angular position or a distal side lobe angular position of the radiation pattern. As such, influence of the antenna radome on radiation pattern of the antenna itself in particular the main lobe is reduced.
Referring to figure 8 which shows input voltage standing wave ratio curves according to an embodiment, the cone angle a is set to be 3-10 degree. It is clear that the radome 1 has little influence on input voltage standing wave ratio performance of the entire microwave antenna.
Reference is further made to figures 5 and 6. The auxiliary reflective portion 13 of the radome 1 is basically arcuated and therefore, the auxiliary reflective portion 13 protrudes towards the opened side of the radome 1. The auxiliary reflective portion 13 is shaped such that its inner surface 16 (See figure 9) is capable of bunching and reflecting electromagnetic wave 26 diffracted at edge. In other words, the reflected electromagnetic wave 27 can be focused intensively on a region of the radome 1.
Figure 9 shows some embodiments of the shape of the auxiliary reflective portion 13, in which (a) represents partially folded convex shape, (b) represents partially arcuate convex shape, and (c) represents partially lid-shaped convex shape. These convex planes 16 all have bunching and reflecting characteristics. Namely, electromagnetic wave 26 diffracted at the edge of antenna aperture plane is reflected against the convex plane 16 at the radomeing side of the radome 1. In turn, the reflected electromagnetic wave 27 is intensively focused on a certain region inside the radome 1 by the convex plane 16.
Reference is further made to figures 5 and 6. Absorbing material 4 is mounted in a region (at the covering side) corresponding to the auxiliary reflective portion 13 of the radome 1 and adjacent to the skirt 18 of the radome 1. Absorbing material 4 generally has an annular shape with certain thickness. The mounting location of the absorbing material 4 may be designed corresponding to the inner surface of the auxiliary reflective portion 13 to ensure that the absorbing material 4 is mostly disposed in a region which is defined together by the skirt 18 and auxiliary reflective portion 13 of the radome 1 and in which the reflected electromagnetic wave focuses. Therefore, the reflected electromagnetic wave is effectively absorbed and electromagnetic wave backwardly diffracted is reduced, thereby improving F/B performance of the microwave antenna.
The absorbing material 4 is optional component and after finishing of the microwave antenna assembling, the material 4 is sandwiched among the skirt 18 of the radome 1, auxiliary reflective portion 13 and rim 28 of the main reflector 2. The material 4 works to absorb electromagnetic wave 27 reflected by the inner surface 16 of the auxiliary reflective portion 13 of the radome 1 and partially diffracted electromagnetic wave 26. The absorbing material 4 may take the form of foam, sponge or rubber.
As shown in figure 10, the radome of the invention significantly improves radiation F/B performance for example by about 10dB.
Referring to figure 11 which is a view showing assembling of the microwave antenna radome 1 and main reflector 2 and feed 3. The optional wave absorbing material 4 may be assembled based on desire. When there is a need for mounting the material 4, the material 4 is at first secured on some locating and holding members 15 provided on a surface of the radome 1 at the covering side. After that, the radome 1 is assembled to the main reflector 2 by fastening the rim 28 of the main reflector 2 with the bolts 14 using some screws 5. At the same time, by locating function of the locating and holding members 15, it is ensured that the radome 1 is tightly secured onto the main reflector 2 so as to form a compact construction.
The radome of the invention may be manufactured integrally by plastic molding process. For example, the bolts 14 and locating and holding members 15 may be formed integrally. As a result, the product thus formed has good uniformity and causes low fabrication cost.
In terms of mechanical characteristics and compared to a conventional protruded or recessed antenna radome, the antenna radome of the invention has small size. In addition, the arcuate auxiliary reflective portion 13 and skirt 28 have further contribution to structural strength of the radome. Furthermore, the antenna radome of the invention has attractive appearance.
In a summary, the microwave antenna radome of the invention is better than a conventional product in terms of both electrical and mechanical performance. As such, a microwave antenna employing the radome of the invention is necessarily better than a conventional antenna.
Though various embodiments of the invention have been illustrated above, a person of ordinary skill in the art will understand that, variations and improvements made upon the illustrative embodiments fall within the scope of the invention, and the scope of the invention is only limited by the accompanying claims and their equivalents.

Claims

A microwave antenna radome used for covering a microwave antenna and of rotatablely symmetrical, comprising the following components all of which are arranged concentrically:
a compensation portion located at a central portion of the radome and used for compensating phase delay of electrical field at the central portion of an antenna aperture plane caused by blocking of a feed;

a main reflective portion located on a periphery of the compensation portion and used for reflecting electromagnetic wave originating from the feed of the microwave antenna at a specific direction biased from the feed; and

an auxiliary reflective portion located on a periphery of the main reflective portion and used for bunching and reflecting diffraction electromagnetic wave at edge of the microwave antenna.
The microwave antenna radome as recited in claim 1, wherein the compensating portion has the shape recessed towards a covering side direction of the radome.
The microwave antenna radome as recited in claim 2, wherein the compensating portion has a gauss shape, conical shape or spherical shape.
The microwave antenna radome as recited in claim 1, wherein the main reflective portion is recessed towards the covering side direction of the radome.
The microwave antenna radome as recited in claim 4, wherein the main reflective portion takes on an inclined conical plane shape.
The microwave antenna radome as recited in claim 1, wherein the auxiliary reflective portion is protruded towards an opened side direction of the radome.
The microwave antenna radome as recited in any one of claims 1-6, wherein the thickness of the compensating portion is smaller than that of the main reflective portion.
The microwave antenna radome as recited in any one of claims 1-6, wherein a specific direction at which electromagnetic wave is reflected by the main reflective portion is defined to be corresponding to a region outside of the main lobe of an entire antenna radiation pattern.
The microwave antenna radome as recited in claim 8, wherein the specific direction corresponds to zero-point angular position or a distal side lobe angular position of the entire antenna radiation pattern.
A microwave antenna comprising a feed, a reflector and a radome, wherein a rim is outwardly defined on an opened surface of the reflector; the radome is that recited in any one of claims 1-9; a skirt engaged with the rim is disposed on the radome at a location adjacent the auxiliary reflective portion; and the rim is secured onto the skirt by means of screw.
The microwave antenna as recited in claim 10, wherein the rim and skirt are assembled together by a plurality of locating and holding members provided on a surface of the radome at the covering side.
The microwave antenna as recited in claim 10, wherein absorbing material is provided on the radome at location adjacent the skirt at the opened side.
The microwave antenna as recited in claim 12, wherein the absorbing material is selected from any one of foam, sponge and rubber.
The microwave antenna as recited in any one of claims 10-13, wherein the diameter of the compensating portion of the radome is equal to that of a sub-reflector of the feed.