Dual-polarized Wide-Bandwidth Antenna

Abstract

The invention relates to a low profile antenna, operating over a wide range of frequencies. The dual-polarized wideband antenna consists of: radiating elements, ground plane, metallic walls, coaxial cables, split-ring slots. The antenna is fed by coaxial cables at feed points, which are surrounded by split-ring slots. The antenna can be utilized as an element in an array to provide particular radiation pattern.

Claims

1. A dual-polarized wideband antenna, comprising: radiating elements, ground plane, metallic walls, coaxial cables, split-ring slots, which are configured in a particular fashion that radiating elements etched on a printed-circuit board using a thin substrate material with low permittivity and dielectric loss (.sub.r=2.2, tan =0.0009); the radiating elements placed above a ground plane with a height of a quarter wavelength of a centre frequency of the operating band; the metallic walls are raised perpendicular to the ground plane forming a cavity below the radiating elements with an optimum height of 0.2 .sub.c; the coaxial cable penetrating through the ground plane and the substrate to feed the antenna; an inner conductor of the coaxial cable connecting to the radiating elements; a split-ring slot surrounding a feed point.

2. A dual-polaried wideband antenna according to claim 1, with optimum dimensions listed below: TABLE-US-00002 Coordinates of the vertex of the radiating elements (unit: mm) V1V2 V2V3 V3V4 V4V5 V5V6 V6V7 V7V8 V8V1 4.2 2.1 3.9 1.9 1.9 3.7 2.1 4.2 and: substrate length of 25 mm; ground plane length of 40 mm; feed-point distance of 3.15 mm; split-ring slot gap of 0.2 mm; slot diameter of 0.51 mm; spacing between radiating elements and ground plane of 6.4 mm; metallic-wall height of 4.5 mm; substrate thickness of 0.508 mm.

3. A dual-polaried wideband antenna according to claim 2 employed as an element in an array to synthesize a particular radiation pattern; the array use elements in both row and column.

4. A dual-polaried wideband antenna according to claim 1 employed as an element in an array to synthesize a particular radiation pattern; the array use elements in both row and column.

5. A dual-polaried wideband antenna according to claim 1, wherein the substrate comprises Rogers RO5880.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1A is the overview of each antenna element;

[0014] FIG. 1B is a top view of the antenna;

[0015] FIG. 1C is a cross-sectional view of the antenna;

[0016] FIG. 2 is the feed parts for radiating elements of the antenna wherein the dielectric substrate is invisible for more clarity;

[0017] FIG. 3 is the reflection coefficient of the antenna;

[0018] FIG. 4 is a 2D plot of the antenna radiation pattern; and

[0019] FIG. 5 depicts how to create a 16-by-1 antenna array from elements.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The following describes the invention with explanations and images.

[0021] FIGS. 1A, 1B and 1C describe the antenna in different views. The antenna includes: radiating elements 102, ground plane 103, metallic walls 104, coaxial cables 105, split-ring slots 106.

[0022] The antenna includes the radiating elements 102 etched on the dielectric substrate 101. The radiating elements are four petals copper flower-shaped patches printed on the dielectric substrate 101. The four petals are identical, generated by a 90 rotation around the axis perpendicular to the substrate plane. Each petal is bounded by a polygon having vertices V1-V8. Initially, V1-V8 are the vertices of the polygon inscribed in a circle having the diameter of V1-V5 distance. The position of each vertex is optimized to obtain the best impedance matching and operating bandwidth. Thanks to the optimized shape, the antenna is composed of multi-segments corresponding to many resonant frequencies.

[0023] The dielectric substrate 101 is made of Rogers RO5880 with the low relative permittivity and loss tangent (.sub.r=2.2, tan =0.0009). Moreover, for reducing dielectric loss, the thickness of the substrate (t) is also small.

[0024] The height between the printed-circuit board and the ground plane 103 is initially assigned of a quarter wavelength at the center frequency (.sub.c/4) of the operating frequency band (i.e. 13 GHz). In the design progress, the height (H) is optimized to satisfy the requirements of antenna bandwidth and radiation pattern. After all, the H value is chosen of 0.27 .sub.c.

[0025] The ground plane 103 is employed to focus the radiated power into perpendicular direction. Theoretically, a larger ground plane 103 results in a higher radiated power. However, if the distance between the printed-circuit board and the ground plane 103 becomes considerable, the current density on the ground plane 103 is small and it is reasonable to reduce ground size.

[0026] Additionally, to avoid the distortion of antenna radiation patterns at high frequencies, metallic walls 104 are perpendicularly built to the ground plane, forming a cavity enclosed in the space under the printed-circuit board antenna. The cavity height H.sub.w is figured out to be 0.2 .sub.c.

[0027] Referred to FIG. 2, the coaxial cables 105 are employed to feed the antenna. The cables 105 penetrate through the ground plane 103 and the substrate 101. Inner conductors of the coaxial cables 105 connect to the radiating elements 102 on the printed-circuit board.

[0028] The antenna is dual-polarized provided that it is fed in pairs of opposite petals (two petals forming an angle of 180 degree).

[0029] In this case, the signals propagating along the corresponding coaxial cable must be out-of-phase (or 180-degree different).

[0030] The feed point in each radiating element 102 is surrounded by a split-ring slot 106. The signal from the coaxial cable 105 is impeded by the slot 106 creating more inductance before flowing into the antenna. The longer the gap of the slot 106 is, the more inductance it provides. The inductance cancels out the intrinsic capacitance of the radiating elements 102, hence, the imaginary of the impedance of the antenna Im(Z.sub.ant) decreases, leaving real part Re(Z.sub.ant) of that closer to the characteristic impedance Z.sub.0 of the system. Therefore, the antenna is better impedance matched, thus, has a better reflection coefficient.

[0031] The fractional bandwidth that is defined as the following formula:

[00002]$\%.Math..Math.\mathrm{BW}=\frac{f_{\max }-f_{\min }}{f_{\max }+f_{\min }}2100.Math.\%$

where f.sub.max and f.sub.min are respectively the lowest and highest frequencies at which the reflection coefficients are lower than a desired value (ex. 10 dB).

[0032] FIG. 3 presents the antenna reflection coefficient. In the regime between f.sub.min=8 GHz and f.sub.max=18 GHz, the antenna possesses the reflection coefficient better than 10 dB, resulting in a fractional bandwidth greater than 75%.

[0033] At frequencies below 18 GHz, the radiation pattern of the antenna is depicted in FIG. 4. However, at frequencies higher than 18 GHz, the pattern is distorted with multiple sidelobes. Hence, the antenna is not ideal above 18 GHz, despite its good impedance-matching level, so the preferred use is below 18 GHz.

[0034] An antenna with the above technical descriptions has a good reflection coefficient and radiation pattern in the range from 8 GHz to 18 GHz. The following table describes an example of antenna with such specifications, thus, the antenna works well in the system.

[0035] The details of the antenna are listed in the Tab. 1 below

TABLE-US-00001 Coordinates of the vertex of the radiating elements (unit: mm) V1V2 V2V3 V3V4 V4V5 V5V6 V6V7 V7V8 V8V1 4.2 2.1 3.9 1.9 1.9 3.7 2.1 4.2 Dimensions of the antenna (unit: mm) L L.sub.g F s D H H.sub.w t 25 40 3.15 0.2 0.51 6.4 4.5 0.508

[0036] Where: [0037] L is the length of the substrate 101; [0038] L.sub.g is the length of the ground plane 103; [0039] F is the distance between the two feed point of the pair; [0040] s is gap of the split-ring slot 106; [0041] D is the diameter of the split-ring slot 106; [0042] H is the height from the ground plane 103 to the substrate 101; [0043] H.sub.w is the height of the metallic wall 104; [0044] T is the thickness of the substrate 101.

[0045] The antenna elements can be used in a different fashion that multiple elements be employed in an array configuration to provide required gain and radiation pattern for the systems. The radiation pattern of the array depends on the number of the antenna. Each element has its maximum gain of 7.5 dBi.

[0046] FIG. 5 describes a 16-element array configured in columning matrix. The array has a single cavity which has extended walls to cover all of its elements. Such an array provides a maximum gain of 15 dBi.

[0047] The number of elements can increase arbitrarily, however, this change causes the unwanted sidelobes that distort the radiation pattern. Hence, consideration must be carefully taken to trade off the array's radiation pattern with sidelobe levels.