A MICROSTRIP DOUBLE SIDED MONOPOLE YAGI-UDA ANTENNA WITH
APPLICATION IN SECTOR ANTENNAS
FIELD OF THE INVENTION
The present invention relates to wireless local area networks and in particular to a novel Yagi-Uda antenna for use in such networks.
BACKGROUND TO THE INVENTION
Modern wireless networks rely on suitable antennas that exhibit desirable performance characteristics while remaining light weight. In many wireless networks, multiple independent antennas may be used, whether in stand-alone mode or as part of a composite antenna.
In most systems, it Is preferable that the performance of each such antenna be consistent across the board and in conformance to designed parameters.
With the emergence of new wireless standards for multiple input multiple output (MIMO) systems, the design of low profile, high gain, efficient and cheap antennas for improving the performance of wireless systems has gained increased importance.
One of the more challenging areas of wireless antenna design is the implementation of high gain sector antennas with vertical polarization for wireless local area network (WLAN) access points.
While a number of different kinds of printed circuit antennas have been considered for wireless applications, none of these conventional antennas have proved suitable - 2a -Attorney Ref: 1227P016CA01 for vertically polarized sector antenna applications. This includes the so-called Yagi-Uda dipole antenna well known in the art, for example, as discussed in microstrip form in United States Patent Nos. 5,712,643 entitled "Planar Microstrip Yagi Antenna Array" and issued to Skladany on January 27, 1998, and 7,015,860 entitled "Microstrip Yagi-Uda Antenna" and issued to Alsliety on March 21, 2006.
The primary difficulty with such conventional antennas is inserting them in on a common disk in a stable vertical position and in providing a feed network therefore.
Additionally, the physical height of such antennas would be half of their operating wavelength.
Accordingly, it is desirable to provide a novel sector antenna that may be produced in quantities while maintaining minimum consistent performance characteristics.
Furthermore, it is desirable to provide a novel sector antenna that maintains stability, good gain, wide bandwidth and low return loss characteristics.
SUMMARY OF THE INVENTION
In a first aspect, this document discloses a Yagi-Uda monopole antenna printed on each side of a double-sided printed circuit board wherein each strip element etched on a first side of the printed circuit board is electrically connected to a corresponding strip element on a second side of the printed circuit board by at least one via hole.
The present invention accomplishes these aims by providing a double-sided printed-circuit board (PCB) monopole Yagi-Uda antenna. Preferably, a plurality of such antennas is vertically mounted in spoke-like fashion around a circular ground plane deposited on one side of a PCB substrate.
- 2b -Attorney Ref: 1227P016CA01 To assist in manufacturability and reproducibility, the monopoles are printed on a monopole dielectric substrate, which provides generally more consistent and improved performance over discrete wire monopole Yagi-Uda antennas. Because the monopoles are printed on both sides of the PCB and then connected by vias, there is no bias in the antenna pattern when vertically mounted as contemplated above and the resulted pattern would be completely symmetrical.
According to a broad aspect of an embodiment of the present invention, there is disclosed a Yagi-Uda monopole antenna printed on each side of a double-sided printed circuit board.
According to a second broad aspect of an embodiment of the present invention, there is disclosed a directional beam antenna comprising a plurality of such Yagi-Uda monopole antennas and a metallic disk, wherein the plurality of Yadi-Uda monopole antennas are mounted substantially normal to the metallic disk and radially outward from an axis thereof in spaced-apart fashion.
BRIEF DESCRIPTION OF THE DRAWINGS
The embodiments of the present invention will now be described by reference to the following figures, in which identical reference numerals in different figures indicate identical elements and in which:
Figure 1 is a perspective view of an antenna in accordance with a preferred embodiment of the present invention as mounted in an exemplary configuration as part of a MIMO sub-assembly;
Figure 2 is a plan view of the layout of a side of a double-sided PCB monopole Yagi-Uda antenna used in the MIMO
sub-assembly of Figure 1; and Figure 3 is a plot of simulated and measured input reflection for the antenna of Figure 2.
Figure 4 is a plot of measured directivity and gain of an antenna in accordance with the present invention.
Figure 5 shows a simulated azimuth and elevation pattern of an antenna in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to Figure 1, there is shown a circular metallic disk 110, preferably deposited upon an antenna PCB
substrate, each of which holds a plurality of directional beam antennas 210, which each comprise the inventive double-sided printed circuit monopole Yagi-Uda antenna vertically oriented around the circumference thereof and connected by a Sub Miniature Version A (SMA) connector soldered therewith.
An omni directional antenna 209 is located on a pedestal 208 at the center of the circular metallic disk 110. This omni directional antenna 209 is a sleeve monopole on a small circular ground plane 208 and is used in different operation modes of MIMO application.
Preferably, the circular metallic disk 110 is deposited on one side of a PCB substrate.
Turning now to Figure 2, each of the monopole antennas 210 are printed on both sides of a dielectric substrate 211. The dielectric substrate thickness and permeability can be a variable in the design.
The use of double-sided PCB manufacturing technology permits more accurate monopole heights that correspond to more accurate beam shapes and design flexibility, while maintaining stability, good gain, wide bandwidth and low return loss characteristics. Experimental results of Figures 3, 4 and 5 have shown that performance is also generally improved over discrete wire monopole Yagi-Uda antennas with the same number of directors.
Each Yagi-Uda antenna 210 has one reflector 212, one driver 213 and two director elements 214, 215. It is made by etching identical strips on both sides of the PCB
dielectric substrate 211. The two identical strips are connected together with via holes (not clearly shown) that help to suppress the destructive effect of surface waves.
The double-sided pattern of such an antenna provides both a symmetrical pattern in the azimuth plane and a higher radiation efficiency over prior attempts to mass produce dipole Yagi-Uda antennas using single sided PCB techniques.
Preferably, the monopole dielectric substrate 211 is thin, of approximately 0.787 mm, to avoid dielectric losses, and manufactured from the low cost Flame Resistant 4 (FR4) material having a permittivity of 4.2 and a tangent loss of 0.02.
In a preferred embodiment, each monopole dielectric substrate has a length of 8 cm and width of 3 cm. To achieve operation in the 2.43 GHz band, as shown in Figure 3, the reflector 212 is preferably 27.5 mm long, the driver 213 is 24.6 mm long, the first director 214 is 21.7 mm long and the second director 215 is 22.4 mm long. The reflector 212 and driver 213 are separated by 25.5 mm, while the driver 213 and first 214 and second 215 directors are each separated by 21.2 mm.
Each strip is preferably 2 mm wide and the distal ends of each strip are connected through the substrate by vias 218. The central conductor 221 of an SMA connector 219 is connected to the driver 213 while its ground 222 is connected to the SMA ground conductors 220 on the antenna board 211.
The inner conductor 221 of a SMA connector 219 is preferably soldered to the driver 213 of Yagi-Uda antenna 210, while the reflector 212 and directors 214, 215 are soldered to ground.
Experimental and simulation results of Figures 3 ,4 and 5 have shown that the double-sided PCB monopole Yagi-Uda antenna 210 of the present invention exhibits wide impedance bandwidth and an azimuth beam pattern that is symmetrical due to the double-sided etching. The experimental input reflection is well below -10dB through a bandwidth of 150 MHz without any extra matching circuits.
The monopole implementation has the advantage of being of shorter length compared to a dipole Yagi-Uda antenna and an easier feed with good matching. In the preferred embodiment, the Yagi-Uda monopole antenna 210 has a height of almost a quarter wavelength, that is, half of the height of conventional printed circuit Yagi-Uda dipole antennas and thus boasts a low profile.
It will be apparent to those skilled in this art that various modifications and variations may be made to the embodiments disclosed herein, consistent with the present invention, without departing from the spirit and scope of the present invention.
For example, a Yagr-Uda antenna can be built on thicker PCBs with higher dielectric constants to reduce the size. Ground planes with bigger radii can be used to improve the gain. The number of directors can be increased to improve the gain. The driver, reflector, or directors, can be deliberately shaped to improve the matching of the antenna without adding any extra cost or complexity to the antenna design. The distance of the Yagi board to the center of the disk can be used as a parameter to control the gain and mutual coupling of antennas in a sector antenna application.
90 Other embodiments consistent with the present invention will become apparent from consideration of the specification and the practice of the invention disclosed therein.