Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
1999-06-21
2001-09-25
Le, Hoanganh (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
Reexamination Certificate
active
06295028
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a dual band antenna, comprising at least one first antenna element and an associated second antenna element for transmitting and/or receiving radio frequency radiation in a first, relatively low frequency band and a second, relatively high frequency band, respectively, and an electrically conductive, substantially planar reflector device, the at least one first antenna element being located close to the associated second antenna element so as to form at least one combined antenna element on a front side of the reflector device and to define first and second radiation beams, respectively, each having a specific azimuth beam width being substantially symmetrical with respect to a central, longitudinal plane oriented perpendicularly to the planar reflector device and extending through the at least one combined antenna element.
Recently, the demand for antennas for mobile wireless applications has increased dramatically, and there are now a number of land and satellite based systems for wireless communications using a wide range of frequency bands. Accordingly, there is also a need for antennas being operable in two or more frequency bands, preferably also with dual polarization in order to accomplish a desired diversity of the radio frequency radiation received by the antenna. Such dual band, dual polarized antennas are especially useful in base station antennas.
Due to the capacity problems encountered in the existing AMPS-800 and GSM-900 MHz systems, many operators have recently aquired licenses for the DCS-1800 or PCS-1900 MHz band as well, i.e. a much higher frequency band which is widely separated from the lower frequency band by approximately an octave. Therefore, in order to make use of the existing sites for the new frequency bands, a favorable way of implementing the new systems is to replace the existing GSM or AMPS antennas by dual band antennas operable, e.g., in the dual bands GSM/DCS or AMPS/PCS.
A dual band antenna of the kind mentioned in the first paragraph is disclosed in the Swedish patent application 9704642-9 (Allgon AB), wherein each dual or combined antenna element comprises aperture coupled, planar, mutually parallel patches being placed one on top of the other and being centered in relation to a central point of a cross-shaped aperture in a ground plane layer serving as a reflector device. Microwave power is fed from a feed network in two separate frequency bands, the microwave power in a first frequency band being fed via the aperture in the reflector device to a first radiating patch, and the microwave power in a second frequency band (the higher band) being fed via the aperture in the reflector device and via a coupling patch and a likewise cross-shaped aperture in the first radiating patch to a second radiating patch, which is smaller and operates in the higher frequency band.
Such an antenna structure with combined antenna elements has turned out to be very advantageous in production and use. However, a practical problem has arisen with regard to the width of the radiating beams on the front side of the antenna. Because of the different wavelengths, e.g., 0.326 m and 0.167 m, respectively, the width of each beam in azimuth, measured as the half power limit (−3dB), will be quite different from one another, the beam in the lower frequency band being much wider than the beam in the higher frequency band.
SUMMARY OF THE INVENTION
Accordingly, a main object of the present invention is to provide a dual band antenna structure which enables a modification of the beam width in the higher frequency band, in particular so as to become close to the beam width in the lower frequency band.
Other secondary objects are to provide an antenna structure which is easy to implement in serial production and which is well suited for practical use in base stations operating in at least two frequency bands, including bands having center frequencies in the regions 800-950 MHz and 1750-1950 MHz. Still another object is to achieve a more favorable front to back ratio of the radiated power.
The main object stated above is achieved, according to the present invention, in that the reflector device, on each lateral side thereof, is provided with an edge portion formed as a groove, which is open towards the front side of the reflector device and which is dimensioned so as to widen the beam width of the second beam (in the higher frequency band), in particular to an angular value being close to that of the first beam (in the lower frequency band). The widening of the beam in the higher frequency band is caused by a secondary radiation, with a horizontal electrical field component, from the edge portions of the reflector device.
The exact configuration and dimensions of the grooves are of course dependent on the particular frequency bands being used, the configuration of the combined antenna elements, the configuration of the reflector device, and the geometry and material of the cover or radome normally mounted as a protective cover on the front side of the antenna.
As a general rule, however, tests have shown that the depth of the groove should be 0.1 to 0.3 times the wavelength of the radiation of the second frequency band (the higher frequency band) and the width of the groove should be about 0.2 times the above-mentioned wavelength. Normally, the groove has such dimensions that it has only a minor effect on the width and other properties of the beam in the first frequency band (the lower frequency band). A typical lateral width of the whole reflector device is 0.2 to 0.3 m, in particular about 0.25 m-0.28 m for an antenna with a 70° azimuth beam width (or about 1.5 times the wavelength in the higher frequency band) and the width of each longitudinal groove at the edges of the reflector is about 0.033 m (or about 0.2 times the wavelength in the higher frequency band).
The geometrical configuration of the grooves can be selected as desired by those skilled in the art, e.g., with a rectangular, arcuate or V-formed cross-section. For practical reasons, the groove is preferably defined by longitudinally extending, substantially planar wall portions, such as two side wall portions and an intermediate bottom wall portion, obtained by bending of a metallic sheet material, such as aluminium, preferably in one piece with the rest of the reflector device.
In a particular embodiment, which has been tested and proven to give excellent performance, the central portion of the reflector device, between the edge portions being formed as grooves, is limited laterally or sideways by lateral, up-standing wall portions and longitudinally along a linear array of seven dual antenna elements (stacked patches) by metallic (aluminium) shield wall elements extending transversely in the region between each pair of adjacent dual elements in the linear array. The total length of this antenna, including the frontal radome, is 1.2 m, the total width thereof being 0.3 m and the depth or thickness thereof being 0.11 m.
The invention will now be explained further with reference to the appended drawings illustrating the above-mentioned preferred embodiment of the dual band antenna.
REFERENCES:
patent: 4241352 (1980-12-01), Alspaugh et al.
patent: 5043738 (1991-08-01), Shapiro et al.
patent: 5087920 (1992-02-01), Tsurumaru et al.
patent: 5422649 (1995-06-01), Huang
patent: 5572222 (1996-11-01), Mailandt et al.
patent: 5661493 (1997-08-01), Uher et al.
patent: 5729237 (1998-03-01), Webb
patent: 5815119 (1998-09-01), Helms et al.
patent: 5896107 (1999-04-01), Huynh
patent: 5952983 (1999-09-01), Dearnley
patent: 6008763 (1999-12-01), Nystrom et al.
patent: 6061032 (2000-05-01), Sandstedt et al.
patent: 9704642-9 (1999-09-01), None
patent: WO97/43799 (1997-11-01), None
Jonsson Stefan
Karlsson Dan
Allgon AB
Dinh Trinh Vo
Jacobson & Holman PLLC
Le Hoang-anh
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