The present invention relates to a dual band microstrip antenna.
In a modern office environment, wireless local access networks (WLAN) are more and more common. Such a WLAN usually uses many antennas to transmit and receive data. IEEE 802.11a (5.2 GHz) and IEEE 802.11b (2.4 GHz) are two widely used standards for WLANs. In a WLAN employing the above-mentioned two standards, dual band antennas are needed.
Among the many types of dual band antennas available, microstrip antennas are widely used for their low profiles and good gains, particularly since they are easy to be built into other equipment.
A conventional dual band microstrip antenna is disclosed in U.S. Pat. No. 5,561,435. Referring to FIG. 1, the dual band microstrip antenna comprises a first, second and third superimposed dielectric layers 4xe2x80x2, 6xe2x80x2, 16xe2x80x2, a ground plane 2xe2x80x2 on one external surface, a radiating patch 18xe2x80x2 on the other, and parallel conductive strips 12xe2x80x2, 14xe2x80x2 at the interface of the dielectric layers 6xe2x80x2, 16xe2x80x2, closer to the radiating patch 18xe2x80x2 than to the ground plane 2xe2x80x2. The dielectric constant of the second dielectric layer 6xe2x80x2 is different from that of the first and third dielectric layers 4xe2x80x2, 16xe2x80x2. A feeder (not labeled) is electrically connected to the dual band microstrip antenna with an inner conductor soldered to the radiating patch 18xe2x80x2 and an outer conductor soldered to the ground plane 2xe2x80x2. By properly choosing the thicknesses and the dielectric constants of the dielectric layers 4xe2x80x2, 6xe2x80x2, 16xe2x80x2, the dual band microstrip antenna can be made to work in two different frequency bands. Matching the line impedance to the antenna impedance in the high frequency band can be achieved by adjusting a soldering position of the inner conductor on the radiating patch 18xe2x80x2. Matching the line impedance to the antenna impedance in the low frequency band can be achieved by adjusting positions of the two conductive strips 12xe2x80x2, 14xe2x80x2.
However, the dual band microstrip antenna mentioned above can not work in two different frequency bands at the same time. Additionally, manufacturing the multiple dielectric layers is costly. Furthermore, achieving impedance matching in the two different frequency bands adds to the difficulty of manufacturing.
Hence, an improved dual band microstrip antenna is desired to overcome the above-mentioned shortcomings of existing dual band microstrip antennas.
A primary object, therefore, of the present invention is to provide a dual band microstrip antenna that can work in two different frequency bands at the same time.
Another object of the present invention is to provide a dual band microstrip antenna with a simple structure and low cost.
A dual band microstrip antenna in accordance with the present invention comprises a dielectric substrate, a ground plane attached to a bottom surface of the substrate, a first and second radiating patches separately elevated an appropriate height above and parallel to a top surface of the substrate, a first and second conductive posts respectively elevating the first and second radiating patches above the substrate and electrically connecting the first and second radiating patches with the ground plane, and a first and second feeder cables. Inner conductors and outer conductors of the feeder cables are respectively electrically connected to corresponding radiating patches and to the ground plane.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of a preferred embodiment when taken in conjunction with the accompanying drawings. A copending application filed on the same date with the invention titled xe2x80x9cMETHOD OF MAKING DUAL BAND MICROSTRIP ANTENNAxe2x80x9d is referenced hereto.