DUAL SLOT RADIATOR SINGLE FEEDPOINT PRINTED CIRCUIT BOARD ANTENNA
RELATED APPLICATIONS This application claims priority to United States Provisional Applications 60/552,933, filed March 12, 2004, and 60/566,911, filed April 30, 2004, titled the same, and incorporated herein as if set out in full. FIELD OF THE INVENTION The present invention relates to antennas and, more particularly, dual frequency printed circuit board antennas.
BACKGROUND OF THE INVENTION Printed circuit board antennas are generally known in the art. FIG. 1 shows a prior art style printed circuit board antenna 100. This antenna has a substrate 102, a ground plane 104, a microstrip line 106, a radiating slot 108, and a shorting strip 110. While antenna 100 functions well enough it has several drawbacks. Some of the drawbacks include single frequency operation and the microstrip line 106 for a power feed at the slot center. Thus, it would be desirous to provide an improved printed circuit board antenna having dual frequency operation and improved power feed.
SUMMARY OF THE INVENTION To attain the advantages and in accordance with the present invention, a multiband antenna is provided. The multiband antenna comprises a ground plane with a first slot radiator of a first length and a second slot radiator of a second length, the first and second slot radiators have first and second feed ends, and first and second terminating ends, respectively. A single power feed extends from a source end attached to a power source to a radiator end. The radiator end has a first branch connected the radiator and a second branch connected to the second radiator. The two radiators may be of different lengths to facilitate multi-frequencies of operation. The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a simplified diagram of a prior art antenna; FIG. 2 is a simplified diagram of an antenna consistent with an embodiment of the present invention; FIG. 3 is a frequency plot of an antenna constructed in accordance with an embodiment of the present invention; FIG. 4 is a simplified diagram of another antenna consistent with an embodiment of the present invention; and FIG. 5 is a simplified diagram of another antenna consistent with an embodiment of the present invention.
DETAILED DESCRIPTION The present invention will now be explained with reference to FIGS. 2- 5. While FIGS. 2-5 show embodiments of the present invention, one of ordinary skill in the art on reading the disclosure will understand different arrangements, configurations, and dimensions are possible and the configuration shown in FIGS. 2-5 should be considered exemplary and not limiting. FIG. 2 shows a printed circuit board antenna 200 consistent with an embodiment of the present invention. Antenna 200 is shown on a substrate 202, but substrate 202 is not necessary for the present invention. When included, substrate 202 is a dielectric material. Antenna 200 comprises a ground plane 204, a first radiating element 206, and a second radiating element 208. First radiating element has a feed end 206f and a terminating end 206t. Second radiating element has a feed end 208f and a terminating end First radiating element 206 and second radiating element 208 may be straight radiating elements or have zigzag, meanderline, curved, or the like geometries. Second radiating element 208 has a L shaped portion 210 at terminating end 208t. L shaped portion 210 could have other configurations, such as a C shape, a curve, a straight or I shape, a step shape or the like. Radiating portion 206 could have an alternative configuration at terminating end 206t if desired. A feed connection 212 is coupled to each first radiating element 206 and second radiating element 208 proximate or at feed end 206f and 208f. Feed connection 212 comprises a microstrip feed line 214 and a tee connection 216. Tee connection 216 has a first branch 218 terminating in a short 218s that shorts the tee connection to ground plane 204 and a second branch 220 terminating in a short 220s that shorts the tee connection to ground plane 204. Short 218s and short 220s reside proximate by a short distance d away from first radiating element 206 and second radiating element 208. Tee connection 216 could take other shapes, such as, a Y shape or the like. A power feed 220 connects to the microstrip feed line 214. If power feed 220 was a coaxial cable power feed, a conductor 222 of coaxial cable would attach to microstrip feed line 214 and a jacket 224 or ground of coaxial cable would attach to ground plane 204. Placement of tee connection 216 allows for impedance matching. Further, while explained using a coaxial cable as the power feed 220, any conventional power feed is possible. In operation, first radiating element 206 (the shorter element) would operate at a higher frequency and second radiating element 208 (the longer element) would operate at a lower frequency. The elements could be tuned by varying the configuration, dimensions, and the like of each element. FIG. 3 shows a possible frequency response of an antenna that was constructed in accordance with the present invention. While two radiating elements are shown to provide two bands of operation, additional radiating elements would allow antenna 200 to operate at still additional frequencies. 90 While antenna 200 is a satisfactory antenna and an improvement over prior art designs, the size of antenna 200 could be reduced. In particular, FIG. 4 shows a half slot antenna 400. Half slot antenna 400 is shown on a substrate 402 (but substrate 402 is not necessary for the present invention). Further, while antenna 400 is referred to as half slot antenna 400, one of 95 ordinary skill in the art will recognize on reading the disclosure that half slot is used generically and the present invention should not be limited by the term half. Antenna 400 comprises a ground plane 404, a first radiating element 406, and a second radiating element 408. First radiating element 406 has a feed end 406f and a terminating end 406t. Second radiating element 408 has a 100 feed end 408f and a terminating end 408t. A feed connection 410 is coupled to each of first radiating element 406 and second radiating element 408 proximate or at feed ends 406f and 408f, respectively. Feed connection 410 comprises a microstrip feed line 412 and a tee connection 414 originating from a feed edge 416 of ground plane 404. 105 Feed line 412 and tee connection 414 are similar to the devices described in connection with FIG. 2 and will not be re-explained in conjunction with FIG. 4. Ground plane 404 has a radiating edge 420 opposite feed edge 416. As shown, radiating elements 406 and 408 terminate at radiating edge 420 of ground plane 404. Thus, ground plane 404 can be of a reduced size. Further, 110 assuming antenna 200 and half slot antenna 400 are designed to function at the same operating frequencies, the overall length of radiating element 406 is about 1A the overall length of radiating element 206 and the overall length of radiating element 408 is about Vi the overall length of radiating element 408 (hence the phrase half slot antenna). Thus, the overall size of antenna 400 is 115 reduced as compared to antenna 200. Referring now to FIG. 5, an antenna 500 is shown. Antenna 500 as a first radiating element 506 and a second radiating element 508. First radiating element 506 has a terminating end 508t that terminates at a radiating edge of ground plane 502. Thus, first radiating element functions similar to 120 radiating element 406. Second radiating element 508 is situated on ground plane 502 and functions similar to radiating element 208. In other words, antenna 500 is a hybrid between antenna 200 and antenna 400. While radiating element 508 could be the half slot element, it makes more design sense to have the lower frequency element as the half slot because the lower 125 frequency element requires a greater length than the higher frequency element. While the invention has been particularly shown and described with reference to an embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made 130 without departing from the spirit and scope of the invention.