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Exemplary embodiments are provided of RFID antenna assemblies having folded patch-antenna structures and that are configured with circular polarization or dual linear polarization. An antenna assembly may generally include two folded patch-antenna structures oriented generally perpendicularly to eac

Exemplary embodiments are provided of RFID antenna assemblies having folded patch-antenna structures and that are configured with circular polarization or dual linear polarization. An antenna assembly may generally include two folded patch-antenna structures oriented generally perpendicularly to each other. Each folded patch may create a linear polarization wave. When each folded patch is fed independently, the antenna assembly radiates two independent waves that are perpendicularly polarized to each other, therefore providing a dual polarized antenna. In other embodiments, the antenna assembly may include two folded patch-antenna structures again oriented generally perpendicularly to each other. By feeding each folded patch with a 90-degree phase delay between them, a circular polarization wave is radiated. A power divider network may be used to feed the two folded patches with the 90-degree phase delay. The two folded patches may be integrated so as to form a cavity or housing for a printed circuit board.

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What is claimed is: 1. An antenna assembly comprising a folded patch-antenna structure including a first folded patch-antenna, a second folded patch-antenna, and a plurality of slots, whereby the antenna assembly radiates through the slots and the slots cooperate to create a first slot array for a

What is claimed is: 1. An antenna assembly comprising a folded patch-antenna structure including a first folded patch-antenna, a second folded patch-antenna, and a plurality of slots, whereby the antenna assembly radiates through the slots and the slots cooperate to create a first slot array for a first polarization associated with the first folded patch-antenna and a second slot array for a second polarization associated with the second folded patch-antenna, wherein each of the first and second folded patch-antennas includes: an elongate medial portion; and spaced-apart end portions each having an upward portion extending upwardly relative to the elongate medial portion and a lateral portion extending laterally relative to the upward portion partially over the elongate medial portion, and wherein: the first slot array is defined by the lateral portions of the first folded patch-antenna and a ground disposed within a space defined by the folded patch-antenna structure; and the second slot array is defined by the lateral portions of the second folded patch-antenna and the ground. 2. The antenna assembly of claim 1, wherein the first and second folded patch-antennas are oriented generally perpendicular relative to each other. 3. The antenna assembly of claim 1, wherein the first folded patch-antenna radiates a linear polarization through the first slot array, and wherein the second folded patch-antenna radiates a linear polarization through the second slot array. 4. The antenna assembly of claim 1, wherein the first and second folded patch-antennas are fed with a ninety-degree phase delay therebetween such that circularly polarized radiation is radiated through the slots. 5. The antenna assembly of claim 4, further comprising a power divider network configured for feeding the first and second folded patch-antennas. 6. The antenna assembly of claim 1, wherein the first and second folded patch-antennas are fed independently from each other such that the antenna assembly radiates independent waves perpendicularly polarized to each other, thereby providing dual linear polarization. 7. The antenna assembly of claim 1, wherein the effective dielectric of the first and second folded patch-antennas is about one. 8. An antenna assembly comprising: a folded patch-antenna structure including a first folded patch-antenna, a second folded patch-antenna, and a plurality of slots, whereby the antenna assembly radiates through the slots and the slots cooperate to create a first slot array for a first polarization associated with the first folded patch-antenna and a second slot array for a second polarization associated with the second folded patch-antenna; a substrate having a lower substrate surface and an upper substrate surface; a transmission line coupled to the upper substrate surface; a metallization coupled to the lower substrate surface and operable as a ground plane for the transmission line and as supporting structure for the patch-antenna structure, and wherein: the first slot array is defined by portions of the first folded patch-antenna and the metallization; and the second slot array is defined by portions of the second folded patch-antenna and the metallization. 9. The antenna assembly of claim 1, wherein each upward portion is folded upwardly at an angle of about ninety degrees relative to the corresponding medial portion, and wherein each lateral portion is folded at an angle of about ninety degrees relative to the corresponding upward portion. 10. The antenna assembly of claim 1, wherein the antenna assembly is tunable to different frequency bands of operation by only changing a length of the lateral portions. 11. A radio-frequency identification (RFID) reader comprising the antenna assembly of claim 1. 12. The antenna assembly of claim 1, further comprising a printed circuit board microstrip network disposed within a space defined by the folded patch-antenna structure for feeding the first and second folded patch-antennas. 13. The antenna assembly of claim 1, wherein the antenna assembly further comprises: a substrate having a lower substrate surface and an upper substrate surface; a transmission line coupled to the upper substrate surface; and a metallization coupled to the lower substrate surface and operable as a ground plane for the transmission line and as supporting structure for the patch-antenna structure. 14. The antenna assembly of claim 8, wherein each of the first and second folded patch-antennas includes: an elongate medial portion; and spaced-apart end portions each having an upward portion extending upwardly relative to the elongate medial portion and a lateral portion extending laterally relative to the upward portion partially over the elongate medial portion, and wherein: the first slot array is defined by the lateral portions of the first folded patch-antenna and the metallization disposed within a space defined by the folded patch-antenna structure; and the second slot array is defined by the lateral portions of the second folded patch-antenna and metallization. 15. The antenna assembly of claim 14, further comprising a first electrically-conductive generally cylindrical probe coupled to the first folded patch-antenna structure and the transmission line, and a second electrically-conductive generally cylindrical probe coupled to the second folded patch-antenna structure and the transmission line, wherein the first and second probes run from the respective first and second folded patch-antennas through the metallization and the substrate to the transmission line. 16. The antenna assembly of claim 12, wherein the printed circuit board microstrip network is operable for feeding the first and second folded patch-antennas with a ninety-degree phase delay therebetween such that circularly polarized radiation is radiated through the pair of slots of each folded patch-antenna. 17. The antenna assembly of claim 1, further comprising a single coaxial cable for feeding the first and second folded patch-antennas. 18. A radio-frequency identification (RFID) reader suitable for use with an RFID tag of an RFID system, the RFID reader comprising first and second folded patch-antennas oriented generally perpendicular to each other and operable for communicating with an antenna of the RFID tag, wherein the first and second folded patch-antennas have spaced-apart end portions and slots cooperating to create a first slot array for a first polarization associated with the first folded patch-antenna and a second slot array for a second polarization associated with the second folded patch-antenna, wherein each of the first and second folded patch-antennas includes: an elongate medial portion; and the end portions each include an upward portion extending upwardly relative to the elongate medial portion and a lateral portion extending laterally relative to the upward portion partially over the elongate medial portion, and wherein: the first slot array includes a first pair of slots defined by the lateral portions of the first folded patch-antenna and a ground disposed within a space defined by the first and second folded patch-antennas; and the second slot array includes a second pair of slots defined by the lateral portions of the second folded patch-antenna and the ground. 19. An RFID system comprising the RFID reader of claim 18 and an RFID tag, the RFID tag including an antenna and an integrated circuit operable for storing information, the tag antenna operable for receiving energy radiated by the RFID reader for powering the integrated circuit, the RFID reader operable for transmitting a signal to the RFID tag and for receiving a response to the signal from the RFID tag to recognize information of the RFID tag. 20. The RFID reader of claim 18, wherein each upward portion is folded upwardly at an angle of about ninety degrees relative to the corresponding medial portion, and wherein each lateral portion is folded at an angle of about ninety degrees relative to the corresponding upward portion. 21. The RFID reader of claim 18, wherein the first and second folded patch-antennas are fed with a 90-degree phase delay therebetween such that circularly polarized radiation is radiated. 22. The RFID reader of claim 18, wherein the first and second folded patch-antennas are fed independently from each other such that the antenna assembly radiates independent waves perpendicularly polarized to each other, thereby providing dual linear polarization. 23. The RFID reader of claim 18, further comprising a single coaxial cable for feeding the first and second folded patch-antennas. 24. A radio-frequency identification (RFID) reader suitable for use with an RFID tag of an RFID system, the RFID reader comprising: first and second folded patch-antennas oriented generally perpendicular to each other and operable for communicating with an antenna of the RFID tag; a ground and a printed circuit board microstrip network disposed within a space defined by the first and second folded patch-antennas for feeding the first and second folded patch-antennas, and wherein: a first pair of slots is defined by portions of the first folded patch-antenna and the ground; and a second pair of slots is defined by portions of the second folded patch-antenna and the ground. 25. The RFID reader of claim 24, wherein the first and second pair of slots cooperate to create a first slot array for a first polarization associated with the first folded patch-antenna and a second slot array for a second polarization associated with the second folded patch-antenna. 26. The RFID reader of claim 24, wherein the first and second folded patch-antennas have spaced-apart end portions and the first and second pair of slots cooperate to create a first slot array for a first polarization associated with the first folded patch-antenna and a second slot array for a second polarization associated with the second folded patch-antenna. 27. The RFID reader of claim 26, wherein each of the first and second folded patch-antennas includes: an elongate medial portion; and the end portions each include an upward portion extending upwardly relative to the elongate medial portion and a lateral portion extending laterally relative to the upward portion partially over the elongate medial portion, and wherein: the first slot array includes the first pair of slots defined by the lateral portions of the first folded patch-antenna and the ground disposed within a space defined by the first and second folded patch-antennas; and the second slot array includes the second pair of slots defined by the lateral portions of the second folded patch-antenna and the ground. 28. An antenna assembly comprising: a patch-antenna structure including first and second pairs of generally opposing end portions and first and second elongate medial portions oriented generally perpendicular to each other and extending between the corresponding first or second pair of end portions, each end portion having an upward portion extending upwardly relative to the corresponding first or second elongate medial portion and a lateral portion extending inwardly at an angle of about ninety degrees relative to the upward portion partially over the corresponding first or second elongate medial portion, the lateral portions of the first pair of end portions defining a first pair of slots, the lateral portions of the second pair of end portions defining a second pair of slots, whereby the antenna assembly radiates through the first and second pairs of slots with each pair of slots cooperating to create a slot array; a printed circuit board microstrip network disposed within a space defined generally by the folded patch-antenna structure for feeding the patch-antenna structure; a substrate having a lower substrate surface and an upper substrate surface; a transmission line coupled to the upper substrate surface; and a metallization coupled to the lower substrate surface and operable as a ground plane for the transmission line and as supporting structure for the patch-antenna structure; the first pair of slots is defined between the metallization and the lateral portions of the first pair of end portions; and the second pair of slots is defined between the metallization and the lateral portions of the second pair of end portions. 29. The antenna assembly of claim 28, further comprising a single coaxial cable for feeding the patch-antenna structure. 30. The antenna assembly of claim 28, further comprising: a first electrically-conductive generally cylindrical probe coupled to the first elongate medial portion and the transmission line, the first probe extending from the first elongate medial portion through the metallization and the substrate of the circuit board to the transmission line; and a second electrically-conductive generally cylindrical probe coupled to the second elongate medial portion and the transmission line, the second probe extending from the second elongate medial portion through the metallization and the substrate of the circuit board to the transmission line. 31. The antenna assembly of claim 28, wherein the patch-antenna structure comprises first and second folded patch-antennas respectively defining the first and second elongate medial portions and the first and second pairs of end portions. 32. The antenna assembly of claim 28, wherein each of the first and second folded patch-antennas creates a linear polarization, and wherein the first and second folded patch-antennas are fed independently from each other such that the antenna assembly radiates independent waves perpendicularly polarized to each other, thereby providing dual linear polarization. 33. The antenna assembly of claim 28, wherein the first and second folded patch-antennas are fed with a ninety-degree phase delay therebetween such that circularly polarized radiation is radiated through the pair of slots of each folded patch-antenna.