Patent Application
20070241983
The present invention relates to a dipole antenna comprising two pairs of dipoles arranged around a central region. An antenna of this kind is conventionally known as a “dipole square” or “dipole box”, although the dipole arms may be formed to present a non-square (for example, circular) shape.
FIG. 1 of U.S. Pat. No. 6,313,809 shows a dipole square with four connecting lines radiating from a centre point. U.S. Pat. No. 6,819,300 shows a dipole square where each dipole is driven be a respective coaxial cable. Various dipole square arrangements are also described in WO 2004/055938.
The exemplary embodiments of the invention provide a dipole antenna comprising a base; first and second pairs of dipoles positioned in front of the base and arranged around a central region; a first feed line which extends from the base towards the dipoles and splits at a first junction positioned in front of the base into a first pair of feed probes each of which is coupled to a respective one of the first pair of dipoles; and a second feed line which extends from the base towards the dipoles and splits at a second junction positioned in front of the base into a second pair of feed probes each of which is coupled to a respective one of the second pair of dipoles.
The exemplary embodiments of the invention also provide a dipole antenna comprising two pairs of dipoles arranged around a central region; and two pairs of feed probes each coupled to a respective dipole, wherein the feed probes are spaced from the dipoles so as to field-couple with the dipoles.
Certain exemplary embodiments of the invention also provide a dipole antenna comprising two pairs of dipoles arranged around a central region; a first pair of feed probes coupled to a first one of the pairs of dipoles; and a second pair of feed probes coupled to a second one of the pairs of dipoles, wherein the first pair of feed probes is positioned on a first side of the dipoles and the second pair of feed probes is positioned on a second side of the dipoles opposite to the first side.
The accompanying drawings which are incorporated in and constitute part of the specification, illustrate embodiments of the invention and, together with the general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.
Referring to
The antenna comprises a line of dipole squares of the kind shown in
The dipoles are identical in construction and only the dipole 3a will be described for illustration. The dipole 3a comprises a pair of legs 5a, 5b which extend radially from the central region 16 and parallel with the base and are separated by a slot 6, and a pair of dipole arms 7a, 7b oriented parallel to and perpendicular with the antenna axis 15.
The dipole 3a is driven by a hook-shaped balun feed probe having a portion 8b running parallel and proximate to the front face of the leg 5b, and a portion 8a running parallel and proximate to the front face of the leg 5a. The balun is mounted to the legs 5a,5b by insulating spacers (not shown). The portion 8a of the balun is connected to a feed line 9 at the centre of the dipole square.
The feed line has a front portion 9a shown in
A V-shaped leg shown in
The portion 9b of the feed line is mounted to the first part 11a of the support leg by a pair of insulating spacers (not shown). The feed line 9 then passes through the slot 10 as shown most clearly in
The dipole 3b is driven by a second hook-shaped balun which is connected to the portion 9a of the feedline at a two-way junction 9d in front of the dipoles.
The dipoles 4a,4b are driven by a similar balun arrangement, but in this case the baluns are positioned on the opposite rear side of the antenna as shown most clearly in
The feed line 12 is similar to the feed line 9, and has a front portion 12a, a portion 12b extending from the base, and a rear portion 12c which has a tab at it end which slots into the base 2.
The portion 12b of the feed line is mounted to the second part 11b of the support leg by insulating spacers (not shown).
The dipole 4b is driven be a second hook-shaped balun which is connected to the portion 12a of the feedline at a two-way junction 12d positioned between the base and the dipoles.
The two pairs of dipoles are proximity fed by the baluns to radiate electrically in two polarization planes simultaneously. The dipole square is configured to operate at a frequency range of 806 Mhz-960 MHz, although the same arrangement can be used to operate in other frequency ranges.
Splitting the feed lines at junctions 9d,12d positioned in front of the base means that only two feed lines (instead of four) are required to couple the dipoles to the feed network (not shown) carried by the base 2. As a result, only two feed lines are required on the base feed network (instead of four). This means that the feed network on the base can be fitted to a conventional crossed-dipole antenna (which only requires two feed lines) as well as the dipole square shown in
The proximity-fed airstrip arrangement (in which the baluns are spaced from the dipoles by an air gap so that they field-couple with the dipoles) results in higher bandwidth compared with a conventional direct-fed antenna (in which the dipoles are physically connected to the feed probe by a solder joint). Also the lack of solder joints resulting from the proximity-fed arrangement results in less risk of intermodulation and lower manufacturing costs compared with a conventional direct-fed antenna.
Placing the baluns on opposite sides of the dipoles also improves isolation between the two polarizations.
A second dipole square 20 is shown in
A third dipole square 30 is shown in
The dipole squares described above are formed in a single piece by diecasting. The dipole squares in the embodiment described below are implemented instead on printed circuit boards (PCBs).
The dipole squares are identical so only the dipole square 40 will be described. The dipole square 40 comprises a dipole PCB formed with dipoles 50a,50b,51a,51b on its front face shown in
The dipoles are identical in construction and only the dipole 50a will be described for illustration. The dipole 50a comprises a pair of legs 56a, 56b which extend radially from a central region 57 and are separated by a gap. A pair of dipole arms 58a, 58b each have a proximal portion oriented at −45° to the antenna axis and a distal portion oriented respectively parallel to and perpendicular with the antenna axis. The dipoles are separated by slots 59 in the corners of the PCB. The dipole square presents a generally octagonal profile.
A support structure for the dipole PCB is provided by a crossed pair of feed PCBs 54,55 (shown in detail in
A feed line 64 extends from the pad 64 away from the base PCB 42 towards the dipoles, and splits at a junction 65 positioned approximately midway between the base PCB 42 and the dipole PCB, and in front of a slot 66 in the feed PCB 54. The feed line 64 splits at the junction 65 into a first feed probe 67a with a pad 68a, and a second feed probe 67b with a pad 68b. The pad 68a is soldered to the balun 52a and the pad 68b is soldered to the balun 52b.
The feed PCB 55 shown in
The dipoles are proximity fed by the baluns to radiate electrically in two polarization planes simultaneously. The dipole square is configured to operate at a frequency range of 1710 Mhz-2100 MHz, although the same arrangement can be used to operate in other frequency ranges.
Splitting the feed line 64 at a junction 65 positioned in front of the base PCB 42 means that only a single pad 63 is required to couple to the feed network on the base PCB 42. As a result, only two feed lines 44,45 are required on the base PCB 42 (instead of four). This means that the base PCB 42 can be fitted to a conventional crossed-dipole antenna (which only requires two feed lines) as well as the dipole square shown in
The proximity-fed arrangement (in which the baluns are spaced from the dipoles on the opposite side of the PCB so that they field-couple with the dipoles) results in higher bandwidth compared with a conventional direct-fed antenna (in which the dipoles are physically connected to the feed line by a solder joint). Also the lack of solder joints resulting from the proximity-fed arrangement results in less risk of intermodulation and lower manufacturing costs compared with a conventional direct-fed antenna.
Although the embodiments described above are all dual-polarized antennas, the invention may also be implemented in a circularly polarized antenna in which the four dipoles are driven 90° out of phase.
Although the embodiments described above can all operate in a transmit mode (in which the antenna transmits radiation) and a receive mode (in which the antenna receives radiation), the invention may also be implemented in an antenna which is configured to operate only in a transmit mode or only in a receive mode.
Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the Applicant's general inventive concept.
