Patent Application
20130009832
This invention relates to UHF antennas and more particularly to a dual dipole/GPS antenna structure.
For systems that require ultra high frequency (UHF) and GPS communications, generally separate GPS antennas and UHF communication antennas are needed. Using two separate antennas in these cases is not a cost effective use of space on any platform. Particularly, small unmanned ground vehicles (SUGV), unmanned aerial vehicles, micro unmanned aerial vehicles, and soldier back pack applications are systems where antenna space is limited and antenna placement is important. A need therefore exists for an antenna design that minimizes antenna space on systems without impacting antenna performance.
More particularly robot vehicles have a requirement to communicate with base stations using UHF band communications. These vehicles also need to report back to the base station their exact location. While it might be thought that GPS L band antennas could be used both for geophysical location and communications, the L band antennas do not work for communications purposes especially in the UHF band. There is therefore a need for a low profile efficient dipole antenna that has its center some distance above the ground for propagation purposes while at the same time supporting GPS functionality.
In addition to the robot applications and applications involving the signaling of position of mobile devices such as remotely controlled vehicles and the like, as well as communicating with these devices, there is also a need for providing precise GPS timing signals to a class of transceivers termed Joint Tactical Radio System (JTRS) radios. In these applications it is not so much the requirement to be able to receive GPS signals for geo-location purposes, rather it is the functionality of such JTRS radios which are in essence software-defined radios. In order for software-defined radios to operate one has to have precise timing signals. This timing is provided in one embodiment through the detection of GPS timing signals both in the L1 and L2 bands, with the timing signals being especially important for the cyber encryption/decryption systems that are utilized with these radios.
Regardless, what is required is a low profile antenna to replace the monopoles in the form of rubber duck types of antennas with an increased gain UHF bands antenna as well as to provide extra height for the antenna. Additionally for JTRS radios they are often times located in backpacks. It is thus important to provide a low profile antenna that has been optimized for use with the new JTRS radios as well as providing these radios with GPS waveform timing signals.
It is noted that the two timing signals that are available from the L1 and L2 bands are required for the precision timing, specifically for crypto applications. In fact, many of the software-defined radios of the JTRS variety are architected to time their waveforms with timing signals from the L1 and L2 bands GPS signals.
There is therefore a necessity to provide a combined UHF/GPS antenna with a stiff but spring loaded housing and to provide the antenna with good UHF propagation characteristics to achieve ranges unattainable by rubber duck type antennas. It is also important to be able to provide the antenna with a sufficient flexibility so that if it contacts a stationary object, the vehicle to which it is mounted is not overturned or alternatively that the antenna is not itself damaged.
In terms of the operating range for such an antenna it would be desirable to have an operating range between 225 MHz and 400 MHz for the UHF antenna, with the two GPS antennas operating in the gigahertz L1 and L2 bands.
To solve the above problems, a combined dual UHF/GPS antenna is provided in which an off center fed UHF tubular dipole is spring loaded at the base and is topped with a stacked pair of quadrafiler helix antennas for the L1 band and L2 band respectively.
The feedlines for the antennas are fed through the tubes making up the UHF dipole, with a lower coaxial feed line feeding the off center fed dipole such that the inner conductor of the lower coaxial feedline feeds the lower section of the dipole and the outer conductor feeds the upper section of the dipole.
The upper coaxial feedline runs up through the center of the dipole which is in one embodiment made of tubular copper, and is coupled to the upper antenna section that carries the GPS antennas. The L1 and L2 bands are separated by a diplexer which is then connected to separate low noise amplifiers that are in turn connected to the helices of two quadrafiler high helix antenna sections, one for the L1 band and the other for the L2 band.
In order to lower the resonance frequency of the UHF antenna, in one embodiment the two coaxial feedlines which extend from the bottom of the UHF antenna are coiled together on an insulating mandrel, with a number of turns overlain with copper tape to provide an LC circuit to lower the operating frequency of the UHF antenna. The tape forms a capacitive strip coupled to the coils to provide a circuit that resonates close to 225 MHz, with the capacitive coupling of the tape over the turns capacitively coupling the turns together. By introducing more capacitance between the turns, the effect is to lower the resonant frequency of the UHF antenna.
The net result is that the two sets of antennas can operate independently of each other without interference, with the coils and tape lowering the resonant frequency of the UHF antenna. In one embodiment the center frequency of the UHF antenna is designed to be 300 MHz to give the UHF antenna a bandwidth between 225 and 400 MHz.
It is noted that in one embodiment the upper coaxial feedline passes through the lower antenna section without affecting the operation of the lower antenna section. In one embodiment the LC circuit at the base of the antenna is made up of seven turns of upper and lower coaxial feedlines around a non-conductive mandrel at the base of dipole.
Noting that the entire antenna structure is rigid, a spring is fixed to the base of the dipole to provide the required flexibility.
In summary, a dual purpose antenna is provided with the UHF antenna in the form of a pair of copper tubes to provide an off center fed dipole, with a pair of quadrafiler helix L1 and L2 GPS antennas stacked on top of the UHF antenna, and with the top section of the UHF dipole providing a ground plain for the GPS antenna. The antennas are fed internally by two coaxial feeds, one feeding the UHF antenna, the other passing through the UHF antenna to feed the GPS antennas. In one embodiment, a tuning coil is provided at the base of the UHF antenna by the coiling of the two coaxial feeds around a non-conductive mandrel, with copper taping placed on top of the coiled coaxial sections to provide an LC circuit to lower the resonant frequency of the UHF antenna to 225 MHz.
These and other features of the subject invention will be better understood in connection with the Detailed Description, in conjunction with the Drawings, of which:
Referring now to
As mentioned above, because the amount of real estate on the robot is relatively small, dual purpose antenna 16 is provided with a UHF band antenna and a pair of GPS antennas to provide for the aforementioned signals. It will be appreciated that such an antenna is relatively short not exceeding 22 inches and as such constitutes a low profile antenna.
Before going into the antenna design, the subject antenna is shown mounted to a backpack-carried radio in
As can be seen in
As illustrated in
It will be seen that the gain of the subject antenna is sufficient to provide adequate range from a large number of orientations and is not blocked by the individual carrying the backpack.
Referring to
The two coaxial feeds for this antenna come out of the base of UHF dipole element 28 and are coiled over an insulating mandrel 52 such that the coax is coiled as illustrated at 54 around the mandrel, with the two coaxial cables running side by side. These two coax cables run out through a spring assembly 60 and through a bracket 62 such that the UHF coax 32 is coupled to a radio 64 and such that the coaxial cable 50 from the GPS antenna here is connected to radio 64 and thence to a GPS receiver 66. It will be noted that the L1 frequency is 1.5754 gigahertz, whereas the L2 frequency is 1.2276 gigahertz. Assuming that the UHF antenna and the GPS antenna are appropriately fed by the associated two coaxial cables and assuming that the operation of the UHF antenna dipole does not interfere with the operation of the GPS antennas and visa versa, then what one has is a low profile rigid antenna mounted on a spring which is usable for unmanned vehicles or JTRS radios so as to provide the communications necessary for these radios.
It will be appreciated that in order to provide for the aforementioned tuning, the coiled together coaxial cables at the base of the antenna are provided with conductive tape 68 which overlies the cables and provides a capacitive coupling between the cables. This capacitive coupling is such that the lower frequency of the UHF dipole is extended downwardly to 225 MHz.
Referring to
It will also be seen that the GPS coaxial cable 50 runs up through the center of the UHF dipole, with the outer braid of the two coaxial cables connected together and bonded as illustrated at 76. Note also that the outer shield of coaxial cable 50 is also bonded to the upper section 30 of the UHF dipole as illustrated at 78.
The center conductor of coaxial cable 50, here illustrated at 80, is connected to diplexer 42 and also to the upper dipole element 30 as illustrated at 82. Thereafter, a pair of low noise amplifiers 44 and 46 are coupled to diplexer 42 and to the helical coils 90 and 92 of GPS antennas 26 and 38.
The net result is that the subject low profile antenna provides a unitary package for the UHF antenna and the GPS antennas, with the GPS antennas stacked on the top of the UHF antenna for better visibility to the satellites.
It has been found that with a two inch tape over coils 54 the antenna has a gain of 3 dBi between 220 and 400 MHz, with an SWR in the 2.5:1 range.
While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications or additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.
This application claims rights under 35 USC §119 (e) from U.S. Application Ser. No. 61/505,141 filed Jul. 7, 2011, the contents of which are incorporate herein by reference.
The invention was made with United States Government assistance under contract no. SUGV W56 HZV-05-C-0724/5EC8385 awarded by the US Army. The United States Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 61505141 | Jul 2011 | US |
