The invention described herein may be manufactured, used, imported, sold, and licensed by or for the Government of The United States of America without the payment to me of any royalty thereon.
The present invention relates generally to the field of microstrip antennas, and more particularly to multiple band compact planar microstrip antennas.
Microstrip antennas with a lightweight, low profile, low cost and planar structure have been replacing bulky antennas. The length of a rectangular microstrip antenna is about a half wavelength within the dielectric medium under a radiating patch. A half wavelength is still relatively large at UHF and VHF frequencies and these frequencies also impose size limitations that can result in bulky and cumbersome antenna structures. However, microstrip antennas, particularly the electrically small microstrip antennas, have a rather narrow bandwidth. This narrow bandwidth has been tolerated because most modern communications systems generally only need a few distinct frequencies, e.g. one to transmit and one to receive, rather than a continuous spectrum of operating frequency. The disadvantages, drawbacks, limitations and shortcomings of conventionally-sized narrow-band microstrip antennas have created a long-felt need for more compact multiple band antenna structures at lower frequencies that are also low-cost, rugged and conformal in nature. Up until now, it has not been possible to employ planar microstrip antennas without the disadvantages, limitations and shortcomings associated with antenna length and size.
Aside from the need for compact multiple band antenna structures, the prior art narrowband microstrip antennas have suffered from a number of other problems. One continuing problem with prior art narrowband microstrip antennas is unwanted antenna length of a half wavelength length within the dielectric medium, and they also suffer from other size-related drawbacks and disadvantages such as excessive cost and cumbersomeness. Thus there has been a long-felt and unsatisfied need for a multiple band electrically small microstrip antenna for the VHF and UHF frequencies.
The present invention makes it possible to fulfill the need for a significantly reduced antenna length and an electrically small multi-band antenna without suffering from the disadvantages, shortcomings and limitations of lengthy, costly and cumbersome conventional microstrip antennas.
The present invention fulfills the long-standing need for a significantly reduced antenna length and an electrically small antenna for the VHF and UHF frequencies with a multiple band electrically small compact planar microstrip antenna comprising a group of unequally dimensioned radiating members positioned on a dielectric substrate which is stacked on a ground plane that permits both a considerably abbreviated antenna length and significantly high efficiency antenna performance. At least two radiating members are separated by a gap.
It is an object of this invention to provide a significantly reduced antenna length and an electrically small microstrip antenna.
It is a further object of this invention to provide a multiple band electrically small compact planar microstrip antenna with a significantly reduced antenna size.
These and other objects are advantageously accomplished with the present invention providing a multiple band electrically small compact planar microstrip antenna comprising stacking a plurality of radiating members, a microstrip dielectric substrate and a ground plane to provide a multiple band electrically small, compact, planar microstrip antenna at VHF and UHF frequencies. The unequally dimensioned radiating members of the present invention advantageously provide an antenna that resonates at a number of different frequencies instead of a single frequency as the prior art microstrip antenna. The multiple band electrically small compact planar microstrip antenna also innovatively filters unwanted signals at other frequencies because of the narrowband nature of each band. This invention also encompasses methods for providing substantial reduction in antenna size at the VHF and UHF frequencies with multiple band electrically small planar microstrip antennas.
The multiple band electrically small compact planar microstrip antenna of the present invention advantageously comprises a number of radiating members positioned on a microstrip dielectric substrate stacked on a ground plane in an innovative stacking arrangement that provides an electrically small, abbreviated length for a microstrip antenna with the advantages of multiple band capability in the VHF and UHF frequencies. This invention's multiple band electrically small planar compact microstrip antenna is electrically small in the sense that its wavelength is less than a tenth of a wavelength within the dielectric medium. One tenth of a wavelength compares favorably with prior art rectangular microstrip antennas with a half wavelength length within the dielectric medium. This is most particularly the case when the prior art one half wavelength in the VHF and UHF regions caused a relatively large antenna length that led to other size-related drawbacks and disadvantages. Further, the unequally dimensioned, or unlike, radiating members are composed of a number of rectangular conductive strips with varying widths that cooperate to reduce the effective impedance of the antenna structure. This advantageous arrangement along with the innovative combination of a multiple band with an electrically small microstrip antenna results in a substantially reduced antenna length that is significantly shorter than conventional prior art microstrip antennas, without suffering from any of the disadvantages, drawbacks and limitations associated with more lengthy prior art conventional microstrip antennas.
Before any further detailed description of the present invention, it may be instructive to briefly review the underlying concepts and theory of compact microstrip antenna operation. In a single frequency microstrip antenna, a junction in the middle of the patch may be introduced to shorten the length of the impedance transition from the center point, where the wave impedance disappears, to the edge of the radiating patch, where the impedance becomes very large. The simplest example of this phenomenon is the illustrative microstrip antenna depicted in
Referring now to
In an effort to make the illustrative single frequency microstrip antenna resonate at two different frequencies, and now referring back to
In a second experiment, a 45.5 mm long 1.4 mm wide gap was made lengthwise down the middle of a narrow strip and wider radiating member, and this resulted in a single resonant frequency of 375 MHz, or 1 MHz higher than the first experiment because of a slight reduction in the area of the narrow strip and wide radiating member, due to the gap. The lengths of the narrow strip and radiating member were changed to provide a longer radiating member of 31.5 mm on one side of the gap and a shorter radiating member of 19.5 mm on the other side. The resultant multiple band electrically small compact planar microstrip antenna resonated at 410 MHz and 669 MHz, i.e. the longer radiating member (31.5 mm in length) caused the 410 MHz resonance and the significantly shorter radiating member (19.5 mm in length) caused the 669 MHz resonance. The combined narrow strip and wide radiating member, when positioned on dielectric substrate 13 and mounted on ground plane 16 operate as a single antenna, and not as a transmission line split into two narrow transmission lines feeding into two patches like a conventional microstrip antenna array does. Therefore, a conventional microstrip antenna with conventional patch lengths of 31.5 mm and 19.5 mm on standard microstrip material would ordinarily provide resonant frequencies of 3.1 GHz and 5.13 GHz. This is approximately 7.7 times higher than the resonant frequencies achievable with the two radiating members measuring of 31.5 mm and 19.5 mm, as described above, so that this invention's microstrip antenna with those dimensions could have an antenna length about seven times shorter than a conventional array antenna.
Some of the long-felt needs for shorter antenna lengths have been fulfilled by U.S. Pat. No. 5,561,435 entitled “Planar Lower Cost Multilayer Dual-Band Microstrip Antenna,” wherein this inventor was a co-inventor, and U.S. Pat. No. 6,362,785 “Compact Cylindrical Microstrip Antenna,” which are hereby incorporated by reference, but those antennas were still very large at the frequencies of interest. To provide an electrically small antenna capable of reaching the VHF and UHF frequencies in accordance with this invention, it is necessary to shrink the antenna even further to make the antenna compact and usable for moving platforms. The present invention focuses the antenna length reduction effort on splitting the radiating element into multiple radiating members with unequal dimensions separated by at least one gap to reduce the wavelength within the microstrip media without making the antenna inefficient. When two radiating members are used, the gap is a longitudinal gap, and when more radiating members are employed multiple gaps are necessary, including a longitudinal gap, an “L” shaped gap and combinations of those or similar gaps.
Variations include using two, three or four unlike radiating members; rectangularly shaped unlike radiating members; a longitudinal gap that terminates at the rear edges for the two member embodiment; two “L” shaped gaps separating the three unlike radiating members in the three member embodiment; a longitudinal gap and two “L” shaped gaps separating the four radiating members in the four-member embodiment with the longitudinal gap terminating at the rear edges and having the unlike radiating members non-rectangularly shaped in a shape such as a triangle.
Referring now to
A number of the previously disclosed variations also apply to this embodiment, including providing non-rectangular unlike radiating members in shapes such as a triangle. A dielectric constant in the dielectric substrate is necessary. The radiating members may be constructed of any good conductive metal, and in the preferred embodiment they are composed of copper. The ground plane may also be made from conductive materials such as copper and aluminum. The unlike radiating members are depicted as being rectangular, but can be configured in numerous shapes so long as the surface areas have unequal dimensions.
Referring now to
Many of the variations to the dual band embodiment of this invention apply equally to this embodiment. Other variations include the use of non-rectangular radiating members.
Referring now to
Many of the variations to the dual band and triple band embodiments of this invention also apply to this embodiment, including the use of non-rectangular radiating members.
The present invention also encompasses methods for abbreviating antenna size for an antenna in the VHF and UHF regions with a multiple band electrically small planar microstrip antenna, comprising the steps of positioning a narrow radiating strip and a group of radiating members on a microstrip dielectric substrate, the group of radiating members being formed with a set of unequal, or unlike, dimensions and a greater width than the narrow radiating strip, stacking the microstrip dielectric substrate on a ground plane; connecting the narrow radiating strip and radiating members at a junction, the antenna having an original length and an effective impedance at the junction; configuring each unlike radiating member with a rear edge opposing the junction; separating the unlike radiating members with at least one gap therebetween that begins in the vicinity of the connector pin and extends through the junction; projecting a connector pin downward through the narrow radiating strip and dielectric substrate to the ground plane; and shorting the narrow radiating strip. Other method steps are folding the narrow radiating member downward to partially cover the dielectric substrate and ground plane to form a front edge opposing the rear edges, the narrow radiating strip terminating at the connector pin; decreasing the effective impedance by connecting the narrow radiating strip and unlike radiating members at the junction, which results in a reduced impedance allowing the original length to be abbreviated; and providing a distinct resonant frequency in the VHF and UHF regions based upon the unlike radiating members being unequally dimensioned.
These embodiments of the present invention are intended to be illustrative and not limiting with respect to the variety of possible embodiments. It is to be further understood that other features and modifications to the foregoing detailed description of the estimating methods and devices are all considered to be within the contemplation of the present invention, which is not limited by this detailed description. Those skilled in the art will readily appreciate that any number of configurations of the present invention and numerous modifications and combinations of materials, components, geometrical arrangements and dimensions can achieve the results described herein, without departing from the spirit and scope of this invention. Accordingly, the present invention should not be limited by the foregoing description, but only by the appended claims.
Number | Name | Date | Kind |
---|---|---|---|
5561435 | Nalbandian et al. | Oct 1996 | A |
6362785 | Nalbandian et al. | Mar 2002 | B1 |
6870506 | Chen et al. | Mar 2005 | B2 |
6958730 | Nagumo et al. | Oct 2005 | B2 |
7042403 | Colburn et al. | May 2006 | B2 |
7265718 | Tsai | Sep 2007 | B2 |
20040012528 | Dai et al. | Jan 2004 | A1 |
20040196187 | Yeh | Oct 2004 | A1 |
20060279464 | Mei | Dec 2006 | A1 |