The present invention generally relates to a planar monopole antenna such as wireless communication applications and in particular to a planar monopole antenna with an ultrawideband characteristic having a microwave absorber on an opposing face of the antenna substrate.
A monopole antenna is characterized by a simple structure and finds applications in various antenna systems including vehicle mounts and personal communication devices. The operating frequency of a planar monopole antenna is largely dependent on the dielectric constant of the material from which the antenna is fabricated and monopole antenna dimensions. As a result, efforts to reduce monopole antenna dimensions without changing operating frequencies have met with limited success owing to these material and dimensional limitations.
Thus, there exists a need for a coplanar waveguide fed planar monopole antenna with an extended operating frequency range for a given antenna substrate dielectric constant and antenna dimensions.
A planar monopole antenna is provided that includes a dielectric substrate with an electrically conductive antenna element adhered to the substrate surface. A coplanar waveguide is also adhered to the same surface of the dielectric substrate to feed the antenna element. A microwave absorber layer is adhered to an opposing rearward surface of the dielectric substrate. The resultant antenna lowers operating frequency compared to an ultrawideband antenna lacking the microwave absorber layer. As a result, the lowest operating frequency of the ultrawideband antenna is lowered by a factor of five when approximately one-inch thick microwave absorber was added to the opposite side of the antenna element and coplanar waveguide.
A better understanding of the present invention will be had upon reference to the following detailed description when read in conjunction with the accompanying figures (not to scale), wherein like reference characters used across multiple figures refer to like aspects throughout the various views. These drawings are intended to be exemplary and not to limit the scope of the appended claims, and in which:
The present invention has utility as a low profile monopole antenna operative in communications. An inventive ultrawideband antenna has an extended operating frequency range through the inclusion of microwave absorber attached to the back of the antenna substrate thereby lowering the operating frequency range of the inventive ultrawideband antenna without increasing antenna footprint.
Referring now to
An antenna element 12, center conductor 18, and ground planes 16A and 16B are formed of highly conductive materials conventional to the art illustratively including copper, copper alloys, gold, gold alloys, and combinations thereof. A dielectric substrate is readily formed from a variety of dielectric substances through recognition that the dielectric constant of the substrate 14 is relevant in determining the physical size of an antenna. Dielectric substrates operative herein illustratively include fiberglass reinforced epoxy laminate (NEMA designation FR-4), polytetrafluoroethylene (PTFE) composites reinforced with glass microfibers (such as those commercially available under the trade name DUROID®); and ceramic material such as alumina.
Regardless of a shape of the antenna element 12, 12a-12d, an inventive monopole antenna 10 has a microwave absorber 22 adhered to the rearward surface 24 of dielectric substrate 14. The microwave absorber 22 affords the advantage of an inventive monopole antenna 10 of down shifting the operating frequency range of the like antenna 10 absent microwave absorber without increasing the antenna footprint. It is appreciated that the thickness of the microwave absorber layer 22 is dictated by factors including microwave absorption coefficient. It is appreciated that numerical operating characteristics of a given antenna configuration can be simulated using 3D electromagnetic computer code such as, by way of example, IE3D® simulation software. Thickness of the microwave absorber 22 is depending on operating frequency band and the material that formed the microwave absorber, and therefore, a user needs to conduct experiments to determine adequate thickness for an antenna or antenna array. Substances suitable for the formation of a microwave absorber layer 22 illustratively include carbon fiber impregnated on a porous material such as sponge or foam. The microwave absorber layer 22 is depicted with parallel surfaces 26 and 28; however, it is appreciated that surface 26 while matching the contours of rearward surface 24 of dielectric substrate 14, opposing surface 28 in fact need not be parallel to surface 26 and is readily contoured or otherwise modified for packaging or to modify operational properties of an inventive antenna 10. A representative contour modification of the absorber 22 is shown at 30 in
The present invention is further detailed with respect to the following examples which are intended to illustrate specific embodiments of the present invention but not to limit the scope of the claimed invention.
An antenna is simulated using a 3D electromagnetic computer code and subsequently fabricated and tested. The antenna has the form of that depicted in
w=152 mm
L=152 mm
h=3 mm
r=55 mm
g=0.393 mm
GW=73.607 mm
GL=20 mm
Cw=4 mm
t=1.575 mm
Measured return loss of this antenna without microwave absorber is shown as a dashed line in
The return loss characteristic of this comparative antenna is radically changed when one-inch thick microwave absorber material is placed on the backside of the dielectric as shown in
It should be noted that a return loss of greater than 10 dB of the inventive antenna goes beyond 10 GHz, and however, a radiation pattern starts to deform from an ideal isotropic radiation pattern beyond 1.2 GHz. Therefore, one may not want to use the inventive antenna at higher than 1.2 GHz using the specific dimensions shown in the Example 1.
It is noted that an inventive antenna does not require a Balun. In addition, the upper frequency data provided in
Patent documents and publications mentioned in the specification are indicative of the levels of those skilled in the art to which the invention pertains. These documents and publications are incorporated herein by reference to the same extent as if each individual document or publication was specifically and individually incorporated herein by reference.
The foregoing description is illustrative of particular embodiments of the invention, but is not meant to be a limitation upon the practice thereof. The following claims, including all equivalents thereof, are intended to define the scope of the invention.
As used herein, ultrawideband (UWB) antenna characteristics are defined as an antenna capable of transmitting and/or receiving wireless information over a fractional bandwidth of greater than 0.2 or bandwidth greater than 500 megahertz where the 500 megahertz band is either continuous or an aggregation of narrower carrier bands totaling in summation at least 500 megahertz. It is appreciated that UWB operative herein includes both modulated and pulsed information signals.
The invention described herein may be manufactured, used, and licensed by or for the United States Government.