Abstract:
A broadband transmit/recieve antenna apparatus which operates at high frequencies and provides for two separate wideband tapered notch regions formed on one coplanar substrate. The tapered notch regions function as radiators for the transmission and reception of electromagnetic signals. The simple and compact design for the broadband antenna permits the transmission and reception of high frequency omnidirectional or directional radiation patterns. The broadband antenna interfaces with an an integrated circuit such as an ASIC which provides a series of pulsed signals and is resident on the antenna. The design of the broadband antenna provides for an optional stop notch to separate the transmitting portion of the antenna from the receiving portion of the antenna. Additionally, the antenna provides for impedance matching by locating transmission lines at an appropriate location with respect to the tapered notch radiators.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 09/384,952 filed Aug. 27, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to printed radiating antennas. More particularly, the present invention relates to a novel antenna structure comprising two separate wideband notch regions formed on one coplanar substrate. 
     2. The Prior Art 
     The use of antennas has become commonplace in electronic devices such as cellular phones, radios, television, and computer networks. An antenna is comprised of a system of wires or other conductors used to transmit or receive radio or other electromagnetic waves. 
     Many antennas are highly resonant, operating over bandwidths of only a few percent. Such “tuned,” narrow-bandwidth antennas may be entirely satisfactory or even desirable for single-frequency or narrowband applications. However, in many situations wider bandwidths are desirable. Such an antenna capable of functioning satisfactorily over a wide range of frequencies is generally referred to as a broadband antenna. 
     One of the well-known prior art antennas is the exponential notch antenna. The exponential notch takes the form of a substrate such as a circuit board having a conductive surface disposed thereon. An exponential notch is removed from the conductive surface and the antenna is coupled to a 50-Ω strip line on an opposing surface of the board. This small broadband antenna is well adapted for printed-circuit fabrication. 
     Another prior art antenna is disclosed in U.S. Pat. No. 4,853,704 issued to Diaz et al. It has a wide bandwidth and one antenna input port. The Diaz et al. antenna comprises a strip conductor, a ground plane separated from and lying parallel to the strip conductor, the grouped plane having a slot therein, the slot extending transverse to the strip conductor, a conductive planar element positioned across the slot and orthogonal to the ground plane, the conductive planar element having curved surfaces extending upwardly and outwardly from the slot. The strip conductor and the ground provided with a slot are generally composed of a dielectric material. 
     U.S. Pat. No. 5,519,408 issued to Schnetzer discloses a printed tapered notch (coplanar) antenna which has wide bandwidths and one antenna input. The antenna includes a radiating tapered notch and is fed by a section of slotline, which in turn is fed by a coplanar waveguide. The transition from the unbalanced coplanar waveguide to the balanced slotline is accomplished by an infinite balun, where the center conductor of coplanar waveguide terminates on the slotline conductor opposite the ground conductor of the coplanar waveguide. One slot of the coplaner waveguide becomes the feeding slotline for the notch, and the other slot terminates in a slotline open circuit. 
     U.S. Pat. No. 5,264,860 issued to Quan discloses a flared notch radiator antenna having separate isolated transmit and receive ports. The assembly includes a flared notch radiating element, a transmit port and a receive port, and a signal duplexer is integrated into the assembly for coupling the radiating element to the respective transmit and receive ports. The duplexer provides for coupling the transmit port to the radiating element so that transmit signals are radiated into free space. The duplexer is described as being capable of coupling the radiating element to the receive port so that signals received at the radiating element are coupled to the receive port, and for isolating the transmit port from the receive port. In its preferred embodiment the duplexer is described as a four port circulator, with a first port connected to the transmit port, a second port connected to the balun which couples energy into and out of the flared notch radiator, a third port connected to the receive port, and a fourth port connected to a balanced load. In this manner, the transmit port is isolated from the receive port, and vice versa. 
     United Kingdom Patent Application No. 2,281,662 issued to Alcatel Espace discloses a printed coplanar notch (single port) with an integrated amplifier. The antenna includes a slot line having an end section with a flared profile to form a Vivaldi antenna. The slot line has an open circuit termination which provides impedance matching so that separate matching circuit is not required between the antenna and an associated low noise amplifier. A series of antennas are disposed in an array to enable localization to be performed by interferometric techniques. 
     These aforementioned approaches and examples appear to resolve some of the problems associated with transmitting and receiving signals over the broadband frequency range. Additionally, the prior art teaches the use of a plurality of broadband antennas for transmitting and receiving radio frequency energy. 
     However, none of these inventions teaches a coplanar antenna with two wideband notch radiators operating in a transmit/receive mode which allows separate paths for the transmit and receive antennas so that the transceiver does not require a selection switch. 
     Accordingly it is an object of the invention to provide a broadband antenna design which is lightweight, simple and compact in design, and inexpensive to manufacture. 
     Another object of the invention is to provide a single transmit and receive antenna that avoids the need to switch between transmit/receive functions. 
     It is a further object to provide a broadband antenna having a plurality of geometric configurations to generate an omnidirectional or directional radiation pattern. 
     Another object of the invention is to provide an antenna that can be used for wireless communication systems. 
     Other objects, together with the foregoing are attained in the exercise of the invention in the following description and resulting in the embodiments described with respect to the accompanying drawings. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention is a simplified coplanar antenna having at least two notch radiators operating in a transmit/receive mode which produce radiation characteristics that are omnidirectional or directional depending on the size of the antenna. 
     The omnidirectional and directional antenna designs of the present invention operate over a specified frequency range. The specified operating frequency range is determined by the relative size and shape of the notched regions performing the receiving and transmitting functions of the antenna. 
     The present invention comprises a transmitting and receiving antenna having separate wideband notch regions on one coplanar substrate. The coplanar substrate has a first face and a second face. The first face has a first wideband notch region for transmission and a second wideband notch region for reception. An optional stop notch may be added to improve the isolation between the transmitting and receiving regions. The second face of the coplanar substrate has two conducting lines acting as transmission lines which are coupled to an integrated circuit. By way of example and not of limitation, such a integrated circuit may include an application specific integrated circuit (ASIC) resident on the second face of the coplanar substrate. The ASIC generates or receives modulated signals which are transmitted or received by the antenna. 
     According to the present invention, each conducting line or radial stub is electrically coupled to the respective wideband notch regions on the first face of the substrate. The electrical coupling between the transmission lines and the notched regions may be performed by resistively coupling the transmission lines and the notched regions using a plated via-hole technique. However, in the preferred embodiment, the conductive line or radial stub is capacitively coupled to the notched regions to reduce errors, complexity, and costs. 
     In operation, a signal is radiated from one notched region of the broadband antenna of the present invention. The signal propagates through the edges of the notched region producing a beam polarized in the direction of the edges. A second notched region comprises the receiving antenna. 
     The antenna of the present invention can be made omnidirectional by fabricating an antenna with a small footprint. One significant design parameter for producing an omnidirectional antenna is size. The specific shape of the antenna periphery is not a critical parameter for generating an omnidirectional radiation pattern. The omnidirectional antenna may be configured as square, rectangle, octagon, circle or any other similar shape. 
     Directional antennas have larger dimensions than omnidirectional antennas operating in the same frequency range. In general, directional antennas have lengths and widths which are double the length and width of the omnidirectional antennas. Additionally, directional antennas may have an additional backplate or a thick strip of metal on the back edge. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     FIG. 1 a  is a top view of a typical prior-art notch antenna on a coplanar substrate consisting of a dielectric sheet sandwiched between a conductive layer and a conductive line transmission line. 
     FIG. 1 b  is a cross sectional view of the prior-art notch antenna of FIG. 1 a.    
     FIG. 1 c  is a bottom view of the prior-art notch antenna of FIG. 1 a.    
     FIG. 2 a  is a top view of a broadband antenna according to the present invention including two notch regions disposed on the corners of a substrate and having an ASIC on the antenna. 
     FIG. 2 b  is a cross sectional view of the antenna of FIG. 2 a.    
     FIG. 2 c  is a bottom view of the antenna of FIG. 2 a.    
     FIG. 3 a  is a top view of a broadband antenna according to the present invention including two notch regions disposed in a symmetrical back-to-back arrangement with connectors on the same side. 
     FIG. 3 b  is a bottom view of the antenna of FIG. 3 a.   
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Persons of ordinary skill in the art will realize that the following description of the present invention is illustrative only and not in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. 
     The present invention is a novel antenna comprising two separate wideband notch regions on one coplanar substrate for transmitting and receiving RF signals. Further details for the invention are provided in provisional application Ser. No. 60/106,734 to inventors Aiello et al., entitled Baseband Spread Spectrum System filed on Nov. 2, 1998, which is hereby incorporated by reference. 
     Referring first to FIGS. 1 a  through  1   c , there is shown a conventional (prior art) notch antenna  10  comprising a substrate formed from a sheet of dielectric material  12  sandwiched between a conducting element  14  and a feed strip transmission line  16 . FIG. 1 a  is a top view showing the antenna face of the dielectric  12 . A single tapered notch  18  is disposed in conducting element  14 . The tapered notch  18  is transverse to the feed strip  16  and is capacitively coupled to the feed strip  16 . 
     Referring to FIG. 1 b , there is shown a cross sectional view of the antenna  10  having notch  18  removed from conducting element  14 . Antenna  10  is capacitively coupled to feed strip transmission line  16  on the opposing face, i.e. bottom, of dielectric material  12 . FIG. 1 c  is a bottom view of the antenna  10  showing feed strip transmission line  16 . Persons of ordinary skill in the art will appreciate that conducting element  14  and feed strip transmission line  16  may be formed on the substrate  12  by numerous methods including plating and etching, and various other known deposition techniques 
     It is well known in the art that a matching circuit (not shown) may be electrically coupled to the conducting element  14  and the feed strip  16  to achieve the required impedance matching. Additionally, it is well known in the art that feed strip  16  may also be referred to as a transmission line. 
     Referring now to FIGS. 2 a  through  2   c , a first embodiment of the broadband antenna of the present invention is shown in top, cross sectional, and bottom views, respectively. 
     FIG. 2 a  is a top view of an omnidirectional broadband antenna  20  according to the present invention. The antenna  20  is formed on a coplanar substrate  22  such as FR-4 or RT-Duroid which is commonly used in circuit board design and is fabricated from a material such as polytetraflouroethylene (PTFE) or fiberglass. One suitable material for the substrate  22  is sold by Rogers Corporation under the trademark “RT Duroid 5000” and has a thickness of about 1.544 mm in the present example. The substrate  22 , in the embodiment of FIGS. 2 a  through  2   c , is rectangularly shaped for an omnidirectional pattern. Selection of the substrate  22  is based on its electrical and electromagnetic properties as well as cost. By way of example and not of limitation, the particular broadband antenna specifications for antenna  20  are designed transmit and receive signals from the 2.5 GHz to 5.0 GHz frequency range and has a length of 135 mm and width of 60 mm. 
     A conductive layer  24  is formed on a first face of the substrate  22  by etching a plated substrate or by electrochemical plating. Generally, the conductive layer  24  is comprised of materials such as copper, silver, conducting alloys or other conducting materials. By way of example and not of limitation, the conducting layer has a thickness which may range from about 0.034 mm to about 0.068 mm. 
     The conductive layer  24  is shaped in an arrangement having three lobes, in which the lobes are separated by the tapered notches  26  and  28 . The tapered notches  26  and  28  are geometrically configured as exponential notches or have a radius of curvature which matches the quadrant of a circle or any other type of similar outline. The shape of the tapered notches  26  and  28  depends on the desired bandwidth, size of the antenna, and matching impedance. Each of the tapered notches  26  and  28  has a respective broad end at the edge of the conductive layer  24  which is shaped to have a width that is of the order of one quarter of the wavelength of the center frequency of the respective frequency range. The broad end of the first tapered notch  26  is disposed on the upper right hand corner of substrate  22  as seen in FIG. 2 a  and functions as a transmitting radiator for electromagnetic signals. The broad end of the second tapered notch  28  is disposed on the bottom right hand corner as seen in FIG. 2 a  and functions as a receiver. Each of tapered notches  26  and  28  taper down to slotlines  29  and  30 , respectively. 
     FIG. 2 b  is a cross-sectional view of the antenna of FIG. 2 a  showing the conductive elements on substrate  22  at feed points  31  and  32 . The first conductive line  34  acts as a first transmission line which is capacitively coupled to the first notch  26  at a feed point  31 . The second conductive line  36  is a second transmission line capacitively coupled to the second notch  28  at a feed point  32 . Alternatively, instead of capacitive coupling, a plated via hole technique may be used to resistively couple the transmission line with the respective tapered notches. However capacitive coupling is preferred because capacitive coupling reduces errors, complexity and costs. Although not shown, a radial stub may may be provided at the end of conducting line  34  and  36  to improve the capacitive coupling between the transmission lines and the notch transducers  26  and  28 . 
     FIG. 2 c  is a bottom view showing conductive lines  34  and  36  positioned orthogonally to each of the notches  26  and  28 . It may be appreciated that first conductive line  34  is electrically coupled to first tapered notch  26  and may operate to either transmit or receive RF signals. However, the electrically coupled first notched region  26  and conductive line  34  can not simultaneously transmit and receive RF signals. The electrical properties of the conductive lines  34  and  36  are similar to the electrical properties of conductive layer  24 . 
     Additionally, as shown in FIG. 2 c , an application specific integrated circuit (ASIC)  38  is electrically coupled to each feed line  34  and  36 . The ASIC  38  transmits and receives modulated signals. Note, that in the prior art it is well known to use a switching type circuit to switch from a transmission signal to a reception signal. However, in this invention a switching circuit is not employed. 
     In FIG. 2 a  and FIG. 2 c , a stop notch  40  separates the transmit and receive portions of antenna  20  associated with tapered notches  26  and  28 . Stop notch  40  is particularly beneficial because it increases the isolation between the transmit and receive portions of antenna  20 . However, for the present invention to perform the transmit/receive functions, stop notch  40  is not a necessary element of the invention. Stop notch  40  is generally formed as a rectangularly shaped slot etched from the conductive layer  24 . 
     In operation, the tapered notched antenna of FIGS. 2 a  through  2   c  transmits and receives pulsed signals in the specified frequency range. Transmitting signals are launched from the first tapered notch  26  which is capacitively coupled to the transmission line comprising conductive line  34 , and generates a beam polarized in a direction parallel to the antenna. Receiving signals are intercepted by the second tapered notch  28  which is capacitively coupled to transmission line  36 . 
     To obtain a radiation pattern that is substantially omnidirectional, the antenna size must be small and the area of the antenna must approximate or be less than 0.6 times the square of the wavelength at the center frequency of the transmitting or receiving frequency range for each antenna. By way of example and not of limitation, for a center frequency of 3.75 GHz the wavelength of the center frequency is 80 mm. For an omnidirectional radiation pattern the area of the antenna must approximate or be less than the square of the 80 mm wavelength multiplied by 0.6 which is 3,840 mm 2  for one antenna, or 7,680 mm 2  for two antennas. For an omnidirectional radiation pattern the shape of the coplanar antenna is immaterial and may be square, rectangular, octagonal, circular or some other shape. It shall be appreciated that antenna  20  comprises two antennas, a receiving antenna and a transmitting antenna, with a total length of 135 mm and a width of 60 mm. The total area for antenna  20  is 8100 mm 2  which closely approximates the area of 7,680 mm 2  for two antennas which generates an omnidirectional radiation pattern. 
     Directional antennas have larger areas than omnidirectional antennas operating at the same frequency range. In general, directional antennas have lengths and widths which are double those of an omnidirectional antenna. Although not shown, it shall be appreciated that directional antennas have an area which is substantially greater than 0.6 tines the square of the wavelength of the center frequency of the transmitting or receiving frequency of each antenna. Additionally, directional antennas may have an additional backplate or a thick strip of metal on the back edge. 
     The bandwidth of the antenna  20  is determined by the shape of the tapered notch regions  26  and  28 . By way of example and not of limitation, if the shape of the taper is exponential or the radius of curvature is a quadrant of a circle, then at least an octave bandwidth range may be achieved. 
     Impedance matching is accomplished by placing each conductive transmission line  34  and  36  in appropriate locations with respect to the tapered transmit notch radiator  26  and tapered receive notch radiator  28 , thereby affecting the capacitance of the electrical coupling between the transmission line and the radiators. Impedance matching may be accomplished over a wide range of frequencies and the ASIC  38  can be matched directly with the antenna receive or transmit functions. Alternatively, the conducting line may be a coaxial cable. In summary, the dimensions and geometric configuration of each feed line affects the impedance matching requirements for the transmitting and receiving antenna. 
     FIGS. 3 a  and FIG. 3 b  illustrate the top and bottom views, respectively, of an alternative embodiment of the antenna of the present invention. The alternative embodiment is also an omnidirectional antenna. In FIG. 3 a , the top view of a broadband antenna  41  has a conductive layer  42  deposited or etched on a substrate (not shown). Conductive layer  42  encompasses two tapered notches  44  and  46 , each having a broad end  48  and  50  tapering down to slotines  52  and  54 . The broad ends  48  and  50  are disposed on opposing edges of the substrate. The general configuration of the tapered notch regions  44  and  46  is a back-to-back, parallel arrangement where the broad ends  48  and  50  are disposed on opposing edges of the substrate. As previously described, the conductive lines  56  and  58  are positioned orthogonally to each of the notches  44  and  46  at the respective feed points. 
     Referring to FIG. 3 b , there is shown the bottom view of antenna  41 . A pair of conductive lines  56  and  58  are positioned orthogonally to each of the tapered notches  44  and  46 . The conductive lines  56  and  58  have associated radial stubs  60  and  62 , respectively, which are capacitively coupled to the tapered notch radiators  44  and  46 , respectively. An integrated circuit such as ASIC  64  is electrically coupled to each of the conductive lines  56  and  58 . ASIC  64  transmits and receives pulsed signals. 
     The geometric parameters defining antenna  41  as depicted in FIGS. 3 a  and  3   b  are for a squarely shaped antenna which has a length and width of 80 mm. The total area for this antenna is 6,400 mm 2 , which less than the 7,680 mm 2  area which is the approximate antenna area needed to generate an omnidirectional radiation pattern. The tapered notches  44  and  46  fan out as an exponential notch or as the quadrant of a circle. The tapered notches  48  and  50  are geometrically configured so that each of the slotlines  52  and  54  are adjacent one another. The edge of slotline  52  is approximately 20.67 mm from the edge of slotline  54 . Tapered notches  44  and  46  are positioned in the center of the conductive layer  42 . 
     Impedance matching for omnidirectional antenna  41  is accomplished in the same manner as described for antenna  20 . Additionally, it shall be appreciated that the omnidirectional antenna can take on a variety of geometric shapes such as round, oval and polygonal, etc. and that the embodiments for antenna  41  should not be construed as limiting. 
     Both the omnidirectional antenna  20  and omnidirectional antenna  41  transmit and receive a wideband of high frequency signals which include but are not limited to pulsed signals. Additionally, it shall be appreciated that the antennas  20  and  41  can be used in an antenna array applying methods well known in art of antenna design. 
     While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art having the benefit of this disclosure that many more modifications than mentioned above are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.