Abstract:
The present invention is a compact directional receiving antenna utilizing true-time-delay methods to achieve a wide pattern bandwidth and small real estate footprint. In one embodiment, two right-triangular-shaped loops are positioned in mirrored relation, one to another, with less than 1/100 wavelength spacing. In another embodiment, two of these pairs of loops are positioned in an orthogonal manner to form an electronically rotatable antenna array. In yet another embodiment, a single loop is provided with a pair of spaced couplers. Finally, in another embodiment, a pair of single loops is arranged in orthogonal relation to form an electronically rotatable array.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to provisional application No. 61/274,619, filed on Aug. 18, 2009, the disclosures of which are incorporated herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to directional antennas, and more specifically to directional antennas that are compact in size relative to their wavelength. 
     BACKGROUND OF THE INVENTION 
     Directional antenna systems for receiving electromagnetic radiation have been practiced for many years. A variety of methods have been used to achieve varying degrees of success using terminated traveling wave antennas, phased arrays, parasitic arrays, and true-time delay arrays. 
     In practice, the antenna designer is often faced with a difficult tradeoff between complexity, gain, directivity, size and bandwidth. For example, for frequencies below 5 MHz, a terminated beverage antenna having a length of multiple wavelengths is known in the art to provide exemplary directivity over a wide bandwidth, but its size makes it difficult to deploy in many settings, especially when multiple antennas are required to achieve desired directional patterns. Rhombic antennas provide exceptional gain for a fixed pattern but also require significant support structure and real estate for effective operation. Curtain arrays provide moderate bandwidth and are moderate in real estate usage and require substantial investment in superstructure. Log Periodic arrays are known for their wide bandwidth and suitable directivity but also require significant investment in superstructure. Parasitic arrays are known for exceptional gain, excellent directivity, and moderate size, but require moderate superstructure and have a very small operational bandwidth. 
     Loop antennas are known in the art for providing a reliable bi-directional pattern for a relatively small size. It is well known that the signal from a loop antenna can be phased with a closely spaced vertical antenna element to achieve a cardiod pattern over a small bandwidth. In addition, including a properly selected and located resistor in series with a loop can provide a similar cardiod pattern. Other examples in the art include multiple loops in phased arrangement, being spaced apart in end fire relation. 
     Others have noted the value of utilizing a true-time-delay method of combining signals from two moderately spaced elements. For example, U.S. Pat. No. 3,396,398 issued to J. H. Dunlavy, Jr. teaches a two element true-time-delay antenna using a pair of shortened dipole elements separated by preferably less than 0.3 times the length of the shortest wavelength handled by the system. Such and antenna promises to provide exceptional bandwidth and reasonable directivity. However, the size of such an array is still considerable if, for example, if the shortest wavelength is twenty meters, the length of the dipole elements is six meters with a separation between elements of three meters. 
     The present invention provides a refreshing option for the antenna designer by providing a compact antenna having structural simplicity, acceptable gain, respectable directivity, fractional size, and exceptional bandwidth. For example, a single loop embodiment having a base length of seven meters provides an operational bandwidth of 0.5-14 MHz. A dual loop embodiment with each loop having individual base lengths of 3.5 meters each, and a separation distance of three centimeters provides an operational bandwidth of 1-22 MHz. 
     In addition, the nature of the arrangement of the loops and associated structure lends itself to configuring orthogonal arrays that can be electronically switched to provide means to rotate the pattern without physical rotation. These and other advantages the present invention will become apparent from a thorough review of this specification. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is a compact directional antenna for receiving signals over a range of frequencies having respective wavelengths comprising a loop antenna element, a first coupler located at a first point, and configured to transfer signals from the loop antenna element, a first transmission line having a characteristic impedance, and a first end connected to the first coupler, and a second end, and operable to provide a first time delay for signals traveling from the first end to the second end, a second coupler located at a second point, and configured to transfer signals from the loop antenna element, a second transmission line having the characteristic impedance, and a first end connected to the second coupler, and a second end, and operable to provide a second time delay for signals traveling from the first end to the second end. The antenna further comprises a signal combiner having a first port having a first impedance, and coupled to the second end of the first transmission line, and a second port having the first impedance, and coupled to the second end of the second transmission line, and a third port, and wherein the signal combiner provides a third time delay for signals traveling from the first port to the third port, and wherein the signal combiner provides a fourth time delay for signals traveling from the second port to the third port. 
     Another aspect of the invention is a compact directional antenna for receiving signals over a range of frequencies having respective wavelengths comprising a first loop antenna element, a first coupler located at a first point, and configured to transfer signals from the loop antenna element, a first transmission line having a characteristic impedance, and a first end connected to the first coupler, and a second end, and operable to provide a first time delay for signals traveling from the first end to the second end, a second loop antenna element, a second coupler located at a second point, and configured to transfer signals from the second loop antenna element, a second transmission line having the characteristic impedance, and a first end connected to the second coupler, and a second end, and operable to provide a second time delay for signals traveling from the first end to the second end, and a signal combiner having a first port having a first impedance, and coupled to the second end of the first transmission line, and a second port having the first impedance, and coupled to the second end of the second transmission line, and a third port, and wherein the signal combiner provides a third time delay for signals traveling from the first port to the third port, and wherein the signal combiner provides a fourth time delay for signals traveling from the second port to the third port. 
     Yet another aspect of the invention is a compact directional antenna for receiving signals over a range of frequencies having respective wavelengths comprising a first, second, third, and fourth loop antenna elements, a first coupler located at a first point, and configured to transfer signals from the first loop antenna element, a second coupler located at a second point, and configured to transfer signals from the second loop antenna element, a third coupler located at a third point, and configured to transfer signals from the third loop antenna element, a fourth coupler located at a fourth point, and configured to transfer signals from the fourth loop antenna element, a first, second, third, and fourth transmission line, each having a characteristic impedance, and each having a first end connected to the respective first, second, third, and fourth coupler, and a second end, and operable to each provide a first time delay for signals traveling from the first end to the second end, a signal routing module having a first, second, third, and fourth ports each connected to the second end of the respective first, second, third, and fourth transmission lines, and a fifth port, and a sixth port, a fifth transmission line having a characteristic impedance equal to the characteristic impedance, and having a first end connected to the fifth port of the signal routing module, and operable to provide a second time delay for signals traveling from the first end to the second end, and a signal combiner having a first port having an impedance equal to a first impedance, and coupled to the second end of the fifth transmission line, and a second port having an impedance substantially equal to the first impedance, and coupled to the sixth port of the signal routing module, and a third port, and wherein the signal combiner provides a third time delay for signals traveling from the first port to the third port, and wherein the signal combiner provides a fourth time delay for signals traveling from the second port to the third port. 
     These and other aspects of the present invention will be described in greater detail hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention are described below with reference to the following accompanying drawings. 
         FIG. 1  is an isometric elevation view of a dual loop embodiment of the compact directional receiving antenna adapted for mounting on a horizontal surface. 
         FIG. 2  is block diagram of dual loop antenna elements and associated antenna couplers. 
         FIG. 3  is an isometric elevation view of a single loop embodiment of the compact directional receiving antenna apparatus adapted for mounting on a horizontal surface. 
         FIG. 4  is a block diagram of a single loop receiving antenna element and associated antenna couplers. 
         FIG. 5  is a block diagram of the transmission lines and signal processor utilized in various embodiments of the compact directional receiving antenna. 
         FIG. 6  is an isometric elevation view of a two orthogonal dual loop embodiment of the compact directional receiving antenna adapted for mounting on a horizontal surface. 
         FIG. 7  is block diagram of a two orthogonal dual loop antenna elements and associated antenna couplers. 
         FIG. 8  is an isometric elevation view of a two orthogonal single loop embodiment of the compact directional receiving antenna adapted for mounting on a horizontal surface. 
         FIG. 9  is block diagram of a two orthogonal single loop antenna elements and associated antenna couplers. 
         FIG. 10  is a block diagram of the transmission lines and signal processor utilized in selected embodiments of the compact directional receiving antenna. 
         FIG. 11  is an isometric elevation view of a controller utilized in a directional receiving antenna. 
         FIG. 12  is a collection of horizontal response patterns for a loop antenna element at selected operational frequencies. 
         FIG. 13  is a collection of horizontal response patterns for a dual loop embodiment of the compact directional receiving antenna at selected operational frequencies. 
         FIG. 14  is a collection of horizontal response patterns for a dual loop embodiment of the compact directional receiving antenna at selected coupling locations for a given frequency. 
         FIG. 15  is a collection of horizontal response patterns for a single loop embodiment of the compact directional receiving antenna at selected operational frequencies. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8). 
     Referring now to  FIGS. 1 and 2 , a dual loop embodiment of a compact directional receiving antenna  10  is illustrated in a fixed installation. The dual loop antenna  10  is shown in a ground mounted configuration, although it could be mounted above the ground without departing from the scope of this invention. The antenna  10  is also illustrated in a stationary configuration, although it can also be built in a mechanically rotatable configuration. 
     The dual loop antenna  10  includes a controller  12  that is provided to power and configure the dual loop antenna  10 , and to transform and deliver captured signals to a receiver (not shown). A feed transmission line  14  connects to the controller  12 , providing a conduit for signals captured from the antenna. In addition, the feed transmission line  14  can be utilized for transmitting power and data from the controller  12 . 
     The feed transmission line  14  is connected to a signal processor  16  located near a base of the dual loop antenna  10 . The signal processor  16  includes signal combining, time delay, impedance matching, and amplification circuitry as will be discussed in further detail in this specification. 
     The dual loop antenna  10  is shown including a vertically oriented center support  18  that is configured to provide a mechanical support. In a preferred embodiment, the center support  18  should be composed on non-conductive material. Additionally, other means of mechanical support may be employed without departing from the scope of this invention. 
     A first loop antenna element  20  is shown borne in part by the center support  18  and is comprised of an endless loop of wire that follows a path defining a shape, and having a path length and an enclosed area. In one embodiment, the shape defined by the element  20  is a right triangle. However, the element  20  may have other shapes without departing from the scope of the invention. In addition, the element  20  can be composed of other types of conductors including tubing, pipe, or printed circuit board traces. One end of first loop antenna element  20  is held in tension by an anchor  22 . 
     A coupler  24  is positioned proximate to a portion of the loop antenna element  20  and is configured to transfer signals that are captured by the loop antenna element  20 . In one embodiment, the coupler  24  is a current transformer formed by running the loop antenna element  20  directly through a single or multiple ferrite beads  50  ( FIG. 2 ) forming a single turn primary winding of a current transformer. Other types of couplers known in the art, including active couplers, may also be used without departing from the scope of this invention. 
     A loop transmission line  26  is connected directly to the coupler  24 . In one embodiment, the loop transmission line  26  is connected to a connector  54  ( FIG. 2 ) that connects to a single turn secondary winding  52  ( FIG. 2 ) of a current transformer formed by the ferrite bead  50  ( FIG. 2 ). The loop transmission line  26  provides a time delay for signals traveling from one end to the other end. 
     A second loop antenna element  30  is shown also borne in part by the center support  18  and is comprised of an endless loop of wire. The path length and area enclosed of the loop antenna element  30  should closely approximate the path length and area enclosed of the loop element  20 . Additionally, in one embodiment, the shape of the loop antenna element  30  is a mirror image of the shape of loop antenna element  20 . The first and second loop antenna elements  20  and  30  respectively should be mounted in a common plane. One end of first loop antenna element  30  is held in tension by an anchor  32 . 
     A coupler  34  is positioned proximate to a portion of the loop antenna element  30  and is configured to transfer signals that are captured by the loop antenna element  30  and should be substantially similar to the coupler  24 . In one embodiment, the coupler  34  is a current transformer formed by running the loop antenna element  30  directly through a ferrite bead  60  ( FIG. 2 ) forming a single turn primary winding of a current transformer. 
     A loop transmission line  36  is connected directly to the coupler  34 . In one embodiment, the loop transmission line  36  is connected to a connector  64  ( FIG. 2 ) that connects to a single turn secondary winding  62  ( FIG. 2 ) of a current transformer formed by the ferrite bead  60  ( FIG. 2 ). The loop transmission line  36  provides a time delay for signals traveling from one end to the other end, and in one embodiment provides a time delay that is substantially similar to the time delay provided the loop transmission line  26 . 
     Referring to  FIG. 1 , a delay line  38  is formed by a transmission line and is shown having both ends connected to the signal processor  16  and introduces a time delay. The delay line  38  can also be formed using other elements as is known in the art without departing from the scope of this invention. The operation of the delay line  38  will be discussed in further detail later in this specification. 
     Signals coming from a reference direction generally indicated by the arrow  40  are preferred when signals from the loop transmission line  26  are routed through the delay line  38  before being combined with signals from loop transmission line  36 . 
     The loop antenna elements  20  and  30  each have a similar loop base length  42 , a coupler to center distance  44 , and a loop apex height  46 . The loop antenna elements  20  and  30  are separated by a loop spacing distance  45 , and have a base height above ground  48 . In one embodiment, when the dual loop antenna  10  is designed for an operational frequency range of 1-22 MHz, the loop base length  42  and loop apex height is equal to approximately 3.5 m, the coupler to center distance  44  is 1.75 m, the loop spacing distance  45  is 3 cm, and the base height above ground  48  is 20 cm. 
     Referring now to  FIGS. 3 and 4 , a single loop embodiment of a compact directional receiving antenna  70  is illustrated in a fixed installation. The single loop antenna  70  is shown in a ground mounted configuration, although it could be mounted above the ground without departing from the scope of this invention. 
     The single loop antenna  70  includes the controller  12 , feed transmission line  14 , signal processor  16 , and center support  18  as discussed above. 
     A single loop antenna element  72  is shown borne in part by the center support  18  and is comprised of an endless loop of wire that follows a path defining a shape, and having a path length and an enclosed area. In one embodiment, the shape defined by the element  20  is a triangle. However, the element  72  may have other, shapes without departing from the scope of the invention. In addition, the element  72  can be composed of other types of conductors including tubing, pipe, or a printed circuit board trace. Each corner of the single loop antenna element  72  is held in tension by the anchors  22  and  32 . 
     The couplers  24  and  34  are positioned proximate to a portion of the loop antenna element  72 . In one embodiment, the couplers  24  and  34  are each current transformers formed by running the loop antenna element  72  directly through ferrite beads  80  and  82  ( FIG. 4 ) forming individual single turn primary windings. 
     The loop transmission lines  26  and  36  are each connected directly to the couplers  24  and  34 . In one embodiment, the loop transmission lines  26  and  36  are connected to a connectors  54  and  640  ( FIG. 4 ) that each in turn connect to separate single turn secondary windings  84  and  88  ( FIG. 4 ) of current transformers formed by the ferrite beads  80  and  82  ( FIG. 4 ). The loop transmission lines  26  and  36  each provide a time delay for signals traveling from one end to the other end. 
     Referring now to  FIG. 3 , the delay line  38  has both ends connected to the signal processor  16  introducing a time delay. Signals coming from a reference direction generally indicated by the arrow  40  are preferred when signals from the loop transmission line  26  are routed through the delay line  38  before being combined with signals from loop transmission line  36 . 
     The single loop antenna element  72  has a loop base length  78 , a coupler to coupler distance  76 , a loop apex height  46 , and the base height above ground  48 . In one embodiment, when the single loop antenna  10  is designed for an operational frequency range of 500 KHz-14 MHz, the loop base length  78  is equal to 7 m, the loop apex height  46  is equal to approximately 3.5 m, the coupler to coupler distance  76  is 6 m, and the base height above ground  48  is 20 cm. 
     Referring now to  FIG. 5 , one end of the loop transmission line  36  is connected to the coupler connector  64 . Another end of the loop transmission line  36  is connected to a first port of signal combiner  90 . One end of transmission line  26  is connected to the coupler connector  54 . Another end of the loop transmission line  26  is connected to a first end of the delay line  38 . A second end of the delay line  38  is connected to a second port of the signal combiner  90 . Within the signal combiner  90  there exists a first signal path  92  and a second signal path  94 . As a practical matter, the first and second signal paths  92  and  94  each introduce signal time delays before signals are combined. Any significant inequality in time delay between the first and second signal paths  92  and  94  must be accounted for by adjusting the length or time delay of the delay line  38  to ensure proper operation. In addition, any inequality in time delay between the first and second signal paths  92  and  94  ideally should be stable over any desired operational frequency range. In one embodiment, the signal combiner  90  is a hybrid coupler having a characteristic impedance that matches the characteristic impedance of the loop transmission lines  26  and  36  as well as the delay line  38 . 
     A combined signal  96  provided by the signal combiner  90  is introduced to a buffer amplifier  98 . The buffer amplifier  98  should ideally have an input impedance over any desired operational frequency range that substantially matches the characteristic impedance of the loop transmission lines  26  and  35  as well as the delay line  38 . 
     Referring now to  FIGS. 6 and 7 , an orthogonal dual loop embodiment of a compact directional receiving antenna  100  is illustrated in a fixed installation. The orthogonal dual loop antenna  100  is shown in a ground mounted configuration, and includes the controller  12 , feed transmission line  14 , and vertically oriented center support  18  as discussed previously in this specification. In this embodiment, the controller  12  is configured to electronically orient the antenna pattern as will be discussed later in this specification. 
     The feed transmission line  14  is connected to a signal processor  102  located near a base of the orthogonal dual loop antenna  100 . The signal processor  102  includes switching, signal combining, time delay, impedance matching, and amplification circuitry as will be discussed in further detail in this specification. 
     The first loop antenna element  20 , second loop antenna element  30 , a third antenna element  120 , and a fourth antenna element  130  are each borne in part by the center support  18  and are each comprised as discussed earlier. Each of the elements  20 ,  30 ,  120  and  130  have a path length and an area enclosed which should each be substantially equal to each other. Each of the elements  20 ,  30 ,  120  and  130  have a shape, and wherein the shape of element  30  and  130  should substantially mirror the shape of elements  20  and  120 . The elements  20  and  30  should be mounted in a common plane and the elements  120  and  130  should be mounted in another plane that is substantially orthogonal to the common plane. 
     The loop antenna elements  20 ,  30 ,  120 , and  130  are each held in tension by anchors  22 ,  32 ,  122  and  132  respectively. 
     The couplers  24  and  34  are each positioned proximate to a portion of the loop antenna element  20  and  30 , and are each configured to transfer signals that are captured by the respective elements. Additional couplers  124  and  134  are similarly positioned proximate to a portion of the loop antenna elements  120  and  130 , and are each configured to transfer signals that are captured by these respective elements in a manner described previously in this specification. 
     In one embodiment, the couplers  24 ,  34 ,  124  and  134  are each formed by routing each of the elements  20 ,  30 ,  120 , and  130  through ferrite beads  50 ,  60 ,  150  and  160  as shown in  FIG. 7 . Secondary windings  52 ,  62 ,  152 , and  152  are each provided to couple signals to connectors  54 ,  64 ,  154 , and  164  ( FIG. 7 ). 
     The loop transmission lines  26  and  36  are each connected directly to the couplers  24  and  34 . Similarly, a transmission line  126  is connected to coupler  124  and a transmission line  136  is connected to coupler  134 . Each of the transmission lines  26 ,  36 ,  126 , and  136 , provide a time delay for signals traveling from one end to the other end, and are selected to provide a substantially similar time delay, one with respect to another. 
     Referring now to  FIG. 6 , the delay line  38  is formed as discussed previously in this specification. Another delay line  138  is provided having both ends connected to the signal processor  16  and introduces another time delay. The delay line  138  can also be formed using other elements as is known in the art without departing from the scope of this invention. The operation of the delay line  138  will be discussed in further detail later in this specification. 
     Signals coming from a reference direction generally indicated by the arrow  40  are preferred when signals from the loop transmission line  26  are routed through the delay line  38  before being combined with signals from loop transmission line  36 . Yet further, signals coming from a reference direction generally indicated by the arrow  140  are preferred when signals from the loop transmission line  126  are routed through the delay line  38  before being combined with signals from loop transmission line  136 . Still further, signals coming from a reference direction generally indicated by a vector combination of the arrow  40  and  140  are preferred when signals from the loop transmission line  26  are combined with signals from loop transmission line  126 , and are routed through the delay line  38  and delay line  138  before being finally combined with signals from a combination of signals from loop transmission line  36  and loop transmission line  136 . 
     The loop antenna elements  20 ,  30 ,  120 , and  130  each have a similar loop base length  42 , a coupler to center distance  44 , and a loop apex height  46 . The loop antenna elements  20  and  30  are separated by a loop spacing distance  45 . The loop antenna elements  120  and  130  are separated by the loop spacing distance  45 . All of the loop antenna elements  20 ,  30 ,  120 , and  130  share the base height above ground  48 . In one embodiment, when the orthogonal dual loop antenna  100  is designed for an operational frequency range of 1-22 MHz, the loop base length  42  and loop apex height is equal to approximately 3.5 m, the coupler to center distance  44  is 1.75 m, the loop spacing distance  45  is 3 cm, and the base height above ground  48  is 20 cm. 
     Referring now to  FIGS. 8 and 9 , an orthogonal single loop compact directional receiving antenna  170  is illustrated in a fixed installation. The orthogonal single loop antenna  170  is shown in a ground mounted configuration, and includes the controller  12 , feed transmission line  14 , and vertically oriented center support  18  as discussed previously in this specification. In this embodiment, the controller  12  is configured to electronically orient the antenna pattern as will be discussed later in this specification. 
     The feed transmission line  14  is connected to the signal processor  102  located near a base of the orthogonal single loop antenna  170 . The signal processor  102  includes switching, signal combining, time delay, impedance matching, and amplification circuitry as will be discussed in further detail in this specification. 
     The first loop antenna element  72  and a second loop antenna element  172  are each borne by the center support  18  and are each comprised as discussed earlier. Each of the elements  72  and  172  have a path length, shape, and an area enclosed which should each be substantially equal to one another. The element  72  is mounted in a common plane and the element  172  should be mounted in another plane that is substantially orthogonal to the common plane. 
     The loop antenna elements  72  and  172  are each held in tension by an anchors  22 ,  32 ,  122  and  132  respectively. 
     The couplers  24  and  34  are each positioned proximate to a portion of the loop antenna element  72  are each configured to transfer signals that are captured by the element. The couplers  124  and  134  are similarly positioned proximate to a portion of the loop antenna element  172  are each configured to transfer signals that are captured by this element in a manner described previously in this specification. 
     The couplers  24  and  34  are positioned proximate to a portion of the loop antenna element  72 . In one embodiment, the couplers  24  and  34  are each current transformers formed by running the loop antenna element  72  directly through ferrite beads  80  and  82  ( FIG. 9 ) forming individual single turn primary windings as discussed previously. The couplers  124  and  134  are positioned proximate to a portion of the loop antenna element  172 . In one embodiment, the couplers  124  and  134  are each current transformers formed by running the loop antenna element  172  directly through ferrite beads  180  and  182  ( FIG. 9 ) forming individual single turn primary windings as discussed previously. 
     The loop transmission lines  26  and  36  are each connected directly to the couplers  24  and  34 . In one embodiment, the loop transmission lines  26  and  36  are connected to connectors  54  and  64  ( FIG. 9 ) that each in turn connect to separate single turn secondary windings  84  and  88  ( FIG. 9 ) of current transformers formed by the ferrite beads  80  and  82  ( FIG. 9 ). Loop transmission lines  126  and  136  are each connected directly to the couplers  124  and  134  respectively. In one embodiment, the loop transmission lines  126  and  136  are connected to connectors  154  and  164  ( FIG. 9 ) that each, in turn, connect to separate single turn secondary windings  184  and  188  ( FIG. 9 ) of current transformers formed by the ferrite beads  180  and  182  ( FIG. 9 ). 
     The loop transmission lines  26  and  36  are each connected directly to the couplers  24  and  34 . Similarly, a transmission line  126  is connected to coupler  124  and a transmission line  136  is connected to coupler  134 . Each of the transmission lines  26 ,  36 ,  126 , and  136  provide a time delay for signals traveling from one end to the other end, and are selected to provide a substantially similar time delay one with respect to another. 
     Referring now to  FIG. 8 , the delay lines  38  and  138  are formed and connected as discussed previously in this specification. The operation of the delay line  138  will be discussed in further detail later in this specification. 
     Signals coming from a reference direction generally indicated by the arrow  40  are preferred when signals from the loop transmission line  26  are routed through the delay line  38  before being combined with signals from loop transmission line  36 . Yet further, signals coming from a reference direction generally indicated by the arrow  140  are preferred when signals from the loop transmission line  126  are routed through the delay line  38  before being combined with signals from loop transmission line  136 . Still further, signals coming from a reference direction generally indicated by a vector combination of the arrow  40  and  140  are preferred when signals from the loop transmission line  26  are combined with signals from loop transmission line  126 , and are routed through the delay line  38  and delay line  138  before being finally combined with signals from a combination of signals from loop transmission line  36  and loop transmission line  136  as discussed previously. 
     The antenna elements  72  and  172  each have the loop base length  78 , the coupler to coupler distance  76 , the loop apex height  46 , and the base height above ground  48 . In one embodiment, when the single loop antenna  170  is designed for an operational frequency range of 500 KHz-14 MHz, the loop base length  78  is equal to 7 m, the loop apex height  46  is equal to approximately 3.5 m, the coupler to coupler distance  76  is 6 m, and the base height above ground  48  is 20 cm. 
     Referring now to  FIG. 10 , a combiner signal bus  200  is connected to a first port of the signal combiner  90 . A delay line signal bus  202  is connected to a first end of the delay line  38 . A second end of the delay line  38  is connected to a first end of a parallel combination of the delay line  138  and a bypass switch  203 . An opposite end of the parallel combination is connected to a second port of the signal combiner  90 . 
     The combined signal  96  provided by the signal combiner  90  is introduced to the buffer amplifier  98 . The resultant signal  99  is provided by the buffer amplifier  98 . 
     A first end of the transmission line  36  is coupled to the connector  64 . A controlled connection is provided between a second end of the transmission line  36  and the delay line signal bus  202  via switch  204 . A controlled connection is also provided between the second end of the transmission line  36  and the combiner signal bus  202  via switch  206 . 
     A first end of the transmission line  26  is coupled to the connector  54 . A controlled connection is provided between a second end of the transmission line  26  and the delay line signal bus  202  via switch  208 . A controlled connection is provided between the second end of the transmission line  26  and the combiner signal bus  202  via switch  210 . 
     A first end of the transmission line  136  is coupled to the connector  164 . A controlled connection is further provided between a second end of the transmission line  136  and the delay line signal bus  202  via switch  212 . A controlled connection is also provided between the second end of the transmission line  136  and the combiner signal bus  202  via switch  214 . 
     A first end of the transmission line  126  is coupled to the connector  154 . A controlled connection is provided between a second end of the transmission line  126  and the delay line signal bus  202  via switch  216 . A controlled connection is provided between the second end of the transmission line  126  and the combiner signal bus  202  via switch  218 . 
     A preferred receive direction can be manipulated for both the orthogonal dual loop antenna  100  ( FIG. 6 ) and the orthogonal single wire loop antenna  170  ( FIG. 8 ) by proper configuration of the switches  203 ,  204 ,  206 ,  208 ,  210 ,  21 ,  214 ,  216 , and  218 . This arrangement will be discussed in further detail in the operation portion of this specification. 
     In one embodiment of the orthogonal dual loop antenna  100  ( FIG. 6 ), the combiner first signal path  92  provides a time delay of 6 nsec relative to the combiner second signal path  94 . In this embodiment, delay line  38  is selected to provide a 20 nsec delay and delay line  138  is selected to provide a 6 nsec delay. As a result, a delay of 14 nsec is realized when the bypass switch  203  is closed, and a delay of 20 nsec is realized when the bypass switch  203  is open. Using these values, an acceptable front-to-back ratio has been achieved using the dimensions provided earlier in this specification. 
     In one embodiment of the orthogonal single loop antenna  170  ( FIG. 8 ), the combiner first signal path  92  provides a time delay of 6 nsec relative to the combiner second signal path  94  as discussed above. In this embodiment, delay line  38  is selected to provide a 27 nsec delay and delay line  138  is selected to provide a 8 nsec delay. As a result, a delay of 21 nsec is realized when the bypass switch  203  is closed, and a delay of 29 nsec is realized when the bypass switch  203  is open. Using these values, an acceptable front-to-back ratio has been achieved using the dimensions provided earlier in this specification. 
     Referring now to  FIG. 11  the controller  12  is housed in an enclosure  230  which supports a selector switch  232 . The selector switch  232  is configured to specify a direction by rotating a knob attached thereto. A plurality of light emitting diodes are arranged about the selector switch  230  and are herein referenced as a north LED  234 , a northeast LED  236 , a east LED  238 , a southeast LED  240 , a south LED  242 , a southwest LED  244 , and west LED  246 , and a northwest LED  248 . 
     A pattern flip push button switch  250  is mounted on the enclosure  230  and is configured to temporarily change a configuration of the signal processor  102  to electronically rotate a response of the antenna  100  or  170  by one-hundred-eighty degrees. 
     A unidirectional push button switch  252  is configured to command the signal processor  102  to provide a response of the antenna  100  or  170  that is generally unidirectional. A bidirectional push button  254  is configured to command the signal processor  102  to provide a response of the antenna  100  or  170  that is generally bidirectional. 
     Referring now to  FIG. 12 , and using the dimensions described earlier, a series of patterns is provided illustrating relative performance of both the antenna  100  or  170  when they are configured to provide a bidirectional response. The pattern generally indicated by the numeral  300  is modeled at a frequency of 1.5 MHz; the pattern generally indicated by the numeral  302  is modeled at a frequency of 3 MHz; the pattern generally indicated by the numeral  304  is modeled at a frequency of 6 MHz; the pattern generally indicated by the numeral  306  is modeled at a frequency of 12 MHz; and the pattern generally indicated by the numeral  308  is modeled at a frequency of 18 MHz. 
     Referring now to  FIG. 13 , and using the dimensions described earlier for the dual loop antenna  10  and orthogonal dual loop antenna  100 , a series of patterns is provided when the antenna  100  configured to provide a unidirectional response. The pattern generally indicated by the numeral  310  is modeled at a frequency of 1.5 MHz; the pattern generally indicated by the numeral  312  is modeled at a frequency of 3 MHz; the pattern generally indicated by the numeral  314  is modeled at a frequency of 6 MHz; the pattern generally indicated by the numeral  316  is modeled at a frequency of 12 MHz; and the pattern generally indicated by the numeral  318  is modeled at a frequency of 18 MHz. 
     Referring now to  FIGS. 1 ,  6 , and  14 , and using the overall dimensions described earlier for the orthogonal dual loop antenna  100 , a relative position of the coupler distance to center  44  to the loop base length  42  impacts the shape of the antenna pattern and will be described briefly below. There is also a relationship between the coupler distance to center  44  and the optimum delay line  38  length. The series of patterns are illustrated for a frequency of 6 MHz, although the pattern shape is largely retained over the operational frequencies. The pattern generally indicated by the numeral  320  is modeled when the coupler distance to center  44  is 90% of the loop base length  42 ; the pattern generally indicated by the numeral  322  is modeled when the coupler distance to center  44  is 50% of the loop base length  42 ; the pattern generally indicated by the numeral  324  is modeled when the coupler distance to center  44  is 37% of the loop base length  42 ; and the pattern generally indicated by the numeral  326  is modeled when the coupler distance to center  44  is 29% of the loop base length  42 . By inspection of  FIG. 14 , it is apparent that forward gain is increased as the coupler distance to center percentage is increased at the expense of front to side ratio. 
     Referring now to  FIG. 15 , and using the dimensions described earlier for the single loop antenna  10  and orthogonal single loop antenna  170 , a series of patterns is provided when the antenna  170  configured to provide a unidirectional response. The pattern generally indicated by the numeral  330  is modeled at a frequency of 1.5 MHz; the pattern generally indicated by the numeral  332  is modeled at a frequency of 3 MHz; the pattern generally indicated by the numeral  334  is modeled at a frequency of 6 MHz; and the pattern generally indicated by the numeral  336  is modeled at a frequency of 12 MHz. 
     Operation 
     The operation of the present invention is believed to be readily apparent and is briefly summarized in the paragraphs which follow. 
     Referring to FIGS.  1 , 2  and  5 , an electromagnetic signal arriving from a direction opposite indicated by the arrow  40  will first induce a signal into loop element  20 , and then, after an induced arrival time delay, into loop element  30 . Each of the loop elements  20  and  30  have a individual response pattern which is represented by the patterns shown in  FIG. 12  at selected frequencies as discussed above. The loop coupler  24  will transfer its signal in phased relationship from loop element  20  to the transmission line  26  and the loop coupler  34  will transfer its signal in phased relationship from the loop element  30  to the transmission line  36 . Each signal experiences a similar time delay when traveling from one end of the transmission lines  26  and  36  if they each have a similar length, velocity factor, characteristic impedance, and are terminated into a similar impedance, which most desirably, is the characteristic impedance of the transmission line. Since this is the case, the delay experienced through the transmission lines  26  and  36  will be substantially similar. 
     After traveling through transmission line  26 , its signal is routed through delay line  38  to induce a further delay into the signal received on the loop element  20 . The delay line  38  is terminated into one port of the signal combiner  90  where it experiences a further delay through the combiner signal path  94 . The transmission line  36  is terminated into another port of the signal combiner  90  where it experiences a further delay through the combiner signal path  92 . The combined signal  96  emerges from a third port of the combiner  90  and is routed to the buffer amplifier  98 , where it is delivered to the feed transmission line  14  via path  99 . The controller  12  conditions the signal provided by the transmission line  14  and makes it available for connection to a receiver (not shown). The controller  12  also provides power for the buffer amplifier  98 . 
     During design of the antenna  10 , the phasing of the couplers as well as the time delay induced by each line and signal path is selected such that signals arriving from the direction opposite that indicated by the arrow  40  are of opposite phase so that they effectively cancel, allowing signals arriving from the preferred direction indicated by arrow  40  to experience a lesser degree of cancellation. More specifically, the sum of the delay provided by the transmission line  26  and the delay line  38  and the signal path delay  94  minus the sum of the delay provided by the transmission line  36  and the signal path delay  92  should be approximately equal to the induced arrival time delay. The results of the signal combining process can be observed by a careful inspection of  FIGS. 13 and 14  as described previously in this specification. 
     Referring now to  FIGS. 6 ,  7 ,  10 , and  11 , elements of one dual loop antenna  10  ( FIG. 1 ) are oriented in a direction generally indicated by the arrow  40  (which follows signals arriving from a northerly direction), and combined in orthogonal fashion with elements of another dual loop antenna  10  ( FIG. 1 ) and oriented in a direction generally indicated by the arrow  140  (which follows signals arriving from an westerly direction) for form an orthogonal dual loop antenna  100 . 
     The signal processor  102  is configured to be responsive to commands provided by the controller  12  as is well known in the art. When the bidirectional push button  254  is pressed, a pair of oppositely positioned light emitting diodes are lit indicating the commanded direction. When the north LED  234  and south LED  242  are each illuminated, a message is sent to the signal processor  102  to close the combiner switch  206 , leaving remaining switches in  FIG. 10  in an open position. Signals arriving at the antenna  100  are induced into loop element  30 , where they are coupled into the transmission line  36  via coupler  34 . These signals are routed through the closed combiner switch  206  and travel through the combiner  90  and follow the path discussed previously in this specification. Since all other switches in the signal processor  102  remain open, no other signal is presented to the combiner  90 , so the pattern of  FIG. 12  is realized with a north-south orientation. In a similar manner, by moving the selector switch  232  so that the east LED  238  and west LED  246  are illuminated, a message is sent from the controller  12  to the signal processor  102  to close combiner switch  218  leaving remaining switches in  FIG. 10  in an open position so the pattern of  FIG. 12  is realized with a east-west orientation. 
     By moving the selection switch  232  so that the northeast LED  236  and southwest LED  244  are each illuminated, a message is sent to the signal processor  102  to close the switches  206  and  218 , leaving remaining switches in  FIG. 10  in an open position. Signals arriving at the antenna  100  are induced into loop elements  30  and  120 , where they are each coupled into the transmission lines  36  and  126  via couplers  34  and  124 . These signals are routed through the closed combiner switches  206  and  218  to the combiner signal bus  200 , traveling through the combiner  90  and following the path discussed previously in this specification. Since all other switches in the signal processor  102  remain open, no other signal is presented to the combiner  90 , so the pattern of  FIG. 12  is realized with a northeast-southwest orientation. 
     In a similar manner, by moving the selector switch  232  so that the southeast LED  240  and northwest LED  248  are illuminated, a message is sent from the controller  12  to the signal processor  102  to close combiner switches  210  leaving remaining switches in  FIG. 10  in an open position so the pattern of  FIG. 12  is realized with a southeast-northwest orientation. 
     Continuing to refer to  FIGS. 6 ,  7 ,  10 , and  11 , when the unidirectional push button  252  is pressed, a light emitting diode is lit indicating the commanded direction. When only the north LED  234  is illuminated, a message is sent to the signal processor  102  to close the switches  206 ,  208  and the bypass switch  203 , leaving remaining switches in  FIG. 10  in an open position. The signal arriving at the antenna  100  is induced into loop element  30 , where it is coupled into the transmission line  36  via coupler  34 . This signal is routed through the closed combiner switch  206  and fed onto the combiner signal bus  200  that is also connected to the combiner  90 . The signal is also induced into the loop element  20 , where it is coupled into the transmission line  26  via coupler  24 . The signal is routed through the closed delay switch  208  and fed onto the delay line signal bus  202  that is connected to the delay line  38  that subsequently is connected to the bypass switch  203  that is also connected to the combiner  90 . At the combiner, signals coming from the favored direction are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. In this way, the antenna patterns shown in  FIG. 13  and  FIG. 14  are realized with a northerly orientation. 
     In a similar manner, by moving the selector switch  232  so that the south LED  242  is illuminated, a message is sent from the controller  12  to the signal processor  102  to close the switches  210 ,  204  and the bypass switch  203 , leaving remaining switches in  FIG. 10  in an open position. In this way, the antenna patterns shown in  FIG. 13  and  FIG. 14  are realized with a southerly orientation. 
     By rotating the selector switch  232  so that the east LED  238  is illuminated, a message is sent to the signal processor  102  to close the switches  218 ,  212  and the bypass switch  203 , leaving remaining switches in  FIG. 10  in an open position. The signal arriving at the antenna  100  is induced into loop element  120 , where it is coupled into the transmission line  126  via coupler  124 . This signal is routed through the closed combiner switch  218  and fed onto the combiner signal bus  200  that is also connected to the combiner  90 . The signal is also induced into the loop element  130 , where it is coupled into the transmission line  136  via coupler  134 . The signal is routed through the closed delay switch  212  and fed onto the delay line signal bus  202  that is connected to the delay line  38  that subsequently is connected to the bypass switch  203  that is also connected to the combiner  90 . At the combiner, signals coming from the favored direction, in this case from the east, are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. In this way, the antenna patterns shown in  FIG. 13  and  FIG. 14  are realized with an easterly orientation. 
     In a similar manner, by rotating the selector switch  232  so that the west LED  246  is illuminated, a message is sent from the controller  12  to the signal processor  102  to close the switches  214 ,  216  and the bypass switch  203 , leaving remaining switches in  FIG. 10  in an open position. In this way, the antenna patterns shown in  FIG. 13  and  FIG. 14  are realized with a westerly orientation. 
     Referring still to  FIGS. 6 ,  7 ,  10 , and  11  and by moving the selection switch  232  so that the northeast LED  236  is illuminated, a message is sent, to the signal processor  102  to close the combiner switches  206 ,  218  and delay switches  208  and  212  leaving remaining switches in  FIG. 10  in an open position. Signals arriving at the antenna  100  are induced into loop elements  30  and  120 , where they are each coupled into the transmission lines  36  and  126  via couplers  34  and  124 . These signals are routed through the closed combiner switches  206  and  218  to the combiner signal bus  200 , traveling through the combiner  90  and following the path discussed previously in this specification. 
     Signals arriving at the antenna  100  are also induced into loop elements  20  and  130 , where they are each coupled into the transmission lines  26  and  136  via couplers  24  and  134 . These signals are routed through the closed delay switches  208  and  212  and fed onto the delay line signal bus  202  that is connected to the delay line  38  that subsequently is connected to the delay line  138  that is also connected to the combiner  90 . At the combiner, signals coming from the favored direction, in this case from the northeast, are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. In practice, it has been found that the delay line  138  is optional, and can be removed if it is permanently bypassed. 
     In a similar manner, by moving the selector switch  232  so that the southeast LED  240  is illuminated, a message is sent from the controller  12  to the signal processor  102  to close combiner switches  210  and  218  and close delay switches  204  and  212  leaving remaining switches in  FIG. 10  in an open position. In this configuration signals coming from the favored direction, in this case from the southeast, are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. 
     Also, in a similar manner, by moving the selector switch  232  so that the southwest  244  is illuminated, a message is sent from the controller  12  to the signal processor  102  to close combiner switches  210  and  214  and close delay switches  204  and  216  leaving remaining switches in  FIG. 10  in an open position. In this configuration signals coming from the favored direction, in this case from the southwest, are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. 
     Finally, in a similar manner, by moving the selector switch  232  so that the northwest  244  is illuminated, a message is sent from the controller  12  to the signal processor  102  to close combiner switches  206  and  214  and close delay switches  208  and  216  leaving remaining switches in  FIG. 10  in an open position. In this configuration signals coming from the favored direction, in this case from the northwest, are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. 
     Referring now to  FIGS. 3 ,  4  and  5 , an electromagnetic signal arriving from a direction opposite indicated by the arrow  40  will induce a signal into loop element  72 . The loop elements  72  each have an individual response pattern that is represented by the patterns shown in  FIG. 12  at selected frequencies discussed above. 
     The signal from the loop element  72  will first transfer the signal to loop coupler  24 , and then, after an induced arrival time delay, transfer the signal to loop coupler  34 . Accordingly, the loop coupler  24  will transfer its signal in phased relationship to the transmission line  26 , and the loop coupler  34  will transfer its signal in phased relationship to the transmission line  36 . 
     After traveling through transmission line  26 , its signal is routed through delay line  38  to induce a further delay into the signal received on the loop element  20 . The delay line  38  is terminated into one port of the signal combiner  90  where it experiences a further delay through the combiner signal path  94 . The transmission line  36  is terminated into another port of the signal combiner  90  where it experiences a further delay through the combiner signal path  92 . The combined signal  96  emerges from a third port of the combiner  90  and is routed to the buffer amplifier  98 , where it is delivered to the feed transmission line  14  via path  99 . The controller  12  conditions the signal provided by the transmission line  14  and makes it available for connection to a receiver (not shown). The controller  12  also provides power for the buffer amplifier  98 . 
     During design of the antenna  10 , the phasing of the couplers as well as the time delay induced by each line and signal path is selected such that signals arriving from the direction opposite that indicated by the arrow  40  are of opposite phase so that they effectively cancel, allowing signals arriving from the preferred direction indicated by arrow  40  to experience a lesser degree of cancellation. More specifically, the sum of the delay provided by the transmission line  26  and the delay line  38  and the signal path delay  94  minus the sum of the delay provided by the transmission line  36  and the signal path delay  92  should be approximately equal to the induced arrival time delay. The results of the signal combining process can be observed by a careful inspection of  FIG. 15  as described previously in this specification. 
     Referring now to  FIGS. 8 ,  9 ,  10 , and  11 , elements of one single loop antenna  70  ( FIG. 3 ) are oriented in a direction generally indicated by the arrow  40  (which follows signals arriving from a northerly direction), and combined in orthogonal fashion with elements of another single loop antenna  70  ( FIG. 3 ) and oriented in a direction generally indicated by the arrow  140  (which follows signals arriving from an westerly direction) to form an orthogonal single loop antenna  170 . 
     When the bidirectional push button  254  is pressed, a pair of oppositely positioned light emitting diodes are lit indicating the commanded direction. When the north LED  234  and south LED  242  are each illuminated, a message is sent to the signal processor  102  to close the combiner switch  206 , leaving remaining switches in  FIG. 10  in an open position. Signals arriving at the antenna  170  are induced into loop element  72 , where they are coupled and routed as described earlier in this specification so the pattern of  FIG. 12  is realized with a north-south orientation. In a similar manner, by moving the selector switch  232  so that the east LED  238  and west LED  246  are illuminated, a message is sent from the controller  12  to the signal processor  102  to close combiner switch  218  leaving remaining switches in  FIG. 10  in an open position so the pattern of  FIG. 12  is realized with a east-west orientation. 
     By moving the selection switch  232  so that the northeast LED  236  and southwest LED  244  are each illuminated, a message is sent to the signal processor  102  to close the switches  206  and  218 , leaving remaining switches in  FIG. 10  in an open position. Signals arriving at the antenna  170  are induced into loop elements  72  and  172 , where they are each coupled into the transmission lines  36  and  126  via couplers  34 , and  124 . These signals are routed through the closed combiner switches  206  and  218  and process as described previously in this specification, so the pattern of  FIG. 12  is realized with a northeast-southwest orientation. 
     In a similar manner, by moving the selector switch  232  so that the southeast LED  240  and northwest LED  248  are illuminated, a message is sent from the controller  12  to the signal processor  102  to close combiner switches  210  leaving remaining switches in  FIG. 10  in an open position so the pattern of  FIG. 12  is realized with a southeast-northwest orientation. 
     Continuing to refer to  FIGS. 8 ,  9 ,  10 , and  11 , when the unidirectional push button  252  is pressed, a light emitting diode is lit indicating the commanded direction as discussed previously in this specification. When only the north LED  234  is illuminated, a message is sent to the signal processor  102  to close the switches  206 ,  208  and the bypass switch  203 , leaving remaining switches in  FIG. 10  in an open position. The signal arriving at the antenna  170  is induced into loop element  72 , where it is coupled into the transmission line  36  via coupler  34 . This signal is routed through the closed combiner switch  206  and fed onto the combiner signal bus  200  that is also connected to the combiner  90 . The signal is also coupled into the transmission line  26  via coupler  24 . The signal is routed through the closed delay switch  208  and fed onto the delay line signal bus  202  that is connected to the delay line  38  that subsequently is connected to the bypass switch  203  that is also connected to the combiner  90  and processed as described earlier. In this way, the antenna pattern shown in  FIG. 15  is realized with a northerly orientation. 
     In a similar manner, by moving the selector switch  232  so that the south LED  242  is illuminated, a message is sent from the controller  12  to the signal processor  102  to close the switches  210 ,  204  and the bypass switch  203 , leaving remaining switches in  FIG. 10  in an open position. In this way, the antenna pattern shown in  FIG. 15  is realized with a southerly orientation. 
     By rotating the selector switch  232  so that the east LED  238  is illuminated, a message is sent to the signal processor  102  to close the switches  218 ,  212  and the bypass switch  203 , leaving remaining switches in  FIG. 10  in an open position. The signal arriving at the antenna  170  is induced into loop element  172 , where it is coupled into the transmission line  126  via coupler  124 . This signal is routed through the closed combiner switch  218  and fed onto the combiner signal bus  200  that is also connected to the combiner  90 . The signal is also induced into the transmission line  136  via coupler  134 . The signal is routed through the closed delay switch  212  and fed onto the delay line signal bus  202  that is connected to the delay line  38  that subsequently is connected to the bypass switch  203  that is also connected to the combiner  90 . At the combiner, signals coming from the favored direction, in this case from the east, are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. In this way, the antenna pattern shown in  FIG. 15  is realized with an easterly orientation. 
     In a similar manner, by rotating the selector switch  232  so that the west LED  246  is illuminated, a message is sent from the controller  12  to the signal processor  102  to close the switches  214 ,  216  and the bypass switch  203 , leaving remaining switches in  FIG. 10  in an open position. In this way, the antenna pattern shown in  FIG. 15  is realized with a westerly orientation. 
     Referring still to  FIGS. 8 ,  9 ,  10 , and  11  and by moving the selection switch  232  so that the northeast LED  236  is illuminated, a message is sent to the signal processor  102  to close the combiner switches  206 ,  218  and delay switches  208  and  212  leaving remaining switches in  FIG. 10  in an open position. Signals arriving at the antenna  170  are induced into loop elements  72  and  172 , where they are each coupled into the transmission lines  36  and  126  via couplers  34  and  124 . These signals are routed through the closed combiner switches  206  and  218  to the combiner signal bus  200 , traveling through the combiner  90  and following the path discussed previously in this specification. 
     Signals are also each coupled into the transmission lines  26  and  136  via couplers  24  and  134 . These signals are routed through the closed delay switches  208  and  212  and fed onto the delay line signal bus  202  that is connected to the delay line  38  that subsequently is connected to the delay line  138  that is also connected to the combiner  90 . At the combiner, signals coming from the favored direction, in this case from the northeast, are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. In practice, it has been found that the delay line  138  is optional, and can be removed if it is permanently bypassed. 
     In a similar manner, by moving the selector switch  232  so that the southeast LED  240  is illuminated, a message is sent from the controller  12  to the signal processor  102  to close combiner switches  210  and  218  and close delay switches  204  and  212  leaving remaining switches in  FIG. 10  in an open position. In this configuration signals coming from the favored direction, in this case from the southeast, are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. 
     Also, in a similar manner, by moving the selector switch  232  so that the southwest  244  is illuminated, a message is sent from the controller  12  to the signal processor  102  to close combiner switches  210  and  214  and close delay switches  204  and  216  leaving remaining switches in  FIG. 10  in an open position. In this configuration signals coming from the favored direction, in this case from the southwest, are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. 
     Finally, in a similar manner, by moving the selector switch  232  so that the northwest  244  is illuminated, a message is sent from the controller  12  to the signal processor  102  to close combiner switches  206  and  214  and close delay switches  208  and  216  leaving remaining switches in  FIG. 10  in an open position. In this configuration signals coming from the favored direction, in this case from the northwest, are attenuated less than are signals coming from the un-favored direction as discussed previously in this specification. 
     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and describe, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.