Directional Coupler For Transmission Lines

Abstract

A directional coupler for detecting and measuring unidirectional wave signals propagated along a transmission line. The coupler includes an insulative board, having a first layer of conductive material secured to one of the faces of the insulative board and a second layer of conductive material secured to the other face of the insulative board to define a predetermined impedance with respect to a ground plane partition member. A coupling element comprising a third layer of conductive material is also secured to the other face of the insulative board to define a predetermined impedance with respect to the second layer of conductive material. The ground plane partition member and the second layer of conductive material serve as a section of the transmission line. The coupling element is connected to a signal measuring network for developing an output signal having a value representative of the value of an unidirectional wave signal propagated along the transmission line. The assembly including the insulative board and plural conductive layers is mounted in a housing, and the partition member is electrically bonded to four of the side walls of the housing in order to define a pair of chambers within the housing and serves the function of substantially preventing the passage of electrical fields between these chambers.

Description

BACKGROUND OF THE INVENTION

This invention pertains to the art of electrical devices for detecting and measuring wave signals propagated along a transmission line, and more particularly, to directional couples for measuring unidirectional radio-frequency wave signals on a transmission line.

In the operation of radio-frequency transmitting equipment, it is frequently necessary to measure radio-frequency wave signals propagated along a transmission line. The data obtained by such measurements may be utilized to compute the standing-wave ratio of the transmission line, forward power propagated along the transmission line, reflected power propagated along the transmission line, et cetera.

Directional couplers have become an important component of transmitting systems. These couplers have been utilized in conjunction with electronic control circuitry for continuously monitoring forward and reflected power on a transmission line and for automatically reducing the input power to a transmitter when the forward or reflected power on the transmission line exceeds a predetermined level.

Various electronic instruments have been employed to monitor and measure wave signals propagated along transmission lines. These instruments have included various types of coupler arrangements and configurations between a primary transmission line and secondary line, or coupling circuit. For example, capacitative coupling circuits, inductive coupling circuits, and resistive bridge networks have been employed either separately, or in various combinations, to transfer a portion of the energy on a primary transmission line to a secondary line for measurement.

These conventional directional couplers have generally comprised a section of coaxial transmission line which is machined in a cylindrical configuration from metal. Normally, inductive and capacitive elements extend through slotted apertures in the side walls of the couplers for connecting a signal measuring network to the transmission line. The coupling elements generally take the form of wire coils and capacitive probes which are supported at one end, and extend into and intercept an electrical field which exists between the center conductor and the outer conductor of the coaxial transmission line. One example of this type of coupler is that shown in conjunction with the directional wattmeter disclosed in U.S. Pat. No. 2,852,741, to J. R. Bird et al, entitled "Directional Wattmeter" and issued on Sept. 16, 1958.

One of the problems associated with directional couplers which are machined as a cylindrical section of a transmission line is that the machining operations in the manufacture of these couplers are quite expensive because the component part must be manufactured to exacting specifications in order to interlock with or threadably engage an adjacent component. Unless exacting specifications are maintained between adjacent components, leakage between components may cause stray electrical fields resulting in inaccuracies of measurement.

Another problem associated with these known directional couplers is the importance of having the various inductive elements and capacitive probes precisely positioned in order to establish a predetermined reactance or inductance with respect to the transmission line. The requirement for exact positioning of these elements creates additional problems and increased manufacturing cost.

SUMMARY OF THE INVENTION

With the ever-increasing use of directional couplers as a single component in transmitting systems, as opposed to the use of directional couplers as a major component of relatively expensive test equipment, it has been found to be highly desirable to provide a directional coupler which may be manufactured at a substantial reduction in cost, as well as a directional coupler which may be mass produced with a high degree of reliability.

Also, transmitting systems are frequently subjected to greater mechanical shock than is normally encountered by test equipment. Thus, it has been found to be desirable to provide a directional coupler which is rugged in construction and immune to damage as a result of normal mechanical shock.

The present invention is directed toward a directional coupler which incorporates mechanical, as well as electrical features, for overcoming the noted disadvantages, and others, of conventional coupler systems.

In accordance with the present invention, there is provided a directional coupler for detecting unidirectional wave singles signals a transmission line. The coupler includes a housing member having a transmission line input connector and output connector mounted thereon and a ground plane partition member mounted within so as to define a first and second chamber within the housing. The ground plane is electrically bonded to the walls of the housing in order to substantially prevent the passage of electrical fields between the two chambers. One of the surfaces of an insulative board having secured thereon a layer of conductive material is attached to the partition member, and a layer of conductive material is secured to the other surface of the insulative board so as to act as a primary transmission conductor to define a predetermined impedance between the conductive layer and the ground plane. In addition, a coupling element comprised of another layer of conductive material, is also secured to the insulative board in spaced relation with respect to the first conductive layer for receiving a portion of the energy of a wave signal which is propagated along the primary transmission line.

The ground plane partition member and the conductive layer comprising the primary transmission line secured to the other side of the insulative board are coupled between the input and output connectors so as to define a section of a transmission line, and the coupling element is connected to an output circuit carried by the partition member at the side opposite to the insulative board to provide an output signal having a value representative of a unidirectional wave signal on the transmission line.

The primary transmission line or first conductive layer is comprised of a thin film or strip of conductive material of a generally elongated rectangular configuration, and includes a pair of L-shaped terminal members each having one leg portion electrically connected to one of the ends of the elongated film of conductive material and another leg portion connected to one terminal of one of the input connectors.

The coupling element is also comprised of a thin film of conductive material of a generally elongated rectangular configuration and is secured to the same face of the insulataive board as the first conductive layer and in spaced parallel relationship with respect thereto. Thus, the coupling element is capacitively coupled to the primary transmission line conductive layer to thereby define a secondary or coupling circuit.

The secondary circuit includes an adjustable capacitive element for varying the capacitance between the primary circuit and the secondary output circuit in order to increase or decrease the coupling between these circuits.

It is therefore an object of the present invention to provide a directional coupler which is simple in construction and which lends itself to being manufactured with a high degree of reliability when mass produced.

Another object of the present invention is the provision of a directional coupler which is of rugged construction and immune to damage as a result of normal mechanical shock.

A further object of the present invention is to provide a directional coupler which may be produced at a substantial savings in manufacturing costs.

Another object of the present invention is the provision of a direction coupler having improved shielding between a radio frequency section of the coupler and electrical components in a signal measuring section of the coupler.

These and other objects and advantages of the invention will become apparent from the following description of a preferred embodiment of the invention as read in conjunction with the accompanying drawings and in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view partly in section illustrating a directional coupler embodying the present invention;

FIG. 2 is a top elevational view of the directional coupler as illustrated in FIG. 1, as viewed along the line 2--2;

FIG. 3 is a bottom elevational view of the directional coupler illustrated in FIG. 1, as viewed along the line 3--3;

FIG. 4 is a sectional view of the directional coupler illustrated in FIG. 2, as viewed along the line 4--4;

FIG. 5 is a sectional view of the directional coupler as illustrated in FIG. 1, as viewed along the line 5--5;

FIG. 6 is an oblique view of the directional coupler as illustrated in FIG. 1 with the housing member removed and the component parts separated for purposes of illustration; and,

FIG. 7 is an electrical schematic diagram in conjunction with a mechanical elevational view of the directional coupler of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

FIGS. 1 through 5 illustrate a directional coupler in accordance with the present invention which generally comprises a conductive rectangular housing member 10 having an input coaxial connector 12 mounted on one end and an output coaxial connector 14 mounted on the other end thereof. For purposes of discussion, the coaxial connector 12 will be referred to as the input connector and coaxial connector 14 will be referred to as an output connector, however, it is to be understood that the circuitry in the directional coupler is symmetrical, and accordingly, the coupler may be connected in a transmission line such that the coaxial connector 14 serves as an input connector and the coaxial connector 12 serves as an output connector.

The outer conductors 16, 18 of the coaxial connectors 12, 14 are electrically bonded to the end walls of the conductive housing member 10, and the inner conductors 20, 22 of the connectors 12, 14 pass through and are insulated from the end walls of the housing.

A ground plane conductive partition member 24 is positioned within the housing member 10 and is electrically bonded to four of the walls of the housing so as to define an upper chamber 26 and a lower chamber 28. The partition member 24 serves as an electrical shield to prevent radio-frequency fields which exist in the lower chamber 28 from passing into the upper chamber 26 and adversely affecting the operation of the voltage measuring circuitry in this chamber.

The partition member 24 is comprised of a generally rectangular plate having a central portion 30 which extends in a horizontal plane, a pair of vertical portions 32, 34, and a pair of outer portions 36, 38 which extend in a horizontal plane above the horizontal plane of the central portion 30, as viewed in FIG. 1.

As illustrated in FIG. 1, partition member 24 is electrically and mechanically bonded to the end walls of the conductive housing 10 through a pair of flange portions 40, 42, and is similarly bonded to the side wall of the housing member through the flange portions 44, 46, 48, 50. The partition member 24 is also bonded to the opposite side wall of the housing member through the tab portions 52, 54, 56, as illustrated in FIG. 6, which extend through interlocking apertures in that wall.

An insulative board 58 which takes the form of a printed circuit board is secured to the central portion 30 of the partition member 24 with three rivets 61, 63, 64. The rivets extend through aligned apertures in the central portion of the partition member 24 and the insulative board 58.

Superimposed between a face of printed circuit board 58 and the partition member 24 is a thin film of conductive material or layer 60 which is secured to the insulative board by conventional printed circuit techniques. The primary line conductor 62 takes the form of strip layer of thin film conductive material which is similarly secured to an opposite face of the insulative board 58. The primary line conductor includes an elongated rectangular central portion having a pair of terminal strips 66, 68 extending from the ends thereof.

Electrical connection is made between the terminal strips 66, 68 and the conductors 20, 22 of the coaxial connectors 12, 14 through a pair of generally L-shaped conductive bracket members 70, 72. The bracket member 70 is secured to the terminal strip 66 of the primary line conductor 62 and the insulative board 58 by a pair of rivets 74, 76. The rivets 74, 76 extend through aligned apertures in one leg portion of the L-shaped bracket member 70, the terminal strip 66, and the insulative board 58. The inner conductor 20 of the coaxial connector 12 extends through an aperture 78 in the other leg portion of the bracket member 70 and is electrically bonded to that leg portion at this aperture.

The bracket member 72 is similarly secured to the terminal strip 68 of the primary line conductor or strip layer 62 and the insulative board 58 by a pair of rivets 80, 82 which extend through aligned apertures in one leg portion of the L-shaped bracket member 72, the terminal strip 68, and the insulative board 58. The inner conductor 22 of the coaxial connector 14 extends through an aperture 84 in the other leg portion of the bracket member 72 and is electrically bonded to that leg portion at this aperture.

It will be noted that the rivets 74, 76, 80, and 82 do not engage or contact the conductive layer 60.

The primary line conductor or strip layer 62 is of a configuration and is spaced from the thin film of conductive material 60 so as to define a predetermined characteristic impedance between the primary line 62 and the thin film of conductive material 60. In view of the fact that the film of conductive material 60 is in direct electrical contact with the partition member 24, the predetermined chacteristic impedance is also maintained between the primary line conductor 62 and the partition member 24.

A forward coupler 86 which takes the form of a generally rectangular thin film conductive strip is secured to an opposite face of the insulative board from the conductive layer 60 in parallel spaced relation with respect to the primary line conductor or layer 62. Similarly, a reverse coupler 88 which also takes the form of a rectangular thin film conductive strip is secured to an opposite face of the insulative board from the conductive layer 60 and in parallel spaced relation with respect to the primary line conductor, but on an opposite side of the conductor from that of the forward coupler 86.

One of the leads of a diode 90 extends through an eyelet 92 of a disc mica capacitor 94 and is electrically bonded to the eyelet 92 and to a terminal of the forward coupler 86. The other lead of the diode 90 extends through an eyelet of another disc mica capacitor 96 and is electrically bonded to the eyelet. The mica capacitor 96 includes a terminal connector 98 which is connected to and extends from the eyelet of this capacitor. The outer conductor of the capacitor 96 is connected through a cylindrical shield 100 to the outer conductor of the capacitor 94, and the outer conductor of the capacitor 94 is electrically bonded to the conductive layer 60 and is therefore in electrical contact with the partition member 24. The shield 100 not only serves to electrically connect the outer conductor of the capacitor 94 and the capacitor 96 to the plate 60, but this shield also serves as a secondary shield for the diode 90 to prevent radio frequency fields which exist in the lower chamber 28 from adversely affecting the operation of the diode.

One of the leads of a resistor 102 is connected to the other terminal of the forward coupler 86 and the other lead of this resistor is connected to a cylindrical shield 104 which is in turn bonded to the conductive layer 60. The terminal 98 of the mica capacitor 96 is connected through a resistor 106 to a forward output terminal 108, and a capacitor 110 is connected between the forward output terminal 108 and the conductive housing member 10.

Similarly, one of the leads of a diode 112 extends through an eyelet 114 of a disc mica capacitor 116 and is electrically bonded to the eyelet 114 and to a terminal of the reverse coupler 88. The other lead of the diode 112 extends through the eyelet in another disc mica capacitor 118 and is electrically bonded to the eyelet. The mica capacitor 118 includes a terminal connector 119 which is connected to and extends from the eyelet of this capacitor. The outer conductor of the capacitor 118 is connected through a cylindrical shield 120 to the outer conductor of the capacitor 116, which is in turn electrically bonded to the conductive plate 60. Thus, the cylindrical shield 120 serves to connect the outer conductor of the capacitors 116, 118 as well as to provide a secondary shield for the diode 112.

One of the leads of a resistor 122 is connected to the other terminal of the reverse coupler 88 and the other lead of this resistor is connected to a shield 124 which is grounded to the conductive plate 60. In addition, the center terminal 120 of the mica capacitor 118 is connected through a resistor 126 to a reverse output terminal 128. A capacitor 130 is then coupled between the reverse output terminal 128 and the conductive housing member 10.

As illustrated, the forward coupler 86 includes a variable capacitive balance tab 132. The balance tab 132 takes the form of a thin apertured rectangular plate. The lead of the resistor which is bonded to the terminal of the forward coupler 86 extends through an aperture in the terminal, through an aperture in a spacer bushing 133, and through the aperture in the balance tab 132. The balance tab 132 is bonded to the resistor lead at the aperature and is positioned to overlay in a spaced relation to the primary conductive line 62. Thus, the balance tab 132 may be bent slightly toward or away from the primary line conductor or strip layer 62, or the tab may be rotated about the resistor lead to vary the amount of capacitive coupling between the forward coupler 86 and the primary line conductor or strip layer 62. A similar balance tab 134 and spacer bushing 135 are bonded to a lead of the resistor 122 at a terminal of the reverse coupler 88.

Reference is now made to FIG. 7 which illustrates in more detail the electrical circuitry of the directional coupler. For purposes of discussion, reference will be made to lumped impedances as opposed to a detailed consideration of the distributed parameters in the circuit.

As previously discussed, one of the terminals of the forward coupler 86 is connected through a resistor 102 to a common ground point. The other terminal of this coupler is connected to one of the terminals of an inductance L which represents the distributed inductance in the secondary circuit. The other terminal of the inductance L is connected to one terminal of a capacitor 94, and the other terminal of this capacitor is connected to ground and to the anode of a diode 90. The cathode of the diode 90 is connected through a capacitor 96 to ground, and the cathode of this diode is also connected through a resistor 106 to the forward output terminal 108. The capacitor 110 is connected directly between the forward output terminal and ground.

A mutual impedance M exists between the strip layer 62 and the forward coupler 86. This mutual impedance is a result of a magnetic field which surrounds the strip layer 62 and intercepts the forward coupler 86 to thereby induce a current in this coupler. A similar current is induced in the strip layer 62 as a result of a magnetic field which surrounds the forward coupler 86. Thus, this mutual coupling or inductance is illustrated as the lumped mutual inductance M. The capacitive coupling between the strip layer 62 and the forward coupler 86 is represented by the lumped capacitance C.sub.4. As discussed previously, this coupling capacitance may be varied by changing the position of the capacitance balance tab 132 with respect to the strip layer 62.

One of the terminals of the reverse coupler 88 is connected through the resistor 122 to ground and the other terminal of this coupler is connected to one of the terminals of a secondary inductance L'. The other terminal of the inductance L' is connected to one terminal of a capacitor 116, and the other terminal of this capacitor is connected to ground and to the anode of the diode 112. The cathode of the diode 112 is connected to one terminal of a capacitor 118 and the other terminal of this capacitor is connected to ground and through a resistor 126 to the reverse output terminal 128. The reverse output terminal 128 is also connected through a capacitor 130 to ground.

As in the case of the forward directional circuit, a mutual inductance exists between the primary line conductor or strip layer and the secondary circuit which is represented by the lumped mutual inductance M'. The capacitive coupling between the primary line conductor and the reverse coupler is indicated as a lumped capacitance C.sub.4 '.

The operation of the forward coupling circuit is substantially similar to that of the reverse coupling circuit. Thus, only the forward circuit will be considered for purposes of discussion.

With a radio frequency signal applied through the directional coupler, a portion of the wave energy in the primary line is transferred from the primary line conductor 62 to the forward coupler 86. The wave energy applied to the forward coupler represents both the forward and reflected traveling wave energy transmitted through the primary line conductor.

The coupler 86 is connected to ground through the resistor 102 and through the inductance L and the capacitor 94. Thus, a current signal induced in coupler 86 is caused to flow from the coupler 86 to ground. This current signal developed across the capacitor 94 is applied to a peak voltmeter comprised of the capacitors 96, 110, the diode 90 and the resistor 106. Accordingly, the current signal on the capacitor 94 is applied to the input capacitor 96 through the diode 90 to thereby cause this capacitor to charge to a voltage equal to the peak voltage of the signal appearing across the capacitor 94. The peak voltage developed across the capacitor 96 is then applied through the resistor 106 to the forward output terminal 108. The capacitor 110 serves primarily as a filtering capacitor for the output signal.

With a direct-current voltmeter G connected between the forward output terminal 108 and ground, it is possible to measure the direct current output signal developed by the forward circuitry in order to determine the value of a forward wave signal propagated along the transmission line.

With traveling wave energy transmitted through the directional coupler from left to right as viewed in FIG. 1, the capacitive balance tab 132 is adjusted so that the voltage which is developed across C.sub.1, which is a function of the primary line voltage, is made equal to the voltage developed across capacitor 94, which is a function of line current. Thus, there will be a 180 degree phase difference at capacitor 94 in the two like magnitude signals, voltage will be approximately zero volts, thereby producing a reading of zero volts on voltmeter G.

With traveling wave energy transmitted from right to left through the coupler as viewed in FIG. 1, the voltage across the capacitor 94 is a function of the primary line voltage and approximates the voltage coupled from the primary line through the mutual impedance M, lumped inductance L, the resistor 102, and the capacitor 94. The phase relation of these voltage signals is equal to zero. Accordingly, the circuit supplies a voltage across the capacitor 94 to thereby provide a direct current signal which is applied through the network including the diode 90, the capacitor 96, the resistor 106, and the capacitor 110 to the voltmeter G.

In other words, if a radio frequency signal is transmitted in one direction only through a transmission line of impedance Z.sub.0, the line current I will be equal to a voltage E divided by the characteristic impedance Z.sub.0 of the line. If the line voltage and current are assumed to be in a zero angular relation with respect to each other, the voltage and current will be at a 180 degree phase relationship with respect to each other for a signal traveling in the opposite direction. At a given frequency, the reactance X.sub.L across the lumped impedance L, and the reactance X.sub.94 across the capacitor 94 become equal to each other. Also, the reactance X.sub.C4 across the capacitance C.sub.4 is relatively large with respect to the reactance X.sub.L across the impedance L and the reactance X.sub.94 across the capacitor 94.

Thus, a current flowing through the inductance L and the capacitor 94 as a result of this line voltage may be defined as E.sub.1, or the line voltage divided by the reactance X.sub.C4. If the reactance X.sub.94 is small relative to the reactance X.sub.C4, the ratio of the voltage across the capacitor 94 to the line voltage will be approximately equal to the ratio of the capacitor C.sub.4 to the capacitance 94.

Thus, assuming that the capacitance C.sub.4 is very small in comparison to the capacitance C.sub.94 across the capacitor 94, and that the capacitance C.sub.94 is very large in comparison to the resistance R.sub.1 of the resistor 102, and that the inductance L is very small in comparison to the resistance R.sub.1 of resistor 102, the above relationships give rise to the following equation:

E.sub.94 = -j (1/.omega.C.sub.94)/-j (1/.omega.C.sub.4) (E.sub.1 (1)

or,

E.sub.94 = C.sub.4 /C.sub.94 (E.sub.1) (2)

where E.sub.94 is equal to the voltage acorss the capacitor 94, C.sub.94 is equal to the capacitance of the capacitor 94, and C.sub.4 is equal to the capacitance of the capacitor C.sub.4.

It should be noted that the "-j" and ".omega." terms in equation (1) do not appear in equation (2) thereby indicating that there is no phase shift and that the circuit is not responsive to changes in frequency.

At a frequency where the reactance X.sub.L of the inductor L is equal to the reactance X.sub.94 of the capacitor 94, the voltage across the capacitor 94 may be represented by the following equation:

E.sub.94 = ( -j.omega.MI/R.sub.1) ( -j)(1/.omega.C.sub.1) (3)

e.sub.94 = - mi/r.sub.1 c.sub.1 (4)

where E.sub.94 equals the voltage across the capacitor 94, M equals the impedance of the mutual inductor M, and I equals the current passing through the capacitor 94. The equations (3) and (4) are essentially correct assuming that the capacitance C.sub.94 is large in comparison to the resistance R.sub.1 across the resistor 102 and that the inductance L is small in comparison to the resistance R.sub.1 of the resistor 102. Again, it should be noted that the "-j" and ".omega." in equation (3) do not appear in equation (4) thereby indicating that there is no phase shift and that the circuit is not responsive to change in frequency.

In view of the fact that equations (3) and (4) include no phase shift factors or frequency factors, and in view of the fact that the voltage and current in a transmission line for a given single direction of wave transmission are defined by the characteristic impedance Z.sub.0, and that the voltage and current on the line are related angularly as either zero or 180 degrees dependent upon the direction of inspection, it is possible to combine the voltage and current coupling. Thus, the voltage E.sub.C1 across the capacitor 94 is of equal magnitude for equal line voltages and currents for a given transmission line at a given characteristic impedance Z.sub.0. Accordingly, by subtracting equation (3) from equation (2), the following equation is derived:

E.sub.94 - E.sub.94 = 0 = (C.sub.4 /C.sub.94) (E.sub.1) + (MI/R.sub.1 C.sub.94 ) (5)

thus, for a wave propagated in a given direction, the voltage across the capacitor is equal to zero indicating that the circuit achieves the desired directivity.

The equation (5) may be re-written as follows:

(C.sub.4 /C.sub.94) (E.sub.1)= - (MI/R.sub.1 C.sub.94) (6)

and substituting (Z.sub.0) (I) for E.sub.1 in equation (6), the following equation is derived:

(C.sub.4 /C.sub.94) (Z.sub.0)(I) = - (MI/R.sub.1 C.sub.94) (7)

or,

Z.sub.0 = (M/R.sub.1 C.sub.4) (8)

thus, equation (8) sets forth the relationship of component values which provide a frequency independent solution to the computation of component values for achieving directivity. Accordingly, the values of the coupling components may be computed from equation (8) in order to achieve directivity.

Although the invention has been described in connection with a preferred embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the appended claims.

Claims

Having thus described my invention I claim:

1. A directional coupler for detecting and measuring undirectional flow of power in a transmission line comprising

an elongated housing of conductive material having a transmission line input and output connectors mounted thereon,

a partition member of conductive material positioned within said housing to define a first and a second chamber for substantially preventing the passage of electrical fields from said first chamber to said second chamber,

an insulative board having first and second oppositely facing surfaces,

a first film layer of conductive material secured to said first surface of said insulative board, said board secured to at least a portion of said partition member with said first film layer sandwiched therebetween,

a second film layer of conductive material secured to at least a portion of said second surface of said insulative board thereby defining a predetermined impedance between said first and second film layers,

a third film layer of conductive material having first and second terminal ends and secured to at least a portion of said second surface of said board in spaced relation with respect to said second film layer thereby defining a predetermined impedance between said second and third film layers,

said transmission line input and output connectors respectively having one terminal coupled to said first film layer and its other terminal coupled to said partition member,

a signal developing network mounted on the side of said partition member opposite said insulative board and coupled to said first and third film layers to develop an output signal representative of the unidirectional line voltage of the signal propagated along the transmission line for a given line characteristic impedance, and

indicator means connected to receive said output signal for producing a visual presentation representative of the value of said output signal.

2. A directional coupler used for detecting and measuring unidirectional flow of power in a transmission line comprising

an elongated hollow metallic housing,

a transmission line input and output terminal at the ends of said housing with each terminal providing a means for connection to the primary and secondary conductors of a transmission line,

a partition member for the full length of said housing and secured to sides and ends thereof forming two separate chambers therein for substantially preventing the passage of electrical fields between said chambers,

the respective ends of said partition members secured to said terminal secondary connection means,

an insulative board secured to a portion of one face of said partition member in one of said chambers,

said board having a first conductive layer secured to one face of said board and in electrical contact with said partition member,

a first elongated strip layer secured to the opposite face of said board from said first layer with its opposite ends connected to said terminal primary connection means,

said insulative board and said layers forming a predetermined impedance coupling,

a second elongated strip layer secured to said board opposite face and positioned in juxtaposed relation to said first elongated strip layer,

a signal developing and measuring network mounted on the other face of said partition member in the other of said chambers and electrically coupled to both said first conductive layer and said second elongated strip layer to develop an output signal representative of the unidirectional line voltage of the signal propagated along the transmission line for a given line characteristic impedance and produce a visual representation thereof.

3. The coupler of claim 2 characterized in that said partition member comprises a central portion and a pair of end portions, said end portions in a plane parallel to said central portion, said end portions secured to the ends of said housing, said network mounted on the top face of said central portion and said insulative board with said conductive layers mounted on the bottom face of said central portion.

4. The coupler of claim 3 characterized in that each of said terminal primary connection means includes a mounting bracket positioned in the space provided below one of said end portions to connect an end of said first strip layer to one of said terminals.

5. The coupler of claim 2 characterized by resistive and diode rectifier means included in said signal developing and measuring network and shield means surrounding said resistive and diode rectifier means for further isolating said resistive and rectifier means from stray electrical fields.

6. The coupler of claim 2 characterized by a third elongated strip layer secured to said board opposite face and positioned in juxtaposed relation to said first conductive layer opposite to said second strip layer, and

a second signal developing network also mounted on the other face of said partition member and electrically coupled to both said first conductive layer and said third elongated strip layer to develop a second output signal representative of the unidirectional line voltage of said propagated signal in a direction opposite to that developed in connection with said second strip layer.