Phase shifter for linearly polarized antenna array

Abstract

There is disclosed herein a linearly polarized mat-strip phased antenna array wherein the antenna array is phased by incorporating in series relationship one or more mat-strip loaded line type phase shifters in the mat-strip power division distribution network for the mat-strip dipole elements and/or a combined mat-strip dipole element and phase inverter. Two embodiments are illustrated.

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 384,188 filed July 31, 1973.

Description

BACKGROUND OF THE INVENTION

This invention relates to linearly polarized phased antenna arrays and more particularly to a linearly polarized phased antenna array employing mat-strip and printed circuit techniques.

The term "mat-strip" as employed herein is defined as a photo etched or printed balanced transmission line printed on opposite surfaces of a printed circuit (PC) board in such a manner that both conductors are superimposed, are equal in width and are equal in length. This is in contrast to a stripline transmission line which is an unbalanced transmission line requiring two ground planes one above and one below a single conductive strip and to a microstrip transmission line which consists of a conductive strip above a ground plane having a much greater width than the conductive strip. A microstrip transmission line is analogous to a two wire line in which one of the wires is represented by the image in the ground plane of the wire that is physically present. Another way of expressing what a mat-strip transmission line is is to state that it is a balanced transmission line in which the image wire of a microstrip transmission line has materialized and the ground plane of a microstrip transmission line has been removed.

An antenna dipole element is mat-strip technique consists of one half of the dipole element (one wing) being disposed on one surface of the PC board having one end thereof connected to one conductor of a mat-strip transmission line and the other half of the dipole elements (the other wing) being disposed on the outer surface of the PC board having one end thereof connected to the other conductor of the same mat-strip transmission line. A ground plane is associated with the dipole elements (it has no function in the mat-strip transmission line) to insure that the radiation from the dipole element is from one surface of the PC board, namely, the surface of the PC board removed from the ground plane.

The realization of high performing, light weight, economical communication, radar or the like phased antenna arrays has been hampered by narrow band lossy phase shifters, complex feed networks, and heavy expensive components. These problems are compounded as the antenna array becomes large and has resulted in the almost exclusive use of fixed beam antennas in tactical microwave communication, radar and the like systems. A typical example is a jeep mounted antenna which affords approximately 33 db (decibel) gain while operating in the 7.25 to 8.4 gigahertz (GHz) communication band. Two configurations of this fixed beam antenna have been constructed, namely, a parabolic reflector employing a dual circularly polarized feed, and a dual circularly polarized array. It is feasible to build either with its mount to weigh less than 50 pounds. The cost for either is less than $1,000 with a manually pointed mount. A comparable phased array antenna would weigh more than 150 pounds when built by conventional construction.

The cost of the phase shifters and driver circuits along can vary from $3,000 for one dimensional steering to $90,000 for two dimensional steering. In addition, an antenna mount would still be required to obtain 360.degree. coverage for azimuth.

Printed circuit phase shifters using PIN diodes have been employed in various designs to obtain minimum weight, broad band operation and low cost. These have several major drawbacks. First, the loss can be as high a 3db. Thus, the antenna efficiency is limited to 50 percent or less. The resulting antenna noise temperatures are more than 150.degree.K (kelvin) even at zenith operation. This is to be compared with noise temperatures under 50.degree.K for fixed beam antennas. A second drawback to these prior art designs is that they are difficult to integrate into a dual circularly polarized system. The phase shifters cannot be integrated directly in the array structure in most cases, but must be connected by external cables, such as miniature coaxial lines. Such connections present frequency sensitive phase shifts of their own and also contribute to the loss of the system. A third disadvantage is that the cost of these devices in quantities of 100 or more is still greater than $100 per unit. This cost stems from the expensive fabrication. techniques and the large number of components required per assembly and, in addition, they require a fair amount of bench alignment.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a mat-strip linearly polarized phased antenna array that overcomes the disadvantages of the prior art mentioned hereinabove and also which is capable of being incorporated in a dual circularly polarized phased antenna array such as disclosed in a copending application of J. C. Ranghelli and E. J. Perrotti, Ser. No. 382,619, filed July 25, 1973, now U.S. Pat. No. 3,854,140 assigned to International Telephone and Telegraph Corp. whose disclosure is incorporated herein by reference.

Another object of the present invention is to provide a mat-strip linearly polarized phased antenna array incorporating the techniques of U.S. Pat. No. 3,681,769 issued to E. J. Perrotti, J. C. Ranghelli and R. A. Felsenheld and assigned to International Telephone and Telegraph Corporation and in particular the techniques of the above cited patent relative to one of the mat-strip linearly polarized arrays and its associated ground plane. The disclosure of the above cited patent is incorporated herein by reference.

A further object of the present invention is to provide a mat-strip loaded line type phase shifter for incorporation in a mat-strip power division distribution network for the mat-strip dipole elements wherein the mat-strip phase shifter is employed singly or a plurality of these phase shifters are coupled in series relation in the distribution network to provide stepped radio frequency phase shifts in the distribution network.

Still a further object of the present invention is to provide a mat-strip linearly polarized phased antenna array incorporating a combined mat-strip dipole and phase inverter either by itself or in combination with the above-mentioned loaded line type mat-strip phase shifters.

A feature of the present invention is the provision of an antenna array comprising: N linearly polarized mat-strip dipole elements disposed on a printed circuit board, each of the N elements having a given orientation, where N is an integer including one; a ground plane superimposed relative to and associated with the N elements; a mat-strip power distribution network disposed on the board coupled to the N elements; the N elements, the ground plane and the distribution network cooperating to produce a linearly polarized antenna beam; and a phase shifting arrangment selectively coupled to the distribution network to control the antenna beam to have different selected angular directions, at least a portion of the phase shifting arrangement being carried out by the board.

Another feature of the present invention is the provision of at least one phase shifter including a one quarter wavelength mat-strip impedance transformer disposed in a mat-strip power distribution network, the transformer and the distribution network being carried by a printed circuit board, a first shunt mat-strip transmission line carried by the board and extending perpendicular from one end of the transformer, a second shunt mat-strip transmission line carried by the board and extending perpendicular from the other end of the transformer parallel to the first shunt transmission line, four normally non-conducting switching diodes carried by the board, each of the four diodes being connected to an end of a different one of the conductors of the first and second shunt transmission lines, and four radio frequency ground terminating and direct current biasing printed circuit pads carried by the board, each of the four pads being connected to a different one of the four diodes; a source of switching voltage; and a switching arrangement connected between the source and each of the four pads to render the four diodes conductive to radio frequency ground the first and second shunt transmission lines by the four pads to provide a predetermined amount of radio frequency phase shift in the distribution network.

A further feature of the present invention is the provision of a mat-strip phase shifting arrangement comprising: a plurality of cascade connected phase shifters disposed in a mat-strip power distribution network carried by a printed circuit board, each of the phase shifters including a one quarter wavelength mat-strip impedance transformer disposed in the distribution network and carried by the board, a first shunt mat-strip transmission line carried by the board and extending perpendicular from one end of the transformer, a second shunt mat-strip transmission line carried by the board and extending perpendicular from the other end of the transformer parallel to the first shunt transmission line, four normally non-conducting switching diodes carried by the board, each of the four diodes being connected to an end of a different one of the conductors of the first and second shunt transmission lines, and fourth radio frequency ground terminating and direct current biasing printed circuit pads carried by the board, each of the four pads being connected to a different one of the four diodes; a source of switching voltage; and a switching arrangement connected between the source and each of the four pads of each of the plurality of the phase shifters to render each of the four diodes of selected ones of the plurality of phase shifters conductive to radio frequency ground the first and second shunt transmission lines by the four pads of the selected ones of the plurality of phase shifters to provide predetermined steps of radio frequency phase shift in the distribution network.

Still a further feature of the present invention is the provision of a combined mat-strip dipole element and phase inverter comprising: a first dipole wing printed with a given orientation at one surface of a printed circuit board spaced from and extending outwardly in one direction from one end of one conductor of a mat-strip power distribution network carried by the board; a first normally non-conducting switching diode interconnecting adjacent ends of the first wing and the one conductor of the distribution network; a second dipole wing printed with the given orientation on the one surface of the board spaced from and extending outwardly in a direction opposite to the one direction from the end of the one conductor of the distribution network; a second normally non-conducting switching diode interconnecting adjacent ends of the second wing and the one conductor of the distribution network; a third dipole wing printed on the outer surface of the board in a superimposed relation with the first wing; a third normally non-conducting switching diode interconnecting adjacent ends of the third wing and the other conductor of the distribution network; and a fourth dipole wing printed on the other surface of the first board is a superimposed relation with the second wing; a fourth normally non-conducting switching diode interconnecting adjacent ends of the fourth wing and the outer conductor of the distribution network; a source of switching voltage; a first switching arrangment connected between the source and each of the first and fourth wings to render each of the first and fourth diodes conductive to connect the first and fourth wings to the distribution network to provide energy flow in the dipole element in a first direction; and a second switching arrangement connected between the source and each of the second and third wings to render each of the second and third diodes conductive to connect the second and third wings to the distribution network to provide energy flow in the dipole element in a second direction opposite to the first direction; said first and second switching arrangements being non-coincidently operated.

BRIEF DESCRIPTION OF THE DRAWING

Above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawing, in which:

FIG. 1 is a plane view of one embodiment of a mat-strip linearly polarized phased antenna array in accordance with the principles of the present invention;

FIG. 2 is a cross section of FIG. 1 taken along line 2--2;

FIg, 3 is a cross sectional view of FIG. 1 taken along line 3--3;

FIG. 4 is a cross sectional view of FIG. 1 taken along line 4--4;

FIG. 4a is a partial schematic illustration of the present invention wherein the primed and unprimed reference numerals correspond to like numerals in FIG. 4.

FIG. 5 is a plane view of another embodiment of a printed circuit mat-strip linearly polarized phased antenna array in accordance with the principles of the present invention; and

FIG. 6 is a partial cross sectional view of FIG. 5 taken along line 6--6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-4 there is illustrated therein a PC mat-strip linearly polarized array and associated ground plane to enable the achievement of a linearly polarized antenna beam which may be steered to be directed at different angles in accordance with the principles of this invention. The antenna array includes a dielectric sheet 1 having disposed thereon by PC techniques a mat-strip dipole antenna element 2 in the form of two dipole wings 3 and 4 where wing 3 is disposed on the lower surface 5 of sheet 1 and wing 4 is disposed on the upper surface 6 of sheet 1. As illustrated, this array includes a plurality of dipole elements 2 interconnected for symmetrical power feed by mat-strip type balanced power division transmission line distribution network 7 including various balanced mat-strip type conductors 8 and 9 to provide power division and parallel feeding of the groups of dipole elements. The linearly polarized dipole element array on sheet 1 is symmetrical in all quadrants as are their distribution networks 7.

It should be noted that as in the above cited patent the mat-strip conductors of the balanced transmission line distribution network 7 are formed by two strip conductors, one strip conductor being disposed in surface 5 of sheet 1 and the other strip conductor being superimposed with respect to said one strip conductor on surface 6 of sheet 1.

The ground plane for the linearly polarized phased antenna array on sheet 1 is provided by the bottom of the metallic housing 10 which is spaced from wings 4 of sheet 1 by one quarter wavelength of the operating frequency of the array.

It will be noted that networks 7 include in each of the strip conductors decreased width portions and increased width portions at the branching locations thereof. The decreased width portions and the increased width portions are each one quarter wavelength long at the operating frequency of the antenna array to provide a reflection less power transformation between the transmission line sections themselves and from the transmission line sections to the dipole elements 2.

The spacing between sheet 1 and ground plane 10 is maintained to the appropriate predetermined value by employment of bolts 11 extending through ground plane 10 and sheet 1 with appropriate length spacers or standoffs 12 disposed thereon to maintain the desired spacing of the stacked arrangement. In addition to these bolts and spacers, the coaxial transmission line portion of the combined balun and power dividing arrangement, to be described hereinbelow, also cooperate in maintaining the desired separation of the stacked members. This separation can also be maintained by a frame structure made of low density foam. This would lend itself to a bonded sandwich construction.

Distribution networks 7 is symmetrically fed from a combined balun and power divider 13 and is of the double ended balun type. Energy is coupled to the array on sheet 1 by waveguide 14 to which is coupled a transmitter or receiver 16. The unbalanced transformation is obtained by the combined balun and power divider 13 which includes coaxial transmission line 17 having inner conductor 18 extending through sheet 1 for electrical contact with strip conductor 19. Conductor 19 extends radially in two directions from center conductor 18 with the ends thereof being respectively connected to the inputs to networks 7. The outer conductor 20 of coaxial transmission line 17 is physically supported and in electrical contact with strip conductor 21 having the configuration illustrated in FIG. 1 which obviously is wider than the width of conductor 19 and the conductors forming networks 7. Thus, the combined balun and power divider provides a direct transition from waveguide 14 to the balanced mat-strip networks 7. It also provides a positive mechanical connection to the balanced mat-strip line of the printed antenna array without the use of solder joints and, in addition, and more importantly provides an immediate power division with a relatively large heat sink formed by conductor 21 thereby enabling the feeding of greater power into networks 7.

The conductors of networks 7 and dipole elements 2 are composed of conductive material, such as copper, copper clad material or the like. Dielectric sheet 1 is composed of low loss dielectric, such as Tellite, Rexilite, Z-Tron and Duroid. The latter two low loss dielectric materials are also high temperature materials and, of course, would be particularly applicable to the present invention under high temperature conditions.

To provide the desired phase shift for antenna beam steering, FIG. 1 illustrates one mat-strip phase shifter of the loaded line type identified as phase shifter 22. Phase shifter 22 is a complete mat-strip type phase shifter except for switching diodes, such as PIN diodes 23, 24 and similar superimposed diodes, such as PIN diode 25 which is superimposed with respect to PIN diode 23. Diodes 23 and 24 and the similar superimposed diodes are all parallel to sheet 1. Phase shifter 22 includes a mat-strip impedance transformer having a one quarter wavelength at the operating frequency of the array to which is coupled a pair of parallel shunt mat-strip transmission lines 27 and 28. Each of the shunt mat-strip lines include a pair of superimposed conductors such as conductors 29 and 30 (FIG. 4). Diodes 23 and 24 and their superimposed diodes are coupled to a different one of each one of the conductors of the shunt transmission lines 27 and 28 each of which has coupled thereto a different one of the conductors of printed circuit type radio frequency grounding and direct current biasing pads 31 and 32. Each of the pads 31 and 32 include two superimposed conductors, such as conductors 33 and 34 (FIG. 4). A direct current bias voltage is supplied from switching voltage source 35 through switch arrangements 36 and 37 as desired to render diodes 23 and 24 and their superimposed diodes conductive to connect the conductors of pads 31 and 32 to the conductors of shunt lines 27 and 28. When diodes 23 and 24 and their superimposed diodes are conductive a radio frequency ground is provided at each of the conductors of the pads 31 and 32 by means of bypass capacitors 38 through which a direct current voltage conductor is passed. When a radio frequency ground terminates shunt transmission lines 27 and 28 a 45.degree. radio frequency phase shift is provided in the distribution networks 7 for the radio frequency energy coupled to elements 2 thereby enabling control of the angualr direction of the antenna beam.

As described above phase shifter 22 is in mat-strip form with no inductors, capacitors or coaxial connectors required. The terminating circuit, the superimposed conductors of pads 31 and 32 for the diodes provide simultaneously a radio frequency short circuit and an arrangement to provide direct current voltage for biasing the diodes in such a manner that a physical arrangement is provided to install the diodes in a parallel relation to dielectric sheet 1. This eliminates machining operation associated with through-the-substrate mounting of the diodes. It will be noted that through the cooperation of the switching diodes (PIN diodes) 23 and 24 and their superimposed diodes a double pole switching arrangement is provided which prevents unbalanced currents.

Referring to FIG. 5 there is disclosed therein another linearly polarized mat-strip phased antenna array which incorporates power division distribution networks 7' similar to networks 7 described with respect to FIG. 1 and also a combined balun and power divider 13' similar to the combined balun and power divider 13 described with respect to FIGS. 1 and 2. In the linearly polarized phased antenna array of FIG. 5 the dipole elements 2', which may be substituted for dipole elements 2 of FIG. 1, include a dipole wing 39 and a dipole wing 40 printed on one surface of sheet 1' and two dipole wings 41 and 42 (FIG. 6) printed on the other surface of sheet 1'. Dipole wings 39 and 40 are connected to conductor 43 of distribution networks 7' by switching diodes, such as PIN diodes 44 and 45 which are parallel to sheet 1. Dipole wings 41 and 42 are coupled to conductor 46 of network 7' by PIN diodes 47 and 48 which are also parallel to sheet 1. Through means of a switching voltage source and switching arrangements similar to source 35 and switching arrangements 36 and 37 (FIG. 2) it is possible to provide combined mat-strip dipole elements and a phase inverter, in other words, a 180.degree. phase shifter. This is accomplished by moving switches of the switching arrangemennt such that a switching voltage is coupled to wings 40 and 41 to render diodes 45 and 47 conductive thereby connecting wing 40 to conductor 43 and wing 41 to conductor 46. Having these two dipole wings active there is energy flowing in a first direction through this dipole element. When the switching voltage is removed from the wings 40 and 41 diodes 45 and 47 are rendered non-conductive and when a switching voltage is applied to wings 39 and 42 diodes 44 and 48 are rendered conductive thereby connecting wing 39 to conductor 43 and wing 42 to conductor 46. With this orientation of the wings of the dipole elements energy will be propagated through the dipole elements in a direction opposite to that when dipole wings 40 and 41 were active. Thus, this technique of providing a mat-strip dipole element and a mat-strip phase inverter includes the printing of two dipoles in mat-strip form which are overlayed to radiate "through" each other according to which dipole is made active (connected to the distribution network) and which is made inactive (disconnected from the distribution network). The diodes are connected to the base or low impedance point of each dipole wing to provide radio frequency switching of the dipole wings to the feed lines. As pointed out hereinabove the 180.degree. phase shift is obtained by inverting the dipole through radio frequency switching of the dipole wings such that a given wire or conductor of the mat-strip distribution network is made to switch from a dipole wing located spatially "above" the wire to one located spatially "below" that wire and concurrently the second wire is switched in a reverse fashion. The technique of biasing or switching each diode with a direct current wire located at the dipole base, the low impedance point, with this wire being perpendicular to the radiated field does not interfere with the radiated field. The direct current wire incorporates a bypass capacitor where the wire passes through the metallic housing to provide a radio frequency terminating short circuit. This technique reduces the interference of the biasing or switching circuit on the radiated pattern and the dipole impedance.

It will be noted that each branch of network 7' feeding a dipole element 2' includes therein three mat-strip phase shifters 22, 22a and 22b which are identical to the mat-strip phase shifter 22 described with respect to FIGS. 1, 3 and 4. With this arrangement it is possible to phase the radio frequency energy in network 74' 45.degree. when phase shifter 22 is inserted into 7', 90.degree. when phase shifters 22 and 22a are switched into network 7' and 135.degree. when phase shifter 22b is switched into network 7. In addition, the phase inverting arrangement provided for dipole elements 2' can be used singly or additively with phase shifters 22 to provide other descrete steps of phase shifts to provide the desired steering or angular direction of the radiated antenna beam.

In accordance with the principles of the present invention a linearly polarized phase antenna array is provided in mat-strip form to provide a compact, flat, light weight array fed from a single input. In this arrangement the total phase shifter losses have been cut to less than half of those for previously employed printed circuit designs (1.25 db total). The bandwidth of operation extends through the range of 7.25 to 8.4 GHz while the total 3 sigma phase error has been limited to 9.1.degree. (or approximately 3.degree. for one sigma) for all states. The phase shifting arrangement including both the inverter arrangement associated with dipole elements 2' and the phase shifters 22 are completely integrated as part of the printed circuit antenna structure and does not need additional bench alignment since it is reproducible due to the PC techniques employed. It is estimated that in quantities of several hundred, the phase shifter cost can be made to approach $30 per unit with this cost being mostly a function of the per unit cost of the PIN diodes.

While we have described above the principles of out invention in connection with specific apparatus it is to be clearly understood that this description is made only by way of example and not as a limition of the scope of our invention as set forth in the objects thereof and in the accompanying claims.

Claims

We claim:

1. A mat-strip phase shifting arrangement comprising:

at least one phase shifter including

a one quarter wavelength mat-strip impedance transformer disposed in a mat-strip power distribution network, said transformer and said distribution network being carried by a printed circuit board,

a first shunt mat-strip transmission line carried by said board and extending perpendicular from one end of said transformer,

a second shunt mat-strip transmission line carried by said board and extending perpendicular from the other end of said transformer parallel to said first shunt transmission line,

four normally non-conducting switching diodes carried by said board, each of said four diodes being connected to an end of a different one of the conductors of said first and second shunt transmission lines, and

four radio frequency ground terminating and direct current biasing printed circuit pads carried by said board, each of said four pads being connected to a different one of said four diodes;

a source of switching voltage; and

a switching arrangement connected between said source and each of said four pads to render said four diodes conductive to radio frequency ground, said first and second shunt transmission lines by said four pads to provide a predetermined amount of radio frequency phase shift in said distribution network.

2. An arrangement according to claim 1, wherein

each of said four diodes is a PIN diode.

3. An arrangement according to claim 2, wherein

each of said PIN diodes is parallel to said board.

4. A mat-strip phase shifting arrangement comprising:

a plurality of cascade connected phase shifters disposed in a mat-strip power distribution network carried by a printed circuit board, each of said phase shifters including

a one quarter wavelength mat-strip impedance transformer disposed in said distribution network and carried by said board,

a first shunt mat-strip transmission line carried by said board and extending perpendicular from one end of said transformer,

a second shunt mat-strip transmission line carried by said board and extending perpendicular from the other end of said transformer parallel to said first shunt transmission line,

four normally non-conducting switching diodes carried by said board, each of said four diodes being connected to an end of a different one of the conductors of said first and second shunt transmission lines, and

fourth radio frequency ground terminating and direct current biasing printed circuit pads carried by said board, each of said four pads being connected to a different one of said four diodes;

a source of switching voltage; and

a switching arrangement connected between said source and each of said four pads of each of said plurality of said phase shifters to render each of said four diodes of selected ones of said plurality of phase shifters conductive to radio frequency ground said first and second shunt transmission lines by said four pads of selected ones of said plurality of phase shifters to provide predetermined steps of radio frequency phase shift in said distribution network.

5. An arrangement according to claim 4, wherein

each of said four diodes of each of said plurality of phase shifters is a PIN diode.

6. An arrangement according to claim 5, wherein

each of said PIN diodes is parallel to said board.