Waveguide And Circuit Using The Waveguide To Interconnect The Parts

Abstract

Rows of generally parallel elongated conducting members, parallel to the polarization of an electromagnetic wave and intersecting a dielectric slab, are used to control the path of such wave. The invention may take the form of a waveguide. A waveguide utilizes a slab of insulating material. Two parallel rows of metallic posts, with each post generally perpendicular to the slab, intersect the slab. The rows of posts are spaced apart a distance at least equal to 0.6.lambda..sub.o where .lambda..sub.o is the free space wavelength for the lower end of the operational wavelength range of the circuit. The radio frequency energy transmitted down the waveguide is polarized electrically in a direction parallel to the axes of the posts. The new waveguide, in one of its forms, is ideally suited to constitute an antenna, and is so shown as one form of the invention. The new waveguide is also ideally suited to interconnect the components of an electric circuit, and therefore I have also illustrated a portion of a circuit with the electronic components interconnected by the new waveguide.

Description

BACKGROUND OF THE INVENTION

The invention pertains to waveguides, to electric components such as antennas which may be constructed upon the principles of waveguides, and to electric circuits having components interconnected by waveguides.

In the frequency range of microwaves, hollow pipes, known as waveguides, are frequently used for the transmission of energy between the various components of microwave systems and as fundamental elements of these components. Using this approach, the metallic structures of more complex microwave circuitry are difficult and expensive to manufacture. Microstrips transmission lines were developed in recent years to simplify the design and the production of such circuitry used in radars and communications equipment. The microstrip circuitry basically consists of a dielectric slab which is completely covered on the bottom surface with an electrically conductive coating which represents a ground plane. Narrow conducting strips on top of the dielectric slab represent the actual transmission-line sections between the individual components of the circuitry. Shorted and open-ended strip-type transmission line sections also form elements of components such as inductances, capacitances, and resonant circuits. The strip structure on top of the dielectric slab is commonly formed starting with a completely coated surface by etching away the undesired parts. This leaves the narrow conducting strips which are separated from the conducting ground plane by the dielectric slab. Complete circuitry can then be designed to be carried on top of a single dielectric slab.

In the high frequency region of microwaves above possibly 15 GHz (15 kilomegacycles per second), commonly termed "millimeter-wave region", the microstrip lines become rather lossy. This is due to the decrease of the skin depth and the increase of the surface resistance on conducting surfaces with increasing frequency and due to the simultaneously increasing loss tangent of the dielectric slab. Both effects cause a considerable increase of the attenuation of microstrip lines at millimeter-wave frequencies. As a consequence, the energy losses along the line sections become appreciable and the characteristics of the components become altered by the losses such that they do not longer perform satisfactorily. A typical example is the Q-value of circuit elements which becomes so low that filters and resonators have unsatisfactory characteristics. As a consequence, waveguides in the form of hollow pipes have to be used in the millimeter-wave regions which interconnect the various components of the circuitry and represent the basic elements of these components. The various components and transmission line sections are coupled together by coupling elements such as coupling flanges which often introduce discontinuities which in turn cause reflections and losses of energy. Such circuitry occupies often relatively large volumes of space and is usually expensive to manufacture.

SUMMARY OF THE INVENTION

A main objective of the invention is to modify or control the path of electromagnetic waves, and to provide a simple and inexpensive device for accomplishing that end.

It is the objective of the present invention to provide a waveguide which permits the integrated design of complete circuitry in one unit and eliminates coupling elements between the components of the circuit.

It is also an objective to provide a waveguide which, having the precedingly noted advantages, has simultaneously lower losses than those obtained in corresponding structures of prior art such as microstrip lines.

The invention has as an additional object the provision of improved electrical components such as antennas in those cases when the components can be constructed according to the principles applicable to waveguides.

It is a further object of the invention to provide an improved electrical circuit of the type in which the components are interconnected by waveguides.

The invention in its broadest aspects utilizes a row of elongated conducting elements projecting from a dielectric slab for modifying the path of electromagnetic waves polarized in a direction generally parallel to said elements.

According to the invention, the waveguide, which usually is part of a more complex millimeter-wave circuit, is composed in its basic form of a dielectric slab with two rows of parallel metallic posts. The posts may take various shapes such as rods, strips, etc. The posts run through the slab, are oriented with their axes generally perpendicular to the slab, and project out evenly for more than a wave length on both sides. The distance between the two rows is usually equal to the width of a standard rectangular waveguide for the same frequency range. The posts of each row are as close as the mechanical strength of the structure permits. If electromagnetic waves are excited in the region between the two rows of the electrically conducting posts with the E-field parallel to the posts, surface waves travel along the dielectric between the two rows of posts. The field-strength amplitudes associated with these surface waves decrease exponentially in the direction from the slab on both sides. The surface waves are bounced back and forth laterally between the two rows of posts in a similar manner as between the side walls in a standard rectangular waveguide carrying transverse electric wave modes (TE.sub.01). Since the electric field vector of the waves is parallel to the conducting posts, the leakage between the posts which represent a wire grid can be kept relatively small. The waveguide behaves generally similar to an open waveguide known under the name "H-guide". Such an H-guide, which has the cross-section of an H, consists of two parallel conducting strips with a centrally located dielectric slab in between. The two strips form the vertical legs of the H and the dielectric slab the horizontal bar in the cross-sectional configuration. Since the fields decrease exponentially toward the lower and upper openings, the radiation losses can be kept small.

In a waveguide according to the invention, the two rows of posts have a function similar to that of the solid sidewalls of the H-guide, namely, to reflect and to confine the waves in the lateral direction. The posts allow the design of complex millimeter-wave circuitry on a single dielectric slab. They confine the waves on the slab along prescribed paths and are essential elements of the components formed by sections of the waveguide. Modern production methods typical in the plastics industry make the outlined structure easily adaptable to the mass production of millimeter-wave circuitry. Other objects, advantages, and the usefulness in circuit design, will become apparent in the following detailed descriptions in relation to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a section of a waveguide according to the invention in its basic form.

FIG. 2 is a perspective view of another embodiment of the invention where metal strips are used to form the side walls which confine the waves in lateral directions.

FIG. 3 is a cross-sectional view of a modified form of the waveguide. In this form there is increased thickness of the dielectric slab in the region between the rows of posts.

FIG. 4 is a cross-section of another modified form of the waveguide. In this form there is a conducting plate placed parallel to the dielectric slab on the bottom with the posts attached to the plate and carrying the total circuit structure.

FIG. 5 is a top view of a directional coupler utilizing my novel waveguide principle.

FIG. 6 is a perspective view of an antenna based upon the principles of the invention.

FIG. 7 is a perspective view of a receiver circuit designed on a single slab by use of the waveguide according to the invention.

FIG. 8 is a cross-sectional view of a modified arrangement of the slab and posts.

With reference to the drawings shown of sections of waveguides and their applications, it will be realized that these figures show a few examples only. Those skilled in the art may design similar and modified structures and great varieties of components based on the concept of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A waveguide module according to the present invention is shown in FIG. 1. It is composed of a dielectric slab 10 and of two parallel rows of metallic posts 11 and 12 crossing the slab 10 with their axes near to normal to the slab. The rows of posts serve as reflectors which confine waves launched into or generated in the region between the posts to this region and force them to travel along the path prescribed by the posts as indicated in FIG. 1 by the arrow. FIG. 1 also shows as an example the launching of the waves by a dipole antenna 9. The waves are polarized electrically with their E-vector parallel to the posts. They are surface waves with their field amplitudes decreasing exponentially above and below the dielectric slab in the region between the rows of posts. By proper choice of the height of the posts, only a small fraction of the power (perhaps 1/100 or 1/1000) is carried along the guide above and below the end plane of the posts. The distance between the two rows of posts is about the same as or larger than that between the sidewalls of standard rectangular waveguides for the same frequency range (equal or larger than 0.6 .lambda..sub.o, .lambda..sub.o = free space wave length). The dielectric slab 10 of the figure may be just a part of a larger slab and the guide shown just a part of a waveguide system which forms a more complex millimeter-wave circuit. By this approach, components, such as power dividers, directional couplers, filters, resonators, or other components, which contain waveguide sections, can be designed as parts of an integrated circuit placed on a single dielectric slab.

Referring to FIG. 2, there is shown, as another example of the embodiment of the invention, a waveguide section with two parallel rows of metallic strips 13 and 14 which confine the waves to the region between the strips and make them travel along a prescribed path along the dielectric slab 10. The section of waveguide may be again a part of a more complex circuit. It will be realized that the posts which form the two sidewalls of the guide may have other cross sections than those shown in FIGS. 1 and 2. Elliptical and square cross-sectional configurations are examples. The two reflector sidewalls may also consist of double and multiple rows of wires or equivalent elements. The single elements crossing the dielectric slab may also be interconnected mechanically and electrically near their ends and bent to increase the mechanical strength of the structure. Since the fields decrease exponentially from the slab toward the upper and lower openings, the structural form, at a distance from the dielectric slab, of the two rows of posts have a minor effect on the basic field configuration of the surface waves guided along the slab.

The embodiment illustrated in FIG. 3 shows a cross-sectional view of the waveguide with two longitudinal dielectric strips 15 and 16 added between the posts on top and bottom of the dielectric slab. The strips cause an increase of the thickness of the dielectric slab in the guide which in turn causes a reduction of the guide wavelength and corresponding reduction of the velocity of the waves traveling in the guide. This reduction reduces the already small leakage of the energy sidewards through the reflecting rows of conducting posts. This can be understood if one realizes that the leakage is practically zero if the guide wavelength and wave velocity are equal to or smaller than the wavelength and velocity for the surface waves outside the guide respectively. Such measures are important to obtain high Q-values in shorted sections of the guide used as resonators and in filters. The increase of the thickness of the dielectric between the posts may be obtained also directly during the manufacturing process of the waveguide instead of by the addition of strips as indicated in the example of FIG. 3. It is also noted that the dielectric slab may be composed of layers of dielectrics with different values of the permittivity in the form of a laminated-dielectric slab and that the air space above and below the slab may be filled with a foamed dielectric with a permittivity approaching that of air.

FIG. 4 shows a cross-sectional view of an arrangement employing a metal plate 17 with good electrical conductivity, as bottom plane which carries the entire circuit. The two rows of posts or wires are fastened in the plate to give the waveguide structure particular mechanical stability. The basic character of the surface wave propagation along the dielectric slab 10 between the posts 11 and 12 remains practically unchanged by this measure.

FIG. 5 illustrates as an example the application of the invention in a directional coupler. The directional coupler may be a part of a more complex circuit which is designed to operate on a single dielectric slab. The part of the dielectric slab on which the coupler is located is indicated in the figure by 10. Two pairs of rows of posts each one composed of posts 11 and 12 form two waveguides. One is the main guide indicated by I and the other the secondary guide indicated by II. Both guides have a common sidewall 18 in the form of posts. The spacing between the posts and/or the length of, the posts forming said common sidewall, vary in such a manner that a desirable distribution of coupling is obtained between the main guide I and the secondary guide II for forming a directional coupler. The example of FIG. 5 shows that the waveguides shown in the preceding figures lead to simple structures for millimeterwave components.

As a further example of applications, an end-fire antenna is illustrated in FIG. 6. The figure shows an antenna section containing two antenna elements of an array. The two elements are composed of two waveguide sections, such as are described in FIGS. 1 to 4, on a common dielectric slab 10. Each element has rows of posts 11 and 12. The lengths of the posts are tapered toward the edge 60 of the dielectric slab 10 as indicated in the figure. This causes gradual radiation of the energy, carried between the rows of posts 11 and 12 along the slab 10 in the waveguide region, beyond the edge 60 of the slab in the direction indicated in the figure by the arrows. The distance between the rows of posts may increase toward the rim similar to the increase of the width in horn antennas.

FIGS. 5 and 6 are indicative to those skilled in the art that the invention as described may be applied to the design of all most common components and may be used for the design of complete millimeter-wave circuitry. The circuits may include waveguide cavities containing active solid state elements, power dividers, directional couplers, filters, mixer elements, below cutoff attenuators, and even the antennas. The simplicity of the waveguide structure permits simple and economical manufacturing by mass production techniques of complicated circuitry without coupling elements on a simple dielectric slab.

FIG. 7 shows a radio receiver circuit. The circuit is designed on a single dielectric slab 10 with rows of conducting posts 11 and 12 as elements of the components and of the waveguide sections connecting the components. The components are: First, a two-element receiving-type antenna 19 each element constructed according to FIG. 6. The antenna 19 is located adjacent the edge of the dielectric slab 10. Secondly, an H-lane T-section of waveguide 20 combines the energies coming from the two antenna elements. Thirdly, a filter 21, composed of two resonators, in the form of shorted waveguide sections, receives the energy from the coupler 20. Coupling between the resonators and to the connecting waveguides is achieved through the gaps between the posts of the transverse grid walls. Finally, the output of the filter is fed via the novel waveguide of this invention to a detector 20 which also can be incorporated in a shorted post-type waveguide section.

FIG. 8 is a cross-sectional view of one form of the invention in which the posts 11a and 12a are not exactly parallel but are generally parallel, and also they depart somewhat from a perpendicular relation with slab 10. For best results they should be parallel to each other and perpendicular to slab 10 but some deviation (for example, as illustrated in FIG. 8) is within the broader aspects of the invention.

In all forms of the invention the posts of any given row should be as close together as practicable except when it is desired to allow some of the energy to pass out of the waveguide as, for example, in the case of sidewall 18 of FIG. 5. Preferably, the spacing between posts should not exceed .lambda..sub.o /8.

The height of the posts should be on the order of one wavelength, as measured from the slab 10, although greater heights will also work well.

From the foregoing, it will be apparent to those skilled in the art that electrical circuit components may be constructed using parallel rows of posts, and moreover, that electrical circuits interconnected by the post-type waveguides are not only more easily manufactured but function in a new and improved manner.

In each form of the invention of the drawings, a dielectric material such as air is located between the rows of posts such as 11 and 12 and above or below the solid dielectric material shown. Preferably the dielectric material, such as air, which is above and below the solid dielectric material shown, has a lower dielectric constant than the solid dielectric material (such as 10) shown.

It is obvious that many other modifications and variations of the present invention are possible based on its previously outlined basic concept. It is understood that equivalents apparent to one skilled in the art after being exposed to the concept outlined above are also covered.

Claims

I claim to have invented:

1. A waveguide for electromagnetic waves comprising at least two juxtaposed dielectric materials of different dielectric constants, one of which is a slab and another of which extends away from both faces of the slab, said slab being oriented generally perpendicular to the direction of polarization of said waves, said dielectric materials taken together constituting means for carrying the electromagnetic waves as surface waves with part of said waves traveling in said slab,

and wave guiding means comprising at least two rows of many elongated conducting members, each such member being embedded in said slab and extending through the slab and away from both sides of the slab and arranged generally parallel to each other member of the same row transverse to the slab, each row constituting reflecting means to form collectively a waveguide so that the waves traveling along the waveguide bounce back and forth between the rows, each of the conducting members in the same row being so closely spaced to each adjacent conducting member as to maintain the major energy flow between the rows, said dielectric slab extending between conducting members of the same row and beyond the rows forming the waveguide.

2. A waveguide as defined in claim 1 in which the conducting members separately extend at least one wavelength away from the slab.

3. A waveguide as defined in claim 1 in which said slab is thicker between said rows of conductors than it is beyond said rows.

4. A waveguide as defined in claim 1 including means for launching the said polarized electromagnetic waves into the waveguide with the direction of polarization generally perpendicular to the slab, the conducting members being generally perpendicular to the slab.

5. A waveguide as defined in claim 1 including a metallic base plate attached, on one side of the slab, to the outer ends of the conducting members.

6. A waveguide as defined in claim 1 in which the spacing between some of the conducting members is increased to allow energy to leak out of the waveguide.

7. A waveguie as defined in claim 6 having a second waveguide positioned to receive the energy that leaks out between the members of increased spacing, said second waveguide comprising two spaced rows of parallel conducting members in said dielectric slab means, the space between rows being interconnected with the first waveguide at the location of said increased spacing.

8. A waveguide as defined in claim 1 in which the height of the elongated conducting members, as measured from the surface of the slab, progressively decreases to form an antenna.

9. A component of a circuit comprising at least one section of a waveguide as defined in claim 1.

10. A plurality of components mounted on a single continuous dielectric slab comprising at least one section of waveguide as defined in claim 1.

11. A plurality of components mounted on a single slab with the waves guided between at least two components by a section of waveguide as defined in claim 1.