Quasi-optical Microwave Component

Abstract

A quasioptical microwave component having a rotatably mounted dielectric body with input and output faces is disclosed. The dielectric body is adapted for connection in an oversize waveguide system such that polarized electromagnetic energy is incident on the input face at the Brewster angle. Rotation of the dielectric body in one direction attenuates the energy transmitted from the output face and rotation in the opposite direction produces a phase shift therein.

Description

ORIGIN OF THE INVENTION

The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of royalties thereon or therefor.

BACKGROUND OF THE INVENTION

This invention relates generally to quasioptical microwave components and, more particularly, relates to microwave components suitable for use in oversize waveguide systems.

Use of conventional, single-mode, rectangular waveguide in the millimeter and submillimeter range is accompanied by waveguide losses, which increase with frequency. One way of minimizing these losses is to use an oversize waveguide in which the propagation can approach that of a plane wave. In these cases, the microwave signals behave in a quasioptical manner, permitting the use of many standard optical components and techniques.

A known example of such a component comprises as its basic element a double prism. According to this device, the input signal is split at the adjustable air gap between the two prisms, part of the signal being reflected as one output and part transmitted as the second output. The energy division depends upon the gap distance and the wavelength. Components of this type are described in IEEE Trans. MTT 11, 338 (1963) and Microwaves, p. 20 Jan. 1964).

Although functioning to attenuate, phase shift or couple microwave energy, the above noted component exhibits a number of disadvantages. For example, because of reflection losses that occur at the input and output surfaces, a fine comb structure cut into the input and output faces normally is used to match impedance and reduce the VSWR. Such a comb structure is narrowband and becomes increasingly difficult to fabricate as the frequency is increased. Other less common impedance-matching methods also are narrowband or lossy or both. Another deficiency of the double prism component is that the parallelism of the inner prism surfaces must be accurately maintained as the gap is varied in order to have accurate and repeatable performance. This requirement presents a mechanical alignment problem. In addition, the energy division provided by the double prism unit is undesirably frequency dependent.

The object of this invention, therefore, is to provide an improved quasioptical microwave component suitable for use with oversize waveguide.

SUMMARY OF THE INVENTION

The invention is characterized by the provision of an electromagnetic component including a base mounted, solid dielectric body having an input face for receiving electromagnetic wave energy and an output face adapted to transmit at least a portion of the wave energy received by the input face. A waveguide supported by the base directs the wave energy toward the input face. Because of the quasioptical behavior of microwave signals transmitted in oversize waveguide, the solid dielectric body functions as a microwave component while eliminating problems associated with gap-separated split-prism devices.

One feature of the invention is the provision of an electromagnetic component of the above including a drive mechanism for rotating the dielectric body so as to selectively vary the angle of incidence between the input face and the polarized electromagnetic wave energy received from the waveguide. Attenuation or phase shift of the signal transmitted by the output face is attained by appropriate rotation of the dielectric body.

Another feature of this invention is the provision of an electromagnetic component of the above featured type wherein the dielectric body includes at least one inner surface adapted to reflect electromagnetic wave energy between parallel input and output faces. This arrangement facilitates use of the output signal which is unidirectional for all rotational positions of the dielectric body.

Another feature of the invention is the provision of an electromagnetic component of the above featured type wherein the drive mechanism permits formation of the Brewster angle of incidence between the input face and the polarized energy received thereby. Establishment of the Brewster angle eliminates reflective losses at both the input and output faces.

Another feature of the invention is the provision of an electromagnetic component of the above featured type wherein the dielectric body includes a pair of parallel inner surfaces making, with the input and output faces, angles equal to

where k represents the dielectric constant of the dielectric body. According to this arrangement, the Brewster angle setting provides a null position with zero attenuation or phase shift. Rotation of the dielectric body in one direction from the null position produces at the internal surfaces attenuation of the signal and rotation in the opposite direction produces phase shift thereof.

Another feature of the invention is the provision of an electromagnetic component of the above featured types wherein the dielectric body is adapted to produce a plurality of reflections at each of the internal surfaces. The plural reflections increase the maximum attenuation or phase shift attainable by rotation of the dielectric body away from the Brewster angle of incidence.

Another feature of the invention is the provision of an electromagnetic component of the above featured types including an output waveguide and wherein both the input and output waveguides include terminal portions adapted for contact with, respectively, the input and output faces of the dielectric body. The terminal portions are biased so as to remain in contact with the input and output faces during rotation of the dielectric body. In this way full energy coupling is automatically maintained during selective adjustment of the component.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and objects of the present invention will become more apparent upon a perusal of the following specification taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic plan view of a preferred embodiment of the invention;

FIG. 2 is a cross-sectional view of the embodiment shown in FIG. 1 taken along lines 2-2;

FIG. 3 is an exploded cross-sectional view of a portion of the embodiment shown in FIG. 1;

FIG. 4 is a coordinate diagram showing certain operating characteristics of the device shown in FIGS. 1--3;

FIG. 5 is another coordinate diagram illustrating other operating characteristics of the device shown in FIGS. 1--3;

FIG. 6 is another coordinate diagram illustrating still other operating characteristics of the device shown in FIGS. 1--3;

FIG. 7 is a schematic diagram illustrating operation of the dielectric body shown in FIGS. 1 and 2; and

FIG. 8 is a schematic diagram of a modified dielectric block suitable for use in the embodiment shown in FIGS. 1 and 2.

DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 and 2 there is shown the electromagnetic device 11 including the solid, unitary dielectric body 12 supported by the base 13. The body 12 is formed of a suitable dielectric material such as polystyrene, lucite, teflon, ceramic, or quartz. As shown in FIG. 2, opposite ends of the dielectric body 12 are formed by the parallel oriented input face 14 and output face 15. The input face 14 and output face 15 are joined by parallel sidewalls of the block 12 that form, respectively, first and second internal surfaces 16 and 17.

The dielectric block 12 is rotatably mounted between support plates 18 and 19 by the axial pin 21 and the drive shaft 22 which extends through both the end plate 19 and the support bracket 23. Fixed to the end of the drive shaft 22 is the dial plate 24. Preferably, the face of the dial plate 24 is marked in degrees which are indicated by the pointer 25 also attached to the support bracket 23.

Mounted on for rotation with the shaft 22 is the spur gear 26. Operatively engaging the spur gear 26 is the mating spur gear 27 of substantially smaller diameter. The control shaft 28 has one end keyed to the spur gear 27 and is rotatably supported between the bracket 23 and the rectangular plate 29. Fixed to the opposite end of the control shaft 28 is the operating knob 31.

Also supported by the base 13 on support brackets 32 and 33, respectively, are the input waveguide 34 and the output waveguide 35. Mounted on the input and output waveguides 34 and 35 are the flanges 36 and 37 adapted for connection to mating flanges of a suitable waveguide system. The energy absorbing pads 38 and 39 are disposed between the end walls 18 and 19 adjacent the dielectric block's side walls that form the internal surfaces 16 and 17. The pads 38 and 39 comprise a suitable microwave energy absorbing material such as foam rubber loaded with graphite.

As shown more clearly in the enlarged sectional view of FIG. 3, the input waveguide 34 is formed by a fixed section 41 and the reciprocable top and bottom sections 42 and 43. Recessed portions 44 in the top and bottom walls of the fixed section 41 slideably accommodate the sections 42 and 43 which are retained vertically by the collar 45. The compression spring members 46 and 47 bias the terminal portions 48 and 49 of, respectively, the reciprocable sections 42 and 43 in contact with the input face 14 of the dielectric block 12 during rotation thereof. Although not shown in detail, the output waveguide 35 includes similar reciprocable sections adapted to remain in contact with the output face 15. Thus, close coupling between the input and output waveguides 34 and 35 is automatically maintained in all rotative positions of the dielectric block 12.

The device 11 is uniquely suited for use with oversize waveguide systems. There the behavior of the TE.sub.10 mode approaches that of a plane wave and certain known optical principles can be applied. If a light wave is polarized in the plane of incidence at a dielectric interface, there is one angle of incidence called the Brewster angle for which the reflected signal is zero. For an air-to-dielectric surface, it is given by tangent .theta..sub.B = n, where n is the refractive index (the square root of the dielectric constant). Therefore, in an oversize waveguide system, if the microwave signal (polarization in the plane of incidence) is incident on the dielectric at .theta..sub.B, there will be no reflective loss and the VSWR= 1.

FIG. 4 illustrates the incident angle induced variation in reflectance for such a microwave signal entering a given air surrounded dielectric. For a dielectric having the form shown in FIG. 7 such that the output beam is parallel to the input beam, the reflectance at the output surface 15 is the same as that at the input surface 14. Point A represents the Brewster angle of incidence at which reflectance equals zero. Thus, FIG. 4 graphically illustrates the degree to which a microwave signal is reflected by either the input face 14 or the output face 15 as determined by the relative orientations thereof with respect to the parallel longitudinal axes of the input and output waveguides 34 and 35.

For the case of a polarized signal going from a region of higher n to a region of lower n, there is an angle of incidence (the critical angle, .theta..sub.c) beyond which reflectance is l. For angles less than .theta..sub.c) decreases rapidly for polarization in the plane of incidence and reflected intensity decreases to zero with only a small change in angle of incidence.

FIG. 5 illustrates this relationship for a signal directed against an internal surface of a given air-enclosed dielectric. Again, reflectance is plotted along the ordinate axis and angle of incidence is plotted along the abscissa axis. Point A on the curve represents the critical angle beyond which reflectance equals 100 percent. Thus, FIG. 5 illustrates graphically the degree to which a microwave signal transmitted by the input waveguide 34 into the dielectric block (FIG. 2) will be reflected by the internal surfaces 16 and 17 as determined by the relative orientations thereof with respect to the internally transmitted signals.

The phase of the refracted signal is the same as that of the incident signal at a dielectric-air interface. Therefore, the input 14 and output 15 faces have no effect on the phase of the transmitted signal.

FIG. 6 represents the phase change experienced by a polarized signal reflected by an internal surface of the assumed air surrounded dielectric material. Again, point A on the curve represents the critical angle .theta..sub.c and as shown the phase change increases for incident angles greater than .theta..sub.c remains zero for incident angles a few degrees smaller than .theta..sub.c and then abruptly shifts to l80.degree.for all other incident angles less than .theta..sub.c. Therefore, FIG. 6 graphically illustrates the phase change of a microwave signal transmitted into the dielectric block 12 and reflected by the internal surfaces 16 and 17 as determined by the relative orientations thereof with respect to the signals being reflected.

The operation of the device 11 as a variable attenuator will be described with reference to FIG. 7 which is a schematic representing of the dielectric block 12 shown in FIGS. 1 and 2. The block 12 is shown with the input face 14 receiving polarized electromagnetic energy from the input waveguide 34 at incident angle .theta..sub.i. A portion of this energy is refracted by input surface 14 to the internal surface 16 which in turn reflects energy toward the internal surface 17 as shown. Finally, energy is reflected by the internal surface 17 to the output face 15 and refracted thereby to the output waveguide 35 at the output angle of refraction, .theta..sub.o which, because of the parallel surfaces, is equal to the input incident angle .theta..sub.i.

Assuming that the orientation of block 12 is such that the input angle of incidence .theta..sub.i and the output angle of refraction .theta..sub.o are equal to the Brewster angle .theta..sub.B for the particular dielectric material utilized, no energy reflection occurs at either the input surface 14 or the output surface 15. This case is represented in FIG. 4 by point A which, as noted above, represents the Brewster angle of incidence. Therefore, the combined effect of the input and output faces 14 and 15 for the assumed .theta..sub.B setting is to produce no attenuation or net phase shift of a polarized microwave signal received from the input waveguide 34 and transmitted to the output waveguide 35.

Before considering any signal modification produced by the internal surfaces 16 and 17, one must determine the internal angles of incidence .theta..sub.r at which polarized energy is received by these surfaces. Assume first that the internal angles of incidence .theta..sub.r are equal to the critical angle .theta..sub.c represented by point A in FIG. 5 for the dielectric block orientation described above i.e. a position wherein the input and output angles .theta..sub.i, .theta..sub.o are equal to the Brewster angle .theta..sub.B. Such a relationship will exist if the angle .alpha. between the input face 14 and the internal surface 16 is equal to

where k represents the dielectric constant of the block 12. Accordingly, all signal energy refracted by the input face 14 is reflected by both internal surfaces 16 and 17 to the output face 15. Also, as shown in FIG. 6, no signal phase change occurs at either of the internal surfaces 16 or 17 with the internal angles of incidence .theta..sub.r equal to the critical angle .theta..sub.c again represented by point A. Thus, for the assumed orientation A, a microwave signal received by the dielectric block 12 from input waveguide 34 is transmitted to the output waveguide 35 without either attenuation or phase shift.

Next, assume that operating handle 31 (FIG. 1) is turned so as to produce via the spur gears 26 and 27 counterclockwise rotation of the dielectric body 12. Obviously, such rotation alters the angles .theta..sub.i, .theta..sub.o and .theta..sub.r existing between the transmitted wave and the four interfaces 14--17 of the dielectric block 12. Assume further that the block 12 is rotated into a position represented by points B in the curves of FIGS. 4--6. It will be noted in FIG. 4 that for this case reflectance at the input and output faces 14 and 15 remains approximately equal to zero. Consequently, these faces continue to provide substantially 100 percent signal transmission. However, as shown in FIG. 5, a substantial decrease in reflectance occurs at internal surfaces 16 and 17 which accordingly produce considerable attenuation of the transmitted signal. It will be noted also that this attenuation varies substantially linearly as the dielectric block 12 is rotated between positions represented by points A and B on the curve of FIG. 5. Consequently, a variable attenuation of the transmitted signal is obtained by selective manipulation of the operating handle 31. Naturally, the magnitude of attenuation is determined by reference to calibrations on the dial plate 24 as indicated by the pointer 25.

FIG. 6 shows that no phase change is induced in the signals reflected by internal surfaces 16 and 17 for all input and output angles .theta..sub.i and .theta..sub.o between and including those represented by points A and B. Thus, the effect of counterclockwise rotation of the dielectric body 12 is to produce selective attenuation of the signal received from the input waveguide 34 without the introduction of any net phase shift therein.

Finally, assume that operating handle 31 is turned so as to produce clockwise rotation of the dielectric body 12 from null position A toward a position corresponding to angles of incidence represented by points C on the curves in FIGS. 4--6. As shown in FIG. 4, substantially no reflection occurs at input and output faces 14 and 15 which continue to provide virtually 100 percent transmission. Also, FIG. 5 indicates that 100 percent reflectance occurs at internal surfaces 16 and 17. Therefore, for clockwise rotation of body 12 from the null position A, the device 11 provides substantially 100 percent energy transmission between input waveguide 34 and output waveguide 35.

As shown in FIG. 6 a significant phase change of the reflected signal is introduced by internal surfaces 16 and 17 upon movement of block 12 into position C. Furthermore, the magnitude of introduced phase change varies rapidly between the null position represented by point A and the assumed new position C. Thus, a variable phase change in the transmitted signal is introduced by selective rotation of the dielectric body 12 in a clockwise direction from the null position A.

Summarizing, the present invention provides a component uniquely suited for use in oversize waveguide systems. The device functions either as a variable attenuator or as a variable phase shifter depending upon the direction in which the dielectric body 12 is rotated with respect to a null position corresponding to the Brewster angle of incidence at the input face 14. Furthermore, the performance of the unit depends only upon the above described geometrical configuration and the dielectric constant of the material used for the dielectric body 12. Because the latter is almost independent of wavelength over a wide bandwidth, the disclosed component is inherently broadband and no impedance matching networks are required. In addition, the overall performance characteristics of the device can be calculated directly from the Fresnel equations. Thus, important advantages provided by the present invention include broadband operation, directly calculable performance, no critical mechanical drive requirements, and lack of requirements for impedance matching elements.

FIG. 9 schematically illustrates a modified dielectric block 51 for use in generally the same manner as described above the dielectric block 12. Again, a suitable polarized signal directed at the input face 52 will produce from output face 53 either an attenuated or phase shifted output signal depending upon the relative orientation of the block 12. However, by increasing their lengths, plural signal reflections occur at each of the internal surfaces 54. For this reason, the above described effects of attenuation or phase shift are amplified, thereby enhancing the useful range of the device.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example only, with minor modifications the disclosed components can be used as directional couplers or modulators. It is to be understood, therefore, that within the scope of the appended claims the invention can be practiced otherwise than as specifically described.

Claims

I claim:

1. An electromagnetic device comprising a base means, a dielectric body supported by said base means, said dielectric body having an input face adapted to receive electromagnetic wave energy and an output surface adapted to transmit at least a portion of the electromagnetic wave energy received by said input face, and waveguide means supported by said base means for guiding plane polarized electromagnetic wave energy in the microwave region up to 300 GHz. toward said input face.

2. An electromagnetic device according to claim 1 including a selective drive means for rotating said dielectric body so as to selectively vary the angle of incidence between said input face and the polarized electromagnetic wave energy received from said waveguide means.

3. An electromagnetic device according to claim 2 wherein said drive means permits establishment of the Brewster angle of incidence between said input face and the polarized wave energy received thereby.

4. An electromagnetic device according to claim 3 wherein said dielectric body comprises at least one inner surface adapted to reflect toward said output face electromagnetic wave energy refracted by said input face.

5. An electromagnetic device according to claim 4 wherein said dielectric body comprises at least two said inner surfaces and is adapted to provide a unidirectional electromagnetic wave energy output from said output face for all rotational positions of said dielectric body.

6. An electromagnetic device according to claim 5 wherein said input and said output faces of said dielectric body are parallel.

7. An electromagnetic device according to claim 6 wherein operation of said drive means in one direction relative to said Brewster angle of incidence produces attenuation of the wave energy received by said input face and operation of said drive means in the opposite direction relative to said Brewster angle of incidence produces a phase shift of the wave energy received by said input face.

8. An electromagnetic device comprising a base means, a dielectric body supported by said base means, said dielectric body having an input face adapted to receive polarized electromagnetic wave energy and an output face adapted to transmit at least a portion of the electromagnetic wave energy received by said input face, selective drive means for rotating said dielectric body so as to selectively vary the angle of incidence between said input face and the polarized electromagnetic wave energy being received, said drive means arranged to permit establishment of the Brewster angle of incidence between said input face and the polarized wave energy received thereby, and wherein operation of said drive means in one direction relative to said Brewster angle of incidence produces attenuation of the wave energy received by said input face and operation of said drive means in the opposite direction relative to said Brewster angle of incidence produces a phase shift of the wave energy received by said input face.

9. An electromagnetic device according to claim 8 wherein said dielectric body comprises at least one inner surface adapted to reflect electromagnetic wave energy refracted by said input face.

10. An electromagnetic device according to claim 9 wherein said dielectric body comprises at least two said inner surfaces and is adapted to provide a unidirectional electromagnetic wave energy output from said output face for all rotational positions of said dielectric body.

11. An electromagnetic device according to claim 10 wherein said input and said output faces of said dielectric body are parallel.

12. An electromagnetic device comprising a dielectric body having an input face adapted to receive electromagnetic wave energy, an output face parallel to said input face and adapted to transmit at least a portion of the electromagnetic energy received thereby, a first internal surface joining said input and output faces and adapted to reflect electromagnetic wave energy refracted by said input face, a second internal surface joining said input and output faces and parallel to said first internal surface and adapted to reflect electromagnetic wave energy received therefrom, said output face being adapted to transmit reflected electromagnetic wave energy received from said second internal surface and wherein said input face and said first internal surface make an angle equal to

where k represents the dielectric constant of said dielectric body.

13. An electromagnetic device according to claim 12 including selective drive means for rotating said dielectric body so as to selectively vary the angle of incidence between said input face and electromagnetic wave energy being received thereby.

14. An electromagnetic device according to claim 12 including a base for said dielectric body, and waveguide means supported by said base and adapted to direct electromagnetic wave energy toward said input face.

15. An electromagnetic device according to claim 14 including selective drive means for rotating said dielectric body so as to selectively vary the angle of incidence between said input face and electromagnetic wave energy being received thereby.

16. An electromagnetic device according to claim 12 wherein each of said first and said second internal surfaces are adapted to at least twice reflect electromagnetic energy transmitted within said dielectric body between said input face and said output face.

17. An electromagnetic device according to claim 16 including selective drive means for rotating said dielectric body so as to selectively vary the angle of incidence between said input face and electromagnetic wave energy being received thereby.

18. An electromagnetic device according to claim 16 including a base for said dielectric body, and waveguide means supported by said base and adapted to direct electromagnetic wave energy toward said input face.

19. An electromagnetic device according to claim 18 including selective drive means for rotating said dielectric body so as to selectively vary the angle of incidence between said input face and electromagnetic wave energy being received thereby.

20. An electromagnetic device according to claim 19 wherein said waveguide means comprises terminal portions adapted for contact with said input face and including adjustment means for aligning said terminal portions with said input face at varying rotative positions of said dielectric body.

21. An electromagnetic device according to claim 20 wherein said waveguide means further comprises an output waveguide having terminal portions adapted for contact with said output face and including output adjustment means for aligning said output waveguide terminal portions with said output face at varying rotative positions of said dielectric body.