US2788440A - Hybrid arrangements for use on micro radio waves - Google Patents

Description

April 9, 1957 J. F. RAMSAY ETA!- 0 HYBRID ARRANGEMENTS FOR USE ON MICRO RADIO WAVES Filed Feb. 4, 1954 5 Sheets-Sheet. 1

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HYBRID ARRANGEMENTS FOR USE on MICRO RADIO wAvss Filed Feb. 4, 1954 3 Sheets-Sheet 3 jwu, i mwrfimgy (M64 77% 1M .79 M @4 7 BMW/ 2 HYBRID ARRANGEMENTS FOR USE 9N MICRQ RADIO WAVES John Forrest Ramsay, Great Baddow, and Edward Marshall Wells, Chelmsi ord, England, assignors to Marconis Wireless Telegraph Company Limited, London, England, a British company Application February 4, 1954, Serial No. 488,082

Claims priority, appiication Great Britain February 6, 1953 8 Claims. (Cl. 25il--6) This invention relates to hybrid arrangements for use on micro radio waves, hereinafter termed, simply microwaves.

There are many known forms but they are all essentially circuit devices in the sense that the energy paths through them are defined and limited throughout, over their whole lengths, by the component parts of the hybrid. They fall, in general, into one or another of two classes, namely (a) that in which the definition of the energy paths is efiected by co-axial or other transmission lines, a typical example being the so-caiied duplexer hybrid, and (b) that in which the definition of the energy paths is effected by wave guides, typical examples being the well known magic-T and rat-race hybrids. All such hybrids tend to be complex and expensive to design, make and install, especially where microwaves are in question and the present invention seeks to overcome these disadvantages.

Though not limited to its application thereto, the invention is of particular advantage when applied to those cases in which there are a number of parallel separate energy channels, each performing the same function and each containing a hybrid. As will be seen later, the present invention provides, it is believed for the first time, what may be termed a free-space hybrid, that is a'hybrid in which the energy paths are not constrained over their whole lengths.

According to the present invention, there is provided a free space unconstrained hybrid for two spatially separated orthogonally polarized radio waves in convergent paths comprising a first linearly polarized plane mirror situated substantially at the intersection of the said paths where the direction of polarization of the mirror is chosen in relation to the directions of polarization of the waves so that the mirror serves as a reflector for one only of the waves and a transmitter for the other of the waves. There is a common path into which the mirror reflects the one wave and transmits the other. A second linearly polarized plane mirror is situated in the common path ith its plane of polarization oriented at 45 with respect to that of the first mirror so that the second mirror is adapted to transmit components of the two radio waves polarized at right angles to said one plane into two further divergent paths respectively.

For a better understanding of the invention and to show how the same may be carried into eiiect, reference will now be made to the accompanying schematic drawings, in which:

Fig. l is a diagram illustrating the properties of a polarized radio mirror;

Fig. 2 is a diagram of a free-space hybrid employing the mirrors of Fig. 1;

Fig. 3 is aplan of an embodiment of the hybrid of Fig. 2;

Fig. 4 is a-plan of another hybrid similar to Fig. 3;

of hybrid arrangements,

2,788,440 Patented Apr. 9, 1957 Fig. 5 is a plan of a free-space hybrid suitable for a radar system, or a so-called radio telescope;

Fig. 6a is a plan of a hybrid showing the local oscillator energy paths, suitable for a superheterodyne balanced mixers for multiple radar systems;

Fig. 6b shows the energy paths of the incoming signals to the hybrid of Fig. 6a; I

Fig. 7 is a schematic perspective view of a receiver employing a free-space hybrid.

Referring to Fig. 1, a polarized mirror M is typified as consisting of a grid or grating of parallel, closely spaced, wires (or strips). If a linearly polarized plane wave is incident normal to such a mirror it is substantially totally reflected, if the plane of polarization is parallel to the wires of the mirror but is substantially totally transmitted if the plane of polarization is at right angles to the wires of the mirror. These reflection and transmission properties hold for waves other than normally incident waves.

In Fig. 1, two orthogonally polarized plane waves are transmitted from S on to the mirror M which is set at 45 to the direction of transmission of the two waves so that the mirror is what is herein termed a 45 vertically polarized mirror-45 because of the angle and vertically polarized because the mirror wires are vertical. T he two waves are represented by their respective field strength vectors A and B it being assumed that the polarization of the wave of field strength A is at 45 to the horizontal and that of the wave of field strength B is at 135 to the horizontal. In general A and B may be complex amplitudes, but, for simplicity, the figure is drawn for the case in which both waves are in phase with each other. The horizontal components of A will be transmitted through the mirror without phase change to a point which is at a given distance from the mirror M but the vertical componentwill be reflected aththe mirror, with a reversal of phase to a point D, which point is the same distance from the mirror as is the point C, the paths from the mirror M to C and D respectively being mutually perpendicular. The horizontal component of B is in antiphase with that of A and is transmitted through the mirror to the point C while retaining its anti-phase relation, but the vertical component of B is in the same phase as that of A' and is reflected by the mirror with a reversal of phase, thereby appearing in phase with the component of A as shown in Fig. 1. The present invention utilizes those properties to provide a free-space hybrid handling two input waves which are not spatially superimposed (at S) as is presumed in Fig. 1.

In Fig.2, the two waves A and B are spatially separated, being introduced from two difierent directions (as is, in practice, the usual requirement) and there are on mirror M2 is but any other angle may be used with suitable changes in the mirror arrangements.

Mirror M2 is a polarized mirror inclined at 45 to the direction of the wave whose" polarization is indicated at A. If, as indicated, this direction lies in a horizontal plane, the mirror M2 will be in a vertical plane. Mirror M2 is polarized at right angles to the polarization of A and the wave in question therefore passes through said mirror unaflected, being then incident upon the mirror M1 which is arranged in the same way as the mirror M of Fig. l and therefore has the same action on wave A as has already been described with reference to Fig. 1. Thus mirror M1 has a plane of polarization orientated at 45 with respect to that of mirror The polarization of wave B is at right angles to that of A and this fact, combined with the angle at which the wave B is incident "on the mirror M2 causes wave B to be reflected at the mirror and follow the same path as wave A to mirror M1, a reversal of phase of B taking place at the mirror M2. The two outputs from mirror M1 correspond to'those from mirror M in Fig. 1 and are indicated in the same way. This structurally simple free space hybrid, which takes two orthogonally polarized, differently directed input waves, thus provides two separated outputs, a push-pull output and a push-push output. Its performance is therefore the same as that of the well known four-arm magic T wave guide hybrid despite its much greater simplicity and economy and absence of positive guiding of the waves by wave guides or transmission lines.

In the arrangement of Fig. 2 it is assumed that the incident radiation is collimated, the incident waves are plane, and the mirrors are of the same size, being sufiicient to be properly illuminated by the incident radiation. It will be evident that where a hybrid is required to handle convergent or divergent beams, the mirrors will, in general, be of different sizes and in some cases this might lead to inconveniently large mirrors and a hybrid of inconvenient overall dimensions. It may, therefore, often be convenient to design the hybrid as part of a system to have its own entrance and exit pupils.

Fig. 3 shows an embodiment of this nature, the prin cipal differences between Figs. 2 and 3 being in the provision, in Fig. 3, of a condenser lens CL provided between the mirrors M2 and M1 and the provision of specific means for feeding energy into and taking it out of the hybrid. On the assumption made in Figs. 1 and 2 that the input end of the hybrid is the right hand end and the output end the left hand end (of course either end can be the input end), AT and BT schematically represent transmitting multi-feed units and'CR and DR receiving multi-feed units. Mirror polarizations and orientations are as in Fig. 2. As will be seen, in spite of the divergent and convergent beams, mirrors of equal size can be used.

In Figs. 2 and 3 the mirrors are shown as parallel to one another as are the mirrors in a periscope. They may, however, be at right angles or at other desired angles so long as appropriate changes are made in the directions of polarization so that the requisite hybrid action is obtained.

I Instead of multi-feed units (a multi-feed, whether transmitting or receiving is, of course, essentially an array of discrete elements) any suitable continuous distribution devices'such as phase corrected mirrors or lenses may be used and any of the multi-feed units of Fig. 3 may be replaced by such a device. In Fig. 4 all four multi-feed units AT, BT, CR, DR are replaced by lenses ATL, BTL, CRL and DRL respectively, which are such as to make the system telescopic, the lenses serving as collimating lenses. The plane waves are incident on the ATL and BTL lenses and emerge from the system by way of the lenses CRL and DRL. This system is completely free space and accepts unguided waves.

The invention has many practical applications one being to the common transmitting-receiving aerial systems of radar installations and another being to balanced mixers for superheterodyne micro-wave receivers.

Fig. 5 shows awide angle metal lens WA through which radio waves are transmitted and received and FL a metal field lens associated therewith. The hybrid comprises two polarized mirrors M1 and M2, located so as to be at right angles to one another with a metal condenser or eye lens CL between them. A transmitting multi-feed unit is indicated at TM and receiving multifeed unit at RM. As in the case of Fig. 3, suitable lenses or phase corrected mirrors could replace these multi-feed units. The hybrid of Fig. 5 may be essentially the same as those of Fig. 3 or 4 except for the addition of a plane mirror M3 parallel to and a short distance behind the mirror M2. This mirror, which is spaced from M2 by a distance of about ARV? (where 2\ is thewave length) reflects energy from one to the other of the two remaining mirrors and its addition in effect combines, in space and time quadrature, two of the arms of what would otherwise be a four arm hybrid (as are the hybrids of Figs. 3 and 4) so that a circularly polarized wave is formed for transmission and a circularly polarized received wave is de-circularized. Thus circular polarization duplexing is efiec'ted.

Referring to Fig. 6a, local oscillatory energy is fed in from a wave guide flare GF via a field lens FL1 to a polarized mirror M2 of the hybrid which also includes the condenser or eye lens CL and the second polarized mirror M1. DM1 and DM2 are two-dimensional arrays of balanced mixers which receive anti-phase oscillator energy from the mirror M1. Balanced mixers are well known per se and a type of mixer suitable for the present application is described in Radiation Laboratory Series (first edition), vol. 16, chap. 6, and shown in Fig. 6.19 of that chapter. The arrangement is such that the local oscillator wave from GF corresponds to wave B of Fig. 2 and accordingly the mixer excitation is anti-phase.

Referring now to Fig. 6b the incoming signal enters the hybrid through the wide angle lens WA and field lens FL2. The arrangement is such that this signal wave corresponds to wave A of Fig. 2 and accordingly, so far as this wave is concerned, in-phase excitation of the mixers may be produced.

It is unnecessary to show the remainder of the system since it forms no part of this invention. It may be said, however, that the outputs from the balanced mixers are taken to suitable intermediate frequency amplifiers (not shown) and will possess the good signal-to-noise ratio exhibited by balanced mixers as normally connected to wave guide hybrids. The great simplicity of the arrangement illustrated, with its straight forward free space hybrid in place of the complex and expensive wave guide hybrids usually employed, will be at once apparent.

In the case of a receiver shown in Fig. 7 which is only required to accept signals from directions restricted to one plane, say the azimuth plane, the arrangements can be still further simplified and ancillary lenses eliminated. In Fig. 7 a hybrid is inserted in the convergent field between the objective and focal regions of a wide angle objective lens WA. The two mirrors, with their differently directed polarizing strips or wires indicated as in Fig. 2, are represented at M1 and M2, the latter being represented as supported on a supporting sheet SS of expanded dielectric. The input from the local oscillator, not shown, is indicated at LO, a shielded cylindrical lens SCL providing a line image of the oscillator at the multiple receivers which are indicated by their orthogonally polarized balanced mixers DM1 and DM2. Mirror M1 is shown broken away to reveal the mixers DMl. The

center line signal path is indicated at SP. The arrow headed lines X and Y crossing the paths SP and L0 indicate the respective polarizations. The cylindricallens SCL can be used for the oscillator feed because there are merely two lines of mixers instead of two-dimensional matrices thereof as in Fig. 6, the said lens SCL focussing on them in elevation and having a horizontal aperture sufiicient to secure substantially uniform excitation thereof in azimuth.

Since in an arrangement in accordance with this inventionpower is transmitted by free space there is no equivalent of the wave-guide or transmission line mode and it is fundamental that not all the energy in the system will do useful work. Thus, for example, it is not possible to devise a primary feed which will accept all the power from the diffraction pattern produced at the focus of an objective of finite aperture. 7

It is important that ancillary apparatus such as lens supports and terminal equipment he so designed that.en ergy falling on them, which of course is lost, does not produce standing waves in space such as wouldint erferc with the desired flow of energy. Lens surfaces and the nominally transmitting aspect of polarized mirrors may, in practice, also produce reflections and similar precautions :have to be taken as regards this. In general, in high performance installations embodying the invention, precautions will have to be taken to prevent deleterious effects due to unwanted reflected waves and also effects due to cross polarization must be reduced. There are various expedients known per so which could be adopted to this end. Among these expedients is the blooming of the lenses or otherwise so arranging them that such reflections as may occur take place along harmless paths, e. g. by profiling the lenses or tilting them; designing and making the lenses so that they are as free as possible from the generation of unwanted polarizations; and deand making polarized mirrors to be as free as possible trom reflection of energy of modes to be transmitted thereby, e. g. by designing and making them so that they act as cut oil wave guide gratings and/or by using, instead of a single mirror, two or more appropriately spaced cascaded mirrors arranged to produce cancellation or material reduction of unwanted reflections. In addition, terminal equipment, receivers, lenses and so on must be as well matched as possible, and supports, frames, holders, and other bodies in the energy paths made in manner known per se to be as energy absorbent as possible.

It is desirable, in practice, that means be provided for experimentally adjusting the various path lengths and experimentally trimming the various polarizations.

All these expedients are matters of design refinement well known per se in the art to which the invention relates and are, therefore, neither illustrated nor described in detail herein.

While we have described our invention in certain preferred embodiments, we realize that modifications may be made, and we desire that it be understood that no limitations upon our invention are intended other than may be imposed by the scope of the appended claims.

We claim:

1. A free-space, unconstrained hybrid for two spatially separated orthogonally polarized radio waves in convergent paths comprising a first linearly polarized plane mirror situated substantially at the intersection of said paths, the direction of polarization of said mirror being so chosen in relation to the directions of polarization of said waves that said mirror is a reflector for one only of said waves and a transmitter for the other of said waves, a common path into which said mirror reflects said one wave and transmits said other and a second linearly polarized plane mirror situated in said common path and with its plane of polarization oriented at 45 with respect to that of said first mirror whereby said second mirror is adapted to transmit components of the two radio Waves polarized at right angles to said one plane into two further divergent paths respectively.

2. A free-space, unconstrained hybrid for two spatially separated, orthogonally polarized radio waves in convergent paths comprising a first linearly polarized plane mirror situated substantially at the intersection of said paths, the direction of polarization of said mirror being so chosen in relation to the directions of polarization of said waves that said mirror is a reflector for one only of said waves and a transmitter for the other of said waves, a common path into which said mirror reflects said one wave and transmits said other, a second linearly polarized plane mirror situated in said common path and with its plane of polarization oriented at 45 with respect to that of said first mirror whereby said second mirror is adapted to transmit components of the two radio waves polarized in one plane and to reflect components of the two radio waves polarized at right angles to said one plane into two further divergent paths respectively and a condenser lens system positioned across said common path between said first and second mirrors.

'3. In combination, two transmitting .multifeed units, situated one at the end of each of two spatially separated, convergent paths, and adapted each to transmit an or? thogonally polarized wave along its own path, a free .unconstrained hybrid comprising a first linearly polarized plane mirror situated substantially at the intersection of said paths, the direction of polarization of said mirror being so chosen in relation to the directions of polarization of said waves that said mirror is a reflector for one only of said waves and a transmitter for the other of said waves, a common path into which said mirror reflects said one wave and transmits said other, a second linearly polarized plane mirror situated in said common path and with its plane of polarization oriented at 45 with respect to that of said first mirror whereby said second mirror is adapted to transmit components of the two radio waves polarized in one plane and to reflect components of the two radio waves polarized at right angles to said one plane into two further divergent paths respectively, a condenser lens system positioned across said common path between said first and second mirrors and two receiving multifeed units, situated each at the end of one of said divergent paths, oneunit being adapted to receive radio waves reflected by said second mirror and the other unit being adapted to receive radio waves transmitted by said second mirror.

4. In combination, two transmitting continuous distribution devices situated one at the end of each of two spatially separated, convergent paths, and adapted each to transmit an orthogonally polarized wave along its own path, a free unconstrained hybrid comprising a first linearly polarized, plane mirror situated substantially at the intersection of said paths, the direction of polarization of said mirror being so chosen in relation to the directions of polarization of said waves that said mirror is a reflector for one only of said waves and a transmitter for the other of said waves, a common path into which said mirror reflects said one wave and transmits said other, a second linearly polarized plane mirror situated in said common path and with its plane of polarization oriented at 45 with respect to that of said first mirror whereby said second mirror is adapted to transmit components of the two radio waves polarized in one plane and to reflect components of the two radio waves polarized at right angles to said one plane into two further divergent paths respectively, a condenser lens system positioned across said common path between said first and second mirrors and two receiving continuous distribution devices, situated each at the end of one of said divergent paths, one device being adapted to receive radio waves reflected by said second mirror and the other device being adapted to receive radio waves transmitted by said second mirror.

5. A free space hybrid as set forth in claim 1 wherein the surfaces of the mirrors are parallel.

6. In a radar system a common channel for transmitting and receiving radio waves, a wide angle radio lens positioned across said common channel, a field radio lens, a free space unconstrained hybrid coupled to said wide angle lens, as respects radio waves, through said field lens, said hybrid comprising a first linearly polarized, plane mirror, the direction of polarization of said mirror being so chosen in relation to the directions of polarization of said Waves that said mirror is a reflector for one only of said Waves and a transmitter for the other of said waves, a common path into which said mirror reflects said one wave and transmits said other, a second linearly polarized, plane mirror situated in said common path and with its plane of polarization oriented at 45 with respect to that of first mirror whereby said second mirror is adapted to transmit components of the two radio Waves polarized in one plane and to reflect components of the two radio waves polarized at right angles to said one plane into two further divergent paths respectively, a condenser lens system positioned across said common path between said first and second mirrors and a third plane mirror located parallel to and spaced from said first mirror, 2. transmitting multifeed unit situated at the end of one of said divergent paths and adapted to transmit radio Waves into said hybrid and a receiving multifeed unit situated at the end of the other of said divergent paths and adapted to receive radio waves from said hybrid.

7. In a superheterodyne, multiple radar system comprising a free space hybrid as set forth in claim 2, a source of local'oscillator energy situated at the end of one of the convergent paths 'of said hybrid, a Wide angle radio lens situated at the end of the other of the convergent paths of said hybrid, a field radio lens positioned across said other convergent path and two two-dimensioned balanced mixer arrays situated one at the end of each of the divergent paths of said hybrid, one array being adapted to accept radio Waves reflected by said second mirror and the other array being adapted to accept radio Waves transmitted by said second mirror.

8. In a superheterodyne, multiple radar system comprising a free space hybrid as set forth in claim 1, a wide angle, objective, radio lens situated at the end of one References Cited in the file of this patent UNITED STATES PATENTS 1,927,394 Darbord et al. Sept. 19, 1933 1,938,066 Darbord Dec. 5, 1933 2,364,371 Katzin Dec. 5, 1944 2,441,598 Robertson May 18, 1948 2,530,826 Kock Nov. 21, 1950 FOREIGN PATENTS 743,533 Great Britain Ian. 18, 1956

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