ANTENNA SYSTEM

Abstract: Receiving antenna system for a projectile. The system combines the reception gain pattern of an antenna exhibiting a null at the projectile axis, with the reception gain pattern of an antenna exhibiting a maximum at the projectile axis. The two patterns are separately detected (28, 30), and the detected outputs are combined in scalar fashion. The composite detected pattern provides substantially omnidirectional coverage to the rear of the projectile.

Description: ANTENNA SYSTEM This invention relates to receiving antenna systems which may be incorporated in fuze actuating systems, and especially in such fuze actuating systems having an in-flight variable range ad¬ justment. Such fuze systems having an in-flight variable range adjust- are shown in the following United States patent specifications in which the inventor is Richard T. Ziemba: Nos. 3, 844,217, 4, 026, 215 and 4, 044, 680. In these fuze or projectile actuating systems it is necessai to communicate between the mechanism for projecting the projectile , e. g. , a gun system, and projectile itself, while the projectile is in-flight- Receiver antennas for spinning projectiles or rockets may be nose-mounted on the projectile, and as so nose-mounted, they are required to provide reception while facing in the rear direction. Alternatively, they may be aft-mounted and as such they are required to provide reception while facing in the forward direction . Receiving antenna structures which are suitable for these purposes, insofar as they were previously known, may be divided into two categories: I. Antenna structures which have a null on the axis of the projectile and subsequent pattern minima at angles which are related to the reciprocal of the projectile diameter measured in wavelengths, or II. Antenna structures which have a maximum on the axis of the projectile and subs-^uent pattern maxima at angles which are related to the reciprocal of the projectile diameter measured in wavelengths. Such an antenna structure has pattern nulls or minima approximately midway between the pattern maxima. The maxima,-n inim a and nulls are those of the reception pattern or reception gain pattern. Regardless of which type antenna is employed, the reception gain pattern coverage has minima which can make inoperable a communication link where the projectile attitude and line of sight between the projectile or rocket, nd the trans¬ mitter antenna., cannot be predicted or controlled. It is an object of this invention to provide a third category (Categoiy πi) of receiving antenna system for a projectile which is nose-mounted and yet provides substantially uniform and omnidirectional reception coverage to the rear of the projectile. For the purpose of attaining these objectives, the present invention provides a receiving antenna system which combines the reception g-ain pattern of the Category I antenna structure, with the reception gain pattern of the Category U. antenna structure to achieve a composite reception gain pattern which has substan¬ tially omnidirectional coverage to the rear of the projectile. The reception gain pattern to the rear of a projectile, exhibited by a nose-mounted antenna, results primarily from diffraction at the base of the projectile. In other words, the reception pattern in the aft direction is basically independent of the specific antenna design. Both Category I and Categoiy π pattern types are mainly determined by the base diffraction such that the minima of one pattern occur at the same angles as the maxima of the other pattern. The present invention proposes to provide a composite of both patterns. Provision of an antenna structure which incorporates plural antennas with different patterns, and arrives at a desired composite pattern, has been previously proposed, primarily for transmitting antennas, see e. g. United States patent specification No.3, 914, 767, Jones. However, these previous approaches are directed to vectorial addition of the radio frequency (microwave) transmissions. The present invention, however, proposes to receive and detect the radio-frequency transmissions separately, and then add or combine the detected outputs, to arrive at a scalar, rather than vector addition of the separate patterns. By such scalar (or arithmetic) com¬ bination, in contrast to vectorial addition, it is possible to virtually eliminate the nulls. The invention will be better understood from the following description together with the accompanying drawings, in which: FIGS 1A, 1B,1C illustrate E-plane reception patterns for Category I, II, EH antennas; FIG. 2 is a longitudinal cross-section of a Categoiy I monopole antenna; FIG. 3 is a typical reception pattern of the Category I monopole antenna of FIG. 2 at 9. 5 GHz; FIG. 4 is a longitudinal cross-section of a receiving antenna having dual monopoles disposed in diametrically opposite slots; FIG. 5 is a perspective view of an antenna having a longitudinally slotted-nose cavity; FIG. 6 is the reception pattern of the antenna of FIG. 5, obtained at 9.5 GHz; FIG. 7 is a schematic diagram of a Category-m antenna in accordance with one embodiment of the invention. FIG. 8 is a perspective view of a dual monopole antenna similar to that of FIG. 7; FIG. 9 is an E-plane pattern for the antenna of FIG.7 or FIG.8; FIG. 10 is a schematic diagra of another Category-m receiving antenna, in accordance with another embodiment of the invention. FIG. 11 is a perspective view of a transmitting antenna, specially suitable to cooperate with Category m receiving antennas of the present invention. Fuze antenna systems for nose mounted antennas which must provide reception coverage to the rear, e.g. , remote set fuzing s stems, can be conveniently divided into the three Categories illustrated in FIGS. 1A, IB, and IC. FIG. 1A depicts a typical Category I reception pattern, which exhibits a null on the projectile axis. Categoi -π antennas, as is shown in FIG. IB, have a pattern maximum on the projectile axis. Categor -m antennas (FIG. IC) by definition use post-detection addition of signals to provide a null-free pattern in the aft direction. Each of the antenna types will be described in detail below. It will be evident from the following discussion that electromagnetic diffraction off the projectile is a major contributor to the far- field pattern in the aft direction for flush-mounted nose antennas. It should be noted that the Category I and LT antennas may be utilized as either transmitting or receiving antennas, based on the reciprocity or dualism as between radiation transmission and reception. Bearing in mind the just given definition, it is clear that Category HI is non-reciprocal, but is applicable solely to receiving antennas. In the case of the Categoiy -I antenna, impinging radiation from the transmitter symmetrically excites the base of the projectile 10. The resulting diffraction contributions to the far- field pattern cancel each other on the axis of the projectile. The simplest antenna in this categoiy is a monopole antenna 12 positioned on the projectile axis as indicated in FIG. 2. A typical reception gain pattern taken of the quarter-wave monopole of FIG. 2, is shown in FIG. 3. The frequency was 9.5 GHz. The projectile diameter was 105mm. The diffraction results in a veiy deep null in the aft direction. If the projectile axis were pointed at the transmitting antenna, there could be no communication. The maximum gain for this pattern occurred approximately 7. 0 off the projectile axis. Another way of realizing a Category I pattern is to vectorially couple-in-phase two monopoles disposed in diametrically opposite slots 14 and 16 (dielectric filled) as shown in FIG. 4. Projectile diffraction produces the pattern in the aft direction without a strong dependence on the specific type of receiver antenna used. The E-plane reception pattern of FIG. 4 antenna in the rearward direction is very similar to that of the monopole antenna of FIG. 2. * With two monopoles in diametrically opposite slots used as the receiver antenna (FIG. 4), the receiver antenna polarization rotates with projectile spin, requiring the transmitting antenna to be circularly polarized. The Category -EC antenna in effect vectorially couples -out-of- phase two radiations impinging on the projectile 10, to produce a pattern maximum on the projectile axis as illustrated in FIG. IB. One technique for achieving this type of coupling is to provide the longitudinally slotted-nose cavity cf FIG. 5. This iype of antenna provides a dipole-like mode to achieve a maximum in the aft direction. A typical E-plane pattern for the antenna of FIG. 5, is shown in FIG. 6 for a 9. 5 GHz operating frequency and a 105mm projectile. When this pattern is compared with the pattern for a Category -I antenna, it is observed that the angular spacing between ripples in the aft direction is almost identical for the two patterns. * Furthermore, the pattern closely resembles that shown by the dotted -line curve of Figure 9. Categoiy-I receiving antennas require that the line-of-sight path to the transmitting antenna be located off the projectile axis. Categor -π receiving antennas allow the transmitting antenna to be located directly on the projectile axis- The preceding discussion pertained to E-plane patterns. The reception gain patterns of the slotted antennas of FIG.4 or 5 are roll sensitive. This sensitivity to roll can be removed in two ways. The first is to use a circularly-polarized transmitting antenna as previously stated. The second is to use four monopole antennas, displaced by 90 spatially, as will be explained subsequently. * The overall advantage of a Category ILT antenna is that a null-free pattern can be achieved in the rear direction. The communication link is then relatively insensitive to the place¬ ment of the transmitting antenna at the gun and to the attitude of the projectile. A slight disadvantage of this type of antenna system is that the antenn and the detector circuit are slightly more complex and the cost of the system is increased somewhat due to the requirement for multiple RF detector diodes. As previously noted, the maxima of the Category I patterns coincide with the minima af the Category E patterns. If the outputs corresponding to each of these patterns are video detected, thereby removing the radio-frequency phase information, and summed necessarily in scalar fashion, a near uniform reception coverage is achieved. Furthermore, both patterns can be simultaneously derived from a modified FIG.4 antenna .system by combining the antenna outputs in a 180° hybrid junction 26 as shown in FIG. 7. As is more clearly shown in FIG. 8, the antenna has monopoles 20 and 22 fabricated in stripline and positioned within a concentric dielectric ring 24. The windscreen 25 is metallic. * This produces 90° progressive phasing, as will be explained subsequently. O Reverting again to FIG. 7, the outputs of the stripline dipoles are combined in the stripline 180 hybrid junction 26. FIG. 9 shows pattern measurements, taken at 11 GHz, for each video detector 28 and 20 separately, one in solid line and the other in dotted line fashion. The detectors 28 and 30 are respec¬ tively connected to the hybrid outputs. A scalar composite of the two characteristics of FIG. 9 is the desired null-free and substantially uniform characteristic, shown by the broken-line curve in FIG. 9. An alternative embodiment of the invention is shown in HG.10 Again, the antenna structure consists of two monopoles 32 and 34. The monopoles are excited through a 90 branch hybrid junction 130 plus a 90 section of the line 40. A simple detector diode 42 and 44 is used for each hybrid output. The outputs of the two detector are summed in scalar fashion, i. e. arithmetically, in the load 46. The monopoles 32 and 34 are fitted into diametrically opposite, dielectric-filled slots, analogous to FIG. 4. In summaiy, the embodiments of Figures 7, 8 and 10 are adaptations of the antenna structure of Figure 4 (with diametrically oppo¬ site slots, or with concentric ring), so as to arrive at a Category ffl antenna. OMPI Either of the two just-discussed methods of achieving 180 phase shift may conveniently be adopted _as shown in FIG. 7, or i n FIG. 10. Further, it should be noted that the video detectors 28 ?mri 30 (shown symbolically as simple diodes in FIG. 7) could well be the simple detector diodes -42 and 44 of FIG. 10, and vice versa. It has been previously indicated that sensitivity to roll can be removed by provision of four, instead of merely two, monopoles. As applied to the embodiment of Figure 7, this is done as follows. Consider the monopoles 20 , 22 to be located at "up" and "down" respectively. Assume that two more monopoles* were provided, both located in a plane perpendicular to the plane of the paper and passing through the projectile axis. These two additional monopoles would be at locations "front" and "rear 31 , essentially symmetrical with respect to the projectile axis (as is also true of the "up" and "down" monopoles 20 and 22). Join the "front" monopole via a 90 line-section (similar to that designated as 40 in FIG. 10) to the line outgoing from the "up" monopole 20, and similarly join the "rear" monopole by a 90 line-section to the line outgoing rom the "down" monopole 22. The embodiment of Figure 10 should be modified similarly, with the following slight changes. Provide additional "front" and "rear" slots, concomitant with the additional "front" and "rear" monopoles. Make the added 90 line-section connections as stated for Figure 7, with the qualification that the 90 line-section outgoing from the "rear" monopole should join the line outgoing from the "down" monopole 34 at a point intermediate of "down" monopole 34 and 90° section 40. * in slots, or in the common concentric ring. For optimum transmitter-receiver cooperation, the transmitter antenna is usually mounted on the gun shield. The transmitter antenna half -power beamwidth (HPBW) and beam steering should be appropriate to illuminate the projectile during its travel range. The transmitter antenna, should be circularly polarized to cooperate with a spinning linearly -polarized projectile antenna. One embodiment of the transmitting antenna 50 is shown in FIG 11. The antenna front surface has an array of slots 52 in a thick metallic plate 54. The antenna slots are filled with a dielectric material 56 such as teflon or a ceramic to provide an environmental seal . Each slot is excited from a teflon glass substrate 58 (about 0.8 mm thick) on which printed copper runs. The substrate is backed by a teflon fiberglass board 60, about 3. 2 mm thick. The sides and back 62 of the antenna are thick metal. The relevant characteristics of the transmitting antenna of FIG. 11 are tabulated as follows: Elevation HPBW 14.5° Azimuth HPBW 10.0° Available Gain 26 decibels 50% Efficiency -3 decibels Steering Loss -2 decibels Realized Gain 21 decibels

Claims: CLAIMS 1. An aftward directed receiving antenna system (Fig. 7; Fig. 10) for disposition in the forward portion of a projectile comprising: a first receiving antenna configuration having a reception 5 gain pattern primarily determined by base diffraction with a null on the axis of the projectile and subsequent pattern minima at angles which are related to the reciprocal of the projectile diameter measured in wavelengths, a second receiving antenna configuration having a 10 reception gain pattern primarily determined by base diffraction with a maximum, on the axis of the projectile and subsequent pattern maxima at angles which are related to the reciprocal of the projectile diameter in wavelengths; means for separately detecting radio frequency waves • 15 incident upon the first and second antenna configurations; and means for combining in scalar fashion the separate outputs of the detecting means. 2. A system according to Claim 1 wherein said detecting means includes a first detector (28; 42) coupled to said first receiving antenna configuration; and 5 a second detector (30; 44) coupled to said second receiving antenna configuration 180 out-of -phase with said first detector's coupling to said first receiving antenna configuration. 3. A system according to Claim 2 wherein the receiving antenna configurations are otherwise similar, but the 180 phase shift is provided by a 180 hybrid junction (26) in the lines to said first and second detectors. 4. A system according to Cl-ai 2, wherein the receiving antenna configurations are otherwise similar, but the 180 phase shift is provided by a 90 hybrid junction (130) in the lines to said first and second detectors, and by a preceding 90° section (40) in one line to the 90 junction. 5. A system according to Claim 3 or 4, whe rein the first and second antenna configurations comprise respectively a first and a second monopole antenna (20,22; 32,34). 6. A system according to Claim 5, further provided with a third and a fourth monopole antenna which are spatially displaced by 90° relative to the first and second monopole antennas respectively, and with a 90° line-section joining the first and the third monopole antennas, and also the second and fourth monopole antennas. 7. A system according to Claim 5 or 6, wherein each monopole antenna is situated within a radially formed slot in the projectile body, each slot being diametrically opposed to another slot. 8. A system according to Clai 7, wherein each slot is filled with dielectric material. 9. A system according to Claim 1 or 2 wherein said minima of said pattern of said first antenna configuration and said maxima of said pattern of said second antenna configuration occur at substantially the same angle. 10. A communication link between a projectile in-flight and a remote station comprising: a remote transmitting antenna, and a receiving antenna system as claimed in Claim 1 or 2, and disposed in the forward portion of the projectile. BU _ O

Inventors: KINZEL J
Applicants: GEN ELECTRIC, GENERAL ELECTRIC CO
Application year: 1980
Main classification: H01Q1
IPC codes: H01Q1, H01Q25