US 2885676 A
Description (OCR text may contain errors)
` May 5, 1959 L. D. BALDWIN ANTENNAS 3 Sheets-Sheet 1 Filed Jan. 23, 1957 /llllllllllll/I.
INVENTOR LEROY D. BALDWIIN ATTORNEY l.. D. BALDWIN LER INVENTOR. OY D. BALDWIN ATTORNEY VSWR May 5, 1959 L. D. BALDWIN 2,885,676
ANTENNAS TTTTTT EY United States Patent D ANTENNAS Lero,v D. Baldwin, Rochester, N.Y., assignor to General Dynamics Corporation, Rochester, N.Y., a corporation of Delaware Application January 23, 1957, Serial No. 635,669
8 Claims. (Cl. 343-767) This invention relates to antennas and is particularlyl directed to antennas for directionally radiating or receiv Such antenna structures are adapted for mounting in the hull of a ship or aircraft with the cavity structure inside the hull and the slot opening covered with an electrical transparent sheet of insulating material ush with the hull.
At the high frequencies, such as 1000 to 10,000 megacycles, the dimensions of the probe and of the cavity become so small, and the manufacturing tolerance so critical for a given radiation characteristic, as to render the unusual slot antenna structure costly and unfeasible in manufacture. The probe size and shape especially should be easily reproduced, and at these high frequencies the said transmission line should be without discontinuities and free of spurious radiations throughout the length of the transmission line.
The object of this invention is to provide an improved y slot type antenna structure.
A more specific object of this invention isto provide an antenna structure adapted for microwave energy that is inexpensive and easily reproduced in manufacture.
A still more specific object for this invention is to provide a microwave antenna which is directional and which easily radiates or receives microwave signals over a wide band of frequencies.
The objectives of this invention are attained by utilizing printed circuit structures comprising a sheet of insulating material of low high-frequency loss characteristics. To one side of t'ne sheet is printed an antenna feed transmission line conductor terminating in a printed flat probe of the desired size and shape. To the other side of the sheet is adhered a conductive sheet of metal called a ground plate and of extended area compared to 'the area of the probe and its transmission line. A window is cut or otherwise formed in the ground plate opposite the probe. A cavity housing is placed over the window, the
lhousing being of measured size and shape to eiiiciently radiate the high frequency energy from the probe outwardly through the window.
Other objects and features of this invention will become apparent to those skilled in the art by referring to the specific embodiments of the invention discussed in the following specification and shown in the accompanying drawing in which Figure l is a plan view of one antenna structure em bodying this invention, s
Figure 2 is a section on line 2 2 of Figure 1,
Figure 3 is a plan view of another antenna structure embodying this invention,
Figure 4 is a section on line 4 4 of Figure 3,
Figures 5 and 6 are plan and sectional views, respectively, of still another structure embodying this invention,
l 2,885,676 Fatented May 5, 1959 "lee Figure 7 is a graph of the voltage standing Wave ratio versus frequency of one specific probe configuration, and
Figure 8 is a polar diagram of the radiation fields of one antenna structure of this invention.
Referring to Figure 1, the antenna of this invention comprises the sheet 1 of insulating material, the sheet being relatively thin and having good high-frequency insulating characteristics. The sheet may comprise, for example, Tellen-impregnated fibre glass. In the preferred embodiment, the underside of the sheet is covered, overall, with a thin foil or plate 2 of copper or other electric conducting metal, preferably glued firmly to the insulating sheet. To the other side of sheet one is formed the;l transmission line 3 terminating in the probe 4. The liueand probe, according to this invention, are printed on the sheet 1. While various printing techniques may be used,A the one which has been found to be easily controlled in manufacture consists of laminating the sheet 1 with thin copper foil-sheets on both sides by any pressure-heat technique which will firmly bond the laminae together. The copper laminate on one side is then smeared with a thin layer of photo-resit varnish, whereupon the varnish is irradiated with a strong light which will chemically fix the varnish, the irradiation being done through a negative of the printed circuit pattern desired on the copper sheet. In this case, the negative pattern would have the precise outline and dimensions of the transmission line 3 and probe 4. After Washing away the unfxed portion of the varnish, the exposed copper plate is then etched away in a suitable etching solution to leave only the metal in the outline of 3 4, Figure l.
According to an important feature of this inventiona "window 5 is removed from the ground plate 2 opposite the probe 4 either by cutting away the metal or by the etching technique above mentioned. The window 5 and probe 4 are so positionally related that the probe overlies the window, preferably but not necessarily, at the center of the window.
-It has been found that where the conductor 3 is spaced from the ground plate 2 by a fraction of the width of the conductor and where the high frequency insulating properties of the sheet are good, radiation from the transmission line is negligible. The thickness of the insulating sheet and the width of the conductor 3 is easily controlled within very narrow tolerance limits, which means that the impedance characteristics of the transmis- `sion line 2 3 are easily controlled in manufacture. Be-
cause the parts of the transmission line, probe, and ground plate are bonded together, relative movement of the parts is not possible in use.
While the window 5 in Figure 1 is shown rectangular in shape, the window may be round, oval, or other shapes depending in part on the directional characteristics of the antenna desired. The ground plate, according to this invention is joined to the housing 6 as by flanges 7 which can be soldered or otherwise aixed to the ground plate 2. The size and shape of the housing 6 is chosen to enclose completely the window. The cavity walls may be set flush with the edge of the window o1' outwardly from the edge, depending on the electrical and space requirements of the cavity. In the example shown in Figure 2, the depth of the cavity formed by the housing is adjustable by the plungeriS carried on the adjusting screw 9. The plunger 8 forms an imperforate barrier to the field within the cavity and yet slideably engages the Walls of the housing. Spring fingers 8a on the plunger slide on the wall. The distance from the probe 4 to the face of the plunger 8 may be made proportional to any small fraction of the wave to be radiated, depending on the mode of cavity operation desired. Where broad band operation is desired, the depth of the cavity may be one quarter wavelength. tOdd numbered quarter wavelengths may be 3 used, .but the Ahigher the `number the narrower becomes the band.
The printed circuit board 1-2-3 with the mounted cavity 6-7-8 may then be mounted, as shown in Figure 2, directly on the metal chassis 10 from or to whichmicrowave energy can be radiated. It will be noted with the ground plate 2 in contact with the wall 10 of the chassis, the ground plane is electrically extended to the limits of the chassis. Alternatively, of course, the cavity structure 6 with anges 7 could be mechanically mounted on the chassis wall, rather than on the ground plate 2 as shown.
The printed circuit board of Figure 2 may be turned over as shown in Figures 3 and 4. Such a reversal places the ground plate to the outside and opposite the cavity housing 6a, and the transmission line and probe 3, 4 adjacent the housing. In such a structure the housing 6a is cutout or relieved at 6b to clear ,the transmission line 3. Bolts 11 through anges on the cavity housing and through the ground plate effectively ground the housing lto the plate.
It has been found convenient on occasion to space the printed circuit board 1 inside the chassis housing 10, as shown in Figures and 6. A window `5a of measured size and shape is formed in the chassis housing in alignment with the window 5 of the ground plate 2. The spacing collar 12 is clamped between the two plates 1 and to electrically continue the cavity of housing 6a to the periphery of Window 5a, and to rigidly mechanically x the parts of the antenna structure together. It will appear that the spacing collar 12 must be provided with a small notch or cutout 12a to clear the transmission line 3. Various circuits kdesigned for microwave operation are conveniently placed in the narrow `spacing between the two plates 1 and 10, and are effectively shielded from equipments that may be mounted on the base plate-side of the sheet 1.
The voltage standing wave ratio of one antenna of this invention is shown in Figure 7, the specilic dimensions of the cavity and of the probe, being shown in the figure. It will be noted that the voltage standing wave ratio is relatively low and uniform from about 340() to 8000 megacycles. It was found that when the area of the printed probe and its cavity were made larger, lower frequency characteristics were displayed. The radiation pattern in the horizontal and elevational planes are quite symmetrical about the medium line of the window as shown in Figure 8. In Figure 8, the radiation pattern in the H plane for 5000 megacycles is plotted by a solid line, and in the E plane radiation is plotted by a dashed line. The symmetry of the patterns about the medium line of the antenna window is attributed to the controllable dimensions and spacings of the printed probe on the board 1. Occasionally, a small spurious lobe is experienced.
Many modifications may be made in the specific structures herewith disclosed Without departing from the spirit of the invention as defined in the following claims.
What is claimed is:
l. An antenna assembly comprising an imperforate self supporting sheet of insulating material, said material having low high-frequency loss characteristics, a ground plate of extended area adhered to one side of said sheet., a window in said ground plate to ,expose .said sheet through the window, a metal box with one open side placed over the window and electrically joined substantially throughout the rim of the open side of said box to said plate to create a closed cavity .open only through the window of said insulating sheet; and a printed conductor on the other side of said sheet vterminating in Asaid window.
2. A slot antenna for microwaves comprising a printed circuit board, said board being a sheet of insulating material with an antenna probe of predetermined size and shape, and a lead-in conductor to the probe, outlined by metallic plating bonded directly to one side of said sheet; a ground plate bonded directly to the other side of said sheet underlying said lead-in conductor, said plate having a cut-out window opposite said probe; and a rigid sheet-metal cavity housing over said window and electrically and mechanically connected to said plate.
3. A unitary antenna assembly comprising a stiff selfsupporting sheet of insulating material, a ground plate adhered directly to one Asurface to said sheet, said plate being of extended area and having an opening therethrough; a printed transmission line bonded on the other surface of said sheet terminating opposite said window, and a housing overlying said window and joined mechanically to said sheet and connected electrically to said plate throughout the periphery of .said window, said housing being closed on all sides and having predetermined internal dimensions so as to funciton as a microwave cavity at lthe operating frequencies.
4. A slot microwave antenna combination comprising an extended sheet of insulating material of good high frequency characteristics, a ground plate laminated to one side of said sheet, said plate having a window of measured .size and shape; and a concaved metal housing with one open side, the opened side of said housing being placed over said window and the edges of the housing around the open side being connected electrically and mechanically to said ground plate.
-5. An antenna assembly comprising a sheet of insulating material, a ground plate adhered to one side of said sheet and a transmission line adhered to the other side vot said sheet, a -window in said ground plate, said transmission line terminating opposite said window; a concaved metal housing with a flat ange throughout the rim .of the housing, vSaid flange being bolted to said sheet to electrically connect said housing throughout said flange to said ground plate.
6. In combination a chassis of sheet metal adapted to contain electrical equipments, a window of measured size and shape cut through one chassis wall; a sheet of insulating material parallel to and spaced from said side wall, said sheet having a ground plate adhered to one surface and va :transmission line printed kon the other surface of said sheet, said ground plate having a window in substantial registry with the mentioned window in said chassis wall; a metal ring mechanically joining said wall and sheet vand surrounding the periphery of said windows, and a cavity housing overlying the ground plate window with the cavity walls in substantial alignment with the inner periphery of said ring.
7. In combination defined in claim 6, said transmission line on said sheet terminating within the boundries ot said windows.
8. In the combination defined in claim 6, said transsion line being disposed on said sheet facing said chassis wall vand yelectrically enclosed by said wall and said ground plate to electively electrically enclose Asaid line and isolate said line from equipments on the other side of said sheet.
References Cited in the tile of this patent UNITED STATES PATENTS 2,412,249 Brown Dec. `10, 1946 2,751,589 Cary June 19, 1956 FOREIGN PATENTS 1,061,149 France .,a Apr. 8, 1954