US 3701161 A
A multiple radiator microwave antenna comprising four separate discretely tuned cavity-backed slot antennas for providing a unidirectional radiated RF energy field in a narrow beam along a common axis at four discrete frequencies.
Claims available in
Description (OCR text may contain errors)
United States Patent Gregory 1 Oct. 24, 1972  FOUR BAND SLOT ANTENNA  References Cited  Inventor: Benjamin F. Gregory, China Lake, UNITED STATES PATENTS Calif. 3,296,616 1/1967 K k 1 Asslsneer TraklMicrowave Corporation, 3,312,976 4/1967 0:50;; 313%;
pa F a.  Filed; May 11 7 Primary Examiner -Eli Lieberman  Appl. No: 36,160 Attorney-R. S. Sciascla and Roy Miller This application goes under Rule 47(b).
 ABSTRACT A multiple radiator microwave antenna comprising four separate discretely tuned cavity-backed slot antennas for providing a unidirectional radiated RF energy field in a narrow beam along a common axis at four discrete frequencies.
6 Claims, 4 Drawing Figures PATENTEDHBI 24 m2 INVENTOR.
MELLE'R ATTORNEY BENJAMIN F GREGORY BY FIG. 3
FOUR BAND SLOT ANTENNA BACKGROUND OF THE INVENTION The present invention is directed to the problem of providing a small, lightweight, flashlight I type of microwave radiator capable of being handheld and projecting beams of microwave energy in the same manner as the dual frequency cavity back slot antenna set forth in US. Pat. No. 3,312,976.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view of the antenna with the protective cover removed;
FIG. 2 is a planned view of the antenna inner body;
FIG. 3 is a cross section of the antenna structure with the protective cover removed taken along line 3 3 of FIG. 1; and
FIG. 4 is a section taken on lines 4 4 of FIG. 1 illustrating the connection used to drive the cavity for the fourth band.
DESCRIPTION OF THE PREFERRED EMBODIMENT The antenna structure comprises a circular front plate of electrically conductive material having narrow radiating slots 11, 12, 13 and 14, therethrough. The radiating length of the individual slots is made to be approximately AM at the radiated frequency.
In the case of the band 3 antenna, slot 13, the physical length of the slot is insufiicient to tune to A wavelength at the frequency of interest. Therefore the curved slots at opposite ends of the horizontal slot add the required reactants to tune the slot.
In the case of the band 4 antenna, slot 14, the curved slots, formed by inner body 15 and an adjacent cylindrical wall 16 of the antenna housing, add additional reactance in combination with the horizontal slot 14 to tune the slot to the frequency of interest.
The front plate 10 is mounted on and supported by a cylindrical metal inner body 15, FIG. 3, having cut into the front face thereof three substantially semicylindrical cavities 18, 19 and 20. A plan view of the inner body 15 is shown in FIG. 2. Slot 11 overlies and opens into cavity 18 along the diameter thereof; slot 12 overlies and opens into cavity 19 along the diameter thereof and slot 13 overlies and opens into the cavity 20 along its diameter. The individual cavities are separated from each other by conductive wall portions of the inner body 15. Slot 14 divides the inner body 15 into two sectrons.
Coaxial conductors 21, 22 and 23 having the inner conductor soldered to front plate 10 are used to drive the respective cavities 18, 19 and 20. The coaxial cables are introduced through apertures in the rear wall 34 of the antenna body.
The back cavity for the band 4 antenna is formed by the volume within the inner housing to the rear of the antenna inner body 15 and the rear member 34. Microwave energy is introduced into the band 4 cavity by means of coaxial conductor 24 having an inner and outer portion, the inner portion of which is attached to the rear surface of the antenna inner body 15 as at 25 (FIG. 4). Impedance matching of the antenna to the 50 ohm coaxial transmission line 24 is accomplished by selecting a point of feed which provides the required impedance transformation from the high impedance of the horizontal SIOI 14. The coaxial cables 21, 22 and 23 which span the band 4 cavity, add reactance to the back cavity which is compensated for by a slight change in the point of feed.
The band 4 antenna, as previously stated, requires additional tuning to approximate 56 wavelength at the radiated frequency. This is further aided by means of the capacitor 26 attached to the rear wall of the inner body portion 15 wherein the parallel flanges of the capacitor brackets 26 and the parallel faces of the horizontal slot in the inner body constitute the capacitor. This assists in tuning the slot to a lower resonant frequency than otherwise possible for the existing physical length of the slot.
Impedance matching of the high impedance antenna 13, band 3, is accomplished by selecting a point of feed for the required transformation to the 50 ohm coaxial transmission line. The depth of the cavity 20 contributes to the location of the proper point of feed.
The band 1 and 2 antennas, i.e., slots 11 and 12 are equal in length to wavelength at the frequency of interest without the aid of curved slots. The coaxial transmission lines 21 and 22 are terminated at a point of feed in the front plate 10 matching the antenna to the 50 ohm impedance of the respective lines.
As was the case the dual frequency cavity back slot antenna of the US. Pat No. 3,312,976, the slots 1 1, 12, 13 and 14 opening into their respective cavities are protected from the intrusion of moisture or other foreign matter which could affect the tuning of the an tenna by dielectric cover plate (not shown) which is adhered to the face of the conductive plate 10 by any suitable means, such as a resin cement.
The design criteria relative to the location of the slots, depth of cavities, length of slots, bill of materials, etc., are not gone into detail in that essentially the same criteria as applied to the design of US. Pat. No. 3,312,976 apply herein.
What is claimed is:
1. A multiple radiator microwave antenna comprismg;
a cylindrical body portion having front and rear members temiinating said body portion;
an electrically conductive member mounted within said body portion abutting said front member and spaced from said rear member;
at least one substantially semicylindrical cavity formed within said conductive member;
a radiating slot in said front member opening into said at least one cavity along the diameter of the cavity;
a substantially cylindrical microwave cavity formed by the volume between said rear member and said electrically conductive member;
another radiating slot in said front member opening into said cylindrical microwave cavity such that a portion of the electrically conductive body is 2. A multiple radiator microwave antenna as set forth in claim 1 and further including;
a second substantially semicylindrical cavity formed within said conductive member;
a second radiating slot in said front member opening into the second cavity along the diameter of the second cavity; and
additional means for introducing electromagnetic energy into the second cavity such that the second cavity is resonant at a particular frequency and radiates energy from the second slot in a narrow beam normal to said front member.
3. A multiple radiator microwave antenna as set forth in claim 2 and further including;
a third substantially semicylindrical cavity formed within said conductive member;
a third radiating slot in said front member opening into the third cavity along the diameter of the third cavity; and
further means for introducing RF electromagnetic energy into the third cavity such that the third cavity is resonant at a particular frequency and radiates energy from the third slot in a narrow beam normal to said front member. 4. A multiple radiator microwave antenna as set forth in claim 1 wherein;
said another radiating slot in said front member opening into said cylindrical microwave cavity divides said electrically conductive member into two physically separate portions. 5. A multiple radiator microwave antenna as set forth in claim 1 wherein;
said another radiating slot in said front member opening into said cylindrical microwave cavity is equal in length to the diameter of said front member and wherein said another radiating slot continues around a portion of said front member at either end of the diameter of the front member. 6. A multiple radiator microwave antenna as set forth in claim 5 wherein;
each of the radiating slots is of the length substantially equal to one half wavelength at the frequency to be radiated and further including; adjustable loading means in said cylindrical cavity for loading said cavity.