Microstrip tee-fed slot antenna

#This invention relates to antennas and, more particularly, to slot antennas which are fed from a microstrip transmission line.

#Due to the high speed of modern aircraft and missiles, it is important that the size of protuberances from the surfaces of the craft be kept small, or possibly eliminated. Such craft usually have electronic equipment which requires antennas. Considerable work has been done toward reduction of the size of such antennas and mounting such antennas flush with the surface of the aircraft. Antennas employing a slot radiator are particularly useful for flush mounting as the slot is located flush with the skin of the craft and is backed by a cavity within the craft.

#These slot antennas comprise a slot from which electromagnetic energy is radiated, a cavity, and a stripline probe for applying energy to the antenna in the cavity. The slot opening itself is usually not an actual opening which will create drag but rather is a sheet of dielectric material flush with the hull. The dimensions of the radiating slot antennas are generally determined by bandwidth and operating frequency. In order to obtain good directivity and gain, it is often necessary to employ an array of these slot antennas. The use of an array of slot antennas also lends itself to beam steering by controlling the phasing of the energy applied to the probe behind each slot.

#The above mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

#FIG. 1 is an exploded perspective view of a prior art stripline slot antenna;

#FIG. 2 is a plan view of the front side of a microstrip tee-fed slot antenna configured according to the principles of this invention; and

#Referring now to FIGS. 2 and 3 of the drawings, there is illustrated thereby an embodiment of a microstrip transmission line tee-fed slot antenna. Although only one antenna element is shown, the principles of the invention can be used to provide arrays of antenna elements each configured similar to the antenna element of FIGS. 2 and 3. The antenna according to his invention is constructed using only a single printed circuit board. FIG. 2 shows the front side of the board and FIG. 3 shows the back side of the board. The board is typically made of a low-loss dielectric material of the type used in fabricating printed circuit boards.

#The front of the board, as shown in FIG. 2, has a layer of copper 30 over the entire surface thereof except for two rectangular areas 32 and 34 which comprise the slot for the slot antenna. The portion of the surface 36 intermediate the two rectangular areas 32 and 34 is the tee feed for the slot antenna. The tee feed is made of the same material as the rest of the board and comprises the same copper deposition. That is, this surface of the antenna is made by depositing copper on the dielectric board and etching away the rectangles 32 and 34. The ends of the tee feed are shorted to the rest of the board inherently by this construction process. Note that in the prior art embodiment of FIG. 1, it was necessary to use connecting pins or the like at the ends of the arms of the tee to provide shorting to the ground plane. Arranged about the slot, formed by the rectangular areas 32 and 34, are a plurality of shorting pins, rivets or plated-through holes 38 which define the periphery of the cavity for the antenna. If desired, the entire surface 30 need not have copper thereon but only the area defined by the pins 38. However, if the antenna is to be used as a single element, it is desirable to leave the copper cladding on the board. Also, for minimizing radar cross-section and proper operation of the antenna, it is preferred that the entire surface 30 have a copper layer thereon.

#The bottom of the board is shown in FIG. 3 and comprises a copper section 40 surrounding the shorting pins, rivets or plated-through holes 38 and providing one ground plane for the antenna. If desired, however, a larger surface of the backside of the antenna may have a copper deposition. However, it is only necessary that the areas forming the cavity be of copper. The copper surface 40 has a cut-out section 42 therein where copper is removed and in the middle of which is provided a microstrip transmission line 44 for feeding energy to the antenna. A pin 46 is provided at the top of the microstrip transmission line for providing a shorting connection between this portion of the microstrip element and the tee in the front of the antenna. Also, the pins 38 make the connections between the front and back sides of the antenna. In constructing this board, typically both sides of the board have copper depositions thereon and the copper is etched to provide the slot made up of rectangular sections 32, 34, the area 42 surrounding the microstrip feed 44 and any other areas of the antenna where copper is removed.