As is known in the art, a so-called patch antenna element (also referred to as “a patch element” or more simply “a patch”) is a basic building block a number of different types of phased array antenna including so-called panel phased arrays (or panel arrays) such as the types described in U.S. Pat. Nos. 7,348,932; 7,671,696; and 8,279,131, all of which are assigned to the assignee of the present application. The patch element is integrated within a panel array to allow for the use of low cost printed wiring board (PWB) processes in the manufacture of the panel array.
Referring now to FIG. 1, a conventional patch element 2 and feed circuit 3 are coupled to provide a conventional patch radiator 4. The patch element is provided from a conductor disposed on a first surface of a substrate. A slot 5 is etched or otherwise provided in the conductor. The feed circuit 4 is provided from a single feed line 7 disposed on a second opposite surface of the substrate. A first end of the feed line corresponds to an antenna feed port 4A and a second end of the feed line 4B is coupled to a ground plane through a conductive via. An open ended stub 8 is coupled to feed line 7 as is generally known. Patch radiator 4 is responsive to radio frequency (RF) signals having a single linear polarization.
In operation, an RF signal provided to the antenna feed port 4A is coupled via feed line 7 to the open ended stub 8 thereby illuminating slot 5, which in turn excites the patch 2. Similarly, signals provided to patch conductor 2 illuminate the slot 5 and are coupled via the open ended stub 8 and feed line 7 to the feed line antenna feed port 4A. Thus, the patch radiator 4 operates for both transmitting and receiving RF signals.
As mentioned above, however, patch radiator 4 can be used only for a single polarization. This is due to the topology of the patch element 2 and feed circuit 3. To support dual and/or circular polarization, a more complicated geometry is required as illustrated in FIG. 2.
Referring now to FIG. 2, to support dual and/or circular polarization in one type of conventional patch radiator, a feed circuit comprising four feed lines (and thus four antenna feed ports) is required. Essentially, the single stub described above in conjunction with FIG. 1 is split into two open ended stubs (e.g. one to excite vertically polarized RF signals and one to excite horizontally polarized RF signals). To support dual linear polarization, both stubs (for each excitation) are driven in phase. This is conventionally accomplished via a microwave power divider circuit (not shown in FIG. 2). Simple geometry dictates the need four feeds. The single polarization example (FIG. 1) places the open ended stub along the center line. However, it is not possible to place two perpendicular open ended stubs, each aligned to the center line without them being shorted to each other. Therefore two open ended stubs are required for each polarization
Circular polarization may be obtained by introducing a ninety (90) degree phase shift between signals provided to (or received from) the horizontal and vertical stubs. Such a 90 degree phase shift can be accomplished using a ninety (90) degree hybrid coupler (not shown in FIG. 2) or by controlling the phases independently in control circuitry (not shown in FIG. 2). Therefore, to extend the operation of a patch radiator from a single linear polarization to operation with dual linear or circular polarization requires the addition of much circuitry (e.g. a power divider or hybrid coupler) to the feed circuit.
In a phased array antenna in which space in limited, it is difficult to fit such additional circuitry (e.g. additional power divider or hybrid coupler circuitry) within a so-called unit cell which includes an antenna element (e.g. one or more patch elements) and the associated feed circuitry. It would, therefore, be desirable to provide a patch radiator operable for use with dual linear or circular polarization RF signals and which is compact enough for use in phased array antennas.