Phased array antenna systems for use in radar applications are generally well-known in the art and include, among other components, a means for distributing a microwave signal to be transmitted, some switching means to control the phase of the distributed signal, and some electrical means to couple the phase shifted signals to one or more remote signal radiating locations. Additionally, appropriate signal radiating means must be selected for these locations for projecting the phase shifted signals into space and in some predetermined phase relationship with like signals projected from adjacent radiators which make up the antenna. The phase of the signals received at a plurality of radiators which form a particular antenna must be shifted by predetermined amounts in order to establish a desired composite radiating wavefront which is projected into space from the complete antenna assembly.
There are several techniques for shifting the phase of incoming microwave signals prior to being transmitted from a microwave antenna, as described above, and among these include diode phase shifters which are connected to microstrip metallization patterns on one side of an insulating substrate. The substrate normally includes a ground plane on the other side thereof, and selected phase shift (bit) metallization patterns form the microstrip circuitry which extends between input and output terminals on one side of the substrate. Microwave switching diodes, such as PIN diodes, may be connected to selected terminals of the phase shift microstrip circuitry and there receive DC control signals which bias the PIN diodes to conduction and non-conduction, respectively, to thereby introduce varying degrees of phase shift into the microwave signals being processed. CL PRIOR ART
In order to couple the phase shifted output signals from an output terminal or terminals of the substrate to appropriate microwave radiating means, it was necessary in the prior art to provide some suitable coupling means between the microstrip phase shifting circuitry and the chosen radiating element. Such coupling had to be both physically and electrically compatible with both the phase shifter and radiator components. For example, in order to electrically couple phase shift microstrip circuitry to a waveguide type of radiating element, one prior approach has been to use a coaxial connection between these two components. Using this approach, the inner coaxial conductor of the coax is connected to the phase shift microstrip circuitry on one side of the substrate and the outer coaxial conductor of the coax is connected to the ground plane on the other side of the substrate. Further, the outer wall of the radiating waveguide member is normally coupled to the above outer coaxial conductor, and the above inner coaxial conductor is connected through a central opening in the waveguide in such a manner as to set up an electromagnetic field which can then be propagated down the length of the waveguide. This type of coaxial interconnect is described, for example, in U.S. Pat. No. 3,686,624 to Napoli et al., and requires separate and distinct spaces for the phase shifting and signal radiating components of the module.
Another prior art technique for coupling phase shifted microwave signals from the output of a phase shifting network to a radiating element is described in U.S. Pat. No. 3,500,428 to C. C. Allen. In this patent, the microwave phase shifting circuitry is deposited as a microstrip on one side of an insulating substrate, and a waveguide type radiator is securely bonded to the other side of the insulating substrate. The rectangular waveguide in this patent is coupled to the above phase shifting circuitry by means of a vertical pin extending through the substrate. This configuration is also typical of the prior art phase shifting and radiating modules which require separate and distinct spaces (layers) of substantial thickness for accomodating these two discrete components which provide these two signal processing functions.
The module configuration in the above Allen patent is comprised of a three-dimensional multilayered structure, and the waveguide member therein is substantially larger in thickness than that of the circuit board (substrate) for the phase shifter. But in addition to the latter space requirements, the completed antenna assembly in FIG. 6 of Allen is configured such that the thickness of his outer case must be at least as great as one dimension of the substrate for the phase shifter. This approach imposes a serious design limitation on large antenna systems where space and weight savings are critical factors.
Thus, in all of the above and other prior art phase shifter and radiator modules known to us, the phase shifting element of the module is comprised of one physical unit of one discrete thickness and the radiating element is comprised of another separate physical unit of another discrete thickness. And as seen in the above Allen patent, this latter thickness is frequently more than twice the thickness dimension of the phase shifting module per se. Therefore, when using these prior art structures, not only must substantial space be allowed for mounting a large number of these units or modules in an antenna assembly, but the cost and weight of these individual units must also be accounted for where large numbers of these modules are used, for example, in large shipboard antennae. In some such antennae, literally thousands of these phase shifting and radiating elements are required for a single composite phased array antenna system.