J. Kelley L. Leopold Tracking & Communications Development Division IV-C-3 SUBARRAY The antenna array is made up of subarrays and each subarray contains elements which are the radiating portions of the antenna structure associated with the microwave generators. It is not necessary that each element be fabricated and assembled as a separate entity, but weight estimates in this report are based upon individual element design and assembly. The subarray reference configuration is a resonant slotted waveguide array where the guides are parallel fed by a "feedguide" which couples energy from the microwave generator into the slotted guides. The radiating surface is rectangular, deviating from a square to facilitate the buildup of multiple subarrays from identical elements for a given power density. The reference configuration maintains a constant output power level from the microwave generator and accomplishes power density variation by appropriate sizing of the element area. a. RATIONALE The function of the radiating elements 1s to couple RF power from the microwave generator into the radiated beam with a minimum power loss. This goal is approached by minimizing I2R losses in the guides, maintaining a uniform amplitude and phase distribution at the radiating slots and providing a radiating surface that is essentially flat and perpendicular to the target line of sight. The goal of uniform amplitude extends to the subarray level and, although amplitude taper is used for beam shaping, a controlled amplitude signal is required for the entire antenna. The net result of these prerequisites: controlled amplitude, minimum feed losses and minimum nonradiatinq area, leads to the selection of a slotted waveguide planar array (as has been the case for previous studies of the SPS A resonant array, as opposed to a traveling wave array, can best fit these requirements, when coupled with the high power (50 kW), high gain (50dB) tube. The tubes can be excited in parallel using relatively low power levels of 2-3 watts and the entire power output fed to the radiating array. The resonant array couples all power, with the exception of I2R losses, through the radiating slots into the RF beam and no power is dumped into a load (as would be the case for a traveling wave array). b. SHAPE Theoretically, the preferred geometry for the radiating surface of each element is a square since this shape minimizes the linear dimensions which in turn tend to reduce the surface error losses. The square configuration also minimizes the transmission line length in the guides, which also minimizes L2R losses. However, neither of these effects is drastically changed by small variations from a square to a rectangular geometry. For example, the minimum transmission line length for a lX4m rectangle is only 5/4 that for a 2X2m square element.
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