At
Randtron Antenna Systems, we have the technology in
place to design and develop slotted array antennas for custom
requirements. Slotted array antenna development has ranged
from compact resonant arrays typically used for airborne fire
control applications to large scanning non-resonant arrays
used for radar applications. Slotted array antennas provide
the highest degree of control and beam shape and sidelobe
levels. Resonant arrays excel in efficiency and beam positioning
stability - while non-resonant arrays can be designed for
beam scanning and higher bandwidths. Because these antennas
are constructed in waveguide, their beamshape and can be accurately
realized via specialized computer design software and CAD/CAM
construction. Our engineers have developed all the techniques
required to design slot array antennas. This list includes
characterization of slot self-admittance, compensation for
mutual coupling, calculation of slot dimensions needed to
produce the required active admittances and the synthesis
of antenna patterns. Our earlier designs focused on the resonant
arrays, including a 144-slot array (shown above) constructed
of 12 half-height resonant sections, each containing 12 broadwall
shunt slots. The feedline is a half-height resonant section,
which couples to each radiating branch via inclined shunt
slots in the common walls. The array was constructed by machining
the unit in several integral sections joined by dip brazing.
CNC machining is used to provide a tolerance of 0.002 inch
or better. The unit achieved the 36 dB design sidelobe level
within 1.5 dB, demonstrating the ability to produce an accurate
design. Some later designs focused on non-resonant slotted
arrays. One example is a frequency scanned planar traveling
wave array capable of scanning in two dimensions (the second
dimension is phase shift scanned). This antenna employs 128
slots and requires low sidelobes only on one side of the main
beam. The sidelobes on the other side are designed for uniform
illumination to achieve maximum gain. Testing of the array
was accomplished using near field probing and was verified
by far zone radiation measurements. The resultant sidelobe
levels and gain were close to the predictions. We also designed,
fabricated and characterized two large traveling wave arrays:
a transmit unit and a receive unit. Both units were approximately
8' x 6' with 20° frequency scanning in azimuth and 30° phase
scanning in elevation. The precise control over approximately
10,000 slots, multiple waveguide runs and precise aperture
flatness combined to produce the required low sidelobe level
requirement.
