Other design approaches
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Because of some inherent difficulties in fabricating radants for certain special mechanical, environmental and electrical requirements—and the increasing interest in such systems, alternate designs were conceived. Extended development effort led to experimental prototypes shown in Fig. 9-11.
The silicone-fiberglass radome-antenna in Fig. 9 consists of a solid outer structure and a one-piece skeleton frame made of the same material. This frame is completely copper plated and includes four dielectric-loaded slot arrays. When the two sections are mated and properly secured with silicone resin, the over-all thickness of the radome is only 1/4-in. The assembly is sturdy and satisfies all mechanical requirements. This method of construction simplifies antenna design and fabrication; it also provides for improved antenna system performance.
The radant of Fig. 10 was intended for short-time exposure to 2000-3000° F environments. The radome can be made from selected heat-shield materials. The three cavity antennas shown are copper-plated monolithic-dielectric structures. The basic antenna is a dielectric-loaded guide with a 50-ohm coaxial input which feeds a tee-bar coaxial-to-waveguide transition. Energy radiates through a thick window (approx. 1/2-in.) which is a party of the cavity. The dielectric is fused silica or other material compatible with the heat shield and the antenna. These antennas are characterized by their unusually small size and good efficiency in L and S bands.
An even smaller antenna that can be easily incorporated in high-temperature radomes is the copper-plated, dielectric-loaded ridge-guide antenna, also shown in Fig. 10. When used as illustrated, the array (0.625 x 1.25 x 10.0-in.) has a gain of approximately 5 dB at L band.
Figure 11 shows use of strip-line and dielectric-loaded slot arrays based on thing, copper-clad dielectric-laminates or printed-circuit boards.
Antenna systems designed as an integral part of a radome, fully utilizing the dielectric radome structure, clearly are feasible. The exploitation of dielectric-loaded waveguide techniques and the electroless copper-plating are instrumental to good performance and low-cost manufacture. Electrical performance is comparable to conventional systems and design techniques described should find widespread use in aircraft, spacecraft, and missile systems. Some of the more obvious advantages realized are:
- The incorporation of the antenna into the radome requires almost no additional space.
- The need for antennas inside the radome is eliminated.
- The design complexity is reduced.
- The rf leakage within the structure is minimized since the interior is completely copper-plated.
- “Slotted Antenna Arrays Can Be Smaller,” Howard S. Jones, Jr., Electronic Design, May 10, 1965.
- “Dielectric Loaded Waveguide Slot Arrays,” Howard S. Jones, Jr., TR-1269, Harry Diamond Laboratories, Jan. 22, 1965.
- “Radiating Slots on a Dielectric-Filled Waveguide,” Bernard R. Cheo, and Louis Pelish, TR400-118, Contract DA-49-186-AMC-183d, New York University, School of Engineering and Science, Aug. 1. 1965.
- “Plated Dielectric Waveguide Components,” Howard S. Jones, Jr., and R.J. Norris, MicroWaves, July, 1965.
- “Electroless Plating,” Product Engineering, p. 221, May, 1953.