A streamlined metallic radome

Abstract

The results of research and development, fabrication, and measured transmission performance for a specsc streamlined metallic radome are contained in this paper. 'he measured results presented demonstrate that highquality radome transmission performance can be attained with a streamlined metallic radome.The conical metallic radome presented is 6 ft 4 in long and has a base diameter of 25.5 in. The specially designed resonant slotted surface of the metallic radome consists of 90 percent metal and, for frequencies within its operating band, the radome permits transmission with any signal polarization over a wide range of scan angles. At its 8.90 GHz resonant frequency the metallic radome introduces less than O S dB signal loss and less than 2 mrad boresight error. This radome has been purposely designed for operation over a narrow frequency band. Over a 200 MHz band, measured insertion loss and boresight error values of 1 dB and 6 mrad, respectively, are attained. I. INTRODUCTIOSThe study of metallic radomes has received increased emphasis in recent years. The increased interest in metallic radomes is largely due t.0 their potential in overcoming the mechanical and electrical limitat.ions of convent.iona1 dielectric radomes in high-speed allweather aircraft applications. -4 metallic radome offers t.he potential for greater overall mechanical strength and enhanced resistance to environmental stresses caused by rain, hail, dust, and lighhing, compared to conventional dielectric or ceramic radomes. The signal reception prcblem caused by static buildup and subsequent. discharge to the airframe, encountered wit.h dielectric radomes, could be eliminated by use of a metallic radome. A metallic radome could also better distribute frictionally induced heating arising from highspeed flight. Finally, a metallic radome could conceivably be made lighter in weight t,han a dielectric radome.The metallic radome concept also represents a useful alternative approach in overcoming the inherent. electrical performance limit.& t.ions of dielectric radomes. Most dielectric radomes are designed with a thickness of about, a half-wavelengt.h, to minimize impedance mismat.ch (i.e., reflection) losses. The opt,imum t,hickness, however depends on the incidence angle, polarization, and frequency of the signal. Therefore, when the beam of the antenna enclosed by the radome is scanned, the radome introduces varying amounts of insertion loss and phase in the t,ransmitted or received signals. The varying insertion phase is particularly troublesome, since it causes a change in the beam direction; this may in t.urn cause a significant deterioration in t.he performance of a tracking radar.The metallic radome presented in the following sections is a laboratory test model, developed and construct,ed to demonstrate that satisfactory t.ransmission performance can be attained with a realist.ically &emlined radome shape. The novel slotted periodic surface design, employed as the radome surface, is shown to provide nearly ideal transmission properties for s...

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