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AFC's dielectric radomes have several advantages over other radome type offerings. For any radome type, panel edges are reinforced into flanges for adjacent panel assembly. When the radome panel flange framework is a dielectric material, the radome is called a Dielectric Space Frame (DSF). In contrast, when the panel framework is metal, the radome is called a Metal Space Frame (MSF) radome. DSF radome walls may be constructed as a thin membrane, composite laminate or as multi-layer hybrid sandwich with internal foam core. For the thin membrane wall radome, the radome panel flange framework has dimensions capable of supporting the environmental wind loads. Often a two or three layer sandwich wall is used where thermal insulation or where high frequency and low transmission loss requirements prevail.
Radome transmission loss is composed of two major loss contributions. The first contribution and typically the smallest is the ordinary insertion loss of a signal passing through the radome wall. The second loss contribution comes from signals scattering off the radome panel flange framework. For most frequency bands, framework scattering loss is several times larger than the radome wall insertion loss. When demanding RF transmission loss specifications and structural environmental (wind) loads compete with requirements, DSF radome RF performance may be optimized by a process called impedance matching. Adjacent DSF panel flanges form a dielectric framework, which behave as capacitive RF loads. Just as the microwave engineer adds inductive circuit elements to impedance match a capacitive circuit load over a required bandwidth, so does the radome engineer. By embedding just the right amount of inductive circuit elements into the dielectric flange framework, scattering loss is "tuned out" significantly improving transmission loss. In contrast, the metal space radome framework blocks the RF energy. You must take what you get without any method or means of improvement. For dielectric radomes, on the other hand, it is the wealth of impedance matching compensation alternatives, from no tuning a pure dielectric framework, to a controlled impedance match using electrical circuit elements, to even creating a synthetic inductive "metal" framework, that the DSF radome outshines any substitute. With impedance matching, a dielectric radome is tuned to customer requirements without compromise. AFC has performed considerable broadband impedance matching work over the 0.1 to 44 GHz frequency range.
AFC's DSF panels are a molded one piece process forming a rigid panel structure. Even for thin DSF membrane panels, for example, they are pre-stressed to form a rigid panel. The pre-stress process eliminates wavy, flapping panel membranes and eliminates the need for pressurization to reduce oil-canning, sound/vibration noise, microphonics and fatigue failure characteristic of metal space frame (MSF) radomes. In contrast, without pressurization, metal space frame radomes fail to meet wind load speed requirements. With a need for pressurization, a metal space frame radome relies on prime power to energize the blower equipment to survive maximum wind loads.
DSF radome panels have never experienced a wall failure. In contrast to metal space frame radomes, no sound deadening pressurization blowers are needed. For unattended radome sites, pressurization blowers add another failure mechanism---thereby reducing up-time operational performance and making the radome survival dependent on prime power outages.
Dielectric radome panels have no metal beams in their framework, which corrode in harsh or salt environments. Minimal maintenance is required for dielectric radome panels. In contrast, the metal space frame (MSF) structural framework members experience corrosion, which washes onto the radome surface, adjacent panels members and adjoining framework beam structure. Not only is corrosion a maintenance problem, but from an RF point of view, corrosion creates a continuous surface of numerous semiconductor diode mixers. These mixers generate intermod interfering signal products in the presence of high power, multi-frequency/carriers, characteristic of modern satellite and radar communications systems. In contrast, AFC's dielectric radomes are intermod free.
Dielectric radomes have no dissimilar metal corrosion problem. Dissimilar metals (for example, Aluminum and Steel) create corrosion in the presence of water moisture. In contrast to dielectric radomes, metal space frame radomes use dissimilar metals at every bolt that joins the metal framework. In addition, since metal space frame radomes require a metal base ring for structural support, a dissimilar metal problem exists between the base framework panels and the base ring. Dissimilar metal corrosion is another source of diode mixers. These mixers further generate intermod interfering signal products in the presence of high power, multi-frequency/carriers. In contrast, AFC's dielectric radomes are intermod free.
AFC introduced the use of corner nodal bolt technology to transfer corner loads to the rest of the radome panels. This creative solution eliminates the need for corner hub load distribution caps common to metal space frame radomes. Nodal bolt technology significantly reduces blockage transmission loss. In contrast, corner hub caps increase antenna blockage and increase radome transmission loss and noise temperature.
When service or antenna update schedules demand radome access for large antenna part removal or entry, DSF panel members are easily removed, reinserted and resealed.
With the DSF panel flanges internal to the radome, dielectric space frame hardware are not exposed to the environment.
AFC has a optional proprietary super-hydrophobic coating, Hydrolam 2000, which meets the demands of real systems. This coating forms a bond to the radome surface, is abrasion resistant and may be reapplied in the field, should the radome surface be damaged. AFC's hydrophobic coating retains its vitality and remains bonded to the surface years longer than any commercial surface preparation.
AFC's thin skin DSF panel membrane is a composite wall with the outer surface layer composed of Tedlar, a material which lasts 20 years. AFC's unique proprietary pre-stress process simultaneously solves the Tedlar pealing problem, characteristic of bonded composites with dissimilar thermal expansion coefficients.
In order to simplify field installation, DSF radome panel sides are letter coded at the factory, "A" through "Z". Since the radome has several different panel types, the letter coding enables installation personnel to assemble like panel code letter edges without relying on misplaced assembly instructions.
For most normal site installations, little to no coordination is required between the radome/installation team and the foundation site preparation group. The reason is that DSF radomes do not require a base ring (compression ring) or precast foundation anchor bolts. (In contrast to metal space frame procurements, no base ring disagreements need take place over whether the base ring is part of the radome or site civil works price estimates.) Now common practice, AFC has pioneered and field tested for the U.S Army and USAF, a radome base panel assembly technique with the radome foundation which eliminates the need for precision foundation bolt placement. Wedge anchor bolts are bored into the foundation at installation by the installation field crew. In contrast to a metal space frame radome, no foundation survey, template preparation and accurate anchor bolt insertion into the wet foundation or compression base ring interface need be scheduled or timing anticipated. Thus foundation construction and radome installation become independent activities----removing the usual need for precise coordination. For example, the DSF radome wedge anchor bolt technique has been used with 80ft (24.4m) diameter radome 200 mph wind speed location sites. Indeed, removing the need for accurate and meticulous foundation and site coordination assures a timely and successful installation, even under the most trying of circumstances.
AFC manufactures, markets and sells worldwide satellite dish antennas, conical horn antennas, radomes, antenna feeds, microwave and waveguide components, ultra low loss waveguide transmission line Tallguide ®, and shelters. Our customers serve the broadcast, communications, radar, weather and cable industry, defense, government, and government agencies worldwide. AFC's quality control manufacturing standards are certified under ISO 9001 : 2008.
A complete Internet WWW AFC site index may be found in Antennas for Communications (AFC) Home Page Document Summary List. Additional radome information is contained in the Dielectric Space Frame Data Sheet and AFC's Radome Capability Brochure.
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