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I’m building a log-periodic dipole array (LPDA) for 100–1000 MHz that won’t be printed on a PCB. What are the optimal substrate or support materials for the boom and elements to maximize durability and electrical performance?

This is for an outdoor, mast-mounted field measurement system. I'm moving away from a PCB-based design due to size and cost. I'll be using metal tubes for the dipoles and a central metal boom. My question focuses on the insulating supports that separate the dipoles from the boom. What materials offer the best trade-off between RF transparency (minimal dielectric loss), UV/weather resistance, and mechanical strength? I'm considering fiberglass rods, PVC, Delrin (POM), or even using isolated metal-to-metal contacts with specific insulating washers.

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By Sumit Batra Answered 1 year ago

For a robust outdoor LPDA, the guiding principle is to minimize dielectric material near the high-impedance, current-sensitive feed points. From my field deployments, the optimal setup is a metal boom (e.g., aluminum square tube) with the dipole elements mounted via insulating brackets made of a low-loss, UV-stable plastic. Glass-filled Polycarbonate or UV-stabilized Delrin (POM) are excellent choices for brackets; they have good structural integrity and low tan δ. Avoid PVC—it becomes lossy above a few hundred MHz and degrades in sunlight. For the very best performance, use a "clamped" design where metal element halves are bolted directly to the boom but are electrically isolated by a thin PTFE (Teflon) washer; this minimizes parasitic capacitance. The boom itself is a passive conductor; its main effect is on the phase velocity, which is already factored into the LPDA design equations.

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