SD3-400

The SD3-400 is an ultra-high-performance TETRA Band Stacked Dipole Array specifically engineered for the 380–420 MHz frequency range. This heavy-duty antenna system consists of two vertically stacked folded dipoles that offer a unique balance of high gain and versatile radiation patterns. Designed for highly populated radio sites, repeaters, and paging systems, the SD3-400 ensures a constant 40 MHz bandwidth with low-noise performance, making it a reliable backbone for mission-critical UHF communication networks.

Design: Adaptive Radiation for Complex Sites

The SD3-400 provides unparalleled field flexibility, allowing operators to change the radiation pattern using common hand tools. When the two dipoles are arranged 180 degrees apart around the central mast, the array produces a 3 dBd omni-directional pattern for 360-degree coverage. Alternatively, by aligning both dipoles collinearly in one direction, a 6 dBd offset pattern is achieved, effectively doubling the signal strength toward a specific target sector. This "null-filling" capability ensures consistent connectivity in dense urban or varying topographical environments.

Construction: Industrial-Grade Durability

Built to withstand the most corrosive environments, the SD3-400 is constructed from 6063T6 architectural anodized aluminum. The radiating structure utilizes two folded dipoles fed in phase through a specialized center-fed phasing harness. To ensure structural integrity and weather resistance, all dipole ends and cable connections are sealed in high-grade epoxy. The phasing harness features molded power splitter joints, eliminating the need for adapters and reducing potential failure points while maintaining an airtight, waterproof N-Female termination.

Reliability: Tactical High-Power Protection

With a robust 500 Watt RF power handling capacity, the SD3-400 is designed for high-traffic infrastructure. Safety is integrated into the mechanical design, as the antenna operates at D.C. ground, providing a low-resistance discharge path to protect equipment against lightning strikes. All mounting hardware and fasteners are manufactured from Type 316 marine-grade stainless steel, ensuring the array remains secure even in wind speeds up to 200 Km/Hr. Its 1.6-meter length is optimized for easy handling and versatile mounting on towers or masts.

Technical Features

• Dual-Pattern Flexibility: Configurable for 3 dBd Omni-directional or 6 dBd Offset radiation patterns to suit specific site geographic needs.
• Optimized 380–420 MHz Bandwidth: Maintains consistent gain and low VSWR across the entire 40 MHz TETRA spectrum.
• Extreme 500W Power Capacity: Engineered for high-duty cycle transmissions in base station, repeater, and paging roles.
• Molded Phasing Harness: Integrated molded splitters minimize signal loss and provide superior waterproofing over traditional connectors.
• Architectural Aluminum Alloy: 6063T6 anodized aluminum construction offers ultra-corrosion resistance and long-term structural rigidity.
• 36-Degree Vertical Beamwidth: Provides a generous vertical aperture, ideal for coverage in hilly terrain or complex urban canyons.
• Integrated Lightning Protection: D.C. ground design shunts atmospheric discharges safely through the high-strength aluminum boom.
• Marine Grade 316 Stainless Steel: All hardware is corrosion-resistant, making it perfect for coastal and high-humidity deployments.
• Compact 1.6-Meter Profile: Easy to ship and install in either assembled or dismantled conditions based on logistical requirements.
• Low Noise Performance: Precision-fed design ensures high-fidelity signal distribution for multi-channel communication systems.

Stacked Dipole Array Configuration Guide: Optimizing the SD3-400

The SD3-400 is a versatile "pattern-shaping" antenna. Unlike fixed-radome collinear antennas, a stacked dipole array allows the installer to physically manipulate the orientation of the elements to match the specific geographic needs of the radio site.

1. The Omni-Directional Configuration (3 dBd Gain)

When the two dipoles are arranged in a 180-degree staggered pattern around the central mast, the antenna produces a balanced, circular radiation pattern.

• Best For: Centrally located base stations in urban areas or industrial campuses where users are scattered in all directions (360-degree coverage).
• The 3 dBd Advantage: By spreading the energy evenly, you ensure no "blind spots" exist within the local network. The vertical stacking of two elements provides a generous 36-degree vertical beamwidth, making it very forgiving for communicating with handhelds in hilly terrain or multi-story buildings.

2. The Offset/Directional Configuration (6 dBd Gain)

By aligning both dipoles collinearly (pointing them both in the same direction), the array transforms into a high-intensity directional antenna.

• Best For: Corridor coverage (highways or railways), coastal sites looking inland, or "edge-of-network" base stations that need to push signals deep into a specific sector.
• The 6 dBd Advantage: This configuration yields an additional 3 dB of gain over the omni pattern—effectively doubling the perceived signal strength in the favored direction. It creates a broad forward lobe that covers roughly 180 degrees horizontally while significantly suppressing radiation to the rear.

3. Center-Fed Phasing & Signal Integrity

The "brain" of the SD3-400 is its center-fed phasing harness. In many stacked arrays, signal delay can cause the beam to "tilt" away from the horizon.

• In-Phase Distribution: The SD3-400 harness ensures that the RF signal reaches both dipoles at the exact same microsecond. This forces the two individual waves to merge into a single, stable wave front that stays parallel to the ground.
• Molded Reliability: Because the power splitters are molded and sealed, there are no internal connectors to vibrate loose or allow moisture ingress. This is critical for preventing "static crashes" and signal degradation in harsh weather.

4. Mechanical Stability & Lightning Hardening

At 1.6 meters (5.2 feet) in length, the SD3-400 is a robust and manageable structure.

• Lightning Path: Every dipole is directly clamped to the high-strength 6063T6 aluminum mast. In the event of a strike, the mast acts as a lightning rod, shunting the current directly to the tower ground and bypassing the delicate phasing harness and base station electronics.
• Wind Shedding: The "open" design of a dipole array allows wind to pass through the structure with much less resistance than a solid fiberglass radome. This reduces the mechanical stress on the tower, which is critical for high-altitude or exposed coastal sites.

Installation & Optimization Checklist

• Mast Verticality: While a 36-degree beamwidth is relatively wide, keeping the mast vertical is still essential for uniform coverage. Use a spirit level during installation to ensure the 0-degree horizon is maintained.
• Side-Mount Offset: If mounting to the side of a large tower, ensure sufficient clearance. Mounting the dipoles too close to a wide steel tower will cause the metal to act as an unintended reflector, distorting your omni-directional pattern.
• Torque & Sealing: While the phasing harness is molded, the primary N-Female input must be hand-tightened and then sealed with a professional weatherproofing kit (butyl and vinyl tape) to prevent moisture wicking.
• Field Reconfiguration: If the site's requirements change (e.g., a new station opens nearby and you no longer need 360-degree coverage), you can simply loosen the U-bolts and re-align the dipoles into the 6 dBd Offset position without removing the mast from the tower.