Cubical Quad Antenna Calculator

The Cubical Quad Antenna Calculator determines individual loop perimeters, side lengths, element spacing, and estimated directional gain for 2-element and 3-element Cubical Quad directional antennas. Highly favored in HF/VHF amateur radio DXing, quad antennas deliver higher gain per boom length and lower rain static noise than equivalent Yagi-Uda arrays.

Enter Frequency, Number of Elements (2 or 3), Velocity Factor exactly in the units shown by this cubical quad antenna. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.

• Frequency — use MHz.
• Number of Elements (2 or 3).
• Velocity Factor.

The results describe the calculated cubical quad antenna values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.

The Cubical Quad Antenna uses λ = 300/f, Driven = 1λ, Reflector = 1.05λ, Director = 0.95λ. Supply Frequency (MHz), Number of Elements (2 or 3), Velocity Factor in the displayed units, then use the calculated values as the first engineering target for this specific antenna types design or analysis.

A Cubical Quad is a directional array of closed full-wave ($1lambda$) square wire loops mounted on non-conductive spreaders (typically fiberglass or bamboo). The driven element perimeter is cut to approximately $1.0\lambda$ ($L_d = 305 / f_{\text{MHz}}\text{ m}$), the reflector is approximately $5\%$ larger ($1.05\lambda$), and the director is $5\%$ smaller ($0.95\lambda$). Because its closed-loop geometry lacks open element tips, it captures less electrostatic precipitation noise and exhibits a higher aperture area compared to linear dipoles.

Construct loop elements using heavy enamel-coated copper wire supported by fiberglass spreaders on a central metallic or non-metallic boom. Element spacing between $0.15\lambda$ and $0.20\lambda$ yields an optimal balance between maximum front-to-back (F/B) rejection ($>20\text{ dB}$) and broad $50\;\Omega$ SWR bandwidth. Feed the driven loop at the bottom side for horizontal polarization, or at a vertical side for vertical polarization. Use a $1:1$ current choke balun at the feedpoint to prevent coaxial shield radiation.