How Does a Yagi-Uda Antenna Work? | Beam Antenna Design & Function Explained

NEC (Numerical Electromagnetics Code) software simulates antenna performance. For a half-wave dipole at 300 MHz (λ = 1m, L = 0.5m): (1) Define geometry: two segments of 0.25m each along the Z-axis, (2) Set frequency: 300 MHz, (3) Define material: perfect conductor or aluminum pipe (diameter 8mm), (4) Add generator at feed point, (5) Set environment: free space. Results: Input impedance ≈ 73 + j45 Ω, Gain ≈ 2.15 dBi, Pattern: omnidirectional in horizontal plane, nulls at ±90° from antenna axis. Shortening the antenna slightly (to 0.245m) reduces reactance to near zero, improving impedance matching.

Antenna modeling software like EZNEC uses the NEC (Numerical Electromagnetic Code) algorithm, originally developed at Lawrence Livermore Laboratories. NEC2 is free while newer versions require payment. The software breaks the antenna wire into segments (at least 10 per half-wavelength) and simulates electromagnetic behavior. Modeling requires specifying physical dimensions, wire type (copper/aluminum), height above ground, and ground conditions (free space, perfect ground, or typical earth). The software predicts radiation patterns, gain, front-to-back ratio, beam width, takeoff angle, feedpoint impedance, and SWR before physical construction.

EZNEC is a professional antenna design software that enables accurate calculation of antenna parameters including radiation patterns, impedance, and SWR across frequencies. The software can model various antenna types including low-noise receiving antennas like the Fedor Olha tri-ann (with 670mm wire segments and 950 ohm load) and directional antennas like the Beveridge antenna (with 182m wire length and 400 ohm termination). Key features include 3D pattern visualization, automatic element length optimization, and the ability to model transmission lines with excitation sources. The software handles complex calculations involving mutual coupling between antenna elements, making it essential for designing and analyzing both passive and active antenna systems.

Antenna modeling programs like EZNEC use numerical electromagnetic code (NEC2) to simulate antenna performance by describing antennas as collections of straight wires, enabling analysis of patterns, gain, impedance, and interactions with other conductors; however, the accuracy of results depends entirely on how well the model represents the real antenna, as computers execute instructions literally without understanding intent.

This tutorial demonstrates how to design and optimize a 16x11el 144MHz Yagi antenna array using EZ-NEC software, covering the DL6WU stacking formula for determining optimal vertical and horizontal spacing distances, analyzing beam width and side lobe patterns, and adjusting spacing to achieve clean radiation patterns with minimal interference; the process involves calculating stacking distances from beam width measurements, testing different configurations through software simulation, and making iterative adjustments to balance gain optimization against pattern purity.

A Log-Periodic Dipole Array (LPDA) is a broadband unidirectional antenna consisting of multiple half-wavelength dipoles arranged in a logarithmic progression, with the longest dipole at the back and the shortest at the front; it achieves continuous broadband coverage with a frequency range ratio of approximately 4:1 through a phasing harness that twists 180° between each antenna element, creating directional characteristics similar to a Yagi antenna while maintaining broadbanded operation.

The Log-Periodic Dipole Array (LPDA) provides wide bandwidth unlike Yagi-Uda. All dimensions vary logarithmically with frequency, with the active resonant element shifting toward smaller dipoles as frequency increases. Key parameters are scaling factor τ = R(n+1)/R(n) = L(n+1)/L(n) < 1 and space factor σ = D(n)/L(n). Design curves show constant directivity for various τ and σ values. For 6.5 dB gain at 54-216 MHz, τ≈0.82 and σ≈0.15 are optimal. The design procedure involves finding the longest dipole (0.5λ at lowest frequency), calculating intermediate lengths using τ, and determining element spacing using D(n)=2σL(n). Adding a reflector behind the longest dipole improves low-frequency gain performance.

Eine Logarithmisch-Periodische Dipolantenne (LPDA) ist eine breitbandige Richtantenne, die aus mehreren elektrisch verbundenen Dipolen besteht, deren Längen und Abstände logarithmisch abnehmen. Im Gegensatz zu Yagi-Antennen mit Reflektor und Direktoren nutzt die LPDA keine Verstärkerelemente, sondern erreicht ihre breitbandige Funktionalität durch die logarithmische Struktur, die mehrere Dipole gleichzeitig für verschiedene Frequenzen resonant macht. Die Antenne deckt typischerweise Frequenzbereiche von mehreren hundert MHz bis zu mehreren GHz ab und wird häufig in TV-Umsetzern, EMV-Messungen und Funkpeilung eingesetzt. Die typische VSWR-Wert liegt bei etwa 1,25, und die maximale Sendeleistung beträgt meist nur 30 Watt.

The log periodic dipole array (LPDA) is a multi-element directional antenna with a narrow beam operating over a wide frequency range. It consists of dipole elements placed along the antenna axis at intervals determined by a logarithmic function of frequency. Elements decrease in size from back to front, with larger elements at the back operating at lower frequencies. The space between elements decreases toward the front. During operation, as frequency varies, a smooth transition occurs along the array, creating an active region for signal transmission and reception.

A Log Periodic Dipole Array (LPDA) is a broadband antenna array where the geometry of parallel dipoles varies according to a logarithmic scale, enabling the same electrical properties (impedance, radiation pattern) to be maintained across multiple frequency decades; the array consists of three operational regions: the inactive transmission line region (dipole length < λ/2, capacitive impedance), the active region (dipole length = λ/2, resistive impedance with maximum current), and the inactive stop region (dipole length > λ/2, inductive impedance).

Mast installation requires strong masts, such as 60mm diameter tubes secured with at least four M8 bolts with plastic sleeves. Non-penetrating mounts must follow local wind loading conditions. To point the antenna, two parameters are required: azimuth angle (referenced to north, corresponding to left/right movement) and elevation angle (referenced to ground, corresponding to up/down movement). Use finder.2-way-install.com to identify location via map, GPS coordinates, or installation address. The spot color configures circular polarization. Use smartphone app for line of sight visualization. Installation position must have clear line of sight with no obstacles, a 10-degree margin from obstructions, and cable distance under 50 meters using standard cable.

For VHF/UHF communication, vertical polarization is optimal for FM simplex and repeater work (where most stations use vertical antennas), while horizontal polarization is better for 2-meter sideband and CW operations; mounting a metal mast along the centerline of a beam antenna acts as a parasitic element that distorts the radiation pattern and increases SWR, whereas replacing it with a non-conductive fiberglass mast restores proper beam performance and significantly improves signal quality.

The Skyline antenna is mounted on a 12-meter telescopic mast at 10 meters height, with a VHF/UHF antenna at the top. The aluminum crossbar attaches to the mast using mounting brackets, with Dyneema tensioning cables preventing sagging and maintaining horizontal alignment. Before mast extension, wind support cables are prepared at three heights with five attachment points each. Three people assist mast extension, each controlling one wind support cable set for balanced, controlled extension. The process requires careful coordination to prevent mast tipping. The installation may include optional modifications like pulleys for a 40m dipole, though such changes are the installer's responsibility.

Polarization provides transmission redundancy with horizontal and vertical signals on the same frequency. Align antennas by adjusting horizontal and vertical orientations while monitoring signal levels to achieve similar strengths in both polarizations. Use shielded cables for outdoor installations to prevent FM radio interference. Mount antennas on self-supporting towers rather than masts for stability. Verify power supplies match equipment requirements. Implement proper grounding and surge protection. Consider antenna dimensions, weight, and wind load for proper mounting. Avoid plastic ties that can break with temperature changes.

This segment covers the complete installation process for an antenna mast system. The speaker demonstrates using bungee cords and vice grips for temporary support during alignment, applying U-clamps to secure brackets to the pole, and drilling a drain hole to prevent water accumulation. The process includes applying cold galvanizing compound to prevent rust on welded joints exposed to hot and humid conditions. The completed mast is nearly 40 feet long, requiring two-person installation. A loop is welded at the top to accommodate a pulley system for antenna wire hoisting. The segment concludes with plans for painting and final assembly.