Yagi Antenna Basics Explained: Gain, Directional Patterns & Applications

A link budget is a systematic calculation that determines whether a communication link will work by comparing the received signal strength (carrier) against the noise floor, accounting for all system components including transmitter power, antenna gains, free space loss, and receiver noise temperature; the link margin (difference between actual and required carrier-to-noise ratio) indicates system performance, with positive margins ensuring reliable communication.

Link budget calculation determines the maximum communication range by accounting for all gains and losses in a radio communication system, including transmitter power, antenna gains, cable losses, atmospheric losses, and receiver sensitivity, using logarithmic formulas to ensure reliable signal transmission over the desired distance.

A complete link budget calculation example demonstrates the process: Given 14 dBi directional antenna, 100m distance, 36 dB system margin, and -90 dBm receiver sensitivity. Steps: Convert 100m to 0.1 km, calculate FSPL = 80 dB, then apply: Tx Power + 14 - 80 + 6 - 36 = Received Signal. This must exceed -90 dBm. Solving gives minimum transmitter power of 6 dBm. This ensures reliable communication despite path losses and system requirements.

A link budget is the fundamental calculation used to determine if a wireless communication system will work. It consists of several components: transmitter output power, antenna gain on both sides, cable losses, free space propagation loss, receiver sensitivity, and any additional losses. The link budget represents the total available signal strength at the receiver after accounting for all gains and losses in the transmission path.

This section covers calculating wireless link budgets to predict signal strength and link reliability. Key parameters include transmitter power (measured in dBm), antenna gain (dBi), cable losses (dB), free space path loss (calculated using FSPL formula), and receiver sensitivity (dBm). The complete calculation combines all factors: transmitter power plus antenna gain minus cable loss minus free space loss minus receiver cable loss minus receiver sensitivity. Results indicate whether received signal exceeds receiver sensitivity threshold for reliable communication. This analytical approach enables engineers to design reliable wireless links before deployment.

Parabolic antennas use curved reflectors to focus radio energy, with gain determined by dish size rather than feed antenna dimensions. They are unidirectional and can be vertically or horizontally polarized to prevent full-duplex interference. Array antennas combine multiple elements (directors, driven element, reflector) to shape radiation patterns, with log periodic designs covering wide frequency ranges through varying element lengths. These advanced systems require substantial space - some installations occupy 20+ acres. The choice between antenna types depends on specific communication requirements, available space, and desired coverage characteristics.

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.

This section covers advanced antenna designs. Parabolic antennas use the property that rays parallel to the axis reflect to the focus, and rays from the focus reflect parallel to the axis, enabling highly directional transmission. They can be constructed with continuous metal or mesh, with mesh spacing smaller than half the wavelength to prevent wave transmission. This allows practical installation in environments with wind or other environmental factors. The section concludes with practical considerations for antenna deployment, emphasizing how antenna design choices affect performance in real-world applications.

This video explains three types of directional antennas used in amateur radio: the Yagi antenna (developed in 1926 by Japanese professors), which uses a single driven element with parasitic reflector and director elements to create directional gain through constructive interference; the log periodic antenna, which has multiple driven elements with logarithmically decreasing lengths and alternating polarity to provide gain over a very wide frequency range; and the phased array antenna, which uses multiple driven elements fed with phase delays to electronically steer the beam direction. Only the Yagi is common in amateur radio, while log periodic and phased arrays are rarer but offer specialized advantages in wideband coverage and electronic beam steering respectively.

A log-periodic antenna is designed using specific mathematical formulas to determine key parameters including bandwidth (3.5 MHz), mast length (1.34 meters), number of elements (10), dipole lengths (ranging from 75mm to 20mm), and inter-element distances (from 24cm to 7cm), with the characteristic impedance calculated as 2.54 ohms; the antenna is constructed using 8mm diameter rods, square tubes, and galvanized materials, with dipoles mounted on insulators at calculated distances and connected via a crossed galvanized cable to a balun, which then connects to a coaxial cable for television reception.

Phased array antennas electronically steer beams by applying controlled phase shifts to individual antenna elements, enabling constructive interference for desired directions and destructive interference for unwanted angles; the beam steering angle is determined by the equation φ = (2πd/λ)sin(θ), where d is element spacing, λ is wavelength, and θ is the steering angle, allowing applications in 5G communications, radar, and satellite systems without mechanical movement.

Phased array beamforming electronically steers antenna beams by applying controlled phase shifts to individual antenna elements, enabling applications in 5G communications, radar, and satellite systems; the beam steering angle is determined by the phase difference between adjacent elements, with the relationship θ = arcsin(m × (λ/d) × phase_shift), where λ is wavelength, d is element spacing, and m is an integer accounting for spatial aliasing (grating lobes); the array factor equation AF = [sin(n·φ/2)] / [sin(φ/2)] describes how the combined signals from n elements create constructive and destructive interference patterns, with side lobes arising from uniform aperture illumination and beam squint occurring when phase shifters replace true time delays for wideband signals.

Beamforming, developed by Cabron in 1905, uses multiple antennas separated by specific distances with controlled signal phases to create focused energy beams through constructive and destructive interference. Modern 5G phased arrays contain hundreds of active elements (e.g., Bell Labs' 384-element array), with millimeter wave frequencies enabling compact antenna designs. The system rapidly steers beams between users without physically moving antennas, creating continuous coverage illusions. At 28 GHz over 2 meters, free space path loss reaches 67 dB (signal weakens 5 million times). This extreme attenuation means successful millimeter wave links represent extraordinary engineering achievements rather than excessive power outputs.

Phased array antennas use multiple small antennas arranged in a grid, where each antenna emits the same signal but with carefully controlled time delays; these signals constructively interfere in one specific direction to form a narrow beam while destructively interfering in other directions, allowing the beam to be electronically steered without physically moving the antenna.

5G antennas use phased array technology, consisting of 128 individual emitters within a square housing. These emitters work cooperatively to form a directional beam of electromagnetic radiation. This system, called beamforming, allows the antenna to direct signals toward specific users. However, this technology creates measurement challenges because the beam direction changes randomly as users move, making it difficult to accurately measure radiation exposure levels.