Beacon Antenna
Dual-Band Omnidirectional UHF/S-Band Beacon Antenna
Compact, rugged dual-band omnidirectional antenna covering 406 MHz (Cospas-Sarsat heritage) and 2.2 GHz (lunar relay) for the emergency beacon, mounted at a topographically prominent point and physically separated from primary communications antennas.
Purpose
Radiate the beacon signal toward any possible receiver (lunar orbiting relay, Earth, future lunar surveyor) without requiring pointing, alignment, or active components — so the beacon can be detected from any direction in the upper hemisphere.
Context
Connected to L3-COM-BEAC-XMIT via a short low-loss feedline. Mounted on a dedicated mast clear of the main HGA structure to ensure survival in scenarios where main comms or Ark structure is damaged.
Principles
- ▸Quarter-wave whip antenna at 406 MHz (~18 cm) has omnidirectional pattern in the azimuth plane and ~2.1 dBi peak gain
- ▸Cylindrical patch or quadrifilar helix at S-band provides hemispherical coverage above the mounting plane
- ▸Dual-band antennas use either two co-located elements, a single broadband element (log-periodic), or a multi-resonant patch design
- ▸Mechanically simple, all-metal construction maximises long-term reliability — no radomes or organic dielectrics to degrade
- ▸Conical groundplane shapes radiation pattern to reduce ground losses and increase elevation gain
- ▸VSWR <2 across bands needed to keep the transmitter operating within efficient impedance window
Typical implementations
- ▸Standard 406 MHz EPIRB whip antennas (1/4 λ vertical)
- ▸Eosol Omni Moon S-Band Antenna — flight-proven all-metal patch array
- ▸Compact polarized omnidirectional helical antenna (US Patent 10,804,618)
- ▸Lunar rover UHF/S-band mast antennas, e.g., on Lunar Pathfinder
- ▸Apollo Lunar Communication Relay Unit S-band omnidirectional antenna
Lunar considerations
- ▸Lunar regolith affects near-field — antenna mounted on dedicated mast at least 2 m above local terrain to dominate over ground effects
- ▸Dust accumulation on antenna surface degrades performance by <0.5 dB if all-metal construction; passive shake mechanism or EDS recommended for long-term cleanliness
- ▸Thermal cycling (–180°C to +130°C) drives mechanical stress — all-metal design with matched CTE coefficients
- ▸Mast must survive seismic events (deep moonquakes) and possible micrometeoroid impacts over 100 years — over-engineered structural margin
- ▸Locate antenna such that it remains accessible to lunar orbiting relays even when primary HGA blocked or damaged
Specifications
Functional
| primary function | Omnidirectional RF radiation/reception for beacon signal |
| inputs | Beacon RF signal from L3-COM-BEAC-XMIT (~200 mW) |
| outputs | Radiated omnidirectional pattern at 406 MHz and 2.2 GHz |
| frequencies mhz | 406, 2200 |
| peak gain dbi | 3 |
| min gain dbi upper hemisphere | -3 |
| polarization | Linear vertical (UHF), RHCP (S-band) |
| vswr max | 2.0 |
| azimuthal pattern variation db | 2.0 |
| elevation coverage deg | 0, 90 |
Physical
| mass kg | 1.2 |
| dimensions | 1.0 m total length (mast + radiating elements) |
| materials | Aluminum 6061-T6 mast and elements, Stainless steel SMA/N-type connector with hermetic feedthrough, Invar interface fitting, All-metal construction (no polymers exposed) |
| operating temperature c | -180, 130 |
| ultimate load g | 8 |
Operational
| power consumption w | 0 |
| thermal range c | -180, 130 |
| lifetime years | 100 |
| mtbf hours | passive |
Interfaces
Provides
- Radiated beacon signal
Requires
- RF input via coaxial feed
- Independent mast structure, physically separate from main comms
Cite this entry
Lunar Ark Codex. "Beacon Antenna" (L3-COM-BEAC-ANT). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-COM-BEAC-ANT
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.