Low-Gain Omnidirectional Antennas
Quadrifilar Helix / Patch Antenna Array
Set of omnidirectional / hemispherical-coverage antennas (UHF/S-band patch and quadrifilar helix elements) providing wide-angle RF coverage independent of pointing — used for safe-mode beacon reception, local mesh links, and contingency Earth communication.
Purpose
Provide a non-articulated, always-available RF link for commanding the Ark in degraded states (HGA failure, pointing failure, attitude loss) and for short-range mesh communication with robots, rovers, and sensors across the Ark site.
Context
Complements the L3-COM-ANT-HGA (narrow beam, high gain) with low-gain, wide-coverage elements. Multiple units mounted on raised masts to clear horizon for hemispherical view. Used by both L2-COM-EARTH (low-rate uplink contingency) and L2-COM-MESH (local network).
Principles
- ▸Quadrifilar helix antennas produce a circularly-polarized cardioid pattern with ~5–7 dBi peak gain and >–3 dBi over the upper hemisphere
- ▸Microstrip patch arrays on a metal groundplane provide compact, low-profile broad-beam patterns with ~2–8 dBi gain
- ▸Helical antennas in axial mode offer 12–15 dBi with wider beamwidth than a parabolic but narrower than QFH — chosen by mission per coverage need
- ▸Circular polarization is preferred for ground-to-space links to avoid polarization-mismatch losses with the rotating spacecraft frame
- ▸Multiple LGAs spatially distributed mitigate body shadowing — one always sees the relay or Earth no matter the attitude
Typical implementations
- ▸Eosol Omni Moon S-Band Antenna — all-metal omnidirectional patch array designed for rover/asset mast integration
- ▸Helical antennas commonly used on lunar rovers (CN103247865A patent: X-band wide beam circularly polarized antenna for lunar rover)
- ▸Mars Pathfinder, MER, MSL, Mars 2020 all carry S/X UHF LGAs as well as HGA
- ▸JUNO LGAs (X-band toroidal patterns) for safe-mode command uplink
- ▸CubeSat patch antennas at S-band (typically 2.2/2.4 GHz) widely qualified
Lunar considerations
- ▸Lunar regolith below antenna alters near-field, changing pattern; ground-plane sized to dominate over regolith effects
- ▸Sleeve dipole antennas have demonstrated ~2.27 dBi peak gain with 585 MHz bandwidth in lunar surface configurations
- ▸Dust accumulation on radomes degrades gain by 0.5–2 dB; periodic cleaning (electrodynamic dust shield) helpful
- ▸Multiple antennas on opposite sides of Ark provide hemispherical coverage compensating for occultation by structure
- ▸Long-term polymer radome degradation under UV/cosmic radiation must be considered; metal-only designs preferred for 100-year missions
Specifications
Functional
| primary function | Wide-beam omnidirectional RF coverage for emergency uplink, mesh, and beacon links |
| inputs | RF transmit signal from L3-COM-EARTH-XBAND (S/X-band) or L3-COM-MESH-NODE (UHF/S-band), Coaxial cable feed from transceiver |
| outputs | Hemispherical radiated RF pattern, Received signals coupled to transceiver |
| antenna types | Quadrifilar helix S-band, Patch array S-band, UHF helix for mesh |
| frequency bands ghz | [0.4, 0.45], [2.0, 2.3], [7.0, 8.5] |
| peak gain dbi | 7 |
| coverage solid angle sr | 5.5 |
| polarization | RHCP (circular) |
| axial ratio db max | 3 |
| vswr max | 1.8 |
| number of antennas | 4 |
Physical
| mass kg per unit | 0.8 |
| total mass kg | 3.2 |
| dimensions per unit mm | 150 × 150 × 200 (incl. mast bracket) |
| materials | Aluminum housing and ground plane, Copper helix windings or microstrip traces on PTFE substrate, Vespel SP-1 or PEEK structural standoffs (vacuum-rated), Optional all-metal construction (no radome) for long-life designs |
| 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
- Backup RF aperture for low-rate contingency uplink/downlink
- RF aperture for short-range mesh network at UHF/S-band
- RF aperture for emergency beacon radiation
Requires
- Mounting masts elevated above local horizon and structure
- Coaxial feed cable carrying TX/RX signal
Cite this entry
Lunar Ark Codex. "Low-Gain Omnidirectional Antennas" (L3-COM-ANT-LGA). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-COM-ANT-LGA
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.