RHCP VHF Antenna

User terminals (Ground)

Status

Completed
Status date

2024-10-30
Activity Code

7C.065

Objectives

*Figure 03 QFH antenna mounted on the railing of the Kongsberg vessel Ocean Space Lab. Credit: Nils Nygaard, Kongsberg Discovery Seatex.*

The purpose of this activity is to design, develop and test a new right-handed circularly polarized (RHCP) VHF antenna to be used on vessels supporting the satellite VHF Data Exchange System.

The objectives are:

Improve the link quality and throughput of the VDES system and demonstrate this in a real operating environment. Part of this is to reduce multipath fading and to look for a design where the gain is high at low elevations.
The antenna should benefit satellite VDES users globally. It should be suitable for vessels operating in the Artic regions, particularly beyond the geostationary satellite coverage area.
The chosen antenna to be industrialised and ready for mass production.

Challenges

Some key challenges:

Finding the right antenna candidate that fulfills all specs
- Around 100 antennas were considered and simulated
- Prototypes were made for the most promising ones
- Size and maximum dimensions
- Narrow band, challenging to match.
- Design accommodating pitch and roll.
- Fulfilling Iso Level Mask.
- Polarization performance:
  - Cross polar discrimination.
  - Specular multipath suppression.
- Low elevation performance and overall gain.
- Nordic climate, ice
During the measurement campaign it was challenging to get representable data for the standard dipole antenna because of noisy environments, making comparisons with the QFH challenging.

Benefits

Increased the gain by more than 4 dB and suppressed specular multipath by more than 10 dB in the whole maritime VHF band.

A standard dipole has shown a signal variation (st. dev) of 4.2 dB, and with a target PER of 1%, a fade margin of 10 dB would be required. Halving the signal variation would reduce the required margin by more than 5 dB. Thus, the improved signal strength and fade margin reduction could improve the link more than 9 dB. Interference is likely to be linearly polarized, and a circularly polarized ship antenna may provide some suppression in harbours and noisy areas.

Expected to improve maritime communication links by enhancing PER and throughput. The antenna design aims to mitigate cross-polar specular multipath fading at negative elevations and ensure strong and consistent satellite signals at positive elevations, accommodating pitch and roll variations up to ±10°.

Enhancing maritime safety and communication efficiency in Arctic regions, particularly beyond the geostationary satellite coverage area.

Increases service quality and throughput. The VDES system already has methods for automatically adjusting the throughput based on link quality.

Field tests have demonstrated the antenna’s capability to outperform systems with vertical dipoles by reducing interference and improving signal reliability

Features

Electrical specifications

Frequency range	156 - 162 MHz
VSWR	< 1.6:1
Nominal impedance	50Ω
Power rating	25W
Gain, horizon (0 degrees)	RHCP: 0 dBic (nominal) Linear V-pol: -4dBi (nominal)
Radiation pattern	Omnidirectional
Polarisation	RHCP
Connector	N Female

Mechanical specifications

Design	Quadrifilar helix antenna. Radiating elements completely enclosed in epoxy/fiberglass laminate. Metal parts are brass, aluminium, and stainless steel.
Dimensions	1.53m tall, Ø166mm fiberglass tube
Weight	5.9kg
Wind rating	55m/s (123mph)
Finish	Polyurethane lacquer
Temperature range	-55°C to +71°C, -67°F to +160°F

System Architecture

The new antenna is one component of the VDES architecture. The VDES satellite transmits with RHCP. A standard dipole antenna with vertical polarization is used as the reference, and both antennas are extensively tested in a maritime environment.

VDES satellite-based network proposed used in this activity

Plan

The project has the following milestones:

Milestone 1 (MS1): System Requirements Review (SRR). Review of technology survey and patent search/study. Review of consolidated requirements and review of simulations and chosen antenna candidates. Date for review 14.09.2022
Milestone 2: Review of technology baseline and verification of detailed design. Planned for January 2023
Milestone 3: Test Readiness review and verified deliverable items. Planned for August 2023
Milestone 4: Final review. Planned for November 2023.

Current status

The activity kicked-off in May 2022 and achieved MS1 System requirements review (SRR) on 14.09.2022.
Comrod created a prototype of the final antenna candidate in January 2023 and started preliminary testing at Tau.
Antenna design finalized June 2023.
Comrod Manufactured and tested five 0-series antennas for test campaign in August 2023.
Test campaign started August 2023, with multiple test locations. Tau, Trondheim, Svalbard.
Measurements for over 300 passes collected at the test locations from August 2023 – May 2024.
Final review and final presentation completed in May 2024.
Project closed September 2024.