European Space Agency

Centaur - Hybrid Electro-Mechanical Scanning Satellite User Terminal Antenna

Objectives

CENTAUR is an antenna development towards an electronically steered antenna in Ka-band, to be used on a gimbaled platform.

Beside the aeronautical the land and maritime segment was targeted as user terminal.

The solution consists of two separate apertures, one to cover the Rx band from 18.3 – 20.2 GHz and another one covering the Tx band from

28.1 – 30 GHz.

Due to design constraints only two bits of phase control per element are available to steer the beam which will degrade the performance of the array due to quantization effects.

In this contribution we focus on the beam synthesis using a biquadratic programming method applied to phase-only optimization to maximize the array gain under these constraints.

For an accurate beam synthesis it is important to have an accurate model of the element patterns of the array. For this purpose, a tool based on the Finite Element Method and Modal Analysis is used to compute the array patterns with a tool from CADMIA Technologies S.L.

The CADMIA tool allows to accurately take into account the finite number of elements, element rotations and the finite size of the ground plane.

The demonstrator Tx array made of 48 antenna elements, based on a COTS phase shifter RFIC by Qorvo,was manufactured and the radiating performance for different scan angles.

Challenges

The antenna radiator element was developed to be integrated into a dense monolithic PCB + RFIC structure, with standard RF-substrates. It was the key challenge to keep a very good circular polarisation over a larger bandwidth.

The beam steering was limited to 2-bit control on the phase shifter RFIC, via SPI lines. Special approach was used by combining the Finite Element and Modal Analysis of the single antenna element inside the array environment, to improve the overall radiation performance.

Benefits

The selected antenna element design is optimized for circular polarisation performance and large bandwidth.

A very compact and thin PCB structure could be achieved. The hybrid antenna approach intends to combine the best features of fully mechanical and fully electronic antennae in a hybrid compromise which offers overall advantages in terms of RF performance, size, power consumption and cost.

Features

  1. Performance typical to a 40-60cm aperture, but with height significantly less (30cm)
  2. Scan range comparable to fully mechanical antennae, but with better pointing speed and acceleration rates (particularly necessary for land-mobile segment)
  3. Power consumption lower than existing fully phased arrays

These attributes together form a unique selling proposition that will result in a successful commercialisation.

System Architecture

The hybrid antenna concept combines electronic and mechanical beam steering system. Aspects of the beam pointing are mechanical or electronic depending on the concept being considered. Generically, the architecture of the antennae is composed of three main parts:

  1. Antenna apertures: including radiators, amplification, filtering and electronic beam scanning circuitry.
  2. Mechanical platform: Structural support, actuators and mounting fixtures.
  3. Automatic Control Unit: process attitude and/or signal information and steer the antenna beam. The ACU includes internal sensors measuring angular rotation and acceleration that maintain the pointing of the antenna beam in mobile conditions, plus it receives information from external devices, either from an IMU or signal quality information, to determine the position of the satellite.

Plan

The plan consists of the following phases:

  1. Consolidation of Antenna Requirements and Reference Antenna
  2. Antenna Preliminary Design and Analysis
  3. Antenna Detailed Design and Analysis
  4. Demonstrator Preliminary Design and Analysis
  5. Demonstrator Detailed Design (Phase 2)
  6. Demonstrator Manufacturing and Test
  7. Antenna Final Design Update. Lessons Learnt and Roadmap

Current status

Project completed:

The demonstrator Tx array made of 48 antenna elements, based on a COTS phase shifter RFIC by Qorvo, was sucessfully manufactured, and the radiation pattern performance for different scan angles measured.

Status date

Tuesday, April 21, 2020 - 14:14