Retrodirective Antenna

Objectives

Address the market needs of K/Ka-band user terminal antennas by simplifying the tracking hardware for mobile applications.
Produce a K/Ka-band self-steered antenna demonstrator breadboard using hybrid analogue/digital retrodirective antenna techniques
The system consists of retrodirective IF circuits developed by QUB and a K/Ka-band frontend developed by IMST
The retrodirective methods used draw on the experience of QUB producing similar antennas at L band frequencies
The retrodirective antenna offers real-time tracking capacity with minimum DSP usage
The K/Ka-band frontend is based on COTS MMIC GaAs components. An additional development plan outlines how further integration can achieve a higher TRL.
This has produced the first practical demonstration of a 2x4 element K/Ka-band retrodirective breadboard prototype employing a hybrid analogue/digital delay locked loop (DLL) phase conjugator.

Challenges

Produce a K/Ka-band retrodirective antenna breadboard with sufficient simplicity, low cost and power consumption to have the potential to be scaled up for applications such as ground user terminals
The ability to operate at K/Ka-band with closely spaced satellites using the same frequency spectrum, and solving some of the related control aspects.
Providing potential for K/Ka-band and retrodirective circuits to be simple enough to be combined onto a custom chip that can be integrated with a K/Ka-band antenna array

Benefits

Real time tracking
Tracking circuits operating in the analogue domain with minimal DSP processing overhead needed.
No requirement for fast A/D and D/A conversion within the tracking circuits since tracking is carried out in the analogue domain
Automatically transmits signal back in the direction from which it receives without prior knowledge of the satellite position
Reduction in the requirement for array calibration since the retrodirective array is self-calibrating
Does not require additional position information of satellite during tracking phase, eg from GPS, accelerometers etc., hence no sensor hardware required
Instant signal acquisition (if the satellite to be acquired is transmitting on a unique frequency)

Features

Retrodirective IF circuits operate at relatively low frequencies and consequently can use low frequency, low powered components
The digital control aspects for the overall array operate in frequencies in the kHz frequency range, therefore can use low powered microcontrollers
The K/Ka-band frontend makes use of IMST’s previous experience in producing high performance frontends

System Architecture

The retrodirective circuit utilises a hybrid analogue/digital phase conjugating architecture drawing on the experience of producing such systems at L-band
In order to deal with some of the more challenging aspects of operating at K/Ka-band, such as the ability to select a particular satellite in a range of closely spaced satellites using the same frequency spectrum, the retrodirective circuits will make use of low powered microcontrollers to provide some “intelligence” to the beam steering
The K/Ka-band frontend consists of up/down conversion chain to an IF frequency compatible with the retrodirective circuits.

Plan

Define specification for K/Ka-band retrodirective antenna
Define specific critical breadboards to be designed – Milestone 1: Consolidated requirements & critical breadboards definition
Critical breadboard design
Critical breadboard Manufacture
Critical breadboard test – Milestone 2: Breadboard Test Report
Baseline design for final breadboard – Milestone 3: Baseline Design Review
Detailed design for final breadboard – Milestone 4: Detailed Design Review
Final breadboard test of – Milestone 5: Test Readiness Review, Milestone 6: Test Review Board
Final review – Milestone 7: Final Review