Variable Dielectric Delay Lines in Liquid Crystals for Phased Array Feeds

Lead Research Organisation: University of Manchester
Department Name: Physics and Astronomy

Abstract

In this project we seek to exploit a novel liquid crystal technology, which
allows a controllable true time delay to be applied to an RF signal of
frequencies up to tens of Giga-Hertz. The basic technology has already been
demonstrated and has a wide variety of applications. We now intend to use this
technology to construct a real astronomical demonstration system for delay
lines and show that these can be integrated into the beam-forming module of an
existing Phased Array Feed (PAF) instrument, dramatically improving its
capabilities.

PAFs are an essential next step for radio astronomy. They offer the
possibility of increasing a telescope's Field-of-View (FoV), of
improved calibration and of allowing operation up to higher
frequency. PAFs have been implemented in instruments such as PHAROS
and can achieve these goals, but over a narrow bandwidth due to the
use of phase shifters in the beam-former hardware. In this project we
seek to implement a true time delay beam-former, which will allow the
whole available bandwidth to be used. This will make use of novel
technology - liquid crystal stripline whose dielectric constant can
be varied by application of an AC voltage. We propose a two year
programme during which we will produce a PAF module using a set of
true-time delay units that will be tested within the PHAROS receiver,
which is available for use on this project and will make an ideal
test-bed. Our focus is on demonstrating the Technology Readiness Level
of these delay lines in the context of a prototype instrument, thereby
addressing integration issues as well as pure technology development.

Planned Impact

Below is a summary of beneficiaries of the proposed research; this is explored in more detail in the Pathways to Impact document. The main beneficiaries are:

- Business/Industry:

The most exciting areas for impact actually lie outside astronomy and this project should be seen as the first step towards realising the potential for LC delay lines operating at higher frequencies and wider bandwidths with a wide variety of applications. The technology has many attractive features: liquid crystal devices are a fundamentally low cost technology with well known manufacturing techniques for volume commercial applications; devices are low power and operate at short wavelengths with the result that components are physically small and hence cheap; at RF-frequencies beyond the capabilities of silicon devices liquid crystal offers an attractive alternative to implementing delays compared with expensive chips developed from e.g. GaAs. Possible future applications include: anti-collision radar; autonomous automobile driving; high frequency telecommunications; medical imaging technologies; security scanners.

There will also be a direct benefit to industry through the development and production of the hardware for the astronomical instruments we envisage being enabled by this project, in terms of financial return, valuable knowledge exchange and IP production.

- Academic:

The areas that will benefit from this project are: radio astronomy technology development and enabling of future experiments; electrical engineering; communication engineering; antennas and propagation engineering. (See Academic Beneficiaries for further details).

- General Public:

The new experimental areas that will be opened up by this project include the deeper understanding of structure formation in the Universe, which has been proven to be of great interest to the General Public as a whole.

- Schools:

Astronomy outreach inspires school age students and so enthuses them to become the next generation of scientists and engineers.
 
Description Liquid crystals placed on top of a microstrip carrying microwave frequency signals can be used to produce a user-controllable time delay in the signal. The dielectric constant of the liquid crystals can be changed by applying an AC voltage across them with the result that the electrical delay through the microstrip changes. By controlling the voltage applied one can therefore vary the time delay. This has many potential applications in RF circuits and radio astronomy. In this project they are used to "phase up" several individual signals from different receivers which are then combined to form an RF beam. The true time delay nature is superior to using a phase shifter since it allows wider bandwidth.

In this project we developed a compact delay line working over the 4-8 GHz band to be deployed on a Phased Array Feed system together with the associated control hardware and software. The modules were approximately 25mm in size but by using a meander topology of the strip line we were able to achieve 20mm of variable path.
Exploitation Route These true time delay modules could be used to develop the PHAROS prototype into a receiver system for the Lovell Telescope which would give it the same field of view as eMERLIN, thus resulting in an order of magnitude increase in survey speed.

The liquid crystal technology could be used at much higher frequency, ~100 GHz, where the desired bandwidth of an array would make an analogue architecture much preferred over a digital beamformer.
Sectors Digital/Communication/Information Technologies (including Software),Electronics
 
Description Doctoral Training Centre in Photonic Systems Development
Amount £12,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 10/2013 
End 09/2014
 
Description CAPE 
Organisation University of Cambridge
Department Centre for Advanced Photonics and Electronics (CAPE)
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution RF testing and integration into PHAROS
Collaborator Contribution LC delay lines
Impact None
Start Year 2013
 
Description CavAP 
Organisation University of Cambridge
Department Department of Physics
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution RF testing and integration into PHAROS
Collaborator Contribution Control hardware and software
Impact None
Start Year 2013
 
Description Merck 
Organisation Merck (KGaA)
Department Darmstadt Site
Country Germany, Federal Republic of 
Sector Private 
PI Contribution Test usability of liquid crystals at GHz frequency range.
Collaborator Contribution Synthesis of liquid crystals for the GHz frequency range.
Impact Liquid crystals synthesized and tested for use as a tunable dielectrics for frequency range 0.1-20GHz
Start Year 2010
 
Description University of Electronic Science and Technology of China 
Organisation University of Electronic Science and Technology of China (UESTC)
Department School of Electronic Engineering
Country China, People's Republic of 
Sector Academic/University 
PI Contribution Design and test of liquid crystal delay lines for various applications at frequency range 0.1-10GHz
Collaborator Contribution Simulation and manufacturing of liquid crystal delay lines for various applications at frequency range 0.1-10GHz
Impact Several delay lines of different geometry and footprint were designed, manufactured and tested for further use.
Start Year 2012
 
Description LC delay lines for PAFs poster 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Poster generated questions
Year(s) Of Engagement Activity 2014
 
Description LC delay lines for PAFs talk to JBCA Technology group 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Questions

Future PAF development studies
Year(s) Of Engagement Activity 2014
 
Description PAF 2015 Workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact KG - ``PHAROS and other cryogenic PAF work''; 6 November 2015
PAF 2015 Workshop; 40 audience
Year(s) Of Engagement Activity 2015
URL http://pafworkshop2015.com/
 
Description PAF work shop 2016 (Sardinia, Italy) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact About 50 pupils attended for the Phased Array Feeds work shop,to report recent update, exchange ideas of research outcomes for the next generation radio telescopes.
Year(s) Of Engagement Activity 2015,2016,2017
URL http://paf2016.oa-cagliari.inaf.it/
 
Description URSI symposium (York) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact About 50 pupils attended for report and exchange ideas of recent research outcomes in science and technology.
Year(s) Of Engagement Activity 2014,2015,2016