Reconfigurable antenna
{{Short description|Antenna capable of modifying its frequency and radiation properties dynamically}}
File:Reconfigurable pixel antenna.jpg
{{Antennas|expanded=techniques}}
A reconfigurable antenna is an antenna capable of modifying its frequency and radiation pattern dynamically, in a controlled and reversible manner.{{cite journal | title=Reconfigurable Antennas |journal=Synthesis Lectures on Antennas |volume=2 |pages=1–66 |year=2007 |doi=10.2200/S00067ED1V01Y200707ANT004 | author=J.T. Bernhard.|s2cid=36417351 }} In order to provide a dynamic response, reconfigurable antennas integrate an inner mechanism (such as RF switches, varactors, mechanical actuators or tunable materials) that enable the intentional redistribution of the RF currents over the antenna surface and produce reversible modifications of its properties. Reconfigurable antennas differ from smart antennas because the reconfiguration mechanism lies inside the antenna, rather than in an external beamforming network. The reconfiguration capability of reconfigurable antennas is used to maximize the antenna performance in a changing scenario or to satisfy changing operating requirements.
Types of antenna reconfiguration
Reconfigurable antennas can be classified according to the antenna parameter that is dynamically adjusted, typically the frequency of operation, radiation pattern or polarization.{{cite book | chapter=Reconfigurable Antennas | title=Modern Antenna Handbook |year=2008 |publisher=John Wiley & Sons | author=G.H. Huff and J.T. Bernhard. | editor=C.A. Balanis}}
= Frequency reconfiguration =
Frequency reconfigurable antennas can adjust their frequency of operation dynamically. They are particularly useful in situations where several communications systems converge because the multiple antennas required can be replaced by a single reconfigurable antenna. Frequency reconfiguration is generally achieved by physical or electrical modifications to the antenna dimensions using RF-switches,{{cite journal|last1=Panagamuwa|first1=C.J.|last2=Chauraya|first2=A.|last3=Vardaxoglou|first3=J.C.|title=Frequency and beam reconfigurable antenna using photoconducting switches|journal=IEEE Trans. Antennas Propag.|date=2006|volume=54|issue=2|pages=449|doi=10.1109/TAP.2005.863393|bibcode=2006ITAP...54..449P|s2cid=8074147|url=https://dspace.lboro.ac.uk/2134/2950}} impedance loading{{cite journal|last1=Erdil|first1=E|last2=Topalli|first2=K|last3=Unlu|first3=M|last4=Civi|first4=O|last5=Akin|first5=T|title=Frequency tunable microstrip patch antenna using RF MEMS technology|journal=IEEE Trans. Antennas Propag.|date=2007|volume=55|issue=4|pages=1193|doi=10.1109/TAP.2007.893426|bibcode=2007ITAP...55.1193E|hdl=11511/35085|s2cid=19335959|hdl-access=free}} or tunable materials.{{cite journal|last1=Liu|first1=L.|last2=Langley|first2=R.|title=Liquid crystal tunable microstrip patch antenna|journal=Electronics Letters|date=2008|volume=44|issue=20|pages=1179|doi=10.1049/el:20081995|bibcode=2008ElL....44.1179L}}
= Radiation pattern reconfiguration =
Radiation pattern reconfigurability is based on the intentional modification of the spherical distribution of the radiation pattern. Beam steering is the most extended application and consists of steering the direction of maximum radiation to maximize the antenna gain in a link with mobile devices. Pattern reconfigurable antennas are usually designed using movable/rotatable structures{{cite book|last1=Chiao|first1=J.C.|last2=Fu|first2=Y.|last3=Chio|first3=I.M.|last4=DeLisio|first4=M.|last5=Li|first5=L.Y.|title=1999 IEEE MTT-S International Microwave Symposium Digest (Cat. No.99CH36282) |chapter=MEMS reconfigurable Vee antenna |date=1999|volume=4|pages=1515–1518|doi=10.1109/MWSYM.1999.780242|isbn=978-0-7803-5135-6|s2cid=7946482}}{{cite journal|last1=Rodrigo|first1=D.|last2=Jofre|first2=L.|last3=Cetiner|first3=B.A.|title=Circular Beam-Steering Reconfigurable Antenna With Liquid Metal Parasitics|journal=IEEE Trans. Antennas Propag.|date=2012|volume=60|issue=4|pages=1796|doi=10.1109/TAP.2012.2186235|bibcode=2012ITAP...60.1796R|s2cid=36089245}} or switchable and reactively-loaded parasitic elements.{{cite journal|last1=Aboufoul|first1=T.|last2=Parini|first2=C.|last3=Chen|first3=X.|last4=Alomainy|first4=A.|title=Pattern-Reconfigurable Planar Circular Ultra-Wideband Monopole Antenna|journal=IEEE Trans. Antennas Propag.|date=2013|volume=61|issue=10|pages=4973|doi=10.1109/TAP.2013.2274262|bibcode=2013ITAP...61.4973A|s2cid=9565138}}{{cite journal|last1=Harrington|first1=R.F.|author-link=Roger F. Harrington|title=Reactively controlled directive arrays|journal=IEEE Trans. Antennas Propag.|date=1978|volume=26|issue=3|pages=390–395|doi=10.1109/TAP.1978.1141852|bibcode=1978ITAP...26..390H}}{{cite journal|last1=Hum|first1=S.V.|last2=Perruisseau-Carrier|first2=J.|title=Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review|journal=IEEE Trans. Antennas Propag.|date=2014|volume=62|issue=1|pages=183|doi=10.1109/TAP.2013.2287296|arxiv=1308.4593|bibcode=2014ITAP...62..183H|s2cid=32075766}} In the last 10 years, metamaterial-based reconfigurable antennas have gained attention due their small form factor, wide beam steering range and wireless applications.{{cite journal|last1=Mookiah|first1=P.|last2=Dandekar|first2=K.R.|title=Metamaterial-substrate antenna array for MIMO communication system|journal=IEEE Transactions on Antennas and Propagation|date=2009|volume=57|issue=10|pages=3283|doi=10.1109/TAP.2009.2028638|bibcode=2009ITAP...57.3283M|s2cid=22859024}}{{cite journal|last1=Gulati|first1=N.|last2=Dandekar|first2=K.R.|title=Learning State Selection for Reconfigurable Antennas: A multi-armed bandit approach|journal=IEEE Transactions on Antennas and Propagation|date=2014|volume=62|issue=3|pages=1027|doi=10.1109/TAP.2013.2276414|bibcode=2014ITAP...62.1027G|s2cid=1061713}} Plasma antennas have also been investigated as alternatives with tunable directivities.{{cite journal |last1=Borg |first1=Gerard G. |last2=Harris |first2= Jeffrey H. |date= 24 May 1999 |title=Application of plasma columns to radiofrequency antennas |journal=Applied Physics Letters |volume=74 |issue=22 |pages=3272–3274 |doi=10.1063/1.123317 |bibcode=1999ApPhL..74.3272B }}{{cite journal |last1=Kumar |first1=Rajneesh |last2=Bora |first2=Dhiraj |date=3 March 2010 |title=A reconfigurable plasma antenna |journal=Journal of Applied Physics |volume=107 |issue=5 |pages=053303–053303–9 |doi=10.1063/1.3318495 |bibcode=2010JAP...107e3303K }}{{cite journal |last1=Alexeff |first1=I. |last2=Anderson |first2=T. |display-authors=1 |date= 18 April 2006 |title= Experimental and theoretical results with plasma antennas |journal= IEEE Transactions on Plasma Science |volume=34 |issue=2 |pages= 166–172 |doi=10.1109/TPS.2006.872180 |bibcode=2006ITPS...34..166A |s2cid=32033839 }}
= Polarization reconfiguration =
Polarization reconfigurable antennas are capable of switching between different polarization modes. The capability of switching between horizontal, vertical and circular polarizations can be used to reduce polarization mismatch losses in portable devices. Polarization reconfigurability can be provided by changing the balance between the different modes of a multimode structure.{{cite book|last1=Simons|first1=R.N.|last2=Donghoon|first2=C.|last3=Katehi|first3=L.P.B.|title=IEEE Antennas and Propagation Society International Symposium (IEEE Cat. No.02CH37313) |chapter=Polarization reconfigurable patch antenna using microelectromechanical systems (MEMS) actuators |publisher=IEEE Antennas Propag. Soc. Int. Symp.|date=2002|volume=2|pages=6–9|doi=10.1109/APS.2002.1016015|isbn=978-0-7803-7330-3|hdl=2060/20020063517|s2cid=108547161}}
= Compound reconfiguration =
Compound reconfiguration is the capability of simultaneously tuning several antenna parameters, for instance frequency and radiation pattern. The most common application of compound reconfiguration is the combination of frequency agility and beam-scanning to provide improved spectral efficiencies. Compound reconfigurability is achieved by combining in the same structure different single-parameter reconfiguration techniques{{cite journal|last1=X.S.|first1=Yang|last2=Wang|first2=B.Z.|last3=Wu|first3=W.|last4=Xiao|first4=S.|title=Yagi Patch Antenna With Dual-Band and Pattern Reconfigurable Characteristics|journal=IEEE Antennas Wirel. Propag. Lett.|date=2007|volume=6|issue=11|pages=168|doi=10.1109/LAWP.2007.895292|bibcode=2007IAWPL...6..168Y|s2cid=7752473}}{{cite journal|last1=Aboufoul|first1=T.|last2=Chen|first2=X.|last3=Parini|first3=C.|last4=Alomainy|first4=A.|title=Multiple-parameter reconfiguration in a single planar ultra-wideband antenna for advanced wireless communication systems|journal=IET Microwaves, Antennas & Propagation|date=2014|volume=8|issue=11|pages=849–857|doi=10.1049/iet-map.2013.0690|s2cid=110598537 |doi-access=free}} or by reshaping dynamically a pixel surface.{{cite journal|last1=Rodrigo|first1=D.|last2=Cetiner|first2=B.A.|last3=Jofre|first3=L.|title=Frequency, Radiation Pattern and Polarization Reconfigurable Antenna Using a Parasitic Pixel Layer|journal=IEEE Trans. Antennas Propag.|date=2014|volume=62|issue=6|pages=3422|doi=10.1109/TAP.2014.2314464|bibcode=2014ITAP...62.3422R|s2cid=22316165|url=http://infoscience.epfl.ch/record/201391 }}{{cite journal|last1=Pringle|first1=L.N.|title=A reconfigurable aperture antenna based on switched links between electrically small metallic patches|journal=IEEE Trans. Antennas Propag.|date=2004|volume=52|issue=6|pages=1434–1445|doi=10.1109/TAP.2004.825648|display-authors=etal|bibcode=2004ITAP...52.1434P|s2cid=25035434}}
Reconfiguration techniques
There are different types of reconfiguration techniques for antennas. Mainly they are electrical (for example using RF-MEMS, PIN diodes, or varactors), optical, physical (mainly mechanical), and using materials. For the reconfiguration techniques using materials, the materials could be solid, liquid crystal, liquids (dielectric liquid{{cite journal |first1=Elizaveta |last1=Motovilova |first2=Shao Ying |last2=Huang|title=A Review on Reconfigurable Liquid Dielectric Antennas |journal=Materials |year=2020 |volume=13 |issue=8 |page=1863 |doi=10.3390/ma13081863 |pmid=32316173 |pmc=7216238 |bibcode=2020Mate...13.1863M |doi-access=free }} or liquid metal).