Is this patch antenna feasible? Microstrip Patch Antenna Calculator. How fringing field developed inside a patch antenna?
The resonant length of the antenna is slightly shorter because of the extended electric 'fringing fields' which increase the electrical length of the antenna slightly. An early model of the microstrip antenna is a section of microstrip transmission line with equivalent loads on either end to represent the radiation loss.
In telecommunication, there are severaltypes of microstrip antennas (also known asprinted antennas) the most common of which is themicrostrip patch antenna or patch antenna. Apatch antenna is a narrowband, wide-beamantennafabricated by etching the antenna element pattern in metal tracebonded to an insulating dielectric substrate with a continuousmetal layer bonded to the opposite side of the substrate whichforms a groundplane. Common microstrip antenna radiator shapes aresquare, rectangular, circular and elliptical, but any continuousshape is possible. Some patch antennas eschew a dielectricsubstrate and suspend a metal patch in air above a ground planeusing dielectric spacers; the resulting structure is less robustbut provides better bandwidth. Because such antennas have a verylow profile, are mechanically rugged and can be conformable, theyare often mounted on the exterior of aircraft and spacecraft, orare incorporated into mobile radio communications devices.
Fields for radiation into space but at the expense of larger element size. Microstrip patch antennas radiate primarily because of the fringing fields between the patch edge and the ground plane. The radiation increases with frequency, thicker substrates, lower permittivity, and originates mostly at discontinuities (Lewin, 1960).
Microstrip antennas are also relatively inexpensive tomanufacture and design because of the simple 2-dimensional physicalgeometry. They are usually employed at UHF and higher frequencies because the sizeof the antenna is directly tied to the wavelength at the resonance frequency. A single patch antennaprovides a maximum directive gain of around 6-9 dBi. It isrelatively easy to print an array of patches on a single (large)substrate using lithographic techniques. Patch arrays can providemuch higher gains than a single patch at little additional cost;matching and phase adjustment can be performed with printedmicrostrip feed structures, again in the same operations that formthe radiating patches. The ability to create high gain arrays in alow-profile antenna is one reason that patch arrays are common onairplanes and in other military applications.
Such an array of patch antennas is an easy way to make a phased array ofantennas with dynamic beamforming ability.[1]
The most commonly employed microstrip antenna is a rectangularpatch. The rectangular patch antenna is approximately a one-halfwavelength long section of rectangular [[microstrip] transmissionline. When air is the antenna substrate, the length of therectangular microstrip antenna is approximately one-half of afree-space wavelength.As the antenna is loaded with a dielectric as its substrate, thelength of the antenna decreases as the relative dielectric constant of the substrateincreases. The resonant length of the antenna is slightly shorterbecause of the extended electric 'fringing fields' which increasethe electrical length of the antenna slightly. An early model ofthe microstrip antenna is a section of microstrip transmission linewith equivalent loads on either end to represent the radiationloss.
The dielectric loading of a microstrip antenna affects both itsradiation pattern and impedance bandwidth. As the dielectricconstant of the substrate increases, the antenna bandwidthdecreases which increases the Q factor of the antenna and thereforedecreases the impedance bandwidth. This relationship did notimmediately follow when using the transmission line model of theantenna, but is apparent when using the cavity model which wasintroduced in the late 1970s by Lo et al.[2] Theradiation from a rectangular microstrip antenna may be understoodas a pair of equivalent slots. These slots act as an array and havethe highest directivity when the antenna has an air dielectric anddecreases as the antenna is loaded by material with increasingrelative dielectric constant.
An advantage inherent to patch antennas is the ability to havepolarization diversity. Patchantennas can easily be designed to have Vertical, Horizontal, RightHand Circular (RHCP) or Left Hand Circular (LHCP) Polarizations,using multiple feed points, or a single feedpoint with asymmetricpatch structures. [3] Thisunique property allows patch antennas to be used in many types ofcommunications links that may have varied requirements.
The half-wave rectangular microstrip antenna has a virtualshorting plane along its center. This may be replaced with aphysical shorting plane to create a quarter-wavelength microstripantenna. This is sometimes called a half-patch. The antenna onlyhas a single radiation edge (equivalent slot) which lowers thedirectivity/gain of the antenna. The impedance bandwidth isslightly lower than a half-wavelength full patch as the couplingbetween radiating edges has been eliminated.
Another type of patch antenna is the Planar Inverted F Antenna(PIFA) common in cellular phones with built-in antennas.[4] Theseantennas are derived from a quarter-wave half-patch antenna. Theshorting plane of the half-patch is reduced in length whichdecreases the resonance frequency. Often PIFA antennas havemultiple branches to resonate at the various cellular bands. Onsome phones, grounded parasitic elements are used to enhance theradiation bandwidth characteristics.
The Folded Inverted ConformalAntenna (FICA)[5] hassome advantages with respect to the PIFA, because it allows abetter volume reuse.
References
^'Welcome to antennas 101'by Louis E. Frenzel, 'Electronic Design' 2008
^Lo, Y.T., Solomon D. and Richards, W.F. 'Theory and Experiment onMicrostrip Antennas,' IEEE Transactions on Antennas andPropagation, AP-27, 1979 pp. 137-149.
^Bancroft, R. Microstrip and Printed Antenna Design NoblePublishing 2004, chapter 2-3
^Taga, T. Tsunekawa, K. and Saski, A., 'Antennas for DetachableMobile Radio Units,' Review of the ECL, NTT, Japan, Vol.35, No.1, January 1987, pp. 59-65.
^Di Nallo, C.; Faraone, A., 'Multiband internal antenna for mobilephones,' Electronics Letters , vol.41, no.9, pp. 514-515, 28 April2005
Externallinks
Fringing Field In Microstrip Patch Antenna Calculator 2017