It is a wave (whether mechanical or electromagnetic) that travels along a surface or an interface between two mediums that have different densities (for mechanical wave) or refraction indexes (for electromagnetic wave) and keeps being trapped between the two mediums. In other words, keeps propagating along the surface unless a discontinuity appears.
Examples:
1) In the case of mechanical waves, they are they waves you see generating on the surface of the water when some energy source (animal) swims above the water surface.
2) In the case of electromagnetic waves, they travel along a real (materials with relative permittivities > 1) or artificial substrates (using a series or metal disks or rods as in Yagi-Uda antennas) without getting radiated, unless a discontinuity appears where reflection and diffraction happens at the edges, giving rise to radiation. Sometimes, the discontinuity is engineered such that the patterns are shaped accordingly.
Since you are inquiring about microstrip antennas, then it is the wave that generates and travels inside the substrates of microstrip antennas and stays confined within the substrate (gets reflected at the air-substrate interface as well as the metal layer). It is a source of problems in array systems where the elements are closely spaced, such that the surface waves generated in one of the elements can continue propagating to the other element, producing undesired coupling, affecting the performance of the array. For a single antenna element, the surface-wave effect is insignificant. Surface waves will generate as a result of the substrate's excited TE and TM modes that resonate at relatively very high frequencies such that the effect on the antenna performance is insignificant, especially for those designed to operate at significantly lower frequencies, which is most probably the case.
The surface-wave phenomenon is extremely useful in designing high performance antennas with end-fire radiation patterns and wide bandwidths.
You may refer to a good reference that explains this with equations to calculate the resonances that give rise to surface waves in relation to the substrate parameters used and so on. Check section 1.51 in "Microstrip Antenna Design Handbook" by Ramesh Garg, Artech House.
https://books.google.com.sg/books?id=_er1LO5pEnUC&pg=PA43&lpg=PA43&dq=surface+wave+in+microstrip+antennas&source=bl&ots=nu6drkej1-&sig=ckBYguHeDaISptmx5E45WZ_RISU&hl=en&sa=X&ei=t9OjVJjUEJCjugTWh4KQCQ&ved=0CCMQ6AEwAA#v=onepage&q=surface%20wave%20in%20microstrip%20antennas&f=false
It is a wave (whether mechanical or electromagnetic) that travels along a surface or an interface between two mediums that have different densities (for mechanical wave) or refraction indexes (for electromagnetic wave) and keeps being trapped between the two mediums. In other words, keeps propagating along the surface unless a discontinuity appears.
Examples:
1) In the case of mechanical waves, they are they waves you see generating on the surface of the water when some energy source (animal) swims above the water surface.
2) In the case of electromagnetic waves, they travel along a real (materials with relative permittivities > 1) or artificial substrates (using a series or metal disks or rods as in Yagi-Uda antennas) without getting radiated, unless a discontinuity appears where reflection and diffraction happens at the edges, giving rise to radiation. Sometimes, the discontinuity is engineered such that the patterns are shaped accordingly.
Since you are inquiring about microstrip antennas, then it is the wave that generates and travels inside the substrates of microstrip antennas and stays confined within the substrate (gets reflected at the air-substrate interface as well as the metal layer). It is a source of problems in array systems where the elements are closely spaced, such that the surface waves generated in one of the elements can continue propagating to the other element, producing undesired coupling, affecting the performance of the array. For a single antenna element, the surface-wave effect is insignificant. Surface waves will generate as a result of the substrate's excited TE and TM modes that resonate at relatively very high frequencies such that the effect on the antenna performance is insignificant, especially for those designed to operate at significantly lower frequencies, which is most probably the case.
The surface-wave phenomenon is extremely useful in designing high performance antennas with end-fire radiation patterns and wide bandwidths.
You may refer to a good reference that explains this with equations to calculate the resonances that give rise to surface waves in relation to the substrate parameters used and so on. Check section 1.51 in "Microstrip Antenna Design Handbook" by Ramesh Garg, Artech House.
https://books.google.com.sg/books?id=_er1LO5pEnUC&pg=PA43&lpg=PA43&dq=surface+wave+in+microstrip+antennas&source=bl&ots=nu6drkej1-&sig=ckBYguHeDaISptmx5E45WZ_RISU&hl=en&sa=X&ei=t9OjVJjUEJCjugTWh4KQCQ&ved=0CCMQ6AEwAA#v=onepage&q=surface%20wave%20in%20microstrip%20antennas&f=false
Surface wave, as the name implies travels along the metal surface of the antenna. In ideal case we want all of our energy to be radiated but due to surface waves the energy is lost in the conductor due to its finite conductivity resulting inn reduced directivity, decreased radiation efficiency.
I also recommend you to check the references by Prof. Akira Ishimaru, a fundamental reference in the description and classification of surface wave, depending on the solutions derived from the wave equation and the applied boundary conditions.
Basically surface wave travels onto the surface between two dissimilar medium of impedance. Surface wave is, in other words, kind of standing wave. in multi-elementary devices it produce resonance frequency.
In brief,
They extract the power. So in desired direction there is less power transmission, because of it we are not able to get good performance in desired direction.
And rest...I think all have mentioned very well.
Regards,
Surface wave travels over a surface of media e. g. earth. The wave propagation has a greater effect of surface conductivity as well as surface smoothness. Mainly, this is observed in a medium wave
A poor conductivity surface will have poor radiation coverage area.
Uneven surface will have polarisation loss. Even to the extent the vertical polarisation can become horizontal one.
from a range of substrate heights available , how do we chose which one is better based on Maximum frequency of operation and Surface wave cut-off frequency?
PBGS aas well as Dumbbell shaped Defected ground structure can suppress surface wave efficiently
Surface wave generates and travels inside the substrates of microstrip antennas and stays confined within the substrate. Many researchers have worked on minimization of it using PBG/EBG/AMC etc. As it extracts power, so less transmission of power occurs in intended direction and affects the radiation pattern.
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