What is Waveguides: Definition and 48 Discussions

A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities decrease according to the inverse square law as they expand into three dimensional space.
There are different types of waveguides for different types of waves. The original and most common meaning is a hollow conductive metal pipe used to carry high frequency radio waves, particularly microwaves. Dielectric waveguides are used at higher radio frequencies, and transparent dielectric waveguides and optical fibers serve as waveguides for light. In acoustics, air ducts and horns are used as waveguides for sound in musical instruments and loudspeakers, and specially-shaped metal rods conduct ultrasonic waves in ultrasonic machining.
The geometry of a waveguide reflects its function; in addition to more common types that channel the wave in one dimension, there are two-dimensional slab waveguides which confine waves to two dimensions. The frequency of the transmitted wave also dictates the size of a waveguide: each waveguide has a cutoff wavelength determined by its size and will not conduct waves of greater wavelength; an optical fiber that guides light will not transmit microwaves which have a much larger wavelength. Some naturally occurring structures can also act as waveguides. The SOFAR channel layer in the ocean can guide the sound of whale song across enormous distances.
Any shape of crossection of waveguide can support EM waves. Irregular shapes are difficult to analyse. Commonly used waveguides are rectangular and circular in shape.

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  1. H

    I Why is the electric field in y direction in a TE guided wave?

    Hi, I have a fairly simple question, but the answer is probably not as simple. I'm not sure to understand why in a guided wave (TE), the electric field is in the y direction. I know ##E_z = 0##, but why ##E_x = 0, B_y = 0##?
  2. warhammer

    Problem on Parallel Plate Waveguide

    The Imgur Link of the Problem with the figure - Problem Link. I did not paste it here as the post upload quality seemed heavily pixelated for some reason. For this problem, what I did was to divide the waveguide into 2 sections of distinct permabilities to calculate the cutoff frequency. Since...
  3. S

    A Evanescent field of a waveguide

    If we look to the figure, in several articles they mentioned that the part of the mode field, the tail of the mode field diameter, travel in the cladding, this maybe I can understand that because of a little change between the refractive indices of the core and the cladding, then the transverse...
  4. E

    Rearranging the equation for the cutoff condition in optical fibers

    Hello! In Optical fibers, let ##k_1## and ##k_2## be respectively the propagation constants in core and cladding, ##\beta## the propagation costant of a mode along the direction ##z##, ##a## the radius of the fiber. Using the normalized quantities ##u=a \sqrt{k_1^2 − \beta^2}## and ##w=a...
  5. tworitdash

    A Dirichlet and Neumann boundary conditions in cylindrical waveguides

    The book of Balanis solves the field patterns from the potential functions. Let say for TE modes, it is: F_z(\rho, \phi, z) = A_{mn} J_m(\beta_{\rho}\rho) [C_2 \cos(m\phi) + D_2 \sin(m\phi)] e^{-j\beta_z z} There is no mention of how to solve for the constant A_{mn} . Then, from a paper...
  6. E

    TE and TM modes in optical fibers

    In a step-index optical fiber, considering Bessel functions of order ##\nu = 0## and no ##\phi## dependence, it is possible to obtain two separate sets of components, which generate respectively TE and TM modes. In the former case, only ##E_{\phi}##, ##H_r##, ##H_z## are involved; in the latter...
  7. BlackPowder

    What is the difference between a waveguide/horn and regular metal pipes?

    What is the difference between those horns/waveguides and regular metal pieces with a same geometry? Why the microwave companies sell those parts at hundreds and thousands dollars? Why we cannot buy some metal sheets or pipes on McMaster-Carr with very low price and make some microwave...
  8. Amartansh

    I Visualization of fields in waveguides

    Can someone provide me intuitive visualization of how E or H field can be longitudinal in a waveguide (TM/TE)? TEM is easy to visualize, but how EM wave can behave like sound in a waveguide (constant phase and amplitude plane in the same direction)? [Moderator: large bold font removed. In the...
  9. C

    Difference between Waveguides and Resonators

    I claim that waveguides are resonators because a resonator is defined as a device which can produce you normal modes of some ' mathematical object' you're looking for, which in waveguide's case is Electromagnetic fields ( waveguide can produce normal modes called TE and TM ). Am I right?
  10. I

    Jackson E&M: Power loss in waveguides for TE & TM modes

    Hi. I'm having trouble with calculating (8.59) from (8.58) (## \vec H_{//} ## is simply ## \vec H ## in Jackson, but that shouldn't matter.) in Jackson. Specifically I think I'm not sure about parallel component of H field here. For example, shouldn't I have two terms for the...
  11. tworitdash

    What is the attenuation below cut-off frequency for TE10?

    It is not useful to talk about the attenuation below cut-off frequency, but I have this doubt about what happens to the wave below cut off for an electric conductor. As we know if we derive the propagation constant, it becomes imaginary saying that there should not be any wave propagating in the...
  12. tworitdash

    I Why different cutoff frequencies for TE and TM in a medium?

    Today in my electro-magnetics class, we were told that the cut-off frequencies of TE and TM waves on a co-axial cable are different. As far as I understand, it says that if there is an electric field with one frequency projected on it and if we know that the problem can be simplified if we see...
  13. C

    Open Circuit Termination for Waveguides in High Frequency Labs

    Hi everyone, I am trying to understand that why do we use open circuit terminator for wave guides or any RF element such as coupler and etc. I know if we just leave it open, it does not work as open circuit. But why?
  14. J

    What is the textbook for optical waveguide theory using matrix notation?

    I remember using matrix notation in my course on optical waveguide theory many years ago. The lecturer was using a textbook which I cannot remember. I have since misplaced my course notes. I was wondering if anyone could direct me to the source textbook? The notation (Eq. 2.20) is attached...
  15. S

    Engineering Eigenfunctions of the vector Helmholtz equation

    Hi everyone, I'm looking for a reference book that treats the theory behind the eigenfunctions solution of the so called vector Helmholtz equation and its Neumann and Dirichlet problems. I've already found a theory inside the last chapter of Morse & Feshbach's Methods of theoretical physics...
  16. S

    Prove That Relationship Given is True for Transmission Lines Homework

    Homework Statement I am having problems with the second part of the question - proving that the relationship given is true. Homework Equations See question. The Attempt at a Solution Firstly, consider a single pair of transmission lines with characteristic impedances ##Z_{1}## and ##Z_{2}##...
  17. F

    Testing RF Waveguides: Using VNA for Freq, Power & Avg

    Hi there i am trying to test RF Waveguides and testing them. Something does not look right to me. i am using Freq range, data points, power and avg option is there anything special we use on VNA for testing Waveguides. Regards, Faheem
  18. E

    Field frequency and angle of incidence in optical waveguides

    Hello! In this previous post, most replies point out that it is not possible to predict the angle of refraction (and so the frequency) at a certain interface, given the wavelength of the original signal. In particular, But when dealing with optical waveguides, it seems to be different. I am...
  19. E

    Modes orthogonality in a dielectric slab

    A typical mode in a dielectric slab like this, with propagation along x, uniformity along z and refractive index variation along y, is represented by the following function: f (y) = \begin{cases} \displaystyle \frac{\cos (k_1 y)}{\cos (k_1 d)} && |y| \leq d \\ e^{-j k_2 (y - d)} && |y| \geq d...
  20. E

    Why is the resonance condition satisfied in a transverse resonance method?

    The Transverse resonance method is used to determine the propagation constant of a wave in several waveguides, like the rectangular waveguide, or also dielectric waveguides. It takes advantage of the fact that a standing wave is present along a certain direction (transverse with respect to the...
  21. rkrishnasanka

    Is pertubation a linear operation?

    My question stems from a discussion I had with my colleague today. In Electomagnetic coupling , like in waveguide structures. We apply pertubation theory to find out the coupling between various modes that get coupled in the device. My colleague said that the coupling interaction was...
  22. R

    Hybrid HE11 mode of corrugated waveguides as source of axion

    Why HE11 mode of corrugated waveguides would not be a natural source of axion field?
  23. J

    Why do small waveguides support less modes than larger ones?

    I've taken several courses on Electromagnetics and Waveguide. It has become common sense to me that small waveguides support less modes than larger ones. I've also learned the graphical method to calculate the number of modes in a 3-layer slab waveguide. What I don't get is why small...
  24. D

    Waveguides and Cavity resonator Equation confusion

    Homework Statement This is not a homework question and I am asking this question out of curiosity. We have been taught rectangular wave guides and cavity resonator recently and I don't want to gulp the wave equations as it is, so the problem that I am facing ( I have written it on paper and...
  25. A

    Solving Vector Modal Equation

    I need help solving the vector modal equation for a step index fiber having a constant refractive index in the core and the cladding. (Under the conditions of zero dispersion and absorption.
  26. vead

    TEM TE and TM Modes for Waveguides ?

    hello ; I need some help.I reading about TEM TE and TM Modes for Waveguides. actually I need some equations for Planar wave guide and optical fiber wave guide. I did google search. I don't understand how to write equation step by step for planar wave guide I found this link...
  27. F

    Why do we aim for Single Mode waveguides?

    I trying to formulate a new project based on waveguides (~1 cm long) for sensing with the evanescent field. In all papers I've seen on similar topics they all aim for single mode (SM) waveguides, but I never understood the reason. Is there a quick answer?
  28. G

    Waveguides and Numerical Aperture

    Hey all, First time posting on here hope this all goes well! I just worked through a problem on dielectric slab waveguides with core and cladding and it was pretty straight forward finding critical angle, critical angle compliment, number of modes, numerical aperture, maximum acceptance angle...
  29. P

    Quarter wave chokes and waveguides?

    hi all, could someone please explain how the above work? Thanks in advance.
  30. Roodles01

    How are modes classified in rectangular waveguides?

    Homework Statement How do I classify modes? If there is a rectangular waveguide how can I show it is operating in TE10, TE20 or TE11 mode. Homework Equations Could someone help clarify how the 10, 11 or 20 comes about? Is it due to the dimensions of the guide or something else?
  31. X

    Principles behind how Waveguides work.

    So I am studying about waveguides and I am going through all this mathematics and then I realized that I do not understand the general concept of how wave guides even work. I can go through the math all I want but I don't understand one thing.. If a wave is radiated in free space and is...
  32. Roodles01

    What is the relationship between frequency and cross section in a waveguide?

    I have a question relating to waveguides. Fine, but having looked at what TE TM modes are I don't really see how I can find the frequency of the μwave with the information I have.Homework Equations A waveguide with dimensions a & b (short & long sides respetively) propogates in the TM10 mode...
  33. E

    Transmission lines and Waveguides

    Ok, it's clear to me that waveguides are for sending EM waves from one place to another (e.g. TEM, TE, TM modes). But what about TLs? I've seen them described as carrying AC signals (V or I) but also EM waves, e.g. TEM waves in coax cable. What gives? Does one imply the existence of the...
  34. P

    Rectangular Waveguides: Effective Index Method

    Homework Statement Is anyone familiar with the effective index method for rectangular waveguides? I have a waveguide for which the width is much greater than the thickness. I think I need to start by treating it as a planar waveguide. But I am supposed to get an effective index which depends...
  35. N

    Question related to Optical Waveguides and power

    I am doing a 2D COMSOL mode analysis of an optical waveguide. The mode analysis shows you the electric/magnetic field and you want to find out the power of the guided mode. How could I do this? Power is P = I*V or dE/dt with units of Joules per second. In the FEM simulation I have given...
  36. R

    Waveguides, cavities and circuits

    Can you make a microwave oven by taking a microwave generator and attaching one lead to one side of a metal box, and the other lead to the other side of the metal box, and putting food in the box and flipping the switch on? If this is possible, can you take a can of food and put two leads across...
  37. R

    Propagation in dielectric Waveguides

    Homework Statement A planar waveguide is formed from a 10mircometer thick film of material of refractive index 1.46 sandwiched in material of refractive index 1.45. Calculate the number of modes of propagation that guide support at the wavelength 1.3mircometer, and estimate the propagation...
  38. P

    Electromagnetism questions - polarisations and waveguides

    Homework Statement These are some general questions I have, related to an old assignment I am looking at. 1) Discuss the applications of polarisation in: a. radio transmission across water b. broadcast TV transmission c. satellite communication 2) Explain why a plane electromagnetic...
  39. T

    Electron Tunneling & Waveguides: A Formal Analogy

    can anyone tell me what's the formal analogy between electron tunneling in terms of quantum mechanics and electromagnetic waveguide modes at frequencies below cutoff ?
  40. K

    TE/TM modes in idelectric waveguides and their effect on light output

    Hello everyone, I just have a few questions concerning TE and TM modes in a dielectric slab symmetrical waveguide. 1) How do the TE and TM mode profiles affect the actual light pattern being output on the waveguide face/facet? What determines the actual light patterns on the waveguide face...
  41. C

    Wavelength -> antenna, waveguides, mirrors ets

    Hi I have this question for sometime, and until i found a recent post here on this forum (wavelength and aperture) i thought i was the only person who just plain didn't get it. My questions arises firstly when i consider antennae and as roughly quote from the many texts i have read "to...
  42. A

    Textbooks that cover plane mirror waveguides

    Anyone know of an E&M textbook that covers plane mirror waveguides in any reasonable detail?
  43. R

    Understanding TE Mode in Waveguides: Effects of Linear Polarization

    So we just went over waveguides in my class, in particular the TE and TEM modes (for a perfect conductor with two infinite planes for waveguides). I know that according to boundary conditions (assuming perfect conductor), the transverse electric field components must be zero at the boundary...
  44. U

    Conductivity of Waveguides

    Homework Statement At frequency f1=9 GHz, the guide wavelength along a certain dielectric-filled conducting waveguide is found to be Lambda1=3.456 cm, for a particular mode. At frequency f2=10GHz, the wavelength is Lambda2=2.345 cm, for the same mode. (a) What is the cutoff...
  45. P

    Programs: solve Maxwell equations for waveguides

    Hi!, Solving Maxwell equations for waveguides is a tedious work. :frown: Are there any programs, which can solve Maxwell equations for different kinds (geometries) of waveguides, and can give analytic solutions (i.e. give symbolic equations)? Therefore, the mathematical expressions of Ex...
  46. J

    Circular apertures in rectangular waveguides

    I wish somebody could tell me if he knows articles or information about modeling circular apertures in a transverse metalic plate in a rectangular waveguide. It appears in the "Waveguide Handbook" by N. Marcuvitz, on page 238. Can anybody help me to find more information about this theme? Thanks...
  47. T

    Acoustic Mirrors, Waveguides & Interference Effects

    Can someone point towards some useful information for me about the frequency dependence (over the audio frequency range) on acoustic mirrors, acoustic waveguides/horns and interfenece and diffraction effects please? Thanks
  48. F

    Why Does Group Velocity of Microwaves Increase with Frequency in Waveguides?

    Do anyone know why the group velocity of microwaves inside a rectangular waveguide goes up when frequency goes up? To me it seems like a higher frequency means a smaller wavelength, and thus a more ZIG ZAG patterns off the walls (to meet the boundary conditions). If the wave is zig zagging...