Ridged waveguide theory

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Ridged waveguide theory

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In the last chapter we studied what happened to the lumped elements of circuits when they were operated at very high frequencies, and we were led to see that a resonant circuit could be replaced by a cavity with the fields resonating inside. Another interesting technical problem is the connection of one object to another, so that electromagnetic energy can be transmitted between them.

In this chapter we want to look into the ways that objects can be interconnected at high frequencies. Another way is to say that we have been discussing the behavior of waves in free space. Now it is time to see what happens when oscillating fields are confined in one or more dimensions. We will discover the interesting new phenomenon when the fields are confined in only two dimensions and allowed to go free in the third dimension, they propagate in waves.

We begin by working out the general theory of the transmission line. The radiation could be stopped by surrounding the line with a metal pipe, but this method would not be practical for power lines because the voltages and currents used would require a very large, expensive, and heavy pipe.

For somewhat higher frequencies—say a few kilocycles—radiation can already be serious. We take the simplest coaxial line that has a central conductor, which we suppose is a thin hollow cylinder, and an outer conductor which is another thin cylinder on the same axis as the inner conductor, as in Fig. We begin by figuring out approximately how the line behaves at relatively low frequencies. We have already described some of the low-frequency behavior when we said earlier that two such conductors had a certain amount of inductance per unit length or a certain capacity per unit length.

Using our results for the infinite filter, we see that there would be a propagation of electric signals along the line. Rather than following that approach, however, we would now rather look at the line from the point of view of a differential equation. Equations If we wish, we could modify them to include the effects of resistance in the conductors or of leakage of charge through the insulation between the conductors, but for our present discussion we will just stay with the simple example.

For a uniform transmission line, the voltage and current propagates along the line as a wave. We can calculate them easily for a coaxial cable, so we will see how that goes. Combining this result with Eq. The wave travels down the line with the speed of light. We will see later that for good conductors at high frequencies, all currents distribute themselves on the surfaces as they would for a perfect conductor, so this assumption is then valid. So long as the cross section is constant and the space between has no material, waves are propagated at the velocity of light.

No such general statement can be made about the characteristic impedance. The next thing we want to talk about seems, at first sight, to be a striking phenomenon: if the central conductor is removed from the coaxial line, it can still carry electromagnetic power. In other words, at high enough frequencies a hollow tube will work just as well as one with wires.The formulas obtained provide possibilities to calculate cutoff wave numbers and electric and magnetic fields distributions for TEMTE and TM modes in the presence of the ridges either on the inner or on the outer conducting cylinder.

Analysis of the dependence of numerical solutions convergence for cutoff wave numbers on the number of basis functions and partial modes has been carried out. It has been shown that for calculation of cutoff wave numbers with residual error less than 0. This is a preview of subscription content, log in to check access. Suntheralingam, N. Mohottige, D. DOI: Dai, Z. Wang, N. Julian, J. Ruiz-Bernal, M. Valverde-Navarro, G.

Goussetis, J. Gomez-Tornero, A. Akgiray, S. Weinreb, W. Antennas Propag. Serebryannikov, O. Amari, J. Microwave Theory Tech. Balaji, R. Yu Rong, K. Weimin Sun, C. Sun, C.Click here to go to our main page on waveguide. Click here to go to our main page on transmission lines.

ridged waveguide theory

Double-ridged waveguide can provide more bandwidth than "normal" rectangular waveguide. Double-ridged waveguide is similar to finline. A pair of ridges protrude into the center of the waveguide, parallel to the short wall. This is where the E-field is maximum. By bringing ground down the ridges, the E-field is further increased. That was a lame explanation Single ridge waveguide is a very interesting structure, it looks similar to rectangular waveguide however with a huge capacitive loading in the middle of its broad wall.

A lot of early ridged WG designs were made in the late nineteen-forties by Mr. Microwave S. Cohnincluding some amazing filters and transitions to coaxial ports. If one is lucky enough he can see the IMS historic exhibition, I personally saw his lab-books where he analyzed such structures, and I was amazed. My luck culminated when he walked right into the exhibit in Boston !

I look at these works with deep respect, which is very much due for Mr. Microwave and his peers, they used their brains, no computers, no HFSS, some good math and lots and lots of intuition. Editor's note: Dr.

Seymour Cohn was given the title of "Mr. Microwave" at the IMS at a special session in his honor. He passed away in September Single ridge waveguide can be thought of as half of a double ridge waveguide with a horizontal perfect electrical conductor PEC inserted at exactly the middle of the gap region.

Microwave Engineering - Waveguides

This waveguide will have the same cut-off frequency of the fundamental waveguide mode, however the higher order modes will be pushed further away in frequency. As usual, the price paid is increased loss and reduced power handling in comparison to double ridge waveguide. Toggle navigation Menu. Filter by alphabets Filter by categories. Double-Ridged Waveguide Click here to go to our main page on waveguide Click here to go to our main page on transmission lines Double-ridged waveguide can provide more bandwidth than "normal" rectangular waveguide.

Single-ridged waveguide Here's a discussion of single-ridged waveguide, from Mohammed.

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Single ridge waveguide offers very interesting set of characteristics: Compared to a rectangular waveguide of the same outer dimensions, ridge waveguide will have a much lower cut-off frequency of its fundamental mode.

In other words for the same cut-off frequency of the fundamental mode, the cross section of the ridge waveguide will be much smaller than the rectangular waveguide which presents an opportunity for compact designs.

By proper choice of the gap dimension g in relation to the b-dimension, the higher order mode can be engineered, i. This can be very useful in filter design for examplewhere the spurious pass-bands associated with higher order modes are pushed very far out sometimes eliminating the need for clean-up low-pass filter. A MEMS actuator or a simple screw in the gap region will provide an almost perfect short circuit, since most of the field is concentrated in that area.

Some useful references: W. Hoefer and M. Theory Tech. Here you can find formulae for calculating the cut-off frequencies, characteristics impedances etc. A comprehensive treatment of this waveguide.Skip to Main Content. A not-for-profit organization, IEEE is the world's largest technical professional organization dedicated to advancing technology for the benefit of humanity. Use of this web site signifies your agreement to the terms and conditions.

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For IEEE to continue sending you helpful information on our products and services, please consent to our updated Privacy Policy. Email Address. Sign In. Access provided by: anon Sign Out. Analysis and design of quadruple-ridged waveguides Abstract: In a previous paper, a unified approach has been proposed for the analysis and design of single- and double-ridged waveguides by a magnetic field integral equation MFIE formulation see ibid.

This paper presents a continuing work with emphasis on the design of quadruple-ridged waveguides. The characteristics of square, circular and diagonal quadruple-ridged waveguides, including cutoff frequencies, attenuation, impedance and modal field distributions, are for the first time systematically analysed and reported. Distinct to being in a single- or double-ridged waveguide, the fundamental-mode in a quadruple-ridged waveguide has a cutoff frequency very close to that of the second-lowest mode, thus the natural single mode bandwidth is very small.

However, when the second-lowest mode is effectively suppressed or not excited, a very wide bandwidth can be achieved. This unique property, plus the capabilities of dual-polarization, high power, and low impedance, makes the quadruple-ridged waveguides well-suited to many antenna and microwave applications.

Article :. Date of Publication: Dec DOI: Need Help?Skip to Main Content.

Waveguide filter

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Eigenmodes of coaxial quad-ridged waveguides. Theory

Sign In. Access provided by: anon Sign Out. Complex Permittivity Measurement Using a Ridged Waveguide Cavity and the Perturbation Method Abstract: A new cavity-based method to measure the complex permittivity of dielectric materials is presented here. The method uses a double-ridged waveguide for the cavity instead of the widely used rectangular waveguides, thus enhancing the operational frequency bandwidth by twofold.

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The bandwidth enhancement is advantageous when measuring the permittivities of frequency dispersive specimens. Building on the perturbation theory, this paper develops the measurement equations required for permittivity extraction.

The measurement errors induced by the approximations in the perturbation theory are evaluated using numerical simulations, and the errors are quantified for different specimen sizes and dielectric constants. The experimental results are also presented. The complex permittivities of three common plastic specimens are measured at frequencies of around 3, 5, and 8 GHz using one double-ridged cavity.

For comparison purposes, the same samples are also measured using two rectangular cavities operating in the S- and X-bands.

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Good agreement in the measured permittivity values is observed. Article :. Date of Publication: 18 October DOI: Need Help?The different waveguide modes have different properties and therefore it is necessary to ensure that the correct mode for any waveguide is excited and others are suppressed as far as possible, if they are even able to be supported.

Looking at waveguide theory it is possible it calculate there are a number of formats in which an electromagnetic wave can propagate within the waveguide. These different types of waves correspond to the different elements within an electromagnetic wave.

Text about the different types of waveguide modes often indicates the TE and TM modes with integers after them: TE m,n. The numerals M and N are always integers that can take on separate values from 0 or 1 to infinity. These indicate the wave modes within the waveguide.

Only a limited number of different m, n modes can be propagated along a waveguide dependent upon the waveguide dimensions and format.

For each waveguide mode there is a definite lower frequency limit. This is known as the cut-off frequency.


Below this frequency no signals can propagate along the waveguide. As a result the waveguide can be seen as a high pass filter. It is possible for many waveguide modes to propagate along a waveguide.

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The number of possible modes for a given size of waveguide increases with the frequency. It is also worth noting that there is only one possible mode, called the dominant mode for the lowest frequency that can be transmitted. It is the dominant mode in the waveguide that is normally used.

It should be remembered, that even though waveguide theory is expressed in terms of fields and waves, the wall of the waveguide conducts current. For many calculations it is assumed to be a perfect conductor. In reality this is not the case, and some losses are introduced as a result, although they are comparatively small.

There are a number of rules of thumb and common points that may be used when dealing with waveguide modes. The waveguide propagation constant defines the phase and amplitude of each component or waveguide mode for the wave as it propagates along the waveguide. The factor for each component of the wave can be expressed by:. In this case no significant propagation takes place and the frequency used for the calculation is below the waveguide cut-off frequency.

It is actually found in this case that a small degree of propagation does occur, but as the levels of attenuation are very high, the signal only travels for a very small distance. As the results are very predictable, a short length of waveguide used below its cut-off frequency can be used as an attenuator with known attenuation. Here it is found that the amplitude of each component remains constant, but the phase varies with the distance z.

This means that propagation occurs within the waveguide. This waveguide theory and the waveguide equations are true for any waveguide regardless of whether they are rectangular or circular. It can be seen that the different waveguide modes propagate along the waveguide in different ways. As a result it is important to understand what he available waveguide modes are and to ensure that only the required one is used. Waveguide modes Looking at waveguide theory it is possible it calculate there are a number of formats in which an electromagnetic wave can propagate within the waveguide.

It is the mode that is commonly used within coaxial and open wire feeders. The TEM wave is characterised by the fact that both the electric vector E vector and the magnetic vector H vector are perpendicular to the direction of propagation. Rectangular waveguide TE modes For each waveguide mode there is a definite lower frequency limit. Rules of thumb There are a number of rules of thumb and common points that may be used when dealing with waveguide modes. For rectangular waveguides, the TE 10 mode of propagation is the lowest mode that is supported.

For rectangular waveguides, the width, i. For rectangular waveguides, the TE 20occurs when the width equals one wavelength of the lower cut-off frequency. Supplier Directory For everything from distribution to test equipment, components and more, our directory covers it.

Selected Video What is an Op Amp? Featured articles.It should be noted from the outset that in general terms the behavior of waves in circular waveguide is the same as in rectangular guides. The laws governing the propagation of waves in waveguides are independent of the cross-sectional shape and dimensions of the guide.

As a result, all the parameters and definitions evolved for rectangular waveguides apply to circular waveguides, with the minor modification that modes are labeled somewhat differently. All the equations also apply here except, obviously, the formula for cutoff wavelength. This must be different because of the different geometry, and it is given by.

To facilitate calculations for circular waveguides, values of kr are shown in Table for the circular waveguide modes most likely to be encountered. One of the differences in behavior between circular and rectangular waveguides is shown in Table Another difference lies in the different method of mode labeling, which must be used because of the circular cross section.

The integer m now denotes the number of full wave intensity variations around the circumference, and n represents the number of half-wave intensity changes radially out from the center to the wall. It is seen that cylindrical coordinates are used here.

There are situations in which properties other than those possessed by rectangular or circular waveguides are desirable. For such occasions, ridged or flexible waveguides may be used. Rectangular waveguides are sometimes made with single or double ridges, as shown in Figure The principal effect of such ridges is to lower the value of the cutoff wavelength.

ridged waveguide theory

In turn, this allows a guide with smaller dimensions to be used for any given frequency. Another benefit of having a ridge in a waveguide is to increase the useful frequency range of the guide.

It may be shown that the dominant mode is the only one to propagate in the ridged guide over a wider frequency range than in any other waveguide. The ridged waveguide has a markedly greater bandwidth than an equivalent rectangular guide. However, it should be noted that ridged waveguides generally have more attenuation per unit length than rectangular waveguides and are thus not used in great lengths for standard applications.

ridged waveguide theory

It is sometimes required to have a waveguide section capable of movement. This may be bending, twisting, stretching or vibration, possibly continuously, and this must not cause undue deterioration in performance.

Applications such as these call for flexible waveguides, of which there are several types. Among the more popular is a copper or aluminum tube having an elliptical cross section, small transverse corrugations and transitions to rectangular waveguides at the two ends. This waveguide is of continuous construction, and joints and separate bends are not required. It may have a polyethylene or rubber outer cover and bends easily but cannot be readily twisted.

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