If you have been in the loop of microwave communications, radar installations, and broadcasting signals, you must have heard about waveguides.  Waveguides are a type of transmission line made of a hollow, metal tube.  They are practically used for signals of extremely high frequency. 

Waveguides commonly point and circulate electromagnetic waves from one point to another.  They transmit high-frequency waves like microwaves, radio waves, and infrared waves.  Waveguides only act as electrical transmission lines for low-frequency waves that are less than one megahertz.  Co-axial cables are used instead.

The most common form of waveguides is a hollow conductive metal pipe that carries high-frequency radio waves.  They can also be in the form of wires, parallel plates, and optical fibers.

How was the waveguide developed?

Interestingly, two people are sharing the credit for inventing the waveguide.  George C. Southworth of Bell Telephone Laboratories and Wilmer L. Barrow of Massachusetts Institute of Technology developed the waveguide without knowing one another.  They learned about each other’s work several weeks before they were both scheduled to present their papers on waveguides to the American Physical Society and Institute of Radio Engineers panel.

Mr. Southworth discovered the waveguides when he observed waves in water-filled copper pipes.  On the other hand, Mr. Barrow found them when he used a hollow tube to feed radio waves to an antenna while locating an aircraft in the fog.  Both have amicably worked out how to share the credit and patent of their invention.

Regardless of who invented the waveguide, it proved vital with the radar systems during the second world war.  After which, both of them garnered numerous recognition for their work.  Until today, waveguides are used as transmission lines in various RF applications necessary in the digital age.

How does a waveguide work?

Within a specific frequency range, a geometrical structure propagates electromagnetic energy from one point to another in its preferred direction.  This is basically what a waveguide does.  The waveguide’s operating bandwidth is a vital factor since the electrical property of the structure determines the lower operating frequency.  It depends on which field the direction of the waves is perpendicular to.  There are two categories by which waves are propagated through a waveguide.  These are:

  • Transverse Electric (TE):  The electric field (E) vector is transverse or perpendicular to the waveguide’s axis.
  • Transverse Magnetic (TM):  The magnetic field (E) vector is transverse or perpendicular to the waveguide’s axis.

In Transverse Electric and Magnetic (TEM) mode, the wave travels along a standard, two-conductor transmission line.  Both fields are oriented perpendicular to the wave travel direction.  Hence, it cannot exist in a waveguide since it is only possible with two conductors.  In other words, waveguides do not operate under transverse electromagnetic modes (TEM) since they are built with a single conductor.

One should remember that the tube wall provides distributed inductance, while the space between the tube walls provides distributed capacitance.  Hence, the spreading of a wave in the waveguide, whether TE or TM, has very different characteristics than the propagation of a wave (TEM) on a transmission line. 

The difference lies in where transmitted waves get reflected from the sides of the waveguide. These reflected waves then interact with each other leading to the generation of an infinite number of discrete characteristic patterns called modes. The modes depend on WG’s size, shape, medium, and frequency.

The fundamental waveguide’s mode is the one with the lowest cut-off frequency. When circulating a wave via WG for a specific mode, the source should continuously operate at a frequency higher than the cut-off frequency. If the source activates at a frequency less than the cut-off frequency of its mode, then the wave will be attenuated.

What is the classification of waveguides?

Waveguides are classified into two types:

  • Metal Waveguides:  These consist of an enclosed conducting metal pipe.  They can be rectangular or circular waveguides and work on the total internal reflection from the conducting walls.
  • Dielectric Waveguides consist of dielectrics, and the reflection from dielectric interfaces helps propagate electromagnetic waves along the waveguide. They can either be dielectric slab waveguides or optical fiber.

What are the various applications?

Waveguides are a significant part of many communication technologies, broadcast signals, and radar systems.  Below are more specific places where they can be applied:

  • Waveguides are broadly used in optical fiber communication.
  • They are utilized in photonic integrated circuits.
  • Extensively, they are used in microwave ovens.
  • Waveguides are a part of various broadcasting and radar installations.
  • Space crafts for exploration beyond also benefit from waveguides.

What are the advantages and disadvantages of waveguides?

Waveguides have undoubtedly benefitted many areas of this age’s technological advancements.  All these are enabled because waveguides provide:

  • Wide bandwidth
  • Low insertion loss
  • High power handling capability
  • Good dispersion characteristics, so they are also used in designing WG filters
  • As a transmission line, they are easier to manufacture and maintain
  • The consistency of a dielectric material, which in a waveguide, is air
  • Moisture is not a problem in waveguides
  • As conduits for electromagnetic energy, they act as a director of the energy rather than as a signal conductor

However, because they are single-conductor elements, electrical energy propagation differs considerably from a two-conductor transmission line.  This and other disadvantages of waveguides are listed below:

  • Challenging to install because special couplings are required
  • Their physical size sometimes becomes a limitation
  • Weak thermal stability
  • 3-D WG execution can be difficult
  • Cost is high

What are Waveguide Components?

Waveguide components are Radio Frequency (RF)-passive components used to transmit, control, amplify, filter, measure, combine, couple, or divide RF signals at high frequencies.

Waveguide components consist of amplifiers, attenuators, transitions, bends, circulators, corner reflectors, feed horns, filters, and others.  These components are broadly used in commercial, military, communications, space, test & measurement, radar, radio, and many other applications.

Waveguide components are usually manufactured but at a large expense.  Did you know that these components can be successfully die-casted at a relatively low cost?  It is a good or even better alternative.

If you compare the price and performance of conventionally manufactured waveguide components versus die-cast parts, you will get significant savings with minimal to no difference in its execution.

At SEI, we are open to working with your Engineering Department so we can reduce your expenditures by custom designing and die casting the waveguide components of your projects.  We offer OMT, filters, WG/Coax Transitions, and cavity filters, to name a few.

Our experienced operators at SEI fully understand the close tolerances of your requirement.  We have developed proprietary manufacturing techniques that enable the production of WG Components to frequencies of 60 GHz, needing little to no post-machining processes.

SEI Castings offer custom castings, enclosures, metal finishing, and waveguide components.  For more information about our products and how we can customize your project, call us at (408) 374-1031.