The well-known and extensively analyzed lumped-element bandpass filter is generally not suitable for the RF/microwave region, but there are many distributed-element, energy-based alternatives. Just say the word “filters,” and for many engineers, the mention of this topic stirs a mix of feelings ranging from fear to relief. Why fear? Because filters as a topic in […]
Lasers, optics, electronics and more yield terahertz sources, Part 4 – Laughing gas
The terahertz part of the electromagnetic spectrum between millimeter waves and optical range remains a largely untapped, difficult-to-use resource; researchers are investigating different techniques for efficiently generating terahertz waves to promote the use of this part of the spectrum. Approach #3: Laughing Gas A team at MIT in close collaboration with one at nearby […]
Lasers, optics, electronics and more yield terahertz sources, Part 3 – Infrared lasers and plasma
The terahertz part of the electromagnetic spectrum between millimeter waves and optical range remains a largely untapped, difficult-to-use resource; researchers are investigating different techniques for efficiently generating terahertz waves to promote use of this part of the spectrum. Approach #2: Infrared Lasers and Plasma A research group based at TU Wein (Vienna University of Technology), […]
Lasers, optics, electronics and more yield terahertz sources, Part 2 – Lasers and acoustics
The terahertz part of the electromagnetic spectrum between millimeter waves and optical range remains a largely untapped, difficult-to-use resource; researchers are investigating different techniques for efficiently generating terahertz waves to promote the use of this part of the spectrum. Approach #1: Lasers and Acoustic Modulation A recent project and paper by a collaborative team from […]
Lasers, optics, electronics and more yield terahertz sources, Part 1 – Context
The terahertz part of the electromagnetic spectrum between millimeter waves and optical range remains a largely untapped, difficult-to-use resource; researchers are investigating different techniques for efficiently generating terahertz waves to promote the use of this part of the spectrum. Electromagnetic energy in the terahertz (THz) region of the spectrum, nominally 300 GHz/0.3 THz to 10 […]
The microstrip antenna, Part 2: Implementation
The microstrip antenna is a convenient, planar, easy-to-fabricate antenna with some attractive attributes and features, as well as some distinct limitations. Part 1 of this FAQ was a brief review of antennas and introduced to microstrip antenna design. This part continues that exploration along with related issues. Q: What’s the difference, if any, between a […]
Vacuum tubes we still (have to) use: The traveling wave tube, Part 1
The previous parts of this article explored the photomultiplier tube (Part 1 and Part 2), which is based on a simple, fairly clear physics principle, although building a high-performance PMT is an art and requires various skills, of course. This part looks at a microwave/mm-wave amplifier called the traveling wave tube (TWT – often pronounced […]
Vacuum tubes we still (have to) use: The photomultiplier tube, Part 2
We live in a world of solid-state active devices that have made most vacuum tubes obsolete, but a few types remain as they are still indispensable. Part 1 of this article explained the basics of the photomultiplier tube. This part looks into other PMT characteristics. Q: Are there solid-state functional equivalents to the PMT? A: […]
What are the applications and measurements of S-parameters? Part 2
Part 1 of this FAQ was a basic introduction to the context and concept of S-parameters. Part 2 looks at their measurement, application, and relationship to the time domain. Q: How do you actually measure S-parameters? A: In general, except for approximate measurements, you cannot use a spectrum analyzer alone for this frequency-domain test. Instead, […]
What are the functions and principles of S-parameters? Part 1
As design frequencies now routinely go into the hundreds of MHz and tens of GHz range, conventional voltage and current measurements are not useful. However, scattering (s) parameters can fully characterize the RF component or path performance. For engineers with experience focused from DC to several hundred megahertz, it is usually sufficient to characterize components […]