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 Now you don't have to wait for a magazine to
publish your technical article. If you would like to have your article posted here,
please attach it to an e-mail in MS Word format (I will convert it to PDF) or PDF
format, along with a brief description to use with the listing.
Suggested topics include radar, electronic warfare, commercial wireless, aerospace,
semiconductors, system design, oscillators, amplifiers, filters, project management,
component specification, testing, homeland security, defense technology and simulation.
Many thanks to all the contributors here for sharing your knowledge with our
visitors. Articles listed here have been submitted by the original authors. Please
direct any questions or comments to the authors.
Here are great articles printed in the trade magazines:
 RF Cafe visitor and former article contributor
Brad Baker* sent a new paper he wrote entitled "High
Frequency Speech Processor." In it, he presents a method for clipping of audio
signals at the baseband stage of an RF transmitter in order to facilitate more efficient
broadcasting of a SSB signal. Mr. Baker's process applies a Hilbert transform
and uses the real part of the complex result to modulate the output. A significant
difference between this and previous schemes is that here a feed-forward circuit
is used rather than a closed-loop feedback circuit. Brad provided an MP3 audio file
which demonstrates various levels of clipping, beginning with a raw, unprocessed
sample. You might wonder why he chose the sentence, "It's easy to tell the depth
of a well," for use. While I cannot say why that particular one was used, a little
research showed that it is a sentence from a list called the Harvard Sentences,
From "IEEE Recommended Practice for Speech Quality Measurements." Revised List of
Phonetically Balanced Sentences. Specific phonemes are employed. I suppose you'd
have to be a voice processing guy to know about that. Now you know...
 RF Cafe visitor Brad Baker, now retired,
sent me this paper entitled, "Tunable
Constant Q Band-Pass Filter Design Using q and k Values," which he wrote
about work he did waaaaay back in the last century before computer simulation
and optimization was available on every desktop. Says Brad, "Attached is a
filter design I did in '86. I got a job working for a small land mobile radio
company as an RF engineer and my first assignment was to design a tunable
band-pass filter that tuned from 29 MHz to 59 MHz. I had been out of school for
about two years at this point. I had quite a bit of design experience during my
co-op semesters doing some RF and baseband filters, IF / analog / baseband
amplifiers but nothing like this. I can tell you I was sweating it a little
bit."
 Lemos International Technologies, founded
in 1996 when wireless technology developed for military and aerospace was beginning
to be transitioned into the commercial realm. As a technology adoption leader, Lemos
just published a white paper entitled
"Multi-Use Radio Service (MURS)" to promote the plug-and-play nature of transmitter
and receiver modules available at very low cost. Use of many type of these self-contained
modules enables wireless connectivity product development with the need for in-house
RF expertise and/or FCC emissions certification. Per the MURS Wikipedia article
: "In the United States, the Multi-Use Radio Service (MURS) is a licensed by rule
two-way radio service similar to Citizens Band (CB). Established by the U.S. Federal
Communications Commission in the fall of 2000, MURS created a radio service allowing
for licensed by rule (Part 95) operation in a narrow selection of the VHF band,
with a power limit of 2 watts. The FCC formally defines MURS as "a private, two-way,
short-distance voice or data...
 by Bree Engineering
The following article is a brief introduction to and explanation of the theory
and application of the named frequency selective devices. A Bias-T is frequency
dependent just as much so as a band splitter or diplexer; it differentiates between
DC (0 Hz) and the RF frequency. Bree Engineering Corporation was founded in
1999 and is a manufacturer of custom electronic filters, multiplexers, filter banks
and other related types of components in the frequency range of 0.1 MHz to
40 GHz. Designs include Chebychev, Bessel, Butterworth, Gaussian, transitional,
elliptic-function and pseudo-elliptic-function filters in lumped element, cavity,
combline, interdigital ...
by Orwill Hawkins, LadyBug Technologies
As technology and measuring techniques advance, the time eventually comes when
continuing to use old methods not only doesn't make sense, but can actually harm
your reputation by providing data that cannot be duplicated by customers who long
ago adopted the new ways. Orwill Hawkins, of LadyBug Technologies, has written a
white paper describing how to make accurate, repeatable peak and pulse power measurements
on waveforms using the precision of modern instruments that provide a graphical
view of the entity being investigated. USB power meters provide an inexpensive means
of obtaining high quality measurements and the benefits of a graphical display environment
(on your computer) at a relatively low cost. I particularly like the use of the
word 'mesial' in describing the midpoint of a pulse's rising and falling edges.
As you might know if you have been an RF Cafe visitor for a while, my life-long
hobby has been model aviation. Many notable people have similarly been aeromodelers
from a young age, including aircraft designer Burt Rutan, Space Shuttle astronaut
Robert "Hoot" Gibson, radio personality Paul Harvey, actor and WWII bomber pilot
Jimmy Stewart, Olympiad Bruce Jenner, catamaran and surfboard designer Hobart "Hobie"
Alter, to name a few. Physicist
Dr. David (Dave) Wineland has just been added to the list
since he won the Nobel Prize in Physics in December 2012 for his work on quantum
computing. The Academy of Model Aeronautics' (AMA) monthly magazine Model Aviation
printed an interview with Dr. Wineland in the January 2013 edition, where he discusses
his history with model airplanes and his work at the National Institute of Standards
and Technology (NIST) in Boulder, Colorado. Model Model Aviation editor
Jay Smith granted permission for me to reprint the article here on RF Cafe since
it will likely be of interest to engineers and scientists who visit the website.
by Ray Gutierrez, Micronda LLC
This paper is a continuation work for the "New High Efficiency Intermodulation Cancellation Technique for Single
Stage Amplifiers." Published in January 2008 on RF Café's Paper section. The
paper describes configurations for dual and multiple parallel amplifiers and uses
the basic Reflect Forward technique for intermodulation cancellation. Some new improvements
were made to the RFAL technique to improve the efficiency and operation.
Short write-up on benefits of LED lighting.
by Kirt Blattenberger, RF Cafe
RF Design Magazine Software Contest Winner November 1992
I just ran across this magazine and decided to scan the article. It is a great
tutorial on mixer spurious product calculation - if I do say so myself ;-)
by Cornell Drentea
Here is a short treatise on the history of radar development, beginning in 1793
with Italian scientist Lazarro Spallanzani's experimentation on a bat's use of ultrasound
for navigation, on up through modern systems.
by Darioush Agahi and William Domino
In the design of wireless portable devices, antenna efficiency is a variable
that can have a great effect on overall system performance, and yet may not always
receive the attention it deserves. As an example, RF engineers must frequently make
critical tradeoffs in receiver design in order to improve sensitivity by mere fractions
of a dB, but a poor antenna efficiency can easily cause a degradation of several
dB. This pitfall can occur in systems such as GSM, where many tests are performed
using a cable connection to the antenna port; a handset may easily pass such tests,
only to be later hampered by its antenna in the field. This paper is targeted at
the very important parameter of antenna efficiency, and a measurement technique
that can be used to quantify it.
by Robert Horvitz
Abstract: Presented at the 1st COMMUNIA Workshop on "Technology and the Public
Domain," NEXA Center for Internet and Society, Politecnico di Torino, Italy, 18
January 2008.
Since early in the 20th century, national governments have asserted sovereignty
over the electromagnetic spectrum. These assertions were initially embraced as a
way to control the monopolistic ambitions and offensive business practices of the
Marconi Wireless Telegraph Company. They are still the basis of radio regulation.
However, as wireless communication moves to higher and higher frequencies - into
the range of infrared (heat) and free space optics (light) - it is becoming obvious
that claiming sovereignty over radio frequencies makes no more sense than claiming
sovereignty over colors of the rainbow. Is radio legally different from light? If
not, might we someday need government permission to use certain colors of light
for certain purposes, as with the invisible colors of radio?
by Jason Millard and Darioush Agahi
Power amplifier control (PAC) for a Global System for Mobile communications©
(GSM©) compatible radio is one of the more challenging aspects of the GSM-based
system design. Not only must the radio meet all output radio frequency (RF) spectrum
specifications, but the Power Amplifier (PA) control loop must also be stable under
varying environmental conditions. This paper starts by looking at the basic control
theory, and discusses its advantages over simple open loop control. It then moves
on to describe each block of the loop in detail. Stability is also discussed, and
then finally, the paper examines a case study radio.
by Ray Gutierrez, Micronda LLC
 A
new design configuration that uses the basic concept of the RFAL distortion cancellation
technique. Previously published configurations using the RFAL uses two main amplifiers,
the new configuration requires only one single main amplifier and low level MMIC
amplifiers in the Intermodulation Cancellation Loop.
The basic RFAL technique uses the behavior of a transistor when driven into its
non-linear operating region. At the high drive level the input reflects not only
the fundamental components of the input signal but also the non-linear distortion
components appearing at the output of the transistor. The level of the distortion
products at the input is sufficiently proportional to the output such that it can
be used and processed as a correction or error signal to cancel the output distortion
of the transistor amplifier.
Block diagrams, schematics, data are included.
See follow-on work:
Reflect
Forward Linearizer for Combined Amplifiers
by
Greg Adams, with the permission of Lockheed Martin Company, NE&SS
SS Math & Physics Seminar
 Synchronous
sampling is typically used with a DFT when testing analog to digital converters
in the laboratory. A pure sine wave test signal is generated at such a frequency
that the input signal goes through a whole number of cycles during the sampling
period.
If the test signal is slightly off frequency, i.e. the input signal doesn't complete
a whole number of cycles within the DFT time window, a distortion called spectral
leakage occurs. A small frequency error has little effect on the main signal, but
has a strong effect on the DFT noise floor.
The relationship between frequency error, and the signal to noise ratio due to
leakage noise has been established. This relationship can be used to determine the
frequency resolution which the sine wave generator must have in order to generate
a sine wave at a sufficiently accurate frequency. A simple calculator program is
provided to evaluate the equations.
ADC Toolkit:
Used with presentation
by S.Y. Skandari, Ch. Ghobadi, J. Nourinia, Urmia Univ., Urmia, Iran
Algorithms
are introduced for increasing the rate of convergence in adaptive algorithms and
new methods for selection of m step-size
are given. Special functions are introduced for the definition of
m which overturn current limitations and
increase the rate of convergence and decrease noise.
by Dr. Nasreddine Benahmed, University of Tlemcen, Algeria
A set of accurate closed-forms formulas for the effective dielectric constants
of the shielded symmetrical bandline.
by Dr. Nasreddine Benahmed, University of Tlemcen, Algeria
Design NMR probes using closed-forms formulas of the primary and secondary parameters
of the shielded split ring and the shielded symmetrical band resonators . These
formulas are based on rigorous analysis by finite element method (FEM) , method
of moment (MoM) and curves fitting techniques.
by Shekar Kulashekaran, shekar.pk@gmail.com
This presentation offers a methodical approach to planning and implementing in-building
solutions for GSM 900 & 1800 MHz, and CDMA phone systems that helps solve the
problem of coverage in offices, garages, shopping centers, etc. Shekar has 6 years
of experience planning and installing these systems.
by Mrunal A. K. & Makarand Shirasgaonkar - MTech Students, Dr. R. M. Patrikar,
Professor, Visvesvaraya National Institute of Technology, Nagpur INDIA.
The
emphasizes on higher data rates and spectral efficiency has driven the industry
towards linear modulation techniques such as QPSK, 64 QAM, or multicarrier configurations.
The result is a signal with a fluctuating envelope which generates intermodulation
(IM) distortion from the power amplifiers. This paper describes a new approach of
using a Diode as a predistorter in view of minimizing non linear distortion introduced
by the high power amplifier in microwave radio links.
 by Andrei Grebennikov, M/A-COM Eurotec
Note: If you get sign-in screens, just close the window
and the file will load.
Lecture 1: Nonlinear Active Device Modeling
Lecture 2: Impedance Matching
Lecture 3: PA Design Fundamentals
Lecture 4: High Efficiency Power Amplifier Design
by Vandana Kalibhat Ramchandra
This paper describes and discusses a procedure of how to design RF/Microwave
Low noise amplifier with minimum noise figure and low VSWR. The initial data available
is S-parameters of the device. This paper references the RF design tool called ADS
by Agilent technology.
by Dr. Dan Dobkin veDr. Dan Dobkin version 1.0,
enigmatics@batnet.com
In this article we shall try to illustrate a simpler and more direct way of understanding
how short wire antennas, and by extension other small antennas, interact with traveling
electromagnetic waves, in which we focus on the potentials that result directly
from charges and currents.
Part II will follow if sufficient interest is shown in this first installment.
by Kamran Ahmed, Institute of Information Technology, University of Sindh, Pakistan
This is an excellent series of lectures on the basics of satellite communications.
▪ Overview
of Satellite Systems
▪ Orbital Mechanics
▪ Orbital Perturbations
▪ Radio Wave Propagation
▪ Polarization
▪ Antennas
▪ Link Budget
▪ Interference
▪ Channel Characteristics
by Christopher K. Horne
In solving electromagnetic
problems where the curl operator is evoked to compute the electric or magnetic fields,
one often forgets the curl has a physical meaning. The purpose of this article is
to support the mathematics of the curl with the physical meaning of its operation.
- See also: "Pulsed S-parameter Measurements for
GSM Amplifiers", MP Digest, June 2004
by Ed Troy, Aerospace Consulting, LLC
Almost everyone uses simulation tools for designing RF, microwave, and high speed
digital circuits today. It is essential. But, very few engineers use those same
tools for troubleshooting of circuits that are not working correctly. It amazes
me that many engineers and technicians still spend days tuning, tweaking, and adjusting
RF circuits that do not work properly on the bench. They could probably find, and
fix, the problems in much less time by firing up their simulation software. It is
much faster to change values, both known and speculated, in a simulation engine
than it is to make the same changes on the test bench.
by Dr. Alfred I. Grayzel, Dr. Ashok (Ash) K. Gorwara, Paul Kuhn Planar Monolithics
Industries, Inc.
A method is presented in this paper for realizing tunable amplifiers with bandwidths
of less than 0.5%; without the use of superconductors and cryogenic cooling. This
method uses a small signal varactor up-converter to achieve these ultra narrow bandwidths.
The equivalent circuit for the up-converter is presented as well as the circuit
configuration of the narrow band negative resistance amplifier. The design and experimental
results are presented for a 0.5% bandwidth negative resistance amplifier at 800 MHz;
using this unique circuit design. These devices and circuits can be used for electronic
warfare applications such as surveillance, electronic reconnaissance, jamming and
frequency hopping.
by LadyBug Technologies
Obtaining accurate, reliable, and useful measurements of RF power in the forward
(transmission) and reverse (reflection) directions requires careful selection of
test devices and detection equipment. LadyBug Technologies has produced a white
paper describing a method for performing reflection and transmission measurements
using a power sensor and a directional coupler. It includes a discussion on coupler
directivity and impedance match as a factor in measurement accuracy.
by Joe Cahak, Sunshine Design Services
This article will cover a recent test experience that utilized some thinking
about the test fixture, the bias requirements and the device mounting and special
calibration offsets needed to de-embed the test fixture response from the device
response within the test fixture. The device also had to have bias on several ports
simultaneously. We had to establish a "reference plane" within the fixture, from
which we can use the Vector Network Analyzer's Port Extension or Phase Offset to
dial out the distance from our 1 port calibration reference plane to the point of
short reference within the fixture. With this phase offset compensation we can then
measure the device capacitance of the part within the fixture and the line length
of the test fixture mostly worked out by the port extension.
by John Lai, Oscilent Corporation
The purpose of this article is to discuss the important design considerations
and development limitations of a Radio Frequency and Surface Acoustic Wave (SAW)
Filter (Both IF Filter and RF Filter). Each of the major Electrical Parameters are
discussed from a development perspective as follows (reference Figure 1 for further
definition): We will also be reviewing RF Filter electrical components.
by Brian B. Donalson
This is a technical paper written to support newly trained satellite operators.
It helps in understanding how signals are received from orbiting satellites. Not
too technical but if you are someone who wanted to learn a little about satellite
communications, this is a good start.
by Brian B. Donalson
This is technical paper written to support newly trained Satellite Operators.
It is a paper that shows the difference between a standard off-set satellite dish
and an inverted off-set Satellite dish. Technical in nature, but easy to understand.
Complete with illustrations to help you understand. A good read even if you know
nothing about satellite dishes.
A brief overview of the 4G system still in its planning and implementation (and
definition) phase, provided by the folks at Broadband Expert.
by Kirt Blattenberger, RF Cafe
The Spur Web chart rapidly identifies both inband and out-of-band spurs, affording
a pictorial view of where conversion system frequencies lie with respect to all
spur products.
by Michael Hopkins, CurrentRF
A
breakthrough in Digital to Analog Conversion and breaching the Nyquist barrier,
any output frequency is now possible from low frequency digital data with the RFDAC.
Achieve optimal baseband DAC noise and AC performance, clearing the way for true
12, 14, and 16 bit performance at any output frequency.
by William Domino, Nooshin Vakilian, and Darioush Agahi
In designing today's wireless handset receivers, it is important to maximize
both receive sensitivity and resistance to undesired signals, also called "interferers",
or "blockers". The starting place for receiver design is the calculation of budgets
for noise figure and linearity, usually facilitated by a spreadsheet. While it is
straightforward to find the cascaded noise figure (NF) and 1dB compression point
(P1dB) using a spreadsheet calculation, it is often not clear how to use these to
predict the actual performance of the receiver in the presence of a large blocker.
To obtain a reasonably accurate prediction may instead require an inconvenient co-simulation
of the system with circuit models embedded. However, a simpler approach is possible,
which is still performed at the level of cascade calculations rather than simulation.
The staff at IMS
ExpertServices™ has prepared a few articles on the subject of expert
witnesses.
by Darioush Agahi, Sykworks
Small size and ruggedness are two important factors in the selection of bandpass
filters for military and OEM applications. Monolithic ceramic block combline bandpass
filters not only offer a size advantage in UHF through L-band frequencies; they
also have other characteristics that make them extremely attractive when compared
to other technologies. The filters are characteristically lower in cost and have
relatively good insertion loss due to their high Q material (Q>10,000). This
paper describes the design technique used for ceramic bandpass filters.
by
Kamaljeet Singh and K Nagachenchaiah Semiconductor Laboratory
(SCL), SAS Nagar, Near Chandigarh, India
Abstract:
Polyimide interface layer on standard silicon substrate extends the use of silicon
for RF applications and is also compatible with the present CMOS technology. This
paper investigates the characteristics of the microstrip lines patterned on polyimide
interface layer up to 40 GHz. The limitation of lossy silicon substrate can be overcome
by this approach. The full wave analysis of the microstrip line has been carried
out using CAD tool. Also the non-ideal ground plane effects along with the concept
of thicker bottom metallization below polyimide have been demonstrated to have lower
losses.
by
Kamaljeet Singh, R. Ramasubramanian, S. Pal Communication Systems
Group, ISRO Satellite Center, Bangalore, India
This paper presents improved characteristics of the hairpin filter topology.
Standard hairpin configuration has the drawback of broader bandwidth, more insertion
loss along with poor skirt rate. This paper demonstrates the approach to overcome
the limitation inherent in hairpin as well as suppression of the harmonic which
is prominent in the microstrip coupled filter topology.
by Dr. Dan Dobkin version 1.0
Note: If you get sign-in screens, just close the window
and the file will load. Part I: Scaling Arguments
How does a wire dipole antenna work? How
do we find the resistance and the reactance?
Why does the reactance vanish at an
appropriate length or frequency? Part II: Detailed Estimates of Scattered Voltage
and Current We will now fill in the details
of the calculation of scattered current
and voltage for a short length of wire with
an impinging potential In
this article we shall try to illustrate a simpler and more direct way of understanding
how short wire antennas, and by extension other small antennas, interact with traveling
electromagnetic waves, in which we focus on the potentials that result directly
from charges and currents.
CHALLENGE
"I will offer a $5 Starbucks gift certificate for each algebraic goof reported
and corrected."
dan@enigmatic-consulting.com
by Kirt Blattenberger, RF Cafe
This Excel workbook demonstrates how easy it is to implement a Smith Chart using
only a standard x-y scatter chart and coordinate conversions.
by Andrei Grebennikov, M/A-COM Eurotec The output network of a class E amplifier
must provide impedance matching at the fundamental frequency and adequate rejection
of harmonic frequencies, while handling DC power to the device.
by Ivan Boshnakov (ivanb@aerial.co.uk), Senior Principal Engineer, Aerial Facilities
Limited (www.aerialfacilities.com)
This article describes and discusses a procedure of how to design RF/Microwave
Class A power amplifiers in a very efficient and highly accurate manner when the
only initial data available are the S-parameters of the transistors. This
paper references the "Tandem RF Software Programs Streamline the Design of
Power Amplifiers" item by Mr. Boshnakov toward the bottom of this page.
by Glen Dash
This tutorial series is graciously provided by Dr. Dash: Part
1: An Introduction Part
2: Why Things Radiate Part
3:
The Difference a Del Makes Part
4: Equations Even a Computer Can Love Part
5: Radiation From a Small Wire Element Part
6: The Method of Moments
These articles provide a magnificently comprehendible presentation of Maxwell's
Equations. They originally appeared in Conformity magazine in 1999, and were pulled
a couple years ago. All six parts have been revised and
condensed into a much small file size to facilitate easier downloads (as of November
15, 2005). Glen Dash is the author of numerous papers on the laws and standards
applicable to electronic equipment. He is a graduate of MIT in Electrical Engineering
and holds a law degree from Harvard. Please send a note of thanks to
Dr. Dash for making these immensely popular articles available.
by Manu V Thayyil and Prince V Thachil, Model Engineering College, Thrikkakra,
Kochi, India
This paper describes the design of an automatic telephone call indication device
with power line as the channel for communication via Amplitude Shift Keying. These
guys are graduate students and welcome feedback -
manuthayyil@yahoo.co.in
by Carl Lodstrom Tricks of the trade for successful use of capacitors for
decoupling.
This
article provides a new design configuration that uses the basic concept of the RFAL
(Reflect Forward Adaptive Linearizer) distortion cancellation technique.
The basic RFAL technique uses the behavior of a transistor when driven into its
non-linear operating region. At the high drive level the input reflects not only
the fundamental components of the input signal but also the non-linear distortion
components appearing at the output of the transistor. The level of the distortion
products at the input is sufficiently proportional to the output such that it can
be used and processed as a correction or error signal to cancel the output distortion
of the transistor amplifier. Author: Ray Gutierrez, Micronda LLC.
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