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Engineering & Science Technical Articles (submitted by RF Cafe visitors)
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 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.
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.
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?
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.
By Ray Gutierrez, Micronda LLC
Spectral Leakage in the Discrete Fourier Transform
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.
By Greg Adams, with the permission of Lockheed Martin Company, NE&SS SS Math & Physics Seminar
The Study of Fast Adaptive Algorithms and Introducing New Methods for Increasing the Rate of Convergence and Its Use in Smart Antennas
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 S.Y. Skandari, Ch. Ghobadi, J. Nourinia, Urmia Univ., Urmia, Iran
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 Dr. Nasreddine Benahmed, University of Tlemcen, Algeria
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.
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.
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.
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
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.
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.
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.
Authors: William Domino, Nooshin Vakilian, & Darioush Agahi
Expert Witnesses
The staff at IMS ExpertServices™ has prepared a few articles on the subject of expert witnesses.
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 Darioush Agahi, Sykworks
CAD Oriented Study of Polyimide Interface Layer on Silicon Substrate for RF Applications
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 & K Nagachenchaiah Semiconductor Laboratory (SCL), SAS Nagar, Near Chandigarh, India-160071
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 Kamaljeet Singh, R. Ramasubramanian, S. Pal Communication Systems Group, ISRO Satellite Center, Bangalore, India
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."
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.
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 Ivan Boshnakov and Jon Divall, Aerial Facilities Ltd., U.K. This article describes a procedure for the design and development of power amplifiers using harmonic-balanced software in tandem with impedance matching network synthesis software. For this purpose a particular design problem will be discussed.
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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