Chris Angove, Independent Professional Contractor
Chris Angove is a highly experienced and MSc qualified chartered electronics engineer specialising in electrical and electronics engineering. He manages and owns Faraday Consultancy Limited (FCL).
This is a selection of some of my favourite non-book references. Some of them are classic papers and have stood the test of time. Perhaps some of the more recent ones will also become classics in due course.
This Agilent application note is essential reading to properly understand how to do accurate vector network analyzer (VNA) measurements. It explains concisely the types and sources of errors and how they are corrected during calibration. It includes the error models used and how they relate to practical measurements requiring various adaptor arrangements. I have used the equations given with Matlab® 2019B to calculate the errors for a very old HP 8505A network analyser which of course did not have processing capability you now find in the latest VNAs.
When you are trying to write well presented and professional documents you need to get the fundamentals right such as the correct use of SI (abbreviated from the French: Systeme International) units and symbols. Often datasheets for components from leading manufacturers get these wrong, such as using the upper case 's' for seconds. Another favourite is not putting a space between the last digit of the numeric value and the unit symbol, such as using 12V and not 12 V.
This is a very interesting paper about oscillators and, in particular, how they are designed to minimise phase noise, ie. in free running and not phase locked mode so we are talking about 'far from carrier' phase noise. In particular I have used the varactor diodes in anti-parallel configuration as the author described. Even in a phase locked oscillator the PLL only reduces the phase noise close to the carrier inside the loop bandwidth.
I designed and tested one of these some years ago and it worked well at the narrow band of millimetre wave frequencies concerned. It produced very good quality Gaussian far field beams in both the E and H planes so it was very effective in coupling efficiently in and out of a very low loss quasi-optic 'beam' waveguide (a waveguide made up using circular dielectric lenses). It was used as a sort of transition between fundamental mode (TE10) rectangular waveguide and the beam waveguide. The Potter horn itself is fed from a circular waveguide so my version also included a rectangular (TE10) to circular (TE11) transition, a simple taper formed with the help of the CNC milling machine. The only drawback was that it was fairly narrow band. If you needed Gaussian beams across a wider frequency band you would need something like a corrugated conical horn, also known as a scalar horn.
I was first given a copy of this paper when I was a student. We had to use the various formulas and nomographs in it to predict the behaviour of some VHF terrestrial propagation paths across the local countryside. Afterwards we took out the suitably equipped radio van, with transceivers and antennas to measure them. My predictions were something like 20 dB out on the low side which I thought was not very impressive. I have since learned that, when we are talking about fading, especially with multipath interference, 20 dB is quite modest: deep fades can easily reach 40 dB or 60 dB or more. VHF frequencies do typically suffer from multipath, especially in urban environments where there are many reflections. However, the case I described was over a rural path so I probably mis-read the nomographs.
One of the many military standards, originally written by the US Department of Defence (DOD), which has stood the test of time and been adopted internationally. This one, originally used on defence hardware, was clearly written by engineers with a big budget so has detailed descriptions of how to set up and perform the tests and verify the results against the requirements. Now it is also used for civilian equipment.
This is another one of those classic papers which described the design of a microwave antenna based on the same principles that were used in the cassegrain optical reflecting telescope. With light having a wavelength of around 600 nm, even a small 4 inch telescope would have a diameter (D) of about 160,000 wavelengths. That compares to D being something like 1000 to 1500 wavelengths across a very large satellite groundstation antenna at Ku band. I guess this still qualifies as a 'large number of wavelengths' which we need to render diffraction effects negligible. I have used this paper to design a cassegrain antenna to be fed with the Potter horn at millimetre wave frequencies which worked well. In this case D was only around 30 to 40 wavelengths. Certainly the cassegrain is used widely for satellite ground station antennas. It is expensive to build, having the more complicated reflector setup (a parabolic main reflector and hyperbolic sub-reflector) which have to be well aligned. That is probably why it does not seem to be used much for the mass market satellite antennas. They seem to be mostly parabolic reflectors with an offset feed.
Although you can still get Hewlett Packard printers and other computer peripherals which I had better not comment on, you probably know that Agilent inherited several of their former businesses including semiconductors and test equipment. Agilent were very quick to disassociate themselves from HP, judging by how quickly they changed the annotation of their application notes from HP to Agilent. More recently, Agilent is now part of Keysight Technologies. This is one of the early HP application notes. It describes how to design an input noise figure matched low noise amplifier extremely well, step by step. So it goes in to the S parameter characterisation of the active device with constant noise figure circles. Then follows matching the input for optimum noise figure whilst allowing for the multilateral S parameter properties of the device.
I photocopied this paper from a bound volume of the Proceedings of the IRE (a predecessor of the IEEE) some years ago to help me with a project I was doing at university on thermal noise. The librarian unlocked the basement for me and I had to search through spider webs and shelves and shelves rather musty smelling volumes to find it. This looks like one of Friis's original papers in which he presents the now well known cascaded noise figure equation which is often named after him. His other famous equation is used in far field antenna theory. In his conclusion he says "...it is hoped that the definitions and symbols suggested will come into general usage...". I am pleased to say that they did. Thanks to his work, it is probably one of the most well known equations in communications theory today.
This short paper (it is more of a 'letter' actually) includes lots of useful information on balanced amplifier configurations. These are popular and offer many advantages for reducing harmonic distortion, increasing bandwidth, and power handling in the case of power amplifiers. Also, balanced amplifiers have fewer single point failure mechanisms than otherwise similar single ended amplifiers. However, they are not so common in the low power stages of a typical receiver where thermal noise performance is usually important, as balanced amplifiers tend to have appreciable front-end loss which adds to the cascaded noise figure. That is where this paper is useful.
This is more of a datasheet really based on the ATF-38143 low noise pseudomorphic high electron mobility transistor (PHEMT) which is very popular for LNAs. It is a basic cheap plastic package and is optimised for typical '2G' and '3G' digital cellular frequency bands probably aimed at mass markets and has very good low noise performance. It includes information on input noise figure matching.
Whilst searching around the Web for useful and freely downloadable papers you usually have to wade through dozens of them which are not really worth spending much time on before finding good ones like this. Superbly written in an entertaining and visual style, it describes the mechanics of quadrature modulation and demodulation using the (polar) complex exponential notation which offers many simplifications compared to rectangular forms. Once you memorise Euler's identity, get to grips with his 3 dimensional vector diagrams and think in terms of the negative frequency it really will become much easier than trying to remember and apply all of those trig identities that we learnt at school.
I was a bit skeptical at first when somebody suggested I design an absorptive notch filter from these articles previously published in Wireless World. Wireless World was a semi-professional magazine with a large radio amateur and 'hobbyist' audience. It became famous for Arthur C. Clarke's article in 1945 suggesting that radio communications might be possible via artificial satellites positioned around the Earth in geosynchronous orbits. The theory and equations are all explained in great detail with several example configurations. I built one of these for operation around 30 MHz, observing the best RF design practices, and it worked superbly. These type of filters come into their own when you wish to attenuate some discrete spurious and simply attenuating it by reflection, as a traditional notch filter would do, would cause problems due reflections. Continuing with good RF design it should be effective at much higher frequencies.
This is such an interesting set of readable articles on PAs and general high power technologies. They are in tutorial style and it does not get bogged down with excessive theory or derivations. However all the references are there, some 120 for the whole set of articles, for anybody who needs to study a particular aspect in more detail. Subjects covered include: history, efficiency, devices, classes, matching, architectures, linearisation and new modulation methods.
Another very good application note from Agilent. This one is very strong on all aspects of S-parameters: theory, properties, conversions to and from other parameters such as T-parameters etc. Other topics include: signal flow graphs, Smith chart properties, stability circles, measurements, high frequency design, constant noise figure and gain circles, broadband design and matching.
A 24 page datasheet on this popular 'pipeline' ADC.
How to do reliable high power VNA measurements without blowing up equipment, causing fires or getting RF burns.
One of many very well written tutorial style documents written by Walt Kester at Analog Devices.