1,048 research outputs found
RF measurements I: signal receiving techniques
For the characterization of components, systems and signals in the RF and
microwave range, several dedicated instruments are in use. In this paper the
fundamentals of the RF-signal sampling technique, which has found widespread
applications in 'digital' oscilloscopes and sampling scopes, are discussed. The
key element in these front-ends is the Schottky diode which can be used either
as an RF mixer or as a single sampler. The spectrum analyser has become an
absolutely indispensable tool for RF signal analysis. Here the front-end is the
RF mixer as the RF section of modern spectrum analysers has a rather complex
architecture. The reasons for this complexity and certain working principles as
well as limitations are discussed. In addition, an overview of the development
of scalar and vector signal analysers is given. For the determination of the
noise temperature of a one-port and the noise figure of a two-port, basic
concepts and relations are shown. A brief discussion of commonly used noise
measurement techniques concludes the paper.Comment: 24 pages, contribution to the CAS - CERN Accelerator School:
Specialised Course on RF for Accelerators; 8 - 17 Jun 2010, Ebeltoft, Denmar
RF engineering basic concepts: the Smith chart
The Smith chart is a very valuable and important tool that facilitates
interpretation of S-parameter measurements. This paper will give a brief
overview on why and more importantly on how to use the chart. Its definition as
well as an introduction on how to navigate inside the chart are illustrated.
Useful examples show the broad possibilities for use of the chart in a variety
of applications.Comment: 22 pages, contribution to the CAS - CERN Accelerator School:
Specialised Course on RF for Accelerators; 8 - 17 Jun 2010, Ebeltoft, Denmar
Status report of the CERN microwave axion experiment
"Light Shining Through the Wall" experiments can probe the existence of
"axion like particles" through their weak coupling to photons. We have adapted
such an experiment to the microwave regime and constructed the table top
apparatus. This work presents an overview of the experimental setup and then
focuses on our latest measurement run and its results. By operating the
apparatus within a superconducting MRI magnet, competitive exclusion limits for
axion like particles to the first generation optical light shining through the
wall experiments have been achieved.Comment: Contributed to the 9th Patras Workshop on Axions, WIMPs and WISPs,
Mainz, June 24-28, 201
RF engineering basic concepts: S-parameters
The concept of describing RF circuits in terms of waves is discussed and the
S-matrix and related matrices are defined. The signal flow graph (SFG) is
introduced as a graphical means to visualize how waves propagate in an RF
network. The properties of the most relevant passive RF devices (hybrids,
couplers, non-reciprocal elements, etc.) are delineated and the corresponding
S-parameters are given. For microwave integrated circuits (MICs) planar
transmission lines such as the microstrip line have become very important.Comment: 27 pages, contribution to the CAS - CERN Accelerator School:
Specialised Course on RF for Accelerators; 8 - 17 Jun 2010, Ebeltoft, Denmar
Status report and first results of the microwave LSW experiment at CERN
To detect or exclude the existence of hidden sector photons or axion like
particles, a table-top "microwaves shining through the wall" experiment has
been set up at CERN. An overview of the experimental layout is given, the
technical challenges involved are reviewed and the measurement procedure
including data-evaluation and its results to date are shown.Comment: Contributed to the 8th Patras Workshop on Axions, WIMPs and WISPs,
Chicago, July 18-22, 201
Status report of the CERN light shining through the wall experiment with microwave axions and related aspects
One way to proof or exclude the existence of axion like particles is a
microwave light shining through the wall experiment. In this publication we
will emphasize on the engineering aspects of such a setup, currently under
development at CERN. One critical point, to achieve meaningful results, is the
electromagnetic shielding between axion-emitter and -receiver cavity, which
needs to be in the order of 300 dB to improve over existing experimental
bounds. The RF leakage or electromagnetic crosstalk between both cavities must
be well controlled and quantified during the complete duration of the
experiment. A very narrow band (in the 10^-6 Hz range) homodyne detection
method is used to reveal the axion signal from background thermal noise. The
current status of the experiment is presented.Comment: Contributed to the "7th Patras Workshop on Axions, WIMPs and WISPs",
Mykonos June 26 - July 1 201
First results of the CERN Resonant WISP Search (CROWS)
The CERN Resonant WISP Search (CROWS) probes the existence of Weakly
Interacting Sub-eV Particles (WISPs) like axions or hidden sector photons. It
is based on the principle of an optical light shining through the wall
experiment, adapted to microwaves. Critical aspects of the experiment are
electromagnetic shielding, design and operation of low loss cavity resonators
and the detection of weak sinusoidal microwave signals. Lower bounds were set
on the coupling constant GeV for axion like
particles with a mass of eV. For hidden sector photons, lower
bounds were set for the coupling constant at a mass
of eV. For the latter we were probing a previously
unexplored region in the parameter space
Interactions of Microwaves and Electron Clouds
The modification of microwave signals passing through an electron cloud can be used as a diagnostic tool for detecting its presence and as a measure for its effective density. This observation method was demonstrated in pioneering measurements at the CERN SPS in 2003 with protons and at PEP-II in 2006 with positron beams in the particle accelerator field. Results and applications of this technique are discussed as well as limitations and possible difficulties. A strong enhancement of the electron related signals due to cyclotron resonance is theoretically predicted and has been observed in different machines. The application of this method can also be extended for space applications and plasma physics where microwave diagnostics is known and used since many years. The question whether suitably chosen microwaves might also be employed for electron-cloud suppression will be addressed. An electron cloud may also emit microwaves itself and the intensity of this emission depends on external parameters such as the electrical bias field and resonator frequencies related to trapped mode resonances in a beam-pipe
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