AMTA Paper Archive
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Intermodulation Analysis and Detection of Radio Broadcasting Services Using Real-Spectrum Monitoring Systems
In this paper, an analysis of the intermodulation effects observed in radio communication signals measurement systems, placed in vicinity of highly congested FM stations sites is presented. This work is required due to intermodulation issues have been a widely-studied topic in frequency analysis for communication stations, nevertheless the perspective of those analysis is mainly focused on avoiding the generation of intermodulation products that represents real spectrum occupancy but there is no an analysis for the intermodulation caused by the susceptibility of monitoring devices that, due to the non-linear behavior of the electronic components, present intermodulation products like real signals. The causes of intermodulation phenomena are discussed, which are mainly due to the non-linear behavior of one or several components of the monitoring system, and due to the proximity between transmission sites or between the measurement system and the site of the transmission. As a complement, a review of technical specifications for different monitoring instrumentation like receptors, active and passive antenna system, amplifiers, and filters and its effects on unwanted Intermodulation generation is done. With the goal of suppressing or minimize the Intermodulation Distortion of the electronic devices used for monitoring, a procedure for identification, according ITU recommendations, based on attenuators for common spectrum analyzers and using passive antennas have been designed and tested in different sites in different countries. The measurements obtained with different active devices and passive devices in the measurement system are presented and compared, identifying with the procedure the spectral characteristics of the intermodulation products and the reduction or filtering of these effects analytically and graphically.
Comparison of Payload Applications in Near Field and Compact Range Facilities
For satellite applications payload measurements are a crucial part of the radio frequency validation campaign before the launch. Parameters like Equivalent Isotropic Radiated Power (EIRP), Input Power Flux Density (IPFD), Gain over Noise Temperature (G/T), Gain over Frequency (G/F), Group Delay, and Passive Intermodulation (PIM) are to be measured in suitable facilities on satellite level. State-of-the-art payload measurements are conducted in compensated compact range facilities which offer a real-time test capability which is easy to setup and use. Closed link tests are straightforward to realize with two compact range feeds employing feed scanning. The measurement techniques as well as the error budgets are well known. Near-field facilities are widely used for antenna pattern measurements. However, there is not much literature available discussing in particular measurements of G/T, G/F, and Group Delay in the near field. Measurements of the above parameters in the near field seem to be feasible, however, the processing of the measured data has to be adapted and further calibration measurements are required. In this paper methodologies for payload parameter measurements in compact range and near field facilities will be described. A comparison of payload measurement campaigns in near field and compact range facilities will be drawn. The techniques will be compared in terms of measurement timing and effort, practicability for satellite applications, and achievable accuracies.
Radiation Pattern Measurement of Passive UHF RFID Tags
Measuring the radiation pattern of passive ultra-high frequency (UHF) radio frequency identification (RFID) tags is challenging due to the special characteristics of RFID systems. In this paper we presented a comparison of radiation pattern measurement techniques for passive UHF RFID tags. Intermodulation-based, backscattered power-based and threshold power-based techniques are used to measure the E and H plane radiation patterns of a dipole-type and slot-type tags. In this study, we have measured the radiation pattern of RFID tags in active mode, i.e. when the tag is characterized in operation with the microchip.
A Data Acquisition System for Monitoring of PIM and Multipaction Events
This paper describes the details of a specialized data acquisition system developed at the David Florida Laboratory. The system acquires, monitors, records and performs post measurement analysis of passive intermodulation (PIM) and multipaction events observed during RF testing. This characterization of components and systems carrying radio frequency signals is an important element of space qualification of satellites and other space faring systems. A National Instruments PXI chassis equipped with a PXI-4462 acquisition card and a LabView based software application was implemented to digitize the resulting data. A second application provided by InfoBright permits the compact storage of hours of measured data in its entirety (multiple channels each sampled at over 200,000 samples per second) using a specialized real time data compression scheme. The application also permits quick retrieval of relevant data segments using SQL query processing. Performance of this solution is presented along with its effectiveness in detecting details of PIM and multipaction events.
Sensitivity Measurements of a Passive Inter-Modulation Near Field Scanner
A passive intermodulation (PIM) near-field XY-scanner for the GSM900 frequency band has been earlier constructed to localize distortion sources in antennas and in other open structures. However, the measured intermodulation level has been relatively high, around 90 dBm. The equipment should be able to measure distortion levels down to 115 dBm with an input power of 2x20W, since the noise floor of a GSM900 base station is typically around 110 dBm. The sensitivity is limited either by thermal noise or by residual intermodulation distortion depending on the sensor coupling. Various causes of residual intermodulation distortion in the PIM near-field measurement are considered and evaluated. Sensitivity measurements of the scanner have been carried out on two test devices. With a sensor coupling of 30 dB, sensitivities of 115 dBm and 105 dBm have been achieved with an electric and a magnetic field sensor, respectively.
Intermodulation Product Second Order Interferers, in Dual-Band Systems
1. Introduction 2. IM2-a new unknown criteria for dual-band systems 3. Theoretical approach 4. Comparing measurements of IM2 and IM3 5. Devices under test (DUT) 6. Measurement results 7. Discussion of results 8. Basic technologies to minimize generation of intermodulation 9. Silver surface 10. Solid inner and outer conductors 11. Solderjoints to corrugated copper cables 12. Summary
Interferrence in Telecomm Systems, From Passive Intermodulation Product Generation -- An Overview
Telecommunications are critical in the lives of every individual on Earth and are rapidly with time. To meet the demand and ever decreasing system cost and bandwidth requirements; many communication systems transmit and receive simultanrously through one antenna path. Any interaction andmixing in the signal paths can produce unwanted mixed (passive intermodulation PIM), if occurring within the receiver band could degrade the system performance. It is therefore critical to ensure that PIM products are insignificant within a receiver band. To achieve this, appropriate system design, build techniques and measurement standards must be used. Although much published work is available, known, repeatable, standardized test methods and data are needed to cost effectively designed down PIM emissions to the required values. Internationally agreed standards for PIM measurement and guidance information, are being written by IEC working group 5. Standards, IEC 1580-2 and IEC 62037 have been published and more are in progress.
Passive Intermodulation Antenna and Microwave Component Measurement Test System
Good communication quality in wireless telecommunication systems requires maintaining an acceptable Carrier-to-Interference (C/I) ratio. Therefore, the goal is to keep 'I' as low as possible. In the ideal case, 'I' would always be below the receiver noise floor. One source of undesired interference is passive intermodulation (PIM). AH components and subsystems in the basestation that carry two or more RF signals along their transmission path have the potential to generate PIM. Consequently, PIM has become an important performance criterion. To bring uniformity and consistency to this difficult measurement, the International Electrotechnical Commission (IEC) has defined recommended test methods for PIM measurements. Assembling and maintaining a test setup that provides the necessary test capabilities can be a formidable task. The test system described herein provides a convenient means for companies to realize this test capability in both an engineering and production environment at a level of performance that exceeds that required for accurate and repeatable measurements.
Passive intermodulation measurements for aeronautical antennas
INMARSAT (International Maritime Satellite Organization) provides satellite communication services to civil aviation operations. Aircraft Earth Station (AES) installations aboard all types of commercial transport and business aircraft must meet strict requirements as specified by INMARSAT. The purpose of these requirements is to ensure that all AES shall be able to perform correctly with standard INMARSAT Ground Earth Station (GES) throughout the INMARSAT space segment, and shall not endanger the integrity of the satellite network. To have INMARSAT approval for multi-carrier mode, the AES must meet specifications for levels of transmitted intermodulation products before satellite access is provided.
Simplified polarization measurements
The mathematical language of wave polarization has been somewhat cryptic; usually involving vectors, tensors, or complex numbers or symbolic equations. By using the Poincare' sphere and dot product multiplication, it is possible to reduce the comutation of wave polarization mathematics to simple trigonometric formulas. Furthermore, visual representation of wave polarization on the Poincare; sphere is straight-forward and simple.
Characterization of aeronautical antennas for INMARSAT communication
Aeronautical SATCOM systems for INMARSAT typically employ circular polarized electronically or mechanically steered multi beam antennas. Characterization of thee antennas requires extensive measurements that differ from conventional antenna pattern measurements. Some of these are: A. Multiple frequently CP gain, axial ratio, and discrimination measurements over a hemisphere for a large number of beams. B. Noise temperature and G/T measurements C. Carrier to multipath rejection D. Intermodulation characteristics E. Receiver and Transmitter system characteristics Details of instrumentation and procedure for these tests are presented with special emphasis on issues such as measurement speed, accuracy and processing of large amounts of data.
R.F. test campaign on the HISPARSAT DBS antenna
Under the scope of the Spanish satellite programme, named HISPASAT, Casa-Space Division has undertaken the design, development, manufacture and test of the D.B.S. antenna. For the final test campaign, mechanical and electrical activities has to be completed. The D.B.S. antenna operates in Ku-band in both transmit and receive, giving coverage over Spain for five TV channels. The antenna is composed of a CFRP 2.2 m diameter reflector and a multibeam feed, which components are all waveguide mechanized. This paper gives a short technical description of the antenna, and presents the procedure and the major results obtained from the electrical test campaign. It comprised the R.F., Multipaction and Passive Intermodulation Product (PIMP) measurements at component level and the final R.F. tests at feeder and antenna levels.
Design and construction of an UHF passive intermodulation set to meet M-SAT requirements
Intermodulation products are generated when multiple frequency signals are applied to a circuit element having a non-linear input/output characteristic. The space community first became aware of the Passive Intermodulation (PIM) problem due to the difficulties encountered by the Fleetsatcom program. This paper describes the design philosophy and construction of an "UHF Test Set" to satisfy the test requirements of the M-Sat program. Predicted response curves of the IM characteristics of HPA's, ferrite isolator and passive hardware are presented as tools for the filter designer interested in the test set design, with the required rejection values for the various filters to be used.
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