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vor 3 Jahren

10-2016

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Fachzeitschrift für Hochfrequenz- und Mikrowellentechnik

RF & Wireless Shielding

RF & Wireless Shielding Material Surface Resistance Ohms/Square Shielding Effectiveness, dB at 10 MHz 100 MHz 1000 MHz Silver Acrylic 0.004 67 93 97 Paint Silver Epoxy 0.1 59 81 87 Paint Silver 0.05 57 82 89 Deposition Nickel 3.0 35 47 57 Composite Carbon 10.0 27 35 41 Composite Arc-Sprayed 0.002 106 92 98 Zinc Wire Screen (0.64 mm Grid) N.A. 86 66 48 Table 1: Effectiveness of shielding materials with (1) 25-µm thickness and for frequencies for which the largest dimension of the shielding plate is less than a quarter of a wavelength of either the victim receiver or the culprit so In those applications where information is passed between systems, a possible time management technique could be utilized where the amount of information transferred is kept to a minimum. This should reduce the amount of time that the receptor is susceptible to any EMI. In communication protocols, for example, essential data could be transmitted in short bursts or control information could be encoded into fewer bits. from a single-ended circuit in which only one lead is changing with respect to ground. Ferrite beads, threaded over electrical conductors, substantially attentuate electromagnetic interference by turning radio-frequency energy into heat, which is dissipated in them. In the second coupling path, a radiated electromagnetic field is converted into a common-mode voltage in the ground plane loop containing the interconnect cable and both boxes. This voltage may be reduced if the loop area is trimmed. Figure 3 illustrates common-mode, radiated fieldto-cable coupling. The third coupling path produces a differential-mode voltage that appears across the input terminals of the EMI receptor. One way of controlling this is to cancel or block the pickup of differential-mode radiation. In a balanced transmission line, this is done by use of twisted-wire pairs and a shielded cable. As for crosstalk, the fourth coupling path – the reduction of capacitive coupling can be achieved by the implementation of at least one of these steps: • Reducing the spacing between wire pairs in either or both of the transmission lines. • Increasing the separation between the two transmission lines. • Reducing the frequency of operation of the source, if possible. • Adding a cable shield over either or both transmission lines. • Twisting the source‘s or receptor‘s wire pairs. • Twisting both wire pairs in opposite directions. The fifth coupling path conductively produces both commonmode and differential-mode noise pollution on the power mains. Among several remedies that can suppress the EMI here are the filters and isolation transformers. There are only about 50 common practical remedies that can be used in most EMI situations. Of these, about 10 suffice in 80 percent of the situations. Most engineers are aware of at least some of these remedies – for example, twisting wires to reduce radiation pickup. In order to attack the EMI problem, one can make use of the information contained in Table 2. First, decide what coupling path has the worst EMI interference problem. From the 11 most common coupling paths listed at the top of the table, find the problem coupling path. Using the numbers found in that table entry, locate the recommended remedy or remedies from the 12 common EMI fixes identified at the bottom of the table. This procedure should be repeated until all significant coupling paths have been properly controlled and the design goal has been met. Inter-System EMI Control Techniques There are many EMI controls that may be carried out to enhance the chances of intersystem EMC. They can be grouped into four categories which we will discuss briefly. The following discussion is not intended to be complete but merely provide an overview of some EMI control techniques available to the intersystem designer and user. Frequency management suggests both transmitter emission control and improvement of receptors against spurious responses. The object is to design and operationally maintain transmitters so that they occupy the least frequency spectrum possible in order to help control electromagnetic pollution. For example, this implies that long pulse rise and fall times should be used. Quite often one of the most convenient, economic and rapid solutions to an EMI problem in the field, is to change frequency Location management refers to EMI control by the selection of location of the potential victim receptor with respect to all other emitters in the environment. In this regard, separation distance between transmitters and receivers is one of the most significant forms of control since interfering source emissions are reduced greatly with the distance between them. The relative position of potentially interfering transmitters to the victim receiver are also significant. If the emitting source and victim receiver are shielded by obstacles, the degree of interference would be substantially reduced. Direction management refers to the technique of EMI control by gainfully using the direction and attitude of arrival of electromagnetic signals with respect to the potential victim‘s receiving antenna. ◄ Radiated Field to Interconnecting Cable CM 2, 7, 8, 9, 11 Radiated Field to Interconnecting Cable DM 2, 5, 6 Radiated Field to Box 12, 13 Box to Radiated Field 12, 13 Interconnecting Cable to Radiated Field CM 1, 3, 9, 11 Interconnecting Cable to Radiated Field DM 1, 3, 5, 6, 7 Box-to-Box Radiation 12, 13 Box-to-Box Conduction 1, 2, 7, 8, 9 Cable-to-Cable Crosstalk 1, 2, 3, 4, 5, 6, 10, 11 Power Mains to Box Conduction 4, 11 Box to Power Mains Conduction 4 Table 2: Electromagnetic interference coupling paths (CM Common-Mode, DM Differential-Mode) 68 hf-praxis 10/2016

RF & Wireless Products Antennas Low-PIM Switches RLC Electronics introduced a series of Low-PIM switches, with offerings from SP2T to SP12T. Switches are available in any frequency range from DC up to 65 GHz, and the low-PIM designs offer the customer the ability to reduce intermodulation in active devices in order to reduce system interference. Typical performance ranges from -160 to -175 dBc, and the high isolation minimizes crosstalk between channels to ensure signal integrity. Customer applications include DAS, Surveillance and Communication Systems. Low passive intermodulation (PIM) is crucial for applications where two or more transmitted signals share a common antenna or whenever the transmitter signal is too high or the receiver is sensitive to high intermodulation. ■ RLC Electronics Inc. www.rlcelectronics.com Multiplexers with Two, Three or Four Channels RLC Electronics‘ Multiplexers are available in two, three of four channel versions. Adjacent passbands may be designed for a contiguous or non-contiguous response. For passband frequencies below 2 GHz, lumped element designs will often achieve the desired response in the smallest package. At higher frequencies (up to 40 GHz), distributed coaxial structures are employed to realize the lowest possible loss. RLC Electronics can supply Multiplexers for most applications, including commercial, telecommunications, and military specifications. ■ RLC Electronics Inc. www.rlcelectronics.com New GPO Filters RLC Electronics introducd a new line of GPO and Miniature-GPO connectorized filters. These filters are available in all filter topologies, including tubular (shown above, left), cavity/ comb (shown above, right) and lumped element, in frequencies up to 26.5 GHz (GPO), 40 GHz (GPPO) and 65 GHz (G3PO). One main benefit of the GPO connector is the ease of mating on the customer board or in the overall system, which potentially eliminates the need for cables. With the GPO connector, RLC is able to offer a more compact filter, resulting in a reduction in overall length. ■ RLC Electronics Inc. www.rlcelectronics.com Waveguide Bends Operating from 5.85 to 90 GHz Pasternack debuted new lines of waveguide bends operating from 5.85 to 90 GHz across twelve frequency bands (from C band to W band). These waveguide bends are commonly used in applications such as instrumentation, test benches, high efficiency RF, microwave and mm-wave transmissions, Satcom, Milcom, radar and telecom. In waveguide systems that require a signal to turn or bend 90 degrees, precision waveguide bends are used as to not degrade the transmission signal. Pasternack’s broad portfolio of in-stock and ready-toship waveguide bends boast low loss and SWR as low as 1.08 and are available in both E-plane and H-plane configurations. These 90 degree waveguide bends are constructed using gold plated, oxygen free hard copper (OFHC) or painted copper alloy depending on the model. The bends are also offered with either a UG-style flange per the military standard or a CPR-style flange. In this portfolio, there are currently 30 unique models of waveguide bends offered from stock at Pasternack. Sizes range from WR-137 (5.85 GHz) to WR-12 (90 GHz). Most models are RoHS compliant. ■ Pasternack www.pasternack.com Octave Band Drop-in Circulators RFMW Ltd. announces design and sales support for the RF Circulator Isolator, Inc (RFCI) model RFCR8801 circulator. The RFCR8801 covers the full S-band (2...4 GHz) in a drop-in package configuration. Broadband performance is outstanding with typical insertion loss 19 dB isolation. Forward power handling is rated at 50 W average and 500 W peak. Reverse power handling is 30 W CW. Ideal for protecting active components from distortion or potentially damaging reflected power over broad frequency ranges, the RFCR8801 is manufactured with high quality materials for performance and value. RFCI offers this circulator in a 38 x 38 x 14.5 mm package. ■ RFMW Ltd. info@rfmw.com www.rfmw.com Broadband UHF Whip Antenna from RFMW RFMW, Ltd. announces design and sales support for broadband, omni-directional whip antenna from Southwest Antennas. The model 1000-029 covers the frequency band of 225 to 512 MHz for broadband radio applications where rugged antenna options are required. The Southwest Antennas’ 1000-029 is fully potted and waterproof to 20 meters when installed, yet is lightweight (1.9 oz) and highly flexible. The TNC male connector is black chrome plated and the antenna is black polyolefin for low visibility and low reflectivity. Providing 2 dBi of gain, horizontal beamwidth is 360 degrees and vertical elevation beamwidth is 82 degrees. The 1000-029 measures 10.93 inches and can handle up to 10 W of RF power. ■ RFMW Ltd. info@rfmw.com www.rfmw.com hf-praxis 10/2016 69

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