Below are the questions asked during the live event, along with their respective answers.
A: The connector ratings given are CW. Pulsed or Peak RF ratings will be higher. The individual connector specifications should be examined to ensure that you are not exceeding the limits of the connectors.
Q: Can you give any examples of how the chamber can affect how to size your test equipment?
A: Test standards will typically give requirements on chamber dimensions with respect to EUTs (Equipment Under Test). When using a reverb chamber, the size will affect the frequency of use. Other parameters can affect chamber performance, such as absorber type used and ground plane effects.
Q: Why is it important to use measured field strength as opposed to theoretical?
A: Measured field strength will give a better indication of the actual presence of field and its uniformity, whereas calculated field strength can only show the evaluator what field ‘should’ be present within the test area.
Q: Do you have any recommendations for high power circulators to minimize VSWR effects? Looking for >5kW for Pulsed amps.
A: For AR amplifiers, not really. We don’t typically utilize circulators for two reasons. (1) It’s very difficult to find one that can cover both bandwidth and power (usually you sacrifice one for the other), and (2) our amplifiers can handle extreme mismatches.
Q: What about the low-frequency range 2 MHz – 1 GHz? Is it easily possible to achieve 200 V at 1 m test distance in the presence of a metallic table between 2 MHz – 1GHz? Can AR offer a solution for 200 V/m at 1 m distance between 2 MHz – 1GHz?
A: AR can offer solutions within this test range. Typically, the real challenge is from 30 MHz to 200 MHz. Within this range, we typically utilize a high power biconical-type antenna up to 100 MHz, and then a log periodic up to 200 MHz. Large amounts of RF power will be needed to achieve the field (2.5 kW to 5 kW). Above 200 MHz, a double ridged guide antenna with 250 to 500 Watts of RF Power can be utilized to achieve the required field.
Q: In the 6-18 GHz range, you did not consider much coax or waveguide loss, which can be substantial in this frequency range. Doubling or quadrupling the required power. Is this a concern?
A: Yes. Given that the losses can be substantial as we increase in frequency up to 18 GHz, we need to be cognizant of the cable/waveguide loss. To mitigate that, we need to use shorter cables, moving the amplifier within the chamber (and placing it within a shielded rack or enclosure, and be sure to use efficient antennas.
Q: When does the chamber size start affecting your tests?
A: It all depends on the chamber, the test sample, the ground plane, and the requirements. The larger the test chamber, the larger the equipment we can test. If we’re in a very small chamber, we may see more reflections and resonances, depending on the construction and the absorber loading and type.
Q: The MIL-STD464 requires very high peak field EME levels such as 27 kV/m for ship operations in the main beam of transmitters. Is it possible to reach these huge values in a laboratory environment and illuminate a whole warplane in a large anechoic chamber?
A: The levels given in MIL-STD-464 are the levels that ‘could’ be seen on a ship when in direct view of the transmitter. Many of those levels are not obtainable with today’s test equipment. However, there is a desire in the testing world to achieve those levels. Given that desire, we would need to use very high gain antennas, which will have a very narrow coverage area. To illuminate any aircraft or other large device, the amplifier and antennas would typically need to be mounted together on a moveable lift to be close enough to the test sample and each small part of the test sample would need to be illuminated.
Q: As the frequency increases the beamwidth tends to narrow – how are the beamwidth variations presented in the antenna specs?
A: The beamwidth angles are typically given in a chart of angle vs frequency. The simplest way to know your coverage area is to calculate the coverage area by the angle, assuming a triangular radiation pattern.
Q: Does AR provide the automation software for this immunity test program, or could other commercially available software be used?
A: AR can provide emcware for automation. Also, commercial software can be utilized to automate testing, such as Nexio, Tile!, and EMC32.