Below are the questions asked during the live event, along with their respective answers.
A: There are numerous things to consider beyond how much amplifier power or antenna gain is available. Typically, systems that require MIL-STD-464 testing are quite large and can be quite heavy. It would likely be impossible to test this equipment in a chamber designed for MIL-STD-461 component testing only. The chamber will be large enough and need to have the weight capacity to house the EUT. Back to amps and antennas, trade-offs must be considered in terms of coverage area of your electric field. In order to generate extreme field strengths, high-gain antennas are important to conserve amplifier power. This results in needing to test an object numerous times to ensure coverage. If higher coverage is required, then you would need more amplifier power to compensate for lower gain antennas.
Q: For very high field strength requirements, how do you calibrate the field, given field probes will not operate at those levels?
A: Commercially available field probes cannot survive many of the high field-strength requirements of MIL-STD-464. This leaves two preferred options. One is to calibrate the required power for a lower field strength and then scale the power to reach the desired field strength. For pulsed fields, this method requires the use of a pulsed field probe or enough power to generate a CW field. This latter case would add an enormous amount of cost associated with high power CW vs pulsed amplifiers. The other option is to use a receive antenna and spectrum analyzer with adequate attenuation. This method allows for closed-loop testing and for real-time measurement of short-duration pulsed fields.
Q: Does AR provide the chambers necessary to house test systems and EUTs of this scale?
A: Through AR’s recent partnership with Comtest, AR/Comtest can provide direct solutions for near any scale of chamber from 1 meter MIL-STD-461 RS103 chambers to chambers 10s of meters in various dimensions capable of housing large vehicles.
Q: What is the test distance between the antenna and EUT for the achieved field levels in the introduced test systems? And what are the offered antennas for the low frequency range below 200 MHz?
A: The required test distance is not specified in MIL-STD-464. Many people use 1 meter as a reference back to RS103, but there is truly no hard requirement. For MIL-STD-464 systems designed by AR, a popular approach is to use AR’s ATP10K100M parallel bar E-field generator up to 100 MHz, then one of our many log-periodic antennas, such as the ATR80M6G for lower powers or ATR26M1G for higher powers up to 200 MHz.
Q: The AR systems tend to install several amplifiers in the same rack such that only 1 amp is used as a time. What is recommended if you have a large number of chambers and want to share individual amps between all the chambers?
A: In many cases, AR systems have been designed and built on mobile platforms, such as those shown in the AS40026 and AS18068 systems. AR has considered other options in the past where equipment cabinets are designed with larger casters so that racks themselves can be wheeled to different locations. Removing individual amps from a system is certainly possible, but introduces error as RF, power and communication connections would continually be stressed.
Q: Are there commercially available test systems that can produce all the high field levels of MIL-STD464 and can illuminate a whole system (a warplane) between 10 kHz and 50 GHz? Or do we have to use alternative methods to full aircraft illumination, such as low-level coupling tests?
A: To our knowledge, there is no single test system that can meet ALL of the External EME requirements of MIL-STD-464. It’s certainly possible to design such a system (maybe with the exception of the 27 kV/m requirement), but systems of that scale become extremely costly. As was mentioned in the presentation, the AS40026 and AS18068 meet the majority of the External EME requirements of MIL-STD-464 with some of the highest-power amplifiers and highest-gain antennas on the market. Achieving even higher field strengths would require less-traditional methods such as magnetrons/klystrons and might require significant R&D to develop higher-power amplifiers.