EMC Engineering Case Analysis

may cause radiation emission in high frequency and interfere with the highly sensitive receiving equipment.

RE102 test is applicable for radiation emissions generated by the cases and all interconnect cables of the equipment or subsystems, but it does not apply to the transmitter’s fundamental or antenna radiation. The purpose of the RE102 test is to protect the sensitive receiver from antenna coupling. The sensitivities of many tuned receivers are on the order of 1 μV, which require stringent requirements to prevent platform problems caused by performance degradation.

There is no implicit relationship between RE102 test and RS103 test. RE102 test is related to the potential effects of an antenna-connected receiver, while RS103 test simulates the field produced by antenna-connected transmitters. Usually, the same equipment is involved in both requirements. For example, a 30 W-ultralong wave AM radio with antennas operates at 150 MHz. In the receiving state, an electric field of 40 dBμv/m (about −81 dBm at the receiver input) can be detected; in the transmitting state, the same equipment will produce a field of 150 dBμV/m (32 V/m) at a distance of 1 m at the same frequency. The two field levels differ by 110 dB.

The RE102 limit curve is based on the relationship between the level of the platform and antenna-connected receivers and the typical amount of shielding associated with the wiring between the antenna and the equipment. Therefore, RE102 draws the limits for surface ships and submarines, the limits for aircraft and space systems, and the limits for ground equipment.

For internally installed equipment, the air force and navy limit curves are developed for aircraft that are not specifically designed with shield volumes, but have a small amount of shielding within the test frequency range. For externally mounted equipment, even a small amount of shielding is not available, so the curve is 10 dB more stringent. Most of these experiences are from fighter size aircraft. Since the tuned antenna effective aperture size (Gλ2/4π) decreases with the increasing frequency, the limit increases by 20 dB/dec above 100 MHz, leaving the coupled power level from the isotropic tuned antenna constant. The curve breaks at 100 MHz are due to the difficulty in maintaining a tuned antenna, because the actual size of the antenna increases with the increase of the wavelength and the coupling decreases with the increase of the wavelength.

For the low-frequency band of the RE102 limit value curve, we mainly consider that the allowed value of the radiation level included in the quality of the power supply may contradict with the curve. For example, on a 115 V 400 Hz power bus, the voltage RMS value is allowed to be about 0.63 V at 15 kHz. In laboratory tests, the radiation field strength at this level is about 76 dBμV/m, which is higher than the narrowband radiation limit of GJB 151 RE102 (A1 class) by 31 dB higher. If the GJB 152 rod antenna is used to measure from the low end to 400 Hz, the indicator level from the power supply waveform is about 1 V/m. Therefore, in order to avoid a conflict between the power quality and this requirement, the RE102 limit should be considered for the aircraft power supply equipment at lower frequencies.

The failure of RE102 test is mainly due to radiation emission from the cases or cables, which may be received by the high-sensitivity receiver in the platform to form interference. It is also possible that the interference signal inserts into the adjacent

cable to form new interference. Moreover, the interference caused by the failure of RE102 is the most difficult to identify. When the equipment is tested in the laboratory, it often uses copper foil or shielding tape to strengthen the shielding of the equipment and cables. However, when the platform is actually installed, there are no additional measures as with testing. Therefore, the interference signal is released and may form real interferences. Under this condition, to find out the real source of interference, it is almost necessary to search the entire platform; i.e., all equipment and cables need to be eliminated one by one, which will waste a lot of human and material resources and time and affect the development progress of the platform.

The failure of RE102 will lead to even worse results—early detection by the enemy’s passive detection system and detected information that can support fine identification.

RS103 ensures that the performance of equipment onboard or external to the platform does not degrade in the presence of electromagnetic fields generated by various transmitting antennas. There is no implicit relationship between RS103 and RE102. The RE102 limit is mainly to protect the antenna-connected receiver, while RS0103 is to simulate the field generated by the antenna transmission.

The limit of RS103 is directly related to the platform environment. Therefore, in the regulation, the platform environment is divided into eight cases. The limits of different platforms are specified according to the expected environmental level during the service life cycle of the equipment. Then, the limit value is further selected based on the frequency range of the army, navy, and air force equipment. These limits do not necessarily represent the worst environmental conditions that the equipment may be exposed to, as the RF environment may vary widely, especially from the field generated by the transmitters outside the platform. However, the level set by this limit requirement is sufficient for most situations.

Due to the variability of the ground installation environment, some tailoring may be tightened. For example, equipment installed within or close to a large ground radar station may be interfered by the back lobe of the antenna with a transmission power exceeding 1 MW. Therefore, the limit requirement must be tightened to a suitable level.

For aircraft and ships, different limits are specified depending on whether the equipment is protected by the platform structure. This basis does not apply to the army systems such as tanks, because the equipment used in a certain structure is also often used in places without structure protection. Army aircraft are all required to be 200 V/m, which is not related to equipment installation location or safety critical equipment. This is based on the use of army aircraft. When encountering high-power transmitters, the army aircraft is often closer in distance with a longer duration, and sometimes, some external environments are even higher than 200 V/m. Usually, the qualified level of helicopters is higher than that of other aircraft.

The failure of RS103 test, on the one hand, is due to the shielding performance of the equipment cases and cables and, on the other hand, is due to the circuit design inside the equipment. When an external interference signal is coupled into the equipment through cases or cables, the equipment performance may be degraded or even damaged. When the equipment installed on the platform has radiation-susceptive