Tunable Filter and Multiplexer for Improved Transmitter Electromagnetic Compatibility

Introduction: The challenge of using high-power transmitters, or “jammers,” is complicated by the desire for these transmitters to be compatible with friendlyforce systems that operate in the same region of the electromagnetic spectrum. Electromagnetic compatibility is particularly difficult to achieve when practical constraints, such as size, weight, and power, dictate that these transmitters operate efficiently — a mode of operation in which their amplifiers are more prone to generate spurious signals that interfere with friendlyforce systems. To address the issue of electromagnetic compatibility in transmitters, MITRE Corporation is developing an extensible transmitter architecture that will broadcast less friendly-force interference. MITRE enlisted NRL to develop filters able to suppress interference transmission without compromising the transmitter’s task. Within a four-month time frame, NRL’s Microwave Technology Branch developed a novel highpower contiguous-channel frequency multiplexer for suppression of amplifier second harmonics and a novel microsecond-tunable notch filter for excision of selectable narrow frequency bands from an amplifier’s input. Figure 1 illustrates the integral role of these filters in the transmitter’s output module.