Development of Adaptive Filtering System to Eliminate CW Interference in Submarine IFM-Based Electronic Support Measure (ESM) Systems

In today's congested electromagnetic environment, broadband receivers for electronic support measures (ESM) are susceptible to interference by both friendly and hostile emitters. To avoid receiver performance degradation due to interference, narrow-band notch filters are often used to suppress interfering signals. Conventional notch filters that rely on the magnetic tuning (i.e. ferrite and YIG devices) are bulky, which makes them unsuitable for use in limited space, such as in periscope-mounted ESM receivers. Hittite Microwave Corporation has developed novel filtering techniques using active devices built in microwave monolithic integrated circuits (MMIC). Hittite has demonstrated tunable notch filters operating in X-band frequencies, built in a gallium-arsenide (GaAs) chip of 1.5 mm x 3 mm dimensions. Hittite's MMIC filters operate with a companion MMIC chip designed to control filter characteristics, and maintain optimum filter performance. This combination of two chips may be used for active and adaptive suppression of interfering signals. In addition, Hittite demonstrated MMIC chips for sampled-data filtering at VHF/UHF frequencies based on the switched-capacitance technique. The GaAs technology also allows extension of low-frequency interference suppression techniques to microwave frequencies. This proposal describes Hittite's approach to suppress interference and provide CW immunity to broadband ESM receivers by using MMIC filtering techniques. The MMIC filter chips can be accommodated in the limited space available in the front-end of submarine ESM receivers. The proposed program will lead to definition of optimum combination of filter techniques for seamless coverage of the receiver band and preliminary design and analyses of filter performance, in preparation for hardware implementation and demonstration in Phase 2.