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Direct Antenna Modulation for Wide-Band HF Communications

Antenna size increases with wavelength in order to maintain the radiation efficiency so, for low frequencies, grows prohibitively large. Because real estate is at premium in any platform, such restrictions produce electrically small antennas with low radiation efficiency and narrow instantaneous bandwidth (IBW), putting severe limitations on transmit data rates. The HF band provides favorable propagation characteristics but legacy HF antenna systems suffer from both radiation efficiency and IBW limitations. This paper describes theoretical and simulation work on demonstrating a HF direct antenna modulation (DAM) scheme to overcome this fundamental trade-off.