Electrically Small Antenna/Sensor for Low Frequency Detection/Direction Finding
AREA(S): Air Platform, Electronics, Ground/Sea Vehicles
PROGRAM: NAE Chief Technology Office
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Develop an antenna/sensor package that provides high frequency/very high
frequency (HF/VHF) detection and direction finding (DF) capabilities in a
7-inch diameter, flight vehicle cavity.
Achieving high-bandwidth antennas in HF/VHF for transmitters and receivers is a
difficult radio frequency (RF) design. References 3 and 4 illustrate that as
antennas become significantly smaller relative to the wavelength of the signal,
the instantaneous bandwidth of the antenna sharply decreases. Traditional
antennas are often at least a quarter of the wavelength of the intended signal,
and in HF/VHF applications, this forces antenna to be > 1 meter in size.
Therefore, traditional design approaches for high-gain and high-bandwidth
antennas onboard tactical and small-unmanned aircraft are not suitable due to
the antenna’s physical size.
Specifically, as antennas are miniaturized relative to the signal wavelength,
their impedance bandwidth sharply decreases. For transmitters, the antenna
rejects and reflects high-bandwidth signals because any frequency outside of
its impedance bandwidth is mismatched with the antenna, preventing efficient
signal acceptance in the antenna. For receivers, the electrical size of the
antenna is so small compared to wavelength, that the gain of the antenna is
small, reducing signal to noise ratio (SNR) and sensitivity of the receiver.
This is fundamentally due to the conductive and material losses overwhelming the
radiation power of the receiver. This prevents the signal from being
distinguishable above the noise floor.
References 1 and 2 illustrate a method for overcoming bandwidth-limited
electrically small antenna utilizing a transistor switch that directly modulates
the signal in order to “time-vary” the impedance boundary conditions of the
antenna. If synchronized well, the signal at the input of the antenna is
matched exactly at the same moment the impedance boundary of the antenna, due
to the transistor, is changed. Yet, both of these references 1 and 2 are
methods for electrically small transmitters, and not for electrically small
For receivers, achieving high-gain, high-bandwidth antennas are difficult as
stated above. References 5 and 6 propose a method for using cryogenic systems
that significantly reduce the antenna temperature so as the incoming SNR of the
signals have significantly lower noise figure at the input of the RF front end.
Still, such proposals require additional physical volume to house
said-cryogenic systems, significantly increasing the physical area needed.
Specifically, this topic seeks a HF/VHF antenna/sensor package capable of
direction finding (DF).
Traditionally, high-gain sensor packages are comprised of arrays capable of
electronic scanning. The physical size of the package directly increases with
demands for higher gain. In rapidly evolving aerodynamic environments,
physically large antennas are not practical for tactical aircrafts, unmanned
vehicles, and weapons applications.
The proposed antenna sensor system must handle up to 10 Watts, physically sized
in all three physical dimensions less than a tenth of the wavelength. The ratio
of the radiated power to the total power (i.e., the sum of the radiated power,
power lost to ohmic losses, and power lost to material losses) must be as high
as possible but greater than 50% or must achieve an antenna gain of at least -6
dBi. The antenna radiation pattern should have a beam width of 3-5 degrees, but
an omnidirectional pattern along a vertical axis is acceptable. Clearly state
the necessary electronics to achieve direction finding. A 360-degree scan
within 2 seconds or a 10 ms dwell time per beam (if antenna is directive) is
An innovative approach to achieving these results would include:
1) Significantly reduce material losses and conduction losses so as the antenna
radiation efficiency is almost 100% (0 dB).
2) Reduce the noise figure and antenna temperature so as the SNR of the signal
at the input of the receiver RF front end is at least 6 dB.
3) Provide information (i.e., direction finding) on where the signal came from
while handling up to 10W of power within an angular resolution of 3-5 degrees.
I: Design and determine the best low-frequency sensing approaches that are
packable into a physically 7-inch diameter volume and used to sense HF/VHF
signals, and provide direction-finding capability. The Phase I effort will
include prototype plans to be developed under Phase II.
II: Develop and prototype a solution that can be ‘flown’ in an anechoic RF
chamber setting whereas HF/VHF performance can be characterized within proposed
electrically small (length, width, height less than tenth wavelength) of
volume. Identify and propose solutions to areas that will be difficult to
transition to high speed flight.
III DUAL USE APPLICATIONS: Finalize design and perform testing to ensure HF/VHF
performance in a flight operational manner where RF performance from chamber
setting is maintained in-flight. Transition final solution to appropriate
platforms and end users. Successful technology development would benefit space
communications, general aviation, wireless infrastructure, and the internet of
Yao, W. and Wang, Y.E. "Direct antenna modulation - a promise for
ultra-wideband (UWB) transmitting." Microwave Symposium, Dig. 2004 IEEE
MTT-S Intl, vol. 2, pp. 1273-1276. https://doi.org/10.1109/MWSYM.2004.1339221
Santos, J.P., Fereidoony, F., Huang, Y., and Wang, Y.E. "High Bandwidth
Electrically Small Antennas through BFSK Direct Antenna Modulation."
Military Communications Conference, MILCOM, 2018. DOI:
Chu, L.J. "Physical limitations of omni-directional antennas." J.
Applied Physics, vol. 19, no. 12, 1948, pp. 1163-1175. https://doi.org/10.1063/1.1715038
Hansen, R.C. "Fundamental Limitations in Antennas." Proceedings of
the IEEE, vol. 69, no.2, 1981, pp. 170-182. DOI: 10.1109/PROC.1981.11950
Clarke, J. "Principles and Applications of SQUIDs." Proceedings of
the IEE, vol. 77, no. 8, August 1989, pp. 1208-1223. https://ieeexplore.ieee.org/document/34120
Kornev, V.K., et. al. "Linear Bi-SQUID Arrays for Electrically Small
Antennas." IEEE Transactions on Applied Superconductivity, vol. 21, no. 3,
June 2011, pp. 713-716. https://ieeexplore.ieee.org/document/5672560
Electrically Small Receiver; HF/VHF Antenna; Direction Finding; DF; Antenna;
** TOPIC NOTICE **
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