Compact and Efficient Magnetron Source for Continuous Wave Microwave Power Generation
Navy STTR 2020.A - Topic N20A-T015
NAVSEA - Mr. Dean Putnam [email protected]
Opens: January 14, 2020 - Closes: February 26, 2020 (8:00 PM ET)
TITLE: Compact and Efficient Magnetron Source for Continuous Wave Microwave Power Generation
Receive Only Cooperative Radar (ROCR) FY20 FNC
OBJECTIVE: Develop and
demonstrate a highly efficient and compact continuous wave S-band magnetron
source with a stabilized output capable of frequency shift keying over a narrow
generation of high continuous wave (CW) power at S-band frequencies is a common
requirement in the field of industrial microwave heating. Magnetrons generating
kilowatts (kWs) to tens of kWs are preferred sources for microwave ovens used
in industrial food processing and for materials processing requiring rapid bulk
heating. However, for such industrial uses, the quality of the generated
microwave power is not critical. The frequency is not critical, noise is not an
issue provided it does not interfere with nearby electronics, and the phase of
the generated signal need not be controlled. Within these loose constraints,
magnetrons have proven to be highly efficient and compact sources, often
achieving efficiencies as high as 70% or more. Additionally, the conventional
magnetron, among all vacuum devices, is exceedingly simple in design and
construction, making it a cheap source of microwave power.
While modern radar and communications systems require far more sophisticated
sources of microwave power, applications remain where the magnetron is still
attractive. For example, radio beacons require relatively simple sources of CW
power. Target emulators, which mimic threat sources for training or live-fire
test purposes, and simple “fire and forget” jammers must be as cheap as
possible since they are essentially disposable. However, even for these
applications some control over the frequency, phase, and noise emitted by the
source is required. A free-running magnetron simply will not do for many
Stabilization of the magnetron frequency and phase as well as improved signal
quality (reduced noise and spurious signal content) can be obtained by
injection locking, where an external “locking” signal is injected directly into
the magnetron output port. The injected signal serves to synchronize the
otherwise free-running magnetron frequency and phase to itself, reducing noise
in the process. In applications where the purpose is solely to reduce noise or
combine the output power of multiple magnetrons, the magnetron output may (if
suitably sampled, filtered, and adjusted in phase) itself be used as the injected
signal. However, injection locking with an external source has also been
demonstrated to provide sufficient control of the magnetron frequency and phase
to make the device viable for some radar and communications functions. In fact,
properly designed, an injection locked magnetron can be phase controlled and
tuned across some small frequency band (typically a few MHz) such that
coherency is achieved while simple modulations such as frequency shift keying
and phase shift keying are applied.
Injection locking, though effective, introduces two complicating factors at the
system level. First, since the interaction circuit of the magnetron is usually
under-coupled to the output, a relatively strong locking signal is required.
Therefore, the technique requires an external source of rather high power to
generate the locking signal. This is especially true if fast frequency or phase
modulation is required, as it has been shown that the ability of the magnetron
to follow sudden changes in injected frequency or phase is proportional to the
injected power level. Likewise, the total range of frequencies over which the
magnetron can maintain lock is also dependent on the injected power. Second,
the locking signal generator must be protected from the magnetron output power
by a circulator. The injection signal generator, circulator, and associated
circuitry therefore add weight, size, and cost to the overall system, somewhat
defeating the purpose for which the magnetron was chosen in the first place.
The Navy needs a novel magnetron source for high power CW microwave generation
at S-band frequencies. The source must be compact, efficient, and affordable.
The source must be capable of fast tuning across a narrow band (at least 5 MHz)
with a locked frequency response sufficient to support a data transmission rate
of 2 Mb/sec using simple frequency shift keying (5 MHz excursion per bit). A
wider narrow band frequency response and capability for other constant-envelope
modulation schemes are desirable, with the figure of merit being the modulation
bandwidth divided by the locking signal power required to maintain the desired
2 Mb/sec data rate. Broadband mechanical tuning (over at least 1 GHz) is
ultimately desired but this need not be demonstrated for this effort. Rather,
show broadband tuning need only as feasible. A minimum output power of 5 kW
(CW) is desired, and the device may be demonstrated at any center frequency
within S-band (demonstration in the 2.45 GHz Industrial-Scientific-Medical band
is encouraged in order to take advantage of the equipment available from the
industrial microwave heating industry). The magnetron source may only use
forced air-cooling (any volume and flow with inlet air assumed to be at room
temperature and pressure).
The goal of this effort is to demonstrate the S-band magnetron source. However,
the application is that of a compact and highly efficient transmitter and the
magnetron should therefore be designed to minimize system weight, power
consumption, and cooling load. Magnetrons are the most efficient, compact, and
cost effective sources of raw microwave power available and it follows that an
innovative technique for efficient and effective direct (i.e. without need of a
circulator) injection locking of a highly efficient magnetron (meeting the
requirements described above) would yield the lowest overall system size,
weight, and power (SWaP). Therefore, an estimate of transmitter system SWaP is
a requirement of this effort. Two figures of merit are relevant when comparing
alternate technical approaches. The first is power density, defined as the
output (CW) microwave power divided by the source weight (including power
supply and any injection locking or other equipment required to make the source
perform as required). The second is wall-plug efficiency, defined as the output
(CW) microwave power divided by the total input electrical power (including any
power consumed by the injection locking, power supply, and other equipment
required to make the source perform as required).
To conclude the effort, the magnetron shall be tested to confirm that it first
meets the modulation and power output requirements. The magnetron efficiency
and cooling requirements shall then be determined. Finally, based on the
demonstrated power and the observed efficiency, an estimate of the resulting
SWaP requirements for the transmitter shall be derived, including estimates of
power density and wall-plug efficiency. The low-SWaP transmitter need not
actually be built and demonstrated, only validated through some combination of
design and analysis.
PHASE I: Develop a
concept for a compact and highly efficient S-band magnetron while meeting the
minimum performance parameters detailed in the Description. Demonstrate the
feasibility of the approach by some combination of analysis and modelling and
simulation; and predict the ability of the concept to achieve optimized power
density, efficiency, and affordability. The Phase I Option, if exercised, will
include a device specification and system interface specification in preparation
for device prototype development and demonstration in Phase II.
PHASE II: Develop and
deliver a prototype compact CW S-band magnetron source that meets the
requirements in the Description.. Test and deliver the prototype to the Naval
Research Laboratory along with a complete system interface description,
performance specification, test data, and system SWaP estimate.
PHASE III DUAL USE
APPLICATIONS: Support the Navy in transitioning the technology for Government
use. Since the prototype resulting from Phase II is a generic demonstration of
the technology, assist in applying the design for specific system applications,
such as expendable target emulators. Assist in scaling the device to different
frequency bands and higher powers, and by implementing broadband tuning if
Since magnetrons already have many non-military applications (e.g., microwave
heating, industrial materials processing), the technology resulting from this
effort, being more compact and efficient, should find a ready application in
these commercial markets.
1. Tahir, Imran, et al.
“Frequency and Phase Modulation Performance of an Injection-Locked CW
Magnetron.” IEEE Transactions on Electron Devices 53, July 2006: 1721-1729. https://ieeexplore.ieee.org/document/1643507
2. Huang, Heping, et al.
“Experimental Study on the Phase Deviation of 20-kW S-Band CW Phase-Locked
Magnetrons.” IEEE Microwave and Wireless Components Letters, 28 June 2018, pp.
3. Fujii, Satoshi, et
al. “Injection-Locked Magnetron Using a Cross-Domain Analyzer.” IEEE Microwave
and Wireless Components Letters, 26 November 2016, pp. 966-968. https://ieeexplore.ieee.org/document/7733137
4. Yang, Bo, et al.
“Experimental Study on Frequency Modulation of an Injection-Locked Magnetron
Based on Full Wave Voltage Doubler.” 2018 IEEE International Vacuum Electronics
Conference (IVEC), pp. 251-251. https://ieeexplore.ieee.org/document/8391497
5. Liu, Zhenlong, et al.
“Experimental Studies on a Low Power Injection-Locked Continuous Wave
Magnetron.” 2017 IEEE MTT-S International Microwave Symposium (IMS), pp.
Injection Locking; Frequency Shift Keying; Phase Shift Keying; Microwave
Heating; Microwave Power