Aerospace & Defense Technology - September 2022 - 42

RF & Microwave Technology
1: Transmission
2: Reflection
dB
-4.00
-8.00
-8.00
-16.00
-12.00
-24.00
-16.00
-32.00
-20.00
-40.00
-24.00
-48.00
-28.00
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1
Log Mag
Log Mag
1
2 3
8 dB/Ref
4 dB/Ref
0.00 dB
0.00 dB
C
C
2
For example, the recently introduced
mmW-FH series of bandpass
filters from Benchmark Lark Technology
filter center frequencies
from 5 to 30 GHz with available
passbands of 2% to 5% (Figure 2).
Housed in SMT packages less than
0.04 inches high, they are compatible
with microstrip and stripline
transmission-line technologies
through mmWave frequencies.
While custom components are
Start 20000.000 MHz
Mkr1
Mkr2
Mkr3
27580 MHz
27265 MHz
27885 MHz
-2.323 dB
-5.324 dB
-5.378 dB
Stop 40000.000 MHz
Figure 3. mmW-FH bandpass filter next to traditional technology filter of a similar frequency, substrate integrated
waveguide design, on ceramic RF/microwave substrate.
frequency spectrum typically exhibits
the highest amounts of passband (and
stopband) ripple. Ripple refers to fluctuations
in magnitude or signal power
with frequency, impacting the phase
response and group delay of an RF filter.
An RF filter's frequency response
plot shows how its magnitude or signal
power changes with frequency; a
Bode plot also shows how the phase is
affected in the passband.
Filter bandwidth is defined in several
ways, especially with differences
in response curves for various RF filter
types. The Fc is often the quickest starting
point when specifying a bandpass,
band-reject, lowpass, or highpass filter
because it identifies a spectral point at
which signal loss changes from low to
high. A lowpass filter typically has a
passband beginning at DC or 0 Hz, but
the actual frequency may also be a function
of the filter's packaging. In a highpass
filter, signals above Fc may transfer
to the output with low loss but not
reach mmWave frequencies because of
the filter's connectors and/or packaging.
42
Practical Solutions
As many A&D applications move
higher in frequency in quest of available
bandwidth at mmWave frequencies,
filter designers are being asked for
responses for systems operating at 30
GHz and higher, often from filters a
fraction of the size of those working at
RF and microwave frequencies. SWaP-C
requirements for miniaturization guide
system designers, and they expect the
same or better performance levels at
mmWaves as at lower frequencies but
in a drop-in or SMT package. For filter
designers, it is the opportunity to apply
their creativity at higher frequencies
to achieve performance, repeatability,
and reliability. In some cases, such as
RF filters for A&D systems that must
comply with International Traffic in
Arms Regulations (ITAR) requirements,
those mmWave filters must also be
manufactured in the United States.
ITAR controls the manufacture, sale,
and distribution of A&D components
and services as defined by the U. S.
Munitions List (USML).
mobilityengineeringtech.com
available based on filtering requirements,
a standard substrate-integrated-waveguide
(SIW) 50- bandpass
model was developed for a center
frequency of 27.95 GHz and 2.2%
passband. It features more than 40
dB rejection outside the 610-MHz
passband and 5-dB insertion loss
at the center frequency and can fit
within an SMT housing measuring
1.00 × 0.25 × 0.03 in. For the same
size and bandwidth, the high-performance
version of this series results
in an insertion loss of better than
2.4 dB at 27.580 GHz (Figure 3). At
even higher frequencies, the same
company's mmW-STL bandpass filters
can be customized with center
frequencies from 5 up to 40 GHz and
passbands from 10% to 25%. A typical
size for a nine-poles SMT mmW-STL
bandpass filter at 39 GHz is in the range
of 0.275 x 0.080 x 0.022 in.
Applications in A&D systems are
moving to higher frequencies to meet
increasing bandwidth requirements.
RF, microwave, and mmWave filters
are key components for minimizing
interference and enabling the growing
numbers of A&D systems even as
they expand into higher frequency
bands. Fortunately, for A&D system
architects, these filters can be supplied
in ever-smaller packages so that the
benefits of RF filtering can be available
without impacting SWaP-C.
This article was written by Francisco
Hirata, Ph.D., R&D Engineer; Ani
Herrera, Director of Engineering; Elizabeth
Obiala, Ph.D, R&D Engineer;
Art Aguayo, Channel Manager, Benchmark
Lark Technology (Tempe, AZ).
For more information, visit https://
www.bench.com/lark.
Aerospace & Defense Technology, September 2022

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Aerospace & Defense Technology - September 2022

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