TMS Filter Facts Types

Filter Facts and Types
Filter Facts
A passive filter consists of inductors
and capacitors arranged in a particular
configuration (layout or topology) so that
a specified band of frequencies are allowed to pass with little attenuation while
undesired frequencies are rejected. There
are four common types of filters using a
variety of electrical functions or topologies. The four typical types of filters are
band-pass, lowpass, highpass and bandstop filters.
Bandpass Filters
A bandpass filter provides a good signal
transmission within its passband and
rejects lower and higher frequencies. The
rejection does not occur as an abrupt or
immediate change but in a sloping of the
side skirts. The side skirts also are called
the guardband or slope of rejection.
The bandpass filter is the most common
filter application. Bandwidths can range
from 1% to 200% of the center frequency,
depending on the application.
Lowpass Filters
A lowpass filter provides
good signal transmission at frequencies below
the cutoff frequency. A
steep rejection or abrupt
change from the passband condition is not
achievable. Similar to the
bandpass filter, a slope or
rejection skirt is required
between the passband
frequency and the desired
rejection frequency.
LC Filter
Typically, lowpass filters
are used to suppress 2nd
and 3rd order harmonics or to reject spurious outputs from nearby transmitters.
band. Similar to the lowpass filter, they
are typically used to suppress the signal of
nearby transmitters.
Highpass Filter
Bandstop Filters
Highpass filters operate as a reverse of the
lowpass filter. They are used to reject or
attenuate frequencies below the frequency
Bandstop filters are also known as Notch
Filters or Band Reject Filters. Bandstop
filters are used when rejection or suppression is needed in the passband while
allowing the signals on either side of the
“notch” to pass.
Typical applications are for receivers
located near a transmitter capable of sending a signal within the receivers operating
range.
Lumped Element Filter
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Filter Facts
Topologies
Teledyne Microwave Solutions (TMS)
technical engineering staff uses computer aided design programs to determine
appropriate electrical function to meet
customers’ specifications. These include:
♦♦
Bessel
♦♦
Butterworth
♦♦
Chebyshev
♦♦
Elliptic
♦♦
Gaussian
Interdigital
Interdigital filters are entirely distributed
networks consisting of an array of short
circuit quarter wavelength lines. Filter
bandwidths from 1% to 80% are achievable. These are in applications where flat
group delay is required.
Advantages:
Lumped Element
♦♦
High Q factors can be obtained (5500)
♦♦
Small size can be traded off with Q
♦♦
Bandwidths from 5% to 100% can be
obtained
♦♦
Designs cover 500 MHz to 12 GHz
The elements in the filter are lumped
(i.e. concentrated over a small area). The
inductors are coils of wire wound around
cylindrical formers, and the capacitors are
parallel plate chips or similar portions of
substrate material.
Combline
Combline filters, also called Cavity
Filters, replace the inductors in a lumped
element filter with distributed inductors
or lengths of transmission line leaving the
capacitors lumped, although distributed
capacitance is sometimes used. Filter
bandwidths can range from less than 1%
to 50%.
Advantages:
♦♦
High Q factors can be obtained (3500)
♦♦
Small size can be traded off with Q
♦♦
Bandwidths from 1% to 66% can be
obtained
♦♦
Designs cover 30 MHz to 18 GHz
♦♦
Handles high power
OFOISR App 06-S-1942
Teledyne Microwave Solutions’ technical engineering
staff uses computer aided design programs to determine
appropriate electrical function to meet customers’
specifications.
LC Filter / Power Divider
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Filter Facts
Suspended Substrate Stripline
These filters are also entirely distributed consisting of both series and shunt
transmission line sections. These filters
consist of a printed circuit board which is
suspended between two parallel ground
planes, providing a reasonably high Q ,
as most of the electric field is in the air.
The wide range of achievable impedance
values make suspended substrate suitable for broadband applications. Typically
units exhibit less than 1 dB of loss in the
passband and 60 dB of rejection within
15% of the 1 dB point. The suspended
substrate filter is able to pass severe vibration requirements and extreme operating
temperature of -54 to +125 degrees C
with amazingly low frequency drift.
Advantages:
♦♦
Very selective devices are standard
♦♦
Designs cover 100 MHz to 40 GHz
Waveguide
The suspended substrate filter is able to pass severe vibration requirements and extreme
operating temperature of -54 to +125 degrees C with amazingly low frequency drift.
Waveguide filters consist of half wavelength cavities separated by inductive
irises. These are made by placing posts
through the guide and soldering them to
the waveguide at both top and bottom.
Advantages:
♦♦
High power handling with low insertion loss
♦♦
Extremely high Q factor can be realized (25,000)
♦♦
Very selective devices can be made
♦♦
Designs cover 2 GHz to 40 GHz
Innovation is second nature to Teledyne KW Microwave
OFOISR App 06-S-1942
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Filter Facts
A passive filter is a device consisting of inductors and capacitors arranged in a particular configuration (topology) so that a group of
specified frequencies is allowed to pass with little attenuation while undesired frequencies are attenuated.
Four common types of filters
Bandpass
0 dBa
Lowpass
0 dBa
F0
3 dBc
F2
F2
Insertion Loss
0 dBc ref
Cutoff Frequency
(FCO)
F1
3 dBc
Attenuation
Attenuation
F1
Insertion Loss
0 dBc ref
F3
F3
F4
Stop
Band
Pass
Band
Pass
Band
Stop
Band
Increasing Frequency
Increasing Frequency
Bandreject
0 dBa
F0
Insertion Loss
0 dBc ref
F2
Insertion Loss
0 dBc ref
3 dBc Cutoff Frequency
(FCO)
F1
F2
Attenuation
F1
Highpass
0 dBa
Attenuation
3 dBc
Stop
Band
F3
Pass
Band
Stop
Band
Increasing Frequency
OFOISR App 06-S-1942
Pass
Band
Stop
Band
Pass
Band
Increasing Frequency
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FILTER TYPES
Lumped Element
Frequency Range: 10 MHz To 25 GHz
High Selectivity
Group Delay Equalized
Small Size
Can Be Used On A Variety Of Applications
Available In The Following Configurations: Bandpass, Lowpass, Highpass And Notched
Teledyne KW Microwave offers ultraminiature discrete filters in a wide range
of frequencies and design approaches.
In-house research and development efforts, coupled with proprietary computer
software, helps maintain Teledyne at the
leading edge of technology.
Filters with excellent thermal characteristics are achievable through the use of high
Q , thermally stable dielectric materials
and special constructions techniques.
High mechanical integrity is achieved
with lightweight aluminum housings
when used in conjunction with our inhouse laser welder.
Teledyne KW Microwave fabricates
its filters using resonators with discrete
capacitors and inductors, i.e. in a lumped
form. High-Q porcelain chip capacitors
and air-spaced inductive coils are soldered
to an RF quality substrate.
Teledyne employs unique proprietary
techniques to compensate for changes
in filter performance over temperature.
Stability of <5 ppm/OC are readily achieve
over the temperature range of -55 to +125
O
C.
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Lumped Element
Typical Performance
Bandpass Filters
Passband
(Ripple)
MHz
.450 - 30
(.75 dBc)
29.85 - 30.15
(2 dBc)
159.5-1605
(3 dBc)
307-323
(1 dBc)
700 - 1600
(2 dBc)
VSWR
Insertion
Loss @ Fo
60dB
Rejection
From Fo
dBcMHz
-30.225
-3060
-5028.3
-5031.7
1.5:1
dB (max)
1.5
2.0:1
8.0
1.5:1
5.0
-35+/-5
2.6 x 1.2 x 1.0
1.5:1
3.0
.57 x .4 x .24
2.0:1
2.0
1226 +/- 10
1575 +/- 10
(3 dBc)
1900 - 5900
(1 dBc)
1.5:1
1.0
-20290
-20340
-58650
-601800-3500
18500
-60800
1.5:1
1.0
-502000
1.5:1
1.0
-70900
-55
7900‑
20000
1.5 x .3 x .25
15.2-25
(1 dBc)
1.5 1
3
-7518.0
.750 x .3 x .3
Dimensions
Inches
2.5 x 2.0 x .8
1.5 x .75 x .27
2.7 x .5 x .3
1.5 x 1.0 x .5
Lowpass Filters
Cut Off
Freq.
MHz
95
VSWR
Stopband
1.5:1
MHz
dBc
-90 @ 123
620
1.5:1
-90 @ 806
1900
1.5:1
5700
1.5:1
11500
1.5:1
Insertion
Loss (max)
dB
2.5
-90
@
2470 - 4950
-90
@
7400 - 15000
7400 - 15000
-30 @ 13000
Dimensions
Inches
1.4 x .4 x .4
2.5
1.9 x .4 x .4
2.5
1.4 x .4 x .4
2.5
1.15 x .4 x .4
1.5
1.25 x .4 x .4
Highpass Filters
Cut Off
Frequency
GHz
.420
VSWR
Passband
Stopband
1.5:1
GHz
.420 - 1.0
GHz (dBc)
-42 @ .350
Insertion
Loss (max)
dB
1.5
1.5:1
1.0 - 4.0
-75 @ .50
1.0
1.75
1.5:1
1.75-10.0
-55 @ .50
1.0
1.0 x .5 x .4
6.0
2.0:1
6.0-18.0
-65 @ 4.0
1.0
.875 x .4 x .35
10.5
1.8:1
10.5 - 18.0
-40 @ 9.1
1.5
.875 x .3 x .3
1.0
OFOISR App 06-S-1942
Dimensions
Inches
1.4 x .4 x .4
1.0 x .4 x .39
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Combline and Interdigital Filters
30 MHz - 18 GHz
Bandwidth Of 1% To 66%
Low Loss
Combline filters are bandpass filters used
in the frequency range of 30 MHz to 18
GHz. The structure consists of a series of
TEM resonators of circular or rectangular
cross-section resonated by a capacitor at
the open circuit end. The bandwidth and
response of the filter is governed by the
coupling of each resonator to its immediate neighbor. This is also a function of
the resonator size, resonator spacing and
ground plane separation. Typical construction is silver plated aluminum. This
achieves the lowest passband loss while
maintaining a light weight. Computer
design programs result in close correlation
between theoretical and actual performance.
In applications where flat group delay narrowband filters are required, linear phase
responses of typically 1 - 5% variations
over 70% of the filter bandwidth can be
achieved.
As the frequency of operation is reduced,
the reactance components increase in
physical size. But, for a given Q , the size
of an air-spaced inductor increases as the
frequency decreases.
Typical Combline Filter
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Combline and Interdigital Filters
Specification
Model K2C
Model K3C
Model K6C
Model K7C
Fo: (standard)
(special)
30 - 450 MHz
400 - 3000 MHz
2000 - 6000 MHz
6000 - 12400 MHz
20 - 600 MHz
250 - 4000 MHz
1500 - 14000 MHz
500 - 18000 MHz
# of Sections
3 to 6
2 to 7
2 to 7
2 to 4
Maximum VSWR
1.5:1
1.2:1
1.2:1
1.5:1
-54° to + 100° C
-54° to + 100° C
-54° to + 100° C
-54° to + 100° C
Temperature Range
Small Combine Filter
Interdigital Filters
Teledyne’s interdigital filters fill the need
for moderate and wide bandwidth filters
in the 1.0 to 12 GHz. frequency range.
Our standard unit is available with up
to 17 sections, while custom designs
can have 20 sections. Teledyne KW
Microwave’s interdigital filters offer low
loss, high “Q” performance in package
styles suitable for many applications,
including space.
OFOISR App 06-S-1942
Specification
Frequency Range
# of Sections
Maximum VSWR
Temperature Range
Standard
Special
1000 - 10000 MHz
3 to 10
1.5:1
500 - 12000 MHz
3 to 20
1.3:1
-54° to +100° C
-54° to 125 °C
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Waveguide Filters
2 GHz To 40 GHz
Bandpass, Lowpass Or Notch Configurations
Provides For Lower Insertion Loss
Good For High Power Requirements
Waveguide Or Coaxial Interface
Waveguide filters can be used in the
frequency range of 2 GHz to in excess
of 40 GHz. Waveguide can support an
infinite number of field patterns (modes),
each with a different guide wavelength.
The normal mode used is the dominant
TE in rectangular waveguide, although
other configurations are used for special
applications.
Rectangular Waveguide Filters
These can have lowpass, bandpass or
bandstop characteristics. Lowpass filters
are formed by means of a corrugated
waveguide structure with adjacent high
and low impedance sections.
The normal construction for bandpass
filters is to place inductive obstacles, typically an array of posts, along a waveguide
at spacings close to a half wavelength
OFOISR App 06-S-1942
The major advantages of waveguide filters are high power handling and low loss performance.
apart. The size, number and transverse
spacings for the posts are the parameters
that vary the filter bandwidth while the
longitudinal spacing determines the center frequency of the filter.
Bandstop filters can be made by placing
short circuited cavities approximately a
quarter wavelength apart along the filter
body.
The major advantages of waveguide filters
are high power handling and low loss
performance. Waveguide filters are fabricated in aluminum, brass, copper or Invar.
Materials are selected to ensure that the
lowest possible passband insertion losses
are achieved. The advantage of Invar
“Waveguide filters
are fabricated in
aluminum, brass,
copper or Invar.”
construction is its low thermal expansion
which provides optimum temperature
stability. Aluminium construction is best
suited were weight is of major importance.
All filters have tuning screws which are
locked and sealed with epoxy.
The interface is normally in the appropriate waveguide size. However, for most
types, integral coaxial transitions on one
or both ports are available as options.
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Iso Filters
Can Apply To Any Catalog Standard Filter
Good Out Of Passband VSWR
Low - Loss Impact
One solution to limit reflected power is to use an
Iso-Filter
Teledyne KW Microwave have a number of
integrated solutions available to improve out
of band performance.
As implied, an Iso-Filter is the combination of an isolator and a filter. The main
advantage of the Iso-Filter is in how the
filter itself works. When a signal hits the
input port of a filter one of two things can
happen to the energy; it can pass through
(transmission) or it can be reflected
(return loss or VSWR). Although the
overall performance of a filter can be set
by the number of sections and the Q or
size of each of the sections almost all of
its selectivity is due to reflectivity of the
device outside of its passband.
OFOISR App 06-S-1942
What this means is the return loss or
VSWR is very bad outside of the passband. Therefore any signals in these
frequency ranges will be reflected back
to the generating source. In most cases,
this is not a problem; but, if it is, there are
a limited number of solutions. They are
listed below:
1. The most simple and cost effective
solution is the use of an attenuator pad.
The worse case return loss will be twice
the loss value of the attenuator pad. For
example a 3 dB pad will have a minimum
of 6 dB return loss. Unfortunately not all
applications can afford the extra insertion
loss.
2. The next simplest solution is an IsoFilter. The isolator will typically be less
than 1 dB of loss with a rejection of better
than 20 dB. These typically cost more
than the attenuator pads.
3. The third alternative is a terminated
complimentary multiplexer scheme. These
have the least amount of effect on the insertion loss, however they are very costly
custom items. This usually relates to long
lead times.
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Diplexers and Multiplexers
10 MHz To 26 GHz
Lumped Element
Combline
Interdigital
Stripline
Waveguide Filters
Suspended Substrate
Contiguous
Non-contiguous
Teledyne KW Microwave has designed
and manufactured a wide variety of multiplexers using lumped element, combline,
interdigital, suspended substrate, stripline,
and waveguide filters. Dimensions range
from 0.3 X 0.6 X 1.0 inches for a L-band
lumped element diplexer, to 2 X 3 X 8
inches for a high power coaxial diplexer in
the same frequency band.
Designs are obtained using analytical
techniques implemented by proprietary
computer programs, and basically are
guaranteed to work with little or no empirical adjustments, apart from the usual
tuning arrangements.
Crossover Frequency (Fc)
Multiplexers provide a passive, low-loss,
means of splitting or combining two or
more signals of different frequencies at a
common port while providing isolation
between the signal ports.
Fc refers the frequency at the point of
crossover. This parameter is important
to the systems designer and provides an
easily identified reference point in the
measurement of multiplexer performance.
In addition to the standard filter parameters, the following specs are required
when defining multiplexer performance.
Narrowband Multiplexers.
Crossover Insertion Loss
The absolute insertion loss at the point of
equal loss between adjacent channels of a
multiplexer.
OFOISR App 06-S-1942
Narrowband multiplexers (channel bandwidths less than 20%) are formed by combining bandpass filters. Contiguous and
non-contiguous multiplexers are available
and, depending on the characteristics required of each channel, may be fabricated
using lumped element, combline, inter-
digital or suspended substrate designs.
In each case, the overall performance is
close to the performance achievable from
discrete bandpass filters in the particular
technology.
If appropriate, hybrid solutions can be
provided.
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Diplexers and Multiplexers
SPECIFYING MULTIPLEXERS
When specifying multiplexers please provide the following information:
Contiguous and non-contiguous multiplexers are available and, depending on the characteristics required of each channel, may be fabricated using lumped element, combline, interdigital or suspended
substrate designs.
Broadband Multiplexers
Broadband diplexers operating from
20-2000 MHz are formed by combining a highpass filter with a lowpass filter
and modifying critical element values to
ensure a good input and output match
and improved rejection in the stopbands.
More complex multiplexers are achieved
by cascading diplexers.
OFOISR App 06-S-1942
1.
2.
3.
4.
5.
6.
7.
Number of Channels
Bandwidth of Channels
Passband Insertion Loss
Stopband Frequencies
Stopband Rejection
Crossover Frequencies
Crossover Insertion Loss
Teledyne KW Microwave is able to offer
the following special options:
AMPLITUDE MATCHING
PHASE MATCHING
GROUP DELAY MATCHING
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Diplexers and Multiplexers
Suspended Substrate Multiplexers
Suspended substrate readily lends itself to
broadband configurations and is widely
used in systems where small size, high
performance and light weight are essential
features.
Using this technology, broadband diplexers covering DC to 26.5 GHz are formed
by combining a highpass filter with a low
pass filter with modifications to critical
values to ensure good input and output
match and improved rejection in the
stop-band. More complex multiplexers
are designed by cascading diplexers. These
diplexers can achieve < 5 dB crossover
insertion loss, 60 dB of rejection within
10-15% of crossover, while exhibiting less
than 1 dB insertion loss within the passband. The passbands are the bands outside
the crossover regions, which are within
+/-5% of the crossover frequencies.
Skirt characteristics can be supplied at
both extreme band edges where 60 dB
attenuation is achieved.
Suspended Substrate Multiplexer
Channelizers
These filter banks are often used in receivers having good resolution, high speed
and high probability of intercept. Such
units are fed from a common antenna
with the common input multiplexed to
provide a bank of channels each defined
by a bandpass filter and terminated in a
video detector.
Depending on the frequency and bandwidth of the receiver, and the bandwidth
and selectivity of each channel, the multiplexing may be achieved in a variety of
ways. Power splitting, tandem circulators,
traditional loss-less multiplexers, lossy and
loss-less manifold multiplexers and hybrid
solutions are utilized.
Typical Performance of Suspended Substrate Multiplexer
Frequency Range:
DC - 26.5 GHz Crossover Frequency Range: 0.5 - 16 GHz
Passband Insertion Loss:
4.5 - 5.0 dB
Selectivity (typical):
>60 dB within 10 - 15% of crossover
Temperature Range:
-55 to +125 OC.
The ultimate channel frequency performance is similar to that obtained from
an individual bandpass filter of the same
format.
OFOISR App 06-S-1942
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Diplexers and Multiplexers
Typical Coaxial Diplexers (Combline and Interdigital)
Passbands/MHz
1773-1973
1825-1845
2318-2354
2383-2419
2330-2344
2394-2408
VSWR
Insertion Loss Across
Passband/dB
1.25:1
1.5
1.25:1
1.5
1.25:1
1.5
Rejection From Fo
dB / MHz
7032
8532
6062
6062
6030
6030
Typical
Dimensions/Inches
7.1 x 3.2 x 1.63
4.90 x 3.0 x 2.065
7.38 x 3.8 x 1.97
Suspended Substrate Diplexers
Frequency
Range/GHz
DC-4.0
Cross-Over
Cross-Over Frequency
Passband
Frequency/GHz
Insertion Loss/dB
Insertion Loss/dB
2.0
4.5
1
VSWR
1.6:1
DC-8.0
4.0
4.5
1
1.6:1
DC-10.0
6.0
4.5
1
1.6:1
DC-12.0
8.0
4.5
1
1.7:1
DC-15.0
10.0
4.5
1
1.8:1
DC-18.0
12.0
4.5
1
1.8:1
DC-20.0
14.5
4.5
1
1.8:1
DC-18.0
8.0
4.8
1
1.9:1
Note: Selectivity typically with 15% of crossover frequency
Selectivity
60 dB / GHz
DC-1.7
2.3-4.0
DC 3.4
4.6-8.0
DC-5.1
6.9-10.0
DC-6.8
9.2-12.0
DC-8.5
11.5-15.0
DC-10.2
13.8-18.0
DC-11.9
16.1-20.0
DC-6.8
9.2-18.0
Dimensions/Inches
3.0 x 2.5 x .65
2.5 x 2.5 x .5
2.0 x 2.0 x .5
1.5 x 1.3 x .5
1.3 x 1.2 x .5
1.0 x 1.0 x .5
1.0 x .5 x .9
1.2 x .8 x .5
Suspended Substrate Triplexers
Frequency
Range/GHz
DC-4.0
DC-12.4
Cross-Over
Frequency/GHz
1.0, 2.0
4.0, 8.0
Cross-Over Frequency
Insertion Loss/dB
5.0
4.8
Passband
Insertion Loss/dB
1.0
1.0
DC-18.0
8.0, 12.0
4.8
1.0
VSWR
Dimensions/Inches
1.8:1
1.7:1
7.75 x 2.6 x 0.65
4.0 x 2.5 x 0.5
1.8:1
2.5 x 1.5 x 0.5
Note: Selectivity typically with 15% of crossover frequency
Suspended Substrate Quadraplexers
Frequency
Range/GHz
Cross-Over
Frequency/GHz
Cross-Over Frequency
Insertion Loss/dB
Passband
Insertion Loss/dB
VSWR
Dimensions/Inches
DC-18.0
DC-18.0
4.0, 8.0, 12.0
6.0, 10.0, 12.0
5.0
5.0
1.0
1.0
2:1
2:1
5.0 x 2.5 x 0.5
4.5 x 2.25 x 0.5
Note: Selectivity typically with 15% of crossover frequency
OFOISR App 06-S-1942
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Switch Filters and PIN Diode Switches
Switch Filters
Teledyne KW Microwave can offer a variety of standard switch filters or custom
designs for a customers unique application. Our current designs extend from
10 MHz to 26 GHz and have a typical
switching time of 500 ns. These switch
filters can be designed for pre-selection,
harmonic rejection, signal leveling or
multiply band frequency separation.
Teledyne KW Microwave will use a
GaAs MMIC or discrete diode to control
the switching technology. The switch
can be integrated with suspended substrate lumped element, combline, printed
microstrip filter technology. High Q
lumped element filters are primarily utilized where size of the package is a major
concern and the need for high output
rejection is required.
PIN Diode Switches
PIN Diode Controlled Switch
Teledyne KW Microwave offers a wide
range of pin diode control products. We
use GaAs Pin Diode or GaAs MMIC
technology to achieve the durability,
switching speed and electrical performance characteristics of our switches.
Our switches have excellent insertion
loss and VSWR performance over a wide
operating band.
Teledyne offers our pin diode control
products with standard logic controls of
TTL, CMOS or ECL.
8 Channel Switch Filter
OFOISR App 06-S-1942
1274 Terra Bella Avenue, Mountain View, CA 94043
Tel: 1.800.832.6869 or +1.650.962.6944 Fax: +1.650.962.6845
[email protected]
Switch Filters and PIN Diode Switches
Typical Switched Filter Requirements
Two 3 channel switch filters in a
single package
1. NUMBER OF CHANNELS
n = (No. of Filters)
2. FILTER SPECIFICATIONS:
Standard Filter Spec’s
3. ISOLATION:
>50 dB
4. Ultimate Rejection:
>60 dB
5. DC Power & Control: + 5 V @ 60 mA -15V@60mA TTL, BCD
6. RF Power:
100 mW
7. Video Leakage:
100 mV P-P
8. Switching Speed :
1 µs (slow)
200 ns (moderate)
100 ns (fast)
9. Connectors:
SMA or PIN
10. Size:
Height .25” - 1.0” Width .5” - 3.5” Length 1.25” - 6.0”
11.Insertion Loss:
2 - 6 dB Typical
12.VSWR:
1.6:1 max.
[1]
Note: [1] Switching too fast with narrowband filters will cause ringing
OFOISR App 06-S-1942
1274 Terra Bella Avenue, Mountain View, CA 94043
Tel: 1.800.832.6869 or +1.650.962.6944 Fax: +1.650.962.6845
[email protected]
Glossary of Terms
Absolute attenuation: Attenuation measured with the zero dB, or reference
point, equal to the signal level present
with the filter removed from the test setup
(straight-through).
Crossover frequency: The frequency at which
Attenuation: Power loss in dB evidenced
Crossover loss: The loss that occurs at the
by a signal passing through a dissipative
network (bandpass filter).
Bandpass filter: A filter that passes one
two adjacent channels (the upper frequency of the lower channel and the lower
frequency of the upper channel) are of
equal amplitude.
crossover frequency.
Cut-off frequency (Fco): The upper passband
band of frequencies and rejects both
higher and lower frequencies.
edge in lowpass filters, the lower passband
edge in highpass filters, or the passband
edge closest to the stopband.
Bandreject filter: A filter that rejects one
Decibel (dB): A unit used to express the
Bandwidth: The width of the passband of
dB = 10LOG10 P1
P2
band of frequencies and passes both
higher and lower frequencies. Commonly
referred to as a notch filter.
a bandpass filter. Typically the frequency
difference between the lower (Fl) and upper (F2) 3 dB relative attenuation points.
Bessel function: A mathematical function
used to yield a maximally constant time
delay in a filter, with little if any consideration for amplitude response. This function is very close to a Gaussian response.
Butterworth function: A mathematical
function used to yield a maximally constant amplitude response in a filter, with
little if any consideration for time delay or
phase response.
Cauer function: See Elliptic function.
Center frequency (Fo): In standard bandpass
filters, the center frequency is geometrically related to the 3 dB points Fl and F2.
Fo = F1xF2
In linear phase (constant delay) band-pass
filters the center frequency is arithmetically related to the 3 dB points Fl and F2.
Fo = Fl + F2
2
OFOISR App 06-S-1942
logarithm of the ratio between two
amounts of power, P1 and P2. By definition:
Diplexer: A two-channel multiplexer of
bandpass/bandpass design or highpass/
lowpass design, with or without additional highpass and lowpass close-up filters.
Dissipation: Energy losses in a filter due to
resistance.
Distortion: Generally, the modification
lated signal as it passes through a filter.
Sometimes called time or group delay,
envelope delay is proportional to the slope
of the phase shift response vs frequency
curve. Envelope delay distortion occurs
when the delay is not constant at all frequencies in the passband region.
Filter Q: An important parameter of
bandpass and bandreject filters that affects
both insertion loss and rejection.
Loaded Q = Center Frequency (Fo)
3 dB Bandwidth
Gaussian function: A mathematical function used to yield a filter that passes a step
function with zero overshoot. Similar to a
Bessel function filter.
Group or time delay: See envelope delay.
Highpass filter: A filter that passes high
frequencies and rejects low frequencies.
Impedance: Usually taken as equal to
L/C where L is total series inductance in
Henrys and C is the total shunt capacity in farads. Characteristic impedance is
measured in ohms (Ω).
of signals that produces undesirable end
effects. These modifications can relate to
phase, amplitude, and delay. The distortion of a sine wave is usually defined as
the percentage of signal power remaining
after the fundamental sine wave component has been removed.
Impulse: A pulse whose width is of such
short duration that it may be regarded as
infinitesimal - a spike.
Elliptic function: A mathematical function
Linear phase filter: A general term that
Envelope delay: The propagation time delay
of the envelope of an amplitude modu-
Load impedance: The impedance that normally must be connected to the out-put
connections of the filter in order to meet
filter specifications.
used to yield the squarest possible amplitude filter response with a given number
of circuit elements. The elliptic function
has a Tchebycheff response in both the
passband and the stopband. The elliptic
function filter has a poorer phase and
transient response than any of the classical
transfer functions.
Isolation: Typically the amount of attenuation between the switched filter’s “On”
channel and the “Off” channel(s).
defines a class of filters that exhibits a
constant change in degrees per unit of
frequency. The plot of frequency vs phase
results in a straight line. This type of filter
ideally provides a constant delay in its
passband.
1274 Terra Bella Avenue, Mountain View, CA 94043
Tel: 1.800.832.6869 or +1.650.962.6944 Fax: +1.650.962.6845
[email protected]
Glossary of Terms
Lowpass filter: A filter that passes low frequencies and rejects high frequencies.
Monotonicity: Characteristic of the filter
response that refers to the changes in
slope of the attenuation response in the
stopband (no comebacks). Properly designed lumped-element filters can exhibit
monotonic responses of two to three
octaves from center frequency.
Multiplexer: A frequency-selective net-
work of filters in which one terminal of
each filter is connected to a common port.
Signals applied to the common port are
separated according to the filter characteristics. Signals applied to the isolated
ports are combined according to the filter
characteristics.
Overshoot: The percentage by which an
output signal exceeds it steady-state value
when subjected to an input step function,
pulse, impulse, or ramp.
Passband: The frequency range in which a
filter is intended to pass signals.
Passband ripple: Variations in attenuation
vs frequency within the passband of the
filter.
Phase shift: The changing of phase of
a signal as it passes through a filter. A
delay in time of the signal is referred to
as phase lag. In normal networks, phase
lag increases with frequency, producing a
positive envelope delay.
Pulse: Two step functions, one in the
positive direction and one in the negative
direction - separated in time by the pulse
width.
Q (component): Quality factor of a capaci-
tor or inductor equal to the ratio of its reactance to its equivalent series resistance.
Ramp: Linear increase or decrease of
voltage or current during a specified time
before reaching steady state.
OFOISR App 06-S-1942
Relative attenuation: Attenuation measure
with the point of minimum attenuation taken as the reference, or zero dB.
Relative attenuation equals attenuation
minus insertion loss.
Response: Used to describe how a filter
responds to input signals defined as the
ratio of the input signal compared to the
output signal (for amplitude and phase
response).
Ringing: A damped oscillation in the
out-put signal as a result of an input step
function, pulse, impulse, or ramp.
Ripple: Refers to the wavelike variation in
the amplitude response of a filter, usually
measured in dB. Tchebycheff and elliptic
function filters ideally have equal ripple
characteristics; i.e., differences it peaks
and valleys of the amplitude response
in the passband are always the same.
Butterworth, Gaussian, and Bessel function filters have no ripple.
LOWPASS:
S = ATTENUATION FREQUENCY
3 dB CUT-OFF FREQUENCY (Fco)
HIGHPASS:
S = 3 dB CUT-OFF FREQUENCY (Fco)
ATTENUATION FREQUENCY
Step function: Sudden rise or drop in voltage or current.
Stopband/reject band: The area of frequencies where it is desirable to reject or attenuate all signals as much as possible.
Switching time: The difference in time be-
tween the input signal reaching 50% of its
steady state and the output reaching 90%
of its RF envelope.
Transitional filter: A filter that compromises
between high-skirt selectivity and flat,
passband group delay.
Tchebycheff function: A mathematical
Rise time: The length of time, on the initial function that produces a filter response
input signal rise, it takes a step function at
the output of a filter to move from 10% to
90% of its steady-state value.
Setting time: The time it takes for the
output signal to settle within a specified
overshoot percentage after the input has
been subjected to a step response pulse,
impulse, or ramp.
Shape factor: A useful way of specifying
filters:
that ripples within certain bounds. This
function produces a more square (greater
rejection) amplitude response than the
Butterworth function, but has greater
phase shift and time-or group-delay
variations. Tchebycheff function filters are
designed to exhibit certain ripple response
within the passband (.01 dB ripple, .05
dB ripple, etc).
Time or group delay: See envelope delay.
Transient response: The filter’s response in
BANDPASS:
S = ATTENUATION BANDWIDTH
time to an input signal.
3 dB BANDWIDTH
BANDREJECT:
S =
3 dB BANDWIDTH
ATTENUATION BANDWIDTH
1274 Terra Bella Avenue, Mountain View, CA 94043
Tel: 1.800.832.6869 or +1.650.962.6944 Fax: +1.650.962.6845
[email protected]
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MICROWAVE SOLUTIONS
Everywhereyoulook
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Tel: 1.800.832.6869 or +1.650.962.6944