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Combline Cavity Filters
ALLEN AVIONICS CMBF series of Combline Bandpass Filters are the answer
when you need superior performance in a small package for Bandwidths
ranging from 0.5% to over 20%. Available over the 500 MHz to 26.50 GHz
frequency band. These filters can be supplied with 3 to 8 "high Q"
resonant sections. Each filter is custom designed to your exact
specifications so that you get optimum performance at the lowest cost.
Allen Avionics Cavity Filters are normally constructed using Silver
Plated Brass and Aluminum for improved electrical characteristics and
current flow. Allen Avionics cavity filters can be supplied with your
choice of connectors. For connector styles see chart below.
Allen Avionics Combline Bandpass Filters are fixed filters that feature
sharp stopband rejection and lower loses than Discrete Element or
Tubular style Bandpass Filters. This filter type offers highQ with
reduced size and excellent Frequency response. Filter performance is
easily predicted using our microwave filter design software. Manufacture
takes place in a state of the art CNC machine and fabrication center
where custom filters can be completed in days not weeks. The CMBF series
of filters are rugged and well suited for severe environments. 
Available
Frequency 
500 MHz –
26.5 GHz 
Available
Bandwidth 
0.5% Up to
20% 
Insertion
Loss 
(Depends on
the number of sections and BW) 
Stop Band
Attenuation 
see graphs 
Number of
Resonator Sections Available 
3 to 9 
VSWR 
1.50:1 
Dimensions 
See
drawings below.
Consult Factory for exact dimensions. 

The curve to the right displays the Relative Attenuation as a function
of the Normalized 3dB Bandwidth for narrow bandwidth filters.(0.5%) The
graphs supplied are designed to give an approximation of the frequency
response for the CMBF series of Cavity filters. Using these curves and a
few simple formulas shown below you can predict the attenuation for a
given number of sections. Curves for narrow bandwidths (0.5%) and wide
bandwidths (5.0%) are also provided. There are many variables that
affect the Frequency Response, Attenuation and Insertion loss of
Waveguide filters so when exact information is required contact the
factory at (516) 2488080 or send email to
sales@allenavionics.com
The Frequency response curves we supply show the approximate attenuation
as a function of the normalized 3dB bandwidth.
Using these graphs we can calculate attenuation at a given frequency for
a specified number of sections or determine the number of sections
required to meet a set of given attenuation points. 

EXAMPLE #1
(Find required # of sections)
We want a
Bandpass filter centered at 10.0 GHz (FO) with a 3dB bandwidth of 100
MHz (FC). We have a stopband requirement of 60dB at 9.80GHz and
10.30GHz.
First we
need to determine the percentage bandwidth (%BW) using the following
formula to find the correct graph to use.
With a 1% bandwidth the graph for .5% above would give us the
best approximation. Now we have to look at the two stopband
requirements. The low side 60db attenuation point is 9.70GHz and
the high side is at 10.30GHz. Now we need to calculate the
number of 3dB bandwidths using the following formula.


Checking the above graph we can see that 6 sections will have well over
60dB attenuation at both stopband requirements. 

EXAMPLE #2 (Find minimum attenuation at specified
frequencies)
We want a Bandpass filter centered at 2.50 GHz (FO) with a
3dB bandwidth of 250 MHz (FC) and we are thinking about
using 6 sections. We need to find the minimum attenuation at
2.00GHz and 3.00GHz for 6 sections.
Using the same formula above we first find the %BW to
determine the correct graph to use. In this problem the %BW
equals 10% so we can use the 16% BW graph to the right. Then
from the second formula we used in the first example we find
that we have four (2) 3dB bandwidths on each side. Checking
the above graph we can see with 6 sections we will have
greater than 40dB attenuation at both 2.0GHz and 3.0GHz for
a filter with 250MHz 3dB bandwidth. Three plots are
provided, 0.5%,
5.0% and 16%, which can be used to 20% so the approximate
response can be determined for any bandwidth in the range of
.0.5% to 20%


Allen Avionics has advanced simulation and modeling software that our
experienced Microwave engineers use in the design and manufacturing of
Combline Cavity Microwave Bandpass Filters. This software combined with
our Numerical Control Machining Centers gives us rapid design and
production capabilities. Our Automated inspection equipment insures
every part will meet their specifications.
Allen Avionics has the ability to manufacture prototypes
and short runs quickly and reduce lead times on large production runs.
Our Microwave and Mechanical engineers are
always available to help with custom designs or applications. The sales
force at Allen Avionics is ready to help with information and prices.
They try to answer all quotes in 48 hours or less and are familiar with
all our microwave products. 
MODEL DESIGNATION
Code 
Description 
1 
Series 
2 
Number of Sections 
3 
Center Frequency (GHz) 
4 
3 dB Bandwidth (MHz) 
5 
Connector Code(Input/Output)
(see chart) 
6 
Material (AL) (BR) 

1 
2 
3 
4 
5 
6 
CMBF/ 
5/ 
20.25/ 
101.25/ 
FS/FS/ 
AL 
COMPLETE Part Number=
CMBF / 5 /
20.25 / 101.25 / FS/FS / AL
Contact Factory With Your Specific Needs
For:
Electrical Performance
Mechanical Configuration
Insertion Loss


CONNECTOR CODE CHART 
FEMALE ("N") 
FN 
MALE ("N") 
MN 
FEMALE ("BNC") 
FB 
MALE ("BNC") 
MB 
FEMALE ("TNC") 
FT 
MALE ("TNC") 
MT 
FEMALE SMA

FS 
MALE SMA 
MS 
2.4 mm FEMALE 
24F 
2.4 mm MALE 
24M 
MATERIAL
The CMBF series of Microwave Bandpass filters
is normally constructed from Aluminum but when better
temperature response is required brass can be used.
When bandwidths exceed the 20.0% limit for this
filter type or when insertion loss, length rejection required or
some other parameter cannot be met, Allen Avionics may have
other Filter constructions available which could be used to
solve the problem.
Contact our sales department for assistance.
(516) 2488080 or
sales@allenavionics.com 
Frequency GHz 
.50  3.0 
3.01  6.0 
6.01  10.0 
10.01  26.5 
Multiplier (H) 
2.00 
1.50 
1.00 
0.500 
% Bandwidth (Fc/Fo) 
0.50  7.0 
7.1  14 
14  20 
Multiplier (A) 
0.30 
0.75 
1.00 

The number of sections, Center Frequency and the
% bandwidth along with the cavity structure are the basic
parameters that determine the overall dimensions of Combline
Cavity Microwave Filters.

Using some basic formulas we can approximate the length for a
given Frequency, and width and number of sections. 

To simplify this approximation we are assuming that
width and height are the same.
From
EXAMPLE #1. We had a Bandpass filter
centered at 10 GHz with 1.0% BW. From the table above we see for 10GHz
the (H) multiplier is 1.0. From the same table we see the % Bandwidth
multiplier (A) is 0.50. Our previous calculations done for example #1
Indicated that we needed 6 sections to meet the required attenuation.
With the number of sections (N), height multiplier (H) and % bandwidth
multiplier (A) we have all the information we need to calculate the
approximate length (L).
N = number of sections.
H = Height and Width in inches
L = Approximate length in inches
A = %Bandwidth Multiplier
ALLEN
AVIONICS INC manufactures many other types of microwave Filters. Our
engineers will help you pick the right filter to meet all the
requirements you have for performance, size and cost. Our advanced
simulation and modeling software will design and do optimization of
Circular Post Coupled filters, MetalInsert Filters, Iris Coupled
Filters, Combline and Interdigital Filters. All of our Filters can be
custom designed for your application and we offer fast prototypes. No
need to wait five or six weeks to test your idea or check your system.
Allen Avionics Inc. started in 1960 And has 50 years
experience in design, Production, quality and they use it on every
product they make. Check out this web site for all their products. 
