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Circular Post-Iris Coupled
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Waveguide Bandpass Filters
ALLEN AVIONICS ROUND POST-IRIS COUPLED Waveguide Filters are available over the 1.12 to 26.50 GHz frequency band.(WR-650 to WR-42) In the CPWB Series Bandwidths may be as small as 0.3% to as large as 7% of the center frequency. These filters are available with 4 to 12 "high Q" resonant sections. Allen Avionics Waveguide Filters are normally constructed using rectangular Brass Waveguide but Copper, Aluminum and Invar are also available. All Waveguide filters are available with additional options like cover flanges, choke flanges or with coaxial transitions to SMA and other connectors.
Available Frequency 1.12 GHz – 26.5 GHz
Available Bandwidth 0.3% Up to 7%
Insertion Loss (Depends on the number of sections and BW)
Stop Band Attenuation see graphs
Number of Resonator Sections Available 4 to 12
VSWR 1.50:1
Standard W/G Sizes WR650 to WR42
Dimensions See drawings below.
Consult Factory for exact dimensions.


2.4 mm FEMALE 24F
2.4 mm MALE 24M
The curve to the left displays the Relative Attenuation as a function of the Normalized 3dB Bandwidth for medium bandwidth filters.(3.0%) The graphs supplied are designed to give an approximation of the frequency response for the CPWB series of Waveguide 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 (0.3%) and wide bandwidths (7.0%) 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) 248-8080 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 .3% 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 8 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 10 MHz (FC) and we are thinking about using 6 sections. We need to find the minimum attenuation at 2.460GHz and 2.540GHz for 6 sections.

Using the same formula above we first find the %Bw to determine the correct graph to use. In this problem the the %BW equals 0.4% so we can use the 0.3%bw graph again. Then from the second formula we used in the first example we find that we have four (4) 3dB bandwidths on each side.

Checking the above graph we can see with 6 sections we will have greater than 50dB attenuation at both 2.460GHz and 2.540GHz for a filter with 10MHz 3dB bandwidth.

Three plots are provided, 0.3%, 3.0% and 7.0% so the approximate response can be  determined for any bandwidth in the range of .0.3% to 7.0%

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

Allen Avionics has advanced simulation and modeling software that our experienced Microwave engineers use in the design and manufacturing of Circular Post Coupled Wave Guide Bandpass Filters.

This software combined with our Numerical Control Machining Center gives us rapid design and production capabilities. 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. All our Microwave products are manufactured in the USA using only American made material.

WR U.S. Mil.
__ /U
Width (a)
WR650 RG69 (b)
RG103 (a)
1.12-1.70 6.500
WR510   1.45-2.20 5.100
WR430 RG104 (b)
RG105 (a)
1.70-2.60 4.300
WR340  RG112 (b)
RG113 (a)
2.20-3.30 3.400
WR284 RG48 (b)
RG75 (a)
2.60-3.95 2.840
WR229 RG340 (c)
RG341 (a)
3.30-4.90 2.290
WR187 RG49 (b)
RG95 (a)
3.95-5.85 1.872
WR159 RG343 (c)
RG344 (a)
4.90-7.05 1.590
WR137 RG50 (b)
RG106 (a)
5.850-8.200 1.372
WR112 RG51 (b)
RG68 (a)
7.050-10.000 1.122
WR90 RG52 (b)
RG67 (a)
8.20-12.40 0.900
WR75 RG346 (c)
RG347 (a)
10.0-15.0 0.750
WR62  RG91 (b)
RG349 (a)
12.40-18.00  0.622
WR51 RG352 (c)
RG351 (a)
15.00-22.00 0.510
WR42 RG53 (b)
RG121 (a)
18.00-26.5 0.420
Code Description
1 Series
2 Number of Sections
3 Center Frequency (GHz)
4 3 dB Bandwidth (MHz)

Connector Code(Input/Output) (see chart)

6 WR Waveguide number

1 2 3 4 5 6
CPWB/ 5/ 20.25/ 101.25/ CPR/CPR/ 42

COMPLETE Part Number=
CPWB / 5 /20.25/ 101.25 / CPR / CPR / 42

Contact Factory With Your Specific Needs For:
-Electrical Performance
-Mechanical Configuration
-Insertion Loss


When bandwidths exceed the 7.0% limit for this filter type or when insertion loss, length rejection required or some other parameter cannot be met, Allen Avionics has many other Filter constructions available which could be used to solve the problem. Contact our sales department for assistance. (516) 248-8080 or sales@allenavionics.com


The number of sections and the Waveguide size are the basic parameters that determine the overall length of Round Post-Iris coupled Microwave Filters.

Using some basic formulas and the wave guide width from the table above you can calculate the approximate length for a given Waveguide and number of sections.

From EXAMPLE #1. We had a Bandpass filter centered at 10 GHz with 1.0% BW. From the table above we see WR90 is the best wave guide size for 10GHz. From the same table we see the width of WR90 is 0.90 inches. Our previous calculations done for example #1 Indicated that we needed 8 sections to meet the required attenuation. With the number of sections, % BW and Waveguide width we now we have all the information we need to calculate the approximate length.

N = number of sections.
a = width of Waveguide in inches
L = Approximate length in inches

For bandwidths 0.3 to 3.0%
L = For 4-8 sections. L= (0.75 x N + 1) a
L = For 9-12 sections. L= (N + 1.0) a

For bandwidths > 3.0% to 7%

L = For 4-8 sections. L= (0.75 x N + 0.667) a
L = For 9-12 sections. L= (0.80 x N + 1.0) a

So for example #1
we have L= (0.75 x 8 + 1) .9 = 6.3 inches

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, Metal-Insert 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.

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Allen Avionics, Inc.
2727 Clinton Street
River Grove, IL  60171
Phone: (708)-453-3238
Fax: (708)-453-0297
E-Mail: Sales@AllenAvionics.com

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