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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 are shown Below.

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Change in frequency ((delta)Fo) caused by operating temperature changes ((delta)T) can be compensated for in the initial design. Integrated Microwave filters shift higher in frequency when exposed to cold temperatures and lower in frequency when exposed to hot temperatures. The following calculations are required to determine the hot and cold operating temperature extremes.

Temperature Coefficient (Tc):
Description Center Frequency TcPPM/°C
Standard lumped element <100 MHz 140
Standard lumped element >100 MHz 75
Stable lumped element <100 MHz 30
Ultrastable lumped element >100<=16000 MHz 10
Cavity (combline, interdigital) 500 - 26500 MHz 25
Stable cavity 500 - 26500 MHz 5
Ultrastable cavity 500 - 26500 MHz 1-2


Temperature ((delta)T) Calculation:
(delta)T (hot) = Hot Temp. Extreme - Ambient Temp.
(delta)T (cold) = Cold Temp. Extreme - Ambient Temp.

Equation:
(delta)Fo (hot) = (delta)T x Fo x Tc/10^6
(delta)Fo (cold) = (delta)T x Fo x Tc/10^6

After both (delta)Fo (hot) and (delta)Fo (cold) have been determined, the (delta)Fo (hot) is added to the lower-rejection frequency point (F3) and the upper-passband frequency point (F2). Likewise, the (delta)Fo (cold) is added to the upper-rejection frequency point (F4) and the lower-passband frequency point (F1) (refer to figure).

Example:
Required performance over operating temperature: -20ºC to +85ºC
Center Frequency: 750 Mhz
3 dB points: 700 MHz
800 MHz
40 dB points: 650 MHz
850 MHz
Calculations: (delta)T(hot) = +85-25 = +60ºC
  (delta)T(cold) = -20-25 = -45º
  (delta)Fo(hot) = +60x750x75/10^6 = +3.48 MHz
  (delta)Fo(cold) = -45x750x75/10^6 = -2.53 MHz
Specifications adjusted for temperature
Center Frequency: 750 MHz
3 dB points: 700 + (-2.53) = 697.47 MHz
800 + (+3.48) = 803.48 MHz
40 dB points: 650+(+3.48) = 653.48 MHz
  850 + (-2.53) = 847.47 MHz
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Standard

Integrated Microwave's standard filter designs are bandpass, lowpass, highpass and band reject in Chebyshev (various ripples) and Butterworth functions. 
 
Electrical      
Number Poles/Sections VSWR (NOM) 3 dB Bandwidth (% of Fo) Average Power Handling
BP (2-12) 1.5:1 1.5 to Multi-octave 1 Watt
HP-LP (2-12)      
BR (2-10)      

Environmental        
Hermeticity atm/cc/sec Gross Shock Vibration Humidity Temperature
1 x 103 50 G's 20 G's 100% -55º to +85º
  11 ms 0 - 500 Hz    
         

Special


If you have special electrical, mechanical, or environmental requirements, please call Integrated Microwave and take advantage of our free engineering design service.
Electrical        
Number Poles/Sections VSWR(NOM) 3 dB Bandwidth(% of Fo) Average Power Handling Matching Phase Group Delay Amplitude
BP (1-20) 1.1:1 0.2 to Multi-octave Consult Factory Phase +/-0.5º G/D +/-.5ns Amplitude +/-0.1 dB
HP-LP(1-20)        
BR(1-12)        

Environmental          
Hermeticity atm/cc/sec Gross Shock Vibration Humidity Temperature
Gross Fine 100 G's 1000 G's 100% -65º to +125º
1 x 10-5 1x10-7 20 ms 0 - 5000 Hz    
           


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Because of increased demand for linear phase (low-ringing and overshoot) filters, Integrated Microwave has developed computer synthesis and analysis models to provide Bessel, Gaussian, linear phase (equiripple error), transitional, and equalized filters.

Transitional filters provide a compromise between the conflict of steep-skirt selectivity and flat group delay. The VSWRs of these filters are not nearly as good as those obtainable with Chebyshev or Butterworth filters. When system requirements demand high selectivity and flat group delay, Integrated Microwave uses specialized delay section in conjunction with highly selective topologies such as Chebyshev, Butterworth, or elliptic (Cauer).

The following graph provides a relative comparison of amplitude and group delay characteristics for the most common filter functions.

Integrated Microwave designs and produces both lumped-element and distributed filters for the various transfer functions. We can provide designs to meet most linear phase or pulse-response requirements. Our solutions are not limited to "standard" designs but are customized to your requirements. Available bandwidths range from less than 1% of center frequency to 50% of center frequency.

Integrated Microwave filters can be phase matched, group delay matched, and amplitude matched in sets of two or more, or they can be matched to a "reference pair". A reference pair is two precision matched filters: one is kept by Integrated Microwave as the "tuning and test standard"; the other is kept by the customer as the "verification standard". Phase matching can be achieved over 3 dB passband if required; however, most applications can be met if matched over the 1 dB or 0.5 dB passband.

Get in touch with Integrated Microwave to discuss your specific requirements

Transfer Function Frequency Domain Characteristics Time Domain Characteristics
  Stopband Phase Group Delay Pulse Response
Chebyshev equal ripple flat steep poor poor very poor
Butterworth max. smooth moderate moderate moderate poor
Gaussian max. smooth weak very flat very flat very good
Gaussian (6 dB) smooth strong flat to moderate flat to moderate good to moderate
Gaussian (12 dB) smooth moderate flat flat good
Bessel max. smooth weak very flat very flat very good


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  Chebyshev
Input Pulse Output Pulse
Group Delay Phase

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  Butterworth
Input Pulse Output Pulse
Group Delay Phase

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  Bessel
Input Pulse Output Pulse
Group Delay Phase

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  Gaussian
Input Pulse Output Pulse
Group Delay Phase

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  Gaussian 12db
Input Pulse Output Pulse
Group Delay Phase

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  Gaussian 6db,
Input Pulse Output Pulse
Group Delay Phase

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Integrated Microwave's Product Description Number is used to concisely define the basic electrical and mechanical requirements of your filter.

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I. CASE STYLES

CASE STYLE CODE

A2 Axial (RF = pins, MTG = screws)

A3 Axial (RF = pins with removable SMAs)

A4 Axial (RF = connectors, MTG = screws)

A5 Axial (RF = pins, axial grounding)

A6 Axial - special (specify)

R2 Radial (RF = pins, MTG = screws)

R4 Radial (RF = pins, MTG = pins)

R6 Radial (RF = pins, MTG = studs)

RS Radial - special (specify)

AR Axial/radial - special (specify)

SP Special (specify)

SM Surface mount

T5 To-5 PC mount

T8 TO-8 PC mount


II. INPUT AND OUTPUT CONNECTORS

CONNECTOR CODE

A Solder Pin (.018" dia.+/-.003") (.46 mm dia. +/-.08 mm)

B Solder Pin (.037" dia.+/-.003") (.94 mm dia. +/-.08 mm)

H Solder Pin - special (specify data)

C SMA (female)

D SMA (male)

E Coax (.047 semirigid)

F Coax (.085 semirigid)

G Coax - special (specify)

K SMB (female)

L SMB (male)

M TNC (female)

N TNC (male)

O Type-N (female)

P Type-N (male)

Q BNC (female)

R BNC (male)


III. MOUNTING

MOUNTING CODE (INCHES)

P1 Ground pin (.018" dia.+/-.003")

P2 Ground pin (.037" dia.+/-.003")

P3 Ground pin - special (specify dia.)

T1 0-80 Tapped, UNF-2B

T2 2-56 Tapped, UNC-2B

T3 4-40 Tapped, UNC-2B

T4 6-32, Tapped UNC-2B

T5 Tapped - special (specify)

T6 Clearance .067" dia. (0-80)

T7 Clearance .093" dia. (2-56)

T8 Clearance .120" dia. (4-40)

T9 Clearance .144" dia. (6-32)

T10 Clearance-special (specify inches)

T11 Stud 0-80, UNF-2A

T12 Stud 2-56, UNC-2A

T13 Stud 4-40, UNC-2A

T14 Stud 6-32, UNC-2A

T15 Stud - special (specify)

T16 Clearance w/recess .067" dia. (0-80)*

T17 Clearance w/recess .093" dia. (2-56)*

T18 Clearance w/recess .120" dia. (4-40)*

T19 Clearance w/recess .133" dia. (6-32)*

T20 None (RF pins only)


MOUNTING CODE (METRIC)

T70 M1.6-.35-6H Tapped

T71 M2-.40-6H Tapped

T72 M3-.50-6H Tapped

T73 M4-.70-6H Tapped

T74 Tapped - special (specify)

T75 Clearance 1.85 mm dia. (M1.6-.35)

T76 Clearance 2.3 mm dia. (M2-.40)

T77 Clearance 3.5 mm dia. (M3-.5)

T78 Clearance 4.5 mm dia. (M4-.70)

T79 Clearance - special (specify mm)

T80 Stud M1.6 -.35-6H

T81 Stud M2-.40-6H

T82 Stud M3-.50-6H

T83 Stud M4-.70-6H

T84 Stud - special (specify)

T85 Clearance w/recess 1.85 mm dia. (M1.6-.35)*

T86 Clearance w/recess 2.3 mm dia. (M2-.40)*

T87 Clearance w/recess 3.5 mm dia. (M3-.50)*

T88 Clearance w/recess 4.5 mm dia. (M4-.70)*

T89 Clearance w/recess - special (specify)


IV. FINISH

FINISH CODE MIL-STD

N1 Nickel QQ-N-290

G1 Gold MIL-G-45204

S1 Silver QQ-3-365

P1 Paint FED-STD-595, Color #26595

N2 Nickel - special (specify)

G2 Gold - special (specify)

S2 Silver - special (specify)

P2 Paint - special (specify)

X2 Other - special finish (specify) <p>

 
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Each Integrated Microwave filter will either be packaged in conformance to your specification or will be packaged in the smallest configuration consistent with high performance, high quality, and low cost. These drawings are not to scale and do not represent relative sizes.


 

Case style A2 - Axial
RF in/out: .018" dia. pins
Mounting: 0-80 UNF 


Length		Width		Height

0.57		0.35		0.15

0.75		0.40		0.20

1.00		0.50		0.25

1.20				0.30

1.50				0.35

2.00	         	    	0.40

				0.50

Case Style A3 - Axial
RF in/out: .018" dia. pins
with field replaceable
SMA- Female 

Length		Width		Height

0.75		0.50		0.25

1.00		0.65		0.30

1.25				0.35

1.50				0.40

2.00				0.50

Case Style A4 - Axial
RF in/out: SMA - Female
Mounting: 0-80 UNF 

Length		Width		Height

0.75		0.375		0.375

1.00		0.400		0.400

1.25		0.500		0.500

1.50				

2.00

Case Style A5 - Axial
RF in/out: .018" dia. pins
Mounting: .020" dia. pins 

Length		Width		Height

0.57		0.30		0.15

0.75		0.40		0.20

1.00		0.50		0.25

1.25				0.30

1.50				0.35

2.00				0.40

				0.50

Case Style A6 -Axial
RF in/out: SMA - Female offset
Mounting: 0-80 UNF 

Length		Width		Height

0.75		0.35		0.375

1.00		0.40		0.400

1.25		0.50		0.500

1.50				

2.00

Case Style R2 - Radial
RF in/out: .018" dia. pins
Mounting: 0-80 UNF 

Length		Width		Height

0.57		0.35		0.20

0.75		0.40		0.25

1.00		0.50		0.30

1.25				0.35

1.50				0.40

2.00				0.50

Case Style R4 - Radial
RF in/out: .018" dia. pins
Mounting: 0.038" dia. pins 

Length		Width		Height

0.57		0.30		0.15

0.75		0.40		0.20

1.00		0.50		0.25

1.25				0.30

1.50				0.35

2.00				0.40

				0.50

Case Style R6 - Radial
RF in/out: .018" dia. pins
Mounting: 2-56 UNF

Note: Ground pins optional



Length		Width		Height

0.75		0.35		0.25

1.00		0.40		0.30

1.25		0.50		0.35

1.50				0.40

2.00				0.50

Note: Lengths > 1.25 2 studs available.


Case Style T5 - Radial TO-5
RF in/out: .018" dia. pins
Mounting: .020" dia. pins 

Height

0.15

0.20

0.25

0.30

0.35

0.40

0.50

Case Style T8 - Radial TO-8
RF in/out: .018" dia. pins
Mounting: .020" dia. pins 

Height

0.15

0.20

0.25

0.30

0.35

0.40

0.50

Case Style S1 - Surface Mount
RF in/out: .017" dia. pins
Ground pins: .017" dia. pins
Mounting: Lugs, screw 

Height

0.15

0.20

0.25

0.30

0.35

0.40

0.50

Case Style S2 - Surface Mount
RF in/out: .017" dia. pins
Ground pins: .017" dia. pins
Mounting: Lugs, screw 

Length		Width		Height

0.75		0.35		0.15

1.00		0.40		0.20

1.25		0.50		0.25

1.50				0.30

2.00				0.35

				0.40

				0.50


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Absolute attenuation (Dba): 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).

Attenuation: Power loss in dB evidenced by a signal passing through a dissipative network (bandpass filter).

Bandpass filter: A filter that passes one band of frequencies and rejects both higher and lower frequencies.

Bandreject filter: A filter that rejects one band of frequencies and passes both higher and lower frequencies. Commonly referred to as a notch filter.

Bandwidth: The width of the passband of a bandpass filter. Typically the frequency difference between the lower (F1) and the 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 point F1 and F2.
In linear phase (constant delay) bandpass filters the center frequency is arithmetically related to the 3 dB points F1 and F2.


Chebyshev function: A mathematical function that produces a filter response 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. Chebyshev function filters are designed to exhibit certain ripple response with the passband (.01 dB ripple, .05 dB ripple, etc.).

Crossover frequency: The frequency at which two adjacent channels (the upper frequency of the lower channel and the lower frequency of the upper channel) are of equal amplitude

Crossover loss: The loss that occurs at the crossover frequency.

Cut-off frequency (Fco): The upper passband edge in lowpass filters, the lower passband edge in highpass filters, of the passband edge closest to the stopband.

Decibel (dB): A unit used to express the logarithm of the ratio between two amounts of power, P1 and P2. By definition:


Delay: See Envelope delay.

Diplexer: A two-channel multiplexer of bandpass/bandspass 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 of signals that produces undesirable 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.

Elliptic function: A mathematical function used to yield the squarest possible amplitude filter response with a given number of circuit elements. The elliptic function has a Chebyshev 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.

Envelope delay: The propagation time delay of the envelope of an amplitude-modulated 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


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 where L is the total series inductance in Henrys and C is the total shunt capacity in farads. Characteristic impedance is measured in ohms.

Impulse: A pulse whose width is of such short duration that it may be regarded as infinitesimal; a spike.

Isolation: For a switch filter bank, typically the amount of attenuation between the switched filter's "On" channel and the "Off" channel(s).

Linear phase filter: A general term that defines a class of filters that exhibits a constant change in phase 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.

Load impedance: The specified impedance that normally must be connected to the output connections of the filter in order to meet filter specifications.

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 stopband (no comebacks). Properly designed lumped-element filters can exhibit monotonic response of two to three octaves from center frequency.

Multiplexer: A frequency-selective network 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 its 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: Variation in attenuation vs. frequency within the passband of the filter.

Phase shift: The insertion phase of a filter, a function of frequency which increases as frequency increases.

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 capacitor 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.

Relative attenuation (dBc): Attenuation measured with the point of minimum attenuation taken as the reference, or zero dB.

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 output signal as a result of an input step function, pulse, impulse, or ramp.

Ripple: Refers to the wavelike variations in the amplitude response of a filter usually measured in dB. Chebyshev and elliptic function filters ideally have equal-ripple characteristic; i.e., differences in peaks and valleys of the amplitude response in the passband are always the same. Butterworth, Gaussian, and Bessel function filters have no ripple.

Rise time: The length of time, on the initial 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.

Settling 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 (Sf): A useful way of specifying filters:


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 between the input signal reaching 50% of its steady state and the output reaching 90% of its RF envelope.

Time or group delay: See Envelope delay.

Transient response: The filter's response in the time domain to an input signal.

Transitional filter: A filter that compromises between high-skirt selectivity and flat, passband group delay.

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