Classic filter application example is receiver or catapult front, if pursue 1, the graph shows 2 times:

 

 

From the graph 1 in can see, filter applies extensively in the radio frequency in receiver, intermediate frequency and base band part. Although be opposite the development of this number technology, use digital filter to have replace base band share even the imitate filter of intermediate frequency part, but the filter of radio frequency part allows to cannot be replaced like that. Accordingly, filter is one of essential decisive components in radio frequency system.

 

The classification of filter has a lot of kinds of methods. For example:

 

The character that chooses by frequency can divide for: Low, connect high, belt, the filter that take block;

 

By implementation means can divide for: LC filter, surface acoustic wave / filter of superconduction of filter of body sound wave, helix filter, medium filter, housing filter, high temperature, planar structure filter.

 

Answer function to be able to divide by different frequency for: Function of Er of Chebyshev, broad sense Chebyshev, Batewosi, gauss, Bei Sai, elliptical function.

 

To different filter classification, basically be the different feature that from different filter character demand describes filter.

 

The numerous feature with the different filter that the place of method of this kind of numerous classification of filter describes, need thinks the to filter demand in centering body to reveal actual project to apply integratedly, when do a design that is to say to user demand, need considers user demand integratedly.

 

When filter chooses, should use what need to decide above all namely low, connect high, take the filter that connect or takes block.

 

What the characteristic classification that chooses by frequency introduces above all below is tall, low, belt and the frequency that takes block answers character and its action.

 

Husband belt connects Batewosiqiebixue filter

 

The husband connects Batewosiqiebixue high filter

 

The most commonly used filter is low connect with belt. Low connect the mirror in first detector part to restrain, the harmonic of frequency cause share is restrained etc have wide application. Belt in receiver front signal the stray after choice, catapult result is put is restrained, frequency source stray is restrained wait for a respect to be used extensively.

 

Filter applies extensively in system of microwave radio frequency, regard one function sex as the component, the electric function index that has its correspondence necessarily is used at describing a system to be opposite the performance demand of this component.

 

Correspondence uses an occasion differently, character of function of certain to filter electric equipment has diverse demand.

 

Describe index of technology of filter report function to have:

 

● rank is counted (progressional)

● absolutely bandwidth / opposite bandwidth

● ends frequency

● standing wave

Restrain outside ● belt

● ripple

● loss

● bandpass evenness is spent

● phasic degree of linearity

● is absolutely group when delay

● group Shi Yanbo is moved

● power capacity

● phasic consistency

● extent consistency

Limits of ● job temperature

 

Filter is faced below these electric function index make one by one explain.

 

Rank number (progressional) : Low to Gao Tonghe connect filter to tell, rank number is a several summation of the capacitance in filter, inductance. Will tell to taking a filter, rank number is the gross of shunt-wound resonator; Will tell to taking block filter, rank number is the gross of series connection resonator and shunt-wound resonator.

 

Absolutely bandwidth / opposite bandwidth: This index is used at taking a filter normally, token can adopt the signal frequency range of filter, reflect the frequency option of filter. Opposite bandwidth is the per cent of absolutely bandwidth and central frequency.

 

5 rank connect filter high

 

End frequency: End frequency follows with Yugaotong normally low connect filter. To low connect filter to end token filter is the most high-energy the frequency range that adopt; To connecting filter high, end the frequency range that lowest of frequency token filter can adopt.

 

Standing wave: Namely the S11 that arrowy net measures, express what filter port impedance and systematic place need impedance to match rate. Express to input signal how to many fail to enter filter and be answered to input end by reflection.

 

9 rank low connect filter to emulate a curve

 

Loss: Loss states signal passes energy of the losing after filter, namely the energy that filter wastes.

 

Bandpass evenness spends: Maximum of the loss inside filter bandpass limits and loss are the smallest the poor absolute value of the value. Token filter is distinguished to what the energy of different frequency signal uses up.

 

Restrain outside the belt: The “ attenuation ” beyond limits of filter bandpass frequency. The token filter choice to the frequency signal that does not need ability.

 

Ripple: The difference between the wave crest that curve of the S21 inside filter bandpass rises and fall and trough is worth.

 

Phasic degree of linearity: Inside limits of filter bandpass frequency phasic be worth with the phasic difference between a transmission line that waits with central frequency Shi Yanxiang. The chromatic dispersion of token filter is characteristic.

 

Absolutely group when delay: The signal inside filter bandpass limits transmits the time that uses to output port place from input port.

 

Group Shi Yanbo moves: Inside filter bandpass limits absolutely group when the difference that delays maximum and the least value. The chromatic dispersion of token filter is characteristic.

 

Power capacity: Of the bandpass signal that can input filter most high-power.

 

Phasic consistency: Same index is same the difference with the transmission phasic signal between different filter is worth batch. The difference between token batch filter (consistency) .

 

Extent consistency: Same index is same the difference of the transmission signal loss between different filter is worth batch. The difference between token batch filter (consistency) .

 

Phasic degree of linearity: Inside limits of filter bandpass frequency phasic be worth with the phasic difference between a transmission line that waits with central frequency Shi Yanxiang. The chromatic dispersion of token filter is characteristic.

 

Absolutely group when delay: The signal inside filter bandpass limits transmits the time that uses to output port place from input port.

 

Group Shi Yanbo moves: Inside filter bandpass limits absolutely group when the difference that delays maximum and the least value. The chromatic dispersion of token filter is characteristic.

 

Power capacity: Of the bandpass signal that can input filter most high-power.

 

Phasic consistency: Same index is same the difference with the transmission phasic signal between different filter is worth batch. The difference between token batch filter (consistency) .

 

Extent consistency: Same index is same the difference of the transmission signal loss between different filter is worth batch. The difference between token batch filter (consistency) .

 

LC filter

 

Surface acoustic wave / filter of body sound wave

 

Acoustical watch uses the means that is electric energy changeover exterior sound wave, use the filter wave that effect of sound wave resonance realizes. The characteristic of filter of this surface acoustic wave is bulk very small, q is worth opposite LC tall, use semiconductor technology to suit batch production. The filter bulk that a 800MHz controls has volume of a 0805 capacitance only probably. Its defect is power capacity small, do not suit small lot custom-built product, cycle of research and development is long, cost of research and development is high.

 

Sound expresses filter to apply in product of terminal consumption electron normally.

 

Helix filter

 

Helix filter:

 

Helix filter is the filter of total parameter of a kind of half collect, its use those who place the helix inductance inside cavity to realize resonator from resonance, the dimensional magnetic field that traverses photograph adjacent resonator realizes coupling.

 

Its advantage is: Bulk relatively housing is small, capacity of Q value, power relatively LC is tall. Its defect is: Realize a broadband harder, inductance of high frequency part comes true not easily.

 

Helix filter is used in 500MHz normally the following 20% opposite bandwidth, 100W average power, have the situation of particular demand to inserting caustic.

 

Medium filter

 

Ripple: The difference between the wave crest that curve of the S21 inside filter bandpass rises and fall and trough is worth.

 

Medium filter

 

Medium filter is the 1/4 accident line that introduces medium fill or the half collect total filter that line of 1/2 open a way realizes. Its advantage is Q value relatively LC is tall, can come true relatively the filter with LC filter tall frequency. Its defect is parasitism closer, resonator need is custom-built.

 

Pectination housing filter

 

Handing in the characteristic that shows filter is the biggest is to be able to realize a broadband, if use redundant and syntonic rod, considering machine adding can be linear, its are opposite bandwidth normally can wide amount to 60% . It is at the same time when K wave band, filter machine adds the pectination of the broadband to cannot be machined basically and debug bolt to cannot be placed, because this is below this condition,use normally hand in point to a structure. Hand in show structure and pectination look are closer than its parasitism bandpass, normally its parasitism bandpass is controlled in 1.8F0. Fall with bulk, hand in point to filter relatively size of pectination filter power is large.

 

Filter is the decisive component with wireless communication essential system.

 

Filter sort is various, all sorts of filter have different function characteristic, because this is when filter choice, use environment and ability of client performance demand actually what need to consider a client integratedly normally to make correct, effective, reliable choice.

 

When the client compares faintness to filter index concept, capacity of frequency of low-key of the need outside needing to ask client bulk, loss, band normally and curb system, power. According to these a few simple index asks to be able to judge a filter sort basically.