Chosen eight major knacks of RF and microwave filter
If has not considered the electric-wave filter type and primitive of the lowest technological specification requirement, may cause the products and be unable to pass " Test " ,The products would be restarted designing again, caused costly production to postpone finally. On the other hand, understand how to confirm the filter parameter accurately, will contribute to production standard and function that make the products produced meet the customer. In fact, while this kind of knowledge contributes to improving the chance of success of the products on the market, control the operating cost.
Begin with foundation
In nowadays wireless field, the competition of the fierce expansion bandwidth forces people to pay close attention to the characteristic of the electric-wave filter further. If confirm the filter parameter inaccurately, will cause the frequency conflict finally, make, design group deal with cross talk, disconnecting, the intersection of data and lose and the intersection of network link and interrupted problem again conversely.
The electric-wave filter defines part of the reason why the incomplete or this inaccurate question produces is that the electronic market is very keen on the digitale Elektronik at present. According to the statistics of some, 80%- 90% of the new electronic design engineers are all software and the the figure one. The knowledge gap lies in this, because no matter transmissive information is a digital form, when information is through the radio or microwave transmission, the carrier signal is always in accordance with the physical law of electro magnetics.
Fortunately, review some important foundations of the electric-wave filter performance parameter fast, can help engineers to find out and satisfy the electric-wave filter of particular application correctly. At the beginning it chosen correct,can save time and money,while ordering these essential components can guarantee good and cheap.
1.Understand basic response curve
The basic response curve of the electric-wave filter includes: Band pass, low-pass, high pass, band elimination, duplexer. Every particular shape has determined what frequency can be passed, which can't pass.
Undoubtedly, the most common one is the band-pass filter in this a series of. All engineers know, the band-pass filter is allowed the signals of two pieces of particular frequency to pass, inhibit the signal of other frequency. Such as the surface acoustic wave filter (SAW) , crystal filter, pottery and housing electric-wave filter. For reference, the coverage of frequency of housing band-pass filter which Anatech Electronics Company makes is 15 MHz- 20 GHz, the bandwidth is in 1%- 100% of the ranges. The table below provides all technical parameters of the lumped element band-pass filter of Anatech Electronics Company. All manufacturers have adopted some methods to define pass-band of decaying with both sides 0.5 dB, 1 dB or 3 dB of center frequency of the electric-wave filter.
2. Include all essential technical parameters
Often presenting this situation, engineer provides one and needs " a 100 MHz band-pass filter " Brief requirement,this requirement is getting less too in information volume obviously. It is really difficult for the electric-wave filter supplier to follow some information in this way to sign a bill.
Provide all essential information and provide all frequency parameters to begin in detail, for instance:
Center frequency (Fo) : Usually define as the band-pass filter ' Or band elimination filter) Two middle point between order 3 dB,so so show with arithmetic mean that two 3 dBs click.
Alpha cut frequency (Fc) : Low-pass filter or high-pass filter coherent to take switch point that stopband begins to, generally 3 dB is clicked on this switch point.
Blanketing frequency: Some particular values or particular frequency or frequency group of the set of the value of signal attenuation. Define the frequency district not including the ideal band pass as the blanketing frequency or frequency group sometimes, the decay undergone is called inhibiting.
The electric-wave filter type has determined the particular frequency. To band pass and band elimination filter, the particular frequency is the center frequency. To the low-pass and high-pass filter, the particular frequency is the alpha cut frequency.
For being intact, the engineer should also define the following characteristics, for instance:
Stopband: Frequency band between the not transmissive particular frequency value of the electric-wave filters.
Isolate: In the duplexer, consider receiving (Rx) Passway in order to inhibit transmitting (Tx) hour The ability of the frequency, consider transmitting (Tx) In order to inhibit receiving (Rx) at the time of the frequency The ability of the frequency, is called Rx/Tx to isolate. Isolation high, electric-wave filter can isolate the intersection of Rx and signal and the intersection of Tx and signal the stronger ability, vice versa. Its result is transmitted and received signal is all cleaner.
Insertion loss (IL) : Represent a value of power consumption in the device, IL =10Log(Pl/Pin) ,Have nothing to do with the frequency, among them Pl is the load power, Pin is the power input from the generator.
Echo return loss (RL) : It is a kind of measurement of the electric-wave filter characteristic, show the electric-wave filter is input and output impedence is close to the intensity of the ideal impedance value. Echo return loss is defined as: RL =10Log(Pr/Pin) ,Have nothing to do with the frequency, among them Pr is the power of the generator of the reflect back to.
Envelope delay (GD) : Linear magnitude of phase place of delay representation device of the cluster. Because phase delay appears on the Ausgang of the electric-wave filter, is it very important for linearity with the change of the frequency to understand this kind of phase shift. If phase shift is with the nonlinear variational of the frequency, distortion will take place in the output waveform. Envelope delay is defined as the derivative that phase shift varies with frequency. Because the derivative of the linear function is a constant, the envelope delay that the linear phase shift causes is a constant.
Shape factor (SF) : The shape factor of the electric-wave filter is usually in order to hinder the bandwidth (BW) The ratio of to 3 dB bandwidth. One kind that it is the marginal precipitous intensity of an electric-wave filter is measured. For example, if 40 dB bandwidth is 40 MHz, 3 dB bandwidth 10 MHz, then the shape factor is 40/10 =4.
Impedance: In units of ohm electric-wave filter source impedance ( Input) And terminate impedance ' Export) . Generally speaking, input impedance is the same as output impedence.
Relative attenuation: The minimum measured decays in some places and decays and inhibits the damped difference that is clicked ideally. Usually, relative attenuation regards dBc as the unit representation.
Ripple (Ar) : Represent the magnitude of the electric-wave filter pass-band flatness, generally represent with decibel. The magnitude of the ripple of the electric-wave filter influences echo return loss. The greater the ripple is, then the more serious echo return loss is, vice versa.
Inhibit: The same.