The filter is one of the important key components that are essential in the RF system, mainly for frequency selection --- to reflect unwanted interference frequencies in need of frequency signals.
The classic filter application example is the front end of the receiver or transmitter, as shown in Figure 1, Figure 2:
As can be seen from Figure 1, the filter is widely applied to radio frequency, intermediate frequency, and baseband portions in the receiver. Although the development of this digital technology is used to replace the analog filter of the baseband portion or even the intermediate frequency portion, the filter of the radio frequency portion is irreplaceable. Therefore, the filter is one of the essential critical components in the RF system.
There are many ways to classify the filter. For example:
The characteristics selected by frequency can be divided into: low pass, high pass, bandpass, band resistance filter, etc.
Implementation can be divided into: LC filter, acoustic surface wave / body acoustic filter, spiral filter, medium filter, cavity filter, high temperature hyperfunction filter, planar structural filter.
According to different frequency response functions, it can be divided into: Bibi Soff, broadly cut Bibi Snow, Badworth, Gauss, Bessel function, elliptic function, etc.
For different filter classifications, different characteristics of the filter are mainly described from different filter characteristics.
The filter is different, and the filter is different, and the concentration reflects that the demand for the filter is needed. That is to say, it is necessary to integrate the design of user needs. Consider user needs.
When the filter is selected, the first thing to determine is to use a low pass, a high pass, a band, or a filter.
Let's first introduce high-pass, low-pass, bandpass, and its role of high pass, low pass, bandpass, and its role in the frequency-selected feature classification.
Badworth Chippikv Belt Filter
Badworth Cutibi Water Pass Filter
The most commonly used filter is low-pass. The low pass in the mirror suppression of the mixer portion, the harmonic suppression of the frequency source portion is widely used. The band is widely used in the front end signal selection of the receiver, and the transmitter is widely used in pseudoquiries, frequency divergence suppression, etc.
The filter is widely used in the microwave radio frequency system. As a functional component, it is inevitably having its corresponding electrical energy index for describing the performance requirements of the system.
There are different requirements for certain electrical performance characteristics of the filters to different applications.
Describe the filter electrical performance technical indicators:
Step (level)
Absolute bandwidth / relative bandwidth
Cutoff frequency
Stand in wave
External inhibition
Ripple
Loss
Passband flatness
Phase linearity
Absolute group delay
Group time delay fluctuation
Power capacity
Phase consistency
Amplitude consistency
Working temperature range
The electrical energy indicators of the filter are explained one by one below.
Level (grade): For high-pass and low-pass filters, the order is the sum of the number of capacitors and inductors in the filter. For bandpass filters, the order is the total number of parallel resonators; for band-blocked filters, the order is the total number of series resonators and parallel resonators.
Absolute bandwidth / relative bandwidth: This indicator is typically used for bandpass filters, which characterizes the frequency selection of the filter by the signal frequency range of the filter. The relative bandwidth is the percentage of absolute bandwidth and center frequency.
Five-order high pass filter
Detection frequency: The cutoff frequency is typically used in Qualcomm and low pass filters. For the low-pass filter cut-off, the maximum frequency range of the eccentric filter; for the high pass filter, the cutoff frequency characterizes the frequency range that the filter can pass.
Resident wave: The S11 measured by the meaning of the JSI network indicates the degree of matching of the filter port impedance and the impedance of the system. Indicates how much input signal is not entered into the filter and is reflected back to the input.
Nine-order low-pass filter simulation curve
Loss: The loss indicates the energy loss of the signal after the filter is lost, that is, the energy consumed by the filter.
Passband flatness: absolute value of the difference in loss of maximum value and minimum loss in the filter passband range. The difference between the energy consumption of different frequency signals is characterized.
External suppression: "decrease" outside the frequency range of the filter. Characterization capabilities of the filter on unwanted frequency signals.
Waves: The difference between the peaks and the troughs from the Pallet and the Valley of the Filter.
Phase Linearity: The phase difference between the phase in the frequency range of the passband frequency range and the transmission line at the center frequency delay phase. Characterization of the dispersion characteristics of the filter.
Absolute group delay: The time used in the filter passband range from the input port to the output port.
Group of time delay fluctuations: the difference between the absolute group delay in the filter passband range and the minimum difference. Characterization of the dispersion characteristics of the filter.
Power capacity: The maximum power of the passband signal of the filter can be input.
Phase Consistency: The same indicator is the difference between the transmission signal between the different filters. The difference between batch filters (consistency).
Amplitude consistency: The same indicator is the difference between the transmission signal loss between different filters. The difference between batch filters (consistency).
Phase Linearity: The phase difference between the phase in the frequency range of the passband frequency range and the transmission line at the center frequency delay phase. Characterization of the dispersion characteristics of the filter.
Absolute group delay: The time used in the filter passband range from the input port to the output port.
Group of time delay fluctuations: the difference between the absolute group delay in the filter passband range and the minimum difference. Characterization of the dispersion characteristics of the filter.
Power capacity: The maximum power of the passband signal of the filter can be input.
Phase Consistency: The same indicator is the difference between the transmission signal between the different filters. The difference between batch filters (consistency).
Amplitude consistency: The same indicator is the difference between the transmission signal loss between different filters. The difference between batch filters (consistency).
LC filter
Acoustic surface wave / body acoustic filter filter
The sound is used to convert the electrical energy into a surface acoustic wave, and utilize the filtering of the sound wave resonance effect. The sound surface wave filter is characterized by very small volume, and the Q value is relatively LC high, and the semiconductor process is suitable for mass production. A filter volume of about 800 MHz is approximately one 0805 capacitance size. Its disadvantage is that the power capacity is small, not suitable for small batch custom products, long research and development cycle, high research and development cost.
The sound filter is usually applied in the terminal consumer electronics.
Spiral filter
Spiral filter:
The spiral filter is a semi-set filter filter that uses a self-resonument placed in a cavity to achieve a resonator, and coupling is achieved by a spatial magnetic field of adjacent resonators.
The advantage is that the volume is smaller than the cavity, the Q value, and the power capacity is higher than LC. The disadvantage is that it is difficult to achieve broadband, and high frequency part inductors is not easy to implement.
Spiral filters are typically used in an occasion of 20% relative bandwidth of 500 MHz or less, 100 W average power, and a certain requirement for insertion loss.
Medium filter
Waves: The difference between the peaks and the troughs from the Pallet and the Valley of the Filter.
Medium filter
The medium filter is a semi-integrated total filter implemented by a quarter-wave length route or one-half open route. The advantage is that the Q value is higher than LC, which can achieve a filter with high frequency of the LC filter. Its disadvantage is that parasitism is close, and the resonator needs to be customized.
Common cavity filter
The greatest feature of the integer filter is that the broadband can be achieved, and if the redundant resonant rod is used, it can be used in view of the machine to be used, and its relative bandwidth can usually be 60%. At the same time, when the K band is in the K band, the broadband comb filter machine is not allowed to process and the debug screw cannot be placed, and thus the integer structure is usually employed under this condition. The intersection structure is closer to the combined band, usually its parasitic passband is around 1.8F0. Under the same volume, the integer filter is large than the comb filter power capacity.
Filters are essential for wireless communication systems.
A wide variety of filters, various filters have different performance characteristics, so in the filter selection, it is often necessary to synthesize the actual use environment of customers and customer performance requirements to make correct, effective, and reliable selection.
When the customer is relatively blurred on the concept of filter indicators, it is often necessary to ask the customer volume, loss, and the frequency of suppression, and inhibitory degree, power capacity, and so on. According to these simple indicators, it can basically determine the type of filter.
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