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Sichuan Keenlion Microwave Technology——Filters

Sichuan Keenlion Microwave Technology——Filters

Sichuan Keenlion Microwave Technology Founded in 2004, Sichuan Keenlion Mircrowave techenology CO., Ltd. is the leading manufacturer of the Passive Mircrowave components in Sichuan Chengdu, China.

We provide high-performance mirrowave components and related services for microwave applications at home and abroad. The products are cost-effective, including various power divider, directional couplers, filters, combiners, duplexers, customized passive components, isolators and circulators. Our products are specially designed for various extreme environments and temperatures. Specifications can be formulated according to customer requirements and are applicable to all standard and popular frequency bands with various bandwidths from DC to 50GHz.


The filter can effectively filter out the frequency of a specific frequency in the power cord or the frequency other than the frequency point, obtain a power source signal of a particular frequency, or eliminates a specific frequency power signal.



The filter is a selection device that allows the specific frequency component in the signal to be passed, and other frequency components are greatly attenuated. This selection effect using the filter can be filtered out of the interference noise or perform spectrum analysis. In other words, it is called a filter that can cause a particular frequency component in the signal to pass, and greatly attenuated or suppress other frequency components. The filter is a device that is filtered by the wave. “Wave” is a very broad physical concept, in the field of electronic technology, “wave” is narrowly limited to the process of extracting the value of various physical quantities over time. The process is converted into a time function of a voltage or current through a variety of physical quantities, or signals. Since the self-variable time is a continuous value, it is called a continuous time signal, and it is conventionally referred to as an analog signal.

Filtering is an important concept in signal processing, and the function of filtering circuit in DC voltage regulator is to minimize the AC component in the DC voltage as possible, retain its DC ingredient, so that the output voltage ripple coefficient is lowered, the waveform becomes Smooth.

The main parameters:

Center frequency: Frequency f0 of the filter passband, generally take f0 = (f1 + f2) / 2, f1, f2 as a band pass or band resistance filter left, right opposite to 1 dB or 3DB edge frequency point. The narrowband filter often calculates the passband bandwidth with the smallest point of the insertion loss.

Deadline: Refers to the path to the path of the passband of the low pass filter and the pass band of the high pass filter. It is usually defined in a relative loss point of 1 dB or 3DB. The reference reference reference relative loss is: the low pass is based on the DC insertion, and the Qualcomm is based on the sufficient high-pass frequency of the parasitic strip.

Passband bandwidth: refers to the spectrum width required to pass, BW = (F2-F1). F1, F2 is based on the insertion loss at the center frequency F0.

Insertion loss: Due to the introduction of the filter to the atmosphere of the original signal in the circuit, the losses in the center or cutoff frequency, such as required to have the whole band loss to emphasize.

Ripple: Refers to the 1DB or 3DB bandwidth (cutoff frequency) range, the insert loss fluctuates the peak of the frequency on the loss mean curve.

Internal fluctuations: Insertion loss in the through band with frequency variations. The band fluctuation in the 1db bandwidth is 1db.

In-band standby: Measure whether the signal in the passband in the filter is good to match the transmission of the transmission. Ideal Match VSWR = 1: 1, VSWR is greater than 1 when mismatch. For an actual filter, the bandwidth satisfying the VSWR is less than 1.5: 1 is generally less than BW3DB, which accounts for the proportion of BW3DB and the filter order and insert loss.

Roop loss: The number of decibels (DB) ratios of port signal input power and reflected power is equal to 20 Log 10ρ, ρ is a voltage reflection coefficient. The return loss is infinite when the input power is absorbed by the port.

Reproduction of the strip suppression: an important indicator of the quality of the filter selection performance. The higher the indicator, the better the external interference signal suppression. There are usually two kinds of proposal: a method for suppressing how much DB inhibition of a given band crossing frequency fs, the calculation method is FS decrease; another indicator for the propose of the symbol filter threading and ideal rectangle approach – Rectangular coefficient (KXDB is greater than 1), KXDB = BWXDB / BW3DB, (X can be 40dB, 30dB, 20DB, etc.). The more rectangular rectangles, the higher the rectangularity – that is, the closer to the ideal value 1, and the difficulty of making the production is of course larger.

Delay: The signal refers to the time required for the signal to transmit the phase function diagonal frequency, that is, TD = DF / DV.

In-band phase linearity: This indicator characterization filter is the phase distortion of the transmitted signal in the passband. The filter designed by the linear phase response function has good phase linearity.

Main classification

Divided into an analog filter and a digital filter according to the signal being processed.

The passage of the passage of the passive filter is divided into low pass, high pass, bandpass, and all-pass filter.

Low pass filter: it allows low-frequency or DC components in the signal to be passed, suppress high frequency components or interference and noise;

High-pass filter: it allows high frequency components in the signal to be passed, suppress low frequency or DC components;

Band Pass Filter: It allows signals to be passed, suppressed signals, interference, and noise below or above the band;

Beltable filter: It suppresses signals within a certain frequency band allow signals other than the band, also known as a notch filter.

All-pass filter: The full-pass filter means that the amplitude of the signal will not change within the full range, that is, the amplitude gain of the full range is equal to 1. General all-pass filters are used to phase phase, that is, the phase of the input signal changes, and the ideal is that the phase shift is proportional to the frequency, which is equivalent to a time delay system.

Both the components used are both passive and active filters.

Depending on the placement of the filter, it is generally divided into a plate filter and a panel filter.

On the board, install on a board, such as a PLB, a JLB series filter. The advantages of this filter are economical, and the disadvantage is that high frequency filtering is not good. Its main reason is:

1. There is no isolation between the input and output of the filter, which is prone to coupling;

2, the grounding impedance of the filter is not very low, weakened the high frequency bypass effect;

3, a piece of connection between the filter and the chassis will generate two adverse effects: one is the electromagnetic interference of the internal space of the chassis, which is directly induced to this line, along the cable, and radiate the filter by means of cable radiation. Failure; the other is that the external interference is filtered by the filter filter on the board, or the radiation is generated directly or directly to the circuit on the circuit board, resulting in sensitivity problems;

Filter array plates, filter connectors and other panel filters are generally mounted on the metal panel of the shielding chassis. Since it is directly installed on the metal panel, the input and output of the filter are completely isolated, the ground is well grounded, and the interference on the cable is filtered over the chassis port, so the filtering effect is quite ideal.

Passive filter

The passive filter is a filter circuit that utilizes a resistor, a reactor, and a capacitor component. When the resonant frequency, the circuit impedance value is minimal, and the circuit impedance is large, the circuit component value is adjusted to a feature harmonic frequency, and the harmonic current can be filtered out; when several harmonic frequenses The tuning circuit is composed, then the corresponding feature harmonic frequency can be filtered, and filtering the main number harmonic (3, 5, 7) is achieved by low impedance bypass. The main principle is for different number of harmonics, designing the harmonic frequency is small, achieving the splitting effect of the harmonic current, providing a bypass passage for prefiltered high harmonics to achieve purification waveform.

Passive filters can be divided into capacitive filters, power plant filter circuits, L-RC filter circuits, π-shaped RC filter circuits, multi-section RC filter circuits, and π-shaped LC filtering circuits. Press to function into a single tuning filter, dual tuning filter, and high pass filter. The passive filter has the following advantages: the structure is simple, the investment cost is low, and the reactive component in the system can compensate for the power factor in the system. It improves the power factor of the grid; the working stability is high, the maintenance is simple, the technical maturation, etc. It is widely used. There are many aspects of the shortcomings of passive filters: the impact of the power grid parameters, the system impedance value and the main number of resonant frequencies often change as the working conditions; the harmonic filter is narrow, only the main number of main times can only be filtered out Harmonics, or due to parallel residues, amplifying harmonics; coordination between filtering and reactive compensation and pressure regulating; as the current flowing through the filter, it may cause an overload operation of the equipment; The consumables are much larger, the weight and volume are large; the operational stability is poor. Therefore, an active filter with better performance is more and more applications.

Post time: Feb-09-2022