Filters play a very useful role in different aspects of electronics. One important area is the RF or radio frequency domain. These RF filters are useful in accepting or removing signals which fall in some certain radio spectrum areas.
They are useful in different instances. Its application list is nearly infinite. Most times, they are used inside the radio receivers so as to offer selectivity coupled with enabling proper frequencies to enter into the set’s latter parts. Also, they are useful in transmitters to make sure that spurious or unwanted mixers get passed to the following stages. This list continues.
What are RF Interference Filters?
Radio-frequency interference or RFI filters can be described as a circuit or electrical device which mitigates the high-frequency electromagnetic noise that is present on signal and power lines. This high-frequency noise can be generated by different electronic and electrical devices like inverters, power supplies, electronic devices, appliances, microprocessors, clock circuits, etc.
The noise usually falls within the frequency range of 9 KHz and 10 GHz and it could prevent or degrade the transmission of signals and/or electronic/electrical equipment’s performance. Furthermore, the quality of power can be affected by the EM noise’ low-frequency components.
Furthermore, an industrial EMI filter offers low impedance lath to a high-frequency noise. It also reduces it by grounding or canceling its neutral components or line. The EMI/RFI filter effectiveness measures as an insertion loss. EMI filters that are very appropriate for electromagnetic noise fall within a frequency range of 9 KHz and 30 MHz that is conducted via the wires.
Frequencies higher than 30 MHz are radiated requiring shielding as well as output/input isolation. For any radiated frequency, its filter mounting is usually more critical compared to its performance of insertion loss.
You can use the EMI filters widely in applications like Computers, Energy Management Systems, Aerospace/Military subsystems and systems, equipment for factory automation, exercise equipment, MRI rooms, shielded rooms/test chambers, automotive battery charger, medical imaging/patient/diagnostic devices and others.
What are the Types of RF Filters?
Filters come in four main types. Each of the types accepts or rejects signals in different ways. When you make use of the right RF filter, you can accept these signals and then reject the undesired ones. Below are the four main types.
Low pass filters
From the name, rf low pass filters are filters that can only allow lower frequencies through. Typically, it stays nominally flat till the point of cut-off and then rolls off.
The roll off’s actual rate is mainly dependent on what is referred to as the filter’s order. The low pass filter has a very simple principle. It makes use of the principle that a capacitor passes high frequency in order to block any low frequency, while the inductor will pass through low frequency in order to block any high frequency.
For any high frequency which has to be cut off, make use of the capacitor for absorbing the inductance as well as prevent its passing. Also, for any low frequency requiring release, the rf low pass filter makes use of the capacitor’s high resistance characteristics and the inductance’s low resistance to allow it to pass.
High pass filters
In so many ways, they are the inverse of low pass filters. It allows only signals which are higher compared to the cut-off frequencies. Asides from this point, it comes nominally flat and less that the cut off frequency of the RF filter, the response will fall away at a specific rate, which is determined by the filter’s order.
The high pass filter’s features are expressed by first order linear differential equations. Its left side is similar to the 1st order low pass filters. Just the right side is the excitation source’s derivative rather than the source of the excitation itself.
RF Bandpass filters
Rf bandpass filters allow only through signals in specific frequencies. Below and above the cut-off frequency, the signals have to be attenuated as well as within the radio frequency’s accepted band, signals will pass through it.
Band Reject Filters
This opposes the band pass filters because it rejects the signals in a specific radio frequency band. The RF filter form is usually used for removing unwanted signals, which are known to be present in the system.
Classification of RF Filters
The ideal filters whether high pass, band pass or low pass filter would exhibit no loss in the pass band, which is the frequency that is below the usual cut-off frequency. When it is above the frequency which is called stop band, these filters could reject the signals.
Frankly speaking, achieving a perfect pass filter isn’t possible and the pass band usually has some loss within it. Also, achieving an infinite rejection in stop bands isn’t possible. Also between the stop and pass bands, a transition exists, whereby a response curve will fall away, and the rejection level rises as frequency moves from its ass bands into the stop bands.
Filter Technology
One important indicator of the radio frequency filter includes insertion loss and quality factor. In the present communication protocol, differences in frequency between the different bands of frequency are becoming smaller. This is why it requires good selectivity to allow the passband’s signals to pass and then block those signals outside of the passband.
When the Q is larger, the filter’s passband bandwidth will be narrower and then you can achieve better selectivity. Aside from the quality factor, another important parameter is the insertion loss. This deals with the passband signal’s attenuation by the filter, which is loss of the signal power.
Presently, one of the major mainstream methods of implementing the RF filters is BAW and SAW. The rf SAW filter refers to surface acoustic RF filters which make use of piezoelectric effect. Also, whenever you apply voltage onto the crystal, this crystal will pass through mechanical deformation, thereby converting the electrical energy to mechanical energy.
Whenever this crystal becomes mechanically extended or compressed, this mechanical energy becomes converted to electrical energy. The charges will be formed on the two sides of the structure of the crystal. This permits the flow of current through its terminals or creating a voltage in-between the terminals. For solid materials, the mechanical deformations alternative could create sound waves with velocity between 3000 and 12000 meters every second.
Reasons Why the RF Filter is Important?
As applications relating to wireless communication continue to develop, people tend to have higher data transmission speed requirements.
2G
During the 2G period, just a few people used their phones to use the internet as well as browse the web’s WAP version, and the data rate required was around 1 kb per second.
3G
During the 3G period when smartphones became popular, the utilization of networks of operators for sending and receiving emails, as well as the utilization of different applications has led to a sudden increase in the network traffic. The data rate required here is around 50 kb per second.
4G
During the 4G period, applications like live broadcast have greatly increased phone communication’s bandwidth requirements, and the data rate required has gotten to 1 mb per second.
5G
Now, talk of the 5G era, which is just coming in, which requires larger and faster data transmission amounts.
Also, corresponding to the data rate increase is the high use of different spectrum resources as well as the complexity of the communication protocols. Both problems are complementary. This is due to the limited resources of the spectrum, to meet the data rate demand of the people, this spectrum has to be completely used.
This is why a phone should be able to cover a very wide range of frequency so that the devices of different people can be utilized in any crowded situation. Only by this can enough allocation of spectrum bandwidth be possible. Also, in order to meet the requirements of data rate, the technology for carrier aggregation has been utilized since 4G. This ensures that devices can make use of different spectrums for their carrier frequency to help in the transmission of data.
When it comes to RF front end modules, RF filters play a significant role. This could filter the noise and out-of-band interference out in order to meet the radio frequency communication and systems protocols’ signal to noise ratio requirements.
Furthermore, as we have already mentioned, as communication protocols get more complex, the communication protocol demand outside and inside this frequency band will become higher. This will also make the filter’s design more challenging.
Also, as the frequency bands which mobile phones require to support keeps increasing since every frequency band which mobile phones must support keeps increasing since every frequency band must have a filter, the amount or number of filters required for use in mobile phones is increasing as well.
Conclusion
The significance of RF filters can never be overemphasized. They are useful in different instances. Its application list is nearly infinite. There are four main types. Each of the types accepts or rejects signals in different ways. When you make use of the right RF filter, you can accept these signals and then reject the undesired ones.
