HF-Band LC Filter : The Basic Breakdown of Its LC and HF Components

Band pass filters utilizing LC components (also known as lumped element filters), particularly inductors and capacitors, are applied in a number of radio frequency applications. These filters allow a band of frequencies to go through the filter, while the ones in the stop band of the filter are rejected. Generally, these filters are utilized where small frequency bands require passage through the filter while all others are being rejected by the filter.

A band pass LC filter with HF frequencies, more commonly known as a HF-Band LC Filter, is commonly used for first-line and backup communications over far-flung distances, mainly in the remote regions and developing countries of the world.

Also, high pass filters are arranged in either a pi or T network. As implied by its name, the pi network has a single series component, and either side of it there’s a component to the ground. In comparison, the T network high pass filter has one component to the ground; placed on either side, there’s a series of in line components.

LC Filter Frequency Limitations

Going up in frequency, lumped elements become less and less ideal until it’s nearly impossible to manufacture a filter this way at all. Designing a microwave design on lumped elements, one needs to re-stimulate the filter including all parasitic elements like parallel resonance of inductors and the series resonances of capacitors, and every resistive contribution.

When discussing topics about lumped elements, of course the two broad categories of inductors and capacitors arise. The first is surface mount parts, which are suited for microwave printed circuit board use. The second category is thin-film lumped elements, which are utilized on microwave integrated circuits (MICs) on alumina or other “hard” substances, as well as in MMIC Implementations.

Surface mount capacitors can be helpful up to the Ku-band, while the inductors basically have self-resonances below X-band. Thin-film capacitors are utilized in a cycle up to 100 GHz in MMICs. Lumped inductors on thin-films (and in MMICs) take the appearance of spiral conductors, and are limited to Ku-band frequencies and lower. Inductors are the main problem when dealing with lumped element filters and with other microwave circuits.

One’s using lumped element filters can gain up to 10%, 100% or more bandwidth. The attraction to these filters is that the filter can sometimes be very compact comparing it to a filter based on have-wave resonant structures.

Other Details on HF filters

In high pass filters, the series components are capacitors and the components to ground are inductors. This way, high frequency filters pass the high frequency signals and rejects the low frequency signals. These filters may be utilized in applications where unwanted signals in a frequency band are present below the terminated frequency and it’s important to pass the wanted signals through a band above the terminated frequency filter.

In addition, in order to provide a greater slope or roll off in HF filters, it can be possible to cascade several other filter sections. When this is accomplished, the filter components from the adjacent section may be fused together.

This is just a basic breakdown of the HF Band LC Filter components. For more details on such, ask AWG Tech for more.