This kind of filter is used to filter out a single frequency (see fig. 1 for frequency response).

Owing to the V-shaped frequency response, this filter is also called a Signal Notch Filter.

Trap Filters were first used in the 1970's in Scrambling / Descrambling systems.

There are two types of Trap Filters, Negative and Positive Trap Filters.

The frequency response curve of a Tier Trap Filter is roughly U-shaped, with a number of ripples in the stop band (see fig. 2).

This effect is due to the fact that Tier Trap Filters are basically made up of a number of Notch Filters.

Tier Trap Filters have two pass bands and one reject band.

Also called Band Deletion Filter.
The Frequency Response Curve of
Band Reject and Tier Trap Filters look
very much alike.
Band Reject Filters are used in the
same way as Tier Trap Filters to
eliminate a band of more than one
channel (or frequencies).

Band Reject Filters usually pass the
CATV Return Path (e.g. 5-42MHz,
5-65MHz, etc.) and UHF Band signals
and reject all other CATV channels
(e.g. 55-500MHz, 85-450MHz, etc.).

    Tier Trap Filters in contrast are used to filter out only a limited number of CATV channels or
    frequencies (e.g. 20-150MHz).

    Tier Trap Filters are therefore used to reject a narrow band, whereas Band Reject Filters are used
    if a wide Reject Band is necessary.

    The reject band of Band Reject Filters can be wider than that of Tier Trap Filters.

Low Pass filters pass lower frequencies / channels and reject the higher ones
(see fig. 4).

High Pass Filters are basically the opposite of Low Pass Filters.

They pass only higher frequencies/channels and reject anything below the cut-off frequency (see fig. 5).

Band Pass Filters have a frequency response that is the opposite of Band Reject Filters
(see fig. 6).

Double Band Pass Filters are similar to Window Filters, but a DBF(Double Band Pass Filter) contains two complete pass bands. (see fig. 8).
 

This type of TBF(Triple Band Pass Filter) contains one complete pass bands, one low pass and one high pass bands. (see fig. 9).
 

    a. Insertion Loss :
    Insertion Loss is the Attenuation of the Pass Band caused by the insertion of the filter.
    Usually Insertion Loss values are provided for typical and maximum values.
    Typical Insertion Loss is the average loss for the filter's pass band.
    Maximum Insertion Loss refers to the point where maximum Insertion Loss occurs.
    The lower the value for Insertion Loss, the better the filter.

    b. Rejection :
    Rejection refers to the Reject Band attenuation, the value by which the filter actually deletes the
    frequency / channel that is supposed to be cut out.
    The Rejection value indicated on the filter is usually the minimum rejection value for the specified
    reject band (see fig. 2 Mark 4 and 5, fig. 4 Mark 6, fig. 6 Mark 2 and 8 and fig. 7 Mark 3, 4 and 8).
    The higher this minimum value, the steeper the slope between Pass and Reject Band.
    A higher Rejection is usually better, but also increases the Insertion Loss and cost of the filter.

    c. Return Loss :
    A filter's Return Loss refers to the attenuation of reflected signals within the Pass Band.
    The higher the Return Loss, the better the filter's impedance match and the lower the reflected
    signals that occur when signals pass from the line through the filter. Return Loss values are usually
    provided in Minimum and Typical or only Minimum values.
    The Minimum Return Loss of any filter should be at least 10dB.
    The higher the Return Loss, the better the filter.