MIL-F-18327 Filters; High Pass, Low Pass, Band Pass, Band Suppression, And Dual Functioning, General Specification ForThis specification covers the general requirements for passive frequency-selective networks, such as dual functioning, band suppression, band pass, low pass, and high pass \(or any combination thereof\) electric-wave filters, including those employing electromechanical and piezoelectric elements, for use over the frequency range of 0 to 500 megahertz. Filters covered by this specification are intended for use where operation under various environmental conditions is required. This specification covers filters weighing not more than 50 pounds and requiring root-mean-square test voltage ratings not greater than 5,000 volts.

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MIL-F-18327F

4.7.8 Electrical characteristics (see 3.11). The electrical characteristics specified shall be determined with rated

voltage applied over the specified frequency range with the specified source and load impedance (see 3.1). Insertion

loss and discrimination characteristics shall be included for all filters. Special characteristics, such as impedance,

phase shift in the pass band, special stability, transient response, harmonic and intermodulation distortion limits, and

reflection coefficient and return loss shall be measured, when specified (see 3.1).

4.7.8.1 Terminal impedance (when specified, see 3.1). Terminal input impedance shall be measured with a rated

load connected across the output terminals of the filter. Terminal output impedance shall be measured with a rated

source impedance connected across the input terminals of the filter. Impedances including vector angles shall be

measured at the specified frequencies (see 3.1) by a bridge or equivalent method approved by the Government.

4.7.8.2 Insertion loss (see 6.5.4) (at reference frequency). The reference frequency and the source and load

impedances shall be as specified (see 3.1). With a constant input voltage, Eg, across the generator, the load voltage,

with and without the filter in the circuit, shall be recorded at the reference frequency. The insertion loss, in decibels,

shall be calculated using the following formula:

ILfr = 20 log E2 dB, E1 > E2.

Where:

ILfr = Insertion loss at reference frequency in decibels, with Eg constant.

E1 = The load voltage with the filters not in the circuit at the reference frequency.

E2 = The load voltage with the filters in the circuit at the reference frequency.

E1 > E2.

A typical test circuit is shown in figure 8.

4.7.8.3 Discrimination . Insertion loss at frequencies other than the reference frequency shall be measured using a

test circuit such as that shown on figure 8. Measurements shall be made at frequencies or over frequency bands, as

specified (see 3.1). The algebraic difference between the insertion loss at a specified frequency and the insertion

loss at the reference frequency, shall be defined as the discrimination (α) at the specified frequency.

ZS = Source impedance.

ZL = Load impedance.

EG = Constant voltage across generator.

E1 = The load voltage with the filter not in the circuit at the reference frequency.

E2 = The load voltage with the filter in the circuit at the same frequency.

FIGURE 8. Typical measurement circuit for insertion loss and discrimination.