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RF Components: Equalizers

Understanding Parabolic Shaped Equalizers

HALF SINE: Attenuation increases and decreases monotonically with frequency and with the maximum attenuation occurring at mid-band. The relative zero attenuation points or minimums are at both band ends. (See Fig. #3) Half Sine Equalizers are primarily used for compensating the gain variation present in wide band traveling wave tubes or solid-state amplifiers where the maximum gain is at or near mid-band

INVERTED HALF SINE: Attenuation decreases monotonically with frequency from both band ends to mid-band where relative zero attenuation occurs. This type of equalizer compensates for accumulative gain variations of a system when the gain is greatest at the highest and lowest operating frequencies, with minimum gain at or near to mid-band.

HOW TO SPECIFY: Certain parameters must be defined prior to ordering these equalizers. The following is a listing of those parameters along with a brief definition and a method for determining your specifications.

ATTENUATION: The maximum attenuation will occur at or near the mid-band frequency, for the Half Sine, and at the band edges for the Inverted Half Sine. This parameter is specified in accordance with your particular system response. Non-symmetrical and distorted half sine curve shapes are also available.

INSERTION LOSS: (See Fig.#3 and Fig. #4) The insertion loss of these devices is the sum of both absorptive and reflective losses, measured at the highest and lowest frequency of operation for the Half Sine, and at mid-band for the Inverted Half Sine. This parameter is specified as a maximum and is referred to at the relative zero attenuation point. Therefore, the specified attenuation level is relative to the insertion loss. A typical method, for approximating insertion loss, would be to take 10% of the maximum attenuation point and add 0.25 dB to that value. For example, if specifying insertion loss of a 10 dB Half Sine Equalizer, the approximate level of insertion loss would be 1.25 dB maximum at both ends unless otherwise specified.

VSWR: This parameter is dependent on many factors such as attenuation level, bandwidth, operating frequency range, size, and configuration and adjustability requirements. Input and output VSWR's under most circumstances, should not exceed 2:1.

ACCURACY: The accuracy of the curve shape is defined as the deviation in dB from the nominal specified curve. This deviation is generally less than ±7% of the maximum attenuation level. For example, if specifying the accuracy of a 10 dB Half Sine Equalizer, the approximate accuracy envelope would be ±0.7 dB.

ADJUSTABILITY: MICA can provide user-friendly adjustments which will allow you to vary the maximum attenuation and the frequency at which it occurs. These adjustment ranges are typically specified as ±15% of the attenuation level and ±5% of the frequency at which the maximum attenuation occurs. For example, with a maximum attenuation of 10 dB, adjustability would be 8.5-11.5 dB for attenuation. If the frequency at which the maximum attenuation occurred was 8 GHz, the maximum loss point could be skewed 400 MHz either higher or lower in frequency from its nominal position. Adjustability of the Inverted Half Sine is somewhat limited and cannot be fully specified until all parameters are determined.

SIZE: Design and size criteria can only be established after determination of all applicable specifications and can then be quoted and outline drawings provided for a detailed mechanical layout.

FIXED or ADJUSTABLE: Parabolic Shaped Equalizers can be made amplitude and frequency adjustable, which will allow you to compensate for changes in amplifier gain response or fixed tuned and pre-set by the factory.

EXTENDED ADJUSTABILITY: In most cases MICA can further extend the standard range of adjustability: However, some trade-offs, such as degradation in VSWR and curve accuracy, may be necessary. A special adjustment feature, which will allow adjustment from maximum attenuation to relative zero, can also be provided on a limited basis.

CONNECTIONS: MICA provides SMA (F) as standard connectors. But other SMA series connectors can be provided on request. TNC and type "N" connectors are not recommended, but can be made available by special order.

WAVEGUIDE: All standard waveguide bands.

INVERTED HALF SINE OPTIONS: Similar to that of the Half Sine Equalizers, the maximum attenuation points will occur at the highest and lowest operating frequencies. Special consideration must be given to the adjustability of this type of equalizer. Therefore, the adjustability data for that of the Half Sine Equalizer may not be applicable. (See Fig. #4)
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