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The main-line loss of a coupler is defined as the loss between the input and output ports. Theoretical loss is defined as that of a perfect (lossless) coupler, for which the input power is the sum of the (main-line) output power and the power at the coupled port. Therefore, the theoretical main-line loss is dependent upon the fraction of the input power that is outputted at the coupled port. The conversion between them can be expressed mathematically. This application note derives the formula and provides a conversion table.

A lossless coupler transfers all input power to the output and coupled ports: Pin = Pout + Pcoupled (1).

In practice, positive decibel values are given for main-line loss and coupling (the fraction of the input power that is outputted at the coupled port):

ML (main-line loss in dB) = 10 log10(Pin / Pout) (2) and

CPL (coupling in dB) = 10 log10 (Pin /Pcoupled) (3)

With these three equations, the CPL to ML conversion can be obtained.

From equation (1), Pout/Pin = 1 – Pcoupled/Pin (4)

From equation (3), Pcoupled /Pin = 10^–CPL/10 (5)

Substitute (4), and then (5), into (2):

ML = 10 log10 (Pin / Pout) = 10 log10 [1/(1 – Pcoupled/Pin)] 

= 10 log10 [1/(1 – 10 ^–CPL/10 )] (6)

Part NumberStatusFrequency MinFrequency MaxCouplingDirectivity
PDC-7984-30-50W-SMAPreliminary7.9 GHz8.4 GHz30 dB ± 0.5 dB Max18 dB Min
PDC-0545-6-SFF-30WPreliminary500 MHz4.5 GHz6 ± 0.5 dB MAX18 dB MIN
PDC-192212-6-20W-SFFPreliminary19.2 GHz21.2 GHz6 dB ±0.7dB MAX10 dB MIN
PDC-3336-6-20W-SFFPreliminary33 GHz36 GHz6 dB ±0.7dB MAX10 dB MIN
PDC-20M6G-24-5D5-12V-SFFPreliminary20 MHz6 GHz
-
-
PDC-12-20-50W-SMAPreliminary1 GHz2 GHz= 20 ± 0.7dB>25 dB
PDC-820-20-25W-SFFActive8 GHz20 GHz20 dB ±1.0dB Max12 dB Min
PDC-418-20-50W-SFFActive4.0 GHz18.0 GHz20 dB ± 0.7 dB max.12 dB min.
PDDC-10M1-40-SKActive0.01 GHz1.0 GHz40dB Nominal> 15dB
RFOC-811-QRC-DC-10Active8 GHz11 GHz10 ± 1.25 dB10 dB Min
PDC-324-10C-292FF-20WPreliminary3.0 GHz24.0 GHz10 ± 1 dB max.12 dB min.
PDC-416-10C-SFF-50WPreliminary4.0 GHz16.0 GHz10 ± 0.7 dB max.15 dB min.
PDC-48-6C-SFF-50WPreliminary4.0 GHz8.0 GHz6 ± 0.7 dB max.22 dB min.
PDC-DC18G-18C-NFF-200WActiveDC18.0 GHz30 dB @ 18.0 GHz
50 dB @ 1.0 GHz
15 dB Min, 22 dB Typ (1.0 to 14.0 GHz)
12 dB Min, 16 dB Typ (14.0 to 18.0 GHz)
PDC-18G40G-10C-SFF-20WPreliminary18.0 GHz40.0 GHz10 ± 1 dB typ.10 dB min.
PDC-2G18G-10C-SFF-50WPreliminary2.0 GHz18.0 GHz10 ± 0.7 dB max.15 dB min.
PDC-0R5G2G-10C-SFF-50WPreliminary0.5 GHz2.0 GHz10 ± 0.4 dB22 dB min.
PDC-2G18G-20C-SFF-50WActive2.0 GHz18.0 GHz20 ± 0.7 dB Max15 dB Min
PDC-1G4G-30C-NFFPreliminary1 GHz4 GHz30 dB17 dB min.
PDC-25M-35M-25-SFFPreliminary0.025 GHz0.035 GHz25 dB ±2dB25 dB min
PDC-26D5G40G-10C-292FFPreliminary26.5 GHz40 GHz10±1.0 dB12 dB min.
PDC-2G6G-35C-NFF-200WPreliminary2 GHz6 GHz35 dB ±1dB15 dB min, 22 dB typ
PDC-2G8G-30C-NFF-200WPreliminary2 GHz8 GHz30 dB ± 1dB18 dB min
PDC-400M500M-20C-SFF-30WPreliminary0.4 GHz0.5 GHz20 ±1.0 dB20 dB min.
PDC-800M3G-30C-NFF-300WPreliminary0.8 GHz3 GHz30 dB ± 1dB22 dB min
PDC-100M500M-40C-NFF-500WPreliminary0.1 GHz0.5 GHz40 dB ± 1dB20 dB min
PDC-2G8G-10C-SFF-50WPreliminary2 GHz8 GHz10 dB max. ±0.5 dB20 dB min.
PDC-800M2D5G-30C-NFF-60W *Active0.8 GHz2.5 GHz30<=±1.0 dB20 dB min
PDC-1G40G-292FF-50WActive1 GHz40 GHz20 dB max.10 dB min.
PDC-800M2D5G-6C-NFF-60W *Active0.8 GHz2.5 GHz6<=±0.5 dB20 dB min
PDC-800M2D5G-10C-NFF-60W *Active0.8 GHz2.5 GHz10<=±0.8 dB20 dB min
PDC-800M2D5G-20C-SFF-50W *Active0.8 GHz2.5 GHz20±1.0 dB20 dB min
PDC-800M2D5G-10C-SFF-50W *Active0.8 GHz2.5 GHz10±1.0 dB20 dB min
PDC-800M2D5G-30C-SFF-50W *Active0.8 GHz2.5 GHz30 < ±1.0 dB20 dB Min
PDC-800M2D5G-6C-SFF-50W *Active0.8 GHz2.5 GHz6<±1.0 dB20 dB min
PDC-800M2D5G-20C-NFF-60W *Active0.8 GHz2.5 GHz20<=±1.0 dB20 dB min