Directional Couplers
A directional coupler is a passive four-port device that samples a controlled fraction of the signal traveling through a main transmission line and delivers it to a coupled port, while allowing the bulk of the power to continue to the through port with minimal disturbance. The fraction of power extracted is defined by the coupling factor, expressed in dB. A 20 dB coupler, for example, delivers 1% of the input power to the coupled port and passes the remaining 99% to the through port.
What makes a directional coupler useful is not just that it taps signal power, but that it does so directionally. The coupling port responds to signals traveling in the forward direction, while the isolated port is matched-terminated and does not pass forward signals.
Octave Band, Special Band, Multi Band and Ultra Wide-Band Models Available
Low VSWR, High Directivity, and Solid Build Construction
Many In-Stock Models and Custom Designs Available
In a dual directional coupler, two coupled ports are available simultaneously, one sampling forward power and one sampling reverse power, allowing a single component to measure both incident and reflected power at the same point in a transmission line.
Three parameters define coupler performance in any application: coupling factor (how much power is extracted), directivity (how well the coupler distinguishes forward from reverse signals at the coupled port), and insertion loss (how much the coupler degrades the main line signal).
MCLI directional couplers are designed for applications that require external leveling, accurate power monitoring, signal mixing, or swept transmission and reflection measurements across frequency bands from 380 MHz to 40 GHz
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Showing 201–300 of 776 results
| Part # | Frequency Range (GHz) | Coupling (dB) | Insertion Loss (dB) | Directivity (dB) | VSWR | Power Avg. (W) | Lead Time | Notes | Action | |
|---|---|---|---|---|---|---|---|---|---|---|
| Min | Max | |||||||||
| C37-10 | 0.8 | 2.3 | 10±1.25 | 1 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-20 | 0.8 | 2.3 | 20±1.25 | 0.45 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-20-CC | 0.8 | 2.3 | 20±1.25 | 0.45 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-30 | 0.8 | 2.3 | 30±1.25 | 0.45 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C43-6 | 0.8 | 0.9 | 6±1.25 | 1.8 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C43-10 | 0.8 | 0.9 | 10±1.0 | 1.2 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C43-20 | 0.8 | 0.9 | 20±1.25 | 0.55 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C43-30 | 0.8 | 0.9 | 30±1.25 | 0.55 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C49-6 | 0.8 | 1.2 | 6±1.0 | 1.9 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C49-10 | 0.8 | 1.2 | 10±1.0 | 1.5 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C49-20 | 0.8 | 1.2 | 20±1.0 | 1 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C49-30 | 0.8 | 1.2 | 30±1.0 | 0.8 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C36-20/NF | 0.8 | 3 | 20±1.25 | 1 | 20 | 1.30:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-10/NF | 0.8 | 2.3 | 10±1.25 | 1 | 20 | 1.30:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-20/NF | 0.8 | 2.3 | 20±1.25 | 1 | 20 | 1.30:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-30/NF | 0.8 | 2.3 | 30±1.25 | 1 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C49-6/NF | 0.8 | 1.2 | 6±1.0 | 1.9 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C49-10/NF | 0.8 | 1.2 | 10±1.0 | 1.5 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C49-20/NF | 0.8 | 1.2 | 20±1.0 | 1 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C49-30/NF | 0.8 | 1.2 | 30±1.0 | 0.8 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C36-6/NMO/TFC | 0.8 | 3 | 6±1.0 | 1 | 20 | 1.30:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-10/NDC | 0.8 | 2.3 | 10±1.25 | 1 | 20 | 1.30:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-10/NF/DC | 0.8 | 2.3 | 10±1.25 | 1 | 20 | 1.30:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-10/NMI | 0.8 | 2.3 | 10±1.25 | 1 | 20 | 1.30:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-10-S/NF | 0.8 | 2.3 | 10±1.25 | 1 | 20 | 1.30:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-20-S/NF | 0.8 | 2.3 | 20±1.25 | 1 | 20 | 1.30:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C37-20-S/NMO | 0.8 | 2.3 | 20±1.25 | 1 | 20 | 1.30:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C101-6-100/NF | 0.8 | 2.5 | 6±1.5 | 2.2 | 19 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C102-6-100/NF | 0.8 | 2.7 | 6±1.5 | 1.3 | 15 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C102-10-100/NF | 0.8 | 2.7 | 10±1.5 | 1.3 | 15 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C102-20-100/NF | 0.8 | 2.7 | 20±1.25 | 1.3 | 15 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C102-30-200/NF | 0.8 | 2.7 | 30±1.25 | 1.3 | 15 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C36-6/NF | 0.8 | 3 | 6±1.0 | 1 | 20 | 1.30:1 | 50 | 2-3 Weeks | N/A | Request Quote |
| HD-42-40 | 0.8 | 4.2 | 40±1.0 | 0.3 | 20 | 1.20:1 | 600 | 6-8 Weeks | N/A | Request Quote |
| HD-42-40/NF | 0.8 | 4.2 | 40±1.0 | 0.3 | 20 | 1.20:1 | 600 | 6-8 Weeks | N/A | Request Quote |
| HD-42-30 | 0.8 | 4.2 | 30 | 0.4 | 20 | 1.35:1 | 600 | 6-8 Weeks | N/A | Request Quote |
| DC37-20 | 0.8 | 2.2 | 20±1.25 | 0.35 | 20 | 1.25:1 | 50 | 2-3 Weeks | N/A | Request Quote |
| DC52-10/NF | 0.8 | 2.5 | 10±1.25 | 0.35 | 20 | 1.25:1 | 50 | 2-3 Weeks | N/A | Request Quote |
| DC52-20 | 0.8 | 2.5 | 20±1.25 | 0.35 | 20 | 1.25:1 | 50 | 2-3 Weeks | N/A | Request Quote |
| DC52-20/NF | 0.8 | 2.5 | 20±1.25 | 0.35 | 20 | 1.25:1 | 50 | 2-3 Weeks | N/A | Request Quote |
| C64-30 | 0.82 | 1.2 | 30±1 | 0.4 | 23 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C77-6 | 0.88 | 0.96 | 6±1 | 0.8 | 25 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C77-10 | 0.88 | 0.96 | 10±1 | 0.8 | 25 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C77-20 | 0.88 | 0.96 | 20±1 | 0.2 | 25 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C77-30 | 0.88 | 0.96 | 30±1 | 0.2 | 25 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C77-6/NF | 0.88 | 0.96 | 6±1.0 | 0.8 | 25 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C77-10/NF | 0.88 | 0.96 | 10±1.0 | 0.8 | 25 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C77-20/NF | 0.88 | 0.96 | 20±1.0 | 0.2 | 25 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C77-30/NF | 0.88 | 0.96 | 30±1.0 | 0.2 | 25 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C99-10/NF | 0.95 | 2.05 | 10±1.25 | 0.9 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C99-20/NF | 0.95 | 2.05 | 20±1.25 | 1.9 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C99-20/NMI/SC | 0.95 | 2.05 | 20±1.25 | 0.2 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C99-20/NMO/SC | 0.95 | 2.05 | 20±1.25 | 0.2 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| DC14-6 | 0.95 | 2.15 | 6±1.25 | 1.5 | 22 | 1.15:1 | 50 | 2-3 Weeks | N/A | Request Quote |
| DC14-10 | 0.95 | 2.15 | 10±1.25 | 1.5 | 22 | 1.15:1 | 50 | 2-3 Weeks | N/A | Request Quote |
| DC15-20 | 0.95 | 1.2 | 20 | 0.2 | 25 | 1.10:1 | 5 | 2-3 Weeks | N/A | Request Quote |
| CB2-6 | 1 | 3.5 | 6±1 | 2 | 23 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB2-10 | 1 | 3.5 | 10±1 | 0.9 | 23 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB2-20 | 1 | 3.5 | 20±1 | 0.4 | 23 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB7-10 | 1 | 18 | 10±1 | 1.6 | 12 | 1.65:1 | 20 | Stock - 1 Week | N/A | Request Quote |
| CB7-16 | 1 | 18 | 16±1 | 1.2 | 12 | 1.50:1 | 20 | Stock - 1 Week | N/A | Request Quote |
| CB7-20 | 1 | 18 | 20±1 | 0.9 | 16 | 1.45:1 | 20 | Stock - 1 Week | N/A | Request Quote |
| CB13-10 | 1 | 12.4 | 10±1 | 1.6 | 14 | 1.65:1 | 20 | Stock - 1 Week | N/A | Request Quote |
| CB13-20 | 1 | 12.4 | 20±1 | 0.9 | 15 | 1.50:1 | 20 | Stock - 1 Week | N/A | Request Quote |
| CB15-20 | 1 | 20 | 20±1 | 1 | 16 | 1.35:1 | 20 | Stock - 1 Week | N/A | Request Quote |
| CB38-6 | 1 | 8 | 6±1 | 2 | 15 | 1.40:1 | 50 | 3-4 Weeks | N/A | Request Quote |
| CB38-10 | 1 | 4 | 10±1 | 0.9 | 19 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB38-20 | 1 | 4 | 20±1 | 1.2 | 14 | 1.65:1 | 20 | Stock - 1 Week | N/A | Request Quote |
| CB51-6 | 1 | 4 | 6±1 | 0.9 | 23 | 1.28:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB51-10 | 1 | 4 | 10±1 | 0.9 | 23 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB51-20 | 1 | 4 | 20±1 | 0.9 | 23 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB51-30 | 1 | 4 | 30±1 | 0.9 | 23 | 1.20:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB52-10 | 1 | 26.5 | 10±1 | 1.6 | 14 | 1.65:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB52-16 | 1 | 26.5 | 16±1 | 1.3 | 12 | 1.60:1 | 20 | 3-4 Weeks | N/A | Request Quote |
| CB52-20 | 1 | 26.5 | 20±1 | 1.2 | 14 | 1.65:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB52-30 | 1 | 26.5 | 30±0.6 | 1.1 | 13 | 1.40:1 | 20 | 3-4 Weeks | N/A | Request Quote |
| CB57-6 | 1 | 4.2 | 6±1 | 0.9 | 23 | 1.28:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB57-20 | 1 | 4.2 | 20±1 | 0.9 | 23 | 1.28:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| CB67-13 | 1 | 65 | 13±1 | 3.3 | 10 | 2.00:1 | 50 | 1-2 Weeks | N/A | Request Quote |
| CB87-10 | 1 | 40 | 10±0.7 | 2.5 | 10 | 1.60:1 | 20 | 3-4 Weeks | N/A | Request Quote |
| CB87-13 | 1 | 40 | 13±0.8 | 1.8 | 11 | 1.70:1 | 20 | 3-4 Weeks | N/A | Request Quote |
| CB87-13/K | 1 | 40 | 13±1 | 2 | 11 | 1.70:1 | 50 | 3-4 Weeks | N/A | Request Quote |
| CB87-20 | 1 | 40 | 20±0.9 | 1.8 | 10 | 1.70:1 | 20 | 3-4 Weeks | N/A | Request Quote |
| CB88-10 | 1 | 20 | 10±1 | 1.6 | 14 | 1.65:1 | 20 | 3-4 Weeks | N/A | Request Quote |
| CB88-16 | 1 | 20 | 16±1 | 1.4 | 16 | 1.35:1 | 20 | 3-4 Weeks | N/A | Request Quote |
| CB90-13 | 1 | 65 | 13±1 | 3.3 | 10 | 2.00:1 | 50 | 3-4 Weeks | N/A | Request Quote |
| CB117-13 | 1 | 50 | 13±0.8 | 2.8 | 10 | 1.90:1 | 16 | 3-4 Weeks | N/A | Request Quote |
| CB140-13 | 1 | 40 | 13±0.8 | 1 | 11 | 1.70:1 | 20 | 3-4 Weeks | N/A | Request Quote |
| CB7-20/NF | 1 | 18 | 20±1 | 0.9 | 12 | 1.50:1 | 50 | 3-4 Weeks | N/A | Request Quote |
| CB20-20/NF | 1 | 10 | 20±1.1 | 0.9 | 15 | 1.40:1 | 10 | Stock - 1 Week | N/A | Request Quote |
| CB52-6 | 1 | 26.5 | 6 | 2 | 13 | 1.50:1 | 20 | 3-4 Weeks | N/A | Request Quote |
| C2-6 | 1 | 2 | 6±1.0 | 1.8 | 25 | 1.15:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C2-10 | 1 | 2 | 10±1.0 | 0.9 | 25 | 1.10:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C2-20 | 1 | 2 | 20±1.25 | 0.2 | 25 | 1.10:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C2-30 | 1 | 2 | 30±1.25 | 0.2 | 25 | 1.10:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C2-40 | 1 | 2 | 40±1.25 | 0.2 | 25 | 1.10:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C2-6/NF | 1 | 2 | 6±1.25 | 2 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C2-10/NF | 1 | 2 | 10±1.25 | 0.9 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C2-20/NF | 1 | 2 | 20±1.25 | 0.2 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
| C2-30/NF | 1 | 2 | 30±1.25 | 0.2 | 20 | 1.25:1 | 50 | Stock - 1 Week | N/A | Request Quote |
Full Product Line Specifications
| Parameter | Range / Options |
|---|---|
| Frequency Range | 380 MHz to 40 GHz |
| Coupling Values Available | 3 dB, 6 dB, 10 dB, 20 dB, 30 dB, 40 dB, 50 dB (model-dependent) |
| Insertion Loss (Main Line) | As low as 0.9 dB on broadband models |
| Directivity | 14 dB and above depending on model and frequency |
| VSWR | As low as 1.40:1 on select models |
| Average Power Handling | Up to high-power ratings on HC and HD series models |
| Configuration Types | Unidirectional, dual directional, bidirectional |
| Construction Technologies | Stripline, lumped element |
| Connector Options | SMA Female standard; Type N available on select models |
| Characteristic Impedance | 50 ohm |
| Series Available | CB (Broadband), C Series, HC/HD (High Power), HCL/HDL (High Power Low Frequency), HXL (Bidirectional) |
| Custom Design | Available. Contact MCLI engineering for non-standard coupling values, frequency ranges, or power levels. |
Where MCLI Directional Couplers Are Used
Forward Power Monitoring and Transmitter Output Leveling
In any transmitter chain, maintaining accurate output power is a system-level requirement. A directional coupler placed at the transmitter output samples a fixed fraction of the forward power at the coupled port. That sampled signal feeds a power detector or power meter, which drives a feedback loop to keep output power constant across temperature, frequency, and component aging. This technique, called external leveling, is standard practice in radar transmitters, base station power amplifiers, satellite uplink systems, and test signal generators. The coupler’s coupling factor determines the signal level presented to the detector, so choosing the right coupling value keeps the detector in its linear operating range.
VNA Swept Transmission and Reflection Measurements
Vector network analyzers use directional couplers internally to separate incident and reflected waves at each test port, but external couplers are also used to extend VNA measurement capability, increase power handling, or add additional signal sampling points in a test fixture. High directivity is the critical specification in this application: when directivity is low, forward signal leakage into the reverse-sampling port creates measurement errors. For accurate return loss measurements, directivity should be at least 10 dB higher than the return loss being measured.
Antenna Beam Forming and Feed Network Monitoring
In phased array and multi-element antenna systems, directional couplers are placed in the feed network to monitor the signal level at each antenna element or sector, detect element failures, and provide amplitude reference signals for beam steering calibration. High power couplers, such as MCLI’s HC and HD series, handle the power levels present in high-power feed networks while still delivering a usable coupled signal level for monitoring circuitry.
Coupler Configuration Guide
MCLI offers three coupler configurations, each suited to different signal routing needs.
Dual Directional Couplers (HDL Series)
A dual directional coupler provides two coupled ports simultaneously, one sampling forward power and one sampling reflected power. Both ports are accessible to the user, unlike a unidirectional coupler where one port is internally terminated. This configuration is the right choice for VSWR monitoring, reflection measurement, and any application where both incident and reflected power need to be measured at the same location without adding a second coupler to the signal path.
Reflected Power Measurement and VSWR Monitoring
When a transmission line is connected to a load that is not perfectly matched, some fraction of the forward power is reflected back toward the source. A dual directional coupler placed in the transmission line samples both forward and reflected power simultaneously at two independent coupled ports. The ratio of those two sampled levels gives the reflection coefficient, from which VSWR and return loss can be calculated. This configuration is widely used in antenna feed systems, power amplifier test setups, and anywhere continuous VSWR monitoring is needed to detect load changes, cable faults, or antenna mismatch conditions.
Electronic Warfare Signal Sampling and Monitoring
Electronic warfare (EW) systems use directional couplers to tap signals from transmit chains for frequency monitoring, signal identification, and coherent jammer reference generation without interrupting signal flow in the main line. Broadband coverage and low mainline insertion loss are the primary requirements in these applications, since EW systems must cover wide frequency ranges and any power lost in the coupler comes directly out of the transmit chain’s power budget.
EMC Testing and Signal Injection
Electromagnetic compatibility (EMC) test setups use directional couplers to inject calibrated signal levels into a system under test or to monitor the signal environment during radiated immunity testing. The coupler’s isolation between the through port and the coupled port prevents the injection signal from disturbing the measurement path.
Unidirectional Couplers (C Series, CB Series, HC/HD Series)
A unidirectional coupler has one coupled port, which samples either forward or reverse signal depending on how the coupler is oriented in the circuit. The isolated port is internally terminated in a 50 ohm matched load. This is the standard configuration for forward power monitoring and transmitter leveling, where only one signal direction needs to be sampled. MCLI’s CB broadband series covers 0.5 to 18 GHz with coupling values from 10 to 30 dB. The HC and HD high power series handles elevated power levels for radar and communications transmitter applications.
Bidirectional Couplers (HXL Series)
A bidirectional coupler is a symmetric four-port device where all ports are accessible and either port pair can serve as the main line or the coupled line. This configuration is used when the direction of signal flow is not fixed, or when the coupler must work equally well in both orientations. Design care is needed to properly terminate any unused ports, since a mismatched load on an unused port reduces effective directivity.
| Configuration | Coupled Ports Available | Internal Termination | Best For |
|---|---|---|---|
| Unidirectional | 1 | Yes (isolated port) | Forward power monitoring, transmitter leveling |
| Dual Directional | 2 (forward and reverse) | No | VSWR monitoring, reflection measurement |
| Bidirectional | 2 (symmetric) | No | Flexible orientation, symmetric signal paths |
Frequently Asked Questions About Directional Couplers
What Is a Coupling Factor and How Do I Choose the Right Value?
The coupling factor tells you how much of the input power is delivered to the coupled port, expressed in dB. A 10 dB coupler delivers 10% of input power to the coupled port and passes 90% to the through port. A 20 dB coupler delivers 1% to the coupled port and passes 99% through. The right coupling value depends on what you are connecting to the coupled port and how much signal it needs. If the coupled port feeds a power detector with a -20 dBm optimal input level and the main line carries 30 dBm, you need a 50 dB coupler. If the detector works at 0 dBm, a 30 dB coupler is correct. Stronger coupling values (lower dB numbers like 3 or 6 dB) also introduce additional mainline insertion loss beyond the coupler’s inherent loss, so this trade-off matters in power-sensitive applications.
What Is Directivity and Why Does It Matter for Return Loss Measurement?
Directivity is the ratio in dB between the power at the coupled port when forward signal is present and the power at that same port when only a reverse signal is present. High directivity means the coupler accurately distinguishes forward from reverse signals. In practice, directivity limits the accuracy of return loss measurements: a coupler with 20 dB of directivity cannot accurately measure return loss values above about 20 dB, because forward signal leakage at the reverse-sampling port masks the measurement. For accurate reflection measurements, specify a coupler whose directivity exceeds the expected return loss by at least 10 dB.
What Is the Difference Between a Directional and a Dual Directional Coupler?
A standard directional coupler has one coupled port that samples signal traveling in one direction, with the other coupled port internally terminated. A dual directional coupler makes both coupled ports externally accessible, so forward and reverse signals can be sampled at the same time. Use a dual directional model when you need simultaneous forward and reflected power measurement at a single point in the circuit, such as for continuous VSWR monitoring in a live transmitter chain.
How Does Mainline Insertion Loss Affect My System?
Insertion loss is the attenuation of the main line signal as it passes through the coupler from the input port to the through port. This loss comes from two sources: the power deliberately coupled to the coupled port (coupling loss), and the coupler’s own resistive and mismatch losses (excess insertion loss). For weak coupling values like 20, 30, or 40 dB, the coupling loss is negligible (0.04 dB for 20 dB coupling). For stronger coupling values like 3 or 6 dB, the coupling loss is significant and must be factored into the system power budget. MCLI’s CB series broadband models achieve as low as 0.9 dB total insertion loss, keeping main line power loss to a minimum.
What Coupling Value Do Most Engineers Use for Power Monitoring?
The most common coupling values for power monitoring and transmitter leveling are 20 dB and 30 dB. A 20 dB coupler delivers 1% of transmitter power to the monitoring port, which is practical when the transmitter output is in the 1 to 20 watt range and the monitoring detector needs a milliwatt-level input. A 30 dB coupler delivers 0.1% of power to the monitor port, which is useful at higher transmitter power levels. For satellite uplink and other high-power applications where even a fraction of a percent represents meaningful power, 30 to 50 dB coupling values keep the monitor port at a safe signal level for the detector while the main line carries full power.
Can a Directional Coupler Be Used in Reverse to Inject a Signal into the Main Line?
Yes. Directional couplers are passive and reciprocal in terms of the through path. A signal applied to the coupled port will appear on the main line at a level reduced by the coupling factor. This technique is used in signal injection applications such as EMC testing and BIT (built-in test) circuit injection. Keep in mind that the power rating of the coupled port is lower than the main line power rating, since the coupled port is normally designed for low-level monitoring signals. Confirm the coupled port power limit in the datasheet before injecting power into it.
Does MCLI Offer Custom Coupling Values or Frequency Ranges?
Yes. MCLI’s engineering team designs directional couplers for coupling values, frequency ranges, power levels, and connector configurations outside the standard catalog. Custom dual directional and bidirectional configurations are also available. Contact MCLI engineering with your electrical and mechanical requirements to initiate a custom design inquiry.