Zero-Bias Diode Detectors

A zero-bias diode detector converts an RF input signal into a DC or video voltage output proportional to the RF power level, without requiring any DC bias voltage to operate. MCLI’s zero-bias diode detectors use Schottky diodes that are sensitive enough to self-bias from the RF signal itself, eliminating the bias circuitry that conventional biased detectors require and simplifying integration into receiver, monitoring, and power detection circuits.

The line covers 10 MHz to 18.5 GHz with flatness of +/- 0.5 dB, low level sensitivity of 0.5 mV/uW, VSWR as low as 1.40:1, and a choice of positive or negative output polarity. SMA Male input connectors are standard, with BNC Female or SMA Female video output options depending on the model.

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Positive and Negative Polarity Models

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Broadband and Flat Frequency Solutions

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High Reliability and Temperature Stability

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Part #	Frequency Range (GHz)		VSWR Max.	Flatness (±dB)	Low Level Sensitivity (mV/uW)	Input Connector	Output Connector	Lead Time	Notes	Action
Part #	Min	Max	VSWR Max.	Flatness (±dB)	Low Level Sensitivity (mV/uW)	Input Connector	Output Connector	Lead Time	Notes	Action
ZD-7-X	0.001	2	1.30:1	0.3	0.5	BNC Male	BNC Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-8-X	0.001	4	1.30:1	0.3	0.5	BNC Male	BNC Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-1-X	0.01	12.4	1.40:1	0.3	0.5	SMA Male	SMA Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-2-X	0.01	12.4	1.50:1	0.5	0.5	SMA Male	SMA Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-3-X	0.01	18.5	1.40:1	0.5	0.5	SMA Male	SMA Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-4-X	0.01	18.5	1.50:1	0.5	0.5	SMA Male	SMC Male	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-5-X	0.01	26.5	1.50:1	1	0.5	SMA Male	SMA Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-6-X	0.01	26.5	1.60:1	1	0.5	SMA Male	SMC Male	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-9-X	0.01	12.4	1.40:1	0.5	0.5	SMA Male	BNC Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-10-X	0.01	12.4	1.40:1	0.5	0.5	N Male	BNC Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-11-X	0.01	18.5	1.50:1	0.5	0.5	SMA Male	BNC Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-12-X	0.01	18.5	1.50:1	0.5	0.5	N Male	BNC Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-14-X	0.01	40	1.80:1	1	0.4	K Male	SMA Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-15-X	0.01	4	1.20:1	0.5	0.5	SMA Male	SMA Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZD-16-X	0.01	50	2.00:1	1	0.4	2.4mm Male	SMA Female	4-6 Weeks	Specify Positive or Negative Polarity when submitting.	Request Quote
ZDI-12	0.01	12.4	1.25:1	0.3	0.5	Pin	Pin	4-6 Weeks	N/A	Request Quote
ZDI-18	0.01	18.5	1.25:1	0.5	0.5	Pin	Pin	4-6 Weeks	N/A	Request Quote
ZDI-26	0.01	26.5	1.25:1	1	0.5	Pin	Pin	4-6 Weeks	N/A	Request Quote

Full Product Line Specifications

Parameter	Value
Detector Type	Zero-bias Schottky diode
Frequency Range	10 MHz (0.01 GHz) to 18.5 GHz
Flatness	+/- 0.5 dB
Low Level Sensitivity	0.5 mV/uW
VSWR	1.40:1 to 1.50:1 (model-dependent)
Input Connector	SMA Male
Output Connector	BNC Female (ZD-11) or SMA Female (ZD-3)
Output Polarity	Positive or negative; specify at time of order
DC Bias Required	None
Lead Time	1 to 2 weeks

Where MCLI Zero-Bias Diode Detectors Are Used

Transmitter Power Monitoring

Detectors placed at the coupled port of a directional coupler sample a small fraction of forward transmit power and convert it to a DC voltage for monitoring by a control circuit. Zero-bias detectors simplify this function by eliminating the need for a bias supply at the detector location, which is particularly useful in distributed antenna systems and remote transmitter installations where adding a DC supply at the detector point is impractical.

Receiver Signal Presence Detection

Radar and EW receivers use detectors in the signal chain to sense the presence of an incoming signal and trigger downstream processing. Zero-bias detectors operating in the square law region produce a video output voltage proportional to RF input power, enabling the receiver to distinguish signal from noise and initiate signal processing on detected events without active bias circuitry in the RF path.

AGC and Leveling Feedback

Automatic gain control loops and leveling circuits require a detected voltage that tracks RF signal level to drive the control input of a variable attenuator or gain stage. Zero-bias detectors provide this feedback voltage across the full 10 MHz to 18.5 GHz operating range with +/- 0.5 dB flatness, keeping the detected voltage proportional to actual RF power across the band.

Frequently Asked Questions: Zero-Bias Diode Detectors

How Does a Zero-Bias Schottky Diode Detector Work Without DC Power?

A Schottky diode has a lower forward voltage threshold than a standard PN junction diode, low enough that moderate RF signal levels provide sufficient energy to forward bias the diode and produce rectified current without any externally applied bias voltage. The resulting DC current flows through a load resistor to produce the video output voltage.

At very low RF input power levels, the diode operates in the square law region where output voltage is proportional to input power. At higher power levels, it transitions to a linear detection region. Zero-bias operation is possible because Schottky diodes are specifically selected for low threshold voltage and high sensitivity.

What Does Output Polarity Mean and How Do I Select It?

Output polarity describes whether the detected video voltage is positive or negative relative to ground for a given RF input level. Some control circuits and ADC inputs require a positive voltage, others a negative voltage. MCLI’s zero-bias detectors are available in both polarities; specify positive or negative polarity when placing your order. If you are unsure which polarity your circuit requires, check the input range and reference configuration of the downstream circuit that will process the detected voltage.

What Is Low Level Sensitivity and How Does It Affect System Design?

Low level sensitivity is expressed in millivolts per microwatt and describes how much output voltage the detector produces per unit of RF input power at low signal levels. MCLI’s detectors provide 0.5 mV/uW sensitivity. Higher sensitivity means the detector produces a usable output voltage at lower RF input power levels, which matters in receiver applications where detected signal levels may be near the noise floor. If your application requires detection of very low power signals, confirm that the detector’s sensitivity is sufficient to produce a video output above the noise floor of your baseband processing circuit.

Can the Detector Output Connect Directly to a Data Acquisition System?

Yes, provided the data acquisition system input impedance and voltage range are compatible with the detector’s output. The BNC Female output on the ZD-11 model is well suited for direct connection to oscilloscopes, power meters, and data acquisition systems using standard BNC cabling. The SMA Female output on the ZD-3 model suits integration into RF assembly housings where SMA connections are preferred throughout. Contact MCLI if your application requires a specific output impedance or voltage range not covered by the standard models.