Product Details

Delay line Generators


RF Delay Line Generator:- About, Design, Types, Application, and Selection Specifications:

A delay line is a device or an instrument that delays the input RF signal by a certain specified time to the output port. 

  • RF Delay Lines are used in radar testing, simulation of communication and telemetry channels, testing of signal processing units etc. 

For very short fixed delays infraction of nanoseconds range requirements delay lines are available as an RF component and RF delay lines are available as an instrument, (which can generate fixed or variable delay) for delay requirements in nano/microsecond range by using coaxial or optical cable loops.

To learn more about RF and Microwave communication systems, we recommend you to check the following books.

To understand the delay lines in a better way, we recommend understanding the following modules.


In this RF and Microwave Delay line article, we will cover,

  • What is RF and microwave delay lines?
  • Types of RF delay lines?
  • Applications of RF delay lines?
  • What are the specifications that need to consider for RF delay lines?
  • RF and microwave delay line manufacturers.

Types of RF Delay Line:

RF delay lines are basically of fixed and variable types. Fixed delay lines are of Coaxial through line packages and the variable delay lines are classified on the base of cables used to generate the delay. 

Coaxial Trough Line fixed delays:

Coaxial Trough dealy Line is an RF component, which will generate a fixed delay between the input and the output signal without varying the other characteristic of the RF and microwave signal.

RF Co-axial cable delay lines:

RF Co-axial cable delay lines are manufactured using the co-axial cable assembled in a box or a pool with the required length for the delay. The input signal will pass through the full length of the cable and the output will be available at the other end with the required delay. This can be suitable for the short delays as the size of the cable assemble will be bulky for the larger delays.

RF over Fiber fixed or Variable delay lines:

RF over Fiber delay lines can be configured for the comparatively higher delay with multiple time delay segment values ( Variable delays). This type of delay line is manufactured using the loop of optical cables assembled in a box or the pool as per the delay requirements.

  • For the variable RF delay lines, additional switching and control circuits will be provided to switch the RF signals among the different optical loops to get the desired RF signal delay. 

The advanced versions of delay line generators will have the display to display the Delay values and a front or remote panel to set the delay increments locally or remotely using the communications interface.

Features & Options available with advanced delay line generators:

  • Fixed or Variable delay setting Options.
  • High Isolation among the channels.
  • Local or remote monitor and controls features.
  • Internal amplifiers with gain control options.
  • Fast delay setting speed. 

Design and Application

RF Delay line Design concept?

Several materials like low-density dielectric material, fibre optical cables, RF coaxial cables are used to design and achieve the required delays. The design engineer can choose the best method for delaying the signals by considering the factors like frequency range, the delay needed, and the size and cost.

Delay using dielectric material:

Fixed delay lines can be constructed using low-density dielectric material which offers lower insertion loss, a wider temperature range. These design concepts can be used only for the development of fixed RF delay lines in low-frequency ranges.

  • Dielectric material RF delay lines are available as RF components with connectors or surface-mount packages and offer lower fixed delays. 

Delay line using coaxial cable:

Delay in RF signal accrued when RF signal passes through the Coaxial cable to the other end of the assembly. The signal delay for the coaxial cable lines can be easily calculated from the propagation of the signal through the cable. These co-axial cables can be used to make a delay line assemble. 

  • Coaxial cable delay lines offer good electrical performance, easily manufactured for the lower delays and frequency range. However coaxial semi-Rigid Cable delay lines are large and introduce high insertion loss, especially for higher frequencies and longer delays in comparison with the optical delay line generators.

Optical delay lines:

Optical delay lines are the ideal design concept for the higher frequency and larger delays with the comparatively small form factor. In optical delay lines, first, the RF signal will convert to the corresponding optical signal using an RF over Fiber (RFoF) converters. These optical signals will propagate over the loop of optical cables with length as per the delay requirements and at the other end received optical signal with propagation delay will be converted back to RF signal using optical to RF converters. 

For the variable delay requirements, additional switching and control circuits will be implemented and switch the signal among various respective optical loops for the desired delays. 

  • The advantage of the optical delay line unit is lower insertion loss and size. Due to the additional requirements of RF over fibre converters, the cost of these designs will be higher than the other concepts.

Latest optical delay lines have options to configure as a variable or a fixed delay line and have the scalable capability to the customers’ delay requirements.

Applications of RF Delay Lines:

RF Delay lines are essential hardware required for the time delay generators as part of systems test and evaluation of the actual scenarios of wireless and wired communication systems.

The additional features of the latest delay lines generators like inbuilt Low Noise Amplifiers, Automatic Gain Control, Remote monitoring and Control help for the automated accurate evaluation of electronic warfare and communication systems. A few of the industrial applications are listed below.

Industrial Applications:

  • Test & Calibration of EW systems in Lab.
  • Checkout testing of satellite payloads.
  • Radar Target Simulation and testing.
  • Software Defined Radio Signal Processing.
  • Phase Noise Testing of communication systems. 

Basics & Selection Feature

Main specifications need to consider in the selection of RF Delay lines: 

When selecting RF delay lines for the test, simulation and calibration requirements, it is necessary to consider the following specifications for the perfect evaluation of the device under test.

Frequency range: 

Delay lines are generally optimized for a specific operating range of frequency. The frequency range indicates the frequency band over which RF delay lines will generate the required delay by meeting all other electrical characteristics.

RF Delay: 

RF Delay is the delay in micro to nanoseconds that accrued when the RF signal passes over the delay line. In variable delay line generators, RF delay can be programmed over the local or remote control units.

Insertion Loss (dB) of delay line:

Insertion Loss of the delay line indicates the loss in the amplitude of the RF signal after passing the signal over the RF delay line. Lower the insertion loss better the device. In general optical delay, lines offer lower insertion loss. 

Power Level of RF Delay line: 

The power level of the delay line indicates the input power level of the RF signal that the delay line can handle. Need to select the delay lines which can handle higher power than the expected power from the RF system.

Monitor & Control Capability of RF delay lines:

Monitor and Control (M&C) capability is required especially for the variable delay lines for setting the delay requirements as per the test requirements. Most of the variable delay lines are available with Local via Front Panel monitor and control feature and remote control using SCPI commands or via Real Term GUI Interface from the PC over Ethernet.

Package and RF connectors:

The package of the RF delay line needs to select as per the size and form factor requirement of the testing. Optical RF delay lines are available in different packages like modules, 19-inch rack assembles or as a benchtop unit based on the delay requirements. 

RF connectors can be easily configured for the delay line generators as per the requirements. Need to select the package and RF connector to optimise the test requirement, by avoiding the additional requirements of the RF adapters to connect to the DUT.


RF delay lines are one of the prime required test instruments for the EW and satellite communication system testing. Now there are many manufactures are available that can offer co-axial and optical RF delay lines with different advanced options like remote interface, very fine-tuning delay step size etc. 

  • Below are the list of top RF and microwave delay line manufacturers for designers to select a suitable product as per the requirement.

If you would like to add any further details about RF and microwave delay line generators to this article, please feel free to contact us over the contact page or the article submission page.

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