--- title: How to Create an RF Diplexer Design description: Various types of RF diplexers require a filter to provide the different transmitter and receiver signals to be separated according to frequency allocation. image: https://blog.epectec.com/hubfs/Blog/rf-frequencies.jpg --- [![Epec Engineered Technologies](https://www.epectec.com/images/logo.png "Epec Engineered Technologies")](https://www.epectec.com/) [![Epec Engineered Technologies](https://www.epectec.com/images/logo.png "Epec Engineered Technologies")](https://www.epectec.com/) - [Articles](https://www.epectec.com/articles/) - [Blog](https://blog.epectec.com/) - [Webinars](https://www.epectec.com/webinar/) - [Videos](https://www.epectec.com/videos/) - [Case Studies](https://www.epectec.com/case-studies/) - [News & Events](https://www.epectec.com/news/) - [Customer Portal](https://system.netsuite.com/c.406760/site/NSlogin.html) - [About](https://www.epectec.com/about/overview/) - Back - [Company Overview](https://www.epectec.com/about/overview/) - [Our History](https://www.epectec.com/about/our-history/) - [Culture](https://www.epectec.com/about/culture/) - [Industries Served](https://www.epectec.com/about/industry/) - [Acquisitions](https://www.epectec.com/about/acquisitions.html) - [Operations](https://www.epectec.com/operations/) - Back - [Operational Excellence](https://www.epectec.com/operations/) - [Quality Philosophy](https://www.epectec.com/operations/quality-philosophy.html) - [Quality Assurance Process](https://www.epectec.com/operations/quality-assurance-process.html) - [Global Operations](https://www.epectec.com/operations/global-operations.html) - [Logistics & Supply Chain](https://www.epectec.com/operations/logistics-and-supply-chain.html) - [Inventory Stocking](https://www.epectec.com/operations/inventory-stocking.html) - [Approvals](https://www.epectec.com/operations/approvals.html) - [ITAR Registered](https://www.epectec.com/operations/itar-registered.html) - [Engineering](https://www.epectec.com/engineering/overview/) - Back - [Engineering Overview](https://www.epectec.com/engineering/overview/) - [Engineering Support](https://www.epectec.com/engineering/support/) - [Design Services](https://www.epectec.com/engineering/design-services/) - [EpecDFx™](https://www.epectec.com/engineering/epecdfx/) - [Free DFM File Check](https://www.epectec.com/engineering/free-dfm.html) - [PCB Impedance Calculator](https://www.epectec.com/engineering/impedance-calculator.html) - [Products](https://www.epectec.com/products/) - Back - [Overview](https://www.epectec.com/products/) - [Battery Packs](https://www.epectec.com/batteries/) - [Flex & Rigid-Flex PCBS](https://www.epectec.com/flex/) - [Cable Assemblies](https://www.epectec.com/cable-assemblies/) - [Printed Circuit Boards](https://www.epectec.com/pcb/) - [CNC Machining](https://www.epectec.com/cnc-machining/) - [User Interfaces](https://www.epectec.com/user-interfaces/) - [Flexible Heaters](https://www.epectec.com/flexible-heaters/) - [EC Fans & Motors](https://www.epectec.com/fans-motors/) - [Design Guides](https://www.epectec.com/guides/) - [Design Guides](https://www.epectec.com/guides/) - Back - Resources - Back - [Articles](https://www.epectec.com/articles/) - [Blog](https://blog.epectec.com/) - [Webinars](https://www.epectec.com/webinar/) - [Videos](https://www.epectec.com/videos/) - [Case Studies](https://www.epectec.com/case-studies/) - [News & Events](https://www.epectec.com/news/) - [Customer Portal](https://system.netsuite.com/c.406760/site/NSlogin.html) - [Contact Us](https://www.epectec.com/contact/) - Back - [Contact Information](https://www.epectec.com/contact/) - [Our Sales Team](https://www.epectec.com/contact/our-sales-team.html) - [Office Locations](https://www.epectec.com/contact/office-locations.html) - [Career Opportunities](https://www.epectec.com/contact/career-opportunities.html) - [InstantPCB*Quote*™](https://www.epectec.com/instantpcbquote/) - Back - [Overview](https://www.epectec.com/instantpcbquote/) - [Login](https://secure.epecpcb.com/epec/) - [Register](https://secure.epecpcb.com/epec/index2.jsp) - [Home](https://www.epectec.com/) - [Blog](https://blog.epectec.com/) - How to Create an RF Diplexer Design Share This Page: [LinkedIn](https://blog.epectec.com/#linkedin) [X](https://blog.epectec.com/#x) [Facebook](https://blog.epectec.com/#facebook) [Email](https://blog.epectec.com/#email) # How to Create an RF Diplexer Design [![Mark Stanley](https://blog.epectec.com/hubfs/Blog-Authors/mark-stanley.jpg "Mark Stanley")](https://blog.epectec.com/author/mark-stanley) Written by [Mark Stanley](https://blog.epectec.com/author/mark-stanley) Posted on October 13, 2017 at 1:52 PM ![Mark Stanley](https://blog.epectec.com/hubfs/Blog-Authors/mark-stanley.jpg "Mark Stanley") - [Tweet](https://twitter.com/share) The typical use of a diplexer (three-port device) enables source transmitters operating on two separate frequencies to use the same antenna. In other applications, the diplexer allows a single antenna to transmit and receive on discrete frequencies. Additionally, a diplexer will provide the ability for an antenna to transmit and receive simultaneously. In all cases, the diplexer's ability to reject or isolate these two signals despite the common port they share is what makes it such a special device. This is achieved within the diplexer by using high-pass and low-pass filters connected to a common input port that combine signals to or from an antenna while isolating the two independent signals. [![Check Out Our Free Ebook on Top 5 Advantages of Distributed Element Circuits!](https://no-cache.hubspot.com/cta/default/707152/9a921cd8-8def-4df7-92c8-d3a618465ac6.png)](https://cta-redirect.hubspot.com/cta/redirect/707152/9a921cd8-8def-4df7-92c8-d3a618465ac6) ## Basic Diplexer Concepts While there are [various types of RF](https://www.epectec.com/rf-products/types-of-rf-filters.html) diplexers, all designs require the use of a filter. The discreet filter design provides the different transmitter and receiver signals to be separated according to each specific frequency allocation. Band pass filters can be utilized but the best rejection is realized through the use of a low pass and a high pass filter. Due to this configuration, two things occur: all signals with frequencies below the cutoff frequency of the low-pass filter are directed to port 2 and all signals above the cutoff frequency of the high-pass filter are directed to port 3. Since there is no path between ports 2 and 3, signals that pass through the low-pass filter will not be able to pass through the high-pass filter and vice versa. The additional benefit of the low/high pass diplexer is that the line or load impedance remains matched to the internal impedance of the receiver or transmitter; it remains constant despite the load impedance connected to the other port. ![Basic Concept of a High/Low Pass Filter Diplexer](https://blog.epectec.com/hs-fs/hubfs/Blog/basic-concept-of-a-high-low-pass-filter-diplexer.jpg?width=550&name=basic-concept-of-a-high-low-pass-filter-diplexer.jpg "Basic Concept of a High/Low Pass Filter Diplexer") *Basic Concept of a High/Low Pass Filter Diplexer* ## Diplexer Requirements When designing an RF diplexer there are many factors to consider. Of the most critical is the degree of isolation or rejection required between the high and low frequency transmitter/receiver ports. The lowest diplexer performance envelope is required when a diplexer is used in a receive mode only, for example when TV and FM signals are combined. The rejection requirement is low, perhaps 15dB of rejection, so a fairly simple filter set would provide adequate isolation to ensure the receivers see the correct impedance and low insertion loss. A step up in performance is required where the diplexer is used in a transmit mode only. It is important to minimize the transmittedpower from one source from being fed back to that of the second source. Any power that is allowed back into the output of an amplifier or transmitter will likely cause intermodulation distortion (IMD) and cause interference. While it is important that each amplifier sees the correct impedance individually, it is even more important that the port 2 transmitter does not affect the impedance seen by the transmitter on port 3. In this case, isolation levels of 40-50dB between the transmitter ports may be necessary. The highest performing diplexer application is where one port is used for transmitting when the other port is being used for receiving in a simultaneous mode. Extremely high levels of rejection are required between the ports to ensure that the minimum level of the transmitter power is fed back to the receiver. If high levels of the amplifier signal reach the receiver, damage can occur. The levels of isolation required for these types of applications may reach 100dB. ![Example of Radio Frequencies](https://blog.epectec.com/hs-fs/hubfs/Blog/rf-frequencies.jpg?width=640&name=rf-frequencies.jpg "Example of Radio Frequencies") *Example of Radio Frequencies* ## Band Pass Filters Where narrow bandwidth diplexers are specified, it is possible to create a design using band-pass filters. This configuration can be used where a wide bandwidth is not required on a transmit and/or receive port. As a commercial example for use of this type of diplexer are cellular repeater applications that receive on one channel and simultaneously transmit on another. [![Need Help with a Custom Design? Get Our Engineers Involved Early. Request Design Support Today!](https://no-cache.hubspot.com/cta/default/707152/cacc4ecf-e651-4184-b45f-16aa1ee289ed.png)](https://cta-redirect.hubspot.com/cta/redirect/707152/cacc4ecf-e651-4184-b45f-16aa1ee289ed) ## Summary While diplexers are used in a broad range of service applications, they are a critical piece of hardware. Military communication antenna systems and cellular transmissions, though very different, would be significantly more complicated without the use of a diplexer. Without the ability to allow antennas to be shared by multiple transmitters, most of the existing broadcast and communication systems as we know them today would be more expensive and less efficient. --- ## Key Takeaways - **Diplexers enable shared antenna use:** RF diplexers allow two transmitters, or a transmitter and receiver operating on different frequencies to share a single antenna, optimizing system design and saving space. - **Filter design is crucial for signal separation:** Effective diplexer performance depends on low-pass and high-pass filter design, which ensures proper signal routing while preventing unwanted interference between ports. - **Isolation levels vary by application:** Diplexer rejection requirements differ significantly depending on the use case: from 15dB in receive-only applications to 100dB in simultaneous transmit/receive setups where receiver protection is critical. - **Impedance matching enhances performance:** A well-designed diplexer maintains matched impedance across all ports, preserving signal integrity and minimizing insertion loss regardless of load conditions. - **Band-pass filters are ideal for narrowband systems:** In applications like cellular repeaters, where only narrow frequency bands are used, band-pass filter diplexers offer a more efficient solution by focusing filtering only on necessary frequencies. - [Tweet](https://twitter.com/share) Topics: [Product Design](https://blog.epectec.com/topic/product-design), [RF Products](https://blog.epectec.com/topic/rf-products) --- [Next](https://blog.epectec.com/suspended-substrate-stripline-vs-lumped-element-rf-filters) | [All posts](https://blog.epectec.com/all) | [Previous](https://blog.epectec.com/the-pcb-jump-scoring-process) [![New Call-to-action](https://no-cache.hubspot.com/cta/default/707152/5927498e-e238-4f6f-90da-2d00e4014239.png)](https://cta-redirect.hubspot.com/cta/redirect/707152/5927498e-e238-4f6f-90da-2d00e4014239) ## Leave a Comment --- ## Related Posts --- ### Recent Posts --- ### Posts by Topic - [Printed Circuit Boards (159)](https://blog.epectec.com/topic/printed-circuit-boards) - [Product Design (133)](https://blog.epectec.com/topic/product-design) - [Battery Packs (119)](https://blog.epectec.com/topic/battery-packs) - [Cable Assemblies (99)](https://blog.epectec.com/topic/cable-assemblies) - [Flex & Rigid-Flex PCB's (93)](https://blog.epectec.com/topic/flex-rigid-flex-pcbs) - [Electronics Industry (61)](https://blog.epectec.com/topic/electronics-industry) - [User Interfaces (54)](https://blog.epectec.com/topic/user-interfaces) - [Quality Solutions (33)](https://blog.epectec.com/topic/quality-solutions) - [Flexible Heaters (30)](https://blog.epectec.com/topic/flexible-heaters) - [Events, Training, and Support (9)](https://blog.epectec.com/topic/events-training-and-support) - [RF Products (7)](https://blog.epectec.com/topic/rf-products) - [CNC Machining (3)](https://blog.epectec.com/topic/cnc-machining) - [Fans & Motors (1)](https://blog.epectec.com/topic/fans-motors) See All --- --- ### Need Help with A Project? 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