With so many options available it can be difficult to know which RF connector is the best choice for your antenna application. This whitepaper offers an introductory guide to many of the common RF connector types used in the antenna industry along with their pros and cons, and why using high-quality RF connectors is paramount to antenna performance and ultimately the performance of the entire RF system. This white paper will also touch on some special RF connector designs specified by Southwest Antennas for specific application needs.
Author: 
Adam Krumbein
03/27/2019

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The Importance of RF Connector Selection in Antenna Design Whitepaper

Introduction

There are a wide variety of RF connector choices available on the market today, offering many options for different application needs.

The selection of RF connector represents an important design choice for antennas and other RF systems and components, with many tradeoffs between RF connector size, weight, ruggedness, electrical performance, and mechanical features.

With so many options available it can be difficult to know which RF connector is the best choice for your antenna application. This whitepaper offers an introductory guide to many of the common RF connector types used in the antenna industry along with their pros and cons, and why using high-quality RF connectors is paramount to antenna performance and ultimately the performance of the entire RF system. This white paper will also touch on some special RF connector designs specified by Southwest Antennas for specific application needs.

1. Importance of RF Connector Quality to Antenna Performance

A high-quality RF connector is a cornerstone of any antenna design. The antenna’s RF connector is critically important through its dual functionality as:

  • a mechanical connection between the antenna and its connected RF system; and
  • as the conduit for RF energy flowing between the connected RF system and the antenna elements located within the antenna’s radome.

The RF connector is also the most common failure point in a deployed antenna. While some antenna designs will incorporate additional mounting support structures such as a flange base that can provide additional stability, most deployed omni-directional antennas still rely on the RF connector as their only mechanical connection point.

Overlooking the importance of this during the design phase by choosing an inexpensive or poorly designed RF connector can reduce the overall electrical performance of the final antenna design in unexpected ways, and can render the antenna susceptible to mechanical failure. These failures can not only result in a loss of communication, data, or video at an inopportune time, but can be life-threatening for first responders or military personnel who depend on robust wireless communication networks for their safety and mission success.

It’s also important to select an RF connector that is most compatible with the antenna’s intended application. For example, an SMA connector is generally well-suited for an indoor or commercial RF application, but might not be appropriate for rugged outdoor military use. For applications in extreme environments, it may be worth the size trade-off to use an RF connector that can withstand more abuse, but takes up more room on the face of the radio and weighs more.

Southwest Antennas has invested considerable engineering resources into working with select RF connector vendors in order to specify custom RF connectors that meet our unique requirements for electrical and mechanical performance. We have found many of these considerations may be overlooked when buying low-cost and poor quality RF connectors.

Some of these performance considerations include:

1.1 Crimped vs. Soldered Connection Between RF Connector and RF Cable

Southwest Antennas has standardized on high-quality soldering processes to connect the RF connector to the antenna cable inside of the antenna’s radome. Using this method, the RF connector’s center pin is soldered to the antenna’s electrical center conductor. If done correctly, this method provides a robust, long-lasting physical connection between the two components, especially when using solid cable. Soldered connections are also less likely to deteriorate with use. We also solder the cable ground shield to the connector’s solder shank instead of crimping for best RF performance and mechanical integrity.

RF connectors being prepped and soldered on a Southwest Antennas assembly line
Figure 1: RF connectors being prepped and soldered on a Southwest Antennas assembly line
 

1.2 Stainless Steel Solder Shank

When using a soldered connection between the RF connector and RF cable, the materials to be soldered together must be compatible metals and of good quality. Southwest Antennas has specified a stainless steel solder shank for our RF connectors in order to ensure a rugged and reliable solder joint. The lower right photo in Figure 1 shows solder shank during the soldering process.

1.3 Quality of Plated Finish for External Surfaces

The quality of an RF connector’s plated finish can have a major impact on the environmental survivability of the connector. Southwest Antennas typically specifies a high-quality nickel-silver or black chrome plated finish for most of its standard RF connectors due to its mechanical performance, while standing up well in harsh environments. The center pin surfaces are gold plated.

1.4 Black Chrome Exterior Connector Plating

For military and law enforcement applications where non-reflective, low-visibility product finishes are preferred, Southwest Antennas has worked with its primary RF connector vendors to specify a unique black chrome plating process for the exterior surfaces of the RF connector.

By plating the black chrome finish it becomes part of the RF connector itself and will not chip or wear off easily. Southwest Antennas has specified a low-toxicity process to eliminate chromium and cadmium used in our black chrome plating process, resulting in a safer and more environmentally friendly product.


Figure 2: Example of black chrome plated RF Connectors on Southwest Antennas products. From left to right: SMA(m), TNC(m), Type-N(m)
 

2. Commonly Used RF Connectors

Within the markets for rugged antennas that Southwest Antennas serves, the most commonly deployed RF connectors are SMA, TNC, and Type-N and their variants such as rotating, non-rotating, reverse polarity, and male and female gender options.

These RF connectors are chosen by end users for a wide variety of reasons, but these commonly available RF connectors are inexpensive, can easily handle commonly used operating frequencies and RF power levels, and have high mating cycles:

SMA(m) RF Connector

 

TNC(m) RF Connector

Type-N(m) RF Connector

Pros:

  • 18 GHz typical maximum frequency
  • Small size, ideal when size or weight reduction is a concern
  • High mating cycle life (500+ cycles)
  • Weatherproof when properly mated
Pros:
  • 11 GHz typical maximum frequency
  • Ideal for applications where ruggedness is a concern
  • Weatherproof when properly mated
  • High mating cycle life (500+ cycles)
Pros:
  • 11 GHz typical maximum frequency
  • Ideal for applications where ruggedness is a concern
  • Weatherproof when properly mated
  • High mating cycle life (500+ cycles)

Cons:

  • Not as robust as larger RF connector choices

Cons:

  • Larger than SMA
  • Heavier than SMA

Cons:

  • Larger than SMA & TNC, not all radios will have space available for this connector
  • Heavier than SMA & TNC

 

The following chart outlines common features available on RF connectors used by Southwest Antennas:

3. Other RF Connectors and Application Examples

3.1 Concealment RF Connectors: U.FL / IPEX / MMCX / SMP

For our line of concealment and embedded antennas, very small RF connectors are a necessity. These antennas are designed to be integrated into RF systems, vehicles, UAVs, environmental enclosures, concealments, or other small spaces without being visible or easily detected.

For these applications where an antenna needs to be installed in a tight space, Southwest Antennas relies on micro RF connectors such as U.FL, IPEX, MMCX, and SMP connectors. These RF connectors feature a snap fit connector instead of threads to secure the RF connectors together.

These types of RF connectors have a locking snap ring or detent internally that keeps them mated. These RF connectors can swivel or rotate freely when mated allowing for flexible RF cable routing options.

The tradeoff of this miniature size is reduced durability. These RF connectors cannot survive nearly as many mating cycles as their full-sized counterparts, generally 30 to 100 cycles (part specific). These RF connectors are not waterproof and must be used within a housing that provides protection from outdoor elements.

Example of a Southwest Antennas L/S-Band concealment antenna with surface-mount U.FL RF connector xample of Southwest Antennas S/C-Band concealment antenna with right angle MMCX(m) RF connector

Figure 3: Example of a Southwest Antennas L/S-Band concealment antenna with surface-mount U.FL RF connector

Figure 4: Example of Southwest Antennas S/C-Band concealment antenna with right angle MMCX(m) RF connector

 

Southwest Antennas C-Band concealment antenna with U.FL RF connector. US Quarter shown for scale.
Figure 5: Southwest Antennas C-Band concealment antenna with U.FL RF connector. US Quarter shown for scale.

 

3.2 Recessed TNC and SMA male RF connectors

Southwest Antennas has developed a line of recessed TNC(m) and SMA(m) RF connectors for applications requiring additional protection from water intrusion and the elements. These RF connectors can be hidden within the antenna’s radome or overmolding, enhancing the RF connector’s ability to withstand use in harsh environments.

Due to the nature of being recessed within the antenna, these RF connectors are non-rotating.


Figure 6: Example of our recessed TNC(m) RF connector inside of Southwest Antennas Part # 1055-283 GPS L1/L2 antenna

Figure 7: Example of our recessed SMA(m) RF connector inside of Southwest Antennas Part # 1001-049 C-Band omni-directional antenna
Figure 7: Example of our recessed SMA(m) RF connector inside of Southwest Antennas Part # 1001-049 C-Band omni-directional antenna
 

3.3 Lock-wired RF connector for aircraft / high vibration environments

To provide an extra level of security in high vibration applications, Southwest Antennas has specified a line of RF connectors where fasteners have holes drilled in them and lock wires are used to keep screws from loosening and falling out over time. Commonly used on vehicles, aircraft, and trains, lock wire is secured through special hex screw heads then twisted and secured. The twisting in the wire serves as a visual indicator that the screws are installed properly, and will help keep the screws from backing themselves out when exposed to high vibrations, such as when an antenna is installed on a helicopter.

Figure 8: Example of lock wire used to secure an RF connector to the antenna mounting flange for use in high vibration environments
Figure 8: Example of lock wire used to secure an RF connector to the antenna mounting flange for use in high vibration environments
 

3.4 RF cable assemblies used with RF connectors on antennas

Not all antennas feature an RF connector that is attached directly to the antenna radome. For some applications, an RF cable assembly is utilized when the antenna must be located away from the radio mounting point. If male gender, the RF connector on the end of the RF cable will rotate, allowing the connector to be tightened without twisting the attached RF cable.

Southwest Antennas omni-directional antenna with integrated RF cable assembly and rotating SMA(m) RF connector
Figure 9: Southwest Antennas omni-directional antenna with integrated RF cable assembly and rotating SMA(m) RF connector
 

3.5 Waterproof SMA Connector

For body worn patch antenna applications where the product must survive immersion in water to 65 feet (20 meters), Southwest Antennas designed a unique waterproof black chrome SMA(f) RF connector with custom flange design to fit the thin form factor of the antenna. The SMA(f) RF connector flange design eliminated exposed screw fasteners by using two press fit posts that install through two holes in the radome, with epoxy used to secure and waterproof the RF connector to the radome.

Southwest Antennas C-Band body worn patch antenna with custom waterproof SMA(f) RF connector
Figure 10: Southwest Antennas C-Band body worn patch antenna with custom waterproof SMA(f) RF connector
 

4. RF Connector Basics

4.1 50 Ohm vs 75 Ohm RF Connectors

For most applications involving antennas in the RF & microwave market, RF connectors will have an impedance of 50 Ohms.

50 Ohms was set as an industry standard in the early 20th century as a good compromise between voltage, power handling, and attenuation, making 50 Ohms a safe choice for solid performance in most applications, able to handle relatively high voltage and power requirements without much attenuation.

In some applications, primarily related to video transmission, 75 Ohm RF connectors and cable will be used instead of 50 Ohm. 75 Ohms is a good choice for video transmission applications which tend to require less power but often rely on longer cable runs, where less attenuation is a benefit for transmission distance.


Figure 11: Plotting Power, Voltage, and Attenuation against Impedance

 

It’s important to match impedance and not use 50 Ohm and 75 Ohm products together in a system without an RF impedance matching device. To reduce system cost and complexity, it’s best to match impedance between system components, such as a 50 Ohm antenna and 50 Ohm RF cable, instead of relying on an impedance matching pads which are inherently lossy devices.

Failure to properly match impedance in a system will result in RF energy being reflected back to the RF transmitter, known as a “standing wave”. Standing waves reduce system efficiency and can result in a loss of RF link budget and thus system range, and can in extreme cases damage transmitter components such as power amplifiers if too much energy is being reflected back into the system.

4.2 Rotating vs. Non-Rotating RF Connectors

Non-rotating RF connectors are often used on omni-directional antennas as it makes the product easy to secure without tools and the connection can be made weatherproof or waterproof depending on antenna design once the two RF connectors are securely mated.

As the name suggests, non-rotating connectors have a fixed outer shell which does not rotate. To secure an antenna with a non-rotating RF connector, the entire antenna must be turned as the male and female RF connectors are tightened together. Since an omni-directional antenna radiates RF energy equally 360 degrees around the antenna, the final stopping position of the antenna as the RF connector is tightened down does not matter.

Southwest Antennas strongly suggests utilizing non-rotating RF connectors on omni-directional antennas due to the following considerations:

  • Ideal for omni-directional antennas where antenna direction doesn’t matter once RF connector is fully mated and tightened.
  • Weatherproof or waterproof RF connection, depending on antenna design and mated radio specification. Ideal for use in outdoor environments or tactical applications.
  • Performance improvement (VSWR over frequency, insertion / return loss over frequency) vs. standard rotating connectors.
  • No sand or dust intrusion between collar or connector, due to lack of rotating parts.
  • No noise or rattling due to lack of moving parts.
  • Ease of antenna installation with a single gloved hand, no tools required.

Non-rotating female RF connectors are also commonly found on directional panel and sector antennas, where the connecting RF cable will have a rotating male RF connector. All female RF connectors are non-rotating.

Rotating RF connectors feature an outside shell that can rotate independently from the rest of the RF connector assembly. The shell has threading inside, which tightens the antenna down to the mated RF connector when turned. Rotating RF connectors are useful on RF cables or coaxial goosenecks where it isn't feasible to rotate the whole product to secure one RF connector to another. Since the shell can rotate freely, it is harder to ensure that rotating RF connectors are completely waterproof once connected, unless specialized connectors are used, or additional waterproofing steps are taken. Rotating RF connectors are generally only available in the male gender configuration.

In certain cases a torque wrench is required to properly secure a rotating RF connector, especially for high-frequency applications from 18 to 24 GHz and higher. In these applications over or under-tightening can result in antenna / system performance degradation. Use of a torque wrench ensures a proper installation and tight fit without damage to the RF connector.

Even with low-frequency applications it’s imperative to never tighten a rotating RF connector with a standard wrench or other hand tool. It’s easy to apply too much force and over-torque the connector and break the shell and interior connector components such as the center pin, rendering the antenna unusable. If a tool is needed to secure a rotating RF connector, a torque wrench should be used to tighten the connector to its specified torque rating.

4.3 Right Angle RF Connectors and Adapters

Right angle RF connectors and RF adapters are useful for applications where antenna or RF cable needs to be set perpendicular from the mated RF connector. These are most commonly available in both 45 degree and 90 degree angle options. These should be avoided wherever possible, but if necessary high-performance versions of these adapters should be used in order to minimize insertion loss which can be introduced by inexpensive and poorly designed right angle adapters, lowering system efficiency and RF link margin.

Poorly designed right angle adapters can have high VSWR numbers and sub-standard return loss causing excessive reflected power in the RF adapter.

For better performance where a right angle adapter is needed, Southwest Antennas recommends the use of “radius bend” RF adapters in place of typical right angle RF adapters. The gradual bend helps preserve RF performance and reduces the introduction of excess insertion loss and VSWR into the RF system.

Example of a 90 degree radius bend high-performance right angle adapter
Figure 12: Example of a 90 degree radius bend high-performance right angle adapter

Example of a standard 90 degree right angle adapter with poor RF performance above 1 GHz
Figure 13: Example of a standard 90 degree right angle adapter that may offer poor RF performance above 1 GHz


High-performance right angle adapters can often cost more than the antenna itself, so it pays to plan ahead and avoid adding using these RF adapters unless absolutely necessary.

4.4 Articulating Connectors

RF connectors that can bend up to 90 degrees are available on a limited number of antennas on the market. These are most commonly seen on commercial products such as Wi-Fi routers, where any signal degradation and mechanical weakness would not hinder overall antenna performance, and the antenna must be positioned vertically from a horizontally mounted RF connector. Cellular band antennas for commercial applications are another common use for articulating RF connectors.

Articulating RF connectors use a mechanical knuckle that allows two or three angular positions to be selected. The RF cable travels through the knuckle, which is not weather sealed. This makes articulating RF connectors risky to use for outdoor applications or rugged environments.

These types of RF connectors are used less frequently on antennas designed for harsh environments or tactical deployments, with the RF connector being mechanically weaker due to the additional moving parts inherent to the articulating design.

Figure 14: example of an antenna with articulating knuckle, which can be positioned straight, 45 degrees, or 90 degrees
Figure 14: Example of an antenna with articulating knuckle, which can be positioned straight, 45 degrees, or 90 degrees

 

4.5 RF Connector Genders and Polarity

RF connectors are supplied in two standard gender configurations, male and female. With larger RF connectors such as SMA, TNC, and Type-N, the male and female connectors have threading which secures the connectors together. Smaller micro RF connectors such a U.FL, MMCX, or other press-fit connectors are kept mated with locking rings or detents.

4.5.1 History of Standard Polarity vs. Reverse Polarity

In addition to male and female genders, RF connectors can also be assigned a polarity. For most applications, standard polarity is used. However there are applications where reverse polarity RF connectors are used, generally to restrict the use of non-approved antennas with a radio system as determined by FCC rules and regulations.

A good example of reverse polarity RF connectors can be seen in common use with Wi-Fi routers with external antennas. In order to comply with CFR 47 Part 15, which regulates unlicensed transmitters. In order to comply with Part 15, the antennas and Wi-Fi radio must be certified together and aftermarket antennas are not to be used as they could change how the transmitter emits RF, causing unwanted interference with other devices, such as medical equipment.

Example of a commercial Wi-Fi router featuring Reverse Polarity RF connectors
Figure 15: Example of a commercial Wi-Fi router featuring Reverse Polarity RF connectors to control after-market antenna use

 

In order to prevent consumers from using aftermarket antennas, manufacturers supplied their routers with Reverse Polarity RF connectors. With the proliferation of antenna and RF connector options available today it’s considered at most a basic deterrent as Reverse Polarity RF connectors are now widely available in the market.

4.5.2 Identifying RF Connector Gender and Polarity

RF connectors of either gender or polarity can be identified by looking at several common attributes.

For this example, we’ll look at a male and female TNC RF connector pair:

TNC(m) RF Connector TNC(f) RF Connector

Figure 16: TNC(m) and TNC(f) RF connectors


A standard polarity male TNC connector plug will have an outer shell, with threading on the inside surface of the shell. A male center pin is visible in the center of the RF connector, surrounded by white teflon dielectric insulator material.

Standard Polarity TNC(m) RF Connector Plug

Figure 17: Standard Polarity TNC(m) RF Connector Plug


A standard polarity female TNC connector jack will have the threading on the outside surface of the shell, which will match up with the threading on the inside of the male plug’s shell. On the inside, there will be a female center pin for the male center pin of the plug to mate into.

Standard Polarity TNC(f) RF Connector Jack

Figure 18: Standard Polarity TNC(f) RF Connector Jack


No matter the RF connector gender or polarization, male RF connectors are called plugs, and female RF connectors are called jacks. For threaded RF connectors, a male plug will have the threading on the inside of the shell, and a female jack will have the threading on the outside of the shell.

How to Spot a Reverse Polarity RF Connector

Reverse polarity RF connectors can sometimes cause confusion as they share some similarities with the opposite gender standard polarity RF connector. For example, an RP-TNC(m) RF connector having a female center pin instead of a male center pin, making it resemble a standard polarity female connector. However there are a few quick tips that make spotting a standard or reverse polarity RF connector easy:

  • Reverse Polarity male connectors will always have threading on the inside of the connector’s shell, with a female center pin.
  • Reverse Polarity female connectors will always have threading on the outside of the connector’s shell, with a male center pin.

The only thing that changes from standard to reverse polarity is the gender of the center pin. Standard is male for plug and female for jack. Reverse polarity is male for jack and female for plug.

Standard polarity RF connectors vs reverse polarity RF connectors

5. Conclusion

The choice of RF connector is an important consideration when designing a new antenna or selecting existing antenna products for an existing project. Selecting an RF connector that is appropriate for the application and end-user environment will help mitigate communication problems and time-consuming troubleshooting down the line.

Many factors can determine if an RF connector is the right choice for a given application. In most circumstances, there will be a tradeoff between size, weight, gender, durability, finish, and other RF connector parameters which will influence if a particular RF connector is the best choice for an application. Southwest Antennas advises to carefully consider these tradeoffs before making a final selection of RF connector when undertaking a new design.

 

About Southwest Antennas

Southwest Antennas specializes in the design and manufacture of rugged, high-performance RF and Microwave antennas, accessory products, and customized antenna solutions built for today’s demanding wireless communication environments. Founded in 2005 and headquartered in San Diego, California, Southwest Antennas manufactures over 2,000 antenna products and accessories and offers a full range of technical services for broadcast video, military / defense, law enforcement, homeland security, surveillance, aerospace, oil and gas, and transportation markets.

For more about Southwest Antennas, including technical product information, application examples, RF calculators, and more visit their website at https://www.southwestantennas.com.