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Hi-Rel Cable Overview

Courtesy of Pasternack : Hi-Rel Cable Overview

Increasing reliance on electronic devices for industrial, aerospace, and military applications compels manufacturers of RF/microwave cable assemblies to offer cables that exhibit high reliability in many types of environments and operating conditions. Some areas of applications that require Hi-Rel components include space, military and defense, test and measurement, wireless mobile communications, automotive, medical, and other industrial applications.

What is High Reliability?

Hi-Rel means “high reliability” which, one would assume, is based upon a reliability measure and it might, depending upon the device or application, but for Hi-Rel coaxial cables reliability can also be gaged by how the cable measures up to standards.  As reliability is thought of as a measure of consistency or repeatability, for coaxial cable, not only do you want your assembly to perform as intended, or accurately, you would want it to perform this way every time. Unfortunately, Hi-Rel coaxial cable is rated differently depending on its application in a particular industry.  Commercial, automotive, U.S. military, or European Union industries have different standards with ranges of acceptable conditions which makes comparison of cables or devices in terms of “Hi-Rel” somewhat inadequate.

Keep in mind, standards are written as “minimum specifications” for components and systems providing a minimum performance level for cable assemblies. Competition in the industry compels manufacturers to make high quality cables that outperform the standards in order to have an advantage over competitors. In other words, these standards allow manufacturers to make cables that are compatible with other cables but have other advantages, either in performance, installation or cost.  Many think industry standards are mandatory but standard compliance is a voluntary, rational approach to coaxial cable design and manufacturing that allows interoperability, upgradability, and cost savings for communication systems.

In the RF industry, reliability refers to an accepted level of performance based on typical usage, without degradation or loss in performance for the lifetime of the cable. In reality, the reliability of a cable assembly may related to one or several performance characteristics which can differ from one application to another when one parameter or the other is performing well for one application but not another. Yet consumers rely on reliability – it is crucial for maintaining service in cellular communications network, in protecting national interests, and in emergency services.  Hi-Rel cable assemblies are used in test-and-measurement facilities where the accuracy and reliability is part of the quality assurance to validate the performance of DUT.

What Factors Constitute Hi-Rel?

Operating Environment

The operating environment of an RF cable assembly has a tremendous impact on its optimum reliability. Unwanted interference from a cable assembly lacking proper EMI shielding would not be acceptable in a surveillance or radar application. High quality materials like low-loss dielectrics or precious metal platings do not necessarily ensure high reliability.  Design for application is key and design testing is a must in the R&D phase of product development. Hi-rel cable assemblies are designed for extreme temperatures, harsh environments, and excessive stress where performance is paramount. The production process of a hi-rel component involves detailed handling procedures, additional conformance testing and inspection to ensure that the product has superior performance and quality to ensure optimum performance and a high survival rate under extreme environments.  These cable assemblies are subject to thermal and mechanical shock tests, exposed to moisture and humidity, and high temperatures to test whether they can withstand the harsh conditions where they are expected to perform.

Testing

Testing and measurements are critical for assessing and determining product reliability. Manufacturers of high-reliability cable assemblies, to be competitive, must embrace new concepts and test these designs to bring innovation to the market.

Measurement parameters include insertion loss, return loss (VSWR), phase stability, and thermal cycling, to name a few. Regular and repeatable measurements and analysis of test results are crucial in the product development process. Computer simulation software can provide a new basis for development of new products and high-performance test systems with reliable (accurate and repeatable) test data feedback to refine the development process. On a final note, be mindful that, depending upon the testing process, a cable assembly or part of the assembly may be referred to as Hi-Rel without being tested against the quality standards.

RF Interconnect Insights for High Speed Digital Signals and Data Communications

RF Interconnect Insights for High Speed Digital Signals and Data Communications Part 2

Courtesy of Pasternack : RF Interconnect Insights for High Speed Digital Signals and Data Communications Part 2

Introduction

In the previous blog, Part 1 of “RF Interconnect Insights for High Speed Digital Signals and Data Communications” two part series, the concept of RF interconnect used in high speed digital applications was introduced. In this section, more insights will be provided on intermodulation distortion concerns and other challenges with trends in high speed digital data transfer and near-future wireless communications that rely on digital signals.

Interconnect Intermodulation

When it comes to reducing interference. some RF connectors are better than others and, as passive intermodulation, or PIM, is a major cause of signal degradation. Especially considering the latest high speed digital data communications for cellular and wireless backhaul, the high peak power ratios make PIM a substantial consideration. PIM is detected as unwanted signals created by the mixing of two or more strong RF signals in a nonlinear device, as a loose or corroded connector, or by rust on the interconnect device.

Unfortunately, the source of PIM isn’t always so easily explained, and for high speed digital data communications, can be a product of material use, cable design, connector design, connector material matchup, connector tightness, and other factors. PIM becomes a problem when, for example, PIM is generated, it increases the noise floor and interferes with wireless device signals leading to access failures, slower data rates, and dropped calls. Conditions that lead to PIM:

<  poor cable termination

damaged or loose connector

over-torqued or broken connector

metal flakes or debris inside the connector or inside the cable

Proper termination on the cable and the connector and proper torquing techniques when installing an interconnect to the interface can greatly reduce the amount of PIM.

Interconnect Challenges

As  RF/microwave technologies are increasingly used in the high speed digital data exchange world, the mix of connector and cable technologies will necessarily become more complex. In the next generation of wireless technology, higher data rates and greater demand for high integrity interconnect will require higher performance capabilities in RF interconnection–with proposed 5G and wireless communication frequencies reaching almost 80 GHz, this means that the digital signal speed and density that drives these communications will also be unprecedented speeds. To meet these high frequency and performance needs, RF interconnects product design and manufacturing is expanding to improve interface compatible designs that are tested and qualified per EIA-364 standards with high GHz performance, high durability cycles.

With high speed digital signals, challenges associated with digital systems such as clock skew, jitter, power consumption, bit error rate (BER), and signal integrity using conventional copper interconnect technology may not meet the needs for current and future Very Large Scale Integration (VLSI) circuits. In order to address these concerns and improve performance to meet high speed demands, adopting RF/wireless interconnects in future on-chip and board-level clock distribution networks may offer desired performances for future high speed clock distribution network operating in multi GHz frequencies.

To learn more about Pasternack’s diverse line of coaxial RF cables, visit:

https://www.pasternack.com/cable-assemblies-category.aspx

RF Interconnect Insights for High Speed Digital Signals and Data Communications Part 1

Courtesy of Pasternack : RF Interconnect Insights for High Speed Digital Signals and Data Communications

RF high speed interconnection is used in many electronic products where signal transmission quality is a critical factor in applications using high speed digital signals. An RF interconnect is the complete path that connects one device to another; RF-interconnect structures include coaxial cable assemblies, microstrip transmission lines, and waveguides with RF connectors, adapters, and attenuators. Many wireless communication systems require numerous RF interconnect paths such as in the case of sensitive sensor modules, RF modules to antennas, and between networked devices. As RF hardware is increasingly digitized, there are more applications that require high speed digital signals for data transmission between RF hardware. Also, the latest high speed digital technologies also leverage RF coaxial transmission lines and microstrip (stripline) transmission lines for connector interfaces, cabling, and chip fan-out.

Achieving maximum performance from RF communication systems and high speed digital data transmission requires close attention to interconnect technology, circuit-to-circuit interconnections, and circuit design. RF interconnectors can perform to hundreds of gigahertz (Gigabits per second) and are used in a variety of high speed digital applications, such as communication devices, high performance computing, and sensors. There are of numerous types of RF interconnect used with high speed digital signals, such as BNC, CX/MMCX, SMT/SSMT, SMA/SSMA, SMB/SSMB, SMC/SSMC, and TNC Connectors, and RF Adapters.

Timing is Everything

Signal timing and the quality of the signal are important concepts in high speed digital designs. A primary concern when designing a digital communication system involves isolating high speed signals, which are more likely to impact or be impacted by other signals, and maintaining signal integrity to ensure a signal reaches its destination. In a communication system, digital signals travel through various interconnections from chip to package, package to RF board trace, and trace to high speed connectors; any electrical discontinuity at the source end, on the transmission path, or at the receiving end, will affect the signal timing and quality.

RF interconnect for high speed digital applications require reasonable isolation and protection from electromagnetic interference. Hence, shielding and connector quality are of great importance. Moreover, many high speed digital applications have high interconnect densities, requiring small pitch distances. Hence, push type connectors and connector assemblies with a multitude of RF connectors, such as pogo-pins and snap-connectors, are common. An important factor to note is that reducing the delay between separate parallel digital signals requires very closely matched transmission line lengths, which is a design challenge considering the complexity of dense digital signal pathways.

Next Blog Preview

In Part 2 of “RF Interconnect Insights for High Speed Digital Signals and Data Communications” we will review concepts, such as intermodulation distortion with high speed digital communications and interconnect challenges with high speed digital applications.

To learn more about Pasternack’s diverse line of coaxial RF cables, visit:

https://www.pasternack.com/cable-assemblies-category.aspx

Coaxial RF Probes

Pasternack Releases Expanded Line of Coaxial RF Probes to 40 GHz with Pogo Pin Design

Courtesy of Pasternack : Coaxial RF Probes to 40 GHz with Pogo Pin Design

Additional RF Probe Models Support Higher Data Rates in Both GS and GSG Configurations

IRVINE, Calif. – Pasternack, a leading provider of RF, microwave and millimeter wave products, has expanded their line of RF coaxial probes into the 40 GHz operating frequency range for use in microwave components, high-speed communications and networking.

Pasternack’s extended line of coaxial RF probes now includes 4 models that deliver 10 dB maximum return loss over the broad frequency range of DC-40 GHz. These probes are offered in GS and GSG configurations with a pitch of 800 or 1500 microns and a 2.92mm interface. They are gold-plated and have compliant pogo pin contacts that allow for a wide range of probing angles. These RF coaxial probes can be used by hand, with or without a probe positioner, and can be cable mounted or mounted with Pasternack’s multi-axis probe positioner. They are ideal for signal integrity measurement, chip evaluation, coplanar waveguide, Gigabit SERDES, substrate characterization and test fixture applications.

“We are excited to offer this unique extension of our already successful line of RF probes. The extended 40 GHz frequency range of these GS and GSG probes will help testers cover a whole new range of applications, including 28 Gbps data channels,” said Dan Birch, Product Manager.

Pasternack’s new expanded line of coaxial RF probes are in stock and ready for immediate shipment with no minimum order quantity. For detailed information on these products, please visit https://www.pasternack.com/pages/rf-microwave-and-millimeter-wave-products/coaxial-rf-probes-and-positioner.html.

For inquiries, Pasternack can be contacted at +1-949-261-1920.

About Pasternack:

A leader in RF products since 1972, Pasternack is an ISO 9001:2008 certified manufacturer and supplier offering the industry’s largest selection of active and passive RF, microwave and millimeter wave products available for same-day shipping. Pasternack is an Infinite Electronics brand.

About Infinite Electronics:
Infinite Electronics is a leading global supplier of electronic components serving the urgent needs of engineers through a family of highly recognized and trusted brands.  Our portfolio brands are specialists within their respective product set, offering broad inventories of engineering-grade product, paired with expert technical support and same day shipping. Over 100,000 customers across a diverse set of markets rely upon Infinite Electronics to stock and reliably ship urgently needed products every day.

Press Contact:
Peter McNeil
Pasternack
17792 Fitch
Irvine, CA 92614
(978) 682-6936 x 1174

Coaxial Connector

Upper Microwave and Millimeter-wave Frequency Coaxial Connector Overview

Courtesy of Pasternack : Upper Microwave and Millimeter-wave Frequency Coaxial Connector Overview

Many coaxial connector types are available in the RF and microwave industry designed for specific purposes and applications with smaller connectors that perform into the GHz and millimeter wave range. Compatibility with other RF microwave components is achieved with universally accepted connector standards so that interconnecting coaxial modules within a system is possible and must retain the coaxial nature of the transmission line with which they are used. As with coaxial cable, impedance, frequency range, power handling, physical size, and cost are the parameters which determine the best type of connector for a given application.

In RF and microwave applications, there are generally three grades of connectors designed for use in production, instrumentation, and metrology. Production grade connectors are low cost simple devices used in components and cables for most common applications. Instrument grade connectors are precision or test connectors the high performance standards of low reflection and good repeatability used in testing and measurement equipment. Metrology grade connectors are high precision connectors with high accuracy and are typically more expensive. Recently, there are more upper microwave and millimeter-wave coaxial cables and connectors being used in prototype and production for military and aerospace applications, which are of a specifically designed nature to meet with the stringent reliability (Hi-rel) standards associated with those industries.

Usually, a connector is identified by its type or the coaxial cable it is connected to along with the term male or female based on design–becoming a connector pair when coupled. A typical connector pairing is reliable from 50 to several hundred cycles depending upon design features and, while two connectors can have identical specifications, a design feature like silver over nickel plating, can yield a measurable difference in performance.

Connector Families and Frequency Limitations

There are several types of RF microwave coaxial connector families. As with coaxial cable lines, the cutoff frequency is a key property of any coaxial cable connector above which the desired TEM mode will no longer be the only mode that propagates. The frequency range of any connector is limited by the propagation mode in the coaxial system. Millimeter-wave coaxial connectors are coaxial connectors for use above 18 GHz.

Connector Type N, BNC and TNC

Developed in the 1940’s, the Type N 50 ohm connector was designed for military systems operating below 5 GHz. The Type N uses an internal gasket with an air gap between center and outer conductor. Later improvements increased performance to 18 GHz but even modern designs begin to mode around 20 GHz producing unpredictable results if used at that frequency or higher. A 75 ohm versions is widely used in the cable-TV industry. The BNC, used in video and RF applications to 2 GHz, uses a slotted outer conductor with a plastic dielectric on each gender connector. At higher frequencies above 4 GHz, the slots may radiate signals up to about 10 GHz. Because the mating geometries are compatible with the N connector, it is possible to temporarily mate some gender combinations of BNC and N. A threaded version, the TNC, helps resolve leakage and stability problems allowing use in applications up to 12 GHz and 18 GHz. The TNC connector is in wide use in cellular telephone RF/antenna connections.

Connector type SMA and SMB Push-On

The SMA, subminiature A, connector uses a 4.2 millimeter diameter outer coax filled with PTFE dielectric with an upper frequency limit ranging from 18 to 26 GHz, depending upon the manufacturer. SMAs are sized to fit a 5/16 inch wrench and will mate with 3.5mm and 2.92mm connectors. The SMB, or subminiature B, is a push-on connectors typically specified for 4 GHz to 12.4 GHz. With frequency demands increasing, these connectors are too large and lack the bandwidth needed for high frequency applications.

Connector type 3.5mm and 2.92mm

These connector types use air dielectric and are compatible with one another and the SMA type. The 3.5 mm connector performs well up to 26 GHz. The 2.92 mm connector performs through 40 GHz.

Connector type 2.4mm and 1.85mm

The 2.4mm and 1.85mm connectors are compatible with each other but not the SMA, 3.5 or 2.92 mm connectors by design, as the less precise connectors can cause irreparable harm to the more expensive and more precise 2.4 and 1.85mm connector.

Connector type 1mm and .8mm

Used for millimeter-wave analysis, these connectors support transmission and repeatable interconnections from DC to 110 GHz.

 

Reference

http://microwave.unipv.it/pages/microwave_measurements/appunti/01b_MM_connectors.pdf

http://www.uniroma2.it/didattica/SMM/deposito/RF_Connectors.pdf

https://www.microwaves101.com/encyclopedias/microwave-coaxial-connectors
Coaxial cables

How High is a Coaxial Cables Max Frequency?

Courtesy of Pasternack : How High is a Coaxial Cables Max Frequency?

Coaxial cable is the most commonly used transmission line for RF and microwave applications, because it provides reliable transmission with the benefits of wide bandwidth and low loss and high isolation. Major manufacturers of transmitting equipment, i.e. radio and TV, radar, GPS, emergency management systems, air and marine craft, use coaxial cables. The uses of coaxial cable apply to any system in which signal loss and attenuation must be minimized. Unlike waveguides, coaxial cable has no lower cutoff frequency but what about its upper frequency?

 

Frequency

Like other parts of the electromagnetic spectrum, radio frequency (RF) is identified by its frequency in Hertz (Hz) or wavelength in meters. An inverse relationship exists between these two concepts such that as frequency increases, wavelength decreases, with the reverse being true as well. The strength of a radio frequency signal is measured in Watts. A frequency band refers to a designated section of the RF spectrum like, for example, the AM and FM band used in radio broadcasting and, within this band, a section of spectrum is referred to as bandwidth. Frequency is identified as the number of reverses or cycles in the flow of alternating current (AC) per second. For example, broadcast stations operate at frequencies of thousands of cycles per second and their frequencies are called kilohertz (kHz); higher frequencies are in millions of cycles per second and are called megahertz (MHz). Radio frequency is the frequency band which is primarily used for transmission of radio and television signals and ranges from 3 MHz to 3 GHz. Microwave frequencies range from Ultra-High Frequency (UHF) 0.3 – 3 GHz, Super High Frequency (SHF) 3 – 30 GHz to Extremely High Frequency (EHF) 30 – 300 GHz.

 

Max Frequency

With some exceptions, most coaxial cables do not have an actual cut-off terms of a specific stop-band frequency but instead use the term cutoff to refer to the highest frequency tested by the manufacturer, or when the frequency reaches a point where the coaxial cable becomes a waveguide and other modes, aside from the transverse-electromagnetic mode (TEM), occur. Hence, a coaxial cable cutoff frequency could be where the coaxial cable remains within specification, or within a reasonable margin to avoid transverse-magnetic (TM) or transverse-electric (TE) propagation modes. Though coaxial cables can still carry signals with frequencies above the TEM mode cutoff, TM or TE transmission modes are much less efficient not desirable for most applications.

 

Cutoff Frequency and Skin-Depth

Two important concepts of note when discussing frequency in coaxial cable are skin-depth and cutoff frequency. Coaxial cable is made up of two conductors, an inner pin, and an outer grounded shield. Skin depth occurs along the coaxial line when high frequencies cause electrons to migrate towards the surface of the conductors. This skin effect leads to increased attenuation and dielectric heating and causes greater resistive loss along the coaxial line. To reduce the losses from the skin affect, a larger diameter coaxial cable can be used but increasing the coaxial cables dimensions will reduce the maximum frequency the coaxial cable can transmit. The problem is that when the size of the wavelength of electromagnetic energy exceeds the transverse electromagnetic (TEM) mode and begins to “bounce” along the coaxial line as a transverse electric 11 mode (TE11), the coaxial cable cut-off frequency is created. Because the new frequency mode travels at a different velocity than the TEM mode, it creates reflections and interference to the TEM mode signals traveling through the coaxial cable. This is referred to as the upper frequency limit or cutoff frequency.

A cutoff frequency is a point at which energy flowing through the EM system begins to be reduced, by attenuation or reflected, rather than passing through the line. TE and TM modes are the lowest order mode propagating on a coaxial line. In TEM mode, both the electric field and the magnetic field are transverse to the direction of travel and the desired TEM mode is allowed to propagate at all frequencies. Higher modes are excited at frequencies above the cutoff frequency when the first higher-order mode, called TE11, is also allowed to propagate. To be sure that only one mode propagates for a clear signal, the signals need to be below the cutoff frequency. Reducing the size of the coaxial cable increases the cut-off frequency. Coaxial cables and coaxial connectors can reach into the millimeter wave frequencies but as the physical dimensions shrink, power handling capabilities are reduced and losses increase.

New Military-Grade RF Cable Assemblies

Pasternack Launches New Military-Grade RF Cable Assemblies with Same Day Shipping

Courtesy of Pasternack : New Military-Grade RF Cable Assemblies

Commercial-Off-the-Shelf MIL-DTL-17 Cable Assemblies Feature Operating Frequencies of up to 12.4 GHz

IRVINE,Calif.– Pasternack, a leading provider of RF, microwave and millimeter wave products, has introduced a new line of military-grade MIL-DTL-17 RF cable assemblies that are ideal for avionics, military electronics, satellite ground stations and autonomous vehicles.

Pasternack’s new series of military-grade cable assemblies consist of 124 basic configurations from six different cable types for a total of more than 700 part numbers that are all available for same-dayshipment. These cables provide operating frequencies of up to 12.4 GHz and VSWRas low as 1.3:1 per connector. They are made from MIL-DTL-17 qualified cable,MIL-PRF-39012 qualified connectors, AS23053 heat shrink and J-STD soldering.The final commercial off-the-shelf (COTS) cable assemblies are 100% tested and includes test report, as well as material lot traceability. They are ideal for defense,aerospace and transportation industries or any place where the cost-of-failureis high.

“We are excited to offer this new line of cable assemblies with such a high service level. In the past, customers would waitweeks or months for cables built to these specifications and with traceability. Now, they can select from hundreds of different COTS solutions and have thecables shipped same-day with test reports,” said Dan Birch, Product Manager.

Pasternack’s new military-grade MIL-DTL-17 cable assemblies are in stock and ready for immediate shipment with no minimum order quantity.For detailed information on these products, please visit https://www.pasternack.com/pages/rf-microwave-and-millimeter-wave-products/mil-dtl-17-high-reliability-rf-cable-assemblies.html.

For inquiries, Pasternack can be contacted at +1-949-261-1920.

Flexible Waveguides

Pasternack Launches a Line of Flexible Waveguides Covering 5.85 GHz to 50 GHz Frequency Range

Courtesy of Pasternack : Pasternack Launches a Line of Flexible Waveguides Covering 5.85 GHz to 50 GHz Frequency Range

New Twistable and Seamless Flexible Waveguide Models Deliver VSWR as low as 1.05:1

IRVINE, Calif. – Pasternack, a leading provider of RF, microwave and millimeter wave products, has introduced a new line of twistable and seamless flexible waveguides operating in the 5.85 GHz to 50 GHz range and cover 10 frequency bands from WR-137 to WR-22. Typical applications include DAS systems, base stations, antennas and test instrumentation.

Pasternack’s newly released line of flexible waveguides is made-up of 78 total models – 39 seamless and 39 twistable. All models operate in the same wide range of frequencies, are available in lengths of 6 to 36-inches and with UG-style square/round cover and CPR-style flanges.

The twistable models are able to twist in different directions, the twist flex material is wound, interlocking brass that allows it to slide on itself. These flexible waveguides provide VSWR as low as 1.05:1, insertion loss as low as 0.15 dB and max power as high as 1.5 kW.

The seamless models are made of a solid piece of brass that is pressed into shape. These flexible waveguides can be used in pressurized applications, deliver VSWR as low as 1.07:1, insertion loss as low as 0.06 dB and max power as high as 5 kW.

“Pasternack’s new family of flexible waveguide components provides designers and engineers with an in-stock source of wide-range, flexible waveguide solutions for their applications up to 50 GHz,” explains Steven Pong, RF Passive Components Product Manager at Pasternack. “Our rapidly expanding, ready-to-ship waveguide family is the largest in the industry and provides customers a comprehensive suite of waveguide solutions”

Pasternack’s new flexible waveguides are in stock and ready for immediate shipment with no minimum order quantity. For detailed information on these products, please visit https://www.pasternack.com/pages/rf-microwave-and-millimeter-wave-products/flexible-waveguides.html.

For inquiries, Pasternack can be contacted at +1-949-261-1920.

About Pasternack:

A leader in RF products since 1972, Pasternack is an ISO 9001:2008 certified manufacturer and supplier offering the industry’s largest selection of active and passive RF, microwave and millimeter wave products available for same-day shipping. Pasternack is an Infinite Electronics brand.

About Infinite Electronics:

Infinite Electronics is a leading global supplier of electronic components serving the urgent needs of engineers through a family of highly recognized and trusted brands, offering a wide portfolio of products ready to ship, and world-class technical support.

Press Contact:
Peter McNeil
Pasternack
17792 Fitch
Irvine, CA 92614
(978) 682-6936 x1174

Beamforming

What is Beamforming?

Courtesy of Pasternack : What is Beamforming?

In array antennas, beamforming, also known as spatial filtering, is a signal processing technique used to transmit or receive radio or sound waves in a directional signal. Beamforming applications are found in radar and sonar systems, wireless communications, and in acoustics and biomedicine equipment. Beamforming and beam scanning are generally accomplished by phasing the feed to each element of an array so that signals received or transmitted from all elements will be in phase in a particular direction. When transmitting, a beamformer controls the phase and relative amplitude of the signal at each transmitter thus creating a pattern of constructive and destructive interference in the wavefront. When receiving, sensors are combined in a way where the expected pattern of radiation is preferentially received.

Beamforming Techniques

Beamforming techniques direct the beam radiation pattern in the desired direction with a fixed response. Array beams can be formed or scanned using either phase shift or time delay systems.

Phase shifting

In narrowband systems, a time delay is known as a phase shift. Beamforming by phase shifting can be accomplished using ferrite phase shifters at RF or IF. Phase shifting can also be done in digital signal processing at baseband. Systems using time delays are preferred for broadband operation because the direction of the main beam does not change with frequency.

Time delays

Time delays are introduced by varying the lengths of transmission lines. As with phase shifting, time delays can be introduced at RF or IF and works well over a broadband, but the bandwidth of a time scanning array is limited by the bandwidth and spacing of the elements. As the frequency of operation is increased, the electrical spacing between the elements increases so that the beams will be somewhat narrower at higher frequencies and, as the frequency is increased further, grating lobes appear. In a phased array, grating lobes are induced when the direction of the beamform extends beyond the maxima of the main beam and the main beam reappears on the wrong side. Elements must be spaced properly in order to avoid grating lobes.

Weights

The weight vector is a vector of complex weights where the amplitude components control the sidelobe level and main beam width and phase components control the angle of the main beam and nulls. Phase weights for narrowband arrays are applied by a phase shifter.

Beamforming Designs

Antennas that are designed to adapt and change their radiation pattern in order to adjust to the RF environment are called active phased array antennas. Examples of beamform designs include the Butler Matrix, the Blass Matrix, and the Wullenweber Array.

Butler Matrix

The Butler matrix uses a combination of 90° hybrids and phase shifters and can cover a sector of up to 360° depending on element design and patterns. Each beam can be used by a dedicated or single transmitter or receiver controlled by an RF switch. Thus controlled, a Butler matrix can be used to steer the beam of a circular array.

Blass Matrix

In broadband operations, the Blass matrix uses transmission lines and directional couplers to form beams by using time delays. A Blass matrix can be designed for use as a broadside beam but can be lossy because of the resistive terminations.

Wullenweber Array

A Wullenweber array is a circular array designed for direction-finding at HF frequencies. This array uses Omni-directional elements or directional elements usually designed with 30 to 100 elements, a third of which are used sequentially dedicated to form a high directional beam. A goniometer is used to connect the elements to the radio with amplitude weighting to control the array pattern and has the ability to scan over 360° with little deviation in pattern characteristics. Time delays are used to form beams radial to the array, enabling broadband operation.

Waveguide Frequencies and Geometries

Courtesy of Pasternack : Waveguide Frequencies and Geometries

Loss, whether due to radiation leakage or conduction resonance, is a common problem in RF microwave transmission lines, especially when high-powered frequency transmissions are involved. The solution? Waveguides.

Waveguide Basics

A waveguide is an electromagnetic feed line used for high frequency microwave signals in high-power transmitters and receivers and is used in radar equipment, in microwave ovens, in satellite dishes or in any RF microwave system where high-power transmission is needed. Waveguides are hollow metallic tubes or light carbon fiber composites constructed with high grade metals like copper, brass, or plated metals. Silver or other plating is used on the inside walls of a waveguide which acts to decrease the resistance loss by shielding and provides efficient isolation between adjacent signals. Transmission lines like microstrip, stripline, or coaxial cable may also be considered to be waveguides and they are usually referred to as dielectric waveguides with a solid center core. However, on high-powered microwave waveguides where the line may get too hot, air in the cavity may be pressurized, recirculated, or a Freon-like gas is used to keep the waveguide cool and also can prevent arcing.

While the disadvantages of using a waveguide include a high production cost, large size and mass of the guide, and the inability of running a DC current alongside the RF signal, the advantages in using a waveguide are that they are completely shielded, high-powered transmission lines that provide good isolation and very low loss that can bend without compromising performance.

Frequencies and Geometries

For the signal to propagate, waveguides need a minimum cross section relative to the wavelength of the signal; these cross sections can be either rectangular, circular, or elliptical. The dimensions of a waveguide determine the wavelengths it can support and in which modes. The lowest frequency range a waveguide will operate is where the cross section is large enough to fit one complete wavelength of the signal. In hollow waveguides, or waveguides using a single conductor, transverse-electromagnetic (TEM) mode of transmission waves are not possible, since Maxwell’s Equations demonstrates that an electric field must have zero divergence and zero curl and be equal to zero at boundaries, resulting in a zero field.

Comparatively, for two-conductor lower frequency transmission lines, like microstrip, stripline, or coaxial cable, TEM mode is possible. In rectangular and circular waveguides, the dominant modes are designated the TE10 mode and TE11 modes.

According to Maxwell’s equations, there are three rules that apply to waveguides:

1 )Electromagnetic waves are reflected by conductors,

2 )Electric field lines that make contact with a conductor must be perpendicular to it,

3 )Magnetic field lines close to a conductor must be parallel to it.

These rules allow for certain modes of propagation such that the TE10 (transverse electric) mode is the mode in which energy propagates in rectangular waveguide. The mode with the lowest cutoff frequency is noted as the dominant mode of the guide.

Because waveguides are the transmission lines for super high frequency (SHF) systems, they must operate with only one mode propagating through the waveguide. Waveguide propagation modes depend on the operating wavelength, polarization, shape, and size of the guide.  Waveguides standards are based on rectangular waveguides and are designed with these characteristics:

one band starts where another band ends, with a band overlapping the two bands in order to allow for applications near band edges,

> the lower edge of the band is approximately 30% higher than a waveguide cutoff frequency thus limiting dispersion and loss per unit length,

>In order to avoid evanescent-wave coupling by way of higher order modes, the upper edge of the band is approximately 5% lower than the cutoff frequency of the next higher order mode,

>the waveguide height is half the waveguide width which allows a 2:1 operation bandwidth – having the height exactly half the width maximizes the power inside the waveguide.

For convenience, our waveguide calculator provides the cutoff frequency, operating frequency range and closest waveguide size for a rectangular waveguide.

Variations on the Waveguide

>The double-ridge rectangular waveguide is a type of waveguide used in RF microwave systems. The ridges in this waveguide design serve to increase the bandwidth but, on the downside, creates higher attenuation and lower power-handling capability.

>The single ridge waveguide is similar to the rectangular waveguide but noted for its large capacitive loading centered on its broad wall.  Compared to a rectangular waveguide, the single ridge waveguide has a lower cut-off frequency with a smaller cross section. However, when compared with the double ridge waveguide, the single ridge yields increased loss and reduced power handling capabilities.

>The slotted waveguide, generally used for radar and similar applications, serves as a feed path with each slot acting as a separate radiator. This antenna structure can generate an electromagnetic wave transmission in a specified narrow and targeted direction.