Narrowband Vs. Wideband
In Antenna 101: Types and Applications, we briefly introduced narrowband and wideband antennas, as well as enumerate examples of antennas that fall under either category. In this post, we will be making some general comparisons between narrowband and wideband communications.
Narrowband refers to radio communications whose signal bandwidth is within the coherence band of a frequency channel.
This means that in narrowband communications, bandwidth of the signal does not significantly exceed the coherent bandwidth of the frequency channel. Narrowband antennas are typically used in many applications that heavily depend on achieving reliable links in different operating environments, such as in handheld and manpack military radios, as well as ISR. They are also used for other shorter-range, fixed-location civilian applications, such as radio-frequency identification (RFID) and commercial vehicle remote keyless entry (RKE) devices.
Wideband refers to broadband communications that use a relatively wide range of frequencies.
Wideband radio channels’ operational bandwidth may significantly exceed the coherence bandwidth of the channel. Generally, the bandwidths over which wideband antennas operate are higher than 1 octave, whereas narrowband antennas operate over bandwidths lower than 1 octave. In addition to ISR, wideband antennas are suitable for SIGINT and EW. JEM Engineering produces wideband antennas in a variety of forms, including spirals, log-periodic antennas, dipoles and Vivaldi notch elements.
Here are some key differences between the two…
Overall complexity. Narrowband systems are comparatively less complex than wideband systems, which require a more diverse network of circuits and stages.
Frequency spectrum. The frequency spectrum of narrowband antennas is divided into as many channels as the frequency allows. In contrast, for wideband antennas, either a significant portion or the entirety of the frequency spectrum is available to its users.
Channel-to-channel isolation. For narrowband systems, transmitted energy can be concentrated on a smaller portion of the spectrum. As a result, channel-to-channel isolation is higher for narrowband antennas, compared to wideband antennas.
Signal strength. In narrowband systems, signals fade uniformly across frequencies. That being said, adding more frequencies will not strengthen the signal. On the other hand, different parts of wideband signals will be affected by the differing frequencies. In general, the signal weakens as the frequency band widens, making it more difficult to send and detect wideband signals.
Signal interference. One of the main benefits of having a smaller signal bandwidth (narrowband) is that the probability of overlap with interfering signals is relatively lower. The larger the bandwidth (wideband), the higher the probability of interference. This means that wideband communications require more filters in order to achieve a higher signal-to-interference-plus-noise ratio (SINR). A class of signal processing, a filter is a device or process that removes some unwanted “noise” from a signal.
Operating power. Narrowband channels have lower operating power requirements, making them preferable for applications that require transmission of limited information over relatively short distances. The tradeoff for wideband channels being able to carry more information over further distances is that they require significantly higher operating power. Also, a wideband channel’s higher operating power helps overcome the higher levels of signal interference previously mentioned.
Data rate. Narrowband systems typically have lower data rate transmissions, whereas wideband systems support relatively higher data rate transmissions. To put simply, wideband systems allow for faster communication.
In summation, narrowband and wideband antennas are suitable for different applications due to their strengths and weaknesses. Our antenna engineers at JEM Engineering specialize in developing the optimum solution for your intended application.
Dipoles: The Simplest, Most Common Antenna
As it’s name suggests, in its basic form, a dipole antenna consists of two conductive elements, unlike a monopole antenna, which has a single conductive element.
The dipole’s identical conductive elements (usually rods or metal wires) sit on either end of the antenna. While separated by a strain insulator, the center-facing ends of these two antenna sections are connected to a feed line or coaxial (RF) cable, which carries current in both the conductors. These currents are equal in magnitude but opposite directions, linking the radiating fields within the cable, and causing the fields to cancel each other out.
The current is maximum and voltage is minimum at the center of the dipole antenna. In contrast, the current is minimum and voltage is maximum at the ends of the dipole antenna.
The radiation pattern is perpendicular to the conductor of the antenna. This means that the dipole antenna radiates energy out into the space, perpendicularly to its axis.
There are many kinds of dipoles, but in this post, we will only describe two variations. A half-wave dipole, also known as a doublet, or the Hertz antenna, is the most commonly used type of dipole antenna. The length of its conductive elements is approximately half of the maximum wavelength (λ/2, the distance between two consecutive maximum or minimum points) in free space at the frequency of operation. A half-wave dipole’s current distribution is that of a standing wave, approximately sinusoidal (having the form of a mathematical sine curve) along its length.
A short dipole is a dipole formed by two conductors with a total length that is significantly shorter than a half wavelength. For applications where a full half-wave dipole would be too large, short dipoles are more suitable. In a short dipole antenna, the feed impedance increases and its response is less dependent upon the frequency changes. The current distribution in the short dipole antenna is almost triangular. The radiation pattern of the short dipole antenna is circular, whereas the current distribution of a half-wave dipole is more oval in comparison.
While dipoles can be used standalone low-gain antennas, they can also be incorporated as driven elements in antenna designs such as the Yagi antenna and driven arrays.
They can be used to feed more elaborate directional antennas such as a horn antenna, parabolic reflector, or corner reflector. Additionally, engineers analyze vertical (or other monopole) antennas on the basis of dipole antennas of which they are one half.
JEM Engineering has experience designing dipoles suitable for HF, VHF, and UHF.
For example, the BCA-620 is a broadband dipole blade optimized for intelligence, surveillance and reconnaissance (ISR), as well as signal intelligence (SIGINT) applications, operating within frequencies from 600 to 2000 MHz.
Anatomy of a Vivaldi Antenna
In a previous post, we briefly introduced broadband antennas and their various types. In this post, we will further discus one particular type of broadband antenna: the Vivaldi antenna.
The Vivaldi antenna, also known as a tapered slot antenna (TSA), is a type of linear-polarized planar antenna invented by Peter Gibson in 1978, who originally called it the Vivaldi Aerial.
A slot antenna, made from a metal ground plane, is named for the one or more holes or “slots” cut out of it. When the plate is excited by a radio frequency current, electromagnetic waves radiate from the slot. A Vivaldi’s upper frequency is limited by the width of the gap, while the lower frequency is limited by the size of the opening. The shape and size of the slot also determines the antenna’s radiation pattern. The Vivaldi antenna is referred to as a tapered slot antenna because its symmetrical radiating elements taper outward from its slot line.
Vivaldi antennas are usually fabricated from a solid piece of sheet metal like thin copper sheets, a printed circuit board, or from a dielectric plate that is metalized on one or both sides.
A simple Vivaldi incorporates a “feed line,” usually a coaxial cable that would connect the antenna to its radio transmitter or receiver via an RF connector.
The Vivaldi’s broadband characteristics make them suitable for ultra-wideband (UWB) signals.
To put briefly, UWB refers to a technology for transmitting information across a wide bandwidth over 500MHz. UVB applications include radar imaging, precision locating, and sensor systems.
Vivaldis also provide a number of other advantages. In addition to providing high peak value for the pulse envelope during radar applications, Vivaldi antennas are also useful for impedance matching. Also, similar to log periodic antennas and fractal antennas, Vivaldis can be scaled for use at any frequency. Additionally, they are characteristically low-profile due to their flat construction.
A dual-polarized Vivaldi is comprised of two coplanar horizontal and two coplanar vertical elements arranged into an array that is symmetric around its axis. These elements are driven with equal phase and amplitude excitation, allowing the antenna to achieve a broadside pattern.
JEM Engineering boast nearly two decades of experience in designing flight-qualified Vivaldi antennas suitable for our clients’ specific requirements.
At our in-house rapid prototyping facilities, we manufacture cutting-edge antenna products and deliver custom solutions. In addition to our two testing chambers, we employ a variety of high-tech tools to support that mission. Our customers also get the added benefit of working with the same testing partners who help us qualify our antennas.
Introduction to Biconical Antennas
In a previous post, we briefly explained that broadband antennas are antennas that operate over a wide band of frequencies, or “bandwidths,” higher than 1 octave. We also explained that broadband antennas come in a variety of forms. In this post, we will discuss a particular type of broadband antenna: the biconical antenna.
The phrase “biconical antenna” describes a broadband antennas that are made up of two roughly conical conductive objects, that are nearly touching at their points. Because of their configuration, they can also be referred to as “bowtie” or “butterfly” antennas.
Larger diameter = more broadband.
Biconical antennas have dipole characteristics. The double cone elements structure contributes to their wider bandwidth. The antenna becomes more broadband as the cone angle increases.
Solid or shell bicones aren’t practical for all operations.
Solid or shell bicone structures can sometimes be too large for most frequencies of operation. Thus, many antennas are designed to mimic the standard biconical geometry, but with altered structure and materials.
The wire bow-tie, for example, reduces the weight and wind resistance of a structure. Although one wire bow-tie would be very narrowband in comparison to actual cone-shaped or triangular sheet antenna, multiple (8+) intersecting wires can achieve the same radiation characteristics of its counterparts.
Bioconical antennas can be used in a number of applications, typically in the VHF and UHF frequency ranges.
JEM Engineering develops low-profile and versatile biconical antennas.
They are often used in electromagnetic interference (EMI) testing either for immunity testing, or emissions testing.
They are more effective than half-wave dipoles, because biconical antennas allow continuous sweeps, allowing for more ease in discovering anomalies.
The LBC-0718, which operates within frequencies from 700 MHz to 18 GHz, weighs about 2 lbs (approx. 0.91 kg) is suitable for SIGINT, signal monitoring, and multi-band communication.
Fractal Antennas, Explained
In previous posts, we discussed how antenna technology is constantly evolving and how one of the main focuses of antenna design is creating powerful antennas in low-profile form factors. This is especially true for applications such as personal communications, small satellite communications, UAV communications, SIGINT and ISR.
In addition to cylindrical dipoles and biconical antennas, fractal antennas can meet the requirements of utilizing the limited available space. Fractal antennas, as the name suggests, are based on the concept of a fractal, which is a recursively generated geometry that has fractional dimensions. While fractals antennas have many complexities that can be discussed at length, in this post, we will examine the basics of fractal antennas.
Fractal Antennas can be classified in two categories: deterministic and random.
Deterministic fractals are those that are generated of several scaled-down rotated copies o themselves. Such fractals can be generated using computer graphics that are repeatedly mapped out by a recursive algorithm. The Sierpinski gasket, for example, is a type of deterministic fractal.
Random fractals also contain elements of randomness that allow simulation of natural phenomena.
Fractal geometries can best be described and generated using an iterative process.
This process can be illustrated graphically, as shown in the illustrations of the Koch snowflake (or Koch fractal loop) and the Minkowski island fractal. The geometry generating process begins with a basic geometry known as the initiator (the triangle and the square, respectively). For Koch snowflake, the middle third of each triangle is replaced with a generator, and for the Minkowski island, each of the four sides of the square is replaced by a generator.
The trend of the fractal antenna geometry can be determined by observing several iterations of the process.
The final fractal geometry is a curve with an infinitely intricate underlying structure whose building blocks are scaled versions of the initiator.
Fractal antennas have space-filling properties that can be used to miniaturize classic antenna elements and overcome some of the limitations of small antennas.
Many fractal element antennas use the fractal structure as a virtual combination of capacitors and inductors. The antenna’s many resonances can vary according to the fractal design. The current on the structure has a complex arrangement caused by the inductance and self capacitance. Due to this reactive loading, the antenna elements can be compacted into a smaller space even if they are electrically long. Additionally, fractal antennas do not require additional components, assuming the structure happens to have the desired resonant input impedance.
Not all fractal antennas are ideal for certain applications.
The antenna’s suitability for a particular application can be determined by RF testing and computer search methods. Generally, the advantages of fractal antennas are good multiband performance, wide bandwidth, and small area.
While some researchers claim that fractal antennas have superior performance, some experts claim the contrary.
In 2003, Steven R. Best wrote in A Comparison of the Resonant Properties of Small Space-Filling Fractal Antennas, “that antenna geometry alone, fractal or otherwise, does not uniquely determine the electromagnetic properties of the small antenna.” However, in 2008 Constantine A. Balanis‘s research concluded that fractal antennas performed relatively similarly to the electrically small antennas they were compared against. More recently, in 2011, authors of Small Antenna Handbook Robert C. Hansen and Robert E. Collin reviewed many papers on fractal antennas. The pair concluded that they offer no advantage over fat dipoles, loaded dipoles, or simple loops, and that “nonfractals are always better.”
Black History Month 2021
As a minority-owned business, JEM Engineering proudly celebrates Black History Month.
This month, we honor the impactful contributions made by African American engineers have made in STEM and American History. In this issue, we celebrate Granville Woods, Marie Van Brittan Brown, and Lewis Latimer by highlighting some of their many achievements.
Granville Woods
1856-1910
Woods was the first African American mechanical and electrical engineer after the Civil War. He held over 60 U.S. patents, including the steam boiler furnace, the automatic break, the safety dimmer and the egg incubator. Additionally, Woods improved numerous inventions, including the safety circuit, telegraph, telephone, and phonograph.
Marie Van Brittan Brown
1922-1999
Together with her husband, Albert, Brown invented the first closed-circuit television security system in 1966. This invention included a radio-controlled wireless system that could stream the video to any television in the house. Along with the video system, the Browns created a two-way microphone system that would allow for communication between the residents and the person at the door. Additionally, Marie created a system to unlock the door remotely. Her invention is the predecessor to the modern-day security systems, used in both residential and commercial spaces.
Lewis Latimer
1848-1928
Latimer was the patent draftsman for several inventions, including the incandescent light bulb. Patented the “Process of Manufacturing Carbons”, an improved method for the production of carbon filaments for lightbulb. He also developed a forerunner of the air conditioner called “Apparatus for cooling and disinfecting.” Latimer was the first African American to join the Edison Pioneers.
What is a Smart Antenna?
The textbook definition of a smart antenna is “an antenna array with digital signal processing algorithms, which identify spatial signatures.” Using these spatial signatures, the smart antenna calculates beamforming vectors, which are then used to track and locate the antenna beam on a mobile or target.
Just as the phrase implies, signal processing algorithms are sequences of computer-implementable instructions for analyzing, modifying, and synthesizing signals (in this case, radiofrequency signals). A spatial signal signature is a response vector of an antenna to a mobile unit at a certain location. An example of a signal signature would be a signal’s direction of arrival (DOA). Calculating a DOA involves finding a spatial spectrum of antenna array and defining its peaks. Because the computations are very intensive, the smart antenna’s signal processing algorithms prove to be very useful.
Some of the most common smart antenna applications include acoustic signal processing, track and scan radar, and cellular systems such as 5G and LTE. The main difference between reconfigurable antennas and smart antennas is that reconfigurable antennas are single-element antennas instead of antenna arrays.
The two main types of smart antennas are switched-beam smart antennas and and adaptive arrays.
Switched-beam systems can choose from one of many predefined patterns in order to enhance the received signal. The overall goal of the switched-beam system is to increase the gain according to the location of the user.
In a previous post, we briefly explained that adaptive beamformers adjust to differing situations in order to maximize or minimize signal-to-interference-plus-noise ratio (SINR), which helps measure the quality of wireless communication.
Smart antennas provide many benefits.
The main benefit of smart antenna systems is its ability to simultaneously increase the useful receiving signal and lower the interference level, increasing the signal-to-interference ratio (SIR) in more densely populated areas. Smart antennas can essentially filter out the unwanted noise made by other users in the system so that important signals can be transmitted and received clearly.
Additionally, because smart antennas are more directional than omnidirectional and sectorized antennas, they can focus their energy toward the intended users, instead of wasting it by directing it in unnecessary directions. This means that base stations can be spaced further apart, as they would be in less-populated areas.
Smart antennas are also harder to tap into. In order to successfully tap into the connection, the intruder must be positioned in the same direction as their user as seen from the base station. Consequently, smart antennas provide more security, making them extremely vital in the present day, where organizations and individuals routinely transmit confidential information to one another.
Lastly, smart antennas’ spatial detection capabilities allow for geo-location services. For example, they can locate humans in emergency situations.
Smart antennas also have their limitations.
Smart antenna transceivers are much more complex than those of traditional base station transceivers in that smart antennas need separate transceiver chains for each array antenna element. This also means that that each transceiver needs to be accurately calibrated at all times. Additionally, smart antenna base stations must be equipped with very powerful digital signal processors to handle the computationally-intensive beamforming. This translates to higher costs in the short-term, however, the benefits will outweigh the costs over time.
Advancements in Aerospace Antenna Design
With the latest advancements brought upon by more research and development, aerospace antenna design has continued to steer away from traditional manufacturing materials and methods.
According to an article featured by Military & Aerospace Electronics, the three main goals for selecting technologies for aerospace and defense are 1) ruggedness, 2) low-loss, and 3) cost-effectiveness.
Naturally, all flight-qualified antennas need to be rugged enough to withstand mechanical shock, vibration, and atmospheric factors. Also, it is generally important for any antenna to transmit and receive radio waves with as little energy loss (return loss) as possible. Higher loss may cause the antenna to overheat and can degrade its sensitivity.
Creating specialized aerospace antennas, especially those used for military and defense, must be a streamlined and repeatable process. Whenever mass production is involved, it is imperative to keep manufacturing costs as low as possible. While machined aluminum and hand-built thermoset radomes have made for very reliable antennas, fabricating such components often involve multiple steps—more labor and more machining means more cost.
Composite Substrates
Aside from yielding higher costs, another drawback of machined aluminum chassis is the added weight. Composite materials, on the other hand, are not only comparatively lighter, but also come in injection-moldable forms that allow for intricate design with higher repeatability.
Composite substrates can also be tailored to specific applications by using a variety of fillers, which have their own dielectric properties. These fillers range from carbon and glass fibers to foaming agents. Conductive-fiber fillers can absorb energy radiated in unwanted directions, increasing antenna gain by decreasing interference.
Most of JEM Engineering’s line of flight-qualified antennas are designed with carefully selected composite substrates, making them effective, rugged, yet extremely lightweight.
Conductive Coatings
Conductive coatings metallize materials such as plastics, chemically resistant composites, glass, and ceramics, in order to create conformal antennas on nearly any shape at minimal cost. High-quality conductive coatings meet flight-qualification standards.
3D Printing
In another post, we described how additive manufacturing is used in prototyping antennas. Mainly, it allows for reduced material waste, lower manufacturing costs, faster turnaround, and more design complexity.
Magnetic Flux Channel Technology
Developed by JEM Engineering, MFC antennas do not utilize electric charge to achieve radiation. Instead, the magnetic flux that resides in the MFC core shapes and supports an efficient form of magnetic polarization current in a specially designed flux channel. Unlike conventional antennas, the MFC may be placed directly on, or even within, conducting structure with no ill-effects on radiation or impedance match performance. For communications in the VHF/UHF bands (30 MHz to 3 GHz) MFC antennas can provide equivalent performance to conventional. To learn more, read our blog post on our proprietary MFC technology.
STEM Day
Every year, JEM Engineering celebrates STEM Day. Because November 8 falls on a Sunday this year, we decided to celebrate it all week!
STEM stands for science, technology, engineering, art, and mathematics skills. These subjects push society forward and these educational programs help to find fun and engaging ways to teach them to students, which is all worth commemorating (NationalToday.com).
JEM Engineering fully support students and professionals in pursuit of careers in STEM, for our company is built on the passions of such individuals.
Radiofrequency Test Fixtures
JEM Engineering offers both on-site and remote RF testing services at our facility in Laurel, Maryland. Our Spherical Near-Field Chamber (SNF) and Tapered Antenna Testing Facility (TATF) can measure a number of antenna performance factors.
While many tests do not require the use of a test fixture, tests that involve a full 3-dimensional measurements in our TATF chamber will require some type of interfacing with our roll arm.
What materials are used for RF test fixtures?
Dielectric (non-conductive) materials, such as foam and wood, for example, are ideal for test fixturing. Such materials can support antennas and radomes without affecting their RF performance characteristics during a test.
Does JEM Engineering provide its own test fixtures?
We house a variety of simple test fixtures, which we use to test our own antennas, as well as our customers’. Our existing structures allow us to fixture multiple antennas during the allotted test time.
Customers may also provide their own test fixture(s).
What about custom fixtures?If the weight of the antenna under test is off-center by more than 36”, or if the antenna requires a more specific configuration, a custom fixture may be necessary.
We have the in-house capability to build custom fixtures. While customers are encouraged to provide their own fixturing specifications (for example, with drawings and dimensions), we are generally able to fabricate the appropriate fixtures based on a unit’s design and specific test requirements.