Loop antennas come in many forms, but their overarching distinction is that they are relatively simply constructed, yet very versatile.
Loop antennas are generally classified under two categories: electrically small and electrically large. If the loop’s overall length (circumference) is less than about one-tenth of a wavelength (C < λ/10), it is usually considered an electrically small antenna. On the other hand, an electrically large loop’s circumference is about a free-space wavelength (C ~ λ).
Electrically small antennas have proportionately small radiation resistances that are usually smaller than their loss resistances, rendering them ineffective for radio communication. They are better suited as probes for field measurements and as directional antennas for radiowave navigation.
Conversely, electrically large loop antennas are primarily used in directional arrays, including helical antennas, Yagi-Uda arrays, and quad arrays. These applications require the maximum radiation of the loop to be directed towards the axis of the loop to form an end-fire antenna. The proper phasing between turns enhances the overall directional properties.
A loop antenna could take virtually any shape, flexible or rigid. Due to its convenient geometrical arrangement the most popular configuration is the circular loop, particularly the small circular loop.
The loop’s mounting orientation will determine its radiation characteristics relative to its ground plane. placing multiple loops side by side on the same plane is one way to form an array.
Most applications of loop antennas are within the high-frequency (HF), very high-frequency (VHF), and ultra-high-frequency (UHF) bands.
Environmental testing is a crucial part of antenna qualification. Depending on which application(s) an antenna is to be used for, the environmental qualification standards for which it has to pass will vary.
JEM Engineering qualifies both our own and our customers’ antenna products in a number of ways, including testing them in at least one of our in-house chambers. Both the Tapered Antenna Test Facility (TATF) and the Spherical Near-Field (SNF) chambers perform a number of measurements at varying frequencies. While these measurements indicate an antenna’s RF capabilities, the antenna is not fully qualified until it is rugged enough for long-term practical use.
Each of JEM’s qualified antennas is a product of a collaborative effort between both electrical and mechanical engineers. For example, the electrical engineer designs the printed circuit boards (PCBs) and various radio frequency components, whereas the mechanical engineer designs the product’s housing, as well as additional internal components that would allow the unit to withstand various environmental conditions. Additionally, the RF test technicians collect quantitative information pertaining to the antenna’s electrical design, while the mechanical engineer must put the unit through rigorous environmental testing, including shock, vibration, heat, immersion, humidity, chemicals, wind, and frost.
There are a number of different standards by which an environmental test may be performed, but because JEM Engineering is a contractor for the United States Department of Defense, we adhere by defense (or “military”) standard, also known as “MIL-SPEC.” While JEM Engineering does not have the capability to perform environmental testing in-house, we work closely with our trusted partners, who handle our required MIL-SPEC tests once we’ve designed and built any necessary fixturing for them.
MIL-SPEC environmental tests are classified by codes. For example, MIL-STD-810 Method 516 measures shock, at values ranging from as low as 20G’s to as high as 75G’s. Similarly, MIL-STD-810 Method 514 denotes a vibration test. Some tests take into account a combination of atmospheric factors. An example of this is MIL-STD-810 Method 520, which involves quantifying the temperature, altitude, humidity, and vibration a product can withstand.
Lastly, for a general overview on what processes are involved in qualifying antennas, you may refer to our blog post, The Makings of a Reliable Antenna.
The term beamforming refers to a method of directing a wireless signal towards a specific receiving device, whereas the alternative would be allowing the signal to spread in all directions from a transmitter the way it naturally would.
By focusing a signal in a specific direction, beamforming delivers higher signal quality to a receiver. This means information is transmitted faster and more accurately. Furthermore, this accuracy can be reached without boosting broadcast power.
An antenna array is comprised of multiple radiating elements, each of which contributes an element pattern to the array’s radiation pattern. Each element pattern is a spatial distribution of RF power arising from the amplitude and phase of the RF signal at the element’s RF feed point. The array’s radiation pattern is determined by the coherent sum of all element fields, each which may be “weighted” by an additional amplitude and phase. Such weighted patterns exemplify beamforming in the array, whereby sidelobe levels and nulls are produced and controlled by adjusting the element weights.
Beamforming techniques loosely fall into two categories: conventional and adaptive. Fixed beamforming generally describes a conventional technique where the antenna array pattern is obtained from fixed element weights that do not depend on the signal environment. Conversely, adaptive beamforming element weights that do depend on —and can adapt to— the signal environment via some feedback mechanism.
Adaptive beamforming, which was initially developed in the 1960s, uses a digital signal processor (DSP) to compute the complex weights using an adaptive algorithm, which then generates an array factor for an optimal signal-to-interference-plus-noise ratio (SINR). Basically, adaptive beamforming systems are designed to adjust to differing situations in order to maximize or minimize SINR, which helps measure the quality of wireless communication.
The average civilian experiences adaptive beamforming technology in their every day life. In fact, wireless carriers use adaptive beamforming to provide next-generation wireless communications (5G) and long-term evolution (LTE) services.
As the phrase suggests, antenna miniaturization is the process of replicating an antenna’s functionality while reducing its physical size.
Over the past several decades, several studies have shown a direct correlation between the size of an antenna and its bandwidth and/or efficiency. Basically, it had been long since believed that the smaller the antenna, the smaller the bandwidth, and the lower the efficiency. In more recent years, however, this idea has become somewhat of a fallacy.
Technological advancements have greatly impacted antenna design, making it possible to miniaturize antennas without sacrificing performance. For example, JEM Engineering’s MBA-0145 is essentially the miniaturized version of the MBA-0127. Both antennas are multi-band (or HexBand) box-type antennas. Size and weight differences aside, the antennas are very similar in specifications.
16″ x 16″ x 2.3″
9″ x 9″ x 2.3″
< 2.5 : 1
< 2.5 : 1
410 – 500 MHz
410 – 500 MHz
Right Hand Circular
Right Hand Circular
While miniaturization has become more doable, there are still some limitations to this process. Just as it takes a combination of keen mechanical design and proficient electrical engineering to successfully miniaturize an antenna, it takes similar expertise to determine whether or not an antenna should be miniaturized or redesigned altogether, given its intended application. A trained team of experts usually performs a feasibility analysis before attempting to miniaturize an antenna.
Since our inception, JEM Engineering has made it our objective to not only excel in delivering antenna solutions, but to also give back to the community.
This November, we have increased our community outreach efforts by donating more funds, as well as resources, to the following charities.
To learn more about the charitable events we have participated in, as well as the organizations we work with, please visit our Community Outreach page.
What is a Magnetic Flux Channel Antenna?
JEM Engineering has developed a series of antennas called Magnetic Flux Channel Antennas, or, as they are nicknamed, MFC Antennas.
Most conventional antennas are made with conducting metals and dielectrics that allow electric charge to vibrate at radio frequencies. For example, in modern communications equipment such as cell phones, the electric charge vibration frequencies (GHz radio frequencies) can be several billion cycles per second. The antenna structure establishes a path to which the vibrating electric charges are confined and further define the antenna pattern they produce. However, when a very low-profile antenna is desired, the close proximity of metal structure to a conventional antenna causes poor performance unless cavities or other bulky structures are allowed.
JEM Engineering’s 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. The MFC core is an inhomogeneous and anisotropic construction whose design and fabrication are proprietary to JEM Engineering. This groundbreaking technology allows for closer proximity and integration within conductors, which cannot be achieved by conventional antennas.
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.
In recent years, the company has incorporated MFC technology into a variety of different antenna designs, including those that fulfill specific conformal/low-profile requirements. The antennas are typically made from high-hesitivity, low-loss material.
The development of these antennas originated from research conducted under the SBIR program.
Antennas: A History
In honor of our seventeenth anniversary, we invite you to take a look at some major developments in antenna research and trends over the past century.
In 1926, Japanese inventor Shintaro Uda, with the help of his colleague, Hidetsugu Yagi, developed the Yagi-Uda antenna. Modern versions of this antenna are used on high frequency (HF), very high frequency (VHF), and ultra high frequency (UHF) bands due to its characteristically high gain.
The directional antenna is primarily an array of linear dipoles with one driven element serving as the feed while additional elements act as “parasitic.” While the feed element is connected to the transmitter or receiver with a transmission line, the additional elements are unattached. The purpose of these parasitic elements (or passive radiators) is to modify the radiation pattern of the radio waves emitted by the driven element, directing them in a beam in one direction. This increases the the antenna’s directivity and consequently, its gain.
Today, this style of antenna is commonly known as the “beam antenna” or the “parasitic array.” However, many still refer to it as the “Yagi antenna.” This is perhaps due to the fact that while Uda was mainly responsible for the antenna’s invention, it was Yagi who helped popularize the antenna in the United States.
1930s: Horn Antenna
A relatively simple and widely used antenna, the horn antenna, can date its origins back to the late 1800s. However, it wasn’t until decades later, during the World War II era, that it became popular. In 1938, American inventor Wilmer Lanier Barrow invented the first modern horn antenna, following his invention of the waveguide in 1936.
Horns can be used in a variety of different applications due to their ease of use and their ability to achieve large gain. As an added bonus, they feature relatively simple construction, which makes them generally cost-effective. An example of an efficient, yet simply constructed modern horn antenna is the JEM-440.
The modern electromagnetic horn can take many different forms, four of the most popular being E-plane, H-plane, pyramidal, and conical. The differences in type, direction, and amount of taper are variables that augment a horn antenna’s overall performance as a radiator.
1960s: Dish Antennas
The “satellite dish” is perhaps the most recognizable type of antenna among consumers. It’s classified as parabolic reflector, a type of antenna which gets its name from its curved surface (parabola). Although the earliest version of the parabolic reflector antenna was developed in 1888 by German physicist Heinrich Hertz, it wasn’t until the 1960s that these types of antennas became commonplace.
Besides satellite television, parabolic antennas are used as high-gain antennas for point-to-point communications, in applications such as microwave relay links that carry telephone and television signals between cities, wireless WAN/LAN links for data communications, and satellite communications. These antennas have also been useful in spacecraft communications for decades.
Additionally, parabolic antennas are widely used as radar antennas for locating ships, airplanes, and guided missiles.
1970s: Microstrip Antennas
Although they originated 1953, microstrip antennas started garnering plenty of attention in the 1970s. Also known as “patch antennas,” they are extremely useful in aircraft, spacecraft, satellite, and missile applications, as well as mobile radio and wireless communications, due to their characteristically low profile. They are also inherently lightweight, inexpensive to manufacture, and easy to install. The RFD-8696 is an example of a very versatile patch antenna.
The defining characteristic of the modern microstrip antenna is that they can be printed directly onto a circuit board.
1980s: Planar Inverted-F Antenna (PIFA)
A form of patch antenna, the Planar Inverted-F antenna (PIFA) is a common component in handheld devices. It gets is name from it’s shape, which resembles an inverted “F.”
The PIFA resonates in an omnidirectional pattern. More importantly, it does so at a quarter-wavelength, allowing manufacturers to increasingly reduce the amount of space the component needs to occupy within a mobile device.
PIFAs also have favorable SAR properties. SAR is a a function of the electrical conductivity, which measures how transmitted RF energy is absorbed by human tissue. It stands for “Specific Absorption Rate.”
All of the aforementioned antenna designs are still being used today. In fact, because there have been numerous developments that improve upon their designs, they have even become more useful than they were when they were first invented. As antenna design continues to evolve at an even faster pace, it is important to quickly and efficiently test the resulted products.
While “interference” generally describes unintentional forms of disruption during wireless communications, “jamming” describes the deliberate interference with or blocking of such communications.
As the name suggests, jamming antennas, (aka jammers) are specifically used to interfere with radio noise or signals. In electronic warfare (EW) these interference are meant to disrupt control of a battle. For example, jammers radiate interfering signals toward an opponent’s radar, blocking the receiver with highly concentrated energy signals.
The two main jamming techniques are noise techniques and repeater techniques. Spot jamming, sweep jamming, and barrage jamming are the three most common types of noise jamming, whereas DRFM jamming is the most common type of repeater jamming.
Spot jamming is a form of noise jamming, where a jammer focuses all of its power on a single frequency, rendering the technique ineffective against a frequency-agile radar. Sweep jamming is the process of shifting a jammer’s full power from one frequency to another. This “sweeping” motion jams multiple frequencies in quick succession, although not all at the same time. Barrage jamming is the jamming of multiple frequencies at once by a single jammer. The main drawback of this technique is that the jammer spreads it’s power across multiple frequencies, making it comparatively less powerful at a single frequency.
Digital frequency radio memory, or DRFM, is a repeater technique that confuses a radar by altering and re-transmitting received radar energy. For example, by changing the delay in transmission of pulses, the jammer can alter the range the radar detects and creating false targets. Many jamming antennas use these types of techniques.
At present, there are several countermeasures against jamming. Similar to jamming techniques, these countermeasures allow for varying levels of effectiveness. Additionally, specifically designed, anti-jam antennas have become available. As new RF technologies emerge, so do developments in electronic warfare.