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.
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 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.
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.
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.
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.
In an earlier post, we touched upon different antenna’s intrinsic characteristics, such as gain, radiation patterns, directivity and VSWR. In this post, we touch upon polarization and how it affects an antenna’s performance.
The polarization of an antenna is loosely defined as the direction of the electromagnetic fields produced by the antenna as energy radiates away from it. These directional fields determine the direction in which the energy moves away from or is received by an antenna.
Linear polarization is the most common polarization.
Vertical polarization refers to the oscillation of an antenna’s electrical field on the vertical plane, whereas horizontal polarization refers to the oscillation on the horizontal plane.
Slant polarization refers to an electrical field that oscillates at a 45-degree angle to a reference plane. JEM Engineering’s LPA-069, for example, is a handheld, direction finding, log periodic antenna that can tilt to a 45-degree angle to receive slant, horizontal, or vertically-polarized signals.
Circular polarization (CP) refers to a radio wave that rotates as the signal propagates. When it rotates to the right, the polarization is referred to as Right-Hand Circular Polarization (RHCP); when it rotates to the left, it’s referred to as Left-Hand Circular Polarization (LHCP). Many of JEM’s multi-band antenna products are circularly polarized. For example, the standard HSA-218 is RHCP, but JEM also makes an LHCP version of the antenna.
Not to be confused with circular polarization, elliptical polarization refers to an electrical field that is propagated in an elliptical helix. Similar to circular polarization, elliptical polarizaton can either be right-hand, or left-hand.
The way an antenna is mounted affects its polarization.
A straight dipole antenna will have different polarizations when mounted either horizontally or vertically. Thus, a horizontally polarized antenna will perform better when mounted near a ceiling, whereas a vertically polarized antenna will perform better when mounted near a side wall.
Omnidirectional antennas can be dual polarized.
Omnidirectional antennas, such as the JEM-0221A, radiate radio frequency energy in all directions perpendicular to the antenna’s axis in a doughnut-shaped pattern. Although omnidirectional antennas are usually vertically polarized, they can also be circularly polarized or dual polarized. Circular polarization helps mitigate the reflections that are common in omnidirectional antennas.
A circularly polarized omnidirectional antenna is insensitive to wave orientation. Thus, they provide particularly effective performance and gain. In receiving antennas, a dual polarized CP omnidirectional antenna offers optimal transfer of electromagnetic energy. Ideal for field-sensing and signal environment monitoring applications, the WSA-0520, is able to receive vertical, horizontal, RHCP and LHCP polarized signals equally.
In a previous post, we introduced microstrip antennas. In this post, we explore their basic characteristics, benefits, and drawbacks.
Microstrip antennas were patented in 1955, although their origins trace back to 1953. They became more commonplace in the 1970s. The antennas consist of a very thin metallic radiating element, or a “patch,” placed small fraction of a wavelength above a ground plane.
There are various substrates used in designing microstrip antennas, Thicker substrates with lower dialectric constants deliver larger bandwidth and better efficiency, while thinner substrates with higher dialectric constants are better or microwave circuitry.
Microstrip antennas have many benefits.
The most notable benefit of microstrip antennas is their versatility. Firstly, they are small and lightweight, as well as easily conformable to planar and nonplanar surfaces. Additionally, they can be are mechanically robust when mounted onto rigid surfaces. Thus, they can be used in an various applications, including aircraft, spacecraft, satellite, missile, mobile radio, and wireless communications.
Another benefit of microstrip antennas is that they are simple and inexpensive to manufacture. These low-profile antennas can be printed directly onto a circuit board.
But they have their drawbacks.
Micostrip antennas do have their disadvantages, one of which is their low efficiency. They also have low power, poor polarization purity, poor scan performance and faulty feed radiation. Additionally, these antennas have very narrow frequency bandwidth, which may be a benefit for some government security systems.
While there are ways to correct some flaws, doing so can negatively affect the antenna’s performance in other ways. For example, increasing the height of the substrate can extend the antenna’s efficiency. However, as the height increases, more surface waves will travel through the substrate, scattering at bends and surface discontinuities, degrading the antenna’s pattern and polarization characteristics. Similarly, while there are ways to increase the bandwidth, in large arrays, there would be a trade-off between bandwidth and scan volume.
Shapes do matter.
Patch elements of microstrip antennas come in various shapes and modes (field configurations), which affect the antennas’ resonant frequency, polarization, radiation pattern, and impedance. These factors are further influenced by adding loads, such as pins and varactor diodes, between the patch and the ground plane.
Square, rectangular, dipole,and circular are very common because they are the easiest to manufacture and analyze. They also have favorable radiation characteristics, especially cross-polarization radiation. Dipoles, in particular, inherently have large bandwidth and occupy less space, making them attractive for arrays.
Linear and circular polarizations are achievable with either single elements or arrays of microstrip antennas. Arrays with either single or multiple feeds may also improve scanning capabilities and directivities.
The textbook definition of a frequency band is an interval in the frequency domain, delimited by a lower frequency and upper frequency. The International Telecommunication Union has assigned designations to these intervals.
Beginning with the lowest and ending with the highest, we will enumerate the ITU-designated frequency bands and provide examples of their corresponding applications.
|Frequency Band Name||Acronym||Frequency Range||Wavelength (Meters)|
|Extremely Low Frequency||ELF||3 to 30 Hz||10,000 to 100,000 km|
|Super Low Frequency||SLF||30 to 300 Hz||1,000 to 10,000 km|
|Ultra Low Frequency||ULF||300 to 3000 Hz||100 to 1,000 km|
|Very Low Frequency||VLF||3 to 30 kHz||10 to 100 km|
|Low Frequency||LF||30 to 300 kHz||1 to 10 km|
|Medium Frequency||MF||300 to 3000 kHz||100 to 1,000 m|
|High Frequency||HF||3 to 30 MHz||10 to 100 m|
|Very High Frequency||VHF||30 to 300 MHz||1 to 10 m|
|Ultra High Frequency||UHF||300 to 3000 MHz||10 to 100 cm|
|Super High Frequency||SHF||3 to 30 GHz||1 to 10 cm|
|Extremely High Frequency||EHF||30 to 300 GHz||1 to 10 mm|
Genetic antennas go through “Evolutions.”
In order for an antenna to be qualified for mounting onto a non-stationary ground plane, it has to meet stricter vibration testing standards than it would for stationary mounting. Additionally, atmospheric factors have to be considered. A stationary antenna, if mounted outdoors, will also have to withstand harsher temperatures and weather conditions, and therefore pass more rigorous temperature, wind, dust, humidity, and corrosion tests, to name a few.
Naturally, a vehicular antenna, especially one mounted onto the exterior of the vehicle, will need to withstand the aforementioned non-climate controlled conditions, in addition to increased shock and vibration. A flight-qualified antenna, however, has to meet even higher standards than a vehicular antenna. Additionally, it has to operate well in high altitudes.
A flight-qualified antenna can come in many different forms.
We are proud to offer a variety of flight-qualified antennas, ranging from flat panel, to box-type, to blades, and even flexible peel-and-stick antennas. These antennas are suitable for a various applications, including multi-band communications, EW, ISR, SIGINT, as well as satellite communications.
|Among our many box-style antennas is the JEM-238MFC, which comes in an ultra-low-profile form factor designed for 1.2″ (3.18 cm) cavity depth. It is one of our Magnetic Flux Channel (MFC) antennas, which means it does not utilize electric charge to achieve propagation. That being said, it be placed directly on, or even within, conducting structure with no ill-effects on radiation or impedance match performance.|
Specifically designed for aerodynamics, blade antennas are often mounted to the exterior surface of an aircraft. Ranging in size and frequency band, our UVW products used for ground-to-ground, air-to-ground, and ground-to-air communication systems. They are also optimal for unmanned aerial vehicle (UAV) communications. The UVW-0430A is suitable for sensor systems and low drag operations.
In addition to readily available antenna products, JEM Engineering offers custom antenna development. We often create special antenna designs to meet our customers’ unique requirements. Our blog post, The Makings of a Reliable Antenna, briefly explains some of our development processes.
JEM Engineering offers all of our customers the added convenience of performing remote radio frequency testing
We find that most of our customers prefer to visit our facilities for their scheduled radio frequency tests. However, JEM also offers the option of remote testing, which may be preferable, depending on the specific requirements and circumstances.
The main purpose of our remote testing is to provide customers with the same quality rf tests without the need to travel (and the expenses associated with travel). Remote testing also comes at no extra cost. Our invoicing only takes into account our current rates and how much chamber time is spent on each test, no more, no less.
The process of scheduling a remote test is as simple as scheduling an onsite test and involves no additional paperwork.
1. Call or email us to begin the quoting process. Whenever a customer inquires after our in-house or remote radio frequency testing services, we walk them through the same steps to determine how much chamber time is needed to complete the test. The customer fills out a form, which outlines the passive test requirements. Once we receive the form (which we commonly refer to as the “Test Plan”), we start generating the quote. Depending on the requirements, we can then determine whether or not the test is suitable for remote testing – and most tests are.
2. We schedule the test together. If a test date has not been specified prior to quoting, our team will consult with the customer to determine the best available date(s) to perform the test.
3. The customer ships the unit(s) and any additional equipment necessary to complete the test. The customer is responsible for any applicable fees associated with shipping and insurance.
4. Upon receipt of the components, we begin the test as scheduled. Throughout the testing process, our experts remain in communication with our customers to eliminate any confusion and ensure accurate results.
5. When the test is complete, we ship everything back, carefully packaged. We work with the recipient to send every component back via their preferred courier.
6. We invoice the customer. Our standard invoicing schedule is Net 10. Any deviation from this payment method will have been discussed prior to scheduling the test.
Our company takes pride in our flexibility when working with customers.
We understand that sometimes an onsite test becomes a remote test. In the event that travel is either inconvenient or no longer feasible, our technicians will perform the test(s) as scheduled, provided that we have received all the necessary components. If there is any delay on the sender’s part, we will also hold customer property for a specified amount of time, as outlined by our Terms and Conditions.*
In summation, almost any and every test performed onsite can be done completely remotely. As long as we have all the applicable components in-house, our experts can perform tests on even the largest units and with the most complex pieces of equipment.
* First-time customers receive a copy of our Terms & Conditions.
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.