In a previous post, we introduced microstrip. 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 efficency, 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|
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.
Flight-qualified antennas 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-type 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 tests remotely.
We find that most of our customers prefer to visit our facilities for their scheduled RF 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 radio frequency 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 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.
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.