What is polarization, and why does it matter?

Vertical polarization is widely used today because it provides an omnidirectional signal path versus a horizontal antenna. Horizontal antennas or directional vertical antennas can be used in high RF congested areas, but by using cross-polarization (vertical to horizontal), 20db signal loss will occur.

What is antenna gain, and why does it matter?

Antenna gain is a measure of the directivity of the antenna’s radiated signal. An antenna is a passive device and never puts out more total power than is put into it. An antenna with gain focuses the power in a particular direction at the cost of reduced power in other directions. This is what gives an antenna gain. The simple fact is the mounting location has more effect on the ultimate gain and radiated pattern than the antenna type does.

Keep in mind that the gain claims of most large antenna companies are exaggerated. Antenna gain rules apply to all antenna systems and like all data, it can be manipulated. If you are not sure please contact Skywave Antennas. We are here to help you solve your system antenna problems, not just sell you an antenna.

What is reciprocity, and why does it matter?

The principle of reciprocity applies to most of the performance parameters of an antenna. Gain, radiation pattern, efficiency, and many other characteristics have the same value whether an antenna is transmitting or receiving a signal. However, this cannot always be achieved, and each application needs to be evaluated.

Is it okay to use inexpensive or “cheap” connectors?

Never use cheap connectors, especially at UHF Frequencies. If the connectors that you use are not using good dielectric properties, the losses could be detrimental to your system performance. Not only so, but it could cause expensive downtime due to maintenance and possibly intermittent operation. Skywave Antennas manufactures all of its connectors in its own factory using stainless steel and high-grade components.

Which antenna configuration do I need?

Although any metallic object will radiate, that doesn’t make it an efficient antenna. There are many antenna configurations: Omnidirectional, Directional arrays, Yagi, Loops, Dipoles, Circular Polarized, Patch, base loaded Whips, and Collinear types just to name a few. Each antenna technology has pros and cons when it comes to its operation. This is where Skywave Antennas can help you determine which one is the best for your particular application.

What kind of performance can I expect from a short antenna even if the VSWR is good?

Every antenna will radiate some type of pattern. However, compact antennas are often less efficient than dipole antennas, and therefore, tend to have negative gain resulting in poorer performance as compared to a half-wave antenna. The VSWR of your antenna only states that it is presenting an acceptable load to the transmitter, but it doesn’t let you know if your antenna is performing efficiently.

What determines my antenna’s range?

Frequency, antenna height, antenna gain, transmitter power, feed line loss, propagation loss, signal-to-noise levels, and receiver sensitivity all affect your antenna’s range.

Can I mount my antenna inside an enclosure?

An antenna should never be located inside a conductive or metal enclosure. If you mount an antenna outside on your metal enclosure, you will need to tune the antenna while mounted because, at that point, the enclosure becomes part of your antenna system. Also, be aware of plastic boxes. Although RF signals pass through most plastics, they will affect your signal strength.

Why does my antenna pattern look different on my ground applications?

When the antenna is mounted at ground level you cannot compare the base station to mobile or portable performance. This is due to the ground losses eliminating most of the low-angle antenna radiation.

What should my antenna’s bandwidth and return loss (RL) be?

The bandwidth of your antenna should offer a low VSWR of at least 2.5:1 at your band edges, and 1.5:1 or better at the center of the frequency band. For the same conditions, the return loss (RL) of the antenna should be -10db or better at the band edges with a deeper notch at the center frequency.

Be careful of advertising claims about bandwidth because otherwise identical installations will have different bandwidths.

What environmental conditions should I look for when installing my antenna?

Once you determine if the antenna will be used indoors or outdoors, identify any chemicals the antenna could be exposed to.

Contact Skywave Antennas and ask for an Antenna Specification Worksheet. By answering the questions on this worksheet, your antenna can be tailored specifically for your application so that you save time and money later.

Why does my antenna not work underground, in a pit, or in an underground case?

In environments where metal objects and the ground come into close contact with the antenna, it will cause reflections, absorption, and detuning of any antenna.

Think of the analogy of a flashlight beam. When it is in the open and free of obstructions, the light beam will shine some distance. When placed in or on the ground it will severely limit the distance the beam can cover. If, on the other hand, you place the flashlight inside of an enclosure, the beam of light will be contained by the enclosure, with the exception of any light escaping through the cracks of the box.

What is the relationship between frequency and range?

A good rule of thumb is double the frequency, half the range.

Is there a trade-off with my signal strength if I increase the transmitter power to overcome losses?

With all things being equal, one may increase the transmitter power to overcome losses due to transmission line loss. However, by doing this you will also lose valuable receive signal strength at the receiver antenna terminals and this cannot be recovered. Even adding an amplifier at the receiver will amplify both noise and receive signal thereby making the Signal to Noise Ratio undesirable.

Does increasing my antenna height increase my range?

In general, higher is better in any antenna installation. Raising the antenna over nearby obstructions may make a dramatic improvement in coverage. Within reason, the greater the height the more the coverage, but this gain must be balanced against feed line losses. Typically, when you double the height, you increase your overall gain by 3db.

How does feed line or coax loss affect my antenna’s transmit/receive signal?

Feed line or coax (as it is most often referred to), is made up of resistance and reactance and will, therefore, act upon a signal traveling along its length. The longer the run of coax between the transceiver and antenna, the more signal loss there will be. This loss of signal depends mainly on the type of coax and is defined in each manufacturer’s datasheet.

Why can’t I just buy an off-the-shelf antenna?

Manufacturers often misrepresent and overexaggerate gain claims. It is not possible to accurately predict how an antenna system will perform based upon a particular unique installation unless the antenna installations are the same. Getting any kind of meaningful estimation would require more than modeling and a physical comparison on a case-by-case basis.

Why is every antenna application and installation unique?

Most terrestrial communications systems do not operate in a free-space environment. Instead, they must account for the effect of the earth’s surface on the propagation path. There are two key effects: ground loss and path blockage.

Do I need a ground plane with my antenna?

There is a lot of confusion about what ground planes are and what actually constitutes a ground plane. Every antenna system needs some sort of ground system to properly operate. This part of the antenna system can make a big difference in the performance of your entire system.

All antennas must have an image for the antenna to work against. You must first consider what type of antenna configuration you are using then evaluate where it is being mounted.

Please contact Skywave Antennas Inc. Engineering to help you with this complex choice.

How does the frequency and modulation scheme used in my system determine what antenna to use?

GSM, CDMA, TDMA, and PCS modulation schemes are used over several frequency ranges. For an antenna designer, it is only important to know the frequency range required. Be careful when asking for an antenna by the modulation scheme, because you may end up with the wrong antenna.

What is a radiation pattern measurement?

A radiation pattern is a graphical depiction of the relative field strength of the electric field component of an antenna application.

We measure antenna field strengths in their far field using a pair of tuned half wave dipoles. A reference measurement is taken. After replacing one of the reference dipoles, we repeat the measurement process. By comparing these two levels we can show graphically the gain and loss of an antenna.

Should I use a multiband antenna?

Although multiband antennas are convenient, there will most likely be some tradeoffs in efficiency and performance. Each application will present its own unique challenges.

What is line of sight communications?

The transfer of energy through space is called propagation. In general, radio waves at UHF and above are line of sight, which means the wave travels almost like a beam of light in a straight line and requires that the transmitter and receiver be within sighting distance of each other.

Other factors sometimes affect the distance when the transmitter and receiver are not in direct visual sight, such as multi-path, reflection, and diffraction of the signal by manmade and other natural surfaces.

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