Here you will find answers to the most frequently asked questions about RF antennas and their performance.

What does polarization mean to me?

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

Antenna gain claims.

Sorry to say but the advertised gain claims of most large antenna companies are exaggerated. There are rules that 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 meant by Antenna Gain?

Antenna gain is a measure of directivity of the antennas radiated signal. Remember antennas are a passive device and will never put out more total power than is put in to 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 affect on the ultimate gain and radiated pattern than the antenna type does.

What does reciprocity mean to me?

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 can’t always be achieved, and each application needs to be evaluated.

A word or two about 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 not only detrimental to your system performance, but would cause expensive down time due to maintenance, and possible intermittent operation. Skywave Antennas manufactures all of their connectors in its own factory using stainless steel, and high grade components.

Antenna configurations?

Although any metallic object will radiate, this doesn’t make it an efficient antenna. There are many antenna configurations: Omnidirectional, Directional arrays, Yagi, Loops, Dipoles, Circular Polarized, Patch, base loaded Whips, Collinear types just to name a few. Each antenna technology has pros, and cons when it comes to their operation. This is where Skywave Antennas can help you best 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 a dipole, 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, not how efficient your antenna is performing.

What's all the mystery and how do I select an antenna for the application?

It’s not as much the mystery of antenna design and performance, as it is the experience of what does and doesn’t work. The simple fact is the application and mounting location has more affect on the ultimate gain and radiated pattern than will the antenna type.

What determines my range?

Frequency, antenna height, antenna gain, transmitter power, feed line loss, propagation loss, signal to noise levels and receiver sensitivity.

Can I mount an antenna inside my 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 the enclosure becomes part of your antenna system at that point. Also be aware of plastic boxes, although RF signals pass through most plastics it 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 can not compare base station to mobile or portable performance which most antenna books describe. This is due to the ground losses eliminating most of the low angle antenna radiation.

Why, is a high gain antenna not good for ground mounted applications? And why does my antenna pattern look different than the antenna data sheet?

There is little you can do to improve the far-field, low angle radiation pattern of a vertically polarized antenna mounted on the ground. Increasing the “Gain” of the antenna will not work. See the previous question “Why does my antenna pattern look different on my ground applications?”

What does, bandwidth, VSWR, RL, and antenna mean to me?

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 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.

Can environmental conditions be a factor with location of my antenna?

The location of the antenna should be considered when selecting an antenna. The overriding application factors are, will the antenna be used indoors or outdoors, and identify any chemicals the antenna could be exposed to. Contact Skywave Antennas and ask for an “Antenna Specification Work Sheet”. By answering the questions on this worksheet, your antenna can be tailored specifically for your application, and save time and money later.

Why will my antenna not work under ground, in a pit, or 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 flash light 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 flash light inside of an enclosure, the beam of light will be contained by the enclosure, with the exception of any light escaping in cracks of the box.

How about frequency verses range?

Good rule of thumb is double the frequency, half the range.

Power verses range?

With all things being equal, one may increase the transmitter power to overcome losses due to transmission line loss, but beware. 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.

Antenna Height verses Range?

In general, higher is better in UHF antenna installations, actually 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’ll increase your overall gain by 3db.

Feed line loss: How does this affect my 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. This loss of signal depends mainly on the type coax, and is defined in each manufactures data sheet. But the rule is: the longer the run of coax between the transceiver, and antenna the more signal loss there will be.

Why can't I depend on an off the shelf antenna to work well?

Let’s be realistic about the gain game many manufactures play. Any designer knows that 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. To get any kind of meaningful estimation would require more than modeling, and would require 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, but rather 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. But remember 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. So, you must first consider what type 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?

We have all heard about GSM, CDMA, TDMA, PCS, etc, but these modulation schemes are used over several frequency ranges. But to an antenna designer it only is important for us to know the frequency range required. Be careful when asking for an antenna by the modulation scheme, you may wind 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 gain and loss of an antenna.

Multi-band antennas verses broadband usability?

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

What is line of sight communications? How does this work?

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 thus requires that the transmitter and receiver be within sighting distance of each other. Although other factors sometimes affects the distance when the transmitter and receiver are not in direct visual sight. These factors are Multi-Path, Reflection and Diffraction of the signal by manmade and other natural surfaces.

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