Antennae Talk – Antennae Terms

Antennae talk will explain some of the terms used in the business of antennae. It will play a part in helping you understand the frequencies and parameters of the various models we supply as are sure we have the right antenna for all your needs. Renair Antennae offer a wide range of ready made products, reducing costs during design stages and product life cycle. However, our expert team of engineers are available for any customisation required to meet all our your needs; just give us a call on +44(0)208 965 3001 and discuss.

An Explanation of Some of the Terms Used

Choosing Your Antenna

The correct Antennae selection is important not only to identify the specification you need, but also to enable you to make comparison to other products.

To achieve the most reliable results It is important to understand the parameters in which the antennas are tested and measured for performance.

To help you find the best product, we have highlighted some of the key points to help antenna selection and comparison.

Testing Parameters

Testing parameters and methods can vary from manufacturer to manufacturer. Testing methods should always be fully disclosed such as free space, metal plate, plastic plate, glass, etc. Installing antennas outside of testing parameters will result in undesired antenna performance.

For example, if a screw mount antenna is measured in free space showing optimal performance results and is installed on a metal surface in the customer device, the antenna will not operate as expected. Renair will always disclose the complete measurement conditions to assure our customers get the most accurate data making the in-device integration of an antenna successful.

In order to make a smart product selection between two manufacturers, we encourage that all testing should be completed with a standard length and high-quality cable in order to optimise antenna performance results. No alterations during testing such as shorter or longer cables should be performed. This will result in inaccurate efficiency, peak gain and average gain results.

Return Loss

The return loss is measured in decibels (dB) and represents how much energy is transferred from the device to the antenna. The lower the measurement the better. For a 50 Ohm system, it is recommended to have a minimum of -5dB or better measurement. Using the return loss to identify how the impedance of the antenna performs across the entire spectrum can help to estimate the bandwidth and operating frequencies.

VSWR Voltage

Standing Wave Ratio (VSWR) is another parameter used to measure how much energy is transferred from the device to the antenna but with a different mathematical scale than the one used for Return Loss. The lower the measurement the better, meaning closer to a 50 Ohm system and it is recommended to have a maximum of 3.5 VSWR. Please review the table below to learn more about the relationship between Return Loss and VSWR as well as other RF parameters and values.

Return Loss to VSWR Conversion Table

Loss (dB)
VSWR Reflection
Coefficient, Γ
Loss (dB)
Power (%)
Power (%)
-1 17.39 0.89 6.87 79.43 20.57
-2 8.72 0.79 4.33 63.10 36.90
-3 5.85 0.71 3.20 50.12 49.88
-4 4.42 0.63 2.20 39.81 60.19
-5 3.57 0.56 1.65 31.62 68.38
-6 3.10 0.50 1.25 25.10 74.88
-7 2.61 0.45 0.97 19.95 80.05
-8 2.32 0.40 0.75 15.85 84.15
-9 2.10 0.36 0.58 12.59 87.41
-10 1.92 0.32 0.46 10.00 90.00
-11 1.78 0.28 0.36 7.94 92.06
-12 1.67 0.25 0.28 6.31 93.69
-13 1.58 0.22 0.22 5.01 94.99
-14 1.50 0.20 0.18 3.98 96.02
-15 1.43 0.18 0.14 3.16 96.84
-16 1.38 0.16 0.11 2.51 97.49
-17 1.33 0.14 0.09 2.00 98.00
-18 1.29 0.13 0.07 1.58 98.42
-19 1.25 0.11 0.05 1.26 98.74
-20 1.22 0.10 0.04 1.00 99.00

Antennae Bandwidth

Bandwidth is a range of frequencies. A short frequency range is a narrow band and wider frequency range is categorised as a Wideband. It is important to select the right antenna with the matching bandwidth as Narrowband and Wideband are not interchangeable.


Antennae efficiency (radiation efficiency) is a measure of the electrical efficiency in which a radio antenna converts the radio frequency power received into radiated power. In other words means how much energy is radiated from the antenna to the air, how good is the antenna to radiate the energy. Being the most important parameter of an antenna in mobile communications. 100% means all energy radiated, 50% means half energy radiated, the minimum recommended is 25% but in some cases can go down to 10%, but the higher the better.

Peak Gain

Antennae gain is the measurement of its ability to direct or concentrate radio frequency energy in a particular direction or pattern. This is typically measured in dBi (Decibels relative to an isotropic radiator). The most crucial parameter in mobile communication is antenna efficiency followed by peak gain. Efficiency measures how much energy is in the air radiating in all directions, while peak gain is only measured in a single direction. While in fixed communication the most important parameter is the peak gain, since all the energy must be concentrated in one single direction. This value comes from a single point in the radiation pattern being the maximum point in the 3D sphere.

Average Gain

Similar to efficiency, the average gain is represented with a different mathematical scale (dB) and takes into consideration any mismatch losses. 100% is 0 dB which is maximum radiated energy, 50% is -3 dB which is half of the radiated energy, etc.

Radiation Patterns

The radiation pattern of an antenna is the strength of radio waves transmitted by the antenna traveling in different directions and angles. Omnidirectional antennas offer a 360-degree doughnutshaped radiation pattern that is uniformly distributed in all directions and are ideal for connecting devices that are on the same plane and to either side of each other. Hemispherical antennas distribute their radiation over a hemisphere (half of the space). Directional antennas radiate into one targeted direction allowing for longer transmission distances with less interference. 


Polarization is the orientation of the electric field of an electromagnetic wave. The two most common polarizations are linear and circular. Measurement and changes of polarization are determined in which the wave transmits through the environment from the transmitting to the receiving antenna. With linear polarization, the electric field vector stays in the same plane were in with circular polarization, the electric field vector is rotating with circular motion completing a full turn for each RF cycle. This rotation can be completed right-hand (RHCP) or left-hand (LHCP).

Ground Plane

Renair Antennae offers both, ground plane dependent and ground plane independent antennas. A ground plane is a surface area or metal that acts as a conductor and reflects the radio waves from other antenna components. The shape, size and the required clear area of the ground plane play an important role in determining radiation characteristics and gain. Low-frequency antennas such as broadcast antennas accept large conducting masses such as the earth or ocean as a sufficient ground plane. For very high frequency (VHF) and ultra-high frequency (UHF) antennas, the ground plane can be smaller and a metal disk, screen or wire is used as a ground plane. In automotive, marine and air equipment metal housing (car / airplane / boat) can serve as a sufficient ground plane. As a general rule, the conduction surface must be at least a quarter of the wavelength of the radio waves in diameter and in ideal condition the bigger the ground plane the better control of the electrical performance is achieved.between Return Loss and VSWR as well as other RF parameters and values.

Maximum Input Power

The Maximum Input Power is the maximum amount of power (in Watts) that can be transmitted to one antenna port without damaging it while maintaining performance.

Antennae Cable and Connector Types

The correct selection of RF cable and connector types is critical to optimal antenna function. The connector serves as a mechanical connection between the antenna and RF system and the cable is the transmission line for radio frequency signals connecting transmitters and receivers. The cable lengths impact signal quality and strength. Selecting a high quality cable and connector that’s compatible with the antenna will ensure the best antenna performance. When considering a product, it is important to determine the correct connector gender, polarity and geometry as well as the cable length prior to a quote request. Renair offers a wide range of high-quality connectors and cables as standard and also offer alternatives for any customisation needs.

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