How To Choose an Antenna Antenna Mounts Antenna Cables Router Enclosures Antenna Cable Adapters Waterproof /Weatherproof antenna connector Top Tips for Long Range WiFi

Tech Support - Antennas

    Spatial Diversity Overcomes Multi-Path Interference | Wireless Links Over Water

    Spatial diversity is a useful feature for overcoming multi-path interference. By providing spatial diversity, the radio's internal circuitry can select between the two receive antennas for better wireless reception.

    Links and connections over water, over long distances, can be very difficult because of the radio beams reflecting off the water, which creates multipath interference for the radio waves.

    In the case of 802.11ac or MIMO applications, two or more spatially or polarization diverse antennas are required for the radio to operate at its highest data rate.

    One challenge with modern wireless commutation is heavy interference from the increasing airwaves transmissions over a limited frequency band. This problem has led to improvement in transmitting technologies towards spectral efficiency. Spatial multiplexing is one of the more successful ways of improving wireless transmission quality.

    Spatial multiplexing (SM, or SMX) is an RF transmission technique used in wireless MIMO systems to transmit streams of independent and uniquely encoded data signal from each of the multiple  antennas. Spatial multiplexing is incorporated in OFMD MIMO transmissions to improve spectral efficiency.

    Orthogonal frequency-division multiplexing (OFDM) is a method used to modulate digital data stream onto multiple carrier frequencies separated by narrowband channels. This multiplexing reduces crosstalk and interference. Most MIMO systems are OFDM based. Several modern applications such as LTE, LTE+, DSL and wireless networks user OFDM in their transmission process.

    The main advantage of OFDM transmission over the alternative single carrier is its ability to cope with channel constraints such as attenuation, interference, and frequency fading due to multi-path. MIMO OFMD currently achieves the highest spectral efficiency and delivers the highest capacity throughput on wireless transmissions.

    Spatially multiplexed MIMO OFDM  omnidirectional antennas can be used in several applications utilizing various frequency bands; standard radio frequencies and also ISM frequency bands.

    Spatial multiplexing is ideal for improving coverage in high-density areas and eliminating potential blind spots. Its ability to cope with heavy interference while still delivering high SNR transmission affords it this purpose.

    Antenna spatial diversity, also called antenna diversity or space diversity, is the practice in radio communications of enhancing a wireless link by using two or more antennas for signal transmission.

    Spatial diversity is always reliant on providing a receiving antenna or antennas with multiple observations of a signal, transmitted by more than one antenna with different locations and positions. In certain environments, a single transmitting antenna may be vulnerable to fading, dropout, lost connections, or other forms of interference. The use of multiple antennas increases the likelihood that you will receive the signal correctly and that a better signal will be received from at least one of the antennas involved. Accurate recovery of the original transmission is also feasible by using the redundancy from the multiple received signals. This physical layer (PHY) strategy is advantageous for data transfer in non-static environments where there is little or no line of sight and signals can be easily corrupted as we explore below.

    Spatial diversity is one of the diversity schemes available to improve signal quality and reliability.

    Spatial diversity is one of a number of methods used in radio communications to improve the robustness of transmitted signals and minimize fading and interference. This is done by using a plurality of communication channels with varying characteristics. Alternate diversity schemes utilize factors such as time, frequency, and Polarization to reinforce signal transmission, but spatial diversity is characterized by the synchronous transmission of a single signal between multiple distinct transmitting and receiving antennas. It is important to note that at least two antennas with the same characteristics must be used and it is not the timing of the signal that produces the diversity but rather the number of antennas involved.

    Key types of antenna diversity.

    Antenna diversity can be further subdivided into:

    ●Transmit diversity: where antenna diversity specifically uses multiple transmitter antennas.

    ●Reception diversity: involving the use of several receiving antennas with the signal inputs being combined for correct recovery of the data packet.

    ●Macro diversity or site diversity describes a spatial diversity arrangement where the networked antennas are far apart as in the case of cellular base stations or wireless access points.

    ●Microdiversity is where the antennas are distanced within one wavelength of one another.

    What is Multipath?

    Multipath is essentially the non-linear propagation of a radio frequency signal between transmitter and receiver. In this circumstance, the electromagnetic waves travel via multiple paths through their environment, created by physical obstructions and surfaces that may absorb or reflect the signal. Radiofrequency signals display optic phenomena such as reflection, refraction, and diffraction, and will bounce off objects like buildings or vegetation leading to delayed, altered, or out-of-phase arrival at the receiver. Each reflection produces multiple new wavefronts that duplicate the original signal. Rather than the original signal, several temporally spaced wavefronts will instead reach the receiver.

    Multipath is a common problem in built-up environments where hard, metallic or reflective surfaces are present for the signal to bounce off. Warehouses, aircraft hangars, and manufacturing areas are particularly susceptible. Materials such as glass, concrete, steel, and other metals in the vicinity of transmitting or receiving antennas will promote the multipath effect.

    Links and connections over water, and across long distances, can also be very difficult because of the radio beams reflecting off the water, creating multipath interference for the radio waves as we explore below.

    The degree of multipath present in radio communications is indicated by delay spread. This is defined as the difference between the time arrival of the first coherent signal components and the last multipath elements. Usually measured in nanoseconds, delay spread varies with the environment in which the signal is transmitted.

    Effects of multipath distortion.

    Tropospheric multipath pertains to the atmosphere closest to the surface of the earth and produces a random pattern of reflections. This form of signal propagation has a number of often difficult to control effects which often lead to corruption of the transmitted signal. This is because the electromagnetic waves will have traveled varying distances and at different speeds to reach the receiver out of phase. These phase shifts, delays, and signal attenuation have a deleterious effect on the received signal.

    The effects of multipath interference experienced may include:

    ●Fading: multipath induced fading is where the original signal becomes attenuated because of the interference of the multiple alternate wavefronts reaching the receiver.

    ●Data corruption takes place when a receiver is overwhelmed by multipath wavefronts and rendered unable to retrieve any coherent data.

    ●Destructive interference or signal nulling: is due to directly out of phase arrival of multipath signal that completely cancels out the original signal.

    ●Constructive interference or increased signal amplitude: involves the arrival of multipath wavefronts in phase with the main signal, increasing its amplitude and strength. However, the quality of the signal may be poor despite the increase in strength.

    Spatial diversity techniques are a critical solution to multipath distortion.

    Antenna diversity is a targeted solution for effective mitigation of adverse multipath effects. These physically separated antennas provide a receiver with several observations of the transmitted signal therefore the signal is observed having passed through a range of interference conditions. This increases the chance that the correct signal can be successfully reconstructed at the receiving end and counteracts the radio nulls and echoes that would necessitate repeated data retries. The physical separation of diversity antennas also ensures that antennas experience varying levels of multipath interference with one or some having better signal quality and overall performance. The collective effect of these antennas working in concert, sending the same data packets over more than one path between transmitter and receiver is a more robust wireless link in challenging conditions. Spatial diversity is ideal for improving coverage in high-density areas and eliminating the potential blind spots that particularly hamper urban and industrial environments.

    Wireless links over water.

    Radiofrequency signals that are propagated over bodies of water are highly susceptible to multipath interference. The water surface, especially if tidal, subject to winds or currents is uneven and extremely reflective leading to the creation of multiple alternate wavefronts and echoes. The temperature interface between air and water can also induce thermal ducting and notable signal loss. The proximity of the wireless link touch water surface will produce the strongest effects and one of the key strategies for ameliorating water-induced multipath is to raise the endpoints of the wireless link high enough to minimize multipath. If this is not possible, antenna diversity with the erection of secondary parallel links can prove effective. Spatial diversity requirements for wireless links over water need careful assessment and geometric separation to achieve adequate connectivity which is usually planned most effectively by a site survey.

    Selecting diversity antennas.

    Antenna selection is critical to the success of a diversity setup. For a properly functioning system, antennas should be closely matched for all characteristics (ie. frequency, impedance, Polarization, pattern, etc), at least being of the same type and gain. Diversity schemes usually involve the antennas being vertically separated, but with enough proximity to be covering the same area. They should be kept as close as possible to the coverage area and one another to avoid excessive cable runs. Diversity setups with two antennas within shared housing are also possible, provided the transmitting and receiving elements are distinct and separately cabled. Though more hardware and cabling is needed than with a single antenna pair, much of the radio frequency circuitry is shared between the transmitting or receiving antennas. At the receiving end, more processing power will be needed for carrier sense functionality that can discern the signal that meets a preprogrammed signal threshold and switch the system to listening to the antenna it came from.

    Practical points on spatial diversity setups.

    There are different types of antenna diversity setups depending on the application and available hardware.

    ●Single Radio Antenna Diversity consists of a pair of matched antennas and one radio.

    ●Dual Radio Antenna Diversity is made up of the paired antennas each being connected to a single radio.

    Diversity schemes are broadly reliant on carrier sense (CS) algorithms. Also known as 'listen before you talk', CS refers to the ability to monitor the signal transmission from the diversity antennas for signal intensity or quality and make a switch to the antenna whose signal exceeds a predetermined threshold. This helps to maintain optimal throughput and data loss or retries to a minimum.

    In a two-antenna system with transmitting antennas, ANT1 and ANT2, the received signal from both antennas will be compared to the CS threshold. The receiver will remain on the antenna that exceeds the threshold. If the ANT1 signal is suboptimal, the signal level will be checked via ANT2.

    Controllers in antenna diversity systems usually have either

    ●an energy-saving single-switch mode which will automatically terminate receiving if a suitable signal is not detected on either antenna


    ●a continuous-switch mode where the receiver actively listens for longer periods for a signal that exceeds the CS threshold.

    Some diversity systems are able to remember the antenna that performed optimally on the previous use and preferentially revisit it when the system is subsequently used, which potentially shortens start-up times.

    The role of frequency in spatial diversity.

    Antenna diversity systems operate at a single frequency. The frequency used will be determined by its application. For the most well known wireless technologies that use antenna diversity, at least two antennas are needed for the radio to perform with the highest data rates.

    1. WiFi

    WiFiantenna diversity is specified in a number of the WiFi Alliance standards including 802.11 a, ac, b, g, n, and utilizes multiple 2.4 GHz or 5 GHz antennas, switching between them to source the best radio frequency signal for data transmission. On a typical router, WiFi antennas are located in separate locations so that each receives a different version of the client signal.

    1. LTE

    LTE connectivity is reliant on the use of multiple antennas, and a number of techniques are used:

    ●Transmit diversity is used to improve signal robustness in poor conditions and improve coverage. It has no effect on data rates.

    ●Receive diversity improves signal quality and enhances coverage by combining multiple versions of the same transmitted signal.

    The LTE data streams transmitted in this way can be allocated to a single user or multiple users across a range of frequencies including 700 MHz, 1700-2100 MHz, and 2500-2700 MHz.

    The matched antennas installed in a diversity scheme should be spaced at a distance apart that is equivalent to a multiple of up to four times the transmitted frequency's wavelength. For example, if ANT1 and ANT2 are being used for a 2.4 GHz radio, they should be spaced at a multiple of 5 inches, the wavelength at 2.4 GHz.

    MIMO and antenna diversity.

    MIMO stands for multiple-input and multiple-output and refers to a method that is used to expand the capacity of a wireless link by using multiple transmitting and receiving antennas. It is a feature of LTE and other wireless technologies but varies from spatial diversity technique as more than one wireless signal is simultaneously received rather than improving a single data signal.

    Rounding up

    Antennadiversity has proven itself as a practical and effective method of overcoming the problem of multipath interference in wireless links. It is capable of being competently set up in a range of environments from densely populated urban districts to open bodies of water. As spatial diversity can work at any frequency, the use of paired or multiple antennas is used with a range of cellular and wireless networking technologies. For optimal performance of a diversity scheme, a careful site survey is always best, with the careful installation of suitably spaced antennas.

    Long-Range Outdoor Wireless

    Posted by

    GPS antennas: Key Physical and Electrical Characteristics

    What is a GPS antenna? A GPS antenna is a radio frequency antenna that provides connectivity with the Global Positioning System , a proprietary, satellite-based radio navigation system designed, created, and owned by the United States Government . When appropriately connected to a GPS transceiver, the GPS antenna is able to transmit and receive the specific radio frequency signals needed for a GPS device [...]

    Read More »

    Antenna Radiation Patterns: H-Plane, E-Plane, XY XZ YZ Planes

    This article explains radiation patterns, detailing how polarization (linear and vertical) relates to the E-Plane and H-Plane, and how XY, XZ and YZ planes correspond to E-Plane and H-Plane. A radiation pattern, or antenna pattern is a graphical representation of how a particular antenna radiates or receives energy. It is unique to an individual antenna and is made up [...]

    Read More »

    Maximum Input Power Rating of Antennas

    Maximum Input Power is defined as: The maximum amount of power (voltage given in Watts) that is able to be transmitted to a single antenna without damage to the antenna port from overloading. Maximum Input Power is a key parameter commonly seen on antenna specifications and datasheets. It may be termed ‘power handling’ or designated as [...]

    Read More »

    Antenna Polarization: Vertical, Linear: Key Factor in Selection of an Antenna

    Polarity is a key electrical characteristic to be considered when selecting an antenna. Like-matched antennas in an RF set-up will have optimal power or signal transfer in point-to-point applications.   Polarity is as important as gain, radiation pattern and VSWR, in the selection of an antenna. Our article on radiation patterns is closely related to polarization and will be very helpful to more fully [...]

    Read More »

    FPV (First Person View) Antennas for Drones

    FPV (First Person View), are remotely controlled vehicles from a pilot’s or drivers point of view. They include unmanned aerial vehicles such as drones and ground vehicles such as RC cars and land moving equipment. FPV video feed and control signals are transmitted across various frequency bands depending on desired range and application. Most FPV [...]

    Read More »

    45-degree Slant Antenna Polarization Overcomes Interference and Issue w/ Dual-Polarization

    Signals received at base station antennas are typically elliptically polarized in a way more like vertical polarization than horizontal polarization. This creates a common problem with dual polarized base station antennas (like the first generation of Ubiquiti dual-polarity antennas) since the vertically polarized antenna element generally maintains a stronger receive signal than the horizontally polarized [...]

    Read More »

    VSWR: Impedance Matching in Antennas & Antenna Cables

    Voltage Standing Wave Ratio (V.S.W.R.) is a key Indicator of antenna performance (along with gain / dBi):  The lower the VSWR, the more efficient the antenna. VSWR is a measure of the efficiency of transfer of RF power from its source into an antenna (which may include transmission of RF power along an antenna cable, adapter, and connectors). VSWR and [...]

    Read More »

    dBi, dB, dBm dB(mW): Defined, Explained and Differentiated

    dBi  = dB(isotropic): The forward gain of an antenna, nmeasured in decibels (dBi),  The dBi value reflects the antenna's directional / beamwidth characteristics, i.e., directional as opposed to omnidirectional:  Generally, the hIgher the gain (dBi), the narrower the beamwidth - the more directional the antenna.   The dBi value also reflects the antenna's electrical efficiency, differentiating [...]

    Read More »

    Operate 2 Antennas from One Radio: Use a "Power Divider" or "Antenna Combiner" - NOT a T-adapter

    Do not use a "T connection" to get one AP to service two antennas: This causes many problems, further described below.  By "T connection," we mean T-adapter (see photo below) to combine two antennas onto the same antenna cable. A "T" is the incorrect way to split to antennas or transmitters. It results in a 2:1 [...]

    Read More »

    Antennas by connector type Signal Loss in Antenna Cables.  LMR-100, LMR-200, LMR-400 Frequency Bands of WiFi, Bluetooth, 5G, 4G, 3G, LTE, GSM, ISM, CDMA

    RP-SMA cables and adapters SMA antenna cables and adapters N-type cables and adapters U.FL cables MHF4 Cables MMCX cables
    Dimensions / Measurements of RP-SMA connectors Signal-loss (attenuation) in LMR-100 and LMR-200 cables BNC cables RP-TNC cables and adapters Roof Mounts for Antennas Cable Glands
    Antenna Cable Adapters Through-hole antenna mounts Adhesive Mount Antennas Tripod Antenna Mounts Combination Antennas LTE GPS WiFi Bluetooth 4G 3G