The Cel-Fi LPDA Antenna is a wideband directional antenna offering 12-14 dBi of gain across all North American cellular frequencies.
A log-periodic dipole array (LPDA) antenna is a powerful directional antenna. It’s very powerful at picking up weak signal in one particular direction and it needs to be set up pointing in the direction of the cell tower. The LPDA antenna reduces signal noise, improving SINR and overall signal quality.
What is an LPDA antenna?
A log-periodic dipole array (LPDA) antenna is a type of directional antenna. Some other manufacturers call these antennas "yagi" antennas, although technically yagi and LPDA antennas are slightly different.
Directional antennas need to be focused at the nearest cell tower. They are very powerful at picking up signal in one narrow direction. They are formed of a long central "boom" with attached metal rods called "dipole elements". The frequencies the antenna picks up depends on the length of the dipole elements.
A "yagi" antenna has dipole elements all of the same size. This means that it will only transmit and receive signals on a very narrow frequency range. Since modern cell networks use a very wide range of frequencies, this means that yagi antennas are usually only suitable for certain public safety situations, or when only one specific network needs to be boosted.
Most directional antennas on this site are log-periodic dipole array antennas. LPDA antennas have a wide range of dipole elements. The elements are spaced at intervals following a logarithmic function of the frequency, known as Σ or sigma. The different length of the dipole elements means that LPDA antennas transmit and receive signals on a wide range of cellular frequencies. The elements taper into a triangle shape (as seen in the image of the Cel-Fi LPDA antenna on this page). The relationship between the lengths is a function known as tau. They are wideband directional antennas that will boost signal on most North American cell carriers and so are well-suited to most cellular booster installations.
The Cel-Fi LPDA antenna leaves the central boom and dipole arrays uncovered, but some other kinds of LPDA antennas have ABS plastic coverings.
Why use an LPDA antenna?
LPDA antennas are ideal for use in situations with low SINR. SINR, or Signal to Interference Plus Noise Ratio, is a measure of an LTE signal's quality. Clear signal has a SINR of over 10 dB, while low quality signal has a SINR of under 5 dB. SINR and signal quality is different to RSRP, or signal strength. RSRP measures signal strength and is boosted by a cellular repeater system's gain. Strong signal power is important for good coverage but despite the importance attached to dB and signal strength bars, low SINR is just as important for clear calls and reliable coverage.
Low SINR results in low throughput, poor sensitivity, poor sound quality, and a generally bad user experience. Managing SINR is vital to a good cellular booster design. High signal power (gain) is not enough to boost signal as signal quality will be poor if the noise level is too high.
A directional LPDA antenna is a great choice if signal quality is strong but noisy (low SINR). Noisy donor signal is usually caused by inter-cell interference from multiple nearby cell towers using the same frequencies. Focussing and amplifying just one of the cell towers will reduce noise and improve signal quality.
The antenna can be mounted to a flat surface or to a pole. It features a mast down-tilt bracket and U-Bolts. The antenna is designed to be mounted at a 45° tilt. It comes with a specially designed mount attachment that enables the antenna to be mounted at a tilt, for optimal matching of macro donor signals. Macro antennas are cross-polarized and Cel-Fi have found considerably better results in the field when tilting the LPDA antenna 45° to match the cross-polarized donor signal.
Ideally the antenna should be pole-mounted at a tilt and aimed to the nearest cell tower. Although it can be a little time-consuming, finding the right antenna location and directionwill greatly improve booster system performance. Cel-Fi products, including the Quatra and GO X, are make aiming a directional antenna as easy as possible. The devices will give you a signal reading that includes both RSRP (signal strength) and SINR (signal quality), on the WAVE app, making it easier to try different antenna locations and directions and find the best signal.
The antenna includes a 10 inch (32’) RG58 pigtail with an N-type Female connector. It is compatible with all N-Female booster kits on our site.