One polarization is typically listened to at a time by most antennas. Through the same aperture, a dual polarized log periodic antenna receives both vertical and horizontal signals simultaneously. In signal intelligence, electronic warfare, and spectrum monitoring work, where you rarely control the polarization of the signal you are trying to catch, this antenna is used frequently. It explains how the antenna accomplishes this, what the specifications indicate, and what to look for when specifying an antenna for actual use.

What is the purpose of dual polarization?

Radio signals have polarization – the orientation of the electric field – and an ordinary antenna matched to one orientation will lose signal, sometimes heavily, when the incoming wave is oriented differently. This is fine for broadcast antennas aimed at a known transmitter. It is a serious concern for intelligence and surveillance work. The reason for this is that you will not be able to determine how the emitter’s signal is polarized, and it may change over time.
Through the use of two independent feeds, a dual-polarized log periodic antenna avoids this problem by simultaneously capturing both vertical and horizontal (E and H) planes. A polarization mismatch does not result in any missed information. This is the primary reason these antennas are suitable for applications such as SIGINT, COMINT, EW, and RF spectrum analysis, where missing a signal can have a significant impact on the analysis.

What is the actual construction of the antenna?

It is more elegant than it appears at first glance. Cross two log periodic dipole arrays at right angles on a common axis and provide each with its own feed system. Due to their shared boresight, the two arrays view the same scene simultaneously, as one array handles vertical polarization and the other horizontal polarization. A receiver can work with both polarizations separately because each feed terminates independently.
It is the log periodicity that provides bandwidth. As opposed to resonating at a single frequency, a log periodic array maintains its pattern and gain over a wide range of frequencies – in the LPDP series, the range is from 20 MHz to 3000 MHz in a single antenna. This span has been achieved without loading, a technique used by some designs to reduce array size at the expense of performance. By skipping loading, the antenna remains consistent across the entire band, although it means that it is the size that physics requires rather than artificially compact.

The circular polarization has been removed

Dual-polarized designs have a useful trick built into them. Using a 90-degree hybrid coupler, feed the two orthogonal arrays 90 degrees out of phase and the antenna will produce circular polarization instead of linear polarization. Furthermore, it can be switched between left-hand (LHCP) and right-hand (RHCP) depending on how the feeds are connected.
A hybrid coupler that performs this function is a separate component and is not typically included with the antenna. Therefore, if circular polarization is part of your requirements, please consider the coupler when planning your installation. It is important to note that one antenna covers both vertical and horizontal polarizations, as well as both circular polarizations. From a single piece of hardware, this provides a great deal of flexibility.

It is important to read the specifications

A few figures will determine whether a model is appropriate for your job. First, there is the frequency range – the LPDP series covers a range of 20 MHz to 3000 MHz, and each model covers a portion of that range, so the LPDP-20-500 and the LPDP-30-1000 are aimed at different bands. Instead of overbuying coverage that you will not require, choose a model that corresponds to the frequencies you actually require.
In addition to range, it is important to consider the electrical basics: gain across the band, a low VSWR to ensure power is not wasted in reflection, and effective isolation between the two ports to prevent polarizations from bleeding into one another. In the field, the mechanical aspect is equally important. DC-grounded designs with low-resistance discharge paths protect against lightning and reduce noise, and the product must maintain its specifications in harsh environments rather than just on a bench. Compact models such as the LPDP-20-80-500 feature a powder-coated finish for environmental protection and a quick-setup mount.

Choosing a manufacturer, a supplier, and an exporter

It is important to know who builds an antenna such as this as it is not a catalogue commodity. The dual polarized log periodic antennas manufacturer in India that designs and builds its own LPDP range can tailor the frequency coverage, connector type, finish, and mounting to meet specific objectives – useful when your requirements do not match standard products. Don’t settle for the nearest stock model without asking if custom configurations are available.
A dual polarized log periodic antenna exporter who is already involved in international defence shipments is likely to understand the documentation and compliance requirements associated with this type of equipment, which are not trivial. There is no greater indicator of a trustworthy supplier than complete datasheets, measured radiation patterns, gain and antenna-factor figures obtained over a proper test range, not just claims made on paper. You can specify with confidence a manufacturer who measures and shares its data.

FAQs

How does an antenna become “dual polarized”?

Using two independent feeds, it captures two orthogonal polarizations simultaneously – vertical and horizontal. As a result, it will not lose a signal due to polarization mismatch, which makes it ideal for use in SIGINT and surveillance applications.

What is the frequency range covered by the LPDP series?

Each model covers a different portion of the range of 20 MHz to 3000 MHz. Choosing the right model depends on the band you require.

Is it possible to produce circular polarization with this device?

Yes, of course. With a 90-degree hybrid coupler, the two arrays can be fed 90 degrees out of phase to produce circular polarization, which is field-selectable between LHCP and RHCP. As a separate component, the coupler is usually not included with the antenna.

Why does the antenna not use loading to reduce its size?

Loading shrinks an array, but at the expense of performance across the spectrum. If it is left out, the gain and pattern will be consistent over the entire frequency range at the expense of a larger physical antenna.

Is it possible to customize these antennas?

It is true. It is possible for a manufacturer to adjust the frequency coverage, connectors, finish, and mounting to meet the needs of a particular mission. As a matter of fact, this is a common requirement for defence and intelligence agencies.

Conclusions

Dual polarized log periodic antennas are able to hear both polarizations at once across a wide band from a single antenna – and with the right coupler, they can also receive circular polarization. Matching the frequency range to your mission is the key to selecting the right one. This process also involves verifying the electrical figures that govern clean reception, as well as confirming that the build will be able to survive in the environment where it will be used. You should work with a manufacturer who designs its own range, measures its own performance, and is capable of adapting the antenna if your requirements are unusual. In this way, you will ensure that your front end captures what it is pointed at rather than losing it due to a mismatch.