Intermodulation products (IMP) are unwanted signal frequencies that can be generated in an antennas when two or more simultaneous desired signals pass through a non-linear junction. This distortion is transmitted along with the desired signals.

The problem is particularly acute because the frequencies of the IMP created in cellular transmitting antennas very often interfere with the desired signal in the base station receivers and cannot be filtered out. These receivers, designed to be sensitive to low level signals, are therefore highly susceptible to interference from IMP.

The effects of this problem are too well known to wireless operators: poor call quality, dropped calls, customer dissatisfaction and costly antenna replacement.

IMP can most often be traced to the action of RF current passing through joints of dissimilar metals or poor contacts of similar metal within an antenna. Here is a typical scenario:

The metal joints, together with moisture in the antenna, form a battery-like device. One metal acts as an anode, the other as a cathode. The condensed moisture is the electrolyte. The chemical action of this "battery" produces new semiconductive compounds. These compounds, forming in the metal-to-metal junction, gradually transform it into a metal semiconductor junction. This "junction" now acts as a non-linear device, distorting the input signal and creating IMP.

Because corrosion develops over time, IMP are not commonly detected in initial testing. They become manifest only when customers start experiencing problems. Only environmental accelerated aging tests, which simulate the action of time and elements, can show how antennas will perform over the course of time.

Since IMP originate where dissimilar metals are joined, or poor metal-to-metal contact exists, antennas assembled using rivets or nuts and bolts are particularly susceptible to IMP. By contrast, IMP can be virtually eliminated by designing antennas with minimal use of dissimilar metals and joints. If such contact areas are unavoidable, then current density flowing through this area must be reduced. An example of such construction is the Phazar planar antennas.

The Phazar planar antennas start with a single sheet of aluminum alloy, formed into a one piece chassis. This housing then accepts a one-piece milled microstrip feed assembly and non contacting dipole radiating elements. Additionally, there are Phazar patented circuits incorporated in the design that effectively eliminate IMP. To ensure non-contact of meatsl, special insulator supports and shoulder washers are used throughout.

Accelerated age tests (Mil-Std-810D) show that the Phazar design maintains IMP below -145 dBc, even after the equivalent of years of use. This performance is as good as, and in most cases better than, our competitors' claims for new antennas.