New additions to the class of radio wave detectors.
New additions to the class of radio wave detectors
Radio wave detectors (radio beam detection devices) with a volumetric detection zone in the form of an ellipsoid of rotation have always played the most important role in security systems, starting from the «Soviet» period to the present. No less bright prospects await them in the future.
But, despite the great attention and the number of various publications, the flow of questions related to their selection and conditions of use is increasing. The huge range of manufactured detectors and their insufficiently clear classification do not inspire confidence in putting things in order in the minds of installers.
A bit from the past and present. It all started with the military-industrial complex and non-departmental security, the «Pion» detectors and others, mainly in the millimeter range, were produced at state enterprises and guarded objects of state importance. These devices were built on parabolic antennas, powerful diode (avalanche and «Gann») generators and detectors. The main frequencies used were in the range from 9 to 36 GHz. The detectors had a narrow detection zone, but the radiation power in the pulse reached several watts, and long-term presence of people near the transmitting units was not recommended.
In addition, the detectors were designed in such a way that the polarization vectors of their plane-polarized antennas were parallel or perpendicular to the surfaces of the earth, barriers, etc.
A lot has changed dramatically at present; transistor microwave generators and amplifiers have appeared. High generator power is no longer required, and advances in filtering and signal isolation have reduced radiation to the level of «natural» background.
However, despite significant positive changes, these detectors have a rather serious drawback. As a result of adding up the «direct» and reflected from foreign objects waves, linearly polarized in one plane, the total signal is weakened or strengthened depending on the phase ratio of the added waves on the receiving antenna of the detector. The influence of surfaces and individual objects located in the detection zone due to interference leads to «unpleasant» consequences, false alarms, and sometimes even to complete loss of functionality. So it is necessary to ensure that the barrier or expected snow cover are at a sufficient distance from the axis of the detection zone. The exception is large-sized detectors with large apertures (antenna sizes ~ 1 m), which have «serious» integrating properties. But they, as a rule, have only one increased size, which does not lead to a solution to the problem in the presence of two perpendicular surfaces, the ground and the barrier.
Now 24…36 Gigahertz detectors with a narrow detection zone are also produced. Increasing the operating frequency in a certain way reduces the chance of the influence of reflected waves by narrowing the detection zone, but this is only up to certain limits. As soon as the zone axis is brought closer to reflective objects, the influence will immediately manifest itself. In addition, excessive narrowing of the detection zone leads to a simultaneous loss of control over part of the site. Which allows the intruder to cross the line “undetected” under or above the detection zone.
Therefore, the use of radio wave detectors until 2007 was mainly limited to “open” areas with a sufficient exclusion zone, without foreign objects, poles, trees, etc.
A new detection method.In 2007, a new detection method was patented, which, when applied to radio wave detectors, eliminated the noted drawback and “introduced” new properties into the detectors.
The essence of the invention is to form a plane-polarized electromagnetic field with a polarization vector formed at an angle of 45 degrees relative to adjacent surfaces (ground, fence, high snow cover, etc.). Signals reflected by adjacent surfaces reach the receiving antenna at an angle of 90 degrees relative to its polarization vector and are practically «invisible». The main requirement was the absence of foreign objects only in the «line of sight» zone, called the main detection zone.
At the same time, at least three new operational properties appear.
1) The possibility of using detectors to protect the metal fence of a lattice (mesh) type and to form a detection zone directly on the fence. As a result of testing and operation, it was noted that the detection zone is adjacent to the fence from the inside (as if «sticking» to it) and practically does not go outside, beyond the territory of the facility. This circumstance allows the detectors to be successfully used in dense urban areas with restrictions on the width of the exclusion zones, but without losing control over the upper and lower parts of the detection zone. Its height does not decrease, so overcoming it by «diving» (bending low) or jumping is blocked.
2) The possibility of transverse overlap of the detection zone with a lattice (mesh) fence without deteriorating the detector's performance.
3) The possibility of adjusting the transverse dimensions of the detection zone (from wide to ultra-narrow) not only by increasing the operating frequency, but also by simply changing the threshold values.
It follows from the above that radio wave detectors manufactured using the new method, regardless of the operating frequency and other «standard» characteristics, have distinctive properties, practically not competing with the previous ones on open borders.
Let's think about the classification. In order to avoid «confusion» in the class of radio wave detectors and lead to a correct understanding of the place of each type in the security system, there is a need to divide it into at least two subclasses. In general, leading specialists in the security market are simply obliged to take part in changing the classification and determining the names of the subclasses. At this stage, you can at least note the main properties of the detectors in the name. For example:
1) «interference-dependent» — with a polarization vector parallel or perpendicular to the surfaces, for open areas;
2) «interference-independent» — with an inclined polarization vector, for any areas.
Of course, these names reflect the physical properties very superficially, but they can help designers and installers in the correct selection of detectors.
Innovative technology is developing and will develop, new classes and subclasses of various products will appear. There is a need to study the paths of evolution and scientifically based predictions of the emergence of new methods and devices. Perhaps the classification should have a certain «gift of foresight», similar to the periodic table, why not. I would like young and talented scientists to direct the technical progress of the security market with their minds, stimulating equally talented engineers to fill in the gaps and move technology forward.