Polarization and Antenna Compilation
Polarization and Antenna Compilation
Article content from radardetectorforum.org member Nine_C1
Radars are either Vertically, Horizontally or Circularly polarized. Planar means flat or lying in one plane. Vertical and Horizontal polarization fall under the Linear (or planar) polarization category. Circular polarization is in it’s own category as it rotates 360 degrees continuously and so passes through the Vertical and Horizontal plains and everything in between. Vertical is compatible with Vertical and Circular because circular rotates through the vertical plain, but is not compatible with Horizontal and vice verse.
This radar is vertically polarized just like the horns in every Escort/Beltronics/Valentine/Whistler and Cobra detector so we already have the best horn orientation. The only issue with Linear polarization is that it’s even more directional in it’s plain of orientation than the typical circularly polarized radar, and therefore doesn’t bounce around as erratically as circular microwaves making it a bit harder to detect off axis or over hills.
LEOs prefer the Circularly polarized radars mostly because they perform better in foul weather. Circular polarization is less attenuated by rain than either vertical or horizontal.
With respect to radar detectors, a vertical horn can still detect a horizontal transmission (due to a phenomena called multi-pathing where some of the signal will change orientation) but the range is drastically decreased.
Only one detector I am aware of uses a planar patch antenna that is Horizontally polarized, and the reason for that is that most radars used in Europe are fixed photo radars that are also horizontally polarized. It’s called the Stinger DSI.
Horns inside Radar Guns
We identified three types of polarization used in police radar, so now we will discuss the antennas.
Conical antennas are the most commonly used in mobile radar units and employs circular polarization. All of the mobile units in this picture have a conical horn inside. To make the antenna as small as possible, the horns are shortened and a corrective lens is put in front to correct for phase errors due to the artificially short horns. These horns serve a dual purpose, used in both the transmitter and receiving circuits. The transmitter and receiver circuitry is isolated through a microwave turn-style circuit to keep from burning out the sensitive receiver.
To the left is a vintage X-band radar that used un-lensed full sized conical horns. It is nearly double in terms of size of it’s lensed counterparts above.
Aside from conical horns, the next common horn (antenna) is the pyramidical horn. The only police radar to use the pyramidal horn was the Stalker ATR. It actually had two horns – one for transmitting and the other for receiving. As the horns were full length, the flat white lens in front was non functional and just acted as a cover. Pyramidal horns are always linearly polarized either Vertically or Horizontally but both are capable of receiving a circularly polarized signal. The horns inside the ATR are vertically polarised. NOTE: The ATR’s vertically polarized, full length, dual horns provided more gain than today’s top of the line DSR 2x conical antennas!
Lastly is the Patch Array antenna. This is an array of metallic patches used to receive or transmit microwave signals. This is a more modern type technology than the horns above and used in modern warships for hi-fidelity targeting of missiles and aircraft. As opposed to a rotating dish, the large arrays (they call them Phased Arrays) on warships are static and the radar beam is steered electronically in the vertical and horizontal plains, which is something not possible with the old dish.
Horns in Radar Detectors
The above mentioned horns (antennas) are found in radars used by law enforcement; however, one particular horn is common to both the radar guns and the radar detectors. To the right is an array of different radar detectors showing their pyramidical horns. Note that these horns are vertically polarized.
To the right, is a close-up of an M4 pyramidical horn found in popular detectors like the 9500ix. Note the ridge down the center of the upper-half of the horn. This ridge serves two purposes. First it gives the horn some of it’s broadband characteristics (ability to receive a wide range of frequencies). The shape and length of that ridge is critical to the horns performance. Secondly, it provides the electrical connection to the microstrip that feeds the signal received off the horn into the 1st mixer inside the receiver. The bottom half of the horn is also connected to the ground plain of the PCB board the mixers are attached to. It’s interesting to note that Escort actually uses real gold plating on the PCB that serves as the lower half of the horn in the M4 in this picture.
Lastly, to the right is another pyramidical horn found in a very popular radar detector – Valentine One. They call it a hi-efficiency double ridged horn using the lower ridge to make the ground plain connection.