The Skew Antenna Planar Wheel is an ancient design of the 50’s:
This antenna gives excellent results in both omnidirectional directivity and in rejection of the reverse polarity, making it one of the best antennas available for the video transmitter.
SIZE AND WEIGHT
This is the graph of the Return Loss parameter of the 1.2GHz antenna, designed to be centered at 1280MHz, and attempting to cover the channels from 1200 to 1360 MHz:
As shown, the worst value within the operating band is -11.39dB at 1200MHz, ie, which engages at least a 92% power of the transmitter in the entire frequency band. This antenna hasn’t got a big bandwidth (because the ratio bandwidth – center frequency is much higher than for the 2.4) but does not mean that for example cannot be used at 1160MHz. At this frequency Return Loss is -8.5dB, which means that “only” 85% power is coupled.
This is the graph of the measured Return Loss of the 2.4GHz antenna, designed to be centered at 2440MHz, and trying to cover the channels from 2370 to 2510 MHz:
As shown, the worst value within the operating band is -15.33dB at 2370MHz, ie, it engages at least a 96% power of the transmitter in the entire frequency band. As a comment, the antenna “has more than enough” bandwidth, as it can be used from 2260MHz to 2780MHz.
Both versions have the typical omnidirectional radiation pattern, uniform at 360 ° in the horizontal plane, and with a radiation null in the axis of the antenna in the vertical plane. The 1.3GHz version looks more “perfect” because the higher the frequency the greater the effect of the inevitable mechanical imperfections.
OPPOSITE POLARIZATION REJECTION
This is especially important in circular polarization. In a simple way: the difference between co-polar component (right hand circular in this case) and cross-polar (left hand circular) is the attenuation that will introduce the antenna to capture the reverse polarization, which will come from the reflected signal that we want to avoid to reduce multipath. In these antennas is around 10dB in all cases, which means that the reflected signal will reach the emitter attenuated at least 10dB with respect to the desired signal, which is great to prevent that it interferes with the desired signal.