Editing Reflective array antenna (section)

===Reflectors===
The gain can be further improved through the addition of a ''reflector''. Generally any conductor in a flat sheet will act in a mirror-like fashion for radio signals, but this also holds true for non-continuous surfaces as long as the gaps between the conductors are less than about {{fract|10}} of the target wavelength.<ref>{{cite web |url=http://radiojove.gsfc.nasa.gov/class/educ/radio/tran-rec/exerc/iono.htm |title= The Effects of Earth's Upper Atmosphere on Radio Signals |website=NASA}}</ref> This means that wire mesh or even parallel wires or metal bars can be used, which is especially useful both for reducing the total amount of material as well as reducing wind loads.

Due to the change in signal propagation direction on reflection, the signal undergoes a reversal of phase. In order for the reflector to add to the output signal, it has to reach the elements in-phase. Generally this would require the reflector to be placed at {{frac|4}} of a wavelength behind the elements, and this can be seen in many common reflector arrays like [[television antenna]]s. However, there are a number of factors that can change this distance, and actual reflector positioning varies.

Reflectors also have the advantage of reducing the signal received from the back of the antenna. Signals received from the rear and re-broadcast from the reflector have not undergone a change of phase, and do not add to the signal from the front. This greatly improves the [[front-to-back ratio]] of the antenna, making it more directional. This can be useful when a more directional signal is desired, or unwanted signals are present. There are cases when this is not desirable, and although reflectors are commonly seen in array antennas, they are not universal. For instance, while UHF television antennas often use an array of [[bowtie antenna]]s with a reflector, a bowtie array without a reflector is a relatively common design in the [[microwave]] region.<ref>{{cite book |chapter= Wideband printed bowtie array for spectrum monitoring |first=S. |last=Raut |date=July 2014 |pages=235–236 |doi= 10.1109/APS.2014.6904449 |title= 2014 IEEE Antennas and Propagation Society International Symposium (APSURSI) |isbn= 978-1-4799-3540-6 |s2cid=42085218 }}</ref>