PCS Electronics product descriptions are © PCS Electronics, who are solely responsible for their contentTheory of Mirrors
Mirrors are fascinating. They reflect nano-meter light waves in such a way that three mirrors set at different angles next to a light bulb create the appearance of more light bulbs, reflect the light in several directions and amplify the amount of light being produced.
What is the bandwidth of a mirror? We only observe the light frequencies, but does it also reflect microwaves and lower; maybe UHF, VHF, on down?
What if a 10-foot mirror next to a 10-foot antenna doubled and maybe aimed the signal in a desired direction? How about one of those 3-way mirrors from a department store dressing room. Would that cause a strong AM radio beam in a specific direction?
-
- Carl Blare's blog
- Login or register to post comments
Comments
RF and Mirrors
Carl,
You have good insight on how directive radio antennas work. A mirror does not "amplify" the light rather it redirects it so the intensity adds in a certain direction but in doing so it blocks the light in its shadow. This is the principal of directive radio antennas.
The mirror reflects light due to the interaction of the light energy with the mirror material. This depends on frequency since light can be considered electromagnetic radiation. The mirror absorbs the light energy and reradiates it in a different direction.
Mirrors and metal plates will reflect microwaves and this is used in microwave dishes. At lower RF frequencies reflection also occurs but the efficiency is lower to the point that the reflection is not significant. A near resonant length of conductor will reradiate efficiently and if the reflected wave phase is such that the "reflected" wave adds to the original wave in a particular direction then the intensity will be increased in that direction. But, as with a mirror, the reflecting element will have a shadow (actually produced by interference between multiple waves unlike the shadow of a mirror) in which the field will be nulled. At RF these elements look just like the images in multiple mirrors and in fact this "image antenna" visualization is useful in analyzing directive antenna characteristics.
When we speak of antenna gain we are referring to the increased intensity in a particular direction but the antenna, like the mirror, does not amplify the signal since the total radiated energy is not increased but is just redirected. At low frequencies the spacing between radiating and reflecting elements is important. This is also true with a multiple mirrors but we don't observe this since the wavelengths are so short and the light is incoherent. For an example of this look up "Newton's Rings".
Neil
Reflections
Thank you Neil, I liked the way you explained that. I am always desperate to think of something new to give the part 15 hobby a boost, since we have such small authority.
Next big idea: how can we make AM radio RF VISIBLE TO THE EYE so we could see our signal pattern. Special glasses? Funny dust chemtrailed from an air plane? Looking through an airport body scatter x-ray machine?
Carl Blare
Visible AM Radio
Visible AM Radio. I can only imagine how weird and yet cool that would look.
The Crow 99.9 & 1650
Serving McKinney Since 2008
http://www.TheCrowRadio.com