IEEE 802.22 wireless regional area network (WRAN) specifies that cognitive radio devices can use TV white spaces whenever required. Using different frequencies will require its antenna size to be changed accordingly. When using lower frequencies, the devices need to have a larger antenna size. How can this be tackled? I mean how we can change the size of a built-in antenna of a device?
Hello Abd,
These radios can use wideband antennas similar to those used for TV. E.g. log-periodics, bowtie and discone-like antennas will work fine in these applications.
Yes, these antennas need to be large relative to the shortest wavelengths.
Dear
I think this article is related to your question, you can check it
https://arxiv.org/pdf/2102.00302.pdf
Article Review on frequency reconfigurable antenna using substrate-i...
I wish you success
Antenna for TV white space could be used the same as fit TV itself. Most problems here are related to transceiver filtering in transmit and receive modes not to degrade performance of either TV channels or TV white space modules...
Since the wavelength of a signal is inversely proportional to frequency, antenna size will grow larger with reducing frequency. That is the simplistic answer.
The larger dilemma for embedded antennas is that it is the radio itself, not the internal antenna, that is doing most of the radiating. The embedded antenna is a decoupled reactive load which allows the eigenmodes to form on the counterpoise (usually the ground plane) of the radio. When you read the impedance of the embedded antenna, you are not seeing the antenna alone ... you are seeing, for the most part, the radiation properties of the counterpoise.
It shold come as no surprise that cell phones are all pretty much the same size, based on allowing the counterpoise to form a quarter-wavelength mode (approximately) to form at the lowest frequency of inended operation.
So the real answer (for an embedded antenna) is "Does the countepoise form a productive eigenmode in the white space?" and "Where do I place the embedded antenna feedpoint in order to support this mode?"
With embedded antennas, reducing frequency into the white space implies a counterpoise that is large enough to radiate at one quarter wavelength in order to create an effective radiating system.
It's not just about the antenna. It's about the overall system.
The good news is that reducing frequency also improves path loss which (all other things being equal) means you may be able to compensate for some additional loss in radiating efficiency.
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