Depends on what you mean by high frequency. The rabbit ears antenna used in broadcast TV is a dipole and is used for VHF.
High frequency is used because of the the size of antennas used to transmit and receive the communications signal. The higher the frequency the smaller the antenna.
A good antenna for general area coverage that features a doughnut pattern and extends horizontal distance in a 360-degree radius is a dipole antenna. Dipole antennas are typically used for omnidirectional coverage, providing consistent signal strength in all horizontal directions while minimizing vertical range. Another option is the omnidirectional vertical antenna, which also offers similar coverage characteristics. These antennas are commonly used in applications like broadcasting and wireless communication.
A transmitter antenna is a tuned circuit and it can be very complex and it even get more difficult at higher frequencies, if it's not a 1/4 wave length of the transmitter frequency it is un tuned and you will have some of your RF power radiated back to the transmitter, that is called SWR, for Standing Wave Ratio and it will damp the RF that is radiated from the antenna and if the SWR is to high it can damage the transmitters final stage. It don't have to be the real physical 1/4 or 1/2 wave and it can even be 5/8 of the wavelength but then a L/C circuit have to be inserted at the input side of the antenna to tune the antenna to the correct frequency one antenna can even be used for two different frequencies, then a L/C tuning circuit have to inserted at a 1/4 wave length of the higher frequency , this type of antenna is used in duplex systems, like a cell phone.
A: It is a terminology to imply that the scanner will be used at the hi end of frequency as opposed to low frequency
Some advantages of the Yagi- Uda Antenna include that this is a widely used design and low cost. The construction also is simple. Some disadvantages are that the receiver of the Yagi-Uda Antenna may have problem receiving signal.
Its resonant frequency is where its length is half a wavelength, so for 100 MHz the wavelength is 3 metres and a 1.5-metre long dipole is resonant. A dipole antenna can be used for many applications within a band of 10-20% around the resonant frequency.
High frequency is used because of the the size of antennas used to transmit and receive the communications signal. The higher the frequency the smaller the antenna.
Dipole
All types... depending on frequency and application. Lower frequency RFID's are typically near field and use inductive antenna designs, higher frequency ones use far-field designs. Low frequency RFID's like the TIRIS pet ID's use coils of wound wire. HF type RFID's like MiFARE use simple planar loop antenna designs. Most VHF RFID's use dipole and modified dipole designs with reflector elements. UHF and microwave RFID's frequently use patch and slot antenna designs.
A full-wave loop antenna can be interchanged with a folded dipole without much difference. The input impedance is similar and the only difference is in the directivity: a full wave loop radiates along the axis of the loop, while a vertical folded dipole is omnidirectional.
1.25MHz
Counterpoise is used in a dipole vertical antenna to improve its performance by providing a balanced electrical path for the antenna. This helps to reduce common-mode currents and improve the antenna's efficiency in transmitting and receiving signals. By using a counterpoise, the dipole antenna can achieve a better radiation pattern and impedance matching.
A dipole antenna, is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other (in line with each other), with a small space between them. The radio frequency voltage is applied to the antenna at the center, between the two conductors. These antennas are the simplest practical antennas from a theoretical point of view. They are used alone as antennas, notably in traditional "rabbit ears" television antennas, and as the driven element in many other types of antennas, such as the Yagi. Dipole antennas were invented by German physicist Heinrich Hertz around 1886 in his pioneering experiments with radio waves.
A straight antenna, often referred to as a dipole antenna, is a type of radio antenna that consists of two conductive elements, typically arranged in a straight line. It is designed to efficiently transmit and receive electromagnetic waves, with its length usually being half the wavelength of the frequency it operates at. Straight antennas are commonly used in various applications, including broadcasting and telecommunications, due to their simplicity and effectiveness.
A Hertz antenna refers to a type of dipole antenna that was invented by the German physicist Heinrich Hertz. It is a simple antenna design with two conductive elements used for transmitting or receiving electromagnetic waves at radio frequencies.
A bipolar antenna, also known as a dipole antenna, consists of two conductive elements, typically in the form of straight rods, that are oriented in opposite directions. It operates by radiating and receiving electromagnetic waves, making it effective for various communication applications. The antenna's length is typically around half the wavelength of the frequency it is designed to transmit or receive, allowing for optimal performance. Bipolar antennas are widely used in radio, television broadcasting, and wireless communication systems.
You can use an inductor or capacitor circuit to electrically lengthen or shorten the antenna. I cant remember which circuit does which but that's how antennas are efficiently used for several frequencies.