Coplanar AM antenna

 The length of an antenna for Amplitude Modulation (AM) radio transmission depends on the frequency of the transmission. For AM radio broadcasting from AM transmitter, the standard carrier frequencies used are in the range of 540 kHz to 1700 kHz. The wavelength of a signal at these frequencies is approximately 560 meters to 557 meters respectively.

The length of a dipole antenna for AM radio transmission is typically half of the wavelength of the signal, therefore an AM antenna for a carrier frequency of 540 kHz would be around 280 meters long, while an antenna for a carrier frequency of 1700 kHz would be around 278.5 meters long.

However, it's worth noting that these are theoretical values and in practice, the actual antenna length may be shorter than half of the wavelength. This is because the actual antenna length is not critical and the antenna efficiency is not greatly affected by small variations in length.

Also, it's worth noting that these are the lengths for a dipole antenna and other types of antennas such as the loop antenna, the long wire antenna, and the ground plane antenna can also be used for AM transmission and their lengths are different from the dipole antenna.

Coplanar antenna for AM

Coplanar antennas can be build and used for Amplitude Modulation (AM) radio transmission and reception. A coplanar waveguide (CPW) is a type of transmission line that can be used as an antenna for AM radio transmission.

coplanar microstrip AM antenna
 A coplanar antenna for AM transmitter typically consists of a center conductor and two ground planes, which are all on the same plane. The center conductor is used to transmit and receive the signal, while the ground planes are used to provide a reference potential for the signal.

The coplanar antenna design is relatively simple and easy to manufacture, and it can be integrated into a printed circuit board (PCB) for compact and low-cost applications. It is also relatively easy to match the coplanar antenna to the transmission line, which is important for the efficiency and performance of the antenna.

It's worth noting that the size and shape of the coplanar antenna, as well as the distance between the center conductor and the ground planes, will affect the performance of the antenna, particularly the bandwidth and the input impedance. Therefore, the coplanar antenna must be designed and optimized for the specific frequency and application.

Also, it's worth noting that the coplanar antenna's performance characteristics are different from the dipole antenna, so it may not be the best choice for all situations.

Building AM coplanar antenna

Here is an example of how to make a coplanar antenna for Amplitude Modulation (AM) radio transmission:

  1. Determine the carrier frequency of the AM signal: The carrier frequency is the frequency of the radio signal that is modulated with the audio signal. For example, the carrier frequency for AM radio broadcasting is in the range of 540 kHz to 1700 kHz.

  2. Calculate the dimensions of the antenna: The dimensions of the antenna are determined by the carrier frequency and the desired performance characteristics. For example, for a carrier frequency of 1000 kHz, the dimensions of the coplanar antenna can be:

  • Center conductor width: 0.5 mm
  • Center conductor length: 15 mm
  • Ground plane width: 2 mm
  • Ground plane length: 30 mm
  • Distance between center conductor and ground plane: 0.3 mm
  1. Print the design on a PCB: The design can be printed on a PCB using a PCB layout software such as Eagle or Altium Designer. The PCB will act as the substrate for the antenna.

  2. Etch the PCB: The PCB is then etched to remove the unwanted copper and leave the desired antenna pattern.

  3. Apply the metal layer: The metal layer is applied to the PCB using a process such as electroplating or vacuum deposition.

  4. Test and tune the antenna: Once the antenna is built, it needs to be tested and tuned for optimal performance. The antenna is connected to a network analyzer and the return loss, gain and input impedance are measured. The dimensions of the antenna can be adjusted to improve the performance.

It's worth noting that this is just an example, and the actual design and construction of a coplanar antenna will depend on the specific requirements of your application, such as frequency, power, size and so on. And it's also important to take into account the characteristics of the PCB material and its effect on the performance of the antenna.


[1] Homogeneous and Inhomogeneous transmission line

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