**3. Type of antennas**

Small antennas for communication systems.

Monopole—quarter wavelength wire antenna.

Dipole—Dipole antenna consists of two quarter wavelength wires. Dipole is a half wavelength wire antenna. The monopole and dipole antennas couple to the electric field of the electromagnetic wave in the region near the antenna. Slot antenna—half wavelength slot: A *slot antenna* consists of a metal surface with a *slot* cut out.

**3.1 Steerable antennas**

steering.

**Figure 1.** *Monopole antenna.*

**5**

mechanically steerable arrays.

*Introductory Chapter: Novel Radio Frequency Antennas DOI: http://dx.doi.org/10.5772/intechopen.93142*

• Arrays with switch-able elements. The array may be partially electronically and

• Hybrid antenna systems—for fully electronically steerable arrays. The design can be based on digital beam forming (DBF). These systems may consist of

• In digital beam forming, the steering is performed directly in a digital level. DBF allows the most powerful and flexible control of the antenna beam

Monopole antenna is usually a one-quarter wavelength-long conductor mounted above a ground plane or the earth as shown in **Figure 1**. Based on the image theory behind the ground plane, the monopole image is located. The monopole antenna and the monopole image form a dipole antenna. Monopole antenna is half a dipole that radiates electromagnetic fields above the ground plane. The impedance of 0.5 λ monopole antenna is around 37 Ω. The beam width of a monopole, 0.25 λ long, is around 40°. The directivity of a monopole, 0.25 λ long, is around 3 dBi to 5dBi. Usually in wireless communication systems, very short monopole antenna is employed. The impedance of 0.05 λ monopole antenna is around 1 Ω with capacitive reactance. The beam width of a monopole, 0.05 λ long, is around 45°. The

Inverted monopole antenna is shown in **Figure 2a**. Loaded monopole antenna is shown in **Figure 2b**. Monopole antennas may be printed on a dielectric substrate as

phase and amplitude shifters for each radiating element.

**4. Monopole antenna for communication systems**

directivity of a monopole, 0.05 λ long, is around 3 dBi.

part of wearable communication devices.

Biconical antennas—biconical half wavelength wire antenna: Biconical antenna is a wideband antenna made of two conical conductive objects.

Loop antennas—Loop antenna is known as a magnetic loop. The loop antenna behaves as an inductor. The loop antenna couples the electromagnetic magnetic field in the region near the loop antenna. Monopole and dipole antennas couple to the electric field.

Helical antennas—helical wire antennas.

Printed antennas—antennas printed on a dielectric substrate.

Aperture antennas for base station communication systems


A comparison of directivity and gain values for several antennas is given in **Table 1**.

**Phased arrays:** Phased array antennas are electrically steerable. The physical antenna can be stationary. Phased arrays, smart antennas, incorporate active components for beam steering.


**Table 1.**

*Antenna directivity versus antenna gain.*
