Slot Antenna Basics and Impedance Explained

This page covers the basics of slot antennas, including their key features and an explanation of the impedance equation.

Definition: A slot antenna is formed by creating a slot in a metallic surface. It essentially consists of an opening, either in a conducting sheet of metal or in the walls of a waveguide.

This type of antenna is typically excited using a coaxial cable or a waveguide with appropriate coupling.

Key Features of Slot Antenna

Figure 1: Rectangular Slot Antenna

Figure 1 illustrates a rectangular slot antenna. This type usually features a slot with a length equal to λ/2 and a width significantly smaller than λ/2.

Excitation is commonly achieved using a coaxial cable at a distance of approximately 0.05λ from one end of the slot, as shown in the figure.

Here are some key features of slot antennas:

• The slot can be circular, rectangular, or any other shape and size.
• Slots are omni-directional and radiate from both sides.
• Arrays of slots are used to achieve higher gain and directivity.
• The electric field within the slot resembles a sinusoidal waveform.

Slot Antenna Impedance Equation

The impedance of a slot antenna can be calculated using the following equation:

Zs = [ ηo² / (4 * Zd) ]

Where:

ηo = 120*π Ohm

Zd = Impedance of the complementary dipole = Rd + j*Xd

• Rd = Real Part
• Xd = Reactive Part