Aperture Coupled Patch Antennas in Portable Wireless Electronic Devices

Key Takeaways

• When an extra layer of dielectric substrate is added to a patch antenna structure, it forms an aperture coupled patch antenna. 

• In an aperture coupled patch antenna, the power in the feed line is coupled to the antenna patch through the aperture in the ground plane.

• When designing an aperture coupled patch antenna, the width and length are design parameters for setting the impedance and frequency of operation, respectively.

Patch antennas are widely used in wireless electronic systems

In portable wireless electronic systems, patch antennas are widely used for transmitting and receiving signals. These antennas are lightweight, low-profile, and low-cost, with inherent narrow impedance bandwidth. However, today’s wireless communication systems require higher frequency bandwidth for high speed and large volume data transfers. Instead of conventional patch antennas, aperture coupled patch antennas are used to satisfy these advanced requirements.

Aperture coupled patch antennas have high radiation efficiency and gain compared to directly-fed patch antennas. Additionally, aperture coupled patch antennas have a higher number of design parameters than conventional directly-patched antennas, which makes designing them more flexible.

Let’s explore these antennas and their advantageous characteristics. 

What Are Patch Antennas?

For mobile and cellular communications, patch antennas are commonly used. These antennas are specially constructed, low-profile radio antennas that are capable of increasing an antenna’s radiation ability while reducing transmission line radiation. They are simpler to manufacture, cheaper to fabricate, and easier to modify post-fabrication than conventional antennas.

Patch antennas consist of two metal sheets, known as patch and ground planes, respectively. In patch antennas, the ground plane is a large metal sheet placed beneath a layer of dielectric substrate. A transmission line is placed on the dielectric substrate and the flat sheet of metal forming the patch is used to cover the top of the substrate. Patch antennas are usually flat, rectangular in shape, and mounted to flat surfaces.

While these antennas are widely used, for some applications requiring higher frequency bandwidth, aperture coupled patch antennas are a better choice. 

Aperture Coupled Patch Antennas

Aperture coupling is a non-contact type feeding technique in antennas, enabling power transfer between the feeding line and patch via a coupling mechanism. When an extra layer of dielectric substrate is added to the bottom part of a patch antenna that contains the feed line, it transforms the antenna into an aperture coupled patch antenna.

An aperture coupled patch antenna consists of two dielectric substrates: antenna substrate and feed substrate. The patch is mounted on the antenna substrate, whereas the feed line is attached to the feed substrate’s bottom part. The ground plane separates the two parallel substrate layers.

Placing the feed line below the ground plane shields the antenna from parasitic feed line radiations and parasitic electromagnetic coupling. This placement of the patch and feed line also allows the independent optimization of both parts. The power in the feed line is coupled to the antenna patch through the aperture in the ground plane.

In the next section, we’ll take a look at a few of the advantageous characteristics of aperture coupled patch antennas. 

Aperture Coupled Patch Antenna Dimensions and Characteristics

The dimensions of an aperture coupled patch antenna play a significant role in defining its characteristics and performance. Each dimension influences a parameter of antenna characteristics. For example, the width of an aperture coupled patch antenna determines the input impedance of the antenna. As the width of the antenna decreases, the input impedance increases and vice versa. Likewise, the length of an aperture coupled patch antenna influences the operating frequency. The length and frequency of operation share an inverse relationship. As the length increases, the operating frequency decreases and vice versa.

When designing aperture coupled patch antennas for specific applications, the width and length are design parameters for setting the impedance and frequency of operation, respectively. By adjusting these values, it is possible to achieve the required input impedance and frequency of operation. Cadence AWR software can help in designing and optimizing aperture coupled patch antennas.

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