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The Pros and Cons of Planar Antennas

Tamara Wilhite is a technical writer, industrial engineer, mother of two, and published sci-fi and horror author.

Introduction

A planar antenna puts both the active and parasitic elements on one plane, making them two dimensional. Planar antennas include microstrip antennas and printed circuit board antennas. The antenna “patches” may be square, triangular or circular.

400 MHz and 2 GHz planar antennas

400 MHz and 2 GHz planar antennas

The Advantages of Planar Antennas

Planar antennas are a low-cost ultra-wideband antenna, especially when they’re mass produced via printed circuit board technology.

They can be very small, making them ideal for wireless applications.

Planar arrays have a large aperture. Directional beam control is achieved by varying the phase of each element.

Planar antennas have a low profile. They’ve been used on aircraft for years, since a planar antenna on a thin, flexible substrate doesn’t affect the craft’s aerodynamics.

When they’re mounted on a rigid surface, they’re robust. For example, the planar design can include built-in heat sinks.

If you’re making a planar antenna with PCB technology, integrating it with other electronic components at the same time isn’t hard or expensive to do. The transmission lines can directly or indirectly feed an integrated planar antenna.

They can support linear and circular polarization, based on the design used.

Examples of wideband planar antennas with circular "patches".

Examples of wideband planar antennas with circular "patches".

The Disadvantages of Planar Antennas

The low profile of planar makes them popular in arrays. However, the elements and feed lines influence each other. This means that planar arrays need to be designed to account for mutual coupling between elements and internal reflections. Yet you need to use an array if you want to increase their efficiency.

Many planar antennas have a narrow bandwidth. This is particularly bad for microstrip antennas.

They have low radiation efficiency.

They have low gain. This can be improved by loading notches and putting a shorting pin in the radiating patch. Gaps between the patches of the planar antenna also improve the gain. This is why you see quad patch antennas with four mid-sized patches instead of an antenna with a single, very large “patch”.

Observations about Planar Antennas

Most planar antennas have low to medium gain.

A planar antenna may have a reflecting screen behind the active plane; this is common in radar systems.

An inverted F antenna consists of a monopole antenna parallel to the ground plane and grounded at one end. A PIF antenna or PIFA is a planar inverted-F antenna. A common use for this type of antenna is as the internal antenna in cell phones. Multi-band version of this antenna may be used in car radio, satellite navigation systems and wireless communication equipment.

Uses of Planar Antennas

Planar antennas are commonly used in wireless applications, especially when the wireless devices could be using any one of a number of frequencies. The classic example of this is a multi-band wifi network. Ultra-wideband planar antennas are commonly used in software defined radio. Wideband planar antennas can be used with signal sources, spectrum analyzers, and cell phone testers. Planar arrays are regularly used in radar systems.

Summary

Planar antennas are found in a variety of forms. In general, they’re cheap, versatile and often used in wide band applications. This comes at the cost of gain, efficiency and range.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: How can I make a pcb mounted planar antenna directional? Most of the micro sized radar sensor boards are omnidirectional.

Answer: The most common planar directional antenna is the patch antenna.

Virtually every Radar application sensor I have seen used directional antennas.

© 2018 Tamara Wilhite

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