24-11-2012, 12:24 PM
UHF MICROSTRIP ANTENNA DESIGN AND SIMULATION
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ABSTRACT
This paper presents a design studies in the development for a lightweight, low volume, low profile planar microstrip antenna in the application for a military band short range radio communication system (UHF), at a frequency range of 200Mhz - 400Mhz. Currently, most military aviation platforms are equipped with UHF communication system for their operational requirements. As most conventional communication antennas fitted onboard the aerial platforms are dipole-type and these antennas are located on the external structure of the platforms, this protruding antenna configuration will increase the aerial platform’s radar cross section (RCS) significantly as these antenna fins will act as a radar reflector. Antenna size is dictated by its operating frequency and the lower the frequency, the larger the antenna. In addition, these antennas will also affect the aerodynamics and handling of the aerial platforms. Altering the antenna size would be more cost-effective than other measures to improve aerodynamics, which may inadvertently affect radar, visual or any other signatures of the aircraft.
INTRODUCTION
Background
Radio Antenna
The antenna is usually the last element considered when designing a RF equipment. However, in a wireless link environment, the transmitting and receiving antenna are directly involved to achieve the desired overall performance.
An antenna is a conductive element which converts electrical energy into an electromagnetic field in the transmitter, or converts an electromagnetic field into electrical energy in the receiver. An important feature is the property of reversibility; the same antenna can be used with the same characteristics as a transmitter or as a receiver antenna [1]. An antenna is characterized by its center frequency, bandwidth (BW), polarization, gain, radiation pattern and impedance [1].
Introduction to Microstrip Antenna
The concept of microstrip antenna dates back to the 1950’s, but it was not until the 1970’s that greater emphasis was given to develop this technology. This is mainly due to the availability of good substrates. Since then, extensive research and development of microstrip antenna and arrays, exploiting the numerous advantages such as light weight, low volume, low cost, planar configuration, compatibility with integrated circuits, have led to diversified applications and to the establishment of the topic as a separate entity within the broad field of microwave antennas [3].
Problem Definition
The two most serious limitation of the microstrip antennas are its narrow bandwidth and low gain. The requirement for a low volume and low profile in the antenna further deteriorates these two parameters. This is because of the fact that there is a fundamental relationship between the size, bandwidth and efficiency of an antenna. As antennas are made smaller, either the operating bandwidth or the antenna efficiency must decrease. The gain is also related to the size of the antenna, which is small antenna typically provides lower gain than larger antenna.
Till date, with the key design considerations such as the size reduction, together with the bandwidth and gain enhancement in wireless communication, many researchers have developed various techniques to enhance the bandwidth and gain of the microstrip antenna and some of the techniques are loading of high permittivity dielectric superstrate, stacked configuration and slotted patch antenna. The use of the superstrate loading technique helps to increase the radiation efficiency. Stack configuration with 2 patches, driven and parasitic, and 2 substrates are used to enhance the gain and increases the bandwidth of the antenna ranging from 10-20%. The patch loaded with slots like the U-slotted patch also can be used to enhance the bandwidth by 10-40%.
Substrates Characteristics
There are many substrates that can be used for the design of microstrip antennas, and their dielectric constants (
r) are usually in the range of 2.2
r 12. Thick substrates are most desirable for antenna performance as their dielectric constants are in the lower end, which provide better efficiency, larger bandwidth, loosely bound fields for radiation into space (better radiation power). However, these are achieved at the expense of larger element size, increase in weight, dielectric loss, surface wave loss and extraneous radiations. Thin substrates with higher dielectric constants, on the other hand, are desirable for microwave circuitry because they require tightly bound fields to minimize undesired radiation and coupling, thus leading to smaller sizes. However, because of their greater losses, they are less efficient and have relatively smaller bandwidth [2].
Method of Analysis
There are many methods of analysis for microstrip antennas. The most popular models are the transmission-line, cavity and full-wave.
The transmission-line model is the easiest of all, it gives good insight and it is adequate for most engineering purposes and requires less computation. However, it is less accurate and it is more difficult to model coupling. Comparing with the transmission-line model, the cavity model is more accurate but at the same time more complex. However, it also gives good physical insight, and is rather difficult to model coupling, although it has been used successfully. In general when applied properly, the full-wave models are very accurate, very versatile, and can treat single elements, finite and infinite arrays, stacked elements, arbitrary shaped elements, and coupling. However, they are the most complex models and usually give less physical insight.
For the design of this project, the transmission-line model is selected as it provides a reasonable interpretation of the radiation mechanism while simultaneously giving simple expressions for the characteristics. In this model, a rectangular microstrip antenna is represented as an array of two radiating narrow aperture (slots), each of width W and height h, separated by a low impedance ZC transmission line of length L.
[attachment=40945]
ABSTRACT
This paper presents a design studies in the development for a lightweight, low volume, low profile planar microstrip antenna in the application for a military band short range radio communication system (UHF), at a frequency range of 200Mhz - 400Mhz. Currently, most military aviation platforms are equipped with UHF communication system for their operational requirements. As most conventional communication antennas fitted onboard the aerial platforms are dipole-type and these antennas are located on the external structure of the platforms, this protruding antenna configuration will increase the aerial platform’s radar cross section (RCS) significantly as these antenna fins will act as a radar reflector. Antenna size is dictated by its operating frequency and the lower the frequency, the larger the antenna. In addition, these antennas will also affect the aerodynamics and handling of the aerial platforms. Altering the antenna size would be more cost-effective than other measures to improve aerodynamics, which may inadvertently affect radar, visual or any other signatures of the aircraft.
INTRODUCTION
Background
Radio Antenna
The antenna is usually the last element considered when designing a RF equipment. However, in a wireless link environment, the transmitting and receiving antenna are directly involved to achieve the desired overall performance.
An antenna is a conductive element which converts electrical energy into an electromagnetic field in the transmitter, or converts an electromagnetic field into electrical energy in the receiver. An important feature is the property of reversibility; the same antenna can be used with the same characteristics as a transmitter or as a receiver antenna [1]. An antenna is characterized by its center frequency, bandwidth (BW), polarization, gain, radiation pattern and impedance [1].
Introduction to Microstrip Antenna
The concept of microstrip antenna dates back to the 1950’s, but it was not until the 1970’s that greater emphasis was given to develop this technology. This is mainly due to the availability of good substrates. Since then, extensive research and development of microstrip antenna and arrays, exploiting the numerous advantages such as light weight, low volume, low cost, planar configuration, compatibility with integrated circuits, have led to diversified applications and to the establishment of the topic as a separate entity within the broad field of microwave antennas [3].
Problem Definition
The two most serious limitation of the microstrip antennas are its narrow bandwidth and low gain. The requirement for a low volume and low profile in the antenna further deteriorates these two parameters. This is because of the fact that there is a fundamental relationship between the size, bandwidth and efficiency of an antenna. As antennas are made smaller, either the operating bandwidth or the antenna efficiency must decrease. The gain is also related to the size of the antenna, which is small antenna typically provides lower gain than larger antenna.
Till date, with the key design considerations such as the size reduction, together with the bandwidth and gain enhancement in wireless communication, many researchers have developed various techniques to enhance the bandwidth and gain of the microstrip antenna and some of the techniques are loading of high permittivity dielectric superstrate, stacked configuration and slotted patch antenna. The use of the superstrate loading technique helps to increase the radiation efficiency. Stack configuration with 2 patches, driven and parasitic, and 2 substrates are used to enhance the gain and increases the bandwidth of the antenna ranging from 10-20%. The patch loaded with slots like the U-slotted patch also can be used to enhance the bandwidth by 10-40%.
Substrates Characteristics
There are many substrates that can be used for the design of microstrip antennas, and their dielectric constants (
r) are usually in the range of 2.2
r 12. Thick substrates are most desirable for antenna performance as their dielectric constants are in the lower end, which provide better efficiency, larger bandwidth, loosely bound fields for radiation into space (better radiation power). However, these are achieved at the expense of larger element size, increase in weight, dielectric loss, surface wave loss and extraneous radiations. Thin substrates with higher dielectric constants, on the other hand, are desirable for microwave circuitry because they require tightly bound fields to minimize undesired radiation and coupling, thus leading to smaller sizes. However, because of their greater losses, they are less efficient and have relatively smaller bandwidth [2].
Method of Analysis
There are many methods of analysis for microstrip antennas. The most popular models are the transmission-line, cavity and full-wave.
The transmission-line model is the easiest of all, it gives good insight and it is adequate for most engineering purposes and requires less computation. However, it is less accurate and it is more difficult to model coupling. Comparing with the transmission-line model, the cavity model is more accurate but at the same time more complex. However, it also gives good physical insight, and is rather difficult to model coupling, although it has been used successfully. In general when applied properly, the full-wave models are very accurate, very versatile, and can treat single elements, finite and infinite arrays, stacked elements, arbitrary shaped elements, and coupling. However, they are the most complex models and usually give less physical insight.
For the design of this project, the transmission-line model is selected as it provides a reasonable interpretation of the radiation mechanism while simultaneously giving simple expressions for the characteristics. In this model, a rectangular microstrip antenna is represented as an array of two radiating narrow aperture (slots), each of width W and height h, separated by a low impedance ZC transmission line of length L.