Technology is advancing in leaps and bounds in today’s world. Communication plays a major part in this rapid growth and antennas are one of the most crucial components. Log Periodic Dipole Array Antennas(LPDA Antenna) are significant in modern broadcasting and telecommunication systems. Log periodic dipole array antennas are directional antennas with multiple elements arranged in a specific pattern. The length of the antenna elements generally decrease towards the front of the antenna and with elements of different lengths, they are able to pick up different frequencies, thus making them ideal for applications that require robust and versatile communication solutions in different frequencies. They are named as log periodic antennas since the impedance of these antennas is a logarithmically periodic function of their frequency. Log periodic antennas are generally used for applications where different frequencies have to be transmitted or received at different angles and different frequencies such as television broadcasting, broadband monitoring, and measurement systems, etc.
History and Development of LPDA Antenna
The log periodic antenna is considered to be invented by American electrical engineer Dwight E. Isbell and his colleague Raymond DuHamel in the 1957-1958 period and they published a paper regarding this. Later the concept was further developed by Paul Mayes. The concept of the log periodic antenna was patented by the University of Illinois in the USA following the work of these inventors. However, it is also believed that it was invented by John Dunlavy in 1952, but was not given due credit as it was invented as a secret mission while working for the United States Air Force.
Design Features of Log Periodic antenna
Log periodic antennas are composed of multiple dipole elements of different lengths and spacings arranged in a linear or planar configuration. Generally, they are arranged such that the length of the elements decreases towards the front of the antenna and with alternating phase between them at specific intervals following a logarithmic function of the frequency. These antenna elements are typically made from conductive materials, such as aluminum or copper, and mounted parallel on either side of a support structure which is usually made of a non conductive material. The performance characteristics of the log periodic antenna depends on the length, spacing, phase difference, and the logarithmic progression of the elements.
Log periodic antennas operate based on the principle of frequency dependent phase reversal. Each element resonates at a different frequency and as the frequency increases the resonant element travels towards the smaller elements creating a wave like signal that moves along the central structure. This mechanism provides a wideband frequency response with a consistent gain and impedance in log periodic antennas.
Key Parameters
Considering the key performance parameters of log periodic antennas, they are able to operate in multiple frequency bands. Log-periodic antennas can operate over a wide range of frequencies, from a few megahertz to several gigahertz, depending on their design. Log periodic antennas are used to have a relatively high gain due to their radiation pattern and directionality. They are able to operate with a peak gain of around 10-11dBi and the gain generally varies between 5 to 15 dBi. The operational range of a log periodic antenna depends on all these factors such as the frequency, gain as well as on the environmental factors and any obstacles or interferences. Log periodic antennas use normal N type female connectors in most cases and are generally pole or mast mounted. But these can vary based on the type of the log periodic antenna as they are also available in very compact panel like designs.
Key features of log periodic antenna
Few of the key features of a log-periodic antenna include the wideband frequency range, the directional gain and their compact design.
- Wideband frequency range
Log periodic antennas, due to the presence of conducting antenna elements of different lengths, have the ability to operate over a wide frequency range. Their coverage across a wide spectrum of frequencies makes them a suitable antenna option for various communication and RF applications. This enables users to use a single antenna to communicate across various channels at different frequencies. Thus, log periodic antennas are extremely useful in applications where the operating environment is dynamic or changes rapidly as they can ensure stable and uninterrupted communication in such scenarios.
- Directional Gain
Log periodic antennas have a stable gain which is a key advantage. They are able to maintain a high and stable directional gain performance even when the frequency varies or fluctuates. Thus log periodic antennas are able to provide a consistent directional gain across different frequency bands. Due to their high directional gain, they are able to target the signals towards a specific direction thus increasing the range of communication in that direction. This feature makes log periodic antennas ideal for applications that require effective and precise long range communication.
- Compact design
Log periodic antennas have a simple design and structure. They are generally compact in size and thus they can be easily used in applications that have space restrictions. They can be used conveniently in both static and mobile applications. Log periodic antennas are relatively easy to manufacture and install due to their compact design.
Types of Log Periodic Antennas
Log periodic antennas are available in different shapes and frequencies. Four of the most common types of antennas are discussed below.
- Log Periodic Dipole Array (LPDA)
This is the most common type of log periodic antenna. As the name suggests, LDPA antennas have an array of dipole antenna elements arranged in increasing length and mounted along either side of a support boom. The antenna elements are connected in parallel to a feed line and the longest dipole acts as a reflector. The LPDA antenna is generally fed from the shortest half-dipole element through a single port. LPDAs usually perform with uniform input impedances, VSWR, and radiation characteristics over a wide range of frequencies. This type of log periodic antennas is typically used for television reception and radio applications.
- Log-Periodic Monopole Antenna
Log periodic monopole antennas are quite similar to LPDAs. In this variation, monopoles are used instead of
dipoles in the antennas and generally mounted on a conductive ground plane. This design has improved performance in terms of gain and is commonly used in ground-based communication systems.
- Planar Log-Periodic Antenna
This type of log periodic antenna has its antenna elements printed on a planar substrate similar to a PCB. Due to their compact design, they are ideal to be used in smaller devices with space limitations as well as for mobile applications. They are also commonly used in radar and microwave applications.
- Wire Log-Periodic Antenna
Similar to other log periodic antennas, wire log periodic antennas also have multiple antenna elements. However, instead of the typical solid elements, these antennas consist of antenna elements made using wires supported on a rigid frame or boom structure.
Log-Periodic antennas vs. Yagi Antennas
LPDA antennas and Yagi antennas are quite similar. However, they have some key differences that make them unique both in terms of physical structure and design as well as in terms of performance parameters.
Log periodic antennas typically have a triangular structure and are composed of multiple antenna elements of different lengths and distances from each other arranged in a specific array on either side of a boom-like structure. Yagi antennas are more linear in structure with their multiple antenna elements which are generally of the same length unlike in log periodic antennas, arranged in an array along a boom-like structure. Due to the similar length antenna elements, Yagi antennas are considered to be slightly easier to construct and manufacture than log periodic antennas. Log periodic antennas are slightly more complex to design and construct as the different lengths of the elements, their spacing, and phase differences have to be precisely calculated and implemented. Also, Yagi antennas are generally bulkier than log periodic antennas. However, log periodic antennas are comparatively easier to install than yagi antennas as Yagi antennas need more precise alignment for optimal performance in a specific direction.
Considering the performance parameters, both log periodic antennas and Yagi antennas are available in a wide range of frequency bands. Log periodic antennas generally operate in frequency ranges between 30 to 4200 MHz while Yagi antennas operate between 30 to 3000 MHz. Log periodic antennas have a broader radiation pattern and hence a lower gain and are low in directionality compared to Yagi antennas. Yagi antennas are highly directional and have a narrow bandwidth and hence have a much higher gain in a specific direction. The signals from a Yagi antenna are focused in a coverage area of an angle of about 45 degree to 90 degree while log periodic antennas are able to have a much broader coverage area due to having antenna elements of different lengths and spacing.
Log periodic antennas and Yagi antennas vary in terms of their applications too. Log periodic antennas are typically usually used in applications that require the signals to be transmitted and received in multiple directions and multiple different frequencies simultaneously. They are used in LPWAN, LoRa, LTE-M, NB-IoT, IoT, M2M applications, etc. Yagi antennas are better for point-to-point communication systems such as in broadcast, domestic, and commercial radio communication applications as they are highly directional and have a high gain towards a specific direction.
The initial installation costs and maintenance costs for both Yagi antennas and log periodic antennas are both relatively similar. However, log periodic antennas are generally considered to be more versatile as they can be used for use cases that require different frequencies. Yagi antennas need more regular maintenance to maintain their performance in one direction at an optimal level.
Advantages of log periodic antennas
Log periodic antennas are an extremely versatile type of antenna used in various communication systems due to their key advantages performance wise. Discussed below are a few of such advantages.
- Wide Bandwidth
Log periodic antennas are able to cover a broad range of frequencies and can operate across multiple frequency bands due to their wide bandwidth without the need for tuning or adjustments. Hence, log periodic antennas are considered to be versatile as a single antenna can replace several antennas designed for different frequency ranges. Due to this, log periodic antennas are versatile and cost effective.
- Directional radiation pattern
Log-periodic antennas have a directional radiation pattern. Thus they are able to focus their energy in a specific direction making them ideal for long-distance communication. The radiation pattern of log periodic antennas has low side lobes, meaning that they radiate most of their energy in the desired direction and minimize energy wasted in other directions. Their directional pattern makes them more resistant towards interference from other unwanted signals and any obstacles. This also helps in improving the signal-to-noise ratio.
- High gain
Log-periodic antennas typically have higher gain due to their directional radiation pattern. Thus, they have the ability to transmit and receive signals over longer distances and with great efficiency. In communication systems, high gain is a crucial parameter to maintain strong and stable signals over a larger range.
- Compact size
Log periodic antennas can be used in applications where there are space limitations as they are generally designed to be small and compact compared to other types of antennas. They are ideal to be used in both fixed and mobile applications.
Overall, log-periodic antennas offer key advantages such as wide frequency range, high gain, directional radiation pattern, and compact size, making them a versatile and convenient option for various applications in communication and broadcasting.
Disadvantages and Limitations
Although log periodic antennas have some key advantages, as always there are few limitations too.
- Complex Design and Construction
Since log periodic antennas are built to operate in multiple different frequencies, their design needs to be precise. The lengths of the antenna elements, their spacing and placement, phase difference between the elements etc. all need to be taken into consideration. Due to the complexity of design and construction, log periodic antennas tend to be relatively expensive.
- Assembly and Maintenance
The installation and maintenance of a log periodic antenna can be slightly complex and time-consuming since they have multiple elements that require precise spacing and placement. Also to ensure that the antenna functions in its optimal state continuously with stable and accurate signal transmission and reception, regular maintenance is required for log periodic antennas.
- Interference
Especially in outdoor applications, log periodic antennas tend to be subject to interferences from other signals as well any physical obstructions. They can also be affected by weather conditions such as strong winds making them susceptible to wind loading.
Applications of log periodic antennas
As discussed throughout the article, log periodic antennas are extremely versatile and hence are used in various applications across different industries. Some of the common use cases are discussed below.
- Television and Radio Broadcasting
Log periodic antennas are commonly used for TV and radio broadcasting to receive and transmit signals as they are able to operate in a wide range of frequencies, thus, enabling them to provide content over multiple channels and stations. With the design and performance characteristics of log periodic antennas, it is feasible to use a single antenna for multiple frequency bands by using log periodic antennas.
- WiFi
Log periodic antennas are also commonly used to establish WiFi networks. They can be used to transmit and receive signals for WiFi applications as they are able to provide a stable and strong wireless internet connection.
- Cellular Networks
Similar to WiFi networks, they are also used in cellular networks to transmit and receive signals from cell towers, enabling mobile communication. Their directionality and gain enables them to focus signals strongly in a certain direction, thus, enabling them to establish connections over long distances.
- Signal Boosters
Log periodic antennas are also commonly used in signal booster systems. Their high gain and directionality enhance the strength and range of signals for better reception and transmission thus making them ideal for signal boosters.
- Distributed Antenna Systems (DAS)
Log periodic antennas are also commonly used for DAS installations. Their wide bandwidth, high gain and directionality are helpful to improve the wireless coverage and capacity of communication systems in large buildings, stadiums, airports, and other public areas.
Installation and Maintenance
The installation process for a log periodic antenna begins with the site selection. It is important to select a location with minimum obstructions and interference to ensure optimal performance. Other weather conditions and environmental factors also need to be taken into consideration. Log periodic antennas are generally mounted on a mast or pole to minimize obstructions in the signal pathways. It is important to securely mount the antennas to ensure stability and proper alignment. High quality coaxial cables and connectors need to be used to minimize signal loss during transmission. Another factor to be considered is proper grounding, which is crucial to protect the antenna from electrical surges that may occur. It is essential to properly place the antenna in correct orientation and align it properly to ensure optimal performance towards a specific direction in a desired frequency range. Finally, it is important to conduct sufficient testing and fine tune it by making necessary adjustments to achieve optimal quality and reliable performance of a log periodic antenna.
Case Studies
Log periodic antennas are used in many industries and have various use cases as understood throughout the article. Described below are a few of the real world scenarios and applications of log periodic antennas.
- Broadcasting
Log periodic antennas are able to cover a broad spectrum of frequencies due to their structure with different lengthened antenna elements and phase differences and hence they are commonly used in both radio and television broadcasting. Thus log periodic antennas are widely used in urban areas and remote areas alike to transmit signals across various channels providing coverage in an efficient and stable manner.
- Military and defense
Log periodic antennas are widely used in the military and defense industry for various defense and safety applications. They are commonly used in aircraft, satellites, radar systems, military equipment etc. for signal transmission and reception. Log periodic antennas are able to provide communication reliably over a wide bandwidth and high directionality, making them ideal for critical missions and surveillance operations in the military. In military and defense, army personnel use devices powered by log periodic antennas to stay connected across different operational locations. This is made possible due to reliability and stability of the signals transmitted and received over log periodic antennas. They are also widely used for surveillance applications in military and defense missions. They are able to transmit and receive signals swiftly, making them important in critical missions. Log periodic antennas enable real time data exchange between remote sensors, drones, and command centers. This enables army personnel to make well informed decisions in time critical applications in military and defense tasks.
- Electronic Warfare
Log periodic antennas are also integral in electronic warfare systems. Their high directional gain and targeted signal transfer can be crucial to identify enemy devices and to intercept and jam enemy communication signals. In electronic warfare, log-periodic antennas are used as part of systems to intercept, jam, or secure communications by leveraging their wideband capabilities and directional performance. This can be crucial in warfare to effectively counterattack enemy communication signals to gain a tactical advantage on the battlefield.
Conclusion
Log periodic antennas are a crucial component in the modern antenna technology landscape. Log periodic antennas are available in various shapes, sizes and configurations and among them, Log Periodic Dipole Array antennas are at the forefront as the most used type of log periodic antennas. LPDA antennas operate such that the impedance of the antenna is a logarithmically periodic function of its operating frequency. They are able to facilitate a wide range of applications from television broadcasting to WiFi and cellular systems to critical military and defence applications. The ability of log periodic antennas to operate across a broad frequency range, its directional capacity, and its compact design make them a versatile device and a convenient go-to solution for consumers looking to enhance their communication systems.
