Frequency Independent Antennas Research Articles

Miniaturization and Bandwidth Enhancement of Fractal-Structured Two-Arm Sinuous Antenna Using Gap Loading with Meandering

A sinuous antenna is a frequency-independent antenna known for its wide bandwidth and consistent gain, which makes it valuable in broadband applications such as ultrawideband (UWB) radar and ground-penetrating radar (GPR). However, sinuous antennas tend to be rather large. Consequently, numerous studies have explored miniaturization methods, with the gap-loading method emerging as a prominent approach. Unfortunately, it is still difficult to achieve broad bandwidths for conventional miniaturized sinuous antennas. In this paper, we use a novel approach incorporating a meander shape into the sinuous curve and employing gap loading with meandering. This innovative technique results in the development of a fractal-structured two-arm sinuous antenna characterized by an ultra-compact size and significantly expanded bandwidth. Adding a meander line in the outermost part maximizes the capacitance, thereby enhancing the gap-loading effect and minimizing the overall size of the sinuous antenna. In addition, the introduction of an inner meander line increases the inductance, contributing to a further expansion of the antenna’s bandwidth. For example, the electrical length of the antenna without the meander line is 0.552 × 0.552 × 0.052 λg3, while the electrical length of the antenna with the meander line is only 0.445 × 0.445 × 0.036 λg3, i.e., 19.4% smaller. The antenna lacking the outermost meander line exhibits a 10 dB impedance bandwidth, spanning from 0.74 to 10.53 GHz. In contrast, the antenna featuring the outermost meander line has a 10 dB impedance bandwidth, extending from 0.51 to 10.72 GHz, which results in a remarkable enhancement in the fractional bandwidth (by 8.1%). Hence, the proposed antenna design is a good candidate for broadband applications that require miniaturization.

Improving absorption performance of resonant metamaterials using self-complementary shapes

In electromagnetics, self-complementary antenna shapes possess a frequency-independent characteristic due to their particular shape. Based on this concept, this paper investigates the potential applications of self-complementary shapes for sound absorption to broaden the bandwidth and enhance the performances of resonators without altering the sizes and resonance frequencies. Self-complementary shapes, such as log-periodic planar tooth and log-spiral shapes, are used to demonstrate the effectiveness of our approach in enhancing the absorption bandwidth and performance of a resonator. Such shapes improve the absorption performance up to 58 % compared to a resonator with an equivalent circular area when the opening area is reduced, whereas they exhibit weak performance for wide opening areas. Numerical and experimental analyses are conducted to verify their performances and to investigate the effect of the materials inside the backing cavity, neck length, opening size, and geometry on absorption. By extending the use of frequency-independent antenna shapes as sound-absorbing structures, this approach overcomes the inherent limitations of resonant metamaterials to achieve an enhanced sound absorption for various applications.

Study of the electrical parameters dependences of oblique log-periodic antennas on the geometric structure of their reducing elements

Antenna systems are an integral part of any transmitter-receiver device. A broad-band and frequency-independent antenna can be created applying a principle of electrical similarity. Its essence is that the electrical parameters of antennas remain unchanged if, with a decrease or increase in wavelength n times and, accordingly, decrease or increase the linear dimensions of the antenna elements. It is very important to guarantee the constancy of the antenna-radiating element’s parameters in a sufficiently wide frequency range. Log-periodic, biconical and various types of helical antennas satisfy these requirements. Structurally, a log-periodic antenna is a complex structure consisting of a symmetrical two-wire or four-wire collecting line. Radiators of the same type are connected to it in a cross order. The paper presents results obtained on the basis of modeling the electrical parameters of wide-range log-periodic antennas of the decameter range with different shapes of radiating elements in the MMANA-GAL environment. The authors considered methods for constructing periodic structures of flat log-periodic antennas. The interrelation of their structural elements is presented. It determines properties of wide-range operation. The electrical parameters dependences of inclined log-periodic antennas on the structural differences of their radiating elements are investigated. The conditions for the vibrator and frame emitters application are substantiated while maintaining the range properties of the log-periodic structure.

Broadband Antennas Based on the Double Moebius Strip

The family of new antenna designs based on the double Moebius strip principle is proposed in this article. Three possible options of the power supply port location had been reviewed in this respect: the cut external strip with the signal port located directly in the cut area is used; the continuous rings without discontinuities are applied, with the signal port located in the gap between the strips; the power supply port is located in the interstrip area, and there is a cut in one of the strips. The radio technical parameters of the antennas were researched by means of their modelling in Ansys HFSS packet. The strip width, its thickness, the interstrip gap, as well as the radius of the cylinder within which the antenna may be enabled, were used as mechanical parameters of the antennas based on the double Moebius strip. The best results were represented by the super-broadband antennas with the port located between two strips. In particular, 2-inch (50.8 mm) frequency independent antenna based on the singular continuous Moebius ring has a bandwidth of 38.648 GHz (from 11 to 49.648 GHz), and the frequency ratio (correlation of maximum operation frequency to the minimum one) exceeds 4.5. The application of the cut in the strip helped to improve the frequency response characteristics of such antenna, having increased its frequency ratio to the value of 5.548. In fact, the synthesized antennas occupy the intermediate niche between the double strip ring and the fractal antennas in terms of their characteristics. It makes it possible to use them in integrated communication, radio location, radio monitoring and navigation, both as independent structural units and as parts of wheeled gear structures of the crewless platforms.

Sinuous Antenna for UWB Radar Applications.

In this paper, the recent progress on sinuous antennas is detailed, focusing the attention on the antenna geometry, dielectric structure, and miniaturization techniques. In the first part, we introduce the basic principles of the frequency-independent antenna, in particular the self-complementary and log-periodic geometries, as well as the antenna geometries, all characterized in terms of angles. The operating principles, main advantages, system design considerations, limits, and challenges of conventional sinuous antennas are illustrated. Second, we describe some technical solutions aimed to ensure the optimal trade-off between antenna size and radiation behavior. To this aim, some special modification of the antenna geometry based on the meandering as well as on the loading with dielectric structures are presented. Moreover, the cavity backing technique is explained in detail as a method to achieve unidirectional radiation. Third, we present a new class of supershaped sinuous antenna based on a suitable merge of the 2D superformula and the sinuous curve. The effect of the free parameters change on the antenna arm geometry as well as the performance improvement in terms of directivity, beam stability, beam angle, gain, and radiating efficiency are highlighted.

On frequency-independent horn antenna design for plasma positioning reflectometers, from simulation to prototype testing

Using a new framework for horn antenna optimization, a first frequency-independent horn antenna for a plasma positioning reflectometer (PPR) is designed.This hardware optimization is a new approach aiming on lowering the computational complexity of PPR interpretative models able to extract profiles and fluctuations of electron density and temperature from reflectometry measurements. PPR measurements are a strong candidate to provide real-time feedback for plasma position control in long-discharge fusion tokamaks such as ITER and DEMO, which requires fast interpretative models. Reducing the computational complexity of these models is therefore critical.In this paper, ray tracing simulations in the poloidal plane are used to compare different radiation patterns and evaluate them on multiple performance criteria. An antenna shape leading to a frequency-independent far-field radiation diagram is found with the PROFUSION optimizer and a prototype of this antenna is tested against an unoptimized conical reference antenna.The ray tracing performance criteria indicate that fundamental Gaussian frequency-independent antennas perform well, albeit in general worse than same-sized frequency-dependent antennas. Furthermore, it is seen that the pyramidal ITER gap 6 antenna performs well given the spatial constraints and that more performant antennas could be used, when more space was available.The prototype testing reveals challenges in obtaining frequency-independent characteristics within a tokamak blanket environment, which is additionally complicated by misalignment risks.

High-Power V-Band-to-G-Band Photonically Driven Electromagnetic Emitters

High-power V-band-to-G-band (50-220 GHz) photonically driven electromagnetic emitters, composed of frequency-independent (FI) antennas and charge-compensated modified unitraveling carrier photodiodes (CC-MUTC PDs), are demonstrated in this article. The designed and fabricated PDs achieve a responsivity of 0.2 A/W and are able to provide up to 12-dBm output power. The impedances of the PD and the FI antennas (the sinuous antenna, the spiral antenna, and the log-periodic antenna) are characterized, showing that different antennas could be selected to provide either highest radiated power or widest bandwidth depending on applications. The measurement results indicate that the integrated emitter with the sinuous antenna and the 8-μm PD achieves a record-high broadside effective isotropic radiated power (EIRP) of 20 dBm with an optical-to-terahertz (THz) power conversion efficiency of 15.7% while maintaining EIRP greater than 0 dBm up through 115 GHz of bandwidth (50-165 GHz). The emitter with the spiral antenna and the 5-μm PD provides a wide 3-dB bandwidth of 34 GHz with a maximum EIRP of 8.8 dBm. These high-power wideband emitters can be used for wireless communications, millimeter-wave (mm-wave) and sub-THz imaging, and radar systems.

Axial Ratio Improvement of Spiral Antenna with Resistive Loading

Spiral antenna belongs to the class of frequency independent antenna. It radiates circularly polarized wave bidirectionally. Due to the finite size of the antenna, the performance at the lower frequency degrades. This could be accounted to the reflection of the current from the truncation. Wide band characteristics from 300MHz to 3.5GHz are able to achieve through the partial resistive loading of the antenna. The lower frequency 3dB axial ratio has been improved significantly from 600MHz for the unloaded case to 200MHz for the loaded case without much effect on the efficiency. At 300MHz, the efficiency is around 60% and axial ratio at within 3dB range.

Investigation of energy stealth of radar stations with band antennas from the radio monitoring complex

Using spectral representation of non-harmonic processes and partial characteristics of antennas, energy equations of transmissionreception of broadband signals in the radio channel with scattering on the object and the direct radio channel between the radar and the radio monitoring (RM) complex have been obtained. Energy of received signals is determined by value of product of spectral density of radiation power and partial moment of transmission-reception averaged in the range of cyclic frequencies. The signal-to-noise ratio at the receiver input reaches the highest value when the partial moment of transmission-reception of signals in the radio channel changes according to a linear law. At fixed average radar power, energy of information signals at incoherent accumulation can be increased due to selection of antennas with partial directive gain amplifying wave processes in areas of their spectra concentration. The range of the radar is proportional to the linear dimensions and significantly depends on the shape of the object. The rules of antenna characteristics selection are justified to ensure radar stealth from RM systems while maintaining the required range of target detection and recognition. When using an antenna with a partial directive gain constant in the range of working cyclic frequencies in the radar, and in the RM complex of an antenna system with a frequency-independent effective area, the partial moment of transmission-reception of signals in the forward radio channel is constant. Its value is determined by the product of partial directive gain at the central frequency of the range. Forms of pulses supplied to input of transmitting antenna and radiated into space coincide, and shape of signal at output of receiving antenna has the form of their derivative. Due to application of frequency-independent antennas in radar and RM complex, energy of probing signals increases compared to levels typical for antenna systems with partial directivity indices varying in proportion to current value of cyclic frequency in the first or second degree. This pattern is due to the significant effective area of the receiving antenna in the lower part of the frequency range, which parries the low efficiency of radiation of low-frequency components of the radar signal spectrum. In radio channels with partial moments of transmission-reception of signals varying with frequency increase according to linear law, energy supplied to receiver input increases in comparison with levels achievable at quadratic and cubic dependencies of partial moments on cyclic frequency due to the same type dependencies of partial directive gain antenna of radar and effective area of antenna of RM complex. Stealth of probing radiation increases as dimensions of radar antennas increase due to increase of partial directive gain and decreases as dimensions of antenna systems of RM complexes increase due to increase of their effective areas. The duty cycle of pulses forming regular sequences, established due to the condition of accumulation of energy of reflected signals due to irradiation of the object, which is required to complete the functional tasks of the radar, decreases in proportion to the increase of the partial directive gain antenna at the central cyclic frequency. Energy of information signals increases in proportion to coefficients depending on relative half-width of their spectra, and decreases with increase of central cyclic frequency to the second degree. As pulse repetition frequency increases at maximum permissible average density of radiation power limited by radar stealth requirements, energy density of probing signals decreases proportionally. The average power of the radar at a fixed level of spectral density varies in proportion to the bandwidth occupied by the probing signals due to a reduction in the following period.

Fully planar frequency independent square Archimedean spiral antenna with impedance transformer for ground penetrating radars

AbstractAn ultra‐wideband unidirectional circularly polarized planar self‐complementary and compact Archimedean square spiral antenna is proposed in this paper. Compared to the conventional center‐fed or vertically‐connected coaxial line spiral antennas, the proposed antenna has a completely planar feed structure. The traditional impedance transformer (balun) in the third dimension is moved to the planar plane based on a wideband microstrip line to coplanar stripline transition to realize a completely planar spiral antenna. This impedance transformer is integrated with the spiral antenna to achieve a planar structure and to adapt the impedance into a conventional 50 Ω coaxial cable. The performance of the proposed antenna is simulated and measured. The proposed antenna has a compact size of 90 × 90 × 1.6 mm3 on an FR4 substrate and can yield a large −10 dB impedance bandwidth ranging from 2.14 to 9.8 GHz which is equivalent to a fractional bandwidth of 102.13% with unidirectional radiation patterns. The VSWR is less than two in the operating bandwidth and the axial ratio (AR) is less than 3 dB in the frequency range of 1‐8 GHz. The simulated radiation efficiency ranges between 20% and 80%. The characteristics of the proposed antenna make it suitable for ground‐penetrating radar applications and many others.

A new approach to nearly constant input impedance of self-complementary antennas

Conformal techniques, based on the covariance of Maxwell's electrodynamics under the full conformal group in four spacetime dimensions, are discussed in relation with the constant input impedance properties of frequency-independent antennas. In particular, we show that by applying suitable conformal transformations to existing self-complementary planar structures like logarithmic spirals, the constant input impedance property is considerably improved, especially in the low-frequency domain, where it usually fails due to the large wavelength involved. This procedure enables to perform a more intelligent truncation with the aim to capture some of the properties left behind in the cutting and to design realistic ultra wideband antennas with a more controlled value of the input impedance in the whole operation range.

Design of Log Periodic Dipole Array Antenna Ranging from 30 to 150 MHz

This paper describes construction of 16 element frequency independent and high bandwidth Log Periodic Dipole Array antenna which works within the frequency range of 30 to 150 MHz. The antenna of gain 8 dBi is designed by calculating the parameters from Matlab. Matlab program is used to calculate the parameters like length of elements, separation between elements, theoretical impedance, standing wave ratio, etc. Thus, the designed antenna was fabricated. The antenna element is a cylindrical aluminum pipe of diameter 9mm and the boom used is rectangular antenna pipe of dimension 1”X1”. Fabrication also includes other materials like M-seal, zip tie, etc for physical stability of the antenna. Log Periodic Dipole Array antenna design described in this paper is fed with 75 ohm coaxial cable to 1:1 balun. Balun is also used for impedance matching between the antenna and coaxial cable. Antenna analyzer is used to measure Standing Wave Ratio and Impedance which are found to be 1.623 and 71.5625 ohm respectively. The antenna can be a receiver or a transmitter type for operating with the signals within Very High Frequency band.

Overview of UWB Feed

This paper briefly introduces the UWB feeds. Firstly, it introduces the basic requirements of the feeds and the performance. Then it introduces the frequencyindependent antenna, traveling wave antenna, combined feeds and tightly coupled antenna. It briefly describes the principles of UWB antenna and introduces the development status. Finally, it is concluded that the phase center of the combined antenna does not vary with the frequency, and combined antenna also has high gain, low sidelobe, which is more suitable for the feed of the reflector antenna.

SARAS MEASUREMENT OF THE RADIO BACKGROUND AT LONG WAVELENGTHS

SARAS is a correlation spectrometer connected to a frequency independent antenna that is purpose-designed for precision measurements of the radio background at long wavelengths. The design, calibration and observing strategies admit solutions for the internal additive contributions to the radiometer response, and hence a separation of these contaminants from the antenna temperature. We present here a wideband measurement of the radio sky spectrum by SARAS that provides an accurate measurement of the absolute brightness and spectral index between 110 and 175 MHz. Accuracy in the measurement of absolute sky brightness is limited by systematic errors of magnitude 1.2%; errors in calibration and in the joint estimation of sky and system model parameters are relatively smaller. We use this wide-angle measurement of the sky brightness using the precision wide-band dipole antenna to provide an improved absolute calibration for the 150-MHz all-sky map of Landecker & Wielebinski (1970):subtracting an offset of 21.4 K and scaling by factor 1.05 will reduce the overall offset error to 8 K (from 50 K) and scale error to 0.8% (from 5%). The SARAS measurement of the temperature spectral index is in the range -2.3 to -2.45 in the 110 to 175 MHz band and indicates that the region towards the Galactic bulge has a relatively flatter index.

A Practical Approach for Controlling the Shape of the Radiation Pattern of a Microwave Log-Periodic Antenna for Wideband Applications [Antenna Applications Corner

The log-periodic antenna (LPA) is a wideband frequency-independent antenna, used in many applications including direction-finding (DF) receivers. The direction finding is an important parameter measured by a direction-finding receiver in electronic support measures (ESM) systems. Amplitude-comparison direction finding (ADF) is one of the widely used angle-of-arrival measurement techniques in electronic support measures systems across the world. Many EW engineers have derived the mathematical equation for the estimation of the angle of arrival based on this popular technique. The angle of arrival accuracy using this technique depends on the number of antennas used in the configuration, channel imbalances, the beamwidth, and the shape factor of the antennas. To obtain good angle-of-arrival accuracy with the amplitude-comparison technique, the log-periodic antenna is one suitable antenna. Normally, electronic support measures systems are wide open in frequency (the bandwidths of electronic support measures receivers are a few thousands of MHz), and hence the antennas exhibit nearly the same beam shape (beamwidth and shape factor) over these wide operating frequency ranges so as to have a uniform angle-of-arrival error distribution across the frequency spectrum. However, a log-periodic antenna offers some variations in half-power beamwidth over a wide frequency spectrum at microwave frequency ranges, which is reasonably good, but is not enough to obtain uniform angle-of-arrival error patterns throughout the operating frequency range. Similarly, a uniform shape factor is also important across the bandwidth. The radiation beam of a log-periodic antenna over a wide operating frequency range thus need to be controlled. A practical solution to this problem, along with experimental results, are presented in the current paper.

Design of Planar Trapezoidal Toothed Log Periodic Antenna using HFSS

Log Periodic Antenna is required to provide wide band width, high gain and broad beam width. This antenna has smaller dimension than other antenna types. This antenna is a type of frequency independent antenna. It is observed from the study that antenna on Teflon substrate provides widest bandwidth among all the substrate antennas. Further, the performance of antenna on Teflon substrate is better than conventional antennas.

The Study about the Effect of Geometric Parameters' and Material Properties’ Changing on the Electromagnetic Performance of BSSAS

This paper introduced a research work on the development of a Broadband Smart Skin Antenna Structure (BSSAS). This structure possessed the load-bearing, shape maintaining and communication capabilities at the same time. A frequency-independent planar log-spiral antenna suitable for electromagnetic communication from 0.8GHz to 8GHz was embedded in a composites sandwich panel. Numerical models have been generated to analyze the effect of geometric parameters and material properties changing on the electromagnetic performance of BSSAS. The numerical results showed that both VSWR and the maximum gain of BSSAS at 1.2GHz and 1.6GHz were not sensitive to the geometric parameters and material properties of the packaging structure.

On the Frequency-Independent Modes of a Four-Arm Modulated Arm Width Spiral

This paper shows that among frequency independent (FI) conformal antennas, the modulated arm width (MAW) spiral has the simplest architecture for measuring both polarization and angle-of-arrival (AOA) instantaneously if frequency is known. The theory, design and performance of equiangular four-arm MAW spiral antennas when utilizing both sum modes (± 1) and difference mode ( +2) for direction-finding applications are discussed. It is shown that simultaneous dual-polarization and multi-mode capability is not achievable in more commonly-used four-arm spiral and sinuous antennas. While the co-polarized modes 1, 2 and 3 are well-researched with single-polarized four-arm equiangular spirals, they have not been utilized or controlled on a four-arm MAW spiral. Effects of modulation period on cross-polarization, pattern symmetry, gain, and impedance for all three pattern modes are investigated. The studies are carried out using full-wave modeling and a prototype MAW geometry is built and evaluated with a beamformer to demonstrate its wideband, dual-polarized, multi-mode capability.

An Octave Bandwidth Frequency Independent Dipole Antenna

Precision measurements of the spectrum of the cosmic radio background require frequency independent antennas of small electrical dimensions. We describe the design of a wide-band fat-dipole antenna with a sinusoidal profile having a frequency independent performance over the octave band 87.5 to 175 MHz. The input return loss exceeds 15 dB and the radiation power pattern is frequency invariant and close to cosine square over the octave bandwidth. The structure has been optimized using electromagnetic modeling, and the design has been validated by constructing a prototype.

SARAS: a precision system for measurement of the cosmic radio background and signatures from the epoch of reionization

SARAS is a correlation spectrometer purpose designed for precision measurements of the cosmic radio background and faint features in the sky spectrum at long wavelengths that arise from redshifted 21-cm from gas in the reionization epoch. SARAS operates in the octave band 87.5–175 MHz. We present herein the system design arguing for a complex correlation spectrometer concept. The SARAS design concept provides a differential measurement between the antenna temperature and that of an internal reference termination, with measurements in switched system states allowing for cancellation of additive contaminants from a large part of the signal flow path including the digital spectrometer. A switched noise injection scheme provides absolute spectral calibration. Additionally, we argue for an electrically small frequency-independent antenna over an absorber ground. Various critical design features that aid in avoidance of systematics and in providing calibration products for the parametrization of other unavoidable systematics are described and the rationale discussed. The signal flow and processing is analyzed and the response to noise temperatures of the antenna, reference termination and amplifiers is computed. Multi-path propagation arising from internal reflections are considered in the analysis, which includes a harmonic series of internal reflections. We opine that the SARAS design concept is advantageous for precision measurement of the absolute cosmic radio background spectrum; therefore, the design features and analysis methods presented here are expected to serve as a basis for implementations tailored to measurements of a multiplicity of features in the background sky at long wavelengths, which may arise from events in the dark ages and subsequent reionization era.