Abstract—A novel log-periodicdipoleantenna for dual-polarized radar systems is presented. The proposed antenna employs meander line technology and matched loads. The simulated and measured results show that the − 6 dB reﬂection coeﬃcient bandwidth of the dual-polarized antenna covers the desired band of 2–8 GHz and the port isolation is higher than 32 dB, along with − 20 dB cross-polarization discrimination for both E - and H -planes.
ABSTRACT: In this paper the functioning of a LogPeriodicDipoleAntenna (LPDA) in VHF frequency range (30 - 300 MHz) is depicted. We made an endeavor in designing a LPDA that suits the criteria, specification and is practical. The LPDA, comprising of nine elements, accomplishes a gain higher than 10 dBi with low noise amplifier. In the paper the analysis, design, and simulation of logperiodicdipoleantenna (LPDA) is represented We can conclude that the log- periodicdipoleantenna (LPDA) is the simplest antenna having consistent bandwidth and gain estimates.
Ultra wideband (UWB) wireless communication allows low power level and high data rate transmissions have embarked great research interests for wireless communications applications in the 3.1 GHz–11.6 GHz frequency band. Printed log-periodicdipoleantenna (PLPDA) is an example of UWB antenna which radiates in end-fire direction within ultra wide frequency band. With the multiple resonance property, its bandwidth can be increased by enhancing the number of the dipole element. The log-periodic array consists of several dipole elements which each are of different lengths and different relative spacing. A distributive type of feeder system is used to excite the individual elements. The element lengths and relative spacing, beginning from the feed point for the array, are seen to increase smoothly in dimension, being greater for each element than for the previous element in the array. It is this feature upon which the design of the LPDA is based, and which permits changes in frequency to be made without greatly affecting the electrical operation. A good LPDA may be designed for any band, HF to UHF at nominal cost, high forward gain, good front-to-back ratio, low VSWR. In logperiodic array there are three regions
Researches on new types of broadband logarithmically periodic antennas structures are studied. The Log-Peri- odic Antenna (LPA) is investigated as a new type of an- tenna, whose properties vary periodically with the loga- rithm of frequency, and provides wide bandwidth, broad beam width, and high gain. This antenna has smaller transverse dimensions than another antenna types. The antennas have pattern and impedance characteristics which are essentially independent of frequency over theoretically unlimited bandwidths. Data transmission at higher rates requires wider bandwidths for the elements constituting a communication link. This required wide- band antennas be designed and used [1,2]. In logarithmi- cally periodicantenna , the electrical properties vary with log of operation frequency. The high frequency an- tenna described by Duhamel and Berry [5,6] was peri- odic structure in which the dimension of successive sec- tions was increased in geometric progression. The logperiodic toothed trapezoidal antenna (LPTTA) can be slightly modified to obtain a refined geometry referred to logperiodic zigzag and cross toothed antennas. The dif- ferent (logperiodic toothed antennas) are also specified by angle in a manner similar to the LPTTA described earlier [7-10]. The important feature of these antennas is that they represent an earlier link to the development of log-periodicdipoleantenna. The initial design based on the concept of logperiodic structure was the logperiodic
Abstract—In this paper, a printed split ring resonator (SRR) loaded log-periodic Koch dipoleantenna (SLPKDA) is proposed. Koch-shaped dipoles when being loaded with split ring resonator (SRR) yielded a compact antenna, still preserving the radiation properties of log-periodicdipoleantenna (LPDA). Measurement results show that the proposed antenna has a wide bandwidth, good impedance match and gain of 4 dBi over the band of frequencies from 0.9 GHz to 2.5 GHz. Both vertical and horizontal dimension reductions are achieved by loading Koch dipoles with SRR.
Frequency independent antennas, as a particular class of wideband antennas, were first studied by Rumsey. His simple but significant theory has become the foundation for studying many wideband antennas, such as log- periodicdipoleantenna (LPDA). The LPDA, whose properties vary periodically with the logarithm of frequency, consists of linear dipoles as basic constituent elements. The elements are fed from a balanced transmission line, each element being placed in an alternating configuration that leads to 180° phase change from the adjacent elements.
In telecommunication, the frequency spectrum is a rare commodity and each band is assigned for a specific application. A log-periodicantenna is a broadband, multi-element, unidirectional, narrow-beam antenna that has impedance and radiation characteristics that are regularly repetitive as a logarithmic function of the excitation frequency. The active logperiodicantenna that the title for A Single Broadband Antenna whose characteristics vary as a periodic function of the logarithm of the frequency. This project is to look into the design of a Broadband antenna that covers the important low-return-loss printed log-periodicdipoleantenna (PLPDA) fed with the aid of a coaxial cable is awarded. The widths of dipole elements are optimized to develop the bandwidth. A study of coaxial cable position is integrated with the intention to enhance the antenna habits. The measured return loss is cut down than 15 dB from2.1 to four.3GHz. The measured gain varies between 6 and 7 dBi. The measurements, including input impedance, gain and radiation patterns, and simulations are in agreement. Apart from software as a excessive fine dimension antenna and course finder, this antenna can also be very good acceptable as a directional antenna for WLAN, Wi-Fi, and different directional communique applications. A small physical antenna-measurement plus low weight will make this antenna a specialty for cell use and the detection of unusable signal sources like army radar, more than a few satellite services and really high frequency bugs.
We investigate a dielectric dipole structure within which notches are cut, whose dimensions vary with logarithmic periodicity. It is found that the antenna offers ultra wide 3:1 VSWR bandwidth of about 6.48 GHz. Further, the experimentally measured radiation patterns show rather broad nature suitable for omni directional coverage. Varying the plane of polarization, it is also observed to have an almost polarization independent behavior. All these characteristics make this new antenna ideally suited for numerous emerging fields of wireless and mobile communications.
The LPDA is utilized in broad band communication in the VHF and UHF range [1- 4]. For LPDA antenna the input impedance or the gain alters periodically in the logarithm of the frequency domain. The basic thought is that a slowly expanding periodic structure array emits mainly when the array elements (dipoles) are close to resonance so that with alterations in frequency the active (radiating) region shifts throughout the array. For a specified frequency, the elements with lengths near to half wavelength resonate . The longest dipole resonates at the lowest frequency (f L ) and the
Microstrip antennas have some attractive advantages such as small volume, very low-profile, light weight, easy fabrication and constant directional radiation patterns, which have been widely used in designing miniaturized antennas. Since the development of printed circuit technology, many traditional antennas could be made into corresponding printed antennas, such as printed monopole antennas , printed log-periodicdipole antennas , etc. Fractal theory is a quite active mathematic branch of nonlinear science, and the research objects of which are certain unsmooth or non- differentiable geometries in nonlinear systems and nature. Fractal technology has been extensively applied to every aspect of science and engineering field, and one significant branch of which is fractal electrodynamics. Meanwhile, fractal antenna is one of fractal electrodynamics’ applications. Fractal structure has self-similarity and space filling characteristics which could realize the miniaturized antenna design. In antenna’s design, the usual fractal structure is Koch fractal , Tree fractal , Hilbert fractal , etc.
The coupling between the coaxial feeding network and the radiating dipoles degrades the antenna matching, especially in the upper frequency band, where the dipoles are very small. In order to improve the antenna performances at high frequencies, a further dipole is inserted immediately before the dipole 1, with the same width and length, and with a spacing equal to the one between dipole 1 and dipole 2. The inclusion of this further dipole does not imply any change in the overall size of the antenna, but is able to lower the return loss below −10 dB in the whole operating bandwidth, as we will show in the following section.
of a LPDA is restricted by the size and figure accuracy of the elements and by the feed which combines concentrated radiation to the receiver. Only 2 or 3 are active at any specified frequency in the operating range though an LPDA consists of a huge number of dipole elements -. The electromagnetic fields created by these active elements add up to make a unidirectional radiation pattern, in which maximum radiation is off the small end of the array. The radiation in the reverse direction is usually 15 - 20 dB below the maximum. Figure 2 shows how the design constant τ varies with the relative spacing σ between the dipole elements in a LPDA antenna -.
The basic positioning of two static antennas to form a uniform wide angle beam is shown in Fig. 5. Artificial convex ground surfaces are placed below each antenna to minimize the effect of ground on the beam shapes. These two antennas form a uniform beam within the angle subtended by them based on the uniform gain power spectrum antenna pattern theorem. Combining the power of more antenna pairs it acts like an array with increased sensitivity and uniform gain.
Fractal geometries have been applied to antenna design to make multiband and broadband antennas. In addition, fractal geometries have been used to miniaturise the size of the antennas. However, miniaturization has been mostly limited to the wire (dipole and loop) antennas. The geometry of the fractal antenna encourages its study both as a multiband solution and also as a small (physical size) antenna. First, because one should expect a selfsimilar antenna (which contains many copies of itself at several scales) to operate in a similar way at several wavelengths. That is, the antenna should keep similar radiation parameters thro ugh several bands. Second, because the space- filling properties of some fractal shapes (the fractal dimension) might allow fractal shaped small antennas to better take advantage of the small surrounding space. The fractal antenna is formed by applying a generator shape repetitively at a constant scale factor and results in an antenna with log-periodic characteristics which is a multiband antenna and a miniaturization characteristic.
Abstract—In this paper, a broadband planar modiﬁed quasi-Yagi antenna using a two-element log- periodicdipole array as a driven element is proposed. To feed the two-element log-periodicdipole array, a simple microstrip to stripline transition as a balun is designed, which converts the unbalanced input to balanced output. The antenna is fabricated on a low cost glass epoxy FR4 substrate with dielectric constant = 4 . 4, substrate thickness = 1 . 6 mm, and loss tangent = 0 . 02. The overall size of the antenna is 84 mm × 111 mm, which is 0 . 41 λ o × 0 . 54 λ o at the center frequency of 1.45 GHz. Measured results show a bandwidth of 41.4% for VSWR ≤ 2. A gain of 6.5 dBi ± 0.5 dB and front to back ratio (F/B) of better than 20 dB are achieved over the bandwidth. Measured results are in good agreement with the simulated ones. This antenna is useful for RFID, portable direction ﬁnding, spectrum monitoring systems, etc.
Directivity is how much an antenna concentrates energy in one direction in preference to radiation in other directions. It is equal to its power gain if the antenna is 100% efficient which means that it is a perfect antenna that radiates equally in all directions. This antenna is called an isotropic radiator. Power gain is expressed relative to a reference such as isotropic radiator or half-wavelength dipole. Figure (13) and (14) shows the Cartesian plot for directivity at phi and theta directions respectively.
A limitation of the LPDA is that the dipole element for the lowest operation frequency in the HF range may become too long to be conveniently handled in the environment of application. This fact has led to numerous modifications to the original structure in order to reduce the transverse dimension. In pursuit of reducing the LPDA size, Berry and Ore  changed the dipole element to a monopole element over a ground plane, which allows half the transverse dimension. Roy and Chatterjee  also proposed log-periodic antennas with helical elements, because the log-periodic helical antenna has a smaller transverse dimension if the helices are designed to operate in the normal mode.
Logperiodic antennas have multiple elements, which resonate in a logperiodic fashion. Using this property, a frequency reconfigurable logperiodicantenna is proposed. Recently, work on reconfigurable logperiodic antennas has been reported. In the logperiodicdipole array described in , ideal switches are used to control each pairs of dipole arm of the antenna. This can switch from a wideband of 1–3 GHz, to several narrow bands. Similar work on this has also been reported in [8–10]. In contrast to wide to narrowband reconfiguration, work in [11–14] demonstrates band notch method for logperiodic antennas. In this paper a novel logperiodicantenna with the potential for switched band functionality to operate in a wideband or narrowband mode is presented. The antenna is an aperture coupled patch array with meandered feed. The feed has modulation to prevent a structural stop bands similar to that used in logperiodic monopole array . The antenna reconfiguration is realized by inserting switches into the slot aperture of the structure. In the array demonstrated here the switches are formed by metal sections, of the same size as a switch, bridging the slot aperture. A wide bandwidth mode is demonstrated from 7.0–10 GHz and three narrowband modes at 7.1, 8.2 and 9.4 GHz can be formed. A prototype has been manufactured. Measured results show good performance of the proposed designs. The proposed antenna is designed to operate from 7–10 GHz. A wider bandwidth can be obtained using more elements. Potentially, the number of sub bands can be increased or decreased, as can the bandwidth of the sub bands by selecting a specific number of active elements. Details of the proposed design are described. Section 2 discusses the advantages in choosing an aperture coupled logperiodic patch array as a candidate for reconfiguration. Sections 3 and 4 discuss the problem of the structural stop band and the procedure for eliminating it. The fabricated antenna is discussed in Section 5. Finally the results are presented in Sections 6 (simulations) and 7 (measurements) and follow by conclusions in Section 8. Some preliminary results of this work were presented in .
feed efficiency >1/2. For comparison reasons, the LPMAs are also optimized by a standard GA and the simplex method. A GA, the Nelder-Mead downhill simplex method and a hybrid GA/Nelder-Mead method are used in  to optimize LPDAs under requirements concerning the average values of the gain and SWR as well as their maximum deviation over the entire bandwidth. GAs are used in  and  to maintain the gain and the SWR over the operating bandwidth, while the LPDA length and the number of dipoles are reduced compared to those of the initial array. In , a multi-objective optimization is applied to LPDAs for operation in the range 3-30 MHz under requirements for minimum SWR, minimum antenna length and maximum gain by employing the Non-dominated Sorting Genetic Algorithm II (NSGA-II). The Particle Swarm Optimization (PSO) is applied in  for a 10-element LPDA operating in the range 450-1350 MHz under requirements for the average values of the gain, the F/B ratio and the SWR. A circular parasitic array of four 12-element LPDAs is optimized in  under constraints for gain close to 8dBi and minimum SWR in the range 3.1-10.6 GHz. The optimization process is implemented by using GAs. A hybrid Taguchi-GA is proposed in  to optimize a wideband zigzag log-periodicantenna, while in  a HF inverted-V LPDA is optimized under constraints for the SWR, the SLL and the gain by using GAs. Due to operation in the range 6-30 MHz, restrictions are set on the antenna size. Planar LPDAs are optimized in  for operation in the S-band by using PSO under constraints for the SWR and the gain, while in  a 13-element LPDA is optimized for operation in the GSM, WiMAX, Bluetooth, Wi- Fi and 3G bands using PSO and under the same constraints as given above. Also, a 10-element LPDA is optimized in  for operation in the GSM, WiMAX and Wi-Fi bands using a GA under requirements for smaller size and higher gain. Finally, three LPDAs composed respectively of six, nine and twelve elements are optimized in  using the Bacteria Foraging Algorithm for operation in the UHF TV band under requirements for the average values of the gain, the F/B ratio, the SLL and the SWR.
The radiation characteristics of an antenna in the presence of a lossy ground depend substantially on the infinite ground conductivity and in homogeneity [5-7]. The problem was conventionally simplified on the basis of a Hertzian dipole with specified current moment for very low frequency range . But, for higher frequency a finite length antenna should be considered. In the present analysis, the array is considered to be symmetric and the element half length is not greater than the limit of 5λ/8. The analysis is carried out by King and Wu’s three term assumption for the current [8-10]. Thus, for a single centre-fed dipole in free space