Strong subscriber growth over the past year has demonstrated the appeal of WiMAX technology ( WiMAX-1 & WiMAX-2) . The IEEE 802.16 working group has been established a new operating band name as Worldwide Interoperability for Microwave access (WiMax). WiMax has three allocated frequency bands. The low band (2.5-2.69 GHz), the middle band (3.2-3.8 GHz) and the upper band (5.2- 5.8 GHz). Printedantennas are attractive because their uniplanar architecture which helps to integrated with active devices or MMIC easily. In this paper, a printed small antenna fed by a microstrip line with a rotated square for bandwidth enhancement is proposed and discussed. Field distribution, gain and Impedance characteristics of this antenna are presented and discussed. A simple 50 ohm microstrip line is used to excite the slot. A rotated squareslot resonator is considered as reference geometry. By embedding a parasitic patch into the center of the rotated squareslot, the lower resonant frequency is decreased and the higher resonant frequency is increased. The measured results demonstrate that this structure exhibits a wide impedance bandwidth, s 11 < -10 which is over ranging from 2.84 to 6.19 GHz.
To achieve relatively wide impedance and AR bandwidths, the printedslotantennas with CP characteristic have been proposed in [5, 11], and the 3 dB axial ratio bandwidth of 18.85% and 12% are obtained, respectively. A proper rotation angle with respect to the center of square wide slot is selected to obtain the other resonant mode operating near one of the conventional wide-slotantennas . The opposite slot in the ground makes the surface current distribution varies anticlockwise and generates the circular polarized radiation. However, the design of single-feed slot antenna with wide AR bandwidth and impedance bandwidth remains a challenging problem for antenna designers.
Planar antennas have become wide area of interest for the antenna designers because of their unique features like compact size, multiband operation etc. Number of researchers has reported their works on wideband and circularly polarized slotantennas [1-14]. Printedslotantennas are widely used in a variety of communication systems because wide-slotantennas have two orthogonal resonance modes . Therefore, printedslotantennas have recently received a great deal of attention from researchers. Each slot shape requires a feed stub of appropriate shape. For example, in , a printed wide-slot antenna fed by a microstrip line with a fork-like tuning stub has been used to obtain broad bandwidth through the proper parameters of the fork-like tuning stub.
There are numerous benefits using CP slot antenna which is they do not require strict orientations between transmitters and receivers, low profile and easy fabrication . The slotantennas also have wider impedance bandwidth –. Several CP antenna designs using printedslot antenna have been proposed , , . A good CP radiation performance can be achieved by printed ring slot antenna . According to , a single-fed slot-aperture hybrid antenna for broadband CP operation that consists of U-shaped slot, a rectangular aperture, and a probing strip fed by a microstrip line. Slotted antenna also can be used for bandwidth enhancement by using slotted rectangular microstrip antenna .
Different Rectangular printedantennas using FR4 material were designed and performance of those antennas were analyzed with various parameters such as gain, directivity, VSWR and return loss. Various structures like RMPA without slots, vertical slot, double horizontal slot and centre slot were proposed. From the performance analysis, Double horizontal slot provides maximum gain (8.61dB), maximum directivity (5.82dBi), minimum VSWR (1.0451) and minimum return loss (-33.918dB). Thus the double horizontal slot antenna produce the better result than the other antennas. Based on the E-field of RMPA the SEMTEX explosive material is detected. When the absence SEMTEX material E-field value is 18.2 dBV/m which is reduced in presence of SEMTEX material. In future work, the proposed antenna will be further developed for the same explosive detection application. A CKNOWLEDGEMENTS
The demand for wireless communication systems is rapidly growing especially ﬂexible and conformal antennas that have become widely researched for diﬀerent ﬁelds of applications. Future wireless systems will provide various services such as broadband multimedia and high speed access. The related literatures to the conformal ﬂexible antenna have been reported by several authors. Reference  presents a curved strip dipole antenna combined to EBG reﬂector; References [2–7] present a curved micro strip antenna with the goal to miniaturize the structure. Furthermore, ﬂexible wireless technologies requires the integration of ﬂexible, light weight, compact, and low proﬁle antennas, Authors in [9–14] developed antennas for various technologies with all this characteristics. In [15–17], authors present ﬂexible antennas that are particularly suitable for use in wearable applications. It is noted that in all the cases authors report the mismatch eﬀect due to the curvature.
Abstract—In this paper, a novel broadband circular polarized (CP) antenna for mobile communication is proposed. The antenna is constructed by a square ring patch with a gap and coplanar waveguide (CPW) feed structure. To achieve a broadband CP wave, a cross patch is embedded at the center of the slotted square ring patch to excite two orthogonal resonant modes with equal amplitude and 90 ◦ phase diﬀerence for CP radiation. Furthermore, on one side of ground a stub is embedded to match impedance bandwidth that can cover the whole CP bandwidth completely. Loading the AMC (Artiﬁcial magnetic conductor) structure on the back of the antenna achieves directed radiation of circular polarized waves. An antenna was fabricated based on simulation and optimization. The simulated and measured results show that the bandwidth with S 11 < − 10 dB is 66.9% from 1.82 GHz to 3.65 GHz, and the 3 dB axial
Abstract—This paper is intended to design a ZigBee wireless network node based on the advanced RISC machines (ARM), so as to facilitate the network usage process. The performance of the new sensor is subject to antenna test and simulation experiment. The HFSS simulation method is adopted, and the anten- na size and scanning frequency are optimized through analyzing the research status of ZigBee technology and the working principle of ZigBee protocol stack based on parameters, such as, the return loss and direction of the antenna, which not only increases the accuracy of analysis and but also reduces the reflection coefficient. The experimental results show that when L2 is 14. 9mm, the effect is the best, and Sll is -26.6 dB. Based on the above findings, it is concluded that the integrated antennas on the printed circuit board (PCB) board can reduce the production cost of the antennas; thus, IFA antennas can meet the requirements of ZigBee based wireless sensor network in term of antenna performance.
Circularly polarized printedslotantennas are widely used in satellite communication and recent wireless communication application due to their advantages such as large impedance bandwidth, low profiles and wide 3dB axial ratio bandwidth. Circularly polarized printedslotantennas are of two types wide and ring slotprintedslot antenna .Compact circularly polarized microstrip antennas are used in various applications like medical implant communication services, RFIDs, compact mobile communication system and portable wireless devices where antenna size is a major consideration . GNSS (global navigation satellite system) is a satellite system with global coverage. GNSS signals are used to meet the high precision positioning, timing and navigation requirements over longer distances. GNSS system depends on the quality of its timing. GNSS technology is important in real time prediction of real or possible critical situations and natural disasters. GNSS receivers use GPS, GLONASS and Galileo/Beidou system for many applications . Beidou Navigation satellite system is a Chinese satellite navigation system. It has been offering navigation services, mainly for customers in china and neighbouring regions, since 2000 at 1.26GHz frequency range .
Abstract—A new design for circularly-polarized (CP) slotantennas is first described. The antenna is a combination of a shorted square-ring slot and an L-shaped linear slot, and its CP operation frequency can be easily tuned under the condition that the slot area is unchanged. Based on the CP design, two reconfigurable slotantennas are then developed. One is a frequency reconfigurable antenna, whose CP operation frequency can be switched between two adjacent frequencies. The other is a polarization reconfigurable antenna, whose polarization can be switched between two orthogonal CP senses. The two reconfigurable antennas are realized using PIN diodes. Details of the designs and experimental results are shown.
Abstract—In this paper, a novel HMSIW slot antenna combines a signiﬁcant bandwidth enhancement and small footprint for inter-satellite communications at C-band. The designed antenna has the capability of achieving a reduction of size with nearly 50% in comparison to conventional SIWs. The results show that the proposed antenna has a bandwidth of 4%, an average gain of 5 . 8 dB, and the radiation eﬃciency of η = 93% at 5 GHz.
Small satellites are extremely small and lightweight. They have a net mass between 0.1 and 1.33 kg . The most common type of small satellites is CubeSat that made up of 10 × 10 × 10 cm 3 units and has a weight less than 1.33 kilograms per unit. CubeSat faces a challenge of extremely stringent accommodation requirements, leading to the need of antenna system to be miniaturized and integrated [1–4]. One approach to the problem is to use planer antennas, which are light weight, planar, compact, and inexpensive. Recently, there has been growing interest in SIW-based antennas [5– 7]. SIW structure preserves the advantages of metallic waveguides, namely high Q -factor (low loss) and high powerhandling capability with self-consistent electromagnetic shielding. SIW has many advantages over rectangular waveguide antennas, such as low cost, high isolation, reduced sizes and easy integration [5, 8]. Moreover, SIW can be easily manufactured using simple printed circuit board (PCB) process which allows monolithic integration of SIW with other planar circuits [5, 9]. Because of its advanced features related to loss and narrow-beam waveguide slot array antennas are very attractive for satellites communication applications. The SIW slotantennas in the literature employ planar SIW structures [6, 7, 10–12]. Both longitudinal slot  and transverse slot  on the broad wall of an SIW can be used as radiating element of a linearly polarized SIW slot array. A nonlinearly polarized SIW slot antenna array can be designed by rotating the slots on the broad wall [14–17]. SIW series-feed arrays  and corporate-feed arrays  with CP characteristic suﬀered from narrow AR bandwidth. Using an SIW based power divider with tapered power division, a low side-lobe level (SLL) longitudinal slots array of SIW is implemented in . Slotted SIW antennas usually allocate constant spacing between slot elements. In , an optimization on the spacing between elements is done by using a combination of genetic algorithm and conjugate gradient method for a given pattern and eﬃciency requirements. SIW can also be used to design other types of antennas, such as H -plane sectoral horn antenna ,
The slot line notch antenna uses an exponential taper to match the impedance of the ring to free space. The gap at the feed point is 1 mm and the gap at the mouth of the antenna is 11.894 mm. The Gunn diode is mounted on a piece aluminum that serves as the heat sink required by the low dc-to-RF conversion efficiency of the diode. The dc bias to the Gunn diode is provided directly to the center ring by a thin wire. The Slot is biased using a broadband bias T (A 391001 from Anritsu). A bias voltage of 9.887 volt is applied to the diode so that it oscillates at 9.646 GHz. A standard gain (18 dB) X-band horn antenna (Vidyut Y Udyog X5041) served the purpose of transmitting antenna. The horn is connected to a microwave generator (sweep oscillator 8350B from HP) generates the injection carrier signal. A 333 kHz sinusoidal tone signal, obtained from a Philips 807/DRF RF oscillator is used to frequency modulates the microwave carrier. The generator has a frequency sensitivity of 6 MHz/Volt and peak to peak swing of the tone signal is 260 mVolt. This gives the FM index
With the rapid development of modern wireless communications, the demand for antennas with multi- frequency, low cost, and compact size has increased. The coplanar waveguide (CPW)-fed antennas not only are suitable for easy integration with the circuit, but also have simple structures and compact size. Also, CPW transmission lines have less dispersion and lower radiation losses than microstrip lines. So, many researchers paid lots of attention to CPW-fed antennas. Thus, several dual-band antennas [1–3] and tri-band antennas [4–13] have been proposed to cover the bands for WLAN or WiMAX applications. The modified planar monopole pattern is constantly adopted to realize dual-band operation because of its easy fulfilment, such as the folded open ended stub monopole , T-shaped monopole , triangular monopole and U-shaped monopole . Although these antennas have the advantage of simple structure, only two bands are included, which leads to low working modes in the communication terminal systems. Several approaches have been demonstrated to achieve tri-band antennas, such as a parasitic circular patch with an inverted-L strip , a rectangular ring with an S-shaped strip , a modified rectangular slot with an inverted-L strip , and a square-ring slot antenna with an asymmetric ground plane . However, these techniques supporting tri-band antennas still suffer from large size. Slot techniques are also used to design and implement tri-band antennas [8–10]. Slot techniques can realize miniaturization, but the antennas are always in complex structures. To solve this problem, different kinds of microstrip resonators are proposed, such as fork-shaped resonator antenna , two spiral ring strips resonator antenna [12, 13], and three inverted-L stubs resonator antenna. The proposed antenna also uses the technique of resonators. The above-mentioned techniques supporting tri-band antennas have not only simple structures, but also compact sizes. Ultra-wideband (UWB) antennas  can also cover all operating bands. However, when the UWB antennas are used in WLAN/WiMAX systems, frequency interference cannot be avoided.
UWB is a short range unlicensed wireless communication system which has a potential to offer high capacity with low power compared with the contemporary wireless systems for short range applications. After the release of UWB for unlicensed application by the Federal Communications Commission (FCC), it receives much much lower than the resonant frequency of the conventional printed antenna with the same patch area. Attention by researchers due to its inherent properties of low power consumption, high data rate and simple configuration . With the rapid developments of UWB
Recently, inorganic salts such as sodium chloride and magnesium chloride solutions have been reported to have the ability to decrease electrical resistance of printed silver nanoparticles (Zapka, Voit, Loderer & Lang, 2008; Layani et al., 2012). The mechanism to decrease electrical resistivity was not clearly explained by Zapka et al. (2008), but it was suggested that the effects of the electrolyte solutions in the sintering process was based on the electrical charges at the surface of the printed silver nanoparticles by Magdassi et al. (2010). One of the advantages of this method is that the coalescence of silver nanoparticles can take place at the room temperature. Although the mechanism of electrolytes in sintering has not been understood, salt sintering has received a great deal of interest because of its simple way of treating printed metal nanoparticles.
Abstract—A new miniaturization methodology suitable for printed linear antennas is presented. Miniaturization is accomplished by replacing a linear radiator element of a conventional antenna with a compact continuously varying-impedance proﬁle governed by a truncated Fourier series. A design example of a printed half-wavelength dipole antenna is designed and realized in microstrip technology. The performance of the proposed antenna is compared with its equivalent uniform dipole to highlight the performance equivalency. With a 25% reduction in the dipole arm length, both antennas show a measured peak gain and a fractional bandwidth of 5.4 dBi and 16%, respectively at 2.5 GHz; hence, the overall electrical performance is preserved. It will be shown that the design procedure is systematic and accurate. The proposed approach has potential for achieving advanced frequency characteristics, such as broad- and multi-band antenna responses.
The explosive growth of the wireless communications industry has led to an increasing demand for low cost, low profile and integrated antennas. Printedantennas enjoy many advantages over standard antennas, such as low manufacturing costs, low profile, and ease of inte- gration in the PCB and with passive and active compo- nents.
Modern telecommunication system require antenna with wider bandwidth and smaller dimensions. Various antennas for wide bandwidth operation have been studied for communication and radar system. The fractal antenna is preferred due to small size, light weight and easy installation. A fractal micro strip antenna is used for wideband application in this project provides a simple and efficient method for obtaining the compactness. An inverted square Koch based fractal antenna is designed for these applications. Its compactness and lighter weight is the major point for designing an antenna. This antenna is providing better bandwidth, return loss and gain.
Slots on the ground plane have been used as antennas with sufficient bandwidth to cover a specific frequency band  to modify the fundamental resonant mode in order to obtain a bandwidth enhancement at low frequencies (GSM850–900) and, at the same time, to act as a parasitic element of the antenna. Thus, a bandwidth enhancement is achieved at high frequencies (DCS1800–1900). In this paper, a new slot is added to the ground plane to enhance even more the bandwidth at high frequencies, reaching the UMTS and Blue-tooth bands.