Bandstop filter (BSF) is first constructed using open stubs and spurline. The stop bandwidth of this conventional structure is further increased by placing a complementary split ring resonator (CSRR) exactly below the 50 Ω microstrip line. By embedding this BSF with a wide rejection band in the input port of the PCML bandpass filter, unwanted passbands of bandpass filter is eliminated. To demonstrate this, we have designed, fabricated and tested a first order Chebyshev bandpass filter centered at 0.9 GHz with 10% fractional bandwidth (FBW). This bandpass filter is cascaded with the newly proposed BSF. Simulation and measured results shows a harmonic rejection upto 5f0 with more than 20 dB rejection level.
A complex dielectric constant for poplar and monstera delicious's obtained by Ulaby at 10 GHz has been revised at 4 mm band. A measurement setup operating at 4 mm was established for making comparison between modeled and measured values. Results basically show that their electromagnetic transparency increases by drying as expected. While moisture content increases from 0% to 60%, transmitted power decreases from 95% down to 22%; reflection goes up to 50% and the absorption reaches from 1% to 20% for monstera leaf. A model developed for poplar responds much better than the model revised for monstera leaves.
The amplitude modulation (AM) and frequency modulation (FM) signal transmission of time modulated linear arrays (TMLA) is studied in this paper. The signal with a certain bandwidth received by a TMLA is time modulated by RF switches, generating many sideband signals at multiples of the time modulation frequency and each of them has the same bandwidth as the original signal. The AM and FM signals received by the TMLA were analyzed, and the requirements of the time modulation frequency for the recovery of the original signal is presented. Simulation results show that the time modulation frequency of the TMLA should be equal to or greater than the bandwidth of the original signal and a band-pass filter (BPF) has to be used to recover the original signal.
The proposed work focuses on the experimental investigation of radiation characteristics of the discarded IC chips mounted on the dielectric substrate when fed trough one of the metal leg pins. Several sets of the experimental results are obtained using Vector Network Analyzer to obtain the return loss characteristics of the proposed structure. The return loss characteristics reveal that at some frequencies the ICs certainly show radiation mechanism. Feeding the same chip at different pin locations, changes the resonant frequency. The measured radiation pattern of the IC chip shows an omni-directional characteristic. This experimental study also reveals that the ICs can be easily interfered by the surrounding radiation prevalent in any wireless environment following the reciprocity principle of an antenna.
A bandpass filter (BPF) is presented for ultra-wideband (UWB) applications with a notched band to reject the unwanted signals from the wireless local area network (WLAN) systems. The proposed UWB BPF consists of two pairs of open-loop resonators on the top layer and one coupled resonator on the bottom layer. The rejection band is introduced by adding an asymmetric open-loop resonator to two outer arms of open-loop resonators. The bandpass filter is designed to be operated within full bandwidth of 3.1 to 10.6GHz and to eliminate the WLAN signals of 5.8GHz. The suppression at 5.8GHz is larger than 15dB. The proposed configuration is proved to be both simple and compact.
A circulator is needed in a C-band airborne synthetic aperture radar system which employs single antenna configuration. The circulator provides full-duplex capability to transmit high-power RF signal and receive the echo signal via the same antenna simultaneously. Commercially available circulators with moderate isolation are inadequate for this application. An innovative Cancellation Network (CN) has been designed to enhance the performance of the conventional circulator. This paper highlights the conceptual design and measurement results of the CN. An improvement of more than 27 dB has been achieved.
This paper aims to complete a published systematic methodology for the design of ladder BAW filters in order to include the effect of the electrodes, since infinitely thin electrodes are assumed in this design methodology. The new procedure is validated against the work of other authors, finding very good agreement between results.
A microstrip-fed planar monopole antenna consisting of an inverted-L monopole and a square parasitic element extending from ground plane directly to obtain wideband operation covering Bluetooth/ISM, 2.5 GHz WiMAX, 3.5 GHz WiMAX and 5.2/5.8 GHz WLAN bands is presented. The proposed antenna employs a shorted parasitic element to improve the bandwidth. The return loss of the suggested antenna geometry was calculated by a commercial HFSS 9 simulator and the results are compared with measured return loss, which shows a good agreement between them. Details of the proposed antenna designs and experimental results of the constructed prototypes are presented.
This paper presents the design of a tri-mode matched feed horn to remove the beam squinting effects in a circularly polarized offset parabolic reflector antenna. In a conical horn, three modes i.e., TE11, TM11 and TE21 are combined in proper amplitude and phase proportion to obtain a tri-mode matched feed configuration. The proposed tri-mode horn is then used as a primary feed device to illuminate the circularly polarized offset parabolic reflector antenna. The simulated data on radiation characteristics of the offset reflector are used to estimate the magnitude of beam squinting and the results are compared with that of a conventional potter horn fed offset reflector. The experimental results on secondary radiation pattern are also incorporated in the paper.
A novel electric small conical antenna working on a very broad band, 0.47-6 GHz, with the height of only 60 mm, is presented. A capacitive ring on the top of the cone and three oblique shorted lines are used to expanding the work band. By changing the width of the ring and the slope of the oblique line, the impedance of the antenna can be matched to 50-ohm feed line commendably. Simulations and experiments results demonstrate that this antenna provides very broadband and low-profile characters, which exhibits a 12.8:1 impedance bandwidth with voltage standing wave ratio (VSWR) below 2:1 (the impedance bandwidth is 11.9:1 with the VSWR below 1.5:1) and with the height only 0.094 wavelength associated to the lowest frequency.
A compact composite ultra wide-band elliptic-function low-pass filter is introduced by combining in cascade a microstrip stepped-impedance resonator using interdigital capacitor and an admittance inverter. A triple cascade low-pass filter is designed, analyzed and tested with this technique accompanied by its equivalent circuit model. This composition acts similar to composite filter with desire attenuation and matching properties in order to obtain wide bandwidth and broad stop-band. The proposed low-pass filter features the sharpness of cut off frequency, low insertion-loss, enhancement of bandwidth up to X-band frequencies and very compact size.
A novel and compact planar ultra-wideband wide-slot antenna with dual band-notched function is proposed. The method of creating dual band-notch function is unique from traditional ones. By embedding a U-shaped parasitic strip and a pair of T-shaped stubs in the wide slot, dual bandstops around 3.5 GHz and 5.5 GHz can be obtained. The measured results demonstrate that the proposed antenna, with a compact size of 20X32.5 mm, has a large bandwidth over the frequency band from 3.1 to 10.6 GHz with voltage standing wave ratio (VSWR) less than 2, except the bandwidths of 3.3~3.7 GHz for WIMAX and 5~6 GHz for WLAN. In addition, the radiation pattern has an excellent omni-directional characteristic in the H-plane and a typical monopole like pattern in the E-plane.
Transitions from circular waveguides to rectangular waveguides are used in many situations. One particular case is between the feed of a circular corrugated horn antenna and following rectangular waveguide structures. Since the field patterns are not the same on both sides the conversion from rectangular to circular waveguide always results in a certain amount of power reflected back in one waveguide. Much effort has been put in designing special converters which reduce this effect. For many designs, reflection is reduced by introducing a certain number of waveguide steps. By adjusting the distance between these steps, one can get destructive interference of the returned signal at specific frequencies. In this paper, an alternative approach, the constant impedance structure (CIS) has been chosen. This eliminates the need to design a waveguide converter for minimum return loss at discrete frequencies. The transition obtained by this approach is compared to a transition based on linear surface interpolation.
A new approach to analyze the behavior of a high-gain antenna covered with a frequency selective surface (FSS) superstrate is presented. Using an image theory and effective constitutive parameter retrieval, properties of impedance and a refractive index of the entire cavity structure are investigated. Through the analysis, we show that our antenna inherently operates in the medium whose maximum index of refraction is lower than ‘0.5'. Furthermore, we also demonstrate that the high-gain feature of the Fabry-Perot cavity antenna is not only due to satisfy a conventional cavity resonance condition, but also for a material of an effectively low index of refraction.
A simple metamaterial resonator structure based efficiency electrically small semi-circular loop antenna (ESSCLA) is proposed. It is demonstrated numerically that capacitive offered by the simple metamaterial resonator structure can counteract inductive impedance of the ESSCLA at the resonance frequency. The overall structures of ESSCLA can be fabricated on one dielectric substrate, and match conjugate to a 50 Ohm coaxial transmission line source without additional matching network. The size of the proposed ESSCLA is ka = 0.6745 by Chu limit. The resonance frequency is 3.2239 GHz, and impedance bandwidth (S11<-10) is from 3.19 GHz to 3.26 GHz about 0.07 GHz, the relative bandwidth is about 2.2%. The measure results accord with the simulation results well. The peak gain is 4.58 dB. The radiation efficiency is 97.81%, the overall efficiency is 96.71% at the resonance frequency. The proposed antenna has advantages of efficiency, high gain, low cost, small size, and light weight and will be applied to wireless communication systems for required small antennas.
Intelligent Transport Systems (ITS) are becoming a reality, driven by navigation safety requirements and by the investments of car manufacturers and Public Transport Authorities all around the world. ITS make it possible to imagine a future in which cars will be able to foresee and avoid collisions, navigate the quickest route to their destination, making use of up-to-the minute traffic reports, identify the nearest available parking slot and minimize their carbon emissions. Also demand for voice, data and multimedia services, while moving in car increase the importance of broadband wireless systems . Efforts are being imparted towards the convergence of mobile communications, computing and remote sensing. Spread spectrum based digital RADAR can be utilized as a remote sensing device in ITS. This motivates us in development of DSSS (Direct Sequence Spread Spectrum) based digital RADAR at our institute. It is quite capable of detecting target in the open field. The experiment was carried out for different standard target like flat plates, spheres etc. The operational digital RADAR is capable of rejecting interference, but fails in a strong multipath scenario. Again RAKE processing is established in communication. Our approach is implementing RAKE processing at the RADAR receiver to exploit multipath.
Full-duplex radio-over-fiber (ROF) transport systems based on distributed feedback laser diode (DFB LD) with main and -1 side modes injection-locked technique is proposed and demonstrated. Improved performances of bit error rate (BER) over a-40 km single-mode fiber (SMF) transmission for down-link, and over an-80 km SMF transmission for up-link were achieved. The characteristic of our proposed systems is the use of one DFB LD with main and -1 side modes injection-locked technique, it reveals a prominent alternative with better performances.
In this paper, a 3-dimensional metamaterial absorber operating at 11.8 GHz was presented. The metamaterial absorber is composed of coplanar magnetic and electric resonators, with the latter in the center part of the former. By carefully adjusting structural dimensions of magnetic and electric resonators, absorbance per unit cell can reach up to 96% at 11.8 GHz with a 6% FWHM (Full Width at Half Maximum). The full-wave simulations confirmed nearly equal permeability and permittivity and large imaginary part of the refractive index at 11.8 GHz and thus proved the effectiveness of the proposed 3-dimensional metamaterial absorber for microwave applications.
A full-duplex radio-over-fiber (ROF) transport system employing semiconductor optical amplifier (SOA)-based optical single sideband (SSB) modulation technique is proposed and demonstrated. For our proposed approach, it is relatively simple to implement as it requires only one SOA to generate optical SSB signal. Over an-80 km single-mode fiber (SMF) transmission, low bit error rate (BER), clear eye diagram, and low third-order intermodulation distortion to carrier ratio (IMD3/C) were achieved. Our proposed full-duplex ROF transport systems are suitable for the long-haul microwave optical links.