The development of near-space hypersonic vehicles is confronted with the ``blackout'' problem of the plasma sheath. As electronic density on the leeward surface is lower than that on the windward surface during the reentry process, a low Earth orbit (LEO) satellite may be used to mitigate this problem. In this study, the Iridium system, as a low-orbit relay satellite system, is utilized to evaluate the feasibility of using a LEO satellite. First, the incident angle of the electromagnetic waves radiating from the vehicles to various potential relay satellites is calculated by the STK software. Second, the transmission coefficient of the electromagnetic wave in the plasma is obtained by using the equivalent wave impedance method to present the attenuation effect of the plasma sheath channel. Finally, the attenuation coefficients of each channel between the aircraft and the potential satellite are used as a parameter to select the best relay in the reentry process of the vehicles. Simulation results show that the use of LEO satellites for relay can significantly reduce the communication interruption time during the reentry process by 32.6% for typical scenarios.
A dual-band omnidirectional circularly polarized (CP) patch antenna with conical radiation patterns is presented in this paper. The antenna consists of a patch with inclined slots, a ground plane with L-shaped slots and a coaxial probe. In addition, by loading shorting vias between the patch and the ground plane, the vertical polarizations of the proposed antenna at TM01 and TM02 modes can be obtained. Two sets of slots etched on the ground and the patch contribute to the horizontal polarizations for the two modes, respectively. Omnidirectional CP fields can be achieved at both resonant modes when the two orthogonal polarizations are equal in amplitude and different in phase by 90°. To verify the design, a prototype operating at 2.4 GHz WLAN and 3.5 GHz WiMAX bands has been fabricated and measured. The measured average axial ratios (ARs) at two resonant modes in the azimuth plane are 1.1 and 1.5 dB, respectively. Experimental results show good agreement with the simulated data.
A low-profile, wideband dual-polarized antenna with unidirectional radiation patterns is the design goal of this paper. To obtain such antenna characteristics, the design is divided into two steps. First, a coax-feed wideband antenna element with a simple geometry is proposed. The antenna element consists mainly of a quasi-square patch-dipole, a coupling E-shaped feeding structure and a shorting pin. The electromagnetic coupling between the feeding structure and the non-contact quasi-square patch can be flexibly controlled by a pair of fan-shaped stubs. Secondly, two pairs of the proposed antenna elements are selected to construct a dual-polarized antenna. To further reduce the profile of the antenna, two techniques are utilized. One is the mutual coupling distributing among the elements while the other is to add four rectangular stubs within the inner region. A prototype of the dual-polarized antenna is fabricated and measured. Measurement results demonstrate that the prototype antenna obtains an overlapped fractional bandwidth of 38.9% from 1.7 to 2.52 GHz with a good isolation higher than 32 dB. Both unidirectional radiation patterns with front-to-back ratios better than 20 dB across the whole frequency band and cross polarization levels lower than -22 dB in most operating frequency band are obtained. Additionally, the dual-polarized antenna achieves average gains about 9.9 dBi and 10.1 dBi for Port 1 and Port 2, respectively.
A novel design of a compact microstrip patch antenna using meandering technique is proposed in this paper where the designed antenna seems to behave as a microstrip patch loaded with conducting strips. A rectangular microstrip patch antenna with addition of conducting strip radiates at much lower frequency than a conventional rectangular microstrip antenna, due to increase of resonant length, but it also causes the increase in total size of the antenna. In this article, the resonant frequency has been lowered significantly by loading a regular rectangular microstrip patch antenna with rectangular slot in a proper position in such a way that the whole structure looks like a strip loaded radiator. About 86.5% size reduction has been achieved experimentally with very good agreement of simulated and measured results. The equivalent circuit and approximate resonant frequency calculation have been discussed in this paper.
In this paper, we report a single layer modified T-shaped dipole antenna for UHF-RFID tag applications. The designed RFID tag antenna consists of a pair of T-shaped dipole strips loaded with four half discs patches and a tag chip placed in the center. The antenna's size is 80×40×1.6 mm3. Performance of the proposed design was investigated with simulations and measurements. The main feature of this design is that the RFID tag antenna can operate effectively at 868 MHz and 915 MHz frequency bands which make it broadband. The maximum reading range measured in an anechoic chamber is 4.25 m and 5.27 m at 915 MHz and 867.5 MHz, respectively. Furthermore, the RFID tag antenna can work on metallic plates when inserting a foam spacer between them. The final result has a simple configuration, low profile and can be suitable for practical applications dealing with free-space and metallic objects.
A novel broadband dual-polarized magneto-electric (ME) dipole antenna is proposed for 2G/3G/LTE/WiMAX applications. The proposed antenna has stair-shaped feeding strips to impart a wide impedance bandwidth to it and a rectangular box-shaped reflector to enhance its stability in radiation patterns and high gain over the operating frequencies. The measured results show that a common impedance bandwidth is 80% with standing-wave ratio (SWR) ≤ 1.5 from 1.68 to 3.92 GHz and port-to-port isolation larger than 25 dB within the bandwidth. The measured antenna gains vary from 9.2 to 12 dBi and from 9.2 to 11.8 dBi for port 1 and port 2, respectively. The antenna has nearly symmetrical radiation patterns with low back-lobe radiation both in horizontal and vertical planes, and broadside radiation patterns with narrow beam can also be obtained.
The evaluation of the magnetic field from double-circuit twisted three-phase power cable lines misses a sound and exhaustive theoretical and experimental treatment in the literature. This paper presents a rigorous approach to the calculation of the magnetic field from double-circuit twisted three-phase cables, whereby the magnetic field generated by such cables is computed as the vector sum of the two individual fields generated by each twisted three-phase cable. This approach is validated by means of extensive measurements of the magnetic field from single- and double-circuit twisted three-phase power cables - provided by Italian utilities - identical to those installed in the field.
A microstrip magnetic dipole Yagi antenna with the feasibility of obtaining a wider bandwidth and relatively smaller size is proposed and demonstrated. The proposed antenna, consisting of a reflector, a driver with backed soldered SMA connector, a coupling microstrip line with three rectangular slots and three modified directors, is designed and fabricated. Good agreement between simulated and measured results is observed. Simulated and measured results reveal that the proposed antenna can provide an impedance bandwidth of 19.2% (4.95-6 GHz). Meanwhile, within the impedance bandwidth, the radiation pattern of the proposed antenna has front-to-back (F/B) ratios ranging from 10.1 dB to 26.1 dB, cross-polarization levels in the endfire direction from 47.1 dB to 73.0 dB, peak gains from 6.4 dBi to 10.4 dBi with an average peak gain of 9.6 dBi and endfire gains from 2.2 dBi to 4.3 dBi with an average endfire gain of 3.1 dBi. Additionally, the measured bandwidth of 19.2% (4.95-6 GHz) not only meets the need for certain Wi-Fi (5.2/5.8 GHz) or WiMAX (5.5 GHz) band communication application, but also provides the potential to implement multiservice transmission.
A circularly polarized (CP) substrate integrated waveguide (SIW) cavity-backed antenna based on dual concentric, orthogonal slot split ring resonators is proposed and experimentally studied. The circularly polarized wave is generated by two split ring-slots etched in the upper metal layer of the SIW cavity resonator. These two slots are excited by a coaxial probe located in the gap of the external slot split ring to radiate the right-handed circularly polarized (RHCP) wave. By rotating the dual split slot ring resonators and the probe by 45 degreesrelative to the backed cavity, a better match characteristic and a slightly higher radiation gain are obtained. Because of theconcentricity of radiant split ring slots, the beamwidth of the circular polarization is obviously increased.From the experimental results, the impedance bandwidth was 10.8% for the reflection coefficient less than -10 dB, the axial ratio (AR) bandwidth was 1.54% for the AR less than 3 dB, and the RHCP gain was 4.44 dBi. Moreover, the 3-dB axial ratio beamwidth at the centre frequency of 10.40 GHz has been extended to 142° in the angular range from -78° to +64°.
Coplanar monopole antennas printed using copper oxide nanoparticles on flexible substrates are characterized in order to study the effect of the ink drop spacing on the antenna parameters. Polyethylene Terephthalate and Epson paper were the chosen flexible substrates, and the antennas were designed to operate at 20 GHz. A maximum conductivity of 2.8×107 Ω−1m−1 was obtained for the films printed on Polyethylene Terephthalate using a drop spacing of 20 μm. The corresponding antenna achieved a gain and an efficiency of 1.82 dB and 97.6%, respectively. Experiments showed that smaller drop spacings lead to bulging of the printed lines while the antenna performance worsens for longer ones. At the same drop spacing, antennas printed on Epson paper substrate showed a -10 dB return loss bandwidth which extended from 17.9 GHz to 23.3 GHz, leading to a fractional bandwidth of 26.0%.
A finite difference method in the frequency domain is evaluated to clarify characteristics of the Lorentz force exerted on a metal nanoscale particle by light irradiation. Numerical results are compared with exact values obtained from Mie theory to show that applying a smoothing algorithm to the surface of a nanoparticle increases the accuracy of the simulation. Analysis of the Lorentz force exerted between two spheres aligned closely indicates that strong forces cause the spheres to attract each other at the plasmon resonant frequency. It was also noticed that application of the smoothing algorithm was indispensable in order to achieve the above result.
In this paper, an antenna with reconfigurable radiation pattern in the H-plane at 2.45 GHz for high power applications is presented. It is based on a 3 slots array in the E-plane covered partially with a wall of plasma in order to reduce the length of the slots and consequently ensure electrically a modification of the radiation pattern in the H-plane. The power distribution of the array is ensured with a power splitter.
A novel single-layer unit cell structure is proposed to design a dual-band dual-linear-polarization reflectarray antenna with different beams for X and Ku bands. The unit cell structure is composed of a circular ring and two cross bow-tie structures combined by a circular patch. Five tunable geometric parameters can be optimized to achieve the required phase distributions of the reflectarray antenna with independent radiation patterns for each band which is a challenge for single-layer linearly polarized reflectarrays. Besides, the proposed unit cell structure has the ability to meet the demand of dual-polarization applications. A 301-element center-fed reflectarray with an octagon-shape aperture operating at X and Ku bands is designed, manufactured and measured to verify the dual-band performance of the proposed unit cell. The measured results show that the object of achieving different beams at different frequencies is realized with good radiation patterns at both designed frequencies. Besides, the similar radiation patterns for both linear polarizations are also achieved at both bands.
In this paper, a three-layered chiral metamaterial composed of three twisted split-ring resonators is proposed and investigated. The simulated and measured results show that the proposed metamaterial can achieve efficient asymmetric transmission of linearly polarized wave and cross-polarization conversion for two distinct bands: X (6.95-10.05 GHz) and Ku (15.55-18.47 GHz). In the X-band, an incident y-polarized wave is almost converted to a x-polarized wave, while an incident x-polarized wave is completely blocked from passing through the structure. In the Ku-band, an incident x-polarized wave is almost converted to a y-polarized wave, while an incident y-polarized wave is blocked from passing through the structure. Moreover, the simulated and measured results confirm that the proposed metamaterial has a good robustness to misalignment, which provides convenience for fabricating in practical applications. Finally, the physical mechanism of this dual-band asymmetric transmission effect can be explained based on the different resonant modes of the proposed structure.
In this paper, the design, fabrication, and test of an additive manufactured double-ridged horn antenna optimized to work in ultra-wide-band frequencies is introduced. In particular, to build this antenna, the fused deposition modeling fabrication method is selected. The plastic-made device is then coated by using conductive ink. The double-ridged horn is conceived as a monolithic block. In this way, performance degradations caused by fabrication inaccuracies are minimized. A very good agreement between the simulations and the antenna measurements is demonstrated. The proof-of-concept prototype has an outstanding operational bandwidth performance of 11.5 GHz (fc 8.25 GHz) with a gain of 6 dBi; its total weight is less than 200 gr, and the total prototyping fabrication costs are less than 10 Euro per antenna with a lead time of less than a week.
A compact planar reconfigurable triple band-notched UWB Microstrip antenna is proposed in this paper for UWB applications. A band rejection at ITU 8-GHz is generated by inserting an inverted U-shaped metallic strip at the slotted ground plane. Moreover, by cutting two slots on radiating patch, the second rejection at 3.5 GHz for WiMAX and the third rejection at 5.5 GHz for WLAN application are generated. Then, by embedding two (PIN) diodes along the patch slots, switchable dual or single band-notched behavior is added to the antenna performance. The simulated and measured results show that the antenna can operate in a wider bandwidth from 3.1 GHz to 11 GHz, and it has a good omnidirectional radiation pattern with stable gain. Furthermore, the designed antenna has a simple structure and compact size of 20×20 mm2. The proposed antenna can use the full potential of UWB frequency range with reconfigurable band-notched behavior at 3.5, 5.5, 8.1 GHz to avoid interference with WiMAX, WLAN, ITU systems respectively.
The instantaneous measurement of RF & microwave frequencies is widely used in electronic warfare (EW) for the determination of unknown signals over a broad frequency band. This paper presents an enhanced frequency measurement accuracy using three stages of novel RF frequency discriminator (FD) for RF front-end IFM Receivers. The appropriate structure of the designed frequency discriminator is implemented using a conventional PCB fabrication process. The frequency discriminator consists of two different hybrid layouts and one Wilkinson power divider, and all these components are implemented in microstrip technology, which is particularly important due to lower cost and easy integration into the PCB. To demonstrate the feasibility of the proposed structure, an RF-FE instantaneous frequency measurement (IFM) receiver has been realized based on 3-stage RF frequency discriminator. Simulation and measurement results have shown a frequency measurement accuracy less than 1 MHz (RMS) over the entire S-band.
A planar reflectarray/transmitarray antenna which reflects/transmits the incident fields radiating from feed antenna is presented. The antenna works as a reflectarray at 13.85 GHz and a transmitarray at 8 GHz. The unit cell is composed of three layers. The first layer consists of a crossed-dipole element and a square ring frequency selective surface (FSS) on the top and bottom surfaces of a dielectric substrate. The second and third layers are identical and consist of a square ring slot element on both sides of a dielectric substrate. An air gap is inserted between layers. The aperture of the antenna is 225 mm which equals 10.4 wavelengths at 13.85 GHz and 6 wavelengths at 8 GHz. The reflectarray/transmitarray antenna is fabricated, and NSI planar near-field system is used to measure the performances of the prototype. Good agreement between the simulated and measured results has been achieved. The measured gain is 27.1 dB in reflection mode at 13.85 GHz resulting in a 38% aperture efficiency and 23.1 dB in transmission mode at 8 GHz resulting in a 45.7% aperture efficiency.
A broadband Perfect Metamaterial Absorber (PMA) on FR-4 Epoxy substrate for X-band and Ku-Band applications is proposed. The unit cell structure is composed of rectangular patches of appropriate shapes and orientation on top of the metal-backed dielectric substrate having a thickness of 2.7 mm (0.16λL). The relative absorption bandwidth is 79% (more than 85% absorption) covering the entire X-band and the Ku-Band of the microwave frequencies. The surface current distributions of the top and bottom planes have been analyzed to elaborate the absorption mechanism of the structure. The broadband characteristics of the design support its claim of being useful to a wide range of applications in both commercial and research sectors. Such applications include military and stealth devices, thermal sensors and electronic-cloaking devices.
Characterization measurements of wideband antennas can be a time intensive and an expensive process as many data points are required in both the angular and frequency dimensions. Parallel compressive sensing is proposed to reconstruct the radiation-frequency patterns (RFP) of antennas from a sparse and random set of measurements. The modeled RFP of the dual-ridge horn, bicone, and Vivaldi antennas are used to analyze the minimum number of measurements needed for reconstruction, the difference in uniform versus non-uniform reconstruction, and the sparsity transform function used in the compressive sensing algorithm. The effect of additive white Gaussian noise (AWGN) on the minimum number of data points required for reconstruction is also studied. In a noise-free environment, the RFP of the antennas were adequately reconstructed using as little as 33% of the original data points. It was found that the RFPs were adequately reconstructed with less data points when the discrete cosine transforms (DCT), rather than discrete Fourier transforms (DFT) was used in the compressive sensing algorithm. The presence of noise increases the number of data points required to reconstruct an RFP to a specified error tolerance, but the antenna RFPs can be reconstructed to within 1% root-mean-square-error of the original with a signal to noise ratio as high as -15 dB. The use of compressive sensing can thus lead to a new measurement methodology whereby a small subset of the total angular and frequency measurements is taken at random, and a full reconstruction of radiation and frequency behavior of the antenna is achieved during post-processing.
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