Adnan Iftikhar

A Frequency-Reconfigurable Series-Fed Microstrip Patch Array With Interconnecting CRLH Transmission Lines

This letter presents the design of a frequency-reconfigurable series-fed microstrip patch array in which the elements are interconnected with composite right/left-handed transmission lines (CRLH-TLs). Reconfigurable CRLH-TLs are used instead of meandered microstrip lines to reduce the overall size of the array and provide two different zero-phase frequencies of operation for broadside radiation in both instances. p-i-n diodes were used to reconfigure the array by changing the electrical lengths of the patches and microstrip sections of the CRLH-TLs. The measurements were taken in an anechoic chamber to verify the simulation results. The array can be reconfigured to operate at 1.97 and 2.37 GHz.

On using graphene-based conductors as transmission lines for feed networks in printed antenna arrays

The use of graphene-based conductors (GBC) as a transmission line (TL) is presented as a conventional TL possessing right-handed (RH) nature and its coupling characteristics are investigated. In order to verify and demonstrate the wave propagation of a GBC TL, a 120 mm long 50 Ω TL was fabricated and tested. Performance of the single GBC TL was then compared to the conventional microstrip TL, analyzing the matching and wave propagation results. To investigate the unwanted coupling that may occur in a feed network, a similar GBC and a conventional microstrip TL, as well as two parallel GBC TLs on the same substrates were separately manufactured and tested to complete the study. It is shown that GBC TLs support the wave propagation in a fashion similar to the microstrip TL with an attenuation of less then 3.0 dB up to 7 GHz. Also the measurements of the near-end coupling showed that the two parallel GBC TLs have fairly good isolation in the frequency band of 4.5 KHz to 8.5 GHz, whereas the far-end coupling exhibits similar properties to that of the parallel microstrip TLs with same distance between them. The results demonstrated that GBC TLs could hence be a potential candidate for the feed network for planar antenna arrays.

A 4 element compact Ultra-Wideband MIMO antenna array

In this paper, a compact planar Ultra-Wideband (UWB) antenna array with 4 monopole radiators is presented. To enhance the isolation, polarization of nearly placed elements is exploited. The proposed MIMO antenna array is electrically small 50 × 39.8 mm2, printed on a low loss 1.524 mm thick Rogers TMM4 laminate with a dielectric constant of 4.5 and a loss tangent of 0.002. Simulation in HFSS and printed prototype results satisfy the return loss requirement of better than 10 dB and isolation better than 17 dB on the entire 2.5 to 12 GHz bandwidth. The calculated envelope correlation value of less than 0.03 and the compactness of the proposed antenna array makes it suitable for small portable handheld devices.

A reconfigurable dual-band metasurface for EMI shielding of specific electromagnetic wave components

Metasurfaces are becoming more of an interest to the research community because of the unusual electromagnetic properties that can be achieved. This paper presents a reconfigurable metasurface for EMI shielding purposes. In particular, a dual-band Jersualem cross is developed and pin diodes are use to interconnect elements to control the specific polarization properties of the shield. It is shown that the response of the shield to specific field components can be controlled with simple control voltages. Simulations are validated with measurements throughout this work.

An initial investigation on the use of carbon microfibers for conformal transmission lines

The use of carbon micro fiber tow (or bundle) for conformal transmission lines (TLs) is initially investigated in this work. Two different microfiber TLs have been synthesized and tested. A 28.2 mm long microfiber TL was manufactured to demonstrate the wave propagating properties. Once these characteristics were determined, a microstrip TL was prepared by attaching 1oz conducting copper tape to a conformal surface and a similar microfiber TL with the same length and on the same substrate was manufactured. This prototype was then used to compare the propagation characteristics of the microfiber TL to the traditional and well established microstrip TL. Overall, it has been shown that the microfiber TL can support wave propagation in a manner similar to a microstrip TL; however, the attenuation constant appears to be rather large for frequencies above 500 MHz.

Radiation performance and Specific Absorption Rate (SAR) analysis of a compact dual band balanced antenna

This paper presents a compact dual-band dipole antenna with meander line radiating elements. The proposed antenna has a balanced structure with dimensions of 35×6×1.52 mm3, and mounted on a 36.2 × 100 mm2 floating ground plane. The balanced operation of the design is validated by incorporating a differential feed in the software simulation and a 180 ° hybrid junction is used for measurement with the network analyzer to verify the balanced concept of the prototype. Simulated and measured results of the S-parameters along with the de-tuning of the antenna in the presence of the human body shows good agreement. Moreover the proposed design is used as an exposure source to the simulated human head model. The human head is modeled as six layers in the Electromagnetic (EM) software HFSS to study the interaction between the proposed balanced antenna and the human head model. The Electric field (E-field) distribution in the six layers of the human head model is shown to estimate the penetration of the field when the antenna is placed at a distance of 7 mm from the proposed design. Also Local Specific Absorption Rates (SARs) and average SARs simulation results at 3.78 GHz and 4.29 GHz are shown. The SARs analysis showed that in all the six layers of the human head model, local SAR values are greater in fat and Cerebrospinal fluid (CSF) for both the frequencies while the average SAR values are not very high.

A note on the fundamental maximum gain limit of the projection method for conformal phased array antennas

New expressions for comparing the maximum gain of a phase-compensated conformal antenna have been analytically derived and validated to measurements. In particular, the newly derived analytical expressions were validated with a conformal phased-array antenna prototype attached to a wedgeand inverted-wedged shaped surface. Phase-compensation techniques based on the projection method were used to correct the radiation pattern. These expressions can be used by a designer to predict the maximum theoretical gain of a phase-compensated conformal antenna on a surface that changes shape with time.

On using the electrical characteristics of carbon microfibers for designing a monopole antenna

In this paper, the use of a carbon microfiber bundle (CMB) is investigated for manufacturing a monopole antenna. In particular, the radiating properties of a carbon microfiber bundle, having filaments of 7 μm in diameter, were studied as a monopole. The proposed monopole was mounted vertically on two separate types of ground plane, i.e., a small copper and a large aluminum ground plane. The monopole design was modeled in HFSS. To analyze the radiation characteristics of the microfibers and its shift in the resonant frequency, CMB monopole antenna prototypes with various lengths were manufactured and tested in an anechoic chamber. Overall, the simulation results agreed well with the measured results. Prototypes manufactured on the larger ground plane showed higher gain as compared to those on the smaller ground plane, with no significant difference in the matching characteristics. Overall, it was demonstrated that the light weight, low cost carbon microfiber bundle can be used to design an antenna for a range of resonant frequencies.

A printed dipole reconfigured with magneto-static responsive structures that do not require a directly connected biasing circuit

An initial study of novel Magneto-static Responsive Structures (MRSs) and their application to the frequency reconfigurability of a printed dipole antenna is presented here. The embodiment of the MRSs consisted of a cylindrical cavity with a diameter of 0.9 mm drilled into a 20.0 mil thick 1.5 mm × 1.5 mm TMM4 substrate. The cavities were partially filled with silver coated magnetic particles and covered on the top and bottom with copper tape. The conducting magnetic particles responded to an externally applied magnetic field and formed columns in the direction of the magnetic field lines. The columns connected the top and bottom conducting planes, acting as a switch. It was demonstrated that the electrical length of an antenna could be changed and the resonant frequencies could be reconfigured from 1.5 GHz to 1.9 GHz by incorporating the MRSs into the dipole antenna and controlling the ON and OFF states of the MRS switch. Overall, it was shown that the simulated results agreed well with the measurements. It was also demonstrated that the proposed MRSs do not need directly connected biasing circuitry, making them particularly useful for complex antenna designs.

An initial study on using carbon microfiber transmission lines in conformal array networks

In this paper, an initial study on the possible use of carbon microfibers as a transmission line (TL) feed network in conformal microstrip antenna arrays was conducted. Initially, a 12.0 cm long 50 Ω microfiber transmission line was manufactured and the wave propagation properties were measured. These characteristics were then compared to the propagation properties of a traditional copper microstrip TL with the same length. Once these propagation characteristics were determined, two parallel TLs with a separation of 4.0 mm were then manufactured to investigate the unwanted coupling that may occur in a feed network of an array. One of these TLs was a copper microstrip line and one was a microfiber TL with similar dimensions. Overall, it has been shown that the microfiber TLs support wave propagation in a manner similar to the copper microstrip TLs but the attenuation constant was larger, as the 3 dB point was at 2.5 GHz. Also it was evident from the measurements that the microfiber TLs were more immune to coupling at high frequencies. The results demonstrated that these properties made microfiber TLs a good possible candidate for the feed network of a conformal microstrip antenna array.