Reza Azadegan

A novel approach for miniaturization of slot antennas

With the virtual enforcement of the required boundary condition (BC) at the end of a slot antenna, the area occupied by the resonant antenna can be reduced. To achieve the required virtual BC, the two short circuits at the end of the resonant slot are replaced by some reactive BC, including inductive or capacitive loadings. The application of these loads is shown to reduce the size of the resonant slot antenna for a given resonant frequency without imposing any stringent condition on the impedance matching of the antenna. A procedure for designing this class of slot antennas for any arbitrary size is presented. The procedure is based on an equivalent circuit model for the antenna and its feed structure. The corresponding equivalent circuit parameters are extracted using a full-wave forward model in conjunction with a genetic algorithm optimizer. These parameters are employed to find a proper matching network so that a perfect match to a 50 /spl Omega/ line is obtained. For a prototype slot antenna with approximate dimensions of 0.05/spl lambda//sub 0//spl times/0.05/spl lambda//sub 0/ the impedance match is obtained, with a fairly high gain of -3dBi, for a very small ground plane (/spl ap/0.20/spl lambda//sub 0/). Since there are neither polarization nor mismatch losses, the antenna efficiency is limited only by the dielectric and ohmic losses.

Design of an efficient miniaturized UHF planar antenna

The design aspects and the measured results of a novel miniaturized planar antenna are described. Such architectural antenna design is of great importance in mobile military communications where low visibility and high mobility are required. Slot radiating elements, having a planar geometry and capable of transmitting vertical polarization when placed nearly horizontal, are appropriate for the applications at hand. Slot antennas also have another useful property, so far as impedance matching is concerned. Basically, slot dipoles can easily be excited by a microstrip line and can be matched to arbitrary line impedances simply by moving the feed point along the slot. Antenna miniaturization can be achieved by using a high permittivity or permeability substrate and superstrate materials and/or using an appropriate antenna topology. We demonstrate miniaturization by designing an appropriate geometry for a resonant narrow slot antenna. A very efficient radiating element that occupies an area as small as 0.12/spl lambda//sub 0//spl times/0.12/spl lambda//sub 0/ is designed and tested. Simulation results, as well as the measured input impedance and radiation patterns of this antenna, are presented. This structure shows a measured gain of 0.5 dBi on FR4 substrate, which has a loss-tangent of the order of 0.01. Also, the effect of finite ground plane size on gain and resonant frequency is investigated experimentally.

Miniature high-Q double-spiral slot-line resonator filters

A new class of low insertion-loss miniaturized filters using slot-line resonators is proposed. Miniaturization is achieved by terminating the slot line with a double-spiral inductive termination at both ends. Using this miniaturized resonator, both positive and negative couplings may be realized, and therefore, both standard coupled-line and cross-coupled quasi-elliptic filters are realizable. The unloaded Q of these slot-line filters is considerably higher than that of miniaturized microstrip filters of comparable dimensions due to the inherent higher Q of the slot line. To demonstrate the validity of the design procedures and the performance characteristics, two different types of filters were fabricated and tested. One is a four-pole Chebyshev filter and the other is a quasi-elliptic filter where, in each case, the full-wave simulations show very good agreement with measurements.

Analytical formulation of the scattering by a slightly rough dielectric boundary, covered with a homogenous dielectric layer

Characterization of the radar response of a multi-layer dielectric media with slightly rough interface has a number of applications, including remote sensing of snow non-destructive evaluation and quality control of multi-layered MMIC, etc. For the case of snow-pack remote sensing, the premise is to compare the scattered fields of the rough surface with snow with that on bare rough surface and then attribute the variation in the scattered power and coherence to the snow parameters. In this approach, first, the snow cover is modeled by a homogenous dielectric layer having a smooth top surface above a ground plane with a rough surface. In situations where the scattering from the rough surface become comparable to with the snow volumetric scattering, the volume scattering is added incoherently to the surface scattering, and then, the coherence is computed. In this paper, a small perturbation solution is developed to predict the bistatic scattering coefficients and the coherence of a slightly rough surface covered with homogenous dielectric layer.

A Broadband Stacked Power Amplifier in 45-nm CMOS SOI Technology

A fully integrated broadband power amplifier (PA) is implemented in a standard 45-nm CMOS SOI technology. The PA is designed using a dynamically biased stacked SOI transistor approach, which constructively adds drain-source voltage signals of individual transistors while keeping their gate voltages within source and drain voltage limits. The design overcomes both low gate-oxide breakdown and low source-drain reach through voltages of nanoscale CMOS transistors. The number, size, and topology of transistors in the stack are optimized to deliver a relatively high linear output power over a wide range of frequencies. The amplifier under a supply voltage of 4.5 V measures a flat gain of 6 dB with -1-dB bandwidth of 6 to 26.5 GHz ( X-band to K-band). At 18 GHz, the PA under a supply voltage of 7.2 V measures a saturated output power (PSAT) of 26.1 dBm ( ~ 400 mW), a linear output power (P1 dB) of 22.5 dBm, and a peak power-added efficiency (PAE) of 11%. With a lower power supply voltage of 4.5 V, the PAE increases to more than 20% and stays above 17% with relatively constant PSAT and P1 dB for several measured frequencies in the range of 6 to 20 GHz. The PA occupies an active chip area of only 0.16 mm2.

Bandwidth Enhancement of Miniaturized Slot Antennas Using Folded, Complementary, and Self-Complementary Realizations

Folded and self-complementary structures are considered as two effective approaches to increase the bandwidth of miniaturized antennas. A folded realization of a previously reported miniaturized slot antenna is devised and shown to provide more than 100% increase in the bandwidth as compared with that of the miniaturized slot antenna with the same size and efficiency. The complementary pair of the miniaturized folded slot, namely, the folded printed wire is also discussed in this paper. It is shown that the folded slot has a much higher radiation efficiency when compared with its complementary folded wire antenna. Another approach for bandwidth improvement is the implementation of the self-complementary structure of the same miniaturized topology to moderate the frequency dependence of the antenna input impedance. To examine this approach, a folded self-complementary miniature antenna is studied, where further increase in bandwidth is observed. A miniaturized folded slot, its complementary miniaturized folded printed wire, as well as their self-complementary realization, were fabricated and tested. These antennas can fit into a very small rectangular area with dimensions as small as 0.065lambdao x 0.065lambdao. While the folded slot ranks the highest in the efficiency/gain, the self-complementary structure falls between the slot and printed wire since it consists of equal proportions of the both slots and strips. A self-complementary H-shape antenna is also introduced to demonstrate that by relaxing the miniaturization to a moderate value, a significant improvement in bandwidth can be accomplished. With yet small dimensions of 0.13lambdao x 0.24lambdao, a very wide bandwidth of (2.3:1) is obtained. For the case of no dielectric substrate, even wider bandwidth of (3:1) is achievable.

A Ku-Band Planar Antenna Array for Mobile Satellite TV Reception With Linear Polarization

We present a high gain linearly polarized Ku-band planar array for mobile satellite TV reception. In contrast with previously presented three dimensional designs, the approach presented here results in a low profile planar array with a similar performance. The elevation scan is performed electronically, whereas the azimuth scan is done mechanically using an electric motor. The incident angle of the arriving satellite signal is generally large, varying between 25° to 65° depending on the location of the receiver, thereby creating a considerable off-axis scan loss. In order to alleviate this problem, and yet maintaining a planar design, the antenna array is designed to be consisting of subarrays with a fixed scanned beam at 45°. Therefore, the array of fixed-beam subarrays needs to be scanned ±20° around their peak beam, which results in a higher combined gain/directivity. The proposed antenna demonstrates the minimum measured gain of 23.1 dBi throughout the scan range (for 65° scan) with the peak gain of 26.5 dBi (for 32° scan) at 12 GHz while occupying a circular aperture of 26 cm in diameter.

Design of miniaturized slot antennas

A procedure for the design of a novel small slot antenna is presented. Using this method enables us to achieve a perfectly matched antenna with a fairly high efficiency for a given arbitrary small size. The miniaturization is achieved by terminating the short slot by an inductor. Inductive loading is realized by coiling the shortened slot line with a length of less than a quarter wavelength. Although the choice of antenna size is optional, it is subject to limitations such as antenna bandwidth and gain/efficiency. However, the directivity of this small dipole-slot antenna, in the limit, is equal to that of the infinitesimal Hertzian dipole, and its gain depends on the substrate material specifications and antenna size. Microstrip line is used to feed the antenna, which provides more stable feeding compared to coaxial feed. Then simulation results for a prototype antenna at 300 MHz as well as the input impedance and radiation pattern of the antenna are presented and compared with measurements.

Miniaturized folded-slot: an approach to increase the bandwidth and efficiency of miniaturized slot antennas

A new miniaturized folded slot antenna is presented as an improved design for miniaturized slot antennas. It demonstrates wider bandwidth and higher radiation efficiency than our previous design (see Sarabandi, K. and Azadegan, R., Antennas and Propagation Society, 2001 IEEE Int. Symp., vol.4, p.446-9, 2001). By fixing the size of the new design to 0.06/spl lambda//sub 0//spl times/0.06/spl lambda//sub 0/, which is almost the same as dimensions as the previous design, the bandwidth of the antenna is increased by 100% with a slight increase in the gain of the antenna.

A compact planar folded-dipole antenna for wireless applications

A new miniaturized printed antenna is presented as a dual structure to the miniature folded slot antenna. It is referred to as a miniaturized printed folded-dipole. This antenna requires neither a ground plane, nor any matching network. Considering its size, this resonant antenna has a fairly wide bandwidth. If a large enough ground plane is readily available, the miniaturized slot antenna exhibits superior efficiency compared to its printed dual.