Saeed I. Latif

Bandwidth enhancement and size reduction of microstrip slot antennas

Reduced size microstrip monopole slot antennas with different slot shapes-straight, L and inverted T, and placed on a small ground plane, are investigated. The ground plane size is 50 mm/spl times/80 mm, which is about the size of a typical PC Wireless card. Detailed simulation and experimental investigations are conducted to understand their behavior and optimize for broadband operation. It is shown that, the variation in the slot shape, from straight to L and T shapes, helps in generating additional resonances, which when coupled to the original resonances of the slot, further increases impedance bandwidths. The bent shapes of the L and T slots reduce their height and provide more space on the ground plane for electronics. A mirror image dual L-slot antenna, placed at two adjacent corners of the ground plane, is also investigated and optimized for the polarization diversity. They provide an impedance bandwidth of 87%, with near orthogonal radiation characteristics. The measured impedance bandwidths (S/sub 11/=-10 dB) of up to 60%, 84%, and 80% are achieved for these straight, L and inverted T slots respectively, by suitably selecting their design parameters. The simulation results are in good agreement with the experimental data considering several practical issues.

An Engineered Conductor for Gain and Efficiency Improvement of Miniaturized Microstrip Antennas

This paper reviews the concept of an engineered conductor, introduced by the authors in order to reduce ohmic losses of miniaturized microstrip antennas [1-4]. Because of the miniaturization, the ohmic losses of microstrip antennas increase, which essentially significantly reduces their gain and efficiency. By the use of the engineered conductor concept, these two important parameters of such antennas can be improved without altering the antennas geometry. The concept is based on using multiple laminated thin conductors, rather than one thick conducting layer, to form the microstrip antenna. The technique is applied to several miniaturized microstrip antennas in order to reduce their ohmic losses. The concept is explained using a microstrip line to demonstrate that the conductor loss can be reduced by increasing the number of layers in the lamination, while keeping the total thickness constant. Using conventional metallized substrates, the lamination reduces the thickness of each conductor layer to approximately or less than the skin depth in that conductor. Studies of two miniaturized antennas - namely, the square-ring antenna and the modified open-ring antenna - have respectively provided about 4.6 dB and 1.5 dB improvements in the gain, and from 30% to 40.7% improvement in the efficiency. Experimental investigations are also presented that confirmed the simulated results.

Pattern Equalization of Circular Patch Antennas Using Different Substrate Permittivities and Ground Plane Sizes

A very unique phenomenon of circular patch antennas (CPA) for obtaining equal E- and H-plane co-polarization patterns, using varying substrate permittivities and ground plane sizes, is investigated in this paper. Pattern equalization is studied for the dominant and the first few higher order modes of the circular patch antenna, using different substrate permittivities (εr) for the infinite ground plane case, and also by varying the ground plane sizes for the finite ground plane case. The angular range, at which the E- and H-plane patterns can be made equal, decreases with increased mode numbers. Also, for a given εr and mode number, there exists a specific ground plane size, which provides nearly equal E- and H-plane co-polarization patterns. For higher order modes, larger ground planes and higher dielectric permittivities are required to obtain pattern equalization with a greater angular range.

Investigation on the EM-Coupled Stacked Square Ring Antennas With Ultra-Thin Spacing

Stacked electromagnetically coupled square ring antennas with extremely thin spacing are studied. The separation between rings is kept very small so that they do not increase the overall antenna height, yet can provide multiband operation. The coupling effects among these very closely placed rings are studied based on substrate parameters so that they can be practically implemented using commercially available microwave substrates. It is observed that with an asymmetric arrangement of the stacked rings, different polarizations can be obtained for different resonances. However, if a fixed polarization is desired, a concentric stacked rings configuration has to be used. Experimental investigations are conducted to confirm simulation results.

Polarization Characteristics of Multiband Loaded Microstrip Annular Ring Antennas

Multifrequency operation can be obtained from the single-layer probe-fed annular ring antenna by loading it with a gap or slit. Two types of loading are studied: vertical and horizontal gap. For each case, two unloaded modes are excited around the dominant TM11 mode of the ring, equally spaced on the frequency spectrum. These multiple modes are excited, when the loading is symmetric on one side of the ring along one axis, and the excitation is off-centered on another side, or vice-versa. By choosing the location of the vertical or horizontal gaps along the y- or x-axis respectively, the polarization of each mode can be controlled. One of the loaded mode frequencies is much lower than the dominant TM11 mode frequency of the annular ring, indicating a miniaturization of antenna to a great extent. Effects of substrate parameters are investigated on the loaded and unloaded mode frequencies, and a design guideline is presented. Simulation results are confirmed by measurements.

Microstrip square-ring antenna with capacitive feeding for multi-frequency operation

In this paper, a new compact microstrip square ring antenna is presented, which can be operated at multiple frequencies. It can be stated that within a stacked microstrip square ring configuration, a third square ring is accommodated, which operates at a higher frequency than that of the stacked configuration. Thus, three resonators are arranged in a compact form and fed capacitively to successfully operate at three frequencies.

Dual-layer square-ring antenna (DLSRA) for circular polarization

In this paper, a dual-layer square-ring antenna is studied. The ring configuration is achieved by removing the central conducting portion from the patch which reduces the resonance frequency. The stacked configuration gives wide impedance bandwidth, compared to the regular microstrip patch antenna. To achieve significant axial ratio bandwidth, diagonal corner truncation of only top or bottom square-ring is not enough; rather a combination of corner truncation in both layers is necessary. Simulated and measured results show wide impedance and axial ratio bandwidths, compared to a single microstrip antenna. This antenna can be used in a GPS system or mobile communication.

Electromagnetically-coupled multiple square rings for multi-frequency operation

In order to achieve multi-frequency operation from square ring antennas, two or more square rings are stacked and electromagnetically excited by a feed line located outside the bottom ring. The separation between rings is kept very small so that, the feed line can excite them all, and the overall height remains small. The number of rings is the same as the resonances in this configuration.

A microstrip line-fed multi-resonant slot antenna in the 4G/LTE band for smartphones

A microstrip line-fed slot antenna is presented in this paper to operate in the entire 4G/LTE band. The slot antenna has the letter ‘L’ shape, and when excited with a transmission line generates multiple modes. These modes are combined to obtain the large bandwidth for covering most of the 4G/LTE band. Several feedlines have been studied to enhance the bandwidth. The slot width is also varied to achieve large impedance bandwidth. The radiation patterns are provided showing the behavior of the antenna. This antenna can be further optimized to provide polarization diversity in the 4G/LTE systems. The slot antenna is located in the upper portion of the ground plane, leaving a large area available for accommodating electronic circuitry for wireless communications or display technology in modern smartphones. This area can also be utilized to incorporate millimeter wave antennas to make the device compatible for future 5G wireless systems.

A double-ridged horn antenna design in canola oil for medical imaging

The design of a double-ridged horn antenna for medical imaging is presented in this paper. The antenna is immersed in canola oil to reduce its size and to achieve efficient coupling of the electromagnetic energy to the breast tissue. The antenna has wideband performance from 1.5 GHz to 5 GHz (3.5 GHz or 108% of impedance bandwidth), which is suitable for radar-based medical imaging. The double-ridged horn antenna has exponential tapered section for impedance matching. The detail design equations and antenna parameters are presented. The fabricated antenna was tested and compared with simulated results, and excellent agreement has been observed.