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Genetic algorithm (GA) has been a popular optimization technique used for performance improvement of microstrip patch antennas (MPAs). When using GA, the patch geometry is optimized by dividing the patch area into small rectangular cells. This has an inherent problem of adjacent cells being connected to each other with infinitesimal connections, which may not be achievable in practice due to fabrication tolerances in chemical etching. As a solution, this paper presents a novel method of dividing the patch area into cells with nonuniform overlaps. The optimized design, which is obtained by using fixed overlap sizes, shows a quad-band performance covering GSM1800, GSM1900, LTE2300, and Bluetooth bands. In contrast, use of nonuniform overlap sizes leads to obtaining a pentaband design covering GSM1800, GSM1900, UMTS, LTE2300, and Bluetooth bandswith fractional bands with of 38% due to the extra design flexibility.

Genetic algorithm (GA) is a powerful optimization technique that has been shown to be useful in a wide area of electromagnetics such as antennas, antenna arrays, and radar systems [

Optimization of patch shape, having random slots in the patch area, provides several resonant current paths. As a result, the MPA resonates at several frequencies. Therefore, GA optimization has been used by researchers to design multiband MPAs. If the dimensions are selected such that these frequencies are close to each other, their resonant bands can overlap to give an increased single bandwidth to the MPA. In case of a GA modified patch shape, a longer current path can be created and the effective electrical length becomes larger compared to classical patches, where the current flows along a straight line. In this sense, shape optimization of the patch has been used to design miniature MPAs.

The basic method in optimization of patch shape is the use of traditional on/off building blocks to make cells contacting by an infinitesimal point [

In contrast, a simple overlapping method based on shifting of the cells parallel to patch width is proposed in this paper. The optimized MPA designed by using uniform overlap method shows a quad-band performance covering GSM1800, GSM1900, LTE2300, and Bluetooth bands. Further, use of nonuniform overlap sizes leads to obtaining a pentaband design including UMTS band too. This paper consists of five sections, where Section

Neltec NX9320 (IM) (tm) which has a relative permittivity of 3.2 and a loss tangent of 0.0025 is used as the substrate for MPAs. The patch printed on the substrate suspends above a ground plane having an air gap of 8 mm (Figure

Antenna configuration. (a) Lateral view of the antenna. (b) Patch fragmented into 63 cells.

In the GA procedure, 63 bits are used to define the patch geometry, by assigning conducting or nonconducting properties to each cell. As there are only two possible values, binary coding is used. Another five genes of the chromosome are used to define the feed position on the patch. Moreover, asymmetric patch geometries are allowed in the optimization, as it gives more flexibility to the GA to find a solution.

The traditional on/off building blocks method with infinitesimal connections is compared with a scheme consisting of overlaps (Figure

(a) Traditional on/off building blocks with infinitesimal connections. (b) Scheme with overlaps. (c) A possible structure with infinitesimal connections. (d) A possible structure with overlaps.

The performance needed to achieve is broadband or multiband performance covering the GSM1800, GSM1900, UMTS, LTE2300, and Bluetooth bands. Therefore, the fitness function is defined as the summation of reflection coefficient values taken at 10 MHz intervals ranging from

MPAs with infinitesimal connections and three different overlap sizes between adjacent cells are examined to obtain multiband performance. Different overlap sizes have been tested to identify the most suitable size for performance improvement of the MPA. The overlap size should be large enough to be compatible for a chemical fabrication process and to contact neighboring cells properly. On the other hand, the overlap size should be small enough to have nonconducting regions on the patch area. Therefore, three different overlap sizes (0.5 mm, 1 mm, and 2 mm) have been investigated for a cell size of approximately 7 × 7 mm^{2}. Further, an optimization is done using the novel nonuniform overlapping scheme.

Initially, an MPA with infinitesimal connections between adjacent cells is optimized for comparison purposes. It operates from 1820 MHz to 1950 MHz, from 1990 MHz to 2030 MHz, and from 2420 MHz to 2530 MHz covering GSM1900 and Bluetooth partially (Figure

The optimized MPA with infinitesimal connections. (a) Optimized design. (b) Reflection coefficient.

The optimized MPA, with an overlap of 0.5 mm, exhibits dual resonance from 1810 MHz to 1950 MHz and from 2300 MHz to 2490 MHz (Figures

The optimized MPAs with uniform overlaps. (a) Optimized design for overlap of 0.5 mm. (b) Optimized design for overlap of 1 mm. (c) Optimized design for overlap of 2 mm. (d) Reflection coefficient.

Bandwidth performances of the optimized designs show that the maximum −10 dB bandwidth is obtained with overlap of 1 mm. Though this overlap size is the most suitable for this design, it may be not applicable for any design. Therefore, if such fixed overlap sizes are used, it is necessary to do several trial simulations with different overlap sizes to find the best size. The question here is whether it is possible to add an extra degree of freedom by letting the GA design an MPA with nonuniform overlaps. The novel method is proposed next.

It is found out whether the bandwidth can be increased further by using nonuniform overlaps. GA is used to assign different overlap sizes to each overlapping position. In this regard, any overlap size out of 0.5 mm, 1 mm, and 2 mm is used at each position. This allows having conducting or nonconducting cells with different sizes instead of fixed sizes as used earlier. The optimized design consists of combination of different overlap sizes, resulting in a larger bandwidth from 1710 MHz to 2500 MHz (Figure

The optimized MPA with nonuniform overlaps. (a) Optimized design. (b) Reflection coefficient.

Radiation patterns at the center of each band. (a) GSM1800 (

As per the results, use of traditional on/off building blocks method has a low probability of creating a high performance MPA, in addition to fabrication problems. Use of overlaps between adjacent cells improves the performance, but the performance depends on the overlap size. However, the most appropriate overlap size changes from design to design and consumes much time for several trial simulations. As a solution, use of nonuniform overlapping is proposed in this paper and GA finds the best patch geometry with improved performance more effectively.

Variations of the best fitness over generations in the optimized designs are shown in Figure

Best fitness over generations. (a) For infinitesimal connections and uniform overlaps. (b) For nonuniform overlaps.

The optimized design with nonuniform overlapping resonates at three frequencies (1800 MHz, 2100 MHz, and 2340 MHz) within the required frequency band. As the resonant frequencies are close to each other, the resonant bands overlap giving the MPA multifrequency broadband performance. The current patterns at these three frequencies follow different paths resulting in a different resonant behavior compared to a classical rectangular patch (Figure

Current paths at resonant frequencies.

Current distribution at resonant frequencies.

This concept can be applied to the design of MPAs for different applications. For example, miniaturized MPAs can be designed by employing techniques such as shorting pins and walls along with this concept. Such a shorted miniature MPA with same patch size and with uniform overlaps is presented in [

This paper proposes a novel nonuniform overlapping method to improve the performance of MPAs by means of bandwidth, without increasing the antenna volume. It is based on nonuniformly shifting the cells parallel to the width of the MPA to avoid cells contacting each other by infinitesimal points. As this method gives an extra degree of freedom to the designer, the bandwidth of the MPA could be improved more easily compared to the fixed overlapping method. A pentaband design covering GSM1800, GSM1900, UMTS, LTE2300, and Bluetooth bands has been presented in this paper using this method. This nonuniform overlapping cell method can also be employed for other optimization problems such as the design of small and high-directivity MPAs.

The authors declare that there is no conflict of interests regarding the publication of this paper.