Microstrip antennas having posts for circular polarization

This paper presents a single-feed circularly polarized (CP) microstrip antenna achieved by defected ground structure. With the proposed DGS, a new resonant mode is added, which is orthogonal to the original resonant mode. These two modes will have the same magnitude and the 90° time-phase difference by adjusting the DGS dimensions, which contributes to achieve the CP radiation. Both the simulated and measured 10-dB impedance bandwidth of the CP microstrip antenna are 30 MHz, while the 3-dB axial-ratio bandwidth is 6 MHz. The CP gain across the 3-dB AR band ranges from 4.6 to 5.0 dBic.

A new circular polarization microstrip antenna having a defected ground plane is presented in this paper. A defect on the ground plane is introduced by inserting a square ring slot just below one of the top corners of the patch. The inserted slot on the ground creates a perturbation in the patch as like as conventional perturbed circular polarization antennas. The measured 3-dB axial ratio bandwidth was 1.26% with a gain of around 6.1 dBic.

A new technique to design single-feed circularly polarized (CP) microstrip antenna is proposed. The CP radiation is obtained by adjusting the dimension of the etched fractal defected ground structure (FDGS) in the ground plane. Parameter studies of the FDGS are given to illustrate the way to achieve CP radiation. The CP microstrip antennas with the second and third iterative FDGS are fabricated and measured. The measured 10-dB return-loss bandwidth of the CP microstrip antenna is about 30 MHz (1.558 to 1.588 GHz), while its 3-dB axial-ratio bandwidth is 6 MHz (1.572 to 1.578 GHz). The gain across the CP band is between 1.7 and 2.2 dBic.

ABSTRACTNew designs of the circularly polarized micro-strip antennas (CPMSAs) based on tree fractal geometries are proposed, examined experimentally, and compared. The excellent circularly polarized (CP) radiation with minimum axial ratio (AR) of 0.26 dB is achieved by optimization of the key parameters (angle, length, and width) of the fractal trees etched on the ground plane. Parametric study revealed that the fractal tree defected ground structures (FTDGS) are responsible for satisfying the condition of CP operation. The micro-strip antennas with third iterative FTDGS and modified third iterative FTDGS are fabricated on FR4 substrate. The measured 10-dB return loss and 3-dB AR are 99 MHz (2.407–2.506 GHz) and 12 MHz (2.443–2.455 GHz), respectively, with stable gain of 4.52 dBic at 2.45 GHz, for third iterative FTDGS antenna. For modified third iterative FTDGS antenna, measured 10-dB return loss and 3-dB AR are 109 MHz (2.354–2.463 GHz) and 26 MHz (2.386–2.412 GHz), respectively, with gain about 4.62 dBic in the vicinity of center frequency 2.4 GHz. The proposed designs can be good candidates for the unlicensed 2.45 GHz industrial, scientific, and medical (ISM) band applications.

A new configuration for a circularly polarised microstrip antenna with an omnidirectional pattern is proposed. This antenna consists of two rectangular patches with perturbation segments, which are arranged back-to-back relative to a coplanar waveguide (CPW) on a ground plane. The characteristics of the proposed antenna were clarified by experiments, and the mechanism to produce the circular polarisation was proved by using an electromagnetic simulator. The radiation patterns and input impedances were measured as a parameter of the width of the perturbation segment. Good circularly polarised radiation patterns with an omnidirectional pattern and input impedance characteristics were obtained.

A number of studies on the characteristics of cylindrical rectangular and circular microstrip antennas have been available in the open literature. The investigations of cylindrical triangular microstrip antennas, however, are relatively scant. Since the triangular patch can be a good substitute for the rectangular patch in microstrip antenna and array designs, due to its physically smaller patch size than the rectangular and circular ones, the related studies become interesting and important. This motivates the present study. In this article, both the cavity-model and full-wave analyses of cylindrical triangular microstrip antennas are described. Curvature effects on the input impedance and radiation characteristics for the antenna with various cylinder radii at its fundamental TM/sub 10/ mode are analyzed. Measured input impedances and radiation patterns are also presented for comparison. In addition, curvature effects on the cross-polarization characteristics of a triangular microstrip antenna at the TM/sub 10/ mode are also analyzed.

A technique is demonstrated to generate circularly polarized (CP) radiation of the compact diagonally asymmetric‐slotted microstrip patch antennas. Design rules for the single‐feed, compact, circularly polarized microstrip antennas (CPMA) with any arbitrary‐shaped slots along the diagonal directions are first summarized. Four, compact, CPMA with circular‐, square‐, cross‐, and square‐ring‐shaped slots along the diagonal directions are proposed and compared based on a fixed overall antenna size. A compact, CP, cross‐shaped slotted, microstrip antenna is fabricated and measured to verify the proposed technique experimentally. The measured 3‐dB axial‐ratio bandwidth of about 6.0 MHz is achieved with 10‐dB return loss bandwidth of 19.0 MHz while measured gain of the antenna is 4.0 dBic at 930 MHz. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1920–1927, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26959

A simple design of a probe-feed microstrip antenna with circular polarization (CP) radiation is presented. By embedding dual slits in a square microstrip and adjusting the sizes of the slits, an H-shaped microstrip antenna with two near-degenerate orthogonal modes for CP radiation can be achieved. This design provides a wide CP bandwidth and relaxed fabrication tolerances. Details of the antenna design are described, and theoretical and experimental results of the CP performance are presented.

The mutual coupling between circular patch microstrip antennas is studied using the reaction theorem and the model of equivalent magnetic current. An analytic formula is derived. The theoretical results are in good agreement with measurements for microstrip antennas with thin substrates. >

The notch cut circular microstrip antenna to realize circular polarization on thinner substrate is proposed. The notch degenerates fundamental TM11 mode into two orthogonal modes, to yield circular polarization. To improve upon the gain and bandwidth, its three layer suspended configuration is proposed. It yields VSWR and axial ratio BW of 60 and 15 MHz, respectively with gain of more than 5 dBi over axial ratio bandwidth. Further formulation in resonant length at two orthogonal modes for notch cut circular patch on non-suspended and suspended configurations is proposed. The frequencies calculated using them closely agrees with the simulated results. Using proposed formulations, the design procedure for notch cut circularly polarized antennas in 1000 to 4000 MHz frequency band, is presented. It gives circularly polarized response with formation of small loop (kink) inside VSWR = 2 circle in the smith chart. Thus the proposed formulation can be used to design circular polarized antenna at any given frequency.

In this paper, a circular polarization switchable microstrip antenna is proposed. In order to realize the circular polarization switchable microstrip antenna, the proposed antenna is excited by a feeding circuit that consists of a 90° hybrid circuit and a novel SPDT switching circuit. The proposed antenna is shown in Fig. 1. The proposed antenna consists of the CP antenna using 90° hybrid circuit and the SPDT switching circuit. It is well known that the CP antenna using a 90° hybrid circuit radiates the circular polarization in Fig. 1(c). According to selection of exciting part of 90° hybrid circuit, LHCP or RHCP is obtained. For circular polarization switching function, the proposed antenna is used the both of input ports of the 90° hybrid circuit and the novel SPDT switching circuit is proposed in Fig. 1(d). Therefore, the CP antenna can be realized to switch the circular polarization. In addition, for a gain enhancement, an array antenna is constructed using this concept as shown. The feeding circuit of the antennas uses a "Both-Sided MIC technology". The excellent design flexibility of the "Both-Sided MIC technology" is very effective for a array arrangement. Therefore, the circular polarization switching antennas are realized with simple structure and operation. In this paper, the characteristics of the integrated feeding circuit are investigated experimentally, and the characteristics of the proposed antennas are simulated by Agilent momentum. Consequently, it is verified that the circular polarization switchable microstrip antenna can be achieved.

To improve the bandwidth of a micro-strip antenna used in sensing moisture contents in materials, such as soil and concrete, a design method of circular double-layer micro-strip antenna is studied in this paper. The paper introduces the circular antenna structure, the algorithm for calculating resonant frequency, and the analysis of the relationship between patch size and bandwidth. Simulation results show that the proposed bandwidth of the micro-strip circular antenna (VSWR < = 2) is 525MHz (about 13% of the center frequency), 8.7 times as its single-layer counterpart (about 1.5%), and wider than its rectangular double-layer counterpart (about 9%). The antenna band is greatly improved by introducing a passive patch which meets working band requirements of the microwave moisture sensor. The numerical simulation results agree with the designed parameters.

A new technique for designing the active microstrip antenna for circular polarization is presented. The circular polarization is achieved by four slits and a pair of truncated corner and the operating frequency is electronically controlled by the bias voltage of varactor diodes. Theoretical modal for an antenna is developed using modal expansion cavity model and circuit theory concept. The results are validated with MoM-based simulator and experimental results. A good agreement between the simulated, calculated, and experimental results is obtained. The tuning range is found to be 40.24% and shows about 71% reduction in antenna size as compare to the conventional circular polarized antenna.

A simple theory based on the cavity model is developed to analyze microstrip antennas excited by a slot in the ground plane. By using an equivalent magnetic current source at the feed, the electric field under the patch is obtained in terms of a set of cavity modes. In particular, the loci of the slot feed location for achieving the circular polarization and the input impedance are computed and found to be in excellent agreement with the experimentally measured results. Simple but surprisingly accurate formulas for slot-fed circularly polarized microstrip antennas are derived and compared with those for probe-fed counterparts.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Utilizing evolutionary algorithms to achieve a low axial ratio of a circularly polarized microstrip antenna over a wide bandwidth and optimal impedance matching is the main aim of this study. A circularly polarized cross aperture coupled microstrip antenna using a 50Ω microstrip feed line is designed. A software simulation program (CST microwave studio) is used to design and compare the performance of the antenna in terms of return loss and axial ratio. Two distinct evolutionary algorithms; Particle Swarm Optimization (PSO) and Genetic Algorithm (GA) have been applied to optimize the fitness function to ensure optimal axial ratio and impedance matching. The optimal patch dimensions, the aperture length, and the microstrip feed line length are obtained from both methods and their performances are compared. Moreover, the antenna is fabricated and the return loss is measured using a network analyzer. A comparative analysis is carried out demonstrating a high agreement between measured and simulated return loss.