D. C. Nascimento

Design of Low-Cost Probe-Fed Microstrip Antennas

The concept of microstrip radiators, introduced by Deschamps in 1953, remained dormant until the 1970s when low-profile antennas were required for an emerging generation of missiles (James & Hall, 1989; Garg et al., 2001; Volakis, 2007). Since then, but mainly over the last three decades, the international antenna community has devoted much effort to theoretical and experimental research on this kind of radiator (Lee & Chen, 1997). Currently, low-loss RF laminates are used in their fabrication and many of their inherent limitations have been overcome (Garg et al., 2001). On the other hand, low-cost solutions are in demand now that both market and technology are ready for mass production (Gardelli et al., 2004). Recently, the design of single-fed circularly-polarized (CP) microstrip antennas manufactured with FR4 substrate was reported (Niroojazi & Azarmanesh, 2004). Unfortunately, the use of low-cost FR4 as the substrate introduces some additional complexity on the antenna design. This is due to the inaccuracy of the FR4 relative permittivity and its high loss tangent (around 0.02). Variations in the FR4 electrical permittivity can shift the operating frequency and the high loss tangent dramatically affects the antenna axial ratio and gain, resulting in poor radiation efficiency. To increase the efficiency, microstrip antenna on moderately thick substrate must be designed. However, the technique used to compensate for the probe inductance, when the patch is fed by a coaxial probe (a known practical way to feed microstrip antennas), still relies on the designer’s expertise. For instance, a series capacitor, which may be constructed in several ways, has been utilized to neutralize this inductance (Hall, 1987; Alexander, 1989; Dahele et al., 1989; Vandenbosch & Van de Capelle, 1994; Nascimento et al., 2006), or the probe geometry has been modified (Haskins & Dahele, 1998; Teng et al., 2001; Chang & Wong, 2001; Tzeng et al., 2005). Unfortunately, due to their complexity, many such techniques are not suitable when the antennas are series-produced in an assembly line. To overcome some of the abovementioned issues, two efficient techniques for designing low-cost probe-fed microstrip antennas are proposed. Using only their intrinsic characteristics, linearlyand circularly-polarized microstrip antennas can now be designed without the need for any external matching network. Limitations of the proposed approach will also be discussed. The chapter is organized as follows: Section 2 covers the design of linearly-polarized microstrip antennas; results obtained with the new approach are compared with those using the standard design technique. Circularly-polarized antennas

Broadband L-Probe Fed Patch Antenna Combined With Passive Loop Elements

A new broadband L-probe fed rectangular patch antenna electromagnetically coupled to parasitic loop elements is presented. The proposed antenna is analyzed numerically using the moment-method-based electromagnetic simulation (IE3D) and high-frequency structure simulation (HFSS) softwares. The calculated results are in a good agreement with measured data. The impedance bandwidth of a prototype manufactured using a dielectric substrate with the relative permittivity epsir = 2.55 is about 15%

Design of Arrays of Linearly Polarized Patch Antennas on an FR4 Substrate: Design of a probe-fed electrically equivalent microstrip radiator.

A new strategy for designing probe-fed electrically equivalent microstrip radiators based on their electrical dimensions is discussed in this article. Radiators on a Flame Retardant 4 (FR4) substrate are synthesized for equivalent performance, aiming at lower H-plane cross polarization over the bandwidth and resistive input impedance at the operating frequency. The effect of mutual coupling is analyzed for two classical arrangements: side-by-side and collinear configurations. With the proposed strategy, a broadside collinear array of linearly polarized rectangular patches is designed to operate at the center frequency of the industrial, scientific, and medical (ISM) band (2.45 GHz) on a moderately thick FR4 substrate. The array is designed for low cross polarization in the H-plane and to comply with the specified directivity and side lobe level (SLL). Special attention to the beamforming circuit design leads to a radiation efficiency near 70%.

CYLINDRICAL: an effective CAD package for designing probe-fed rectangular microstrip antennas conformed onto cylindrical structures

This paper presents a computer-aided design tool named CYLINDRICAL. The algorithm utilizes the cavity model to design and analyze linearly and circularly polarized probe-fed rectangular microstrip antennas conformed onto cylindrical structures. A brief description of the program is given. CYLINDRICAL was used to design a circularly polarized antenna to operate in the L1 band of GPS. Validation was further done with the Ansoft HFSS package. It was shown that the antenna dimensions given by the design algorithm of CYLINDRICAL needed to be only slightly changed in order to obtain an optimized circularly polarized radiator according to the HFSS software. The tool is also very suitable for teaching graduate courses on microstrip antennas.

Low-cost Yagi-Uda monopole array

The Yagi-Uda antenna - invented in 1926 by H. Yagi and S. Uda at Tohoku University [1] in Japan, but first published in English only in 1928 [2] - has been extensively used as an end-fire antenna since then. Instead of the cylindrical antenna elements from the original work, radiators of small overall dimensions are presently achieved by means of other topologies, such as printed dipoles. Recently, a novel uniplanar quasi-Yagi design, combining both the compactness of resonant-type antennas and the broadband characteristics of traveling-wave radiators, was presented [3-4]. A current potential application of Yagi-Uda antennas is in GPRS (General Packet Radio Service), a packet-based data service over the existing GSM network. In general, the operation of mobile terminals requires antennas with omnidirectional radiation patterns; however, in case the mobile terminal is far removed from the base station, a directional antenna must be used [5]. In this paper, a new Yagi-Uda antenna topology, made up of printed monopoles, is proposed. The goal is achieving a compact, low cost, efficient radiator for GPRS applications.

Analysis and Design of Rectangular Microstrip Antennas for Educational Purposes

This paper discusses how the transmission-line model can be used in an introductory course on antennas for the analysis and design of thin rectangular microstrip antennas. As a result of adaptations made to the model, the antennas electrical parameters are shown to agree very well with experimental data and with simulations performed using commercial software. This new approach proves suitable for undergraduate courses.

New considerations in the design of low-cost probe-fed truncated corner microstrip antennas for GPS applications

Antennas produce circularly polarized waves when two orthogonal field components with equal amplitude but in phase quadrature are radiated. Probe-fed microstrip patches, classified as resonator-type antennas, are able of satisfying these requirements [1]. Nowadays, design procedure for truncated corner square patches and also for the almost square radiators is available in the literature, for instance in [2, 3]. Following this procedure, antennas with excellent axial-ratio (AR) in the operating frequency can be synthesized. Unfortunately, their input impedances are inherently inductive, mainly if thick substrates are used. A useful method of compensating for the inductance is to etch a capacitive gap on the patch, concentric (or not) with the feed probe [4, 5]. In this paper, instead of applying this standard method, a new approach is used to design truncated corner patches, printed on thick substrates. The purpose is to get the best axial-ratio and return loss at the same frequency.

Low-cost truncated corner microstrip antenna for GPS application

This paper reported a step-to-step procedure to design a low-cost FR4 GPS TCMA radiator. In order to reach the GPS specifications, in particular an acceptable value for the radiation efficiency, a thick substrate had to be used. As expected, this procedure improved the radiation efficiency but produced an input impedance that is more inductive, making difficult the antenna matching. To overcome this problem, new capacitive fractal gap geometry was designed. Experimental and simulated results indicate that it is possible to manufacture microstrip antennas with substrates having high loss tangent (like FR4) without severe degradation of their electrical performance, especially the radiation efficiency

Design of cavity-backed circularly-polarized cylindrical microstrip antennas

This paper reports the design of a cavity-backed probefed circularly-polarized cylindrical microstrip antenna. An efficient approach is used such that the best values of axial ratio and reflection coefficient magnitude occur both at the operating frequency.

Design of probe-fed circularly-polarized rectangular-patch thick microstrip antenna revisited

Circularly polarized (CP) microstrip antennas are largely employed in GPS receivers. Consequently, the international antenna community has devoted much effort to the theoretical and experimental research on this kind of radiator [1], overcoming many of its inherent limitations [2]. However, in spite of these efforts, the technique used to compensate for the probe inductance, when a coaxial probe is used to feed an electrically thick (a known practical way to increase bandwidth [1]-[3]) microstrip antenna, still relies on the expertise of the designer [4]-[5]. To overcome this limitation, an efficient technique for designing probe-fed CP rectangular-patch electrically thick microstrip antenna without any external network is proposed.