Abstract

Radial line slot array (RLSA) antenna was initially developed for satellite antenna receivers at a frequency of Ku-band. The success of this development inspired researchers to continue the study to other bands and other applications, such as Wi-Fi at 5.8 GHz. Wi-Fi applications need small antennas that lead to the diminution of RLSA antennas. Small-RLSA antennas experienced high reflection due to the small number of slots. One of the techniques that effectively eliminates the reflection was developed and named as extreme beamsquint technique. Several researches have successfully developed small-RLSA antennas by implementing this technique for Wi-Fi applications. Furthermore, for the future, it is possible to widen the researches to other frequencies and other features of RLSA antennas such as multibeam, multiband, and diminution by cutting off RLSA antennas.

Keywords: RLSA antennas, extreme beamsquint, small RLSA, RLSA for Wi-Fi, future RLSA antennas

### 1. Introduction

Radial line slot array (RLSA) antennas are a type of cavity or waveguide antennas. These antennas were firstly developed for satellite receivers as an option besides parabolic antennas. Unlike parabolic antennas, RLSA antennas have an advantage of having feeders at the back of the antenna, so that the feeders do not block out incoming signals. The other advantage is their flat shape so that they are more aesthetic compared to parabolic antennas. Nowadays, RLSA antennas are developed for different frequency applications such as Wi-Fi, 5th G, etc.

This chapter discusses briefly all about radial line slot array (RLSA) antennas, especially for the linearly polarized (LP)-RLSA antennas. Firstly, in Section 2, the review of RLSA antennas including the development of RLSA antennas, their applications, their development obstacles and the developed technique to overcome the obstacles are reviewed. Secondly, in Section 3, the theory of RLSA antennas is explained which includes how the antenna works and several equations to calculate antenna parameters. Thirdly, in Section 4, the mechanism of reflections in RLSA antennas, which is due to slot reflections and due to remaining power in antenna perimeter, is discussed. Fourthly, in Section 5, the theory of extreme beamsquint technique is also explained in detail. Lastly, in Section 6, the idea of future research in topic of RLSA antennas is briefly explained, including the idea of cutting off RLSA antennas to smaller size, multibeam RLSA antennas, utilizing background as

radiating element and multiband RLSA antennas. It is hoped that the ideas can inspire researches for the next development of RLSA antennas.

et al. used a technique for matching slot pair in order to reduce the remaining power at the antenna perimeter of small-aperture RLSA, so that this technique can minimize the reflection coefficient [21, 22]. Akiyama et al. also used the same technique for matching slot pair [23, 24]. However, the technique for matching slot pair is only used to radiate the remaining power at the antenna perimeter and does not contribute to the antenna gain. Reference [25] introduced the use of long slots in order to increase the ability of slots to radiate power, so that it can reduce the remaining power at the perimeter of small-aperture RLSA antennas, thus reducing the reflection coefficient. However, although this method can reduce the reflection coefficient, this method also can decrease the antenna gain. This is because that

In 2002, Malaysian and Australian researchers started to investigate the application of RLSA antennas for wireless LANs. Tharek and Ayu successfully fabricated a low-profile RLSA antenna at a frequency of 5.5 GHz with a broad radiation pattern of 60° used for indoor wireless LANs [26]. Bialkowski and Zagriatski investigated the design of RLSA antennas for wireless LANs and successfully fabricated a dualband 2.4/5.2 GHz antenna [27, 28]. Furthermore, Imran et al. reported the design and test of RLSA antennas for outdoor point-to-point applications at the frequency of 5.8 GHz [29–31]. However, this design utilized a beamsquint technique that is similar with the technique used to design RLSA antennas for satellite applications. Hence, the diameter of this antenna is still considered large with a diameter of 650 mm, so that it is not applicable for small Wi-Fi devices. Islam reported the utilization of low-cost FR4 materials to fabricate RLSA antennas at the frequency of 5.8 GHz for wireless LANs. This invention is quite innovative since FR4 materials are a low-cost material and easy to be fabricated [32, 33]. However, there are some drawbacks in designing this antenna, such as a design of overlap slots, a loss cavity due to the use of several FR4 boards and the use of material loss of FR4. These all

Purnamirza et al., in 2012, introduced a technique called extreme beamsquint technique in order to overcome the problem of high reflection in small-RLSA antennas [34]. This technique uses the beamsquint values higher than 60°. The theory of how the high values of beamsquint can significantly minimize the reflection coefficient is explained. Purnamirza also developed RLSA antennas that mimic the specification of other types of antenna that is available in markets [35–38].

This section discusses the theory of RLSA antennas including the structure, the theory of how RLSA antennas work as well as several formulas to design RLSA

Figure 1 shows the illustration of the structure of a RLSA antenna. The figure shows the structure of RLSA antennas consisting of a radiating element, a cavity, a background and a feeder. The radiating element usually is a circular plate made of metals, such as aluminium, copper or brass. The radiating element consists of many slot pairs. One slot pair acts as one antenna element so that all the slot pairs form an array antenna. The background is a metal plate just like the radiating element, but the background does not have slots. The cavity is a dielectric material that has the form of a tube. Together with the radiating element and the background, the cavity operates as a circular waveguide that guides the signal from the feeder to propagate

the long slots cannot radiate a focus power.

Radial Line Slot Array (RLSA) Antennas DOI: http://dx.doi.org/10.5772/intechopen.87164

lead to low gain (only 8 dB) and low bandwidth (75 MGhz).

3. Basic theory of RLSA antennas

3.1 Structure of RLSA antennas

antennas.

187
