Ring slot antenna
The design of a microstrip-fed annular-ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3-dB axial ratio (AR) bandwidth that can cover the WiMAX GHz (– MHz, – MHz) and WLAN GHz (– MHz) bands, a novel technique of extending an inverted. The design of a switchable microstrip-fed half annular ring slot antenna for multi-frequency operation is proposed. By incorporating three switches along the meandered tuning stub that is loaded. An array antenna is disclosed wherein each one of the antenna elements includes at least two concentric slots formed in a conductive sheet. The conductive sheet is disposed on a dielectric support and a ground plane is found on the opposite surface of such support. The inner one of the slots enables the outer slot to radiate radio frequency energy having a wavelength greater than the.
US4208660A - Radio frequency ring-shaped slot antenna - Google Patents
When assembled, the array antenna 10 provides a compact flush-mountable array antenna adapted to operate at 1. Those switches are positioned in the slot places underneath the patch. The resonant frequency of the TM 11 mode could be expressed as  The inner one of the slots enables the outer slot to radiate radio frequency energy having a wavelength greater than the circumference of such outer slot. It also occupies less volume than reported antenna [1, 12].
A Frequency Reconfigurable Half Annular Ring Slot Antenna Design
The asymmetry introduced in the proposed design is a meandered-slot section and the proposed CP design can be applied to printed square and annular ring slot antennas.
Prototypes of the proposed design have been implemented. Experimental results show that good CP radiation performances are obtained and the 3 dB axial-ratio CP bandwidths obtained for the square and annular ring slot antennas are about 4.
The reader antenna is one of the most important component in an RFID system which is designed for circular polarization CP operation, because circularly polarized antennas can fairly communicate with linearly polarized antennas with random orientations and also avoid the polarization losses and mismatches caused by multipath effects.
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By incorporating three switches along the meandered tuning stub that is loaded on top of the half circular patch located within the circular slot, easy reconfigurability of four frequency bands over a frequency ratio of approximately 1. Furthermore, the proposed antenna structure does not require additional DC biasing circuit.
Simulation and measurement results have demonstrated that the four frequency bands can exhibit good impedance matching, stable radiation patterns and desirable gains. Several frequency-reconfigurable slot-based antennas appeared recently in the literature. Single-element antennas were presented in  —. In, microstrip-fed-based frequencyreconfigurable half annular ring slot antenna was presented. The frequency bands covered were 2. Single-element antennas were presented in—.
In  , microstrip-fed-based frequencyreconfigurable half annular ring slot antenna was presented. Such reconfigurable antennas are important for achieving optimum performance of wireless systems under various environmental conditions. Compared with frequencyswitched antennas which operate at some predefined separate frequency bands ,  , frequency-tunable antennas can achieve dynamic control of relatively narrow instantaneous bandwidths, thus allowing operation over a larger bandwidth.
Compact communication systems working in these standards required a compact size, low cost and multiband antenna. Meander technologies are the most investigated for the design of reconfigurable structures  , which allows small size designs, by increasing the electric length of the patch, and wide band operations. Several meander reconfigurable antenna designs were reported in the literature for wireless applications.
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