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The loading effects of the superstrate with various thickness on the circular polarisation (CP) performances of a cross-slot-coupled micro-strip antenna are first investigated. Then, for improving the shifted centre frequency, the bad impedance matching, and the increased axial ratio, which are due to the superstrate effects, the key dimensions of the loaded antenna are adjusted to regain or even enhance the original unloaded CP performances. From the obtained experimental results, it is found that the CP bandwidth of the loaded antenna can be increased when the thickness of the superstrate is properly selected. [ABSTRACT FROM AUTHOR]

A novel design of a printed ring-slot antenna with circular polarisation (CP) is first proposed. The CP radiation of the slot antenna is achieved by a series microstrip-line feed configuration. Using the single CP slot antenna as an array element, the 1 × 2 and 2 &times 2 slot arrays are constructed and measured. To obtain wider CP bandwidth, phase sequential rotation technique is applied to the feed network of these printed slot arrays. The experimental results show that the 2 × 2 slot array antenna is capable of 15% bandwidth for an axial ratio of less than 3 dB. [ABSTRACT FROM AUTHOR]

A design for dual-frequency microstrip antennas with conical radiation patterns is studied. The dual-frequency operation is achieved by exciting two different resonant modes of the square microstrip patch antenna with four symmetrical shorting walls. Then, a method to enhance the impedance bandwidths of the dual-frequency antenna is proposed, and the experimental results show bandwidths are increased by 19 and 31% at the lower and higher operating frequencies, respectively. Simulation analyses are also performed to support the measured results. [ABSTRACT FROM AUTHOR]

A stacked slot antenna is proposed and studied to improve the performance of a circularly-polarised (CP) annular-ring slot antenna that has the disadvantages of a narrow bandwidth, a lower gain and bidirectional radiation. The stacked antenna structure is composed of a circular wide slot, a parasitic patch and a metallic reflector, and its CP radiation is excited through the proximity coupling of an L-shaped microstrip line. A 4×4 array using the stacked slot antenna as an element is also developed and designed at X-band. Details of the antenna design and obtained results are presented. [ABSTRACT FROM AUTHOR]

A circularly-polarised microstrip antenna capable of switching polarisation sense is presented. The proposed microstrip antenna has a circular radiating patch and is excited by an open-loop microstrip line through the coupling of a ring slot in the ground plane. Two ends of the open-loop microstrip line can be taken for the input ports to excite right-hand and left-hand circular polarisations, respectively. A prototype using PIN diodes to electrically switch the input ports is implemented, and the measured results show the 3 dB axial ratio bandwidth of more than 10% can be obtained at the two polarisation senses. [ABSTRACT FROM AUTHOR]

A compact design of a single-feed circularly polarised (CP) microstrip antenna with relaxed manufacturing tolerances is presented. The CP operation of the microstrip antenna is achieved using a cross slot embedded on the radiating patch. By cutting an additional cross slot on the ground plane, not only the CP operating frequency can be decreased but also the slot-length ratio of the cross slot on the radiating patch can be considerably increased. In addition, the performance of the proposed design, such as CP bandwidth and peak gain, have no significant reduction. [ABSTRACT FROM AUTHOR]