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The design of an aperture-coupled microstrip patch antenna whose radiation can be switched between circular polarisation (CP) and linear polarisation (LP) states is presented. For the proposed design, the CP and LP radiations are excited through the couplings of a ring slot and an open-ring slot in the ground plane, respectively. The effects of the key parameters of the proposed design on the CP and LP performances are investigated in details. A prototype that uses a pin diode to reconfigure the coupling slot is implemented and tested. From the obtained results, the prototype has a cross polarisation level of more than 25 dB when it is operated at the LP state and an axial ratio of less than 3 dB when it is operated at the CP state. Moreover, the two states share a 10 dB input impedance bandwidth. Consequently, the proposed reconfigurable microstrip antenna has the feature of polarisation diversity at a fixed frequency band. [ABSTRACT FROM AUTHOR]

The design of an equilateral triangular microstrip antenna embedded with dual V-shaped slots and two shorting walls is proposed and experimentally studied. By properly selecting suitable dimensions for this microstrip antenna, dual frequency operated at TM11 and TM21 modes, with frequency ratio ranging from 1.28 to 1.5 can be achieved with a single probe feed. The experimental procedures on achieving such operation with a maximum gain of around 11 dBi are presented and discussed. [ABSTRACT FROM AUTHOR]

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]

The design of a square-ring microstrip antenna with circular polarisation (CP) is presented. To compact the antenna size and overcome the high impedance problem, the CP antenna is excited by a coupling strip located inside the square-ring patch. Several prototypes of the squarering CP antennas with various substrate thickness (0.013–0.09l0) have been constructed and studied experimentally, and their coupling-strip designs and CP performance are described. [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 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 single-feed dual-frequency microstrip patch antenna that can produce dual circular polarisations (CP) is presented. The microstrip antenna has an annular-ring patch and is excited by an L-shaped microstrip line through the coupling of a ring slot in the ground plane. The occurrence of the dual CP is because the magnetic currents circulating along the ring slot at two specific frequencies have opposite flowing directions. Both simulated and measured results are provided to validate the CP performance of the proposed antenna. [ABSTRACT FROM AUTHOR]

A microstrip antenna with broadband circular polarisation (CP) is presented. The proposed microstrip antenna has a circular patch and is excited by a series microstrip-line-feed configuration through the coupling of a ring slot in the ground plane. The broadband operation is achieved by coupling two CP resonant elements, which are due to the circular patch and the ring slot, respectively. A typical prototype using foam material of thickness 5 mm as the antenna substrate is constructed. Measured results show the 3 dB-axial-ratio bandwidth centred at 2500 MHz is more than 10%. [ABSTRACT FROM AUTHOR]

The design of a wideband patch antenna with monopole-like conical radiation patterns is presented. The antenna has a square patch that is shorted to the ground plane through two shorting walls and is excited by a top-loaded coaxial feed centred below the square patch. Several prototypes with various antenna heights are implemented and measured. A prototype with impedance bandwidth of about 50% is achieved when its height is less than 0.09 free-space wavelengths. [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]

Presents the novel design of the circular polarization (CP) for an annular-ring antenna operated at its TM11 and TM12 modes. Indication that the CP radiations of the proposed design are achieved by placing an L-shaped strip connected to two orthogonal sides of the inner boundary of the annular patch; Observation that broadside radiation patterns with good CP characteristics can be obtained at the two operating resonant modes.

Proposes a single-feed triangular microstrip patch antenna that can be operated at two distinct resonant modes. Ability of the two resonant modes to radiate an omnidirectional dipole-like pattern with linear polarization and a broadside pattern with circular polarization, respectively; Study of several designs of the proposed antennas with different substrate thickness and patch sizes to achieve the required frequency ratio of the two operating frequency bands.

A design of generating tilted beam radiation from microstrip antennas is described in this paper. The antenna has a coplanar annular patch, and it is excited by a top-loaded probe through gap coupling. When the antenna is operated at the TM02 mode of the ring patch, its radiation pattern can be changed from a uniform conical beam to a tilted beam by moving the feed point from the antenna center. The direction and directivity of the tilted beam are related to the feed position and the offset distance, respectively. Experimental results indicate that the directivity of the tilted beam is 2 dB higher than that of the original uniform conical beam, and they have good agreements with simulated results carried out with HFSS. [ABSTRACT FROM AUTHOR]

The design of an aperture-coupled microstrip antenna with switchable polarisation and frequency agility is studied. Switching between two orthogonal linear polarisations (LPs) is realised by mounting two switching pin diodes on the antenna. To achieve multi-operating frequency (frequency agility) on one of the LPs, a voltage-controlled varactor diode is loaded between the top-loaded square patch and the ground plane. From the measured results, a good cross-polarisation level is observed when operated in both linear states at around 2 GHz. [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 (CP) microstrip antenna with polarisation and frequency diversities is presented. The antenna has a square radiating patch and is excited through the coupling of a cross-slot with unequal lengths. Two diodes are used to reconfigure the radiating patch, and by controlling the states of the diodes, the polarisation sense of the antenna can be switched between left-hand and right-hand circular polarisation. Moreover, the two CP modes are operated at different frequencies. An antenna prototype is implemented and the obtained results are shown. [ABSTRACT FROM AUTHOR]

A microstrip antenna with the functions of switchable pattern and polarisation is presented. The antenna is composed of a square-ring radiating patch and four shorting walls. The shorting walls are connected to each edge of the square-ring patch through one pin diode. By controlling the states of the pin diodes, the square-ring microstrip antenna can radiate two complementary patterns (conical and broadside); moreover, dual orthogonal linear polarisations are provided for the broadside radiation. These diversity functions are operated at the same frequency band. An antenna prototype has been implemented and the results obtained are given. [ABSTRACT FROM AUTHOR]