Chi-Yuk Chiu

Reduction of Mutual Coupling Between Closely-Packed Antenna Elements

A simple ground plane structure that can reduce mutual coupling between closely-packed antenna elements is proposed and studied. The structure consists of a slitted pattern, without vias, etched onto a single ground plane and it is therefore low cost and straightforward to fabricate. It is found that isolations of more than -20 dB can be achieved between two parallel individual planar inverted-F antennas (PIFAs) sharing a common ground plane, with inter-antenna spacing (center to center) of 0.116 lambdao and ground plane size 0.331lambdao 2. At 2.31 GHz it is demonstrated that this translates into an edge to edge separation between antennas of just 10 mm. Similarly the structure can be applied to reduce mutual coupling between three or four radiating elements. In addition the mutual coupling between half wavelength patches and monopoles can also be reduced with the aid of the proposed ground plane structure. Results of parametric studies are also given in this paper. Both simulation and measurement results are used to confirm the suppression of mutual coupling between closely-packed antenna elements with our slitted ground plane.

Compact Three-Port Orthogonally Polarized MIMO Antennas

Two designs for three-port orthogonally polarized antennas using dipole antennas and half-slot antennas are proposed in this letter. Each of the antennas constitutes three mutually perpendicular radiating elements to achieve good isolation and low antenna signal correlation between ports. The antennas are fabricated on FR4 epoxy boards and experimental results are provided. Experimental results show that the antennas resonate at 2.55 GHz and have a mutual coupling of less than -18 dB between elements. In addition, experimental results for the diversity performance and the multiple-input-multiple-output (MIMO) channel capacity are also provided for these antennas and these show that the proposed antennas offer good diversity gain and the channel capacity can be increased by as much as three times by using these antennas.

Compact Four-Port Antenna Suitable for Portable MIMO Devices

In this letter, a compact four-port antenna structure with an area of 40 times 40 mm2 and constructed from inexpensive FR-4 printed circuit board is described. The antennas operate at 2.48 GHz, and in terms of wavelengths have a compact overall area of 0.33 lambdao times 0.33 lambdao and this would usually result in very strong mutual coupling between the four antenna ports. However, in our proposed structure, the mutual coupling between antenna elements is better than -10 dB. Although this is not low mutual coupling by some standards it is suitable for multiple-input-multiple-output (MIMO) communications in portable devices as verified by our experimental MIMO testbed capacity results. Furthermore measurements and characteristics of the antenna structures are provided.

Bandwidth enhancement technique for quarter-wave patch antennas

A novel technique that improves the performance of a conventional quarter-wave patch antenna is proposed. Two different geometries (U-slot and L-slit) are investigated experimentally. With the inclusion of a folded inner small patch, we achieve impedance bandwidths of 53% and 45% for the U-slot and L-slit, respectively, for a voltage standing wave ratio less than 2. Radiation patterns are stable across the whole operating frequency bands.

24-Port and 36-Port Antenna Cubes Suitable for MIMO Wireless Communications

We describe 24-port and 36-port antennas based on a cube structure. The antennas are formed by densely packing individual antennas onto a cube. The 24-port antenna cube has a volume of 0.72 lambdao 3 while the 36-port antenna has a volume of 1.13 lambdao 3. Even though the individual antennas are densely packed, most combinations of mutual couplings between ports exhibit better than -20 dB isolation. The basic 24-port cube antenna is formed by utilizing cross polarized quarter-wave slots at the cube edges. This provides polarization diversity on every edge of the cube, and both spatial and polarization diversities on the entire structure, leading to good isolation. Additionally 6 pairs of half-wave slot antennas are placed on each surface of the cube to provide 12 extra ports and therefore form our 36-port antenna. The cube antennas are made from FR-4 printed-circuit-boards (PCB), which is low-cost and allows ease of prototyping. The proposed cubes are investigated by simulation and measurement. One potential application for the cube antennas is in multiple-input-multiple-output (MIMO) wireless communication systems. The expected channel capacity of the 36-port cube with both mutual coupling and channel correlation considered is between 131-159 b/s/Hz at an SNR of 20 dB per receiver branch (compared to an ideal channel capacity of 197 b/s/Hz) when MIMO channels in a rich scattering environment with sufficient multipath are available.

A Tunable Via-Patch Loaded PIFA With Size Reduction

A novel tunable planar inverted-F antenna (PIFA) is described. A via-patch is introduced under the main radiating element to create a capacitive coupling effect and lower the operating frequency. The antenna size is reduced by half when compared to the conventional PIFA. Incorporating with an L-shaped opening on the ground plane, the proposed via-patch loaded PIFA exhibits a 10-dB return-loss bandwidth of 8.91% for 2.4 GHz ISM band applications. In the proposed approach, the capacitive patch is connected to the ground through a via while a coaxial feed is directly connected to the radiating element. This is different from other capacitive-loading, size-reduction schemes in which the capacitive patch is connected to the coaxial feed, thus not able to provide frequency tuning. By simply replacing the via in our antenna with a screw and adjusting the height of the via-patch by turning the screw, a tuning range of 0.8 GHz from 2.5-3.3 GHz can be achieved. This makes the proposed PIFA a convenient tunable small antenna. Both simulation and measurement results are presented together with parametric studies on the via-patch and L-shaped opening ground plane

Study of a small wide-band patch antenna with double shorting walls

A small wide-band patch antenna with double shorting walls is presented. By employing two shorting walls and an additional aperture on the upper patch of a folded patch feed antenna, a 0.365/spl lambda//sub 0/ patch antenna with impedance bandwidth of more than 70% (VSWR/spl les/2) is achieved experimentally. Measured radiation patterns and gain across the frequency band are given.

Frequency-Reconfigurable Pixel Slot Antenna

A new frequency-reconfigurable antenna structure which we denote as a pixel slot antenna is proposed and studied in this communication. The antenna makes use of a canonical switched slot element that is concatenated together to form various radiating structures. The resonant path of the pixel slot antenna can be a conventional slot or a slot plus a loop, so higher degrees of freedom in generating various resonant frequencies is achieved. The maximum-to-minimum achievable resonance values of a demonstrated 4-switch single-pixel slot antenna are 3.30 GHz to 1.56 GHz in which the feed mechanism remains unchanged. Other frequency tuning ranges are also achievable by changing the switch allocation along the slot structure. We also provide a model for the RF MEMS switches which can improve the simulation accuracy of the reconfigurable antenna simulation results.

Small dual-band antenna with folded-patch technique

This letter presents a novel dual-band patch antenna developed by combining the folded-patch and U-slot techniques. The electrical length of the antenna is 0.147 wavelengths at the center frequency of the lower band. The lower band of the antenna ranges from 2.400 to 2.480 GHz, while the upper band covers both frequency bands from 5.150 to 5.350 GHz and 5.725 to 5.875 GHz with an average gain of 2 dBi. It is suitable for short-range wireless applications.

Design and Implementation of a Compact 6-Port Antenna

A pair of half-wavelength slot and narrow patch antennas stacked closely together to form a set of nearly colocated antennas for achieving polarization diversity is described. A reduced-size version is then proposed by utilizing a quarter-wavelength slot and planar inverted-F antenna (PIFA) pair, respectively. When three sets of these antennas are placed on each orthogonal axis, a compact 6-port antenna is constructed. Key characteristics of the antennas are found through electromagnetic simulation and physical measurements.