Half-width microstrip leaky-wave antennas (HW-MLWAs) are generally single band. Here, we present a new method to achieve dual-band operation from an HW-MLWA by periodically loading the antenna with U-shaped slots. These dual-band MLWAs are able to steer the beam in forward directions in one band and in backward directions in the other band. One of the antenna designs was prototyped and tested, and excellent agreement between the predicted and measured results were observed. The measured 10-dB return loss bandwidth of the first and second bands are $19.5 \% $ (5.24–6.37 GHz) and $13.2 \% $ (7.9–9.02 GHz), respectively. The antenna can steer the main beam from $30^\circ $ to $65^\circ $ in the first band and from $-46^\circ $ to $-10^\circ$ in the second band by sweeping the frequency from 5.25 to 6.25 GHz and 7.75 to 9 GHz, respectively. The measured peak gain of the antenna is 12.2 and 14.1 dBi in the first and second bands, respectively. Although the antenna parameters are optimized for dual-band operation, the radiation properties in another higher frequency band (third band) are also explored. In the third band, the antenna beam continuously scans from backward to forward direction as frequency increases. Moreover, this U-slot loaded single-layer half-width LWA is easy to fabricate.

Periodic U-Slot-Loaded Dual-Band Half-Width Microstrip Leaky-Wave Antennas for Forward and Backward Beam Scanning

In this article, an inductance-based decoupling scheme is proposed to reduce the mutual coupling between extremely closely spaced microstrip antennas. The original strong coupling can be effectively suppressed by simply inserting a lumped inductance in between. To offer a systemic design guideline for this decoupling strategy, a mode cancellation method, based on the synthesis of common mode (CM) and differential mode (DM), is proposed. The inserted inductance plays a role of tuning CM and DM impedances to a similar status, which has an equivalent decoupling effect according to the theory of microwave network. Alternatively, the lumped inductance could also be replaced by an inductive connecting strip for a concise topology. To validate the proposed decoupling concept, a prototype is simulated, fabricated, and measured. The experimental results show that the poor isolation of 5 dB is improved to better than 15.4 dB across the entire matched bandwidth of 2.394–2.530 GHz, with an extremely close edge-to-edge distance of $0.016~\lambda _{0}$ and center-to-center distance of $0.44~\lambda _{0}$ . Furthermore, the validation of extending to large-scale 1-D and 2-D arrays is also discussed. Featuring simple structure, compressed dimension, strong-coupling suppression, and good radiation performance, the proposed decoupling scheme possesses promising potential for antenna array applications.

Decoupling Between Extremely Closely Spaced Patch Antennas by Mode Cancellation Method

Wideband microstrip leaky-wave antennas (LWAs) that radiate two symmetrical side beams are described. The two beams are steered simultaneously by sweeping the operating frequency. To achieve this, the second higher order mode of the microstrip is excited. Two electric field nulls are created between the microstrip and the ground plane using via arrays to suppress lower order modes. To test the concept, one of the antenna designs was prototyped. The prototyped antenna is capable of steering two symmetrical beams within a range of 37° when frequency is swept between 6.92 and 8.75 GHz. The measured peak gain of the antenna is 12.7 dBi and the variation of gain from 6.92 to 8.75 GHz is 3.1 dB. The measured 10-dB return loss bandwidth is 23%, which is very large for a dual-beam microstrip LWA. Such a wide impedance bandwidth is essential to achieve beam scanning over a wide angular range by sweeping frequency. Another advantage is that this single-layer antenna is easy to fabricate.

Wideband Microstrip Leaky-Wave Antennas With Two Symmetrical Side Beams for Simultaneous Dual-Beam Scanning

A framework for optimization of wideband antennas including statistical reliability considerations is proposed. Using predetermined tolerances of the manufacturing process, the reliability analysis provides a failure probability of the considered antenna according to imposed specifications. In addition, a sensitivity analysis is conducted in order to quantify the relative weight of the antenna’s parameters on the variability of ${\vert S_{11}\vert }$ . On this basis, a reliability-aware definition of optimization parameters can be derived to minimize failure probability during fabrication. For demonstration, a particular type of antenna, namely the tapered half-mode substrate-integrated waveguide (HMSIW) leaky-wave antenna, is chosen for the reliability analysis and optimization. This antenna is optimized for operation in the band from 7 to 14 GHz (with specification ${\vert S_{11}\vert ) with a calculated failure probability of less than 1%. A fabrication of the designed prototype yields measurements showing a strict adherence to specifications, which exemplifies the relevance of the statistical analysis. The study can be generalized to any wideband antenna provided that a fast computation of cost function can be obtained.

Reliability-Aware Optimization of a Wideband Antenna

The detailed analysis, design, and optimization of a reconfigurable antenna based on a periodically stub-loaded half-mode substrate-integrated waveguide (HMSIW) cavity is presented in this paper. The analysis demonstrates an excellent prediction of the resonance frequency for the cavity with an error of less than 2% compared to numerical simulations performed over a wide range of parameters. The fast computation of the resonance frequency based on the analytical model gives deep insight into the antenna operation and allows an efficient optimization process. The reconfigurable antenna has been designed and optimized to cover the whole S-band (WR-284 waveguide band), i.e., 2.60–3.95 GHz, using three varactors with measured capacitance varying from 0.149 to 1.304 pF. Experimental results validate the concept across the whole tuning range, with a return loss and antenna gain greater than 15 and 2.1 dB, respectively at resonance.

Analysis and Design of a Reconfigurable Antenna Based on Half-Mode Substrate-Integrated Cavity

A new technique to implement fixed-frequency beam scanning using a half-width microstrip leaky-wave antenna (HW-MLWA) is presented The main beam direction is electronically controlled by changing the reactance between the one edge of a microstrip and the ground This is achieved through a set of patches periodically placed along the free radiating edge of the microstrip line, with the second edge of the microstrip line is grounded The patches can be connected to or isolated from the ground using PIN diodes thus facilitating a sub-nanosecond means of controlling the reactance The full-wave numerical simulations show the ability to control the main beam direction from 21° to 37° at 65 GHz within the first quadrant

Reconfigurable half-width microstrip leaky-wave antenna for fixed-frequency beam scanning

A leaky-wave antenna (LWA) on a substrate integrated waveguide (SIW) with continuous beam-scanning capabilities and improved gain is presented. A one-dimensional (1-D) longitudinal slot-array SIW antenna is used as the main radiating element. It was found that due to the capacitive effect of the slot, an open-stopband (OSB) restrains broadside radiation. Although a reduction of the bandgap can be achieved when the slots are closer to the center, the radiation performance of the LWA degrades around the broadside as the beam scans from backward to forward. Initially, the capacitive effect was mitigated, and hence, the OSB was suppressed by introducing a group of three shorting vias at the opposite side of each longitudinal slot. However, the gain of the antenna drops significantly around its upper scan angles in the forward directions. To improve the radiation performance further, the center via of each of the via group is replaced by a transverse slot. The new unit cell is then used to design a modified 1-D slot-array LWA, and the antenna is analyzed, prototyped, and measured to verify the concept.

Continuous Backward-to-Forward Scanning 1-D Slot-Array Leaky-Wave Antenna With Improved Gain

A multiband antenna, having a reflector, and a first array of first radiating elements having a first operational frequency band, the first radiating elements being a plurality of dipole arms, each dipole arm including a plurality of conductive segments coupled in series by a plurality of inductive elements; and a second array of second radiating elements having a second operational frequency band, wherein the plurality of conductive segments each have a length less than one-half wavelength at the second operational frequency band.

Cloaked low band elements for multiband radiating arrays

An electronically controlled half-width microstrip leaky-wave antenna (HW-MLWA) that can scan the main beam at a fixed frequency is presented. A technique is described to change the upper and lower limits of the beam direction without changing the scanning range itself. By varying the reactance profile at the free edge, the main beam of the proposed antenna can scan a range of 23° in discrete steps. There are 30 stubs positioned at the free edge of the antenna that gives the freedom to the designer to change the upper and lower scanning limits of the antenna without changing the scanning range itself.

Controlling the beam scanning limits of a microstrip leaky-wave antenna

Modern wireless networks such as 5G require multiband MIMO-supported Base Station Antennas. As a result, antennas have multiple ports to support a range of frequency bands leading to multiple arrays within one compact antenna enclosure. The close proximity of the arrays results in significant scattering degrading pattern performance of each band while coupling between arrays leads to degradation in return loss and port-to-port isolations. Different design techniques are adopted in the literature to overcome such challenges. This paper provides a classification of challenges in BSA design and a cohesive list of design techniques adopted in the literature to overcome such challenges.

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D. N. P. Thalakotuna

Papers

Reconfigurable half-width microstrip leaky-wave antenna for fixed-frequency beam scanning

Continuous Backward-to-Forward Scanning 1-D Slot-Array Leaky-Wave Antenna With Improved Gain

Cloaked low band elements for multiband radiating arrays

Controlling the beam scanning limits of a microstrip leaky-wave antenna

A Review on 5G Sub-6 GHz Base Station Antenna Design Challenges