Debabrata K. Karmokar

An Array of Half-Width Microstrip Leaky-Wave Antennas Radiating on Boresight

An array of four uniform half-width microstrip leaky-wave antennas (MLWAs) was designed and tested to obtain maximum radiation in the boresight direction. To achieve this, uniform MLWAs are placed at 90 ° and fed by a single probe at the center. Four beams from four individual branches combine to form the resultant directive beam. The measured matched bandwidth of the array is 300 MHz (3.8-4.1 GHz). Its beam toward boresight occurs over a relatively wide 6.4% (3.8-4.05 GHz) band. The peak measured boresight gain of the array is 10.1 dBi, and its variation within the 250-MHz boresight radiation band is only 1.7 dB.

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

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° to 65° in the first band and from -46° to -10° 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.

Fixed-Frequency Beam Steering of Microstrip Leaky-Wave Antennas Using Binary Switches

This paper presents a novel, easy-to-fabricate and operate, single-layer leaky-wave antenna (LWA) that is capable of digitally steering its beam at fixed frequency using only two values of bias voltages, with very small gain variation and good impedance matching while scanning. Steering the beam of LWAs in steps at a fixed frequency, using binary switches, is investigated, and a new half-width microstrip LWA (HW-MLWA) is presented. The basic building block of the antenna is a reconfigurable unit cell, switchable between two states. A macrocell is created by combining several reconfigurable unit cells, and the periodic LWA is formed by cascading identical macrocells. A prototype HW-MLWA was designed, fabricated, and tested to validate the concept. To achieve fixed-frequency beam scanning, a gap capacitor in each unit cell is independently connected or disconnected using a binary switch. By changing the macrocell states, the reactance profile at the free edge of the microstrip and hence the main beam direction is changed. The prototyped antenna can scan the main beam between 31° and 60° at 6 GHz. The measured peak gain of the antenna is 12.9 dBi at 6 GHz and gain variation is only 1.2 dB.

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

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.

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

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.

Numerical analysis of impedance matched Inverted-L antennas for Wi-Fi operations

This paper presents the numerical simulations of Inverted-L and stair inverted-L antennas capable of generating high gain with less than 1.5 dBi gain variation within the −10 dB return loss bandwidth for 5.5 GHz wireless-fidelity (Wi-Fi) operation with and without resistor-inductor-capacitor (RLC) impedance matching network. Moreover, the proposed antennas can provide bandwidth of 510 and 120 MHz respectively, making it easily cover the required bandwidths for Wi-Fi operation in the 5.5 GHz band. In application of matching network, the input impedance of the antennas well matched to the feeding cable, also improvement in return loss and voltage standing wave ratio (VSWR) is achieved.

Numerical and Experimental Analysis of Impedance Matched Inverted-L and Stair Inverted-L Antenna for 5 GHz WLAN Operation

This paper presents impedance matched high gain inverted-L antenna (ILA) and stair ILA for 5 GHz wireless local area network (WLAN) by means of numerical and experimental analysis. Numerical simulation is carried out using method of moments in Numerical Electromagnetic Code (NEC-2) and agilent vector network analyzer, watts antenna trainer, and microwave engineering trainer are used for the measurement. The experimental results show that ILA and stair ILA has 10-dB return loss bandwidth of 650 MHz (5170 - 5820 MHz) and 360 MHz (5320 - 5680 MHz) respectively covering the unlicensed national information infrastructure (U-NII) mid frequency bands for 5 GHz WLAN operation. Omnidirectional radiation patterns are achieved for both antennas in XY plane and the antennas have peak gain of 6.65 and 10.987 dBi respectively at center frequency (5.5 GHz) of antenna operating bandwidth. Moreover, the antennas have radiation efficiency of greater than 84% and 91% respectively within the return loss bandwidth.

Four-branch microstrip leaky-wave antenna array for radiation towards broadside

A half-width microstrip leaky-wave antenna (HW-MLWA) array for radiation towards broadside is presented. One of the main challenges of leaky-wave antennas is to radiate towards broadside. This can be achieved by a half-width MLWA array. Four uniform HW-MLWAs, terminated by 50O SMA coaxial loads, are used in the array. The full-wave numerical simulations show the ability of the proposed HW-MLWA array to radiate effectively towards broadside in a 200 MHz band around 4 GHz.

Fixed-frequency leaky-wave antenna for simultaneous forward and backward scanning

A half-width microstrip leaky-wave antenna (HW-MLWA) is presented for simultaneous beam scanning in forward and backward directions at a fixed frequency. The directions of two main beams are controlled by changing the admittance between the radiating edge of the microstrip line and the ground plane. This is achieved by using gap capacitors at the radiating edge of the microstrip line and controlling their connection to the ground plane using digital switches. Two main beams of the proposed antenna can be steered from broadside (0°) to 33° in both forward and backward directions simultaneously at 6.25 GHz.

Low-Profile Impedance Matched Wideband Double Inverted-F Antenna for WiMAX/Wi-Fi Operations in a Laptop Computer

In this paper a wire type low-profile impedance matched wideband double inverted-F (DIFA) antenna for WiMAX/Wi-Fi operations in a laptop computer is presented by means of numerical simulations. The antenna has a compact size of 9×20 mm2 and provides a wider bandwidth of 2.5 GHz (5050~7550 MHz) which fully covers the 5.5 GHz operating band. Moreover it has very high peak gain of 7.0 dBi with less than 1.5 dBi gain variation within the 5.5 GHz operating band. In application of matching network, the input impedance of the antenna well matched to the antenna feeding, also improvement in return loss and voltage standing wave ratio (VSWR) is achieved. In addition the antenna has good return loss and radiation characteristics.