For many leaky-wave antennas (LWAs), it is challenging to realize beam scanning through broadside. A problem is the presence of an open stopband (OSB), which restricts radiation in the broadside direction. In this paper, a novel substrate integrated waveguide (SIW)-based LWA is described to overcome the OSB problem and provide beam scanning continuously from the backward to the forward direction from a conventional periodic LWA. It is demonstrated that the $n =-1$ spatial harmonic can be excited efficiently from an SIW LWA and enables broadside radiation. However, it was found in our initial design that when the beam scans through the broadside, the cross-polarization level increases significantly compared to the beam close to the backfire direction. A technique is developed to reduce the cross-polarization level. As a result, a new antenna configuration is created. The antenna design has been realized and measured to validate the concept. The measured beam scanning range of the prototype is from −74° to +45° (119° of beam scanning) when the frequency sweeps from 7.625 to 11 GHz, and the measured cross-polarization level is 20.8 dB low at the main beam direction for the broadside beam.

Substrate Integrated Waveguide-Based Periodic Backward-to-Forward Scanning Leaky-Wave Antenna With Low Cross-Polarization

In this letter, a substrate integrated waveguide-based leaky-wave antenna with wide beam scanning is presented to mitigate open stopband (OSB). The unit cell of this proposed antenna consists of a longitudinal slot and a post placed oppositely offset from the center line. By introducing inductive post along with the longitudinal slot in each unit cell, the OSB is suppressed resulting in continuous beam scanning. An equivalent circuit of the proposed unit cell is developed to explain the impedance matching technique used here to suppress OSB. Dispersion diagram is also used to analyze this seamless scanning. This antenna can scan from –49° to +69° through broadside because of wide impedance matching. Finally, the antenna is prototyped and experimentally verified. Measured results are in accord with simulated results. This antenna provides maximum gain of 14.2 dBi and low level of cross polarization.

SIW-Based Leaky-Wave Antenna Supporting Wide Range of Beam Scanning Through Broadside

A novel circularly polarized (CP) complementary source antenna with endfire radiation is proposed in Ka-band. With the existence of two antipodal notches etched at the edges of the two broad walls of an open-ended substrate-integrated waveguide, two orthogonal electric field components radiated from the equivalent magnetic current, and the electric currents separately can be excited simultaneously. The magnitude and phase differences between the two filed components can be controlled effectively by properly tuning the dimensions of the notches. The operating mechanism and the design procedure of the antenna are analyzed in detail. Wide −10 dB impedance and 3 dB axial ratio bandwidths of 64% and 51%, a gain varying from 3.1 to 6.4 dBic, and the symmetrical radiation pattern are obtained. In order to further increase the gain and front-to-back ratio (FTBR) of the antenna, a dielectric rod structure is then integrated with the antenna. An overlapped operating bandwidth of 41%, an improved gain up to 12 dBic and the stable radiation pattern with an FTBR close to 20 dB are verified by a fabricated prototype. The antenna presented in this paper provides a new mean to design the wideband endfire CP antenna with a simple configuration, which would be attractive for future millimeter-wave wireless systems.

Millimeter-Wave Wideband Circularly Polarized Planar Complementary Source Antenna With Endfire Radiation

In this paper, we propose and develop a leaky-wave antenna (LWA) by periodically loading shunt radiation element pairs along a host transmission line (TL). Each pair of radiation unit consists of one capacitive element and one inductive element, which are susceptance-complementary with each other. The complementary radiation element loading leads to an effective open-stopband (OSB) suppression, thereby facilitating a continuous leaky-wave beam scanning from backward, through broadside, to forward. Compared with the previously studied OSB-suppressed LWAs containing only one type of susceptive radiation elements, the proposed LWA features two unique properties: constant radiation efficiency over the operation band, and unit cell period only related to the host TL regardless of parameter values of the radiation elements. The aperture synthesis of the proposed LWA is hence straightforward as the radiation elements can be designed to be equally spaced. Experimental prototypes are designed and fabricated based on microstrip line structure as a proof of concept. Desired measured results agree well with the theoretical predictions.

Periodic Leaky-Wave Antenna Based on Complementary Pair of Radiation Elements

A simple single-layer reconfigurable leaky-wave antenna (LWA) is presented that has polarization agility and beam-scanning functionality. This LWA system realizes a scanned beam that can be switched between all of its linear polarization (LP) and circular polarization (CP) states using only one dc biasing source. A slot-loaded substrate-integrated waveguide (SIW)-based LWA is first explored to attain CP performance with continuous beam scanning through broadside. This CP LWA realizes a measured CP performance with a 3 dB gain variance within 2.75–3.35 GHz for scan angles ranging from −28.6° to +31.5°. A row of shorted stubs is then incorporated into the CP LWA to obtain similar LP performance. Finally, by introducing p-i-n diodes into this LP LWA configuration to facilitate reconfigurable connections between the main patch and the shorted stubs, the radiated fields can be switched between all of its CP and LP states. The measured results of all three antennas confirm their simulated performance. It is demonstrated that the main beam of the polarization-reconfigurable LWA can be scanned from −31.5° to +17.1° with gain variations between 9.5 and 12.8 dBic in its CP state and from −34.3° to +20° with them between 7.8 and 11.7 dBi in its LP state.

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Polarization-Reconfigurable Leaky-Wave Antenna With Continuous Beam Scanning Through Broadside

In this communication, a dielectric image line (DIL)-based leaky-wave antenna is proposed with planar feeding. The dominant mode of DIL is perturbed by making holes periodically in the DIL and fast-wave space harmonics are generated. The proposed antenna is designed for Ku-band (12–18 GHz) and its impedance bandwidth in the fast-wave region is 36% (11.8–17 GHz). The scan range of the proposed antenna in the working band is 90° (−65° to 25°) and the gain is varying from 10 to 16 dBi in the fast-wave region. The proposed antenna can be directly scaled to other frequency bands by taking into account the corresponding dispersion characteristic in respective frequency bands. This scaling property is demonstrated in $V$ -band. A prototype is fabricated and measured in Ku-band, which fairly agrees with simulated results.

Dielectric Image Line-Based Leaky-Wave Antenna for Wide Range of Beam Scanning Through Broadside

Leaky wave antenna for wide range of beam scanning through broadside in dielectric image line environment

In this letter, a linearly tapered dielectric waveguide antenna with planar substrate integrated waveguide (SIW) feeding is presented for Ku-band (12–18 GHz) application. To make the feeding network planar, the SIW and central part of antenna are fabricated on a single substrate. Two metal strips are mounted on each top and bottom side of the central part of the antenna element for matching purpose. The antenna is designed and optimized using Ansoft HFSS. The optimized prototype is fabricated and measured. An endfire radiation pattern is achieved with low sidelobe (around 12 dB) and cross-polarization (around 20 dB) level in both E- and H-planes. The measured impedance bandwidth and maximum gain are 33.3% (11.5–16.1 GHz) and 12.4 dBi, respectively.

Planar Excitation of Dielectric Waveguide Antenna for Broadband and High-Gain Application

In this paper, a novel transition from co-axial probe-to-substrate integrated waveguide (SIW) and from SIW-to-dielectric image line (DIL) is proposed in Ku-band (12–18 GHz). The proposed transition is designed on a single substrate and thus eliminates complex multi-layer fabrication process for implementation of dielectric image line two port network. The proposed design is simulated on Ansoft HFSS and exhibits wide bandwidth performance. For probe-to-SIW back-to-back transition, the relative bandwidth (−20dB) is 38.5% and for back-to-back transition from probe-to-SIW and from SIW-to-DIL, the relative bandwidth (−15dB) is 24.5%. The insertion loss is better than 3.2 dB throughout the operating bandwidth. Detailed studies on dimensions of the matching network is also discussed. The results are also verified by using CST Microwave Studio.

Efficient probe excitation of dielectric image line using substrate integrated waveguide based matching network

In this letter, a broadband planar substrate truncated tapered microstrip line-to-dielectric image line transition on a single substrate is proposed The design uses substrate truncated microstrip line which helps to minimize the losses due to the surface wave generation on thick microstrip line Generalized empirical equations are proposed for the transition design and validated for different dielectric constants in millimeter-wave frequency band Full-wave simulations are carried out using high frequency structural simulator A back-to-back transition prototype of Ku-band is fabricated and measured The measured return loss for 80-mm-long structure is better than 10 dB and the insertion loss is better than 25 dB in entire Ku-band (40% impedance bandwidth)

Chandra Shekhar Prasad

Papers

Dielectric Image Line-Based Leaky-Wave Antenna for Wide Range of Beam Scanning Through Broadside

Leaky wave antenna for wide range of beam scanning through broadside in dielectric image line environment

Planar Excitation of Dielectric Waveguide Antenna for Broadband and High-Gain Application

Efficient probe excitation of dielectric image line using substrate integrated waveguide based matching network

Broadband Planar Transition to Dielectric Image Line by Substrate Truncated Microstrip Line for Millimeter-Wave Circuit Integration