Conformal four-beam antenna arrays with reduced sidelobes

Investigations on sidelobe reduction in multibeam conformal antenna arrays are presented. The recently presented concept of sidelobe reduction in planar multibeam antenna arrays in conjunction with the phase compensation technique has been applied for the design of reduced sidelobe multibeam conformal antenna arrays. Six- and eight-element antenna arrays fed by modified Butler matrices have been investigated and minimum radii have been found for which the sidelobe level is comparable to the respective planar multibeam arrays. A novel fully integrated six-element four-beam antenna array has been successfully designed in which sidelobes equal -14 dB for all four beams have been achieved.     

Aperture coupled to stripline antenna element for integrated antenna arrays

A new stripline-fed aperture coupled antenna element is proposed. An additional slot in a ground plane allows achievement of efficient electromagnetic coupling with the radiating element and good return loss of the antenna fed by a stripline. The described radiating elements can be easily integrated with a feeding network designed in the most commonly used stripline technique when a large antenna array is to be developed.     

Design of Compensated Coupled-Stripline 3-dB Directional Couplers, Phase Shifters, and Magic-T's—Part I: Single-Section Coupled-Line Circuits

The problem of discontinuities in coupled-stripline 3-dB directional couplers, phase shifters, and magic-T's, regarding the connections of coupled and terminating signal lines, has been comprehensively investigated for the first time. The proposed equivalent circuit of these discontinuities, of which parameters can be computed in a process of fitting curves of the circuit and electromagnetic analyses, has been used for accurate modeling of coupled-stripline circuits. It has been shown that parasitic reactances, which result from connections of signal and coupled lines, severely deteriorate the return losses and the isolation of such circuits, and that these discontinuity effects can be substantially reduced by connecting compensating shunt capacitances to both coupled and signal lines. Results of measurements carried out for various designed and manufactured coupled-line circuits are most promising and prove the efficiency of the proposed compensation technique. This paper describes the technique of capacitive compensation of discontinuity effects in single-section coupled-line circuits     

Broadband low-cost planar sector antenna element for WLAN applications

A novel planar antenna element for applications in sector antennas is proposed. The antenna element consists of three patches coupled both electromagnetically and through the feeding network to ensure 90deg beamwidth in a wide frequency range. A suspended microstrip technique has been used to ensure simultaneously low production costs and low losses within the feeding network. The designed antenna element operates within a frequency range of 5.1-5.9 GHz.     

Microstrip antenna array with series-fed `through-element? coupled patches

A new microstrip antenna array with series-fed patches is proposed. To reduce the length of feeding lines the `through-element' feeding technique has been developed. A microstrip patch in which the input feeding line is directly connected and the output line is coupled to a patch is investigated. By adjusting the length of the coupling region an appropriate coupling level is achieved. A 4times1 antenna array operating within the 24 GHz frequency band for radar sensor applications is designed using the proposed feeding technique     

Integrated four-beam dual-band antenna array fed by broadband Butler matrix

A four-beam dual-band antenna array fed by a single 4times4 Butler matrix is presented, for the first time. A broadband Butler matrix designed in a stripline technique has been used as a basic element of a feeding network. To separate signals frequency diplexers have been designed. All designed elements of the feeding network have been integrated together with two antenna rows operating in two separate frequency bands     

Reduced sidelobe four-beam antenna array fed by modified Butler matrix

A novel four-beam antenna array fed by a modified 4/spl times/8 Butler matrix is proposed. Four 180/spl deg/ directional couplers in conjunction with a 4/spl times/4 Butler matrix are applied to provide a tapered excitation of a linear eight-element switched-beam antenna array. Sidelobes as low as -20 dB for all four beams have been both theoretically and experimentally achieved. A proposed technique of antenna element rotation simplifies the design of a feeding network.     

Bandwidth improvement of rat‐race couplers having left‐handed transmission‐line sections

A novel broadband rat‐race coupler has been investigated. The coupler utilizes an artificial left‐handed transmission line section for broadband phase response realization. Moreover, a narrowband model of left‐handed section has been shown to prove the couplers equivalent circuit at the center frequency. To broaden the operational bandwidth multisection quarter‐wave transformers have been proposed. The exemplary rat‐race coupler with two‐section impedance transformers has been designed and manufactured. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:341–347, 2014.     

Broadband 4 $times$ 4 Butler Matrices as a Connection of Symmetrical Multisection Coupled-Line 3-dB Directional Couplers and Phase Correction Networks

An innovative approach for realization of broadband 4 times 4 Butler matrices, in which broadband symmetrical multisection 3-dB/90deg directional couplers are used as basic elements, has been presented. A new technique for realization of center crossover together with 45deg phase shifters is proposed where phase correction networks, consisting of a number of coupled-line sections, are applied. The use of the proposed phase correction networks allows to achieve equal-ripple 45deg differential phase characteristics in a wide frequency range. Numerical results for the design of broadband 4 times 4 Butler matrices consisting of multisection symmetrical 3-dB/90deg directional couplers having three, five, seven, and nine coupled-line sections in conjunction with phase correction networks having an appropriate number of coupled-line sections are given in a tabular form. A method of performance improvement for broadband Butler matrices by the combinatory use of directional couplers consisting of different number of coupled-line sections is also proposed. To verify the presented analysis a broadband 4 times 4 Butler matrix consisting of six 3-dB/90deg three-section symmetrical coupled-line directional couplers and two single-section coupled-line phase correction networks has been designed, manufactured, and measured. Results of measurements of the designed Butler matrix fully confirm the validity of the proposed technique of broadband 4 times 4 Butler matrix realization.     

Design of low‐loss directional couplers with compensated coupled‐line sections in suspended microstrip technique

Design of coupled line 3dB directional couplers realized in suspended microstrip technique has been presented. The main goal was to minimize the insertion losses of the coupler, what has been achieved by a proper choice of the realization technique. As the chosen coupled line geometry is asymmetric to achieve good electrical performance of the resulting coupler, capacitive compensation technique has been utilized to equalize capacitive and inductive coupling coefficients. Furthermore, a distributed‐element approach has been investigated for realization of compensation capacitances, due to their physical size resulting from the dielectric structure. The proposed coupler has been designed in two versions, having center frequencies equal to 0.89 and 1.1 GHz, manufactured and measured. The measurement results show good agreement with electromagnetic analyses and prove the correctness and usefulness of the presented design method. The manufactured couplers exhibit insertion losses as low as 0.08 dB at the center frequency.