To reduce side lobe level of slotted array antennas using nonuniform waveguides

In this article, a method is presented to reduce the side lobe level of slotted waveguide array antennas while the gain to be constant. In this method, the H‐plane dimension of the waveguide is considered as the variable rather than constant. The nonuniformity of waveguide walls obviates the need for offset of slots and thereby reduces the side lobe level of radiation pattern. A slotted nonuniform waveguide is designed at frequency 10 GHz and then fabricated and tested. © 2015 The Authors International Journal of RF and Microwave Computer‐Aided Engineering Published by Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:42–46, 2016.     

A wideband dielectric resonator antenna array using air‐bridgeless coplanar waveguide power divider

In this communication a 2 × 2 dielectric resonator antenna (DRA) array is proposed with a wideband frequency response. An air bridgeless coplanar waveguide (CPW) power divider network is first time used to feed the 2 × 2 DRA array. Four rectangular DRAs are used as array element and exited in TE₁₁₁ mode by four slots at the end of the CPW lines in the feed network. The straight CPW phase delay line in feed network is further meandered resulting an enhanced radiation performance. The proposed DRA array exhibits a wideband response with an impedance bandwidth of 16% while maintaining a stable broadside radiation pattern with the gain range from 8 to 9.4 dBi. The proposed design is fabricated and measured, reaching good agreement with simulation results.     

Solving the cutoff wave numbers in partially filled rectangular waveguides by the Cauchy integral method

An efficient root‐finder method for the cutoff wave‐number resolution in a rectangular partially filled waveguide based upon the Cauchy integral method is presented. The great advantage that this method, valid for lossy dielectric and magnetic materials, has over others is that no initial seed is necessary for the localization of zeros, and also that no roots are lost inside the region under study, which guarantees that all modes are taken into account when the full‐wave problem is solved. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

A computer‐aided approach for designing dielectric‐covered planar array antennas consisting of longitudinal slots

A straightforward design approach is proposed to design arrays of longitudinal slots covered with dielectric slabs. The design of the arrays is accomplished via linking the slotted array antennas fed by the waveguides to a corresponding array of the loaded slots cut in an infinite ground plane and covered with dielectric slab. In this regard, the Elliott's design equations are modified for the dielectric‐covered longitudinal slotted array antennas. The introduced design equations are employed to find the final dimensions of the slot antennas while the updated mutual admittances of the corresponding array of the loaded slots are used iteratively in the design equations. Employing the introduced design equations, a two by three slotted array antenna was designed, simulated and tested. The proposed design approach is verified by the simulation and the measurement results.     

Nonuniform reflect‐array antennas

A center‐fed reflect‐array antenna with nonuniform substrate as a reflecting surface is proposed. To design and analyze this kind of antennas, a simple method based on an equivalent circuit model is introduced. Using this method a low cross‐polarization of about ?21 dB below the main beam peak and wide 3‐dB gain bandwidth of 19.5% are obtained at X‐band frequency. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

A low‐profile circularly polarized dielectric patch antenna and array

A square dielectric patch (DP) resonator fusing with the bottom substrate is studied for designing low‐profile circularly polarized (CP) antenna. Based on the theoretical investigation using the constructed analysis model, it can be found that the proposed DP resonator possesses a pair of degenerate dominate modes (TM₁₀₁ and TM₀₁₁), which can be split by introducing perturbations on the DP resonator and then used to design CP antenna fed by a microstrip line directly. To verify the proposed idea, a 2 × 2 array fed by a dual Marchand balun network is designed and implemented. Reasonable agreement between the measured and simulated results is observed. Experimental results show that a measured impedance bandwidth is 380 MHz (5.18‐5.56 GHz) for |S₁₁| < ?10 dB and the 3‐dB axial ratio bandwidth is 90 MHz (5.32‐5.41 GHz). The measured gain is up to 11.77 dBic with a cross polarization of about ?20 dB in the boresight direction.     

A coplanar‐waveguide‐fed planar integrated cavity backed slotted antenna array using TE33 mode

This short communication presents a substrate integrated waveguide planar cavity slotted antenna array. The proposed antenna array, excited in its TE₃₃ higher mode, incorporates a grounded coplanar‐waveguide (CPW) CPW‐feeding excitation mechanism. The electromagnetic energy is coupled to the air through 3 × 3 slot array etched on top metallic layer. The proposed antenna operates in the X‐band for the frequency range around the 10 to 11 GHz with resonances at 10.4 and 10.8 GHz frequencies. The proposed antenna array was fabricated and tested. Experimental results show good impedance matching with enhanced radiation characteristics, in terms of peak gain, cross‐polarization level, and low back‐radiation. The proposed antenna has the advantages of low‐footprints, lightweight, high gain, low‐cost, and ease of integration with other electronic circuits. With these characteristics, the proposed antenna array can find its applications in compact wireless digital transceivers.     

Millimeter‐wave planar high gain SIW antenna using half elliptic radiation slots

This article reports a high gain millimeter‐wave substrate integrated waveguide (SIW) antenna using low cost printed circuit board technology. The half elliptic slots which can provide small shunt admittance, low cross polarization level and low mutual coupling are etched on the board surface of SIW as radiation slots for large array application. Design procedure for analyzing the characteristics of proposed radiation slot, the beam‐forming structure and the array antenna are presented. As examples, an 8 × 8 and a 32 × 32 SIW slot array antennas are designed and verified by experiments. Good agreements between simulation and measured results are achieved, which shows the 8 × 8 SIW slot array antenna has a gain of 20.8 dBi at 42.5 GHz, the maximum sidelobe level of 42.5 GHz E‐plane and H‐plane radiation patterns are 22.3 dB and 22.1 dB, respectively. The 32 × 32 SIW slot array antenna has a maximum measured gain of 30.05 dBi at 42.5 GHz. At 42.3 GHz, the measured antenna has a gain of 29.6 dBi and a maximum sidelobe level of 19.89 dB and 15.0 dB for the E‐plane and H‐plane radiation patterns. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:709–718, 2015.     

A novel suspended stripline‐fed printed square slot array antenna with high‐gain

A novel suspended stripline‐fed square slot array antenna with high gain is presented. Its basic structure is a suspended stripline comprising of three layers. On the top layer, 4 × 4 square slots are etched and act as radiation elements. The middle layer consists of a suspended stripline power divider, and the bottom layer is a metal ground. After optimization by a parallel Genetic Algorithm (GA) on a cluster system, a prototype antenna is fabricated and tested. The measured results agree well with the simulated data, and show a high gain of 18.7 dBi and an impedance bandwidth of 5.7% for S11<‐10 dB are obtained. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

Wideband circularly polarized hybrid dielectric resonator antenna with bi‐directional radiation characteristics for various wireless applications

In this article, a wideband circularly polarized (CP) dielectric resonator (DR) over an asymmetric‐slot radiator based hybrid‐DR antenna is proposed with bi‐directional radiation characteristics. Bi‐directional CP radiation of the dual sense is obtained using a rectangular‐DR over asymmetric‐rectangular‐slot radiator with L‐shaped feed line. The asymmetric‐slot radiator feed by L‐shaped stub with the coplanar waveguide is used for generating two orthogonal modes, namely TE ^x _δ11 and TE^y_1δ1 in the combined (rectangular‐DR and asymmetric‐slot radiator) hybrid‐DR antenna, which is verified by the distribution of electric field inside the rectangular DRA. The measured reflection coefficient bandwidth (S₁₁ < ?10 dB) and axial ratio (AR) bandwidth (AR < 3 dB) of the hybrid‐DR antenna are 80.5% (1.87‐4.39 GHz) and 43.8% (1.75‐2.73 GHz), respectively. The antenna radiation is in the broadside (θ = 0°, ? = 0°) direction as well as in the backside (θ = 180°, φ = 0°) direction with equal magnitudes in both the directions. Right‐handed and left‐handed CP waves are achieved respectively, in the boresight (+Z) and the backside (?Z) directions. The proposed CP hybrid‐DR antenna gives an average gain of 3.55 dBic and radiation efficiency of 95.0% in both directions. The proposed antenna covers various wireless useful bands such as ISM 2400 band, Wi‐Fi, Bluetooth, and Wi‐MAX (2.5‐2.7 GHz).     

Wideband microstrip‐fed tapered slot antennas and phased array

Two wideband tapered slot antennas are designed, fabricated, and tested. The first antenna, which is fabricated on a high dielectric constant substrate (?_r = 10.2), shows a measured return loss of better than 10 dB from 1.6 to 12.4 GHz (7.7:1 bandwidth), and an antenna gain varying from 3.6 to 7.8 dBi. The second antenna is built on a low dielectric constant substrate (?_r = 2.2), and demonstrates return loss of better than 10 dB from 1.8 to 15.2 GHz (8.4:1 bandwidth). The second antenna also has improved antenna gain, from 5 to 15.6 dBi, and is used to build a wideband 1 × 4 H‐plane phased array with a total gain of 9–17 dBi and a beam steering angle of ±15° from 3 to 12 GHz. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

Investigation of higher order modes excitation through F‐shaped slot in rectangular dielectric resonator antenna for wideband circular polarization with broadside radiation characteristics

In this article, a wideband circularly polarized rectangular dielectric resonator antenna (RDRA) with broadside radiation characteristics has been proposed. By using modified ground plane having an F‐shaped slot, the proposed structure able to generates three sets of modes i.e., fundamental as well as higher order modes. To obtained circular polarization, an orthogonal mode (TE₁₁₃) in the RDRA has been generated by using the F‐shaped slot on the modified ground plane. The resonance frequency of fundamental mode (TE₁₁₁) in the rectangular dielectric resonator (DR) has been calculated by using dielectric waveguide model method. The same has been confirmed through E‐field distribution in RDRA. Here, wide axial ratio (AR) bandwidth of the proposed antenna is due to the generation of and modes. It is observed that input impedance bandwidth has been broadening with a pair of excited modes ( and modes) in the proposed antenna structure. All these modes have been excited and merged to form a wide input impedance bandwidth and wide AR bandwidth of the designed antenna. The proposed antenna shows measured input reflection coefficient (S₁₁ < ?10 dB) of 50.55% and measured AR bandwidth (AR < 3 dB) of 14.28%. The designed antenna shows left‐handed circular polarization in broadside direction and offering an average gain and radiation efficiency of 4.29 dBic and 92.22% respectively.     

A novel wideband circularly polarized modified square‐slot antenna with loaded strips

In this article, a novel inverted L‐shaped microstrip‐fed wideband circularly polarized (CP) modified square‐slot antenna is designed. By cutting a pair of triangle chamfers and introducing a pair of triangle patches at the square‐slot, the antenna achieves a wideband CP radiation. Moreover, CP performance of the antenna can also be remarkably enhanced by protruding an L‐shaped strip and embedding a tuning rectangle slot into the slot ground. The measured results demonstrate that the axial‐ratio bandwidth for AR < 3 is 75.1% (from 4.45 to 9.8 GHz) and the impedance bandwidth (|S₁₁| < ?10 dB) reaches 65.8% (from 4.95 to 9.8 GHz). In addition, surface current studies are performed to illustrate the operating mechanism of CP operation, and the antenna has bidirectional radiation characteristics with an average gain of ~4 dBic within the CP band.     

Broadband T‐bar fed slot antenna array with stable horizontally polarized omnidirectional radiation

A broadband horizontally polarized omnidirectional antenna array is proposed, which consists of a circular array of four identical broadband T‐bar fed cavity‐backed slot antenna elements and a 1‐to‐4 power divider. The proposed omnidirectional antenna array has a compact diameter of only 0.44λ₀, a broad bandwidth of 75.9% (450‐1000 MHz) and a favorable omnidirectional radiation pattern in the azimuth plane with a gain variation below 3 dB in the operating band. Moreover, the cavity‐backed structure makes the proposed antenna array hardly affected by metal environment and the all metal construction allows for high‐power applications, and the reserved cable channel behind the cavities of the antenna elements ensures the extensionality and stability of the proposed array when longitudinal array expansion is needed. Design procedures of the proposed antenna array have been described in detail, simulations and measurements of the proposed antenna array have also been carried out to validate its performance in this article.     

Wide‐bandwidth dielectric resonator antenna with omni‐directional radiation patterns for beam focusing properties in a circular array

Investigation results are presented for a cylindrical dielectric resonator antenna (DRA) with a central airgap, which is excited using a coaxial probe connected to a wire monopole. By selecting the proper values of airgap and monopole heights, a desired impedance bandwidth (S₁₁ ≤ ?10 dB) from 40% to 67% can be achieved. The proposed DRA provides monopole like omni‐directional radiation patterns with low crosspolarization levels throughout the bandwidth. Prototype DRA was fabricated with equal heights of the airgap and monopole and experimentally verified for both the impedance matching and radiation performance. Simulated and measured bandwidths of 67% and 64%, respectively, were obtained with acceptable peak realized gain. The simulated and measured radiation patterns agree well. Furthermore, this DRA is investigated for beam focusing properties when implemented in a circular array consisting of four‐elements on a circular finite ground plane. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:92–101, 2014.     

Mode‐matching analysis of H‐plane ferrite‐loaded rectangular waveguide discontinuities

The full set of eigenmodes existing in a ferrite‐slab‐loaded rectangular waveguide is first obtained and then used to compute the scattering matrix of a junction between an air‐filled rectangular waveguide and an H‐plane ferrite‐slab‐loaded rectangular waveguide by using the mode‐matching method. Numerical results for the scattering parameters of the H‐plane waveguide discontinuity are compared to experimental data and those obtained by Ansoft's HFSS. Good agreement is observed. To demonstrate the usefulness of this structure, a computer‐optimized 90° nonreciprocal phase shifter is designed using an H‐plane ferrite‐slab‐loaded waveguide. With only one‐step impedance matching sections at both ends of the ferrite slab, a compact design is achieved to have 2° phase error and less than ?30 dB return loss over about 5% bandwidth. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 259–268, 2003.     

Wideband and low‐loss waveguides of nonuniform cross‐section

Waveguides of nonuniform cross‐section are introduced, analyzed and then their cross‐section is optimized to reach wideband and low‐loss waveguides. The waveguide cross‐section is defined as a Fourier series whose unknown coefficients are optimized using genetic algorithm to reach a proper cross‐section for waveguide. A verified finite difference method is used in analysis stage of optimization. The results show that optimum designed nonuniform cross‐section waveguides have lower conductor attenuation constant in comparison with double ridged waveguides of the same bandwidth. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:115–121, 2015.     

Untilted slot array antenna at the narrow wall of the waveguide using double‐ridge

In this article a novel array antenna composed of untilted slots in the narrow wall of the double‐ridge waveguide, with significantly improved cross‐polarization, is presented. In the first step, suitable radiating elements for designing a linear slot array antenna were created. An untilted slot which is created the narrow wall of the double‐ridge waveguide is suggested to be used as the radiating resonance slot. The concave and convex ridges are located under the untilted slots only. It is shown that the concave and convex double ridge waveguides can produce an orthogonal current distribution in the place of the slots. They are also placed successively to produce the required phase inversion between adjacent slots. The linear array consists of nine uniform resonant untilted slots in the double ridge waveguide and is designed at the frequency of 5 GHz using the normalized conductance of each radiating slot. Analyzing the simulation results shows that cross‐polarization of the designed array was significantly improved, it was also found that the cross‐polarization and the SLL were respectively about ?65 and ?16 dB. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

A dual‐band dual‐mode microstrip Yagi antenna with quasi‐end‐fire radiation

A dual‐band dual‐mode microstrip Yagi antenna with quasi‐end‐fire radiation patterns is proposed in this paper. It consists of five radiating patches driven by a single slot‐loaded patch placed in the middle. Meanwhile, two slot‐loaded parasitic patches are symmetrically located on two sides of the driven patch, respectively. In the lower band, the five patches involved resonate at TM₀₁ mode. While in the upper band, all the patches resonate at TM₀₂ mode. In order to ensure quasi‐end‐fire radiations in the both bands, four slots are symmetrically etched around the strongest surface currents of each patch resonating at TM₀₂ mode. As a result, the resonant frequency of TM₀₂ mode is decreased dramatically, while the resonant frequency of TM₀₁ mode almost remains unchanged. With these arrangements, the separations between any two of the adjacent patches at their centers satisfy the requirements in design of the microstrip Yagi antenna in both bands, so as to realize the dual‐band dual‐mode microstrip Yagi antenna on a single‐layer substrate. Finally, an antenna prototype is fabricated and tested. The measured results reveal that the dual operating bands of 2.76~2.88 and 4.88~5.03 GHz for |S₁₁| < ?10 dB are satisfactorily achieved. Most importantly, the proposed antenna can indeed realize the quasi‐end‐fire radiation patterns in dual operating bands.     

A broadband slant polarized cavity backed microstrip‐fed wide‐slot antenna array

This article deals with the design of a broadband cavity‐backed microstrip‐fed wide‐slot antenna array for L‐band applications. For verification purpose, a sample 1 × 4‐element antenna array has been designed, manufactured and tested. Experimental results have shown satisfactory agreement with the simulation. The proposed antenna array exhibits a measured impedance bandwidth of 1.4 GHz (90%) with frequency of 0.85 to 2.25 GHz and the gain is higher than 11 dBi. The designed antenna has small size and low weight and can be fabricated using a low‐cost fabrication process for easy integration with RF circuits and microwave components. This work is useful for some radar applications and radio frequency identification systems.