Proximity fed Broadband Microstrip Antennas

Abstract

broadband microstrip antenna is realized by fabricating the patch on lower dielectric constant thicker substrate in conjunction with proximity feeding technique. Using thicker substrates, a formulation for an edge extension length and design guidelines for strip dimensions in proximity fed broadband antennas, are not available. In this paper, first by designing suspended rectangular and circular microstrip antennas on different substrate thickness and at various frequencies in 800 to 6000 MHz frequency band, graphs for an edge extension length are developed. Using them an edge extension length at given frequency and substrate thickness is calculated. The suspended patches were further designed using edge extension length graphs which give closer result with the desired frequency. Further by using proposed equations, proximity fed microstrip antennas were optimized at various frequencies in 800 to 6000 MHz frequency band. Using these optimized designs, a formulation for coupling strip parameters is proposed. By using proposed formulations for edge extension length and strip parameters, proximity fed antennas were re-designed at different frequencies in 800 to 6000 MHz frequency band. In all the configurations, broadband response with formation of loop inside VSWR = 2 circle is obtained. Also by using the proposed formulation, design procedure for proximity fed U-slot cut rectangular microstrip antenna is explained. The U-slot cut antenna gives bandwidth of more than 450 MHz at center frequency of around 1000 MHz. The proposed formulations can be used to design broadband antennas using thicker substrate at any given frequency. Keywordsctangular microstrip antenna, Circular Microstrip Antenna, Equilateral triangular microstrip antenna, Edge extension length, Proximity feeding, Broadband microstrip antenna coupling strip which is either placed below or in the plane of the patch. A larger BW is realized due to electromagnetic coupling between the patch mode and the strip. This method yields broader BW for thickness more than 0.060. The BW of MSA is also increased by cutting a slot inside the patch (4 - 8). Further increase in the BW of slot cut MSA is realized by using proximity feeding technique (9). In proximity feeding method, for the given patch and strip substrate thickness, design parameters are, the strip dimensions and its position below or in the plane of the patch. In the available literature on proximity feeding, the design guidelines for given substrate thickness and operating frequency are not available. In this paper, design formulations for broadband proximity fed MSAs on thicker substrates are proposed. First by designing rectangular MSA (RMSA) and circular MSA (CMSA) at a given frequency and for different substrate thickness in 800 to 6000 MHz frequency band, plots for an edge extension length against substrate thickness are developed. Using them an edge extension length at any given frequency and substrate thickness is calculated. By using the proposed graphs, patch was re-designed at different frequencies in the above frequency band. It gives patch resonance frequency at nearly the same desired value with an error less than 2%. Further broadband proximity fed RMSA, CMSA and equilateral triangular MSA (ETMSA) were designed at different frequencies in the 800 to 6000 MHz frequency band. Using their optimum designs, the formulations for strip dimensions and its position below the patch for the given patch substrate thickness is proposed. Using edge extensions graphs and the formulation for strip dimensions, proximity fed RMSA, CMSA and ETMSA were re-designed at different frequencies in 800 to 6000 MHz frequency band. A broadband response with the formation of loop inside the VSWR = 2 circle is obtained. Using proximity fed formulations, a detail design procedure for proximity fed U-slot cut RMSA is also presented. It gives broadband response with BW of more than 450 MHz (>45%). The above study was carried out using IE3D software followed by experimental verifications (10). In IE3D simulations an infinite ground plane was used. In measurements the antennas were fabricated using the copper plate having finite thickness and were supported in air using the foam spacer support placed towards the antenna corners. The antenna was fed using N-type connector of 0.32 cm inner wire diameter. At all the frequencies, measurements were carried out using R & S vector network analyzer (ZVH 8 model) using finite square ground plane of side length 100 cm. This larger ground plane simulates the effect of infinite ground plane. The radiation pattern was measured in minimum reflection surroundings with required minimum far field distance between reference antenna and antenna under test (11). The antenna gain was measured using three antenna method (11). The proposed