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In this paper, a broadband planar modified quasi-Yagi antenna using a two-element logperiodic dipole array as a driven element is proposed. To feed the two-element log-periodic dipole array, a simple microstrip to stripline transition as a balun is designed, which converts the unbalanced input to balanced output. The antenna is fabricated on a low cost glass epoxy FR4 substrate with dielectric constant = 4.4, substrate thickness = 1.6 mm, and loss tangent = 0.02. The overall size of the antenna is 84 mm × 111 mm, which is 0.41λ o × 0.54λ o at the center frequency of 1.45 GHz. Measured results show a bandwidth of 41.4% for VSWR ≤ 2. A gain of 6.5 dBi ± 0.5 dB and front to back ratio (F/B) of better than 20 dB are achieved over the bandwidth. Measured results are in good agreement with the simulated ones. This antenna is useful for RFID, portable direction finding, spectrum monitoring systems, etc.

In this study, a broadband planar multilayer monopulse antenna at the X‐band for monopulse tracking applications is presented. A monopulse comparator has been designed using four hybrid ratrace for feeding the radiating elements of the antenna. Each radiating part of the monopulse antenna consists of 4 × 4 electromagnetically coupled microstrip antenna array. To achieve circular geometry as well as better side‐lobe level (SLL), a hybrid feeding technique is used in radiating antenna array by adding a few elements in series at the end elements of the parasitic layer of a 4 × 4 corporate fed array. The prototype has been fabricated, tested and measured results are compared with simulated results. The simulated impedance bandwidth for |S11| ≤ −10 dB is 21% (8.6–10.6 GHz). A measured peak sum beam gain of 24.4 dBi has been obtained. Measured SLL of <−15 dB has been achieved in both elevation and azimuth planes along with a null depth of <−35 dB for difference patterns in both the planes. The radiation pattern is symmetrical in both the planes with half‐power beamwidth nearly equal to 9.0°.