PERANCANGAN ANTENA MIKROSTRIP MEANDER LINE FREKUENSI 1090 MHz UNTUK TRANSPONDER ADS-B PADA PESAWAT UDARA // DESIGN OF A 1090 MHz MEANDER LINE MICROSTRIP ANTENNA FOR AN ADS-B TRANSPONDER ON AN AIRCRAFT

Automatic Dependent Surveillance-Broadcast (ADS-B) merupakan sistem surveillance penerbangan yang menyiarkan informasi posisi, identitas, ketinggian, kecepatan, dan arah pergerakan pesawat secara otomatis. Pada sistem 1090 Extended Squitter, data ADS-B dipancarkan melalui transponder Mode S pada frekuensi 1090 MHz. Kinerja pemancaran tidak hanya dipengaruhi oleh transponder, tetapi juga oleh antena dan pencocokan impedansi terhadap saluran transmisi 50 Ω. Ketidaksesuaian impedansi menyebabkan sebagian daya dipantulkan kembali sehingga energi yang dapat diteruskan ke antena berkurang.
Penelitian ini bertujuan merancang, mensimulasikan, memfabrikasi, dan mengevaluasi prototipe antena mikrostrip meander line pada frekuensi 1090 MHz untuk transponder ADS-B. Penelitian dibatasi pada pengujian prototipe di laboratorium dan tidak mencakup pemasangan pada pesawat, integrasi dengan transponder operasional, maupun uji terbang. Metode yang digunakan adalah penelitian rancang bangun Research and Development Level 4 dalam lingkup prototipe laboratorium dengan pendekatan deskriptif kuantitatif dan komparatif. Tahapan penelitian meliputi penetapan kebutuhan dan kriteria perancangan, perhitungan dimensi awal, pemodelan menggunakan CST Studio Suite 2022, simulasi awal, optimasi geometri, fabrikasi pada substrat FR-4 berketebalan 1,6 mm, serta pengukuran menggunakan RF Vector Network Analyzer R&S ZND-B1. Struktur antena terdiri atas patch meander line, saluran pencatu, substrat, ground plane, dan konektor SMA 50 Ω. Optimasi dilakukan melalui perubahan panjang dan lebar jalur meander, celah antarjalur, dimensi saluran pencatu, serta ukuran ground plane.
Parameter simulasi yang dianalisis meliputi frekuensi resonansi, return loss, Voltage Standing Wave Ratio (VSWR), impedansi, gain, dan bandwidth. Pengukuran prototipe difokuskan pada return loss, VSWR, dan impedansi pada frekuensi 1090 MHz. Kriteria utama yang digunakan adalah return loss ≤ -10 dB, VSWR ≤ 2, impedansi mendekati 50+j0 Ω, gain ≥ 0 dBi, dan rentang bandwidth mencakup frekuensi 1090 MHz.
Hasil simulasi setelah optimasi menunjukkan frekuensi resonansi 1090 MHz, return loss -24,14 dB, VSWR 1,13, magnitudo impedansi 51,35 Ω, gain 2,38 dBi, dan bandwidth 346,73 MHz pada batas return loss ≤ -10 dB. Hasil tersebut menunjukkan bahwa model simulasi memenuhi kriteria utama perancangan dan memiliki pencocokan impedansi yang baik. Setelah desain direalisasikan menjadi prototipe, hasil pengukuran pada frekuensi 1090 MHz memperoleh return loss - 5,94 dB, VSWR 3,07, dan impedansi 28,368+j38,957 Ω. Nilai tersebut menunjukkan bahwa prototipe belum memenuhi kriteria pencocokan impedansi karena komponen resistif masih berada di bawah 50 Ω dan komponen reaktif positif menunjukkan sifat induktif. Bandwidth prototipe tidak dapat ditentukan pada batas -10 dB karena respons return loss tidak mencapai batas tersebut di sekitar 1090 MHz. Gain prototipe juga tidak diukur karena penelitian tidak menggunakan metode pengukuran ruang bebas atau ruang anekoik.
Berdasarkan penelitian terdahulu, deviasi antara hasil simulasi dan pengukuran dapat berkaitan dengan toleransi fabrikasi, perubahan geometri antena, karakteristik aktual substrat FR-4, serta sistem pencatuan dan pemasangan konektor SMA. Faktor-faktor tersebut diposisikan sebagai kemungkinan penyebab karena pengaruh masing-masing faktor belum diuji secara terpisah dalam penelitian ini. Penelitian menyimpulkan bahwa rancangan antena memenuhi kriteria pada tahap simulasi, tetapi prototipe hasil fabrikasi belum mampu mempertahankan kinerja tersebut. Pengembangan selanjutnya diarahkan pada verifikasi dimensi aktual, penggunaan metode fabrikasi yang lebih presisi, penyesuaian parameter material pada simulasi, serta penyempurnaan sambungan antara konektor SMA dan feedline sebelum dikembangkan menuju pengujian integrasi dengan sistem ADS-B pada pesawat udara. // Automatic Dependent Surveillance-Broadcast (ADS-B) is an aviation surveillance system that automatically broadcasts aircraft position, identity, altitude, speed, and direction of movement. In the 1090 Extended Squitter system, ADS-B data are transmitted through a Mode S transponder at a frequency of 1090 MHz. Transmission performance is influenced not only by the transponder but also by the antenna and its impedance matching to a 50 Ω transmission line. Impedance mismatch causes part of the transmitted power to be reflected toward the source, thereby reducing the energy delivered to the antenna.
This study aims to design, simulate, fabricate, and evaluate a 1090 MHz meander line microstrip antenna prototype for an ADS-B transponder. The study is limited to laboratory prototype testing and does not include aircraft installation, integration with an operational transponder, or flight testing. A Level 4 Research and Development engineering design method was applied within the scope of a laboratory prototype using quantitative descriptive and comparative approaches. The research stages included establishing design requirements and criteria, calculating initial dimensions, modeling using CST Studio Suite 2022, conducting initial simulations, optimizing the geometry, fabricating the antenna on a 1.6 mm thick FR-4 substrate, and measuring the prototype using an R&S ZND-B1 RF Vector Network Analyzer. The antenna structure consists of a meander line patch, feedline, substrate, ground plane, and a 50 Ω SMA connector. Optimization was conducted by adjusting the length and width of the meander path, the spacing between conductive paths, the feedline dimensions, and the ground plane size.
The simulated parameters included resonant frequency, return loss, Voltage Standing Wave Ratio (VSWR), impedance, gain, and bandwidth. Prototype measurements focused on return loss, VSWR, and impedance at 1090 MHz. The main design criteria were return loss ≤ -10 dB, VSWR ≤ 2, impedance approaching 50+j0 Ω, gain ≥ 0 dBi, and a bandwidth range covering 1090 MHz.

The optimized simulation produced a resonant frequency of 1090 MHz, return loss of -24.14 dB, VSWR of 1.13, impedance magnitude of 51.35 Ω, gain of 2.38 dBi, and bandwidth of 346.73 MHz at the return loss threshold of ≤ -10 dB. These results indicate that the simulated model satisfies the main design criteria and provides good impedance matching. After the design was fabricated into a prototype, measurements at 1090 MHz produced a return loss of -5.94 dB, VSWR of 3.07, and impedance of 28.368+j38.957 Ω. These values indicate that the prototype does not yet satisfy the impedance-matching criteria because the resistive component remains below 50 Ω and the positive reactive component indicates inductive behavior. The prototype bandwidth could not be determined at the -10 dB threshold because the measured return loss response did not reach this level around 1090 MHz. Prototype gain was also not measured because the study did not employ free-space or anechoic chamber measurement methods.
Based on previous studies, the deviation between simulation and measurement results may be associated with fabrication tolerances, changes in antenna geometry, the actual characteristics of the FR-4 substrate, as well as the feeding system and SMA connector installation. These factors are considered possible contributors because their individual effects were not tested separately in this study. The study concludes that the antenna design satisfies the required criteria at the simulation stage, whereas the fabricated prototype is not yet able to maintain the same performance. Further development should focus on verifying the actual fabricated dimensions, employing more precise fabrication methods, adjusting material parameters in the simulation, and improving the connection between the SMA connector and the feedline before proceeding to integration testing with an ADS-B system on an aircraft.